PROGENITOR INC
S-1/A, 1996-08-16
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>
   
    AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON AUGUST 16, 1996
    
                                                      REGISTRATION NO. 333-05369
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                            ------------------------
 
   
                                AMENDMENT NO. 2
                                       TO
                                    FORM S-1
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
    
                            ------------------------
 
                                PROGENITOR, INC.
 
             (Exact name of Registrant as specified in its charter)
 
<TABLE>
<S>                             <C>                         <C>
           DELAWARE                        2836                     31-1344193
 (State or other jurisdiction       (Primary Standard            (I.R.S. Employer
     of incorporation or                Industrial            Identification Number)
        organization)              Classification Code
                                         Number)
</TABLE>
 
                               1507 CHAMBERS ROAD
                              COLUMBUS, OHIO 43212
                                 (614) 488-6688
               (Address, including zip code and telephone number,
       including area code, of Registrant's principal executive offices)
                            ------------------------
 
                         DOUGLASS B. GIVEN, M.D., PH.D.
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                PROGENITOR, INC.
                               1507 CHAMBERS ROAD
                              COLUMBUS, OHIO 43212
                                 (614) 488-6688
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)
 
                            ------------------------
 
                                   COPIES TO:
 
<TABLE>
<S>                                            <C>
            GAVIN B. GROVER, ESQ.                      CHARLES W. MULANEY, JR., ESQ.
          KRISTIAN E. WIGGERT, ESQ.                        SKADDEN, ARPS, SLATE,
             EDA S.L. TAN, ESQ.                               MEAGHER & FLOM
           MORRISON & FOERSTER LLP                         333 WEST WACKER DRIVE
            345 CALIFORNIA STREET                         CHICAGO, ILLINOIS 60606
       SAN FRANCISCO, CALIFORNIA 94104                        (312) 407-0700
               (415) 677-7000
</TABLE>
 
                            ------------------------
 
        APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
   As soon as practicable after the Registration Statement becomes effective.
 
                            ------------------------
 
    If  any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to  Rule 415 under the Securities Act  of
1933, please check the following box./ /
 
    If  this Form  is filed  to register  additional securities  for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration statement  number  of  the  earlier
effective registration statement for the same offering./ /
 
    If  this Form  is a post-effective  amendment filed pursuant  to Rule 462(c)
under the Securities Act, please check the following box and list the Securities
Act registration statement number of the earlier registration statement for  the
same offering./ /
 
    If  delivery of the Prospectus is expected  to be made pursuant to Rule 434,
please check the following box./ /
                            ------------------------
 
    THE REGISTRANT HEREBY  AMENDS THIS  REGISTRATION STATEMENT ON  SUCH DATE  OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE  A  FURTHER  AMENDMENT  THAT  SPECIFICALLY  STATES  THAT  THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE  IN ACCORDANCE WITH SECTION 8(a)  OF
THE  SECURITIES ACT  OF 1933  OR UNTIL  THE REGISTRATION  STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION  8(a),
MAY DETERMINE.
 
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>
                                PROGENITOR, INC.
                             CROSS-REFERENCE SHEET
                   PURSUANT TO ITEM 501(B) OF REGULATION S-K
 
<TABLE>
<CAPTION>
                      ITEMS OF FORM S-1                                       LOCATION IN PROSPECTUS
- --------------------------------------------------------------  --------------------------------------------------
<C>         <S>                                                 <C>
   Item 1.  Forepart of the Registration Statement and Outside
             Front Cover Page of Prospectus...................  Facing Page of Registration Statement; Outside
                                                                 Front Cover Page
 
   Item 2.  Inside Front and Outside Back Cover Pages of
             Prospectus.......................................  Inside Front and Outside Back Cover Pages
 
   Item 3.  Summary Information, Risk Factors, and Ratio of
             Earnings to Fixed Charges........................  Prospectus Summary; Risk Factors
 
   Item 4.  Use of Proceeds...................................  Use of Proceeds
 
   Item 5.  Determination of Offering Price...................  Outside Front Cover Page; Underwriting
 
   Item 6.  Dilution..........................................  Risk Factors; Dilution
 
   Item 7.  Selling Security Holders..........................  Not applicable
 
   Item 8.  Plan of Distribution..............................  Outside Front and Inside Front Cover Pages;
                                                                 Underwriting
 
   Item 9.  Description of Securities to be Registered........  Description of Capital Stock
 
  Item 10.  Interests of Named Experts and Counsel............  Legal Matters; Experts
 
  Item 11.  Information with Respect to the Registrant........  Outside Front and Inside Front Cover Pages;
                                                                 Prospectus Summary; Risk Factors; Dividend
                                                                 Policy; Capitalization; Selected Financial Data;
                                                                 Management's Discussion and Analysis of Financial
                                                                 Condition and Results of Operations; Business;
                                                                 Management; Certain Transactions; Principal
                                                                 Stockholders; Shares Eligible for Future Sale;
                                                                 Description of Capital Stock; Financial
                                                                 Statements
 
  Item 12.  Disclosure of Commission Position on
             Indemnification for Securities Act Liabilities...  Not applicable
</TABLE>
<PAGE>
INFORMATION   CONTAINED  HEREIN  IS  SUBJECT   TO  COMPLETION  OR  AMENDMENT.  A
REGISTRATION STATEMENT  RELATING TO  THESE SECURITIES  HAS BEEN  FILED WITH  THE
SECURITIES  AND EXCHANGE  COMMISSION. THESE SECURITIES  MAY NOT BE  SOLD NOR MAY
OFFERS TO BUY BE ACCEPTED PRIOR  TO THE TIME THE REGISTRATION STATEMENT  BECOMES
EFFECTIVE.  THIS  PROSPECTUS  SHALL  NOT  CONSTITUTE AN  OFFER  TO  SELL  OR THE
SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE  SECURITIES
IN  ANY STATE IN WHICH SUCH OFFER,  SOLICITATION OR SALE WOULD BE UNLAWFUL PRIOR
TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF ANY SUCH STATE.
<PAGE>
   
                  SUBJECT TO COMPLETION, DATED AUGUST 16, 1996
    
PROSPECTUS
 
                                2,500,000 SHARES
                                     [LOGO]
                                  COMMON STOCK
 
    All of the 2,500,000 shares of Common Stock offered hereby are being sold by
Progenitor, Inc. ("Progenitor" or the  "Company"). Prior to the Offering,  there
has  been no public market for the Common  Stock of the Company. It is currently
estimated that the  initial public  offering price  will be  between $11.00  and
$13.00  per share.  See "Underwriting"  for a  discussion of  the factors  to be
considered in determining  the initial  public offering price.  The Company  has
applied  to list the  Common Stock for  quotation on the  Nasdaq National Market
under the symbol "PGEN."
 
    THE COMMON STOCK OFFERED  HEREBY INVOLVES A HIGH  DEGREE OF RISK. SEE  "RISK
FACTORS" BEGINNING ON PAGE 5.
 
THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
    EXCHANGE  COMMISSION OR ANY  STATE SECURITIES COMMISSION  NOR HAS THE
       SECURITIES AND  EXCHANGE COMMISSION  OR ANY  STATE  SECURITIES
           COMMISSION  PASSED  UPON THE  ACCURACY OR  ADEQUACY OF
               THIS PROSPECTUS. ANY REPRESENTATION    TO  THE
                        CONTRARY IS A CRIMINAL OFFENSE.
 
<TABLE>
<CAPTION>
                                                             UNDERWRITING
                                                             DISCOUNTS AND     PROCEEDS TO
                                           PRICE TO PUBLIC  COMMISSIONS(1)     COMPANY(2)
<S>                                        <C>              <C>              <C>
  Per Share..............................         $                $                $
  Total(3)...............................         $                $                $
</TABLE>
 
(1)  The  Company  has  agreed to  indemnify  the  Underwriters  against certain
    liabilities, including  liabilities under  the Securities  Act of  1933,  as
    amended. See "Underwriting."
 
(2)  Before deducting expenses of the Offering payable by the Company, estimated
    at $850,000.
 
(3) The Company has granted the Underwriters  a 30-day option to purchase up  to
    375,000  additional shares of Common Stock  on the same terms and conditions
    set forth above, solely to cover over-allotments, if any. If such option  is
    exercised  in full,  the total Price  to Public,  Underwriting Discounts and
    Commissions and Proceeds to Company will be  $      ,  $      and  $       ,
    respectively. See "Underwriting."
 
                            ------------------------
 
    The  shares of Common Stock offered by the Underwriters are subject to prior
sale,  receipt  and  acceptance  by  them  and  subject  to  the  right  of  the
Underwriters  to  reject  any  order  in whole  or  in  part  and  certain other
conditions. It is  expected that delivery  of such  shares will be  made at  the
offices  of the agent of Vector Securities International, Inc., in New York, New
York on or about             , 1996.
 
                             ---------------------
 
Vector Securities International, Inc.
 
                                     Tucker Anthony
                                         Incorporated
 
                                                          Genesis Merchant Group
                                                             Securities
 
                        , 1996
<PAGE>
[A  schematic  diagram  entitled  "Genomic  Discoveries  through   Developmental
Biology"   illustrating  Progenitor's  functional   genomics  approach  for  the
development of its three  primary discovery programs. The  upper portion of  the
diagram  indicates the basis for Progenitor's  approach with arrows denoting the
interaction between  Molecular  Biology,  Developmental  Biology  and  Medically
Relevant  Function in Early Cells and Tissues. The middle portion of the diagram
depicts Progenitor's three Primary  Discovery Programs: Leptin Receptors;  DEL-1
Gene;  and BFU-e Factor. The lower portion  of the diagram depicts the Potential
Therapeutic Applications  for  each  of  Progenitor's  three  Primary  Discovery
Programs.]
 
    IN  CONNECTION WITH THIS OFFERING, THE UNDERWRITERS MAY OVER-ALLOT OR EFFECT
TRANSACTIONS WHICH STABILIZE OR MAINTAIN THE MARKET PRICE OF THE COMMON STOCK OF
THE COMPANY AT  A LEVEL ABOVE  THAT WHICH  MIGHT OTHERWISE PREVAIL  IN THE  OPEN
MARKET. SUCH STABILIZING, IF COMMENCED, MAY BE DISCONTINUED AT ANY TIME.
    Progenitor  and  the Progenitor  logo are  trademarks  of the  Company. This
Prospectus may contain trademarks and servicemarks of other parties.
<PAGE>
                               PROSPECTUS SUMMARY
 
    THE  FOLLOWING SUMMARY  IS QUALIFIED  IN ITS  ENTIRETY BY  THE MORE DETAILED
INFORMATION AND FINANCIAL  STATEMENTS AND NOTES  THERETO APPEARING ELSEWHERE  IN
THIS PROSPECTUS. THE COMMON STOCK OFFERED HEREBY INVOLVES A HIGH DEGREE OF RISK.
SEE "RISK FACTORS."
 
                                  THE COMPANY
 
    Progenitor  is  a  functional  genomics company  engaged  in  the discovery,
characterization and validation of novel  genes, receptors and related  proteins
as  therapeutic  leads and  targets  for the  treatment  of major  diseases. The
Company's functional genomics approach combines developmental biology  expertise
and  proprietary  technology with  gene sequencing  and other  molecular biology
techniques to accelerate the discovery process. Using its developmental  biology
approach  to  functional genomics,  the  Company has  made  several discoveries,
including the discovery of the B219  leptin receptor, for which it filed  patent
applications in September and December 1994. Leptin is believed to have roles in
blood  cell formation  ("hematopoiesis"), reproduction and  obesity. The Company
has entered  into a  collaboration with  Chiron Corporation  ("Chiron") for  the
development  and  commercialization  of  the  Company's  proprietary  T7T7  gene
delivery system, and a collaboration with Novo Nordisk A/S ("Novo Nordisk")  for
the isolation, development and commercialization of blood cell growth factors.
 
    Developmental  biology is the study of  the genetic and cellular events that
control the development of a single fertilized egg into a fully-formed,  complex
organism.  Many genes involved in the process of cell growth and differentiation
may be expressed exclusively,  or at enhanced levels,  during certain stages  of
early  development and may become  inactive in the cells  of adult organisms. By
comparing the sequential expression of genes from one stage of early development
to the next, the Company believes it can identify, isolate and sequence specific
genes, receptors and  other proteins  which play key  roles in  cell growth  and
differentiation. The Company believes that early developmental cells and tissues
are  a rich and largely unexploited source  for genes and proteins that may lead
to the development  of treatments  for diseases characterized  by aberrant  cell
growth  and differentiation, such  as cancer, blood  and immune system disorders
and degenerative diseases associated with aging.
 
    Progenitor possesses a number  of proprietary technologies  that it uses  in
its  discovery programs. The Company has  developed proprietary methods and cell
lines using mouse (murine) embryonic stem cells for studying the differentiation
of cells in  the early development  of tissues and  organs. Progenitor also  has
developed  proprietary  techniques to  isolate,  grow, maintain  in  culture and
differentiate cells from the murine yolk sac. The yolk sac contains the earliest
cells in development that are committed to differentiate into the blood,  immune
and  vascular systems.  In addition,  Progenitor has  developed proprietary gene
cloning and screening  techniques to  identify genes that  encode receptors  for
growth  factors believed to be important in hematopoiesis and cancer therapy, as
well as the growth and development of neural and other tissues.
 
    Progenitor has used its functional genomics approach to make three principal
discoveries. In addition to its B219 leptin receptor discovery, the Company  has
discovered,  in  collaboration  with Vanderbilt  University  ("Vanderbilt"), the
developmentally-regulated endothelial cell locus ("DEL-1") gene. The DEL-1  gene
is  involved in the early growth and  development of blood vessels and bone. The
Company  believes  that  DEL-1  may  have  potential  applications  in  diseases
accompanied by excessive blood vessel formation, such as cancer, and in diseases
such  as cardiovascular and other disorders that may be treatable by stimulating
blood vessel growth.  The Company  also has  identified a  murine burst  forming
units-erythroid  ("BFU-e") red  blood cell  growth factor  activity. The Company
believes that a BFU-e factor may be useful in the development of treatments  for
a variety of blood disorders.
 
    The  Company  currently  is  focusing  its  efforts  and  resources  on  the
discovery, characterization and  validation process  and intends  to enter  into
strategic alliances for the development and commercialization of drugs and other
products  based on its discoveries.  In March 1995, the  Company entered into an
agreement with Chiron for the development and commercialization of the Company's
T7T7 gene delivery system  for selected applications. In  May 1995, the  Company
entered  into a  development and  commercialization agreement  with Novo Nordisk
relating to the BFU-e red blood cell growth factor.
 
   
    The  Company  was   incorporated  in   Delaware  in  February   1992  as   a
majority-owned  subsidiary of Interneuron Pharmaceuticals, Inc. ("Interneuron"),
and commenced operations in May  1992. Following the Offering, Interneuron  will
own   51.8%  of  the   Company's  Common  Stock   (49.3%  if  the  Underwriters'
over-allotment option is exercised in full). The Company's executive offices are
located at 1507 Chambers Road, Columbus, Ohio 43212, and its telephone number is
(614) 488-6688.
    
 
                                       3
<PAGE>
                                  THE OFFERING
 
   
<TABLE>
<S>                                                          <C>
Common Stock offered.......................................  2,500,000 shares
Common Stock to be outstanding after the Offering..........  7,377,936 shares (1)
Use of proceeds............................................  To fund research and development activities, to fund
                                                             expansion of facilities and acquisition of equipment,
                                                             and for working capital and general corporate
                                                             purposes. See "Use of Proceeds."
Nasdaq National Market symbol..............................  PGEN
</TABLE>
    
 
                             SUMMARY FINANCIAL DATA
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
 
   
<TABLE>
<CAPTION>
                                                                                                   NINE MONTHS ENDED
                                                                  YEARS ENDED SEPTEMBER 30,            JUNE 30,
                                                               --------------------------------  ---------------------
                                                                 1993       1994        1995       1995        1996
                                                               ---------  ---------  ----------  ---------  ----------
<S>                                                            <C>        <C>        <C>         <C>        <C>
STATEMENT OF OPERATIONS DATA:
  Revenues...................................................  $  --      $  --      $    2,821  $   2,602  $    1,150
  Expenses:
    Research and development.................................      3,116      4,113       4,228      3,270       2,659
    General and administrative...............................      1,339      1,275       1,116        857       1,167
    Interest.................................................        246        648         352        320         104
                                                               ---------  ---------  ----------  ---------  ----------
      Total expenses.........................................      4,701      6,036       5,696      4,447       3,930
                                                               ---------  ---------  ----------  ---------  ----------
  Net loss...................................................  $  (4,701) $  (6,036) $   (2,875) $  (1,845) $   (2,780)
                                                               ---------  ---------  ----------  ---------  ----------
                                                               ---------  ---------  ----------  ---------  ----------
  Pro forma net loss per share (2)...........................                        $    (0.63)            $    (0.58)
                                                                                     ----------             ----------
                                                                                     ----------             ----------
  Pro forma weighted average shares outstanding (2)..........                         4,536,481              4,780,787
                                                                                     ----------             ----------
                                                                                     ----------             ----------
</TABLE>
    
 
   
<TABLE>
<CAPTION>
                                                                                        JUNE 30, 1996
                                                                          -----------------------------------------
                                                                                                       PRO FORMA
                                                                           ACTUAL    PRO FORMA (3)  AS ADJUSTED (4)
                                                                          ---------  -------------  ---------------
<S>                                                                       <C>        <C>            <C>
BALANCE SHEET DATA:
  Cash and cash equivalents.............................................  $      28    $     178       $  27,228
  Working capital.......................................................       (683)        (533)         26,517
  Total assets..........................................................      1,400        1,550          28,600
  Long-term obligations.................................................      2,408          172             172
  Deficit accumulated during development stage..........................    (17,454)     (17,454)        (17,454)
  Total stockholders' equity (deficit)..................................     (2,530)        (145)         26,905
</TABLE>
    
 
- ------------------
   
(1) Based on shares  outstanding as of  August 15, 1996  and an assumed  initial
    public  offering price of $12.00 per  share. Excludes: (i) 606,625 shares of
    Common Stock  issuable upon  exercise  of stock  options outstanding  as  of
    August  15, 1996, with a weighted average exercise price of $6.62 per share;
    (ii) 26,126  shares  of Common  Stock  issuable upon  exercise  of  warrants
    outstanding  as of  August 15,  1996, with  an exercise  price of  $9.18 per
    share; and  (iii) 836,700  additional shares  of Common  Stock reserved  for
    issuance  under the Company's stock plans. See "Capitalization," "Management
    -- Stock Plans" and "Description of Capital Stock."
    
 
(2) See Note 1 of Notes  to Financial Statements for information concerning  the
    computation of pro forma net loss per share.
 
(3)  Gives pro forma effect, assuming an initial public offering price of $12.00
    per share, to: (i) the conversion of a convertible debenture and  promissory
    note held by Interneuron into Common Stock upon the closing of the Offering;
    and  (ii) the purchase by The Ohio University Foundation of 25,000 shares of
    Common Stock at a  price of $6.00  per share, pursuant  to a stock  purchase
    right. See "Capitalization" and "Certain Transactions."
 
(4)  Pro  forma as  adjusted to  give effect  to  the issuance  and sale  of the
    2,500,000 shares of Common Stock  offered hereby (after deducting  estimated
    underwriting  discounts and  commissions and  the estimated  expenses of the
    Offering) and  the receipt  and application  of the  estimated net  proceeds
    therefrom  at an assumed initial public  offering price of $12.00 per share.
    See "Use of Proceeds" and "Capitalization."
                               ------------------
 
   
    EXCEPT AS OTHERWISE  NOTED, ALL  INFORMATION IN  THIS PROSPECTUS,  INCLUDING
FINANCIAL  INFORMATION, SHARE AND PER SHARE  DATA: (I) REFLECTS THE CONSUMMATION
OF A 1-FOR-2 REVERSE STOCK  SPLIT TO BE EFFECTED  PRIOR TO OR CONCURRENTLY  WITH
THE  OFFERING; (II) REFLECTS THE AUTOMATIC  CONVERSION OF ALL OUTSTANDING SHARES
OF PREFERRED STOCK INTO  AN AGGREGATE OF 1,774,014  SHARES OF COMMON STOCK  UPON
THE  CLOSING OF THE  OFFERING; (III) REFLECTS THE  CONVERSION OF THE CONVERTIBLE
DEBENTURE AND PROMISSORY NOTE HELD BY  INTERNEURON INTO AN AGGREGATE OF  226,143
SHARES  OF COMMON STOCK (BASED ON THE OUTSTANDING BALANCE AS OF AUGUST 15, 1996)
UPON THE  CLOSING  OF THE  OFFERING;  (IV) REFLECTS  THE  PURCHASE BY  THE  OHIO
UNIVERSITY  FOUNDATION OF 25,000 SHARES OF COMMON  STOCK AT A PRICE OF $6.00 PER
SHARE, PURSUANT TO  A STOCK PURCHASE  RIGHT; AND (V)  ASSUMES AN INITIAL  PUBLIC
OFFERING  PRICE  OF  $12.00  PER  SHARE AND  NO  EXERCISE  OF  THE UNDERWRITERS'
OVER-ALLOTMENT OPTION.  SEE  "CERTAIN  TRANSACTIONS,"  "DESCRIPTION  OF  CAPITAL
STOCK" AND "UNDERWRITING."
    
 
                                       4
<PAGE>
                                  RISK FACTORS
 
    IN  ADDITION  TO THE  OTHER INFORMATION  IN  THIS PROSPECTUS,  THE FOLLOWING
FACTORS SHOULD BE CONSIDERED CAREFULLY  BY POTENTIAL INVESTORS IN EVALUATING  AN
INVESTMENT  IN  THE  SHARES  OF COMMON  STOCK  OFFERED  HEREBY.  THIS PROSPECTUS
CONTAINS, IN ADDITION TO HISTORICAL INFORMATION, FORWARD-LOOKING STATEMENTS THAT
INVOLVE RISKS  AND  UNCERTAINTIES. THE  COMPANY'S  ACTUAL RESULTS  COULD  DIFFER
SIGNIFICANTLY FROM THOSE DISCUSSED IN THE FORWARD-LOOKING STATEMENTS.
 
    UNCERTAINTIES  RELATING TO TECHNOLOGICAL APPROACH OF  THE COMPANY.  To date,
the Company has not  developed or commercialized any  products. There can be  no
assurance  that the Company's functional approach  to genomics will enable it to
discover genes,  receptors or  other  proteins with  functions relevant  to  the
treatment  of diseases. The Company's  discovery programs are primarily directed
to complex diseases. There is  limited scientific understanding relating to  the
role of genes, receptors and other proteins in these diseases and relatively few
products  based on genetic discoveries have been developed and commercialized to
date. Accordingly,  even if  the  Company is  successful in  identifying  genes,
receptors  or other proteins associated with  specific diseases, there can be no
assurance that the Company  will be successful in  marketing its discoveries  to
pharmaceutical   companies  for  use  in  the  development  of  therapeutic  and
diagnostic products or  that any  such resulting products  will be  successfully
commercialized.
 
    The  development of products based on the Company's discoveries also will be
subject to the risks of failure inherent in the development of products based on
new technologies. These  risks include  the possibility that  any such  products
will be found to be ineffective or toxic, or otherwise fail to receive necessary
regulatory approvals; that any such products will be difficult to manufacture on
a commercial scale or will be uneconomical to market; that proprietary rights of
third parties will preclude the Company or its strategic partners from marketing
any  such products;  or that  third parties  will market  superior or equivalent
products. As a result, there can be no assurance that the Company's research and
development activities or those of  its licensees and collaborators will  result
in  any  commercially  viable  products.  See  "--  Uncertainty  of  Patents and
Proprietary Rights," "Business  -- Progenitor's  Functional Genomics  Approach,"
"--   Progenitor's   Discovery   Programs"  and   "--   Strategic  Collaboration
Agreements."
 
    Genomics,   biotechnology,   developmental   biology   and    pharmaceutical
technologies  have undergone and  are expected to continue  to undergo rapid and
significant change. The Company's  future success will depend  in large part  on
its   ability  to  maintain  a  competitive   position  with  respect  to  these
technologies. Rapid  technological developments  by the  Company or  others  may
result  in compounds, products or processes becoming obsolete before the Company
recovers any  expenses it  incurs in  connection with  the development  of  such
products. See "-- Intense Competition; Rapid Technological Change" and "Business
- -- Competition."
 
   
    HISTORY OF OPERATING LOSSES; ANTICIPATION OF FUTURE LOSSES.  Progenitor is a
development  stage company that commenced operations in May 1992. As of June 30,
1996, the Company had an accumulated deficit of approximately $17.5 million  and
a  working  capital  deficit of  $683,000.  Losses have  resulted  from expenses
incurred in the  Company's research and  development programs and,  to a  lesser
extent,  from  general and  administrative  and interest  expenses.  Neither the
Company nor any  of its collaborative  partners has yet  developed any  products
which  have entered clinical trials or generated any revenues to the Company. To
date, all of the Company's revenues  have resulted from payments from  strategic
partners and a development grant from a governmental agency. The Company expects
to  incur substantial additional losses over  the next several years and expects
cumulative losses  to increase  substantially  as it  expands its  research  and
development  activities.  Payments  from collaborative  partners,  license fees,
payments under governmental grants and investment income, in each case, if  any,
are  expected to be the only sources  of revenue for the foreseeable future. The
Company has not yet  generated any revenues from  the achievement of  milestones
under  its collaborative agreements. Royalties or other revenues from commercial
sales of products are not expected for a number of years, if at all. To  achieve
profitable
    
 
                                       5
<PAGE>
operations,  Progenitor,  alone  or  with  others,  must  successfully  discover
medically relevant genes, receptors or related proteins and thereafter use these
discoveries to  develop  products,  conduct  preclinical  studies  and  clinical
trials,  obtain  required  regulatory  approvals  and  successfully manufacture,
introduce and market such products, of which there can be no assurance. The time
required to reach or sustain profitability is highly uncertain and there can  be
no  assurance  that the  Company  will be  able  to achieve  profitability  on a
sustained basis, if at all. Moreover, if profitability is achieved, the level of
profitability cannot be  predicted and  may vary significantly  from quarter  to
quarter.  See "Management's Discussion  and Analysis of  Financial Condition and
Results of Operations."
 
    EARLY   STAGE    OF    DEVELOPMENT;    UNCERTAINTY    OF    FINAL    PRODUCT
DEVELOPMENT.   Significant discovery,  research and development  efforts will be
required prior  to the  time any  of  the Company's  genes, receptors  or  other
protein  discoveries may develop  into product candidates  or result in products
that may be brought to the market,  if at all. Products, if any, resulting  from
the  Company's  research  and  development  programs  are  not  expected  to  be
commercially available for a number of years, if at all. Significant  additional
research  and development efforts and extensive preclinical studies and clinical
trials will be required  prior to submission of  any regulatory application  for
commercial  use. There can be no assurance  that the Company or any collaborator
or licensee will  be permitted  to undertake  clinical trials  of any  potential
products,  if developed, that sufficient numbers of patients can be enrolled for
such trials, or  that such clinical  trials will demonstrate  that the  products
tested  are safe and efficacious. Even  if clinical trials are successful, there
can be no assurance that the Company or any collaborator or licensee will obtain
regulatory approval for any indication, that an approved product can be produced
and distributed in commercial quantities at reasonable costs or gain  acceptance
for  use by physicians  and other health  care providers, or  that any potential
products will be successfully marketed at  prices that would permit the  Company
to  operate profitably. The failure of any of these events to occur could have a
material adverse  effect  on the  Company's  business, financial  condition  and
results of operations. See "Business -- Progenitor's Discovery Programs" and "--
Government Regulation."
 
    NEED FOR ADDITIONAL CAPITAL; UNCERTAINTY OF ADDITIONAL FUNDING.  The Company
expects  negative cash flow from operations to  continue and to increase for the
foreseeable future. The  Company will  require substantial  additional funds  to
continue  research  and development,  conduct  preclinical studies  and clinical
trials, conduct  activities  relating  to commercialization  of  rights  it  has
retained   in   strategic   collaboration  agreements,   if   any,   and  expand
administrative capabilities. The Company estimates  that at its planned rate  of
spending, any existing cash and cash equivalents, together with the net proceeds
from  the Offering and the  interest income thereon, will  be sufficient to meet
its capital  requirements for  at least  the next  18 months.  There can  be  no
assurance,  however, that the Company's  assumptions regarding its future levels
of expenditures and operating losses  will prove accurate. The Company's  future
capital  requirements  will depend  on  many factors,  including  the scientific
progress in and the breadth of the Company's research and development  programs;
the results of research and development, preclinical studies and clinical trials
conducted by the Company or its collaborative partners or licensees, if any; the
acquisition and licensing of products and technologies; the Company's ability to
establish  and maintain relationships with corporate and academic collaborators;
competing technological and market developments; the time and costs involved  in
filing,  prosecuting, defending  and enforcing patent  and intellectual property
claims; the receipt of  licensing or milestone fees  from any current or  future
collaborative   arrangements,   if   established;  the   continued   funding  of
governmental research  grants; the  timing of  regulatory approvals;  and  other
factors. To the extent undertaken by the Company, the time and costs involved in
conducting   preclinical  studies   and  clinical   trials,  seeking  regulatory
approvals, and scaling-up  manufacturing and  commercialization activities  also
would increase the Company's capital needs.
 
    The  Company  will  need to  raise  substantial additional  capital  to fund
operations. Prior to this Offering, Interneuron has funded substantially all  of
the  Company's  operations.  Interneuron,  however, is  under  no  obligation to
provide, and the  Company does  not expect  that Interneuron  will provide,  any
additional  funds in the future. The  Company intends to seek additional funding
through public or
 
                                       6
<PAGE>
private equity or debt financing and collaborative arrangements. There can be no
assurance that additional financing will be  available when needed, or that,  if
available,  such financing will be available on terms acceptable to the Company.
If additional  funds  are  raised  by issuing  equity  securities,  dilution  to
existing  stockholders will  result. In addition,  in the  event that additional
funds are  obtained  through  arrangements  with  collaborative  partners,  such
arrangements  may require  the Company  to relinquish  rights to  certain of its
technologies or potential products  that it would otherwise  seek to develop  or
commercialize  itself. If funding is insufficient at any time in the future, the
Company may be required  to delay, scale  back or eliminate some  or all of  its
research  and  development  programs  or  cease  operations.  See  "Management's
Discussion and  Analysis of  Financial Condition  and Results  of Operations  --
Liquidity and Capital Resources."
 
    DEPENDENCE  ON COLLABORATORS.   The  Company's strategy  for development and
commercialization of drugs and other products from its discoveries depends  upon
the  formation of various corporate collaborations.  The Company expects to rely
on collaborative partners  to research and  develop potential products,  conduct
clinical  trials, obtain  regulatory approvals,  and manufacture  and market any
resulting products. The Company has entered into agreements with Chiron and Novo
Nordisk. The Company's revenues will be dependent on the success of the products
developed by these  and any future  collaborative partners. The  failure of  the
Company's  collaborative partners to develop, obtain regulatory approval of, and
market products incorporating  the Company's discoveries  would have a  material
adverse  effect on  the Company's business,  financial condition  and results of
operations. There can be no assurance that any collaborative partner will commit
sufficient   development    resources,   technology,    regulatory    expertise,
manufacturing,  marketing and other resources  towards developing, promoting and
commercializing  products  incorporating  the  Company's  discoveries.  Further,
competitive  conflicts may  arise among these  third parties  that could prevent
them from  working cooperatively  with the  Company. The  amount and  timing  of
resources  devoted  to these  activities  by such  parties  could depend  on the
achievement of milestones  by the Company  and generally will  be controlled  by
such  partners. In  addition, the  Company's collaborative  agreements generally
provide the Company's collaborator with the right to terminate the agreement  in
part  or  in  full  under  certain  circumstances.  Any  such  termination would
substantially reduce  the likelihood  that the  collaborative product  candidate
will  be developed,  would obtain regulatory  approvals and  be manufactured and
successfully commercialized and  any such termination  could, therefore, have  a
material  adverse  effect on  the  Company's business,  financial  condition and
results of operations. The Company's  royalties from sales of products  licensed
to  collaborators, if any, may be less  than the revenues the Company could have
generated had it commercialized  and marketed products itself.  There can be  no
assurance  that the  Company will  be successful  in establishing  additional or
maintaining existing collaborative arrangements, that any collaborative partners
will be  successful  in developing  and  commercializing products  or  that  the
Company will generate revenues from royalties sufficient to offset the Company's
significant  investment  in  research  and  development  and  other  costs.  See
"Business -- Strategic Collaboration Agreements" and "-- License Agreements."
 
    INTENSE COMPETITION; RAPID TECHNOLOGICAL CHANGE.   Research in the field  of
genomics  is highly competitive. Competitors of the Company in the genomics area
include, among others, public companies such as Genome Therapeutics Corporation,
Human  Genome   Sciences,  Inc.,   Incyte  Pharmaceuticals,   Inc.,   Millennium
Pharmaceuticals,   Inc.  ("Millennium"),  Myriad   Genetics,  Inc.  and  Sequana
Therapeutics, Inc.,  as  well  as private  companies  and  major  pharmaceutical
companies  and  universities and  other  research institutions,  including those
receiving funding from the  federally funded Human Genome  Project. A number  of
entities  are attempting to rapidly identify and patent randomly-sequenced genes
and gene fragments.  In addition,  certain other  entities are  pursuing a  gene
identification,  characterization and product development strategy based on gene
mapping.  The  Company's  competitors  may  discover,  characterize  or  develop
important  genes in advance of the Company,  which could have a material adverse
effect on any related Company discovery program. The Company expects competition
to intensify in genomics  research as technical advances  in the field are  made
and become more widely known.
 
                                       7
<PAGE>
    In  addition,  the  Company  faces,  and  will  continue  to  face,  intense
competition from pharmaceutical and biotechnology companies, as well as academic
and research institutions and governmental  agencies. The Company is subject  to
significant competition from organizations that are pursuing the same or similar
technologies  as those which  constitute the Company's  discovery platforms, and
from organizations that are pursuing  pharmaceutical or other products that  are
or  may be  competitive with the  Company's or its  collaborators' or licensees'
potential products. Many of  the organizations competing  with the Company  have
greater   capital  resources,   larger  research  and   development  staffs  and
facilities, greater  experience in  drug  discovery and  development,  obtaining
regulatory  approvals  and  pharmaceutical  product  manufacturing,  and greater
marketing capabilities than the Company.
 
    The Company also is aware of a number of companies and institutions that are
developing or considering the development of potential gene-based and cell-based
treatments, including early-stage gene  therapy companies, large  pharmaceutical
companies,  academic and  research institutions,  government agencies  and other
health care providers. Many of these entities are more advanced than the Company
in their product development programs for gene and cell-based therapies and have
more experience with regulatory agencies and clinical trials. The fields of gene
and cell-based therapies are new and many competitive approaches are being taken
to discover  practical  means by  which  these  technologies can  be  made  into
products.  Rapid  technologic  advances  could  result  in  actual  or  proposed
technologies, products or processes  of the Company  becoming obsolete prior  to
successful commercialization.
 
    The  Company is and  will continue to  be reliant on  strategic partners for
support  of  its  programs,  including  preclinical  and  clinical  development,
manufacturing  and  marketing of  its initial  products.  Each of  the Company's
present and future partners is  conducting multiple product development  efforts
within  each disease or technology area that is the subject of the alliance with
the Company. Any product candidate or technology of the Company, therefore,  may
be subject to internal competition with a potential product under development or
technology  platform under evaluation by a strategic partner. See "-- Dependence
on  Collaborators,"   "Business  --   Background  --   Overview  of   Genomics,"
"-- Progenitor's Functional Genomics Approach" and "-- Competition."
 
    UNCERTAINTY  OF PATENTS AND PROPRIETARY RIGHTS.   The Company's success will
depend to a  significant extent on  its ability to  obtain and enforce  patents,
maintain   trade  secret  protection  and  operate  without  infringing  on  the
proprietary  rights  of   third  parties.  Because   the  patent  positions   of
biotechnology   and  pharmaceutical  companies  can   be  highly  uncertain  and
frequently involve complex legal  and factual questions,  the breadth of  claims
allowed  in  biotechnology and  pharmaceutical  patents or  their enforceability
cannot be predicted. Commercialization of pharmaceutical products can be subject
to substantial delays as a result of the time required for product  development,
testing  and regulatory approval. The value of any patents issued or licensed to
the Company may depend upon the remaining term of patent protection available at
the time products that utilize the patented technology are commercialized.
 
   
    The Company actively  pursues a policy  of seeking patent  protection for  a
number  of its  proprietary products  and technologies.  Progenitor has licensed
from Ohio  University  one U.S.  patent  and pending  U.S.  patent  applications
relating  to  stem cell  technology  and to  gene  delivery technology  (and has
received  a  notice  of  allowance  relating  to  a  gene  delivery   technology
application),  along with certain corresponding  foreign patent applications and
one issued foreign patent. Progenitor  has filed eight U.S. patent  applications
relating  to certain leptin receptors (including  various isoforms of the leptin
receptor), including patent applications filed  in September and December  1994.
In  March 1996,  Progenitor's international patent  application covering certain
leptin  receptors  was  published.  The  Company  believes  that  there  may  be
significant  litigation regarding patent and  other intellectual property rights
relating to leptin and  leptin receptors. The Company  is aware that  Millennium
has  filed a patent application relating to a receptor for leptin and its use in
obesity applications,  and has  licensed  to Hoffmann-La  Roche Inc.  rights  to
develop  certain  therapeutics for  obesity  using Millennium's  discovery  of a
leptin receptor.
    
 
                                       8
<PAGE>
    Millennium has recently filed  a "Protest" in the  United States Patent  and
Trademark  Office (the "USPTO")  in connection with  the Progenitor applications
relating to leptin receptors, including the applications filed in September  and
December  1994. A Protest  is an available  procedure sometimes used  by a third
party to provide the patent examiner  who is reviewing the involved  application
or  applications with what the third  party believes to be relevant information.
The Protest  procedure  does  not  afford  any  right  to  the  third  party  to
participate  in the patent prosecution process  beyond the filing of its written
Protest. Millennium's  Protest  primarily  argues that  any  claims  allowed  to
Progenitor should not be so broad as to cover Millennium's own leptin receptor.
 
    There   can  be  no  assurance  that  Millennium's  patent  application,  or
additional patent applications filed by Millennium or others, will not result in
issued patents covering a leptin receptor, the leptin protein or other  ligands,
or  any of their respective  uses, including obesity. There  can be no assurance
that the invention by Millennium will  be accorded an invention date later  than
Progenitor's  invention date, that  any patent will issue  to Progenitor or that
any such  patent issued  to Progenitor  would be  broad enough  to cover  leptin
receptors  of Millennium or others. Progenitor's failure to obtain a patent on a
leptin receptor,  or its  failure to  obtain  a patent  that covers  the  leptin
receptors  of Millennium or others, or the issuance of a patent to a third party
covering a leptin receptor, the leptin protein or other ligands, or any of their
respective uses, including obesity, could have a material adverse effect on  the
Company's business, financial condition and results of operations.
 
    A  number of other groups are  attempting to identify partial gene sequences
and full-length genes, the functions of  which have not been characterized.  The
public  availability  of partial  gene sequence  information before  the Company
applies  for  patent  protection  on  a  corresponding  full-length  gene  could
adversely  affect the Company's ability to obtain patent protection with respect
to such gene. To the extent any  patents issue to other parties on such  partial
or  full-length genes,  and as  other patents  issue with  the expansion  of the
biotechnology industry,  the  risk increases  that  the potential  products  and
processes  of the Company or its collaborative  partners may give rise to claims
of patent infringement.
 
    The patent positions  of pharmaceutical and  biotechnology firms,  including
the  Company, are uncertain and involve  complex legal and factual questions for
which important legal principles are largely unresolved, particularly in  regard
to  human therapeutic  uses. Substantial periods  of time pass  before the USPTO
responds to patent applications. In addition,  the coverage claimed in a  patent
application   can  be   significantly  reduced   before  a   patent  is  issued.
Consequently, the Company  does not know  whether any of  its pending or  future
patent  applications will result in  the issuance of patents  or, if any patents
are issued,  whether  the  patents  will be  subjected  to  further  proceedings
limiting  their  scope, and  whether they  will provide  significant proprietary
protection or competitive  advantage, or  will be  circumvented or  invalidated.
Because patent applications in the United States are maintained in secrecy until
patents  issue and patent applications in  certain other countries generally are
not published  until  more  than 18  months  after  they are  filed,  and  since
publication  of discoveries in scientific or patent literature often lags behind
actual discoveries, the Company  cannot be certain that  it or any licensor  was
the  first creator of inventions covered  by pending patent applications or that
it or  such  licensor  was  the  first  to  file  patent  applications  on  such
inventions.
 
    There  can be no assurance  that the Company's patents,  if issued, would be
held valid or enforceable by a court  or that such patents would cover  products
or   technologies  of  the  Company's   competitors.  Competitors  or  potential
competitors may have filed applications for or received patents, and may  obtain
additional  patents and  proprietary rights  relating to  compounds or processes
competitive with those of  the Company. To protect  its proprietary rights,  the
Company  may be required to participate  in interference proceedings declared by
the USPTO to determine priority of invention, which could result in  substantial
cost to the Company. Moreover, even if the Company's patents issue, there can be
no  assurance that they  will provide sufficient  proprietary protection or will
not be later limited, circumvented or invalidated. Accordingly, there can be  no
assurance  that  the  Company  will develop  proprietary  technologies  that are
patentable, that the Company's patent applications will result in patents  being
 
                                       9
<PAGE>
issued  or that, if  issued, patents will  afford protection against competitors
with similar technology  or products, nor  can there be  any assurance that  the
Company's patents will be held valid by a court of competent jurisdiction.
 
    In  addition to patent protection, the  Company also relies to a significant
extent  upon  trade  secret  protection  for  its  unpatented  confidential  and
proprietary   information  including   many  of  the   Company's  key  discovery
technologies, such  as its  proprietary methods  of isolating  and  manipulating
murine  ES cells. There can  be no assurance that  others will not independently
develop substantially  equivalent  proprietary  information  and  techniques  or
otherwise   gain  access  to  the  Company's  trade  secrets  or  disclose  such
technology. To protect its  trade secrets, the  Company requires its  employees,
consultants,  scientific  advisors and  parties  to collaborative  agreements to
execute confidentiality  agreements upon  the  commencement of  employment,  the
consulting  relationship or the  collaboration with the Company.  In the case of
employees, the agreements also provide  that all inventions resulting from  work
performed  by them while employed by the  Company will be the exclusive property
of the Company. There can be  no assurance, however, that these agreements  will
provide  meaningful  protection  of  the  Company's  trade  secrets  or adequate
remedies in the  event of unauthorized  use or disclosure  of such  information,
that  the  Company  can  meaningfully  protect  its  rights  in  such unpatented
proprietary technology through other means, that any obligation to maintain  the
confidentiality   of  such  proprietary  technology  will  not  be  breached  by
employees, consultants,  advisors, collaborative  partners  or others,  or  that
others  will not independently develop  substantially equivalent technology. The
loss  of  trade  secret  protection  of  any  of  the  Company's  key  discovery
technologies  would materially  and adversely  affect the  Company's competitive
position and could  have a material  adverse effect on  the Company's  business,
financial condition and results of operations. Finally, disputes may arise as to
the  ownership of proprietary rights to the extent that outside collaborators or
consultants apply technological information  developed independently by them  or
others to Company projects or apply Company technology to other projects and, if
adversely  determined, such disputes could have a material adverse effect on the
Company's business, financial condition and results of operations.
 
    The Company may incur substantial costs  if it is required to defend  itself
in patent suits brought by third parties or if the Company initiates such a suit
to enforce the Company's patents or to determine the scope and validity of other
parties'  proprietary  rights.  Any  legal action  against  the  Company  or its
collaborators or licensees  claiming damages  and seeking  to enjoin  commercial
activities relating to the affected products and processes could, in addition to
subjecting  the Company to potential liability  for damages, require the Company
or its collaborators or licensees  to obtain a license  or licenses in order  to
continue to manufacture or market the affected products and processes. There can
be no assurance that the Company or its collaborators or licensees would prevail
in  any such action or that any license required under any such patents would be
made available on commercially acceptable terms, if at all. Any adverse  outcome
of  such  litigation  could have  a  material  adverse effect  on  the Company's
business, financial condition  and results  of operations. In  addition, if  the
Company  becomes involved  in such  litigation, it  could consume  a substantial
portion of  the Company's  managerial and  financial resources.  The Company  is
unable  to predict  how courts  will resolve any  future issues  relating to the
validity and scope of its patents should they be challenged.
 
    It is uncertain whether any third-party patents will require the Company  to
alter  its products or  processes, obtain licenses,  cease certain activities or
pay substantial damages. If any licenses are required, there can be no assurance
that the  Company  will be  able  to obtain  any  such license  on  commercially
acceptable  terms, if at  all. Failure by  the Company or  its collaborators and
licensees to obtain a  license to any technology  required to commercialize  the
Company's  discoveries  may  have a  material  adverse effect  on  the Company's
business, financial  condition  and  results of  operations.  See  "Business  --
Patents and Proprietary Rights."
 
    UNCERTAINTIES  RELATED  TO  CLINICAL  TRIALS.    Before  seeking  regulatory
approvals for  the  commercial  sale  of any  products  that  may  be  developed
incorporating  the  Company's  discoveries,  the  Company  or  its collaborative
partners will  be  required  to  demonstrate  through  preclinical  studies  and
clinical  trials that such products are safe and effective for use in the target
indications. To date, no product candidates
 
                                       10
<PAGE>
incorporating the  Company's  discoveries  have  entered  clinical  trials.  The
results from preclinical studies and early clinical trials may not be indicative
of  results that will  be obtained in  large-scale testing, and  there can be no
assurance that any clinical trials,  if undertaken, will demonstrate  sufficient
safety  and efficacy to obtain the requisite regulatory approvals or will result
in marketable products. Clinical trials  also are often conducted with  patients
having  advanced  stages  of  disease. During  the  course  of  treatment, these
patients can die or  suffer other adverse medical  effects for reasons that  may
not  be related to the product candidate being tested but which can nevertheless
affect clinical  trial  results. A  number  of companies  in  the  biotechnology
industry  have suffered significant  setbacks in advanced  clinical trials, even
after achieving promising results  in earlier trials.  If products developed  by
the Company or its collaborative partners are not shown to be safe and effective
in  clinical trials, the resulting delays in developing other product candidates
and conducting related preclinical testing and  clinical trials, as well as  the
need  for  additional financing,  would have  a material  adverse effect  on the
Company's business, financial condition and results of operations. See "Business
- -- Progenitor's Discovery Programs."
 
    GOVERNMENT REGULATION;  NO  ASSURANCE  OF REGULATORY  APPROVAL.    Prior  to
marketing,  any  new drug  or  other product  developed  by the  Company  or its
collaborative partners must undergo an extensive regulatory approval process  in
the  United States and other countries.  This regulatory process, which includes
preclinical studies and clinical trials, and may include post-marketing studies,
of each product candidate  to establish its safety  and efficacy, usually  takes
many  years and  require the  expenditure of  substantial resources. Preclinical
tests include laboratory evaluations and  will require animal studies  conducted
in  accordance the United States Food  and Drug Administration's ("FDA") current
Good Laboratory Practices ("cGLP") regulations to assess the product's potential
safety and efficacy. Data obtained from preclinical studies and clinical  trials
are  susceptible to varying  interpretations that could  delay, limit or prevent
regulatory approval. Delays  or rejections  also may be  encountered based  upon
changes  in FDA  policies for  drug or  biologic approval  during the  period of
product development  and FDA  regulatory  review of  each new  drug  application
("NDA")  submitted in the case of  new pharmaceutical agents, or product license
application ("PLA")  in  the  case  of biologics.  Product  development  of  new
pharmaceuticals is highly uncertain, and unanticipated developments, clinical or
regulatory  delays, unexpected  adverse side  effects or  inadequate therapeutic
efficacy could slow or  prevent the product development  efforts of the  Company
and  its collaborators or licensees, and have a materially adverse effect on the
Company's business, financial condition and results of operations. There can  be
no  assurance that regulatory approval  will be obtained for  any drugs or other
products developed by the  Company or its  collaborative partners or  licensees.
Furthermore,  regulatory approval may entail limitations on the indicated use of
a drug or other product. Because certain  of the products likely to result  from
the Company's discovery programs involve the application of new technologies and
may  be based upon a  new therapeutic approach, such  products may be subject to
substantial additional review by various government regulatory authorities other
than the FDA and, as a result, regulatory approvals may be obtained more  slowly
than  for products  using conventional  technologies. Under  current guidelines,
proposals to conduct  clinical research involving  gene therapy at  institutions
supported  by the National Institutes of Health  ("NIH") must be approved by the
Recombinant DNA  Advisory  Committee  ("RAC") and  the  NIH.  Furthermore,  gene
therapies  are relatively new technologies and  have not been tested extensively
in humans.  The regulatory  requirements governing  these products  and  related
clinical procedures for their use are uncertain and are subject to change.
 
    Even  if  regulatory  approval  is  obtained,  a  marketed  product  and its
manufacturer are subject to continuing review. Among the conditions for  product
approval  and  continued  marketing approval  is  that the  quality  control and
manufacturing procedures of the Company or its collaborative partners conform to
the FDA's current good manufacturing practice ("cGMP") regulations which must be
followed at all times. In  complying with cGMP requirements, manufacturers  must
expend  time,  money and  effort  on a  continuing  basis in  production, record
keeping and  quality control.  Manufacturing establishments,  both domestic  and
foreign,  are subject to inspection by or under  the authority of the FDA and by
other federal, state and  local agencies. Failure to  pass such inspections  may
subject the manufacturer to
 
                                       11
<PAGE>
possible  FDA actions  such as the  suspension of manufacturing,  seizure of the
product, withdrawal of approval or other regulatory sanctions. The FDA also  may
require the manufacturer to recall a product from the market.
 
    Discovery  of previously  unknown problems with  a product  may have adverse
effects on the Company's business, including withdrawal of the product from  the
market.   Violations  of   regulatory  requirements  at   any  stage,  including
preclinical studies and clinical trials, the approval process or  post-approval,
may  result in various adverse consequences  to the Company, including the FDA's
delay in approval  or refusal to  approve a product,  withdrawal of an  approved
product  from the  market or  the imposition  of criminal  penalties against the
manufacturer  and  NDA  or  PLA  holder.  The  Company  has  not  submitted   an
investigational  new drug application ("IND") for  any product candidate, and no
product candidate has been approved  for commercialization in the United  States
or elsewhere. The Company intends to rely primarily on its strategic partners to
file INDs and generally direct the regulatory approval process. No assurance can
be  given that  the Company  or any of  its strategic  partners will  be able to
conduct clinical testing or obtain the necessary approvals from the FDA or other
regulatory authorities for any products. Failure to obtain required governmental
approvals will delay or preclude the Company's strategic partners from marketing
drugs or other products developed by the Company or limit the commercial use  of
such  products  and  could  have  a material  adverse  effect  on  the Company's
business, financial  condition  and  results of  operations.  See  "Business  --
Government Regulation."
 
    DEPENDENCE  ON  KEY PERSONNEL.   The  Company is  highly dependent  upon the
principal members of its scientific and management staff and the services of Dr.
Douglass B.  Given, President  and Chief  Executive Officer,  and Dr.  H.  Ralph
Snodgrass, Vice President, Research and Chief Scientific Officer, in particular.
The  Company has no employment agreements with its executive officers other than
Dr. Given. The loss of any of these persons could have a material adverse effect
on the Company's  business, financial  condition and results  of operations.  In
order to support the Company's existing operations, the Company will be required
to   hire  and  retain  additional   management,  administrative  and  financial
personnel,  including  a  chief  financial  officer.  Recruiting  and  retaining
qualified  scientific personnel and advisors to perform research and development
work in the future also will be critical to the Company's success. There can  be
no  assurance that the Company will be able to attract and retain such personnel
and  advisors  on  acceptable  terms   given  the  competition  among   numerous
pharmaceutical,  biotechnology  and  other  companies,  universities  and  other
research institutions  for  experienced  personnel and  advisors.  In  addition,
Progenitor's  anticipated growth and  expansion are expected  to place increased
demands on the  Company's resources and  management skills. The  failure of  the
Company's  existing personnel to handle such  increased demands or the Company's
failure to attract  and to  retain additional personnel  with such  capabilities
could  have  a  material adverse  effect  on the  Company's  business, financial
condition and results of operations. See "Management."
 
    DEPENDENCE ON RESEARCH COLLABORATORS AND  SCIENTIFIC ADVISORS.  The  Company
has  relationships  with collaborators  at academic  and other  institutions who
conduct research in  cooperation with  the Company. Such  collaborators are  not
employees  of  the Company.  All of  the Company's  consultants are  employed by
employers other than the Company and  may have commitments to, or consulting  or
advisory contracts with, other entities that may limit their availability to the
Company. As a result, the Company has limited control over their activities and,
except as otherwise required by its collaboration and consulting agreements, can
expect  only limited  amounts of  their time  to be  dedicated to  the Company's
activities. The potential success of the Company's discovery programs depends in
part  on  continued  collaborations  with  researchers  at  academic  and  other
institutions.  There  can be  no  assurance that  the  Company will  be  able to
negotiate  additional   acceptable   collaborations  at   academic   and   other
institutions  or  that  its existing  collaborations  will be  maintained  or be
successful.
 
    The Company's research collaborators and scientific advisors sign agreements
which provide for confidentiality of  the Company's proprietary information  and
results of studies. There can be no assurance, however, that the Company will be
able    to    maintain    the   confidentiality    of    its    technology   and
 
                                       12
<PAGE>
other confidential information in connection  with every collaboration, and  any
unauthorized  dissemination of the Company's confidential information could have
a material adverse  effect on  the Company's business,  financial condition  and
results of operations. See "-- Uncertainty of Patents and Proprietary Rights."
 
    LACK    OF    COMMERCIAL    MANUFACTURING,    DISTRIBUTION    OR   MARKETING
CAPABILITIES.   To  date,  the  Company  has  focused  its  hiring  on  research
scientists  and  a small  administrative and  managerial staff  and has  made no
investment in manufacturing, marketing or  product sales resources. The  Company
does not generally expect to engage directly in manufacturing, marketing or sale
of  products  and  intends  to  contract with  others  in  order  to  pursue the
commercialization of any  products developed based  upon its discoveries.  There
can  be  no  assurance  that  the  Company  will  be  able  to  enter  into such
arrangements on acceptable terms, if at all. The Company will be dependent to  a
significant  extent on collaborative  partners, licensees or  other entities for
development, manufacturing and commercialization of products. If the Company  is
unable  to obtain or retain third-party manufacturing on commercially acceptable
terms, its ability to commercialize products  may be delayed or foreclosed.  The
Company's dependence upon third parties for the manufacture, marketing and sales
of  products may adversely  affect the Company's ability  to develop and deliver
products on a timely and competitive basis. The Company's current facilities and
staff are inadequate for commercial production and distribution of products.  If
the  Company  chooses  in the  future  to  engage directly  in  the development,
manufacturing and marketing  of certain  products, it  will require  substantial
additional funds, personnel and production and other facilities. There can be no
assurance  that  any of  these resources  will  be available  to the  Company on
acceptable terms, if at all. See "-- Need for Additional Capital; Uncertainty of
Additional Funding" and "-- Dependence on Collaborators."
 
    UNCERTAINTY   OF    HEALTH   CARE    REFORM   MEASURES    AND    THIRD-PARTY
REIMBURSEMENT.    The business  and  financial condition  of  pharmaceutical and
biotechnology  companies  will  continue  to  be  affected  by  the  efforts  of
third-party  payors,  such  as  government  health  administration  authorities,
private health insurers and other organizations,  to contain or reduce the  cost
of  health care. In the United States and in certain foreign jurisdictions there
have been, and the Company expects that  there will continue to be, a number  of
legislative  and regulatory proposals aimed at  changing the health care system.
While the  Company cannot  predict whether  any such  legislative or  regulatory
proposals  will be  adopted or the  effect that  such proposals may  have on its
business, the consideration or approval of such proposals could have a  material
adverse  effect on the  trading and market price  of the Common  Stock or on the
Company's ability  to  raise  capital  or  to  obtain  additional  collaborative
partners,  and  the adoption  of such  proposals could  have a  material adverse
effect on the Company's business, financial condition and results of operations.
 
    In both domestic  and foreign  markets, successful commercial  sales of  the
Company's  or its collaborators' or licensees' potential products will depend in
part  on  the   availability  of  reimbursement   from  government  and   health
administrative authorities, private health insurers or other third-party payors.
Third-party payors are increasingly challenging the price and cost-effectiveness
of  medical  products and  services. Significant  uncertainty  exists as  to the
reimbursement status of newly approved health care products. Future  legislation
and  regulations affecting  the pricing  of pharmaceuticals  could further limit
reimbursement for medical products and services. There can be no assurance  that
any  of the  Company's potential products  will be  considered cost-effective or
that adequate third-party reimbursement will be available to enable  Progenitor,
its collaborators or licensees to maintain price levels sufficient to realize an
appropriate  return on  its investment.  In addition,  the trend  toward managed
health care  in the  United States  and the  concurrent growth  of managed  care
organizations,  such as health maintenance organizations, which could control or
significantly influence the purchase  of health care  services and products,  as
well  as legislative  proposals to  reduce government  insurance programs, could
result in  pricing pressure  for any  products that  might be  developed by  the
Company.  If  adequate reimbursement  is not  provided  by government  and other
third-party  payors  for  the  Company's  or  its  collaborative  partners'   or
licensees'  potential products, there would be  a material adverse effect on the
Company's business, financial condition and results of operations. See "Business
- -- Government Regulation."
 
                                       13
<PAGE>
    RISK OF PRODUCT LIABILITY.  The testing, manufacture, marketing and sale  of
pharmaceutical  and other products entail the  inherent risk of liability claims
or product recalls and associated  adverse publicity. Clinical trials and  sales
by  the  Company  or  its  collaborators  or  licensees  of  potential  products
incorporating the  Company's discoveries  may expose  the Company  to  potential
liability  resulting from the use of  such products. Such liability might result
from claims made directly by consumers or by regulatory agencies, pharmaceutical
companies or others selling such products.  The Company currently has a  limited
amount  of  clinical  trial  and product  liability  insurance  coverage through
Interneuron. The Company will seek to obtain its own coverage upon completion of
this Offering  and  to maintain  and  appropriately increase  such  coverage  as
clinical  development of any  product candidates progresses and  if and when its
products are ready  to be  commercialized. There can  be no  assurance that  the
Company  will  be able  to  obtain such  insurance  or, if  obtained,  that such
insurance can  be acquired  at a  reasonable cost  or in  sufficient amounts  to
protect  the Company  against such liability.  Certain of  the Company's license
agreements require it  to indemnify licensors  against product liability  claims
arising  from products developed using the licensed technology. Also, certain of
these agreements  and  other collaboration  agreements  require the  Company  to
maintain  minimum levels of insurance coverage.  The failure to maintain product
liability coverage, the occurrence of any product liability claim or a recall of
products of the Company or its  collaborators or licensees, if developed,  could
inhibit  or prevent commercialization of products being developed by the Company
and could have a  material adverse effect on  the Company's business,  financial
condition  and results  of operations.  In addition,  to the  extent any product
liability claim  exceeds the  amount of  any insurance  coverage, the  Company's
business,  financial condition and results of operations could be materially and
adversely affected. See "Business -- Strategic Collaboration Agreements" and "--
Product Liability Insurance."
 
    NO PRIOR TRADING MARKET;  NO ASSURANCE OF  ACTIVE TRADING MARKET;  POTENTIAL
VOLATILITY  OF STOCK  PRICE. Prior  to this Offering,  there has  been no public
market for the Common Stock and there can be no assurance that an active  public
market for the Common Stock will develop or be sustained after the Offering. The
initial  public offering price  will be determined  through negotiations between
the Company  and  representatives  of  the Underwriters  and  there  can  be  no
assurance  that future market prices  for the Common Stock  will equal or exceed
the initial public offering price. The stock market has experienced  significant
price  and  volume  fluctuations  that  are  often  unrelated  to  the operating
performance  of  particular  companies.  In  addition,  the  market  prices   of
securities  of  other  biotechnology  companies in  the  past  have  been highly
volatile and the market price of the Company's Common Stock also may  experience
such volatility. Factors such as the results of preclinical studies and clinical
trials  by the Company or its  collaborative partners, licensees or competitors,
evidence  of  the  safety  or  efficacy  of  products  of  the  Company  or  its
competitors,  announcements  of  technological innovations  or  new discoveries,
product opportunities or products by the Company or its competitors, changes  in
governmental  regulations or third-party reimbursement policies, developments in
patent  or  other  proprietary  rights  of  the  Company  or  its   competitors,
fluctuations  in the Company's  operating results and  changes in general market
conditions for biotechnology stocks could have  an adverse impact on the  future
price of the Common Stock. See "Underwriting."
 
   
    CONTROL   OF  COMPANY  BY,   AND  POTENTIAL  CONFLICTS   OF  INTEREST  WITH,
INTERNEURON.   Following  the  Offering,  Interneuron  will  own  51.8%  of  the
outstanding   Common  Stock   of  the   Company  (49.3%   if  the  Underwriters'
over-allotment option  is  exercised  in full).  Accordingly,  Interneuron  will
continue  to control the  election of directors  of the Company  and voting with
respect to matters submitted to stockholders, including extraordinary  corporate
transactions  such as  a merger  or sale of  substantially all  of the Company's
assets. In  addition,  the Company  and  Interneuron  intend to  enter  into  an
intercompany services agreement that will provide among other things that in the
event  of any future equity  offering by the Company,  Interneuron will have the
right to  purchase (at  the same  price and  on the  same terms  as such  equity
offering)  a  portion  of  the  shares  being  offered  so  as  to  maintain its
fully-diluted interest in Progenitor immediately prior to such equity  offering,
subject  to certain limitations. Interneuron's  ownership of a substantial block
of the Company's voting  stock could have the  effect of delaying or  preventing
sales  of additional securities of the Company or a sale of the Company or other
change of  control  supported by  the  other  stockholders of  the  Company.  In
addition, the Company may be subject
    
 
                                       14
<PAGE>
to  various  risks  arising  from  Interneuron's  influence  over  the  Company,
including conflicts  of interest  relating to  new business  opportunities  that
could  be pursued by the Company or by Interneuron and its other affiliates, and
significant corporate transactions for  which stockholder approval is  required.
See  "Certain  Transactions  -- Relationship  with  Interneuron"  and "Principal
Stockholders."
 
   
    ANTI-TAKEOVER CONSIDERATIONS.  After the Offering, the Company will have the
authority to issue  up to 5,000,000  shares of  Preferred Stock in  one or  more
series  and to  fix the  powers, designations,  preferences and  relative rights
thereof without any further  vote or action by  the Company's stockholders.  The
Company  has no current plans  to issue shares of  Preferred Stock. However, the
rights of the holders of Common Stock  will be subject to, and may be  adversely
affected by, the rights of the holders of any Preferred Stock that may be issued
in  the future. The issuance of Preferred Stock would dilute the voting power of
holders of Common  Stock and  could have the  effect of  delaying, deferring  or
preventing  a change  in control  of the  Company. In  addition, all outstanding
options under the Company's 1992 Stock Option Plan and 1996 Stock Incentive Plan
become exercisable, and purchase  dates under the  1996 Employee Stock  Purchase
Plan  could be accelerated, upon certain changes  in control of the Company. The
Company is subject  to the  provisions of Section  203 of  the Delaware  General
Corporation Law, which could delay or make more difficult a merger, tender offer
or  proxy contest involving the Company and  may have the effect of discouraging
takeovers which  could be  in  the best  interest  of certain  stockholders.  In
general,  the  statute  prohibits  a  publicly  held  Delaware  corporation from
engaging in  a "business  combination" with  an "interested  stockholder" for  a
period  of three  years after the  date of  the transaction in  which the person
became an interested stockholder, unless the business combination is approved in
a prescribed manner. There can be  no assurance that this provision, the  rights
of  option holders and the  Company's ability to issue  Preferred Stock will not
have an adverse effect on the market value of the Company's stock in the future.
See "Management -- Stock Plans" and "Description of Capital Stock."
    
 
    HAZARDOUS AND RADIOACTIVE  MATERIALS; ENVIRONMENTAL MATTERS.   Research  and
development  conducted by the  Company involves the  controlled use of hazardous
materials,  chemicals,  biological  materials  and  radioactive  compounds.  The
Company,   and  its  collaborative  partners,  as  applicable,  are  subject  to
international, federal, state and local laws and regulations governing the  use,
manufacture, storage, handling and disposal of such substances and certain waste
products.  The  Company  believes that  the  safety procedures  relating  to its
in-house research and development and production efforts comply in all  material
respects  with the standards currently prescribed  by such laws and regulations.
However, the risk  of accidental  contamination or injury  from these  materials
cannot  be completely eliminated. In the event  of such an accident, the Company
could be held  liable for any  resulting damages, and  any such liability  could
exceed  the Company's  resources. Moreover, there  can be no  assurance that the
Company's collaborative partners are and will continue to be in compliance  with
such  standards or that  the Company will  not be required  to incur significant
costs in the future to  comply with new or  modified standards. In such  events,
there  would be a  material adverse effect on  the Company's business, financial
condition and results of operations. See "Business -- Government Regulation."
 
    MANAGEMENT DISCRETION AS TO USE OF PROCEEDS.  The Company anticipates  using
the  net proceeds  of the  Offering primarily  to fund  research and development
activities, the expansion of facilities,  working capital and general  corporate
purposes.  The Company also may  use the net proceeds  of the Offering for other
purposes,  including  the   acquisition  of  technology   rights,  products   or
businesses. Accordingly, management will retain broad discretion over the use of
the  net proceeds of the Offering. There can be no assurance as to the timing or
application of such proceeds,  or that the application  thereof will not have  a
material adverse effect on the Company's future business, financial condition or
results of operations. See "Use of Proceeds."
 
   
    SHARES  ELIGIBLE  FOR  FUTURE SALE;  REGISTRATION  RIGHTS;  POSSIBLE ADVERSE
EFFECT ON STOCK  PRICE.  Sales  of substantial  amounts of Common  Stock in  the
public  market after the  Offering, or the possibility  of such sales occurring,
could adversely affect  prevailing market  prices for  the Common  Stock or  the
future  ability of the  Company to raise  capital through an  offering of equity
securities. Of the 7,377,936  shares to be outstanding  after the Offering,  the
2,500,000   shares   of   Common   Stock   offered   hereby   will   be   freely
    
 
                                       15
<PAGE>
   
tradeable without restriction in the public  market unless such shares are  held
by  "affiliates" of the Company,  as that term is defined  in Rule 144 under the
Securities Act  of  1933,  as  amended (the  "Securities  Act").  The  remaining
4,877,936  shares of Common Stock are restricted securities under the Securities
Act and may be sold in the public market only if they are registered or if  they
qualify  for  exemption  from  registration  under Rule  144  or  701  under the
Securities Act. Pursuant to "lock-up" agreements, all of the Company's executive
officers and directors and certain stockholders who collectively hold 902,541 of
such restricted securities have agreed not  to offer, sell or otherwise  dispose
of  any of their restricted securities for a period of 180 days from the date of
this  Prospectus  without  the  prior  written  consent  of  Vector   Securities
International,   Inc.  Interneuron  will  hold   3,820,134  of  such  restricted
securities and has agreed pursuant to a lock-up agreement not to offer, sell  or
otherwise  dispose of any of its restricted  securities for a period of 365 days
from the date  of this Prospectus  without the prior  written consent of  Vector
Securities  International, Inc.  The Company  has also  agreed that  it will not
offer, sell or otherwise dispose of Common  Stock for a period of 180 days  from
the  date  of  this  Prospectus  without the  prior  written  consent  of Vector
Securities International, Inc.,  other than  pursuant to  existing stock  option
plans.  Upon termination  of the  lock-up agreements,  approximately 409,413 and
3,593,991 of  the restricted  securities will  be available  for immediate  sale
beginning  181  days  and  366  days,  respectively,  after  the  date  of  this
Prospectus, in the public market subject  to certain volume, manner of sale  and
other  limitations  under  Rule 144  and  385,450  shares will  be  eligible for
immediate sale 181  days after the  date of this  Prospectus without  limitation
under  Rule  144(k).  Vector Securities  International,  Inc. may,  at  its sole
discretion and at any  time without notice,  release all or  any portion of  the
shares   subject  to  such  lock-up  agreements.  The  Securities  and  Exchange
Commission has proposed revisions to Rule 144,  the effect of which would be  to
shorten the holding periods under Rule 144. If enacted, these proposed revisions
would  increase, potentially substantially,  the number of  shares that would be
available for sale in the public market following the expiration of the  lock-up
agreements.  See "Description of Capital Stock"  and "Shares Eligible for Future
Sale."
    
 
   
    After the Offering,  holders of  an aggregate  of 287,399  shares of  Common
Stock  (including  26,126  shares  of Common  Stock  issuable  upon  exercise of
outstanding warrants) will  be entitled to  certain rights with  respect to  the
registration  of such shares  for resale under the  Securities Act. In addition,
the Company intends to file Registration  Statements on Form S-8 after the  date
of  this Prospectus to register  an aggregate of 606,625  shares of Common Stock
reserved for  issuance upon  exercise of  outstanding options,  an aggregate  of
736,700  shares of Common Stock reserved  for issuance pursuant to future option
grants under the Company's 1992 Stock  Option Plan and the Company's 1996  Stock
Incentive  Plan and an aggregate of 100,000  shares of Common Stock reserved for
issuance under  the  Company's  1996  Employee  Stock  Purchase  Plan.  If  such
registrations  cause a large number  of shares to be  registered and sold in the
public market, such sales could have an  adverse effect on the market price  for
the  Company's Common Stock.  See "Description of  Capital Stock -- Registration
Rights" and "Shares Eligible for Future Sale."
    
 
   
    DILUTION.  Investors purchasing shares of Common Stock in the Offering  will
incur  immediate and substantial  dilution equal to  $8.33 per share. Additional
dilution is likely to occur upon the exercise of outstanding warrants and  stock
options. See "Dilution."
    
 
    ABSENCE OF DIVIDENDS.  The Company has never declared or paid cash dividends
on its Common Stock. The Company currently intends to retain any future earnings
to  finance the growth and development of  its business and, therefore, does not
anticipate paying any cash  dividends in the  foreseeable future. See  "Dividend
Policy."
 
                                       16
<PAGE>
                                USE OF PROCEEDS
 
    The  net proceeds  from the  sale of  the 2,500,000  shares of  Common Stock
offered hereby at an assumed initial  public offering price of $12.00 per  share
are   estimated  to  be  approximately  $27.1  million  ($31.2  million  if  the
Underwriters' over-allotment  option  is  exercised in  full),  after  deducting
estimated  underwriting discounts and commissions  and estimated expenses of the
Offering payable by the Company.
 
    The Company anticipates using the net proceeds of the Offering primarily  to
fund  research and development  activities, to fund  the expansion of facilities
and acquisition  of equipment,  and for  working capital  and general  corporate
purposes. The Company may also use a portion of the net proceeds of the Offering
to  acquire  technology rights,  products  or businesses.  No  such transactions
involving a material amount of consideration are being negotiated as of the date
of this Prospectus. The amounts actually  expended for each purpose will  depend
on numerous factors, including the scientific progress in and the breadth of the
Company's  research  and  development  programs;  the  results  of  research and
development, preclinical studies and clinical trials conducted by the Company or
its collaborative partners or licensees,  if any; the acquisition and  licensing
of  products and technologies;  the Company's ability  to establish and maintain
relationships with corporate and academic collaborators; competing technological
and market developments;  the time  and costs involved  in filing,  prosecuting,
defending  and enforcing patent and intellectual property claims; the receipt of
licensing  or  milestone   fees  from  any   current  or  future   collaborative
arrangements,  if established;  the continued  funding of  governmental research
grants; the  timing of  regulatory approvals,  if any;  and other  factors.  The
Company estimates that, at its planned rate of spending, the net proceeds of the
Offering  and the interest  income thereon, together with  any existing cash and
cash equivalents, will  be sufficient to  meet its capital  requirements for  at
least the next 18 months. There can be no assurance, however, that the Company's
assumptions  regarding its  future levels  of expenditures  and operating losses
will prove accurate. Pending  such uses, the Company  intends to invest the  net
proceeds  of the Offering in  investment grade, interest-bearing securities. See
"Risk Factors -- History  of Operating Losses;  Anticipation of Future  Losses,"
"--  Need  for  Additional  Capital;  Uncertainty  of  Additional  Funding," "--
Management Discretion as to  Use of Proceeds"  and "Management's Discussion  and
Analysis  of  Financial Condition  and Results  of  Operations --  Liquidity and
Capital Resources."
 
                                DIVIDEND POLICY
 
    The Company  has never  declared or  paid cash  dividends on  shares of  its
Common  Stock. The Company  currently intends to retain  any future earnings for
its business and,  therefore, does not  anticipate paying any  dividends in  the
foreseeable future.
 
                                       17
<PAGE>
                                 CAPITALIZATION
 
   
    The  following table sets forth the capitalization of the Company as of June
30, 1996  (i) on  an actual  basis as  if the  1-for-2 reverse  stock split  had
occurred  prior to  June 30,  1996; (ii)  on a  pro forma  basis to  give effect
(assuming an initial public offering price of $12.00 per share) upon the closing
of the Offering  to (a) the  automatic conversion of  all outstanding shares  of
Preferred  Stock into an aggregate of 1,774,014  shares of Common Stock, (b) the
conversion of a convertible  debenture and promissory  note held by  Interneuron
into  an aggregate of 186,279  shares of Common Stock  (based on the outstanding
balance as  of June  30,  1996) and  (c) the  purchase  by The  Ohio  University
Foundation  of 25,000  shares of  Common Stock  at a  price of  $6.00 per share,
pursuant to a stock purchase right; and  (iii) on a pro forma basis as  adjusted
to reflect the issuance and sale of the 2,500,000 shares of Common Stock offered
hereby (after deducting estimated underwriting discounts and commissions and the
estimated  expenses  of the  Offering),  and the  receipt  of the  estimated net
proceeds therefrom. See "Use of Proceeds" and "Description of Capital Stock."
    
 
   
<TABLE>
<CAPTION>
                                                                                         JUNE 30, 1996
                                                                              ------------------------------------
                                                                                                      PRO FORMA AS
                                                                               ACTUAL     PRO FORMA     ADJUSTED
                                                                              ---------  -----------  ------------
                                                                                         (IN THOUSANDS)
<S>                                                                           <C>        <C>          <C>
Long-term obligations.......................................................  $   2,408   $     172    $      172
Stockholders' equity:
  Preferred Stock, Series A, $.01 par value: 2,120,000 shares authorized;
   2,020,496 shares issued and outstanding, actual; no shares authorized,
   issued or outstanding, pro forma and pro forma as adjusted...............         20          --            --
  Preferred Stock, Series B, $.01 par value: 880,000 shares authorized;
   349,000 shares issued and outstanding, actual; no shares authorized,
   issued or outstanding, pro forma and pro forma as adjusted...............          3          --            --
  Preferred Stock, $.001 par value: 5,000,000 shares authorized; no shares
   issued or outstanding, actual, pro forma and pro forma as adjusted.......         --          --            --
  Common Stock, $.001 par value: 39,000,000 shares authorized; 2,852,779
   shares issued and outstanding, actual; 4,838,072 shares issued and
   outstanding, pro forma; 7,338,072 shares issued and outstanding, pro
   forma as adjusted (1)....................................................          3           5             7
  Additional paid-in capital................................................     14,898      17,304        44,352
  Deficit accumulated during development stage..............................    (17,454)    (17,454)      (17,454)
                                                                              ---------  -----------  ------------
    Total stockholders' equity (deficit)....................................     (2,530)       (145)       26,905
                                                                              ---------  -----------  ------------
      Total capitalization..................................................  $    (122)  $      27    $   27,077
                                                                              ---------  -----------  ------------
                                                                              ---------  -----------  ------------
</TABLE>
    
 
- ------------------------
   
(1) Excludes: (i) 606,625 shares of Common Stock issuable upon exercise of stock
    options outstanding as of August 15, 1996, with a weighted average  exercise
    price  of $6.62 per share; (ii) 26,126  shares of Common Stock issuable upon
    exercise of warrants  outstanding as of  August 15, 1996,  with an  exercise
    price  of $9.18  per share;  and (iii)  836,700 additional  shares of Common
    Stock reserved for issuance under the Company's stock plans. See "Management
    -- Stock Plans" and "Description of Capital Stock."
    
 
                                       18
<PAGE>
                                    DILUTION
 
   
    Pro  forma net tangible book  value per share is  equal to the Company's net
tangible assets (tangible assets of the Company less total liabilities)  divided
by  4,838,072 shares of Common Stock outstanding as  of June 30, 1996 (as if the
1-for-2 reverse split of the Company's  Common Stock had occurred prior to  June
30,  1996), assuming (i)  the automatic conversion of  all outstanding shares of
Preferred Stock into an aggregate of  1,774,014 shares of Common Stock upon  the
closing  of the  Offering, (ii)  the conversion  of a  convertible debenture and
promissory note  held by  Interneuron into  an aggregate  of 186,279  shares  of
Common  Stock upon the closing of the Offering (based on the outstanding balance
as of June 30, 1996) and (iii) the purchase by The Ohio University Foundation of
25,000 shares of Common Stock at a price of $6.00 per share, pursuant to a stock
purchase right. The pro forma net tangible book value of the Company as of  June
30, 1996 was approximately negative $145,000 or negative $.03 per share. Without
taking into account any other changes in pro forma net tangible book value other
than  to give effect to the sale of  the 2,500,000 shares of Common Stock in the
Offering (at an assumed initial public  offering price of $12.00 per share)  and
the  receipt of the estimated net proceeds therefrom, the pro forma net tangible
book value of  the Company as  of June  30, 1996 would  have been  approximately
$26.9  million or $3.67 per share. This  represents an immediate increase in pro
forma net tangible book value of $3.70 per share to existing stockholders and an
immediate dilution of $8.33 per share to new investors. The following table sets
forth the per share dilution to new investors in the Offering:
    
 
   
<TABLE>
<S>                                                                   <C>        <C>
Assumed initial public offering price per share.....................             $   12.00
  Pro forma net tangible book value per share as of June 30, 1996...  $    (.03)
  Increase per share attributable to new investors..................       3.70
                                                                      ---------
Pro forma net tangible book value per share after the Offering......                  3.67
                                                                                 ---------
Dilution per share to new investors.................................             $    8.33
                                                                                 ---------
                                                                                 ---------
</TABLE>
    
 
   
    The following table summarizes, on  a pro forma basis  as of June 30,  1996,
the  differences between existing stockholders and new investors with respect to
the number  of shares  of Common  Stock purchased  from the  Company, the  total
consideration  paid and the average price paid  per share (at an assumed initial
public offering  price  of  $12.00  per share  and  before  deducting  estimated
underwriting discounts and commissions and estimated offering expenses):
    
 
   
<TABLE>
<CAPTION>
                                                 SHARES PURCHASED         TOTAL CONSIDERATION        AVERAGE
                                              -----------------------  --------------------------   PRICE PER
                                                NUMBER      PERCENT       AMOUNT        PERCENT       SHARE
                                              ----------  -----------  -------------  -----------  -----------
<S>                                           <C>         <C>          <C>            <C>          <C>
Existing stockholders.......................   4,838,072       65.9%   $  17,309,599       36.6%    $    3.58
New investors...............................   2,500,000       34.1       30,000,000       63.4         12.00
                                              ----------      -----    -------------      -----
    Total...................................   7,338,072      100.0%   $  47,309,599      100.0%
                                              ----------      -----    -------------      -----
                                              ----------      -----    -------------      -----
</TABLE>
    
 
   
    The  foregoing tables reflect no exercise of outstanding options or warrants
subsequent to June  30, 1996.  As of  August 15,  1996, there  were (i)  606,625
shares of Common Stock issuable upon exercise of outstanding stock options, with
a  weighted average exercise price of $6.62 per share; and (ii) 26,126 shares of
Common Stock issuable upon  exercise of outstanding  warrants, with an  exercise
price of $9.18 per share. To the extent these options or warrants are exercised,
there  will be further  dilution to the new  investors. Furthermore, the Company
has reserved 836,700 additional  shares of Common Stock  for issuance under  its
stock  plans.  The Company's  currently  outstanding shares  of  Series A  and B
Preferred Stock have antidilution and conversion adjustment provisions that will
increase or decrease the number of shares of Common Stock outstanding as of June
30, 1996,  above or  below  the number  of shares  used  in the  calculation  of
dilution to new investors in the event that the initial public offering price is
less than or greater than $12.00 per share. See "Capitalization," "Management --
Stock  Plans," "Description of  Capital Stock -- Preferred  Stock" and "-- Stock
Purchase Right and Warrants."
    
 
                                       19
<PAGE>
                            SELECTED FINANCIAL DATA
 
   
    The following table sets forth selected  financial data of the Company.  The
selected  financial  data  for each  of  the  three years  in  the  period ended
September 30, 1995 and the balance sheet data as of September 30, 1994 and  1995
are derived from the financial statements of the Company which have been audited
by Coopers & Lybrand L.L.P., independent accountants. The selected statements of
operations data for the period from May 8, 1992 (date of inception) to September
30,  1992, and  the balance sheet  data as of  September 30, 1992  and 1993, are
derived from audited financial statements not included herein. The statement  of
operations  data for the  nine months ended June  30, 1995 and  1996 and for the
period from May 8,  1992 (date of  inception) to June 30,  1996 and the  balance
sheet  data as  of June  30, 1996,  have been  derived from  unaudited financial
statements which include all adjustments, consisting solely of normal  recurring
adjustments,   which  management  considers  necessary  to  fairly  present  the
financial information set forth  herein. The results for  the nine months  ended
June  30, 1995  and 1996, are  not necessarily  indicative of the  results to be
expected for  future periods.  The selected  financial data  should be  read  in
conjunction  with "Management's  Discussion and Analysis  of Financial Condition
and Results  of  Operations" and  the  Financial Statements  and  related  Notes
thereto and other financial information included elsewhere herein.
    
 
   
<TABLE>
<CAPTION>
                                                                                                              MAY 8, 1992
                                      MAY 8, 1992                                                               (DATE OF
                                       (DATE OF                                          NINE MONTHS ENDED     INCEPTION)
                                     INCEPTION) TO      YEARS ENDED SEPTEMBER 30,            JUNE 30,              TO
                                     SEPTEMBER 30,   --------------------------------  ---------------------    JUNE 30,
                                         1992          1993       1994        1995       1995        1996         1996
                                    ---------------  ---------  ---------  ----------  ---------  ----------  ------------
                                                            (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                 <C>              <C>        <C>        <C>         <C>        <C>         <C>
STATEMENT OF OPERATIONS DATA:
  Revenues........................     $      --     $      --  $      --  $    2,821  $   2,602  $    1,150   $    3,971
  Expenses:
    Research and development......           775         3,116      4,113       4,228      3,270       2,659       14,891
    General and administrative....           264         1,339      1,275       1,116        857       1,167        5,161
    Interest......................            23           246        648         352        320         104        1,373
                                         -------     ---------  ---------  ----------  ---------  ----------  ------------
      Total expenses..............         1,062         4,701      6,036       5,696      4,447       3,930       21,425
                                         -------     ---------  ---------  ----------  ---------  ----------  ------------
    Net loss......................     $  (1,062)    $  (4,701) $  (6,036) $   (2,875) $  (1,845) $   (2,780)  $  (17,454)
                                         -------     ---------  ---------  ----------  ---------  ----------  ------------
                                         -------     ---------  ---------  ----------  ---------  ----------  ------------
  Pro forma net loss per
   share (1)......................                                         $     (.63)            $     (.58)
                                                                           ----------             ----------
                                                                           ----------             ----------
  Pro forma weighted average
   shares outstanding (1).........                                          4,536,481              4,780,787
                                                                           ----------             ----------
                                                                           ----------             ----------
</TABLE>
    
 
   
<TABLE>
<CAPTION>
                                                                          SEPTEMBER 30,
                                                            ------------------------------------------
                                                              1992       1993       1994       1995     JUNE 30, 1996
                                                            ---------  ---------  ---------  ---------  -------------
                                                                                 (IN THOUSANDS)
<S>                                                         <C>        <C>        <C>        <C>        <C>
BALANCE SHEET DATA:
  Cash and cash equivalents...............................  $      35  $      11  $      10  $   1,174    $      28
  Working capital.........................................       (379)      (562)      (988)      (269)        (683)
  Total assets............................................        568        979        977      2,395        1,400
  Long-term obligations...................................      1,210      6,150     11,767        705        2,408
  Deficit accumulated during development stage............     (1,062)    (5,763)   (11,799)   (14,674)     (17,454)
  Total stockholders' equity (deficit)....................     (1,057)    (5,755)   (11,791)      (101)      (2,530)
</TABLE>
    
 
- --------------------------
(1) See  Note 1 of Notes to  Financial Statements for information concerning the
    computation of pro forma net loss per share.
 
                                       20
<PAGE>
                      MANAGEMENT'S DISCUSSION AND ANALYSIS
                OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS
 
    THE FOLLOWING  DISCUSSION AND  ANALYSIS  OF THE  RESULTS OF  OPERATIONS  AND
FINANCIAL  CONDITION  OF THE  COMPANY  SHOULD BE  READ  IN CONJUNCTION  WITH THE
FINANCIAL STATEMENTS AND NOTES THERETO INCLUDED ELSEWHERE IN THIS PROSPECTUS.
 
OVERVIEW
 
   
    A development stage  company, Progenitor was  incorporated in February  1992
and  commenced operations in May 1992. The Company has devoted substantially all
of its resources since inception to research and development programs. To  date,
all  of the  Company's revenues have  resulted from  payments from collaborative
partners and a grant from the  U.S. Department of Commerce's National  Institute
of Standards and Technology Advanced Technology Program ("ATP") that was awarded
to  the Company in November 1994.  Payments from collaborative partners, license
fees, payments under governmental grants and investment income, in each case, if
any, are expected to be the only sources of revenue for the foreseeable  future.
Certain  payments  under  collaborative  arrangements  are  contingent  upon the
Company meeting certain  milestones. Payments under  collaborative or  licensing
arrangements,  if any, will be subject to significant fluctuation in both timing
and amount and therefore the Company's results of operations for any period  may
not be comparable to the results of operations for any other period. The Company
has  not yet received any royalties or  other revenues from the sale of products
or services  and does  not expect  to receive  any such  revenues for  the  next
several  years,  if  at all.  As  of June  30,  1996,  the Company  had  a total
stockholders' deficit of $2.5 million, including an accumulated deficit of $17.5
million. See  "Risk Factors  --  History of  Operating Losses;  Anticipation  of
Future Losses."
    
 
   
    Interneuron  provided the  initial funding of  the Company  and had invested
$14.9 million in Progenitor in equity and debt financings through June 30, 1996.
Interneuron owns a majority of the outstanding capital stock of the Company  and
will own 51.8% (49.3% if the Underwriters' over-allotment option is exercised in
full)  of the  outstanding Common Stock  following the closing  of the Offering.
Interneuron has no obligation to invest any additional funds in the Company, and
the Company  does  not  expect  Interneuron  to  do  so.  Progenitor  raised  an
additional $1.6 million in net proceeds through a private placement of Preferred
Stock  in fiscal  1995. The Company  intends to seek  additional funding through
public or private equity or debt financing and collaborative arrangements. There
can be no assurance, however, that  additional financing will be available  when
needed,  or  that,  if available,  such  financing  will be  available  on terms
acceptable to the  Company. See "Risk  Factors -- Need  for Additional  Capital;
Uncertainty  of Additional  Funding" and  "Certain Transactions  -- Relationship
With Interneuron."
    
 
    Significant discovery,  research and  development efforts  will be  required
prior to the time any of the Company's gene, receptor or protein discoveries may
develop into product candidates or result in products that may be brought to the
market,  if at all. Products, if any,  resulting from the Company's research and
development programs are not expected to be commercially available for a  number
of  years, if at all, even if any are successfully developed and proven safe and
effective. Significant additional research and development efforts and extensive
preclinical studies and clinical trials will be required prior to submission  of
any  regulatory application for commercial use. See "Risk Factors -- Early Stage
of Development; Uncertainty of Final Product Development."
 
RESULT OF OPERATIONS
 
   
  NINE MONTHS ENDED JUNE 30, 1995 AND 1996
    
 
   
    Revenues decreased from $2.6 million for the nine months ended June 30, 1995
to $1.2  million for  the  nine months  ended June  30,  1996. The  decrease  in
revenues  was largely attributable to a  decrease in receipts from the Company's
collaboration agreement  with  Chiron  from  $2.5 million,  paid  by  Chiron  in
    
 
                                       21
<PAGE>
   
April  1995 as a license fee and  reimbursement of past research and development
expenses in connection  with the  execution of the  collaboration agreement,  to
$500,000,  paid  by Chiron  for continued  funding  of research  and development
expenses pursuant to  such collaboration agreement.  This decline was  partially
offset  by an increase in  revenues recorded by the  Company under its ATP grant
(which began in June  1995 and provides for  aggregate payments of $2.0  million
over  three  years) from  $65,000 for  the nine  months ended  June 30,  1995 to
$576,000 for the nine months ended June 30, 1996.
    
 
   
    Research and development expense  decreased from $3.3  million for the  nine
months  ended June 30, 1995  to $2.7 million for the  nine months ended June 30,
1996. The  decrease was  largely  attributable to  a $750,000  reimbursement  to
Chiron  for certain start-up manufacturing costs that was recorded in June 1995.
Other research  and development  expenses consisted  primarily of  salaries  and
consulting  fees, sponsored  research projects  and expenditures  for laboratory
supplies and animal  facilities. The  Company expects  research and  development
expense  to increase in  the future. Continued growth  in such expense, however,
will be dependent on the availability of capital.
    
 
   
    General and  administrative expense  increased from  $857,000 for  the  nine
months  ended June 30, 1995  to $1.2 million for the  nine months ended June 30,
1996. The increase was largely due to increases in annual salaries, legal  fees,
travel   expenses  and  occupancy  charges.  The  Company  expects  general  and
administrative expenses to increase in the  future as it expands its  operations
and hires additional employees.
    
 
   
    Interest  expense decreased from $320,000 for the nine months ended June 30,
1995 to $104,000 for the  nine months ended June  30, 1996. From its  inception,
the  Company  has  incurred interest  expense  resulting from  the  debt funding
provided by Interneuron.  The decrease in  interest expense for  the nine  month
period  ended June  30, 1996  was attributable  to a  decrease in  the Company's
average outstanding borrowings,  due to  the conversion into  equity in  January
1995 of $11.5 million of the Company's debt payable to Interneuron.
    
 
  FISCAL YEARS ENDED SEPTEMBER 30, 1993, 1994 AND 1995
 
    The  Company  recognized  no  revenue  for  fiscal  1993  and  1994. Revenue
increased to $2.8 million in fiscal 1995. The Company's revenues in fiscal  1995
were attributable to an initial cash payment of $2.5 million under the Company's
collaboration  agreement  with Chiron  and  recognition of  $260,000  of revenue
related to a payment under the Company's ATP grant.
 
    Research and  development expense  increased from  $3.1 million  for  fiscal
1993,  to $4.1 million for fiscal 1994 and  to $4.2 million for fiscal 1995. The
increase in fiscal 1994 was largely due  to the addition of senior research  and
development  management in late fiscal 1993  as well as annual salary increases,
increased short-term sponsored research  commitments and increased  depreciation
expense  resulting from additions of  laboratory, office and computer equipment.
The increase in  research and  development expense  in fiscal  1995 was  largely
attributable to the incurrence of $750,000 as reimbursement for certain start-up
manufacturing costs related to the Chiron collaboration.
 
    General  and administrative  expense was  $1.3 million  for fiscal  1993 and
fiscal 1994, and decreased to $1.1 million for fiscal 1995. The slight  decrease
between  fiscal  1994  and  fiscal  1995  resulted  from  a  reimbursement  from
Interneuron of employee benefit expenses.
 
    Interest expense increased  from $245,000  for fiscal 1993  to $648,000  for
fiscal  1994 and decreased to $352,000 for fiscal 1995. The increase from fiscal
1993 to fiscal  1994 was due  to an  increase in the  Company's borrowings  from
Interneuron.  The decrease  in interest  expense in fiscal  1995 was  due to the
conversion into  equity  of $11.5  million  of  the Company's  debt  payable  to
Interneuron,  resulting  in a  lower average  debt balance  in fiscal  1995. The
Company began  incurring interest  expense related  to equipment  financings  in
fiscal  1994.  The Company  expects  to continue  financing  equipment purchases
through sale-leaseback  arrangements, if  favorable terms  are available,  which
could result in an increase in interest expense.
 
    No  income tax provision or benefit has been provided for federal income tax
purposes as the Company has incurred losses since inception. As of September 30,
1995, the Company had deferred tax
 
                                       22
<PAGE>
assets of $5.7 million. Because of uncertainties surrounding the realization  of
these  favorable tax attributes in  future tax periods, all  of the net deferred
tax assets have been fully offset by a valuation allowance. As of September  30,
1995,  the Company had  total net operating loss  carryforwards of $13.1 million
and tax credits of approximately $468,000, both of which expire on dates through
2009. The Company's ability to utilize  the net operating loss carryforwards  in
future years may be limited in some circumstances, including significant changes
in  ownership interests, due to certain  provisions of the Internal Revenue Code
of 1986, as amended.
 
LIQUIDITY AND CAPITAL RESOURCES
 
   
    Since inception, Progenitor  has financed its  operations primarily  through
debt  and equity financings  from Interneuron of $14.9  million through June 30,
1996, a private  financing of  $1.6 million  in net  proceeds from  the sale  of
Preferred  Stock in fiscal 1995 and a private financing from The Ohio University
Foundation in February, 1996  of $350,000. In addition,  the Company received  a
$2.5 million payment from Chiron in April 1995 and received a payment of $65,000
in  August 1995 under  the ATP grant. The  Company also completed sale-leaseback
transactions generating $88,000  in cash  during fiscal 1995.  The Company  used
these  sources of financing to  fund its operations. During  fiscal 1995 and the
first nine months of  fiscal 1996, respectively, the  Company used $1.6  million
and  $3.1 million  of cash  in operating  activities. As  of June  30, 1996, the
Company had cash and cash equivalents totaling $28,000.
    
 
    The Company expects negative  cash flow from operations  to continue and  to
increase  for  the  foreseeable  future. The  Company  will  require substantial
additional funds  to  continue  research and  development,  conduct  preclinical
studies and clinical trials, conduct activities relating to commercialization of
rights it has retained in strategic collaboration agreements, if any, and expand
administrative  capabilities. The Company estimates that, at its planned rate of
spending, its existing cash and cash equivalents, together with the net proceeds
from the Offering and  the interest income thereon,  will be sufficient to  meet
its  capital  requirements for  at least  the next  18 months.  There can  be no
assurance, however, that the Company's  assumptions regarding its future  levels
of  expenditures and operating losses will  prove accurate. The Company's future
capital requirements  will  depend on  many  factors, including  the  scientific
progress  in and the breadth of the Company's research and development programs;
the results of research and development, preclinical studies and clinical trials
conducted by the Company or its collaborative partners or licensees, if any; the
acquisition and licensing of products and technologies; the Company's ability to
establish and maintain relationships with corporate and academic  collaborators;
competing  technological and market developments; the time and costs involved in
filing, prosecuting, defending  and enforcing patent  and intellectual  property
claims;  the receipt of licensing  or milestone fees from  any current or future
collaborative  arrangements,   if   established;  the   continued   funding   of
governmental  research grants; the  timing of regulatory  approvals, if any; and
other factors.  To the  extent undertaken  by the  Company, the  time and  costs
involved   in  conducting  preclinical  studies  and  clinical  trials,  seeking
regulatory  approvals,  and   scaling-up  manufacturing  and   commercialization
activities  also would  increase the Company's  capital needs.  The Company will
need to raise substantial additional capital  to fund operations. Prior to  this
Offering,  Interneuron has funded substantially all of the Company's operations.
Interneuron, however, is under  no obligation to provide,  and the Company  does
not expect that Interneuron will provide, any additional funds in the future.
 
    The  Company intends  to seek additional  funding through  public or private
equity or  debt  financing  and  collaborative arrangements.  There  can  be  no
assurance  that additional financing will be  available when needed, or that, if
available, such financing will be available on terms acceptable to the  Company.
If  additional  funds  are  raised by  issuing  equity  securities,  dilution to
existing stockholders will  result. In  addition, in the  event that  additional
funds  are  obtained  through  arrangements  with  collaborative  partners, such
arrangements may require  the Company  to relinquish  rights to  certain of  its
technologies  or potential products  that it would otherwise  seek to develop or
commercialize itself. If funding is insufficient at any time in the future,  the
Company  may be required  to delay, scale back  or eliminate some  or all of its
research and development programs or cease operations. See "Risk Factors -- Need
for Additional Capital; Uncertainty of Additional Funding."
 
                                       23
<PAGE>
                                    BUSINESS
 
    Progenitor is  a  functional  genomics company  engaged  in  the  discovery,
characterization  and validation of novel  genes, receptors and related proteins
as therapeutic  leads and  targets  for the  treatment  of major  diseases.  The
Company's  functional genomics approach combines developmental biology expertise
and proprietary  technology with  gene sequencing  and other  molecular  biology
techniques  to accelerate the discovery process. Using its developmental biology
approach to  functional  genomics, the  Company  has made  several  discoveries,
including  the discovery of the B219 leptin  receptor, for which it filed patent
applications in September and December 1994. Leptin is believed to have roles in
blood cell formation  ("hematopoiesis"), reproduction and  obesity. The  Company
has  entered into  a collaboration  with Chiron  Corporation ("Chiron")  for the
development  and  commercialization  of  the  Company's  proprietary  T7T7  gene
delivery  system, and a collaboration with Novo Nordisk A/S ("Novo Nordisk") for
the isolation, development and commercialization of blood cell growth factors.
 
BACKGROUND
 
    Genes play an important role in the structure and function of an  organism's
cells and therefore provide a fundamental basis for understanding the causes of,
and potentially developing treatments for, many human diseases. Genes consist of
discrete  sequences of DNA that are  comprised of unique orderings of nucleotide
base pairs. These  genetic sequences provide  instructions to the  cell for  the
synthesis  of proteins through a process  known as gene expression. Proteins are
responsible for the structure and biological functions of all organisms  through
their  regulation of, and participation in, cell structure, growth and activity,
as well as  their involvement  in communications and  interactions among  cells.
Cells  often communicate through receptor-mediated  interactions using a protein
or other  ligand that  binds specifically  to a  cell-surface protein  receptor.
These  receptor-mediated communications  are fundamental  to the differentiation
and organization of cells during the early development of an organism.
 
    Although most cells  contain an  organism's entire  genome, or  full set  of
genes,  only a small fraction of an organism's genome is expressed in each cell.
The genes expressed, as well as the order, level and timing of their expression,
determine the function of different cells within an organism. Intrinsic  defects
in  genes, or defects caused  by external stimuli, may  lead to inappropriate or
inadequate production of  proteins, resulting in  abnormal or degenerative  cell
functions   that  characterize  various  diseases  such  as  cancer.  Therefore,
determining the role of specific genes, receptors and related proteins  involved
in  cell functions  may provide  a basis  for understanding  the causes  of, and
developing possible treatments for, these diseases.
 
  OVERVIEW OF DEVELOPMENTAL BIOLOGY
 
    Developmental biology is the study of  the genetic and cellular events  that
control  the  transformation of  a single  fertilized  egg into  a fully-formed,
complex organism. This transformation is orchestrated by the interactive up- and
down-regulation of gene expression by a small fraction of the organism's  genes.
The  expression of these  regulatory genes results in  the synthesis of proteins
that regulate the expression of other  genes and control cell functions,  direct
cell  to  cell communications  and affect  development  of cells  throughout the
embryo. Many genes involved  in the process of  cell growth and  differentiation
may  be expressed exclusively,  or at enhanced levels,  during certain stages of
early development and may  become inactive in the  normal cells of  fully-formed
organisms. The Company believes that the discovery and characterization of genes
involved  in early development,  and the proteins  they produce, may  be used to
develop treatments for a range of diseases characterized by aberrant cell growth
or differentiation.
 
    Developmental biology seeks to  define the process  and mechanisms by  which
non-committed,  immature cells (stem cells) differentiate into specialized cells
performing specific functions. For example, the blood and immune systems develop
from a  few precursor  stem cells  that  grow in  the yolk  sac, a  tissue  that
surrounds  the developing embryo. In early  stages of development, each of these
yolk sac stem cells
 
                                       24
<PAGE>
is capable of developing into any of the mature cells of the blood. However,  as
development  progresses, individual  cells differentiate into  specific types of
blood and immune cells as a result of patterns of specific gene expression.  The
yolk  sac also is  the source of  the earliest endothelial  cell precursors that
grow and differentiate to form blood vessels. These endothelial cell  precursors
also  express proteins that  direct the growth and  differentiation of the blood
cells. The following diagram illustrates the development of a single  fertilized
egg into a seven-day-old mouse embryo.
 
    [Diagram  showing  five  stages  in  the development  of  an  embryo  from a
fertilized egg cell to the blastula  stage (fertilized egg cell, cleavage,  four
cells,  sixteen cells and  blastula), above the  caption "Embryonic Development"
and a drawing of a seven-day-old mouse embryo with its yolk sac and three  types
of mature cells that develop from the yolk sac.]
 
  OVERVIEW OF GENOMICS
 
    Recent  developments in  the study of  the genome  (genomics), including the
introduction and  improvement  of  automated equipment,  have  allowed  for  the
identification   of  genes  that  may  contribute  to  or  inhibit  abnormal  or
degenerative cell activity  common to certain  diseases. Genomics may  therefore
represent  a  useful  first  step toward  discovering  and  developing effective
diagnostic processes and therapies to detect and treat these diseases.
 
    Traditional genomics companies may be  divided broadly into those  employing
high-volume  gene sequencing techniques and those  engaged in gene mapping. Gene
sequencing companies use high-throughput equipment to identify randomly the  DNA
sequences of a large number of genes, generally without any initial reference to
their  biological  function. Individual  gene sequences  then are  selected from
among these randomly generated sequences by using screening techniques based  on
the  similarity  of  the  selected sequence  to  sequences  within  known genes.
Selected genes then  are subjected to  an extensive series  of assays to  define
their  biological function  and determine  their potential  therapeutic role, if
any. High-throughput gene  sequencing as a  primary means of  gene discovery  is
capital intensive, requires extensive effort to sift through the large volume of
identified   sequences,  and  produces  a  relatively  low  yield  of  potential
therapeutic targets.
 
                                       25
<PAGE>
    Gene mapping companies analyze the differences between genetic sequences  of
well-defined   healthy   and   diseased  populations   of   genetically  related
individuals, in order to  identify and sequence  genes that may  play a role  in
specific  diseases.  Gene mapping  is  a labor  intensive, technically-demanding
process that typically  seeks to  identify a single  disease-related gene.  This
approach  often is even more complex  for diseases involving multiple genes. The
success  of  this  approach  depends  upon  identifying  a  sufficiently   large
population  of  related  individuals  with  strong  evidence  of  a  genetically
transmitted disease. As a  result, the use  of this approach  may be limited  to
those  diseases where discrete  populations of genetically  related, healthy and
diseased individuals are readily accessible.
 
PROGENITOR'S FUNCTIONAL GENOMICS APPROACH
 
    Progenitor uses developmental  biology as a  discovery platform to  identify
novel  genes,  receptors  and  related proteins  that  control  cell  growth and
differentiation through which the blood, immune, vascular and other systems  are
developed.  By comparing  the sequential expression  of genes from  one stage of
early development to the next, the Company believes it can identify, isolate and
sequence specific genes,  receptors and related  proteins which play  functional
roles  in this process. The  Company believes that its  approach provides a rich
and largely unexploited source  for the discovery  of medically important  leads
and  targets to develop  treatments for diseases  characterized by aberrant cell
growth or  differentiation.  These diseases  include  cancer, blood  and  immune
system disorders and degenerative diseases associated with aging.
 
    Progenitor's  approach starts with the  identification of medically relevant
biological functions that  are involved  in the  differentiation of  early-stage
stem  cells, tissues, and systems derived from various murine embryonic sources,
including yolk sac stem  cells and embryonic stem  ("ES") cells. Progenitor  has
isolated  proprietary cell  lines from these  murine sources, which  it uses for
analyzing relevant biological  functions, such  as the  normal establishment  of
organ  systems. The  Company then  develops and  applies proprietary  assays and
model systems to further characterize a selected biological function.  Following
function  characterization, the Company uses gene sequencing and other molecular
biology techniques to identify the genes, receptors or other proteins associated
with that function.  The Company  also uses a  wide variety  of other  classical
developmental  and  molecular  biology  techniques,  including  enhancer  traps,
promoter traps, IN SITU hybridization, subtractive cloning, gene knock-outs  and
transgenic  methods to supplement its proprietary capabilities. These techniques
allow the Company  to correlate  gene expression with  biological function.  The
Company  then  screens for  biological  activity in  adult  tissues in  order to
validate the  potential of  isolated genes,  receptors and  related proteins  as
therapeutic  leads  and targets.  The  Company believes  that  its developmental
biology approach  to  functional  genomics  will  permit  more  accelerated  and
cost-effective  discoveries of  therapeutically relevant  drug development leads
and targets than traditional genomics approaches.
 
    The Company conducts its initial  research in murine systems because  murine
cells  and tissues are  accessible and can  be manipulated in  ways not feasible
with humans cells and tissues. In addition, the genetic composition and patterns
of gene expression in murine cells are highly similar to those in humans.  These
similarities  enable the Company  first to identify  and isolate relevant murine
genes, receptors or  proteins and then  to identify the  equivalent human  gene,
receptor or protein without the need for complex and time-consuming assays using
human  cells  and  tissues.  See  "Risk  Factors  --  Uncertainties  Relating to
Technological Approach of the Company."
 
PROGENITOR'S PROPRIETARY DISCOVERY TECHNOLOGIES
    The Company possesses a number of key proprietary technologies that it  uses
in  its discovery  programs. The Company  seeks protection  of these proprietary
technologies  through  maintenance  of  trade  secrets  and  by  filing   patent
applications,  where  appropriate.  Progenitor's  key  proprietary  technologies
relate to ES cells, yolk sac stem cells, discovery techniques for  hematopoietic
growth  factors and  receptors and  gene delivery  systems. See  "-- Patents and
Proprietary Rights."
 
                                       26
<PAGE>
  EMBRYONIC STEM CELL TECHNOLOGY
 
    The Company has developed proprietary methods and cell lines using murine ES
cells for  studying  cell differentiation  in  the development  of  tissues  and
organs.  The Company maintains murine ES cells in culture in an undifferentiated
state and then modifies the culture conditions to control the progression of the
ES cells from one stage  of development to the  next. Using this technique,  the
Company  is able to  control and time  the cell differentiation  process and can
accurately isolate and modify cells from the earliest stages of the formation of
the blood, immune,  vascular and  other systems. These  capabilities enable  the
Company  to take  multiple "molecular snapshots"  in order to  isolate the genes
associated with these critical developmental stages.
 
    These methods  and cell  lines also  serve  as assay  systems in  which  the
expression  of discovered  genes can  be manipulated  in order  to clarify their
function further. The ES cells can be  manipulated in order to study the  effect
of  the  addition  or deletion  of  specific  genes on  normal  cell  growth and
differentiation, either IN VITRO or IN VIVO. The Company currently is using this
technology to identify the genes, receptors and related proteins involved in the
development of the blood and vascular systems, and to develop assays for cloning
the murine burst-forming units-erythroid ("BFU-e") red blood cell growth  factor
and its human equivalent.
 
  YOLK SAC STEM CELL TECHNOLOGY
 
    Progenitor  has developed proprietary techniques  to isolate, grow, maintain
in culture and differentiate cells isolated  from the murine yolk sac. Yolk  sac
stem  cells appear  later in  development than  ES cells,  and are  committed to
develop only into cells of the  blood, immune and vascular systems. The  Company
believes  the mammalian yolk  sac to be  one of a  number of tissues  that is an
enriched source of novel genes that may be expressed exclusively or at  enhanced
levels during early development.
 
    Progenitor has used cultured yolk sac stem cell lines to identify its murine
BFU-e  red blood cell  growth factor activity.  The Company is  using these cell
lines in its program to isolate the  factor and clone its gene, and to  identify
other   genes,  receptors  and  related   proteins  with  potential  therapeutic
applications. The Company has a pending patent application relating to  cellular
compositions  derived from the  mammalian yolk sac and  methods of obtaining and
using such  compositions.  See  "Risk  Factors --  Uncertainty  of  Patents  and
Proprietary Rights."
 
  TECHNOLOGY FOR DISCOVERY OF NOVEL RECEPTORS
 
    Progenitor  has developed proprietary gene  cloning and screening techniques
to identify novel members of a family of genes that encode receptors for  growth
factors  involved in normal blood cell formation ("hematopoiesis") as well as in
the growth and development of neural and other tissues. The Company's techniques
rely  on  enhancements   to  traditional  cloning   techniques,  including   the
development  of  proprietary screening  algorithms used  in  the selection  of a
targeted family of genes. The Company applies its receptor discovery  techniques
to  enriched gene  sources produced  through a  combination of  proprietary cell
lines,  freshly   isolated  cell   subpopulations,  and   proprietary  ES   cell
differentiation  methods.  The Company  used these  methods to  discover certain
leptin receptors (including various isoforms of the leptin receptor), for  which
it  filed U.S.  patent applications in  September and  December 1994. Progenitor
intends to  use its  discovered receptors  to identify  and clone  novel  growth
factors,  to  screen  for  small molecules  that  activate  or  inhibit receptor
functions, and to identify and purify unique bone marrow cells.
 
  T7T7 GENE DELIVERY SYSTEM
 
    The  Company,  in  collaboration  with  Ohio  University,  has  developed  a
proprietary  nonviral gene delivery  system known as  T7T7. The Company believes
that the T7T7 gene delivery system may enable it
 
                                       27
<PAGE>
to express  genes in  cells  in order  to  facilitate the  characterization  and
validation  of  its discoveries.  The Company  believes  that its  gene delivery
system, in addition to  other gene delivery techniques,  may allow it to  assess
efficiently the biological effects of discovered genes while saving the time and
expense  of  producing and  characterizing quantities  of purified  protein that
would otherwise be required for these studies.
 
    The T7T7 system is a nonviral, naked DNA plasmid that can effect  expression
of the gene it carries in the cytoplasm of a cell and works IN VIVO and IN VITRO
in  both dividing and  nondividing cells. In contrast,  most other gene delivery
systems must  reach  the cell  nucleus  to be  effective  and function  only  in
dividing cells.
 
   
    The  Company  has  exclusively  licensed two  U.S.  patent  applications and
corresponding foreign applications relating to the T7T7 gene delivery system. In
March 1996, the USPTO issued a notice of allowance on one patent application for
claims covering the composition of matter and methods for using the T7T7 system.
The  Company   currently   is  working   with   Chiron  to   explore   potential
commercialization  of the T7T7 system in clinical gene therapy applications. The
Company has licensed certain technologies  incorporated in the T7T7 system  from
Associated  Universities, Inc. and the Wisconsin Alumni Research Foundation. See
"Risk Factors -- Uncertainty of Patents and Proprietary Rights."
    
 
PROGENITOR'S DISCOVERY PROGRAMS
 
    The Company, using  its proprietary  cell lines and  technologies, has  made
three  principal  discoveries to  date.  These discoveries  and  their potential
therapeutic applications are described below.
 
  LEPTIN RECEPTORS
 
    The Company has  utilized its proprietary  receptor discovery technology  to
identify  gene  sequences  that  encode  various  isoforms  of  the  B219 leptin
receptor. Leptin receptors recently  have been implicated  in the regulation  of
obesity and the control of appetite and metabolic activity. However, in a recent
publication  of NATURE MEDICINE, the  Company disclosed findings suggesting that
leptin receptors may play  a broader and more  fundamental biological role  than
has  been  recognized previously.  The Company  has  demonstrated IN  VITRO that
leptin, acting on a leptin  receptor, stimulates the growth and  differentiation
of  certain hematopoietic cells, including cells  found in adult bone marrow. In
addition, the Company demonstrated IN  VIVO that leptin receptors are  expressed
in  ovarian  cells  critical  for  controlling  the  growth  and  development of
reproductive cells, and that leptin is found in high levels in the ovarian fluid
surrounding the  reproductive cells.  Progenitor believes  that these  receptors
could  provide  a  means  to  identify novel  proteins,  or  ligands,  and other
molecules that have unique and important therapeutic and diagnostic applications
in hematopoiesis,  reproduction  and  obesity.  In  addition,  leptin  receptors
potentially  may be used to sort  immature blood cells and create subpopulations
of cells expressing a desired receptor for use as therapeutic leads. In order to
characterize  further  the  function  of   leptin  receptors,  the  Company   is
researching  the  role of  the leptin  protein in  the hematopoietic  and immune
systems, as  well as  its role  in the  growth and  development of  reproductive
cells. The Company intends to establish strategic corporate partnerships for the
development  and  commercialization of  its leptin  receptors. In  September and
December 1994, the Company filed U.S.  patent applications relating to the  B219
leptin receptor (including varous isoforms of the leptin receptor). There can be
no  assurance that patents will issue  from these applications, that, if issued,
any resulting patents  will provide  the Company with  meaningful protection  or
rights,  that  the Company  will be  successful  in entering  into collaborative
agreements  or  that  any  drugs  or   other  products  will  be  developed   or
commercialized from the Company's leptin receptor discoveries. See "Risk Factors
- --  Early Stage of  Development; Uncertainty of  Final Product Development," "--
Dependence on Collaborators," "-- Uncertainty of Patents and Proprietary Rights"
and "-- Dependence upon Research Collaborators and Scientific Advisors."
 
                                       28
<PAGE>
  DEL-1 GENE
 
    Progenitor has discovered, in collaboration  with Vanderbilt, DEL-1, a  gene
that  encodes  a novel  cell-surface protein  involved in  the early  growth and
development of  blood  vessels  and  bone.  The  growth  of  new  blood  vessels
(angiogenesis)  is an important activity in development that is typically absent
in normal adult tissues, but may be present in certain disorders such as  cancer
and  diabetic retinopathy. Progenitor  and Vanderbilt have  shown that the DEL-1
gene is expressed uniquely in areas of developing blood vessels and bone but  is
inactive  in normal, mature animal systems.  Moreover, Progenitor has shown that
mice implanted with  human tumors express  the murine DEL-1  gene in  developing
blood vessels that feed the tumor.
 
    The  Company believes that targeting the protein expressed by the DEL-1 gene
(Del-1) to inhibit the  growth of new blood  vessels may represent an  important
new  therapeutic  approach to  treating cancer.  The rapidly  dividing malignant
cells of a tumor require a large, continuous and ever-increasing blood supply. A
substantial body of research in animals  and humans suggests that attacking  the
growth  of tumor blood vessels  may be an effective  treatment for cancer. Since
the DEL-1 gene is normally not expressed in the adult, and the Del-1 protein  is
accessible  in  the lining  of  blood vessels,  the  Company believes  the Del-1
protein may  be  a  highly  specific,  accessible  and  stable  target  for  the
development  of cancer therapeutics, diagnostics and imaging agents. Other genes
identified to date that are involved in the regulation of blood vessel formation
are also expressed in  normal adult tissues  and thus may  not provide the  same
potential  selectivity as the Del-1 protein as a target for cancer detection and
therapy.
 
    The Company intends to enter  into academic and corporate collaborations  to
pursue the research, development and commercialization of the DEL-1 gene and the
Del-1  protein for  the treatment of  diseases characterized  by excessive blood
vessel formation, such as cancer, and diseases such as cardiovascular and  other
disorders that may be treated by stimulating blood vessel growth.
 
    Progenitor  and Vanderbilt have  fully sequenced the  human and murine DEL-1
genes, respectively.  Progenitor  and Vanderbilt  have  filed two  joint  patent
applications  relating  to the  DEL-1  nucleotide sequences,  the  proteins they
encode, methods of expressing functional gene products, and methods of using the
DEL-1 gene  and protein  and  engineered cells  in  various normal  and  disease
conditions.  The  Company has  an exclusive,  worldwide license  to Vanderbilt's
commercial rights under  these patent  applications. There can  be no  assurance
that  patents will issue from these applications, that, if issued, any resulting
patents will provide the Company with meaningful protection or rights, that  the
Company will be successful in entering into collaborative agreements or that any
drugs  or products will be developed  or commercialized from the Company's DEL-1
discoveries. See "Risk  Factors --  Early Stage of  Development; Uncertainty  of
Final Product Development," "-- Dependence on Collaborators," "-- Uncertainty of
Patents and Proprietary Rights" and "-- Dependence on Research Collaborators and
Scientific Advisors."
 
  BFU-E RED BLOOD CELL GROWTH FACTOR
 
    Progenitor  has identified from its murine yolk sac stem cell lines a growth
factor activity that stimulates the formation and development of red blood cells
from the BFU-e red blood cell precursors, which are found in adult bone  marrow.
The  identified activity  is distinct  from that  of erythropoietin  ("EPO") and
other known growth factors. The Company is attempting to purify the BFU-e growth
factor and clone its gene.
 
    The Company believes  there is a  large and growing  market for agents  that
stimulate new blood cell development. These include support therapy for patients
with  inherited anemias, or patients who  are undergoing kidney dialysis, cancer
chemotherapy or bone marrow transplantation. In order to address these potential
markets, Progenitor has entered into an agreement with Novo Nordisk, through its
subsidiary,  ZymoGenetics,   Inc.  ("ZymoGenetics"),   for  the   research   and
development  relating  to  the  BFU-e  red  blood  cell  growth  factor activity
identified by the Company.  Progenitor, along with Novo  Nordisk, is seeking  to
clone  the murine BFU-e red  blood cell growth factor  and its human equivalent.
There can be  no assurance  that the  Company will  be successful  in cloning  a
murine BFU-e red blood cell
 
                                       29
<PAGE>
growth  factor or validating its significance as a therapeutic lead or that Novo
Nordisk will be successful in developing  or commercializing any drugs or  other
products  based on the BFU-e red blood  cell growth factor. To date, the Company
has not  filed any  patent applications  relating to  the BFU-e  red blood  cell
growth  factor  activity.  See  "Risk Factors  --  Early  Stage  of Development;
Uncertainty of Final Product Development," "-- Dependence on Collaborators," "--
Uncertainty of Patents and  Proprietary Rights" and  "-- Dependence on  Research
Collaborators and Scientific Advisors."
 
  OTHER PROGRAMS
 
    GENE  THERAPY.  The Company believes that the T7T7 gene delivery system will
enable it to deliver genes to cells IN VIVO and IN VITRO in order to  facilitate
the characterization and validation of its discoveries. In addition, the Company
has  entered into a collaborative agreement with Chiron to explore clinical uses
of the Company's  T7T7 gene delivery  system. Under this  agreement, Chiron  has
agreed  to develop and potentially to commercialize the T7T7 system for selected
applications. Progenitor has retained the right  to market and license the  T7T7
system  for other applications and to use  and license joint technologies of the
collaboration as well as technological improvements  to the T7T7 system made  by
Chiron. The initial T7T7-based gene therapy product being developed by Chiron is
intended  for treatment  of solid-tumor cancers.  The Company  intends to pursue
opportunities with other corporate partners to develop gene therapies using  the
T7T7   system  for  applications  retained  by  Progenitor.  See  "--  Strategic
Collaboration Agreements -- Chiron Agreement" and "Risk Factors -- Dependence on
Collaborators."
 
    NOVEL RECEPTORS.    The  Company continues  to  apply  discovery  techniques
similar  to  those  used in  its  early  discovery of  certain  leptin receptors
(including various  isoforms  of  the  leptin receptor)  in  order  to  identify
additional novel gene sequences and receptors. These techniques have resulted in
the  identification  of over  30 additional  novel  genes that  are structurally
similar to members of the hematopoietin receptor gene family. While the  Company
has  not fully  characterized the  discovered genes,  it believes  that they may
represent potential  targets  for  discovering  additional  growth  factors  and
isolating  important cell subpopulations for  therapeutic approaches to diseases
characterized by aberrant cell growth or differentiation.
 
STRATEGY
 
    The Company's strategy includes the following elements:
 
    EMPLOY  DEVELOPMENTAL  BIOLOGY   APPROACH.    The   Company  is  using   its
developmental biology approach to functional genomics in order to accelerate the
discovery,   characterization  and  validation  of  medically  important  genes,
receptors and related  proteins as drug  development leads and  targets for  the
pharmaceutical  industry. The Company intends to enhance its technology platform
and supplement  its  internal  research  and  development  capabilities  through
further  academic collaborations.  In order  to increase  the efficiency  of the
discovery process once a targeted  biological function has been identified,  the
Company  also  intends  to  acquire additional  advanced  molecular  biology and
genomics equipment and capabilities, including high-throughput gene  sequencing,
bio-informatics, robotic cloning, biological assays and protein analysis.
 
    ENTER  INTO STRATEGIC  ALLIANCES FOR  PRODUCT DEVELOPMENT.   The  Company is
focusing its  resources on  the discovery,  characterization and  validation  of
novel  genes, receptors and  related proteins that  may play key  roles in major
diseases. The  Company  intends  to  enter  into  strategic  alliances  for  the
development  and  commercialization of  drugs and  other  products based  on its
discoveries. This strategy  is intended to  enable the Company  to maximize  the
effectiveness  of  its  discovery  technologies and  to  use  its collaborators'
expertise and resources in research and development, clinical testing, obtaining
regulatory approvals, and manufacturing and marketing. The Company believes this
strategy will allow it  to benefit from  the development of  any drugs or  other
products    that   may   result   from   its   discoveries   without   incurring
 
                                       30
<PAGE>
the substantial costs associated with such development. The Company has  entered
into  an agreement with Chiron for the development of gene therapies for certain
cancers using the Company's T7T7 gene delivery system, and with Novo Nordisk for
the isolation and development of a BFU-e growth factor.
 
    PURSUE PATENT PROTECTION.  The Company  will continue to seek protection  of
its  discoveries  and  proprietary  technologies  through  maintenance  of trade
secrets  and  by  filing  patent  applications,  where  appropriate.  There   is
substantial   uncertainty  regarding  the  strength  of  patents  for  partially
sequenced genes or for genes without a known function. The Company believes that
its functional genomics approach improves the Company's ability to identify  and
correlate gene sequences with known biological functions and thereby may enhance
the  likelihood of ultimately securing patent  protection for its discoveries of
novel genes, receptors and related proteins and their uses.
 
STRATEGIC COLLABORATION AGREEMENTS
 
  CHIRON AGREEMENT
 
    In March 1995,  Progenitor entered  into an  agreement with  Chiron for  the
development and commercialization of the Company's T7T7 gene delivery system for
selected  applications.  The  agreement grants  Chiron  an  exclusive, worldwide
license to  the  T7T7 gene  delivery  system for  (i)  all products  carrying  a
specified  gene, which has potential applications  for tumor ablation; (ii) four
infectious disease vaccine constructs; (iii)  products used for the  prevention,
therapy  or  diagnosis  of  human restenosis;  (iv)  five  additional constructs
designated by Chiron; and (v)  additional constructs, with certain  limitations,
that  may be designated by Chiron upon payment of a fee for each such additional
construct. Progenitor also may grant licenses to third parties to constructs for
fields of use not licensed  to and not in  conflict with the exclusive  licenses
granted  to Chiron. Any such third-party  licenses are subject to Chiron's right
of first refusal for any construct of the T7T7 gene delivery system not  already
covered by the agreement for the development of a noninfectious disease vaccine.
Pursuant  to the agreement, Chiron and  Progenitor will develop jointly the T7T7
tumor ablation product for the treatment of cancer. The parties will own jointly
all preclinical and clinical data from  the collaboration, which may be used  by
either  party  for any  purpose  subject to  the  exclusive licenses  granted to
Chiron. Progenitor has the right to  collaborate and jointly invest in  Chiron's
development   efforts  on  the  tumor   ablation  product,  with  the  Company's
participation in  any resulting  product revenues  based on  its  contributions.
Under  the  agreement,  Chiron  has  committed  to  use  reasonable  efforts  to
commercialize one or more licensed products and has certain manufacturing rights
and obligations  for  any  resulting  products. If  Chiron  chooses  to  abandon
development  of a construct,  its license rights terminate  with respect to that
construct. Subject to  the foregoing  rights, the agreement  provides that  each
party  will retain  ownership of all  inventions (and any  related patents) made
solely by its  employees and  arising from  the activities  performed under  the
agreement.
 
    The  agreement terminates  upon the later  of the expiration  of the patents
upon which it is based or, within  any given country, ten years after the  first
commercial  sale of a product developed under the agreement within such country.
In  such  events,  Chiron's  affected  license  rights  become  fully-paid   and
non-exclusive.  Chiron may also terminate the  agreement earlier with respect to
any particular construct upon  30 days' notice, and  either party may  terminate
the  agreement in  the event  of a  material breach  by the  other party  of its
obligations under the agreement. In  such events, Chiron's license rights  would
revert to Progenitor, but Chiron would retain exclusive rights to inventions and
discoveries  made solely by its employees,  and joint rights to discoveries made
jointly with Progenitor.  Chiron also would  be required to  pay Progenitor  all
royalties accrued before termination.
 
    Progenitor  received a $2.5 million payment  upon execution of the agreement
as a license fee  and reimbursement of past  research and development  expenses,
and an additional $500,000 in January 1996 for continued funding of Progenitor's
research  and development expenses. Progenitor has paid Chiron $750,000 pursuant
to the agreement, in full  satisfaction of Progenitor's obligation to  reimburse
Chiron for certain start-up manufacturing costs. Under the agreement, Progenitor
is entitled to receive up to an
 
                                       31
<PAGE>
additional $4.3 million in various fees and milestone payments for each licensed
product   if  all  specified  research,  clinical  development,  regulatory  and
marketing approval milestones are achieved, plus additional fees for development
of specific  constructs  and for  the  first product  developed.  The  agreement
encompasses  a minimum of eleven potential  products that Chiron may develop. In
the event that all  such milestones are achieved  and all contemplated  products
reach  market, Progenitor would receive an aggregate of $51.3 million (including
payments already received) plus royalties on net product sales. There can be  no
assurance  that  the Company  and  Chiron will  be  successful in  developing or
commercializing any drugs or products utilizing Progenitor's T7T7 gene  delivery
system  or that such  agreement will not  terminate prior to  its expiration. As
such, there can be no assurance that any milestones will be achieved or that any
royalties or other payments contemplated by the agreement will ever be made. See
"Risk Factors -- Dependence on Collaborators."
 
  NOVO NORDISK AGREEMENT
 
    In  May  1995,   Progenitor  and  Novo   Nordisk,  through  its   subsidiary
ZymoGenetics,   entered  into  a  research,  development  and  commercialization
agreement under which Novo Nordisk  received an exclusive, worldwide license  to
any  and all rights  of the Company related  to the BFU-e  red blood cell growth
factor activity  identified  by  the  Company  for use  in  any  and  all  human
therapeutic  and  small  molecule drug  design  uses. Under  the  agreement, the
development effort  is divided  into  two stages.  During  the first  stage,  if
commenced,  Novo Nordisk will attempt to purify,  clone and sequence a BFU-e red
blood cell growth  factor and  other growth factors  with similar  hematopoietic
functions.  If this stage is successfully  completed, Novo Nordisk will have the
right to decide whether to proceed to the second stage, in which Progenitor will
conduct research  to establish  the biological  function of  the growth  factor.
During  the second stage, if commenced, Progenitor may be entitled to receive up
to $4.0 million in research fees from Novo Nordisk.
 
    The agreement with Novo Nordisk terminates  upon the expiration of the  last
patent related to the Company's growth factor discoveries. Novo Nordisk also has
a  right to earlier termination  of the agreement upon  30 days' notice. If Novo
Nordisk exercises this right before payment  of any license fees required  under
the  agreement,  it  would be  obligated  to  grant to  Progenitor  an exclusive
worldwide license to  all of  Novo Nordisk's  rights arising  from the  research
conducted  pursuant to the agreement to make,  use and sell related products. In
the event  that Novo  Nordisk had  paid the  Company at  least $4.0  million  in
research  fees under the  agreement prior to  such early termination, Progenitor
would be obligated to pay Novo Nordisk royalties for any sales of products  made
using the licensed technology.
 
    If  Novo  Nordisk  decides to  develop  any  licensed products,  it  will be
obligated to pay Progenitor a one-time license fee of $5.0 million and up to  an
additional   $18.0  million  for  each  product  if  certain  clinical  testing,
regulatory and marketing approval  milestones are met,  plus an additional  $1.0
million  for  milestones related  to the  first  licensed product.  In addition,
Progenitor has the right  to royalties for sales  of any resulting products.  In
the  event that all milestones  are reached with respect  to the BFU-e red blood
cell growth factor, Progenitor would receive an aggregate of $28.0 million under
the agreement, plus royalties on net  product sales. Novo Nordisk has the  right
to  manufacture and  market any such  products on an  exclusive worldwide basis.
There can be  no assurance that  the Company or  Novo Nordisk will  successfully
clone the murine BFU-e red blood cell growth factor or its human equivalent, or,
if cloned, that Novo Nordisk will continue the program, that the Company will be
able  to establish  the biological  function of the  growth factor  or that Novo
Nordisk will be successful in developing and commercializing any drugs or  other
products utilizing the BFU-e red blood cell growth factor. As such, there can be
no  assurance that  any milestones  will be achieved,  or that  any royalties or
other payments  contemplated by  the  agreement will  ever  be made.  See  "Risk
Factors -- Dependence on Collaborators."
 
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<PAGE>
LICENSE AGREEMENTS
 
  OHIO UNIVERSITY
 
   
    Progenitor   entered  into  research  and  licensing  agreements  with  Ohio
University as of January 1992  relating to yolk sac stem  cells and as of  April
1993  relating  to  the  T7T7  gene delivery  system.  The  April  1993 research
agreement terminated as of June 30, 1996 upon completion of research thereunder.
The licensing agreements,  as amended, grant  Progenitor an exclusive  worldwide
license  to the yolk sac stem cells and T7T7 gene delivery system, respectively,
and related  technologies  covered in  Ohio  University's existing  patents  and
patent  applications,  as  well as  any  technology developed  from  its related
sponsored research. In exchange, the Company is obligated to pay certain license
and research fees  as well  as royalties  based on  net sales  of any  resulting
products.  In addition,  under the  1992 license  agreement and  the terms  of a
related stock purchase agreement, The  Ohio University Foundation received a  5%
equity  interest in the  Company subject to  certain antidilution protection and
was granted the right to purchase 25,000 shares of Progenitor's Common Stock  in
the  event  of an  initial public  offering, merger  or other  similar corporate
transactions at a price equal to 50% of the anticipated public offering price or
merger or other consideration, as applicable. The Ohio University Foundation has
agreed to exercise  such right in  full prior  to the closing  of the  Offering.
Under  the license  agreement, The Ohio  University Foundation has  the right to
designate two  representatives to  the Board  of Directors  of Progenitor  until
Progenitor  consummates an initial public offering. See "Certain Transactions --
The Ohio University Foundation."
    
 
  VANDERBILT UNIVERSITY
 
    In July 1995, Progenitor  entered into a  license agreement with  Vanderbilt
pursuant  to  which  Progenitor  obtained  an  exclusive  worldwide  license  to
Vanderbilt's commercial  rights under  a jointly  owned patent  application,  to
develop  and market products and processes  utilizing technology relating to the
DEL-1 gene. The gene was co-discovered by Progenitor and Vanderbilt. Under  this
agreement,  Progenitor is  obligated to pay  royalties on  any resulting product
sales. Vanderbilt University may  terminate the agreement  after three years  if
Progenitor  has not made adequate efforts to commercialize products based on the
gene.
 
ADVANCED TECHNOLOGY PROGRAM GRANT
 
    In November 1994, the Company was  awarded a $2.0 million, three-year  grant
to  study the immunology  of yolk-sac-derived endothelial  cells for therapeutic
applications under the  ATP. The  grant specifies the  research and  development
therapeutics  based  on  an  understanding  of  the  biology  of  development of
endothelial  cells.  The  research  agreements  between  the  Company  and   its
subcontractors  under the ATP grant (the  University of Colorado, The University
of Wisconsin,  Ohio University,  Vanderbilt University  and Bio  Support,  Inc.)
require  that all parties assign rights to any inventions made by them under the
grant to  the Company.  The ATP  grant provides  that the  Company retains  full
rights to any intellectual property developed as part of the project.
 
   
    The ATP grant is administered by United States Department of Commerce. As of
June  30, 1996, the Company  had received $646,000 under  the ATP grant, and had
accrued $188,000 in  additional funds payable  to the Company  through June  30,
1996.  Under the  terms of  the grant,  the Company  is scheduled  to receive an
aggregate of $702,000  payable in  equal quarterly installments  for the  period
from  June 1, 1996 through May 31, 1997.  The balance of the grant, $518,000, is
payable in equal quarterly installments during  the period from June 1, 1997  to
May 31, 1998. The grant is subject to yearly appropriations by the United States
Congress  for the ATP program, and  legislation has been introduced to eliminate
the program. The National Institute of Standards and Technology has informed the
Company that, although it could not comment on the availability of funds for the
Company's grant for the year ending May 31, 1998, there are sufficient funds  in
the   ATP  grant  program's  current  budget   to  support  grant  payments  for
    
 
                                       33
<PAGE>
currently funded grants for the year ending May 31, 1997, and that therefore  it
is  likely that Progenitor will receive  grant payments expected through May 31,
1997. There can be no assurance, however, that funding for the ATP program  will
not be reduced or eliminated at any time.
 
PATENTS AND PROPRIETARY RIGHTS
 
   
    Patents  and  licenses  are  important  to  the  Company's  businesses.  The
Company's  policy  is  to  file  patent  applications  to  protect   technology,
inventions  and improvements to inventions that  are considered important to the
development of its business. The Company also relies on trade secrets, know-how,
continuing technological innovations and licensing opportunities to develop  and
maintain its competitive position. To date, the Company has filed or exclusively
licensed  a number of pending  patent applications in the  USPTO relating to its
various core technology programs, as well as foreign counterparts of certain  of
these  applications in Europe, Japan and  certain other countries. These pending
patent applications include the following:  eight U.S. applications relating  to
leptin  receptors (including various isoforms of  the leptin receptor); two U.S.
applications  relating  to  its  vascular  biology  program  (DEL-1);  two  U.S.
applications  relating  to  its  gene  delivery  system  (T7T7);  and  one  U.S.
application relating to yolk sac stem cells. No United States or foreign  patent
has issued to the Company to date. However, the Company has an exclusive license
from  Ohio University to one  issued U.S. patent covering  a method of providing
tissue-specific  expression  of  exogenous  genetic  material  in  a  mammal  by
genetically transformed embryonic carrier cells such as yolk sac cells. A notice
of  allowance has been received  for one patent application  with respect to the
Company's T7T7 gene delivery  system. The Company  has exclusive licenses  under
the  patent applications  relating to  the T7T7  gene delivery  system from Ohio
University, the patent  application relating to  yolk sac stem  cells from  Ohio
University,  and  the  patent  applications  relating  to  the  DEL-1  gene from
Vanderbilt University. The  Company has  also licensed two  issued patents  that
relate to its T7T7 gene delivery program on a nonexclusive basis from Associated
Universities, Inc. and the Wisconsin Alumni Research Foundation.
    
 
    The  Company's success will depend to a significant extent on its ability to
obtain and enforce patents, maintain trade secret protection and operate without
infringing on  the  proprietary rights  of  third parties.  Because  the  patent
positions  of biotechnology and pharmaceutical companies can be highly uncertain
and frequently  involve complex  legal  and factual  questions, the  breadth  of
claims   allowed   in  biotechnology   and   pharmaceutical  patents   or  their
enforceability cannot be predicted. Commercialization of pharmaceutical products
can be  subject to  substantial delays  as a  result of  the time  required  for
product  development, testing and regulatory approval.  The value of any patents
issued or licensed to the Company may  depend upon the remaining term of  patent
protection  available at the time products  that utilize the patented technology
are commercialized.
 
   
    The Company actively  pursues a policy  of seeking patent  protection for  a
number  of its  proprietary products  and technologies.  Progenitor has licensed
from Ohio  University  one U.S.  patent  and pending  U.S.  patent  applications
relating  to  stem cell  technology  and to  gene  delivery technology  (and has
received  a  notice  of  allowance  relating  to  a  gene  delivery   technology
application),  along with certain corresponding  foreign patent applications and
one issued  foreign  patent.  Progenitor has  filed  eight  patent  applications
relating  to certain leptin receptors, including applications filed in September
and December 1994. In March 1996, Progenitor's international patent  application
covering certain leptin receptors was published. The Company believes that there
may  be significant litigation regarding  patent and other intellectual property
rights relating  to leptin  and  leptin receptors.  The  Company is  aware  that
Millennium  has filed a patent application relating to a receptor for leptin and
its use in  obesity applications,  and has  licensed to  Hoffmann-La Roche  Inc.
rights  to develop certain therapeutics for obesity using Millennium's discovery
of a leptin receptor.
    
 
    Millennium has recently filed  a "Protest" in the  USPTO in connection  with
the   Progenitor  applications  relating  to  leptin  receptors,  including  the
applications filed in  September and December  1994. A Protest  is an  available
procedure  sometimes used by a third party to provide the patent examiner who is
reviewing the involved  application or  applications with what  the third  party
believes to be relevant
 
                                       34
<PAGE>
information.  The Protest procedure does not afford any right to the third party
to participate  in the  patent  prosecution process  beyond  the filing  of  its
written  Protest. Millennium's Protest primarily  argues that any claims allowed
to Progenitor  should  not be  so  broad as  to  cover Millennium's  own  leptin
receptor.  Progenitor  intends to  proceed with  the  prosecution of  its leptin
receptor patent  applications  in the  normal  course  in order  to  obtain  the
broadest allowable claims with regard to its leptin receptor discoveries.
 
    There   can  be  no  assurance  that  Millennium's  patent  application,  or
additional patent applications filed by Millennium or others, will not result in
issued patents covering a leptin receptor, the leptin protein or other  ligands,
or  any of their  respective uses including  obesity. There can  be no assurance
that the invention by Millennium will  be accorded an invention date later  than
Progenitor's  invention date, that  any patent will issue  to Progenitor or that
any such  patent issued  to Progenitor  would be  broad enough  to cover  leptin
receptors  of Millennium or others. Progenitor's failure to obtain a patent on a
leptin receptor,  or its  failure to  obtain  a patent  that covers  the  leptin
receptors  of Millennium or others, or the issuance of a patent to a third party
covering a leptin receptor, the leptin protein or other ligands, or any of their
respective uses, could have a material adverse effect on the Company's business,
financial condition and results of operations.
 
    A number of other groups are  attempting to identify partial gene  sequences
and  full-length genes, the functions of  which have not been characterized. The
public availability  of partial  gene sequence  information before  the  Company
applies  for  patent  protection  on  a  corresponding  full-length  gene  could
adversely affect the Company's ability to obtain patent protection with  respect
to  such gene. To the extent any patents  issue to other parties on such partial
or full-length  genes, and  as other  patents issue  with the  expansion of  the
biotechnology  industry,  the risk  increases  that the  potential  products and
processes of the Company or its  collaborative partners may give rise to  claims
of patent infringement.
 
    The  patent positions  of pharmaceutical and  biotechnology firms, including
the Company, are uncertain and involve  complex legal and factual questions  for
which  important legal principles are largely unresolved, particularly in regard
to human therapeutic  uses. Substantial periods  of time pass  before the  USPTO
responds  to patent applications. In addition,  the coverage claimed in a patent
application  can  be   significantly  reduced   before  a   patent  is   issued.
Consequently,  the Company does  not know whether  any of its  pending or future
patent applications will result  in the issuance of  patents or, if any  patents
are  issued,  whether  the  patents will  be  subjected  to  further proceedings
limiting their  scope, and  whether they  will provide  significant  proprietary
protection  or competitive  advantage, or  will be  circumvented or invalidated.
Because patent applications in the United States are maintained in secrecy until
patents issue and patent applications  in certain other countries generally  are
not  published  until  more than  18  months  after they  are  filed,  and since
publication of discoveries in scientific or patent literature often lags  behind
actual  discoveries, the Company cannot  be certain that it  or any licensor was
the first creator of inventions covered  by pending patent applications or  that
it  or  such  licensor  was  the  first  to  file  patent  applications  on such
inventions.
 
    There can be no  assurance that the Company's  patents, if issued, would  be
held  valid or enforceable by a court  or that such patents would cover products
or  technologies  of  the   Company's  competitors.  Competitors  or   potential
competitors  may have filed applications for or received patents, and may obtain
additional patents and  proprietary rights  relating to  compounds or  processes
competitive  with those of  the Company. To protect  its proprietary rights, the
Company may be required to  participate in interference proceedings declared  by
the  USPTO to determine priority of invention, which could result in substantial
cost to the Company. Moreover, even if the Company's patents issue, there can be
no assurance that they  will provide sufficient  proprietary protection or  will
not  be later limited, circumvented or invalidated. Accordingly, there can be no
assurance that  the  Company  will develop  proprietary  technologies  that  are
patentable,  that the Company's patent applications will result in patents being
issued or that, if  issued, patents will  afford protection against  competitors
with  similar technology or  products, nor can  there be any  assurance that the
Company's patents will be held valid by a court of competent jurisdiction.
 
                                       35
<PAGE>
    In addition to patent protection, the  Company also relies to a  significant
extent  upon  trade  secret  protection  for  its  unpatented  confidential  and
proprietary  information  including   many  of  the   Company's  key   discovery
technologies,  such  as its  proprietary methods  of isolating  and manipulating
murine ES cells. There  can be no assurance  that others will not  independently
develop  substantially  equivalent  proprietary  information  and  techniques or
otherwise  gain  access  to  the  Company's  trade  secrets  or  disclose   such
technology.  To protect its  trade secrets, the  Company requires its employees,
consultants, scientific  advisors and  parties  to collaborative  agreements  to
execute  confidentiality  agreements upon  the  commencement of  employment, the
consulting relationship or the  collaboration with the Company.  In the case  of
employees,  the agreements also provide that  all inventions resulting from work
performed by them while employed by  the Company will be the exclusive  property
of  the Company. There can be no  assurance, however, that these agreements will
provide meaningful  protection  of  the  Company's  trade  secrets  or  adequate
remedies  in the  event of unauthorized  use or disclosure  of such information,
that the  Company  can  meaningfully  protect  its  rights  in  such  unpatented
proprietary  technology through other means, that any obligation to maintain the
confidentiality  of  such  proprietary  technology  will  not  be  breached   by
employees,  consultants,  advisors, collaborative  partners  or others,  or that
others will not independently  develop substantially equivalent technology.  The
loss  of  trade  secret  protection  of  any  of  the  Company's  key  discovery
technologies would  materially and  adversely affect  the Company's  competitive
position  and could  have a material  adverse effect on  the Company's business,
financial condition and results of operations. Finally, disputes may arise as to
the ownership of proprietary rights to the extent that outside collaborators  or
consultants  apply technological information developed  independently by them or
others to Company projects or apply Company technology to other projects and, if
adversely determined, such disputes could have a material adverse effect on  the
Company's business, financial condition and results of operations.
 
    The  Company may incur substantial costs if  it is required to defend itself
in patent suits brought by third parties or if the Company initiates such a suit
to enforce the Company's patents or to determine the scope and validity of other
parties' proprietary  rights.  Any  legal  action against  the  Company  or  its
collaborators  or licensees  claiming damages  and seeking  to enjoin commercial
activities relating to the affected products and processes could, in addition to
subjecting the Company to potential  liability for damages, require the  Company
or  its collaborators or licensees  to obtain a license  or licenses in order to
continue to manufacture or market the affected products and processes. There can
be no assurance that the Company or its collaborators or licensees would prevail
in any such action or that any license required under any such patents would  be
made  available on commercially acceptable terms, if at all. Any adverse outcome
of such  litigation  could have  a  material  adverse effect  on  the  Company's
business,  financial position  and results  of operations.  In addition,  if the
Company becomes  involved in  such litigation,  it could  consume a  substantial
portion  of the  Company's managerial  and financial  resources. The  Company is
unable to predict  how courts  will resolve any  future issues  relating to  the
validity and scope of its patents should they be challenged.
 
    It  is uncertain whether any third-party patents will require the Company to
alter its products or  processes, obtain licenses,  cease certain activities  or
pay substantial damages. If any licenses are required, there can be no assurance
that  the  Company will  be  able to  obtain  any such  license  on commercially
acceptable terms, if  at all. Failure  by the Company  or its collaborators  and
licensees  to obtain a  license to any technology  required to commercialize the
Company's discoveries  may  have a  material  adverse effect  on  the  Company's
business,  financial condition and  results of operations.  See "Risk Factors --
Uncertainty of Patents and Proprietary Rights."
 
COMPETITION
 
    Research in the field of genomics is highly competitive. Competitors of  the
Company  in the  genomics area include,  among others, public  companies such as
Genome  Therapeutics   Corporation,   Human  Genome   Sciences,   Inc.,   Incyte
Pharmaceuticals,   Inc.,   Millennium,   Myriad  Genetics,   Inc.   and  Sequana
Therapeutics, Inc.,  as  well  as private  companies  and  major  pharmaceutical
companies and
 
                                       36
<PAGE>
universities  and other research institutions, including those receiving funding
from the  federally  funded Human  Genome  Project.  A number  of  entities  are
attempting  to  rapidly identify  and patent  randomly-sequenced genes  and gene
fragments.  In   addition,  certain   other  entities   are  pursuing   a   gene
identification,  characterization and product development strategy based on gene
mapping.  The  Company's  competitors  may  discover,  characterize  or  develop
important  genes in advance of the Company,  which could have a material adverse
effect on any related Company discovery program. The Company expects competition
to intensify in genomics  research as technical advances  in the field are  made
and become more widely known.
 
    In  addition,  the  Company  faces,  and  will  continue  to  face,  intense
competition from pharmaceutical and biotechnology companies, as well as academic
and research institutions and governmental  agencies. The Company is subject  to
significant competition from organizations that are pursuing the same or similar
technologies  as those  which constitute  the Company's  discovery platform, and
from organizations that are pursuing pharmaceutical or diagnostic products  that
are  competitive with  the Company's  or its  collaborators' potential products.
Many of  the  organizations competing  with  the Company  have  greater  capital
resources,  larger  research  and  development  staffs  and  facilities, greater
experience in drug discovery and development, obtaining regulatory approvals and
pharmaceutical product manufacturing,  and greater  marketing capabilities  than
the Company.
 
    The Company also is aware of a number of companies and institutions that are
developing or considering the development of potential gene-based and cell-based
treatments,  including early-stage gene  therapy companies, large pharmaceutical
companies, academic  and research  institutions, government  agencies and  other
health care providers. Many of these entities are more advanced than the Company
in their product development programs for gene and cell-based therapies and have
more  experience with regulatory agencies and clinical trials. The field of gene
and cell-based therapy is new and many competitive approaches are being taken to
discover practical means by which these technologies can be made into  products.
Rapid  technologic  advances could  result in  actual or  proposed technologies,
products or  processes of  the  Company becoming  obsolete prior  to  successful
commercialization. See "Risk Factors -- Intense Competition; Rapid Technological
Change."
 
    The  Company is and  will continue to  be reliant on  strategic partners for
support  of  its  programs,  including  preclinical  and  clinical  development,
manufacturing  and  marketing of  its initial  products.  Each of  the Company's
present and future partners is  conducting multiple product development  efforts
within  each disease or technology area that is the subject of the alliance with
the Company. Any product candidate or technology of the Company, therefore,  may
be subject to internal competition with a potential product under development or
technology  platform under evaluation by a  strategic partner. See "Risk Factors
- -- Dependence on Collaborators."
 
GOVERNMENT REGULATION
 
    Prior to marketing, any new drug  or other product developed by the  Company
and  its collaborative  partners must  undergo an  extensive regulatory approval
process in the United States and other countries. This regulatory process, which
includes preclinical studies and clinical trials, and may include post-marketing
studies, of each product candidate to establish its safety and efficacy, usually
takes  many  years  and  require  the  expenditure  of  substantial   resources.
Preclinical tests include laboratory evaluations and will require animal studies
conducted  in  accordance the  FDA's cGLP  regulations  to assess  the product's
potential safety  and  efficacy.  Data obtained  from  preclinical  studies  and
clinical  trials are  susceptible to  varying interpretations  that could delay,
limit  or  prevent  regulatory  approval.  Delays  or  rejections  also  may  be
encountered  based  upon changes  in  the FDA's  policies  for drug  or biologic
approval during the period of product  development and FDA regulatory review  of
each  NDA submitted in the case of new pharmaceutical agents, or PLA in the case
of biologics. Product  development of new  pharmaceuticals is highly  uncertain,
and  unanticipated  developments,  clinical  or  regulatory  delays,  unexpected
adverse side effects or  inadequate therapeutic efficacy  could slow or  prevent
the  product  development  efforts  of  the  Company  and  its  collaborators or
licensees,  and   have   a   materially  adverse   effect   on   the   Company's
 
                                       37
<PAGE>
business,  financial  condition  and  results of  operations.  There  can  be no
assurance that  regulatory approval  will be  obtained for  any drugs  or  other
products  developed by the  Company or its  collaborative partners or licensees.
Furthermore, regulatory approval may entail limitations on the indicated use  of
a  drug or other product. Because certain  of the products likely to result from
the Company's discovery programs involve the application of new technologies and
may be based upon a  new therapeutic approach, such  products may be subject  to
substantial additional review by various government regulatory authorities other
than  the FDA and, as a result, regulatory approvals may be obtained more slowly
than for  products using  conventional technologies.  Under current  guidelines,
proposals  to conduct clinical  research involving gene  therapy at institutions
supported by the NIH must be approved by the RAC and the NIH. Furthermore,  gene
therapies  are relatively new technologies and  have not been tested extensively
in humans.  The regulatory  requirements governing  these products  and  related
clinical procedures for their use are uncertain and are subject to change.
 
    Even  if  regulatory  approval  is  obtained,  a  marketed  product  and its
manufacturer are subject to continuing review. Among the conditions for  product
approval  and  continued  marketing approval  is  that the  quality  control and
manufacturing procedures of the Company or its collaborative partners conform to
the FDA's cGMP  regulations which must  be followed at  all times. In  complying
with  cGMP requirements, manufacturers  must expend time, money  and effort on a
continuing  basis   in  production,   record   keeping  and   quality   control.
Manufacturing   establishments,  both  domestic  and  foreign,  are  subject  to
inspection by or under the authority of the FDA and by other federal, state  and
local agencies. Failure to pass such inspections may subject the manufacturer to
possible  FDA actions  such as the  suspension of manufacturing,  seizure of the
product, withdrawal of approval or other regulatory sanctions. The FDA also  may
require the manufacturer to recall a product from the market.
 
    Discovery  of previously  unknown problems with  a product  may have adverse
effects on the Company's business, including withdrawal of the product from  the
market.   Violations  of   regulatory  requirements  at   any  stage,  including
preclinical studies and clinical trials, the approval process or  post-approval,
may  result in various adverse consequences  to the Company, including the FDA's
delay in approval  or refusal to  approve a product,  withdrawal of an  approved
product  from the  market or  the imposition  of criminal  penalties against the
manufacturer and NDA or PLA holder. The Company has not submitted an IND for any
product  candidate,   and   no  product   candidate   has  been   approved   for
commercialization in the United States or elsewhere. The Company intends to rely
primarily  on  its strategic  partners  to file  INDs  and generally  direct the
regulatory approval process. No assurance can  be given that the Company or  any
of its strategic partners will be able to conduct clinical testing or obtain the
necessary  approvals  from  the  FDA or  other  regulatory  authorities  for any
products. Failure  to  obtain  required governmental  approvals  will  delay  or
preclude the Company's strategic partners from marketing drugs or other products
developed  by the Company or limit the commercial use of such products and could
have a material adverse  effect on the  Company's business, financial  condition
and results of operations.
 
    In  addition to regulations enforced by the FDA, the Company also is subject
to regulation under the  Occupational Safety and  Health Act, the  Environmental
Protection  Act, the Toxic Substances Control Act, the Resource Conservation and
Recovery Act  and other  federal,  state and  local regulations.  The  Company's
research  and  development activities  involve the  controlled use  of hazardous
materials, chemicals, biological materials  and radioactive compounds.  Although
the  Company believes that  its safety procedures for  handling and disposing of
such materials comply with the current standards prescribed by state and federal
laws and regulations, the risk of accidental contamination or injury from  these
materials cannot be completely eliminated. In the event of such an accident, the
Company  could be held liable  for any resulting damages  and any such liability
could  exceed  the  Company's  resources.   See  "Risk  Factors  --   Government
Regulation" and "-- Hazardous and Radioactive Materials; Environmental Matters."
 
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<PAGE>
PRODUCT LIABILITY INSURANCE
 
    The  testing, manufacture,  marketing and  sale of  pharmaceutical and other
products entail the  inherent risk of  liability claims or  product recalls  and
associated  adverse publicity. Clinical  trials and sales by  the Company or its
collaborators or  licensees of  potential products  incorporating the  Company's
discoveries may expose the Company to potential liability resulting from the use
of  such  products. Such  liability might  result from  claims made  directly by
consumers or by regulatory agencies, pharmaceutical companies or others  selling
such  products. The Company currently has a limited amount of clinical trial and
product liability insurance coverage through Interneuron. The Company will  seek
to  obtain its own coverage upon completion of this Offering and to maintain and
appropriately increase  such coverage  as clinical  development of  any  product
candidates   progresses  and  if   and  when  its  products   are  ready  to  be
commercialized. There  can be  no assurance  that the  Company will  be able  to
obtain  such insurance or, if obtained, that such insurance can be acquired at a
reasonable cost or  in sufficient amounts  to protect the  Company against  such
liability.  Certain of the  Company's license agreements  require the Company to
indemnify licensors  against  product  liability claims  arising  from  products
developed  using the licensed technology. Also,  certain of these agreements and
other collaboration agreements require the Company to maintain minimum levels of
insurance coverage. The failure to  maintain product liability coverage, or  the
occurrence  of any product liability  claim, or a recall  of any products of the
Company or  its  collaborators or  licensees,  if developed,  could  inhibit  or
prevent  commercialization of products being developed  by the Company and could
have a material adverse  effect on the  Company's business, financial  condition
and  results of  operations. In  addition, to  the extent  any product liability
claim exceeds  the amount  of any  insurance coverage,  the Company's  business,
financial  condition and results of operations could be materially and adversely
affected. See "Risk Factors -- Risk of Product Liability."
 
HUMAN RESOURCES
 
   
    As of June 30, 1996, Progenitor had 24 full-time employees, of whom 11  hold
Ph.D.  or M.D. degrees. Of the Company's  full-time employees, 19 are engaged in
research  and  development   activities  and  five   are  engaged  in   business
development,  finance  and administration.  None of  the Company's  employees is
covered by  a  collective  bargaining  agreement,  and  the  Company  has  never
experienced any strike or work stoppage. The Company believes its relations with
its employees to be good.
    
 
    In  order to support the Company's  existing operations, it will be required
to  hire  and  retain   additional  management,  administrative  and   financial
personnel,  including  a chief  financial  officer. The  Company's  success will
depend in large  part on its  ability to  attract and retain  key employees  and
scientific  advisors.  Competition  among biotechnology  and  pharmaceutical and
other companies  for  highly  skilled scientific  and  management  personnel  is
intense.  There  can be  no assurance  that  the Company  will be  successful in
retaining its  existing  personnel  or advisors,  or  in  attracting  additional
qualified  employees.  See "Risk  Factors --  Dependence on  Collaborators," "--
Dependence on Research Collaborators and Scientific Advisors" and "-- Dependence
on Key Personnel."
 
FACILITIES
 
   
    Progenitor currently occupies approximately 19,000 square feet of laboratory
and office space in  a single facility in  Columbus, Ohio. Total lease  payments
for  fiscal  1995 were  $106,970.  In addition,  the  Company leases  a separate
facility with  approximately 7,000  square feet  of space  from The  Ohio  State
University for laboratory animals. Space in this facility is leased on the basis
of  a per diem  for each animal housed.  Total lease payments  to The Ohio State
University in fiscal 1995 were $23,582. The current lease on the laboratory  and
office  facility expires  on December  31, 1996  and includes  an option  for an
additional  one-year  extension.  Although  the  Company  believes  that   these
facilities  will be adequate to meet its projected needs for the next two years,
it may be required  to locate additional or  alternative facilities within  this
time frame, depending on the Company's growth and development.
    
 
                                       39
<PAGE>
                                   MANAGEMENT
 
DIRECTORS AND EXECUTIVE OFFICERS
 
    The current executive officers and directors of the Company are as follows:
 
   
<TABLE>
<CAPTION>
                    NAME                           AGE                                POSITION
- ---------------------------------------------      ---      ------------------------------------------------------------
<S>                                            <C>          <C>
Douglass B. Given, M.D., Ph.D................          44   President, Chief Executive Officer and Director
H. Ralph Snodgrass, Ph.D.....................          46   Vice President, Research and Chief Scientific Officer
Stephen J. Williams, Ph.D....................          42   Vice President, Corporate Development
Glenn L. Cooper, M.D.(1).....................          43   Chairman of the Board
Robert P. Axline(2)..........................          60   Director
Alexander. M. Haig, Jr.......................          71   Director
Morris Laster, M.D...........................          32   Director
Jerry P. Peppers(2)..........................          50   Director
David B. Sharrock(1).........................          60   Director
</TABLE>
    
 
- ------------------------
   
(1) Member of the Compensation Committee.
    
 
   
(2) Member of the Audit Committee.
    
 
    DOUGLASS  B. GIVEN,  M.D., PH.D.  has served  as President,  Chief Executive
Officer and Director of the Company since June 1994 and served as Executive Vice
President and Chief Operating Officer from  January 1993 to June 1994. Prior  to
joining Progenitor, Dr. Given was Vice President at the Schering Plough Research
Institute, a pharmaceutical research facility, from March 1989 to December 1992.
Dr.  Given also serves as  a Director of the  Edison BioTechnology Center, is on
the Dean's Advisory Council of  the University of Chicago  and is on the  Dean's
Advisory  Council of The Ohio  State University. Dr. Given  received an M.D. and
Ph.D. in  Biological Sciences  from  the University  of Chicago,  performed  his
post-doctoral  training in Internal Medicine  and Infectious Diseases at Harvard
Medical School and Massachusetts  General Hospital and  received an M.B.A.  from
the Wharton School of Business at the University of Pennsylvania.
 
    H.  RALPH SNODGRASS, PH.D. has served  as Chief Scientific Officer since May
1996 and has served as Vice President,  Research since he joined the Company  in
July 1993. Prior to joining Progenitor, Dr. Snodgrass was Assistant Professor of
Microbiology  and Immunology  at the University  of North  Carolina, Chapel Hill
from January 1988 to June 1993. Dr. Snodgrass has held appointments at The  Ohio
State  University  as  Clinical  Associate Professor,  Division  of  Bone Marrow
Transplantation, Department of Internal Medicine since July 1994, and as Adjunct
Associate Professor,  Department of  Medical Microbiology  and Immunology  since
July 1995. Dr. Snodgrass received his Ph.D. in Immunology from the University of
Pennsylvania  and performed his  post-doctoral training at  The Fox Chase Cancer
Center, Philadelphia.
 
    STEPHEN  J.  WILLIAMS,  PH.D.  has  served  as  Vice  President,   Corporate
Development  since May  1996 and previously  served as  Vice President, Business
Development from  June  1994 to  May  1996.  Prior to  joining  Progenitor,  Dr.
Williams  was  Medical  Director, Strategic  Product  Planning  at Bristol-Myers
Squibb from  March  1993 to  June  1994;  and Associate  Director,  New  Product
Planning at DuPont Merck Pharmaceutical Company from January 1991 to March 1993.
Dr. Williams received his Ph.D. in Pharmacology from Duke University.
 
    GLENN  L. COOPER, M.D. has  served as Chairman of  the Board of Directors of
the Company since June 1994,  and has been a  director since December 1992.  Dr.
Cooper has been President, Chief Executive Officer and a director of Interneuron
since May 1993 and served as President and Chief Executive Officer of Progenitor
from  September 1992 until June  1994. Prior to joining  Progenitor in 1992, Dr.
Cooper was  Executive  Vice President  and  Chief Operating  Officer  of  Sphinx
Pharmaceuticals Corporation from
 
                                       40
<PAGE>
August  1990.  Dr. Cooper  serves  as Chairman  of  the Boards  of  Directors of
Intercardia, Inc.  and  Transcell  Technologies,  Inc., and  is  a  director  of
InterNutria,  Inc., each  of which  is a  subsidiary of  Interneuron. Dr. Cooper
received his M.D.  from Tufts University  School of Medicine  and performed  his
post-doctoral  training in Internal Medicine and  Infectious Diseases at the New
England Deaconess Hospital and Massachusetts General Hospital.
 
    ROBERT P. AXLINE  has been a  Director of  Progenitor since June  1992 as  a
designee  of The  Ohio University Foundation.  Mr. Axline has  been President of
Image Data Systems  Inc. since 1995  and Chairman of  Plastic Card Systems  Inc.
since  1987. Both companies are  engaged in the manufacture  and sale of plastic
identification card machines and supplies.
 
    ALEXANDER M. HAIG,  JR. has  been a  Director of  Progenitor since  December
1992. General Haig has served as Chairman and President of Worldwide Associates,
Inc.,  a marketing consulting firm, since  1984. Previously, General Haig served
as Secretary of State of the United  States from January 1981 to July 1982,  and
President  and Chief Operating  Officer of United  Technologies Corporation from
November 1979 to  January 1981, where  he remains a  Senior Consultant.  General
Haig  has also served as Supreme Allied  Commander of NATO and White House Chief
of Staff under the Nixon and  Ford Administrations. General Haig also serves  on
the Board of Directors of Interneuron, MGM Grand, Inc. and America Online, Inc.
 
    MORRIS  LASTER,  M.D.  has served  as  a  Director of  Progenitor  since its
inception and served as Chief Executive Officer from its inception to  September
1992.  Dr.  Laster has  been  Vice President  of  The Castle  Group,  Ltd. since
February 1990. He has also served as Chief Executive Officer of Synpro, Ltd.,  a
biotechnology  firm,  since  November  1995. Previously,  he  was  interim Chief
Executive Officer of  Xenograft Technologies, Ltd.,  a biopharmaceuticals  firm,
from January 1993 to September 1993. Dr. Laster received his M.D. from Downstate
Medical Center, New York, and received post-doctoral training in surgery at Case
Western Reserve University Hospital.
 
    JERRY  P. PEPPERS joined Progenitor's  Board of Directors in  June 1992 as a
designee of The Ohio University Foundation. He  is a partner in the law firm  of
Winthrop,  Stimson, Putnam & Roberts,  where he has served  as an attorney since
1971. Mr. Peppers received his J.D. from Duke University.
 
    DAVID B. SHARROCK has been a Director of Progenitor since January 1994 and a
Director of Interneuron  since January  1995. Mr. Sharrock  has been  associated
with  Marion Merrell Dow,  a pharmaceuticals company,  or its predecessors since
1958, most recently as Executive Vice President and Chief Operating Officer  and
Director  from January  1990 until his  retirement in December  1993. Since that
time he has served as an independent  consultant. Mr. Sharrock also serves as  a
Director of Cincinnati Bell Inc., Unitog Company, Inc. and Intercardia, Inc.
 
BOARD OF DIRECTORS COMMITTEES AND OTHER INFORMATION
 
   
    At  present, all  directors are  elected annually  and serve  until the next
meeting of  stockholders  or  until  the election  and  qualification  of  their
successors. In addition, The Ohio University Foundation is entitled to designate
two  directors. Messrs. Axline  and Peppers currently serve  as the designees of
The Ohio University Foundation. The rights of The Ohio University Foundation  to
designate  two members of the Board of Directors will terminate upon the closing
of the Offering. Pursuant to the  intercompany services agreement to be  entered
into  by  the  Company with  Interneuron,  Interneuron  will have  the  right to
nominate one designee for  election to Progenitor's Board  of Directors, for  so
long  as Interneuron  reports Progenitor's  financial results  on a consolidated
basis, on an equity basis or otherwise on a basis pursuant to which a portion of
Progenitor's results of operations appear in the financial results of operations
of Interneuron. See "Certain Transactions --Relationship with Interneuron and --
The Ohio University Foundation."
    
 
   
    Effective August  9,  1996, the  Board  of Directors  established  an  Audit
Committee  and a Compensation Committee. The  Audit Committee, which consists of
Messrs. Axline and Peppers, is responsible for
    
 
                                       41
<PAGE>
   
overseeing the  actions by  the Company's  independent auditors  and review  the
Company's   internal  financial  and  accounting   controls  and  policies.  The
Compensation Committee,  which  consists of  Dr.  Cooper and  Mr.  Sharrock,  is
responsible for determining salaries, incentives and other forms of compensation
for  officers and  other employees  of the  Company and  will administer various
incentive compensation and benefit plans.
    
 
    All executive officers serve  at the discretion of  the Board of  Directors,
subject to the terms of any employment agreements. Currently, the Company has an
employment  agreement only  with Dr.  Given. There  are no  family relationships
among the  Company's  directors  and  executive  officers.  See  "--  Employment
Agreement."
 
   
    Mr.  Mark N. K.  Bagnall has agreed  in principle to  serve as the Company's
Chief Financial Officer effective as of the closing of the Offering. Mr. Bagnall
has served as Vice President of  Finance, Chief Financial Officer and  Secretary
of  Somatix Therapy Corporation ("Somatix"), a biotechnology company, since July
1992. Previously, he served as Treasurer  and Secretary of Somatix from  January
1991  to July 1992, and of its  predecessor, Hana Biologics, Inc. ("Hana"), from
January 1990 to January 1991. He also served as Hana's Controller from May  1988
to  January 1990.  Mr. Bagnall is  a Certified Public  Accountant. In connection
with Mr. Bagnall's appointment, the Board  of Directors has approved a grant  of
options  under its 1996 Stock  Incentive Plan to purchase  110,000 shares of the
Company's Common Stock, to  be effective upon the  closing of the Offering.  The
exercise  price of these options shall be equal to the price of the Common Stock
sold in the Offering.
    
 
DIRECTORS' COMPENSATION
 
   
    Effective after the  Offering, the Company's  non-employee directors  (other
than  those who are employees of  Interneuron) will receive cash compensation in
the amount of $2,000 for  attendance at meetings of  the Board of Directors  and
any  committee thereof, and directors may  be reimbursed for certain expenses in
connection with attendance at Board of Directors and committee meetings. A total
of 75,000 shares of  Common Stock under Progenitor's  1996 Stock Incentive  Plan
have  been reserved for issuance to  non-employee directors of Progenitor (other
than those who are employees  of Interneuron) pursuant to compensation  policies
for  such directors to be  adopted by Progenitor in the  future. To date none of
such shares have been granted.
    
 
   
    Pursuant to a letter agreement dated January 26, 1994, the Company has  paid
Mr.  Sharrock  $2,000  for each  meeting  of  the Board  that  he  attends. Upon
execution of this agreement,  the Company also granted  Mr. Sharrock options  to
purchase  2,500 shares of Common Stock, at an exercise price of $4.00 per share,
one-third of  which vest  each January  21 beginning  January 21,  1995.  During
fiscal  1995, the Company paid Mr.  Sharrock $6,000 pursuant to this arrangement
and accrued an additional $2,000 in fees.
    
 
   
    The Company,  along with  Interneuron and  Transcell Technologies,  Inc.,  a
subsidiary  of Interneuron ("Transcell"),  is a party  to a consulting agreement
with Mr.  Sharrock, entered  into on  February 1,  1994, pursuant  to which  Mr.
Sharrock  receives $2,000 per day in exchange for his service as a consultant on
the  development   and   commercialization   of   each   company's   technology.
Collectively, the three companies must use Mr. Sharrock's services for a minimum
of  20 days  per year  during the term  of the  agreement. The  Company paid Mr.
Sharrock $4,000  during  fiscal  1995  under  this  arrangement.  The  agreement
provides  that Mr. Sharrock will not compete with the Company during the term of
the agreement and for a period of one year thereafter. This agreement terminates
on February 1,  1997, with automatic  one-year extensions with  respect to  each
company  unless Mr. Sharrock  or such company  gives notice at  least sixty days
prior to expiration of the then-current term. The Company intends to amend  such
agreement  with  Mr.  Sharrock  such  that cash  compensation  paid  to  him for
attendance of  meetings of  the  Board of  Directors  or any  committee  thereof
pursuant  to the Company's director compensation policy  will be in lieu of such
consulting fees and will be credited towards the aggregate 20 days of consulting
per year required to be granted to Mr. Sharrock under the consulting agreement.
    
 
                                       42
<PAGE>
    During fiscal 1995, the Company was party to a consulting agreement with Dr.
Laster,  pursuant to which the Company paid  him $500 per month for his services
as a scientific advisor. Dr. Laster  received $7,000 pursuant to this  agreement
in fiscal 1995, including $1,000 in fees accrued but not paid in fiscal 1994.
 
EXECUTIVE COMPENSATION
 
    The  following table sets forth for the fiscal year ended September 30, 1995
the compensation for  services rendered to  the Company in  all capacities  with
respect  to its Chief Executive Officer and each of its other executive officers
with annual compensation in excess of $100,000 (the Chief Executive Officer  and
such  other  executive  officers  are  hereinafter  referred  to  as  the "Named
Executive Officers"):
 
                           SUMMARY COMPENSATION TABLE
 
   
<TABLE>
<CAPTION>
                                                                                       LONG-TERM
                                                                                     COMPENSATION
                                                                                        AWARDS
                                                              ANNUAL COMPENSATION   ---------------
                                                                                      SECURITIES
                                                             ---------------------    UNDERLYING        ALL OTHER
                NAME AND PRINCIPAL POSITION                    SALARY      BONUS      OPTIONS (#)     COMPENSATION
- -----------------------------------------------------------  ----------  ---------  ---------------  ---------------
<S>                                                          <C>         <C>        <C>              <C>
Douglass B. Given, M.D., Ph.D.  ...........................  $  185,000  $  46,250        95,000        $   1,065(1)
 President and Chief Executive Officer
Doros Platika, M.D.(2) ....................................     153,000     35,700        40,000(3)        --
 Executive Vice President, Research and
 Development
H. Ralph Snodgrass, Ph.D.  ................................     123,000     30,000        30,000(4)        --
 Vice President, Research and Chief Scientific
 Officer
Stephen J. Williams, Ph.D.  ...............................     135,000     --            17,500           --
 Vice President, Corporate Development
</TABLE>
    
 
- --------------
(1) Consists of premiums paid by the Company on a term life insurance policy for
    Dr. Given.
 
(2) Dr. Platika's employment with the Company terminated effective as of May 24,
    1996,  pursuant  to  a  Separation  Agreement  and  Release.  See   "Certain
    Transactions -- Transactions with Directors and Executive Officers."
 
(3)  Includes options exercisable for 7,500 shares of Common Stock, all of which
    vested on  September  14, 1995,  the  date of  grant.  As a  result  of  the
    termination  of  Dr. Platika's  employment by  the Company,  options granted
    during fiscal 1995 that  were vested as of  May 24, 1996 remain  exercisable
    until  August 24,  1996, and  all other  options granted  during fiscal 1995
    terminated effective May 24, 1996 in  accordance with the terms of the  1992
    Stock  Option Plan. See "Certain Transactions -- Transactions with Directors
    and Executive Officers."
 
(4) Includes options exercisable for 12,500 shares of Common Stock, all of which
    vest upon the earliest of the achievement of performance milestones relating
    to the  leptin receptor  program  or the  BFU-e  growth factor  program,  or
    September 14, 2002.
 
COMPENSATION COMMITTEE INTERLOCKS AND INSIDER PARTICIPATION
 
    The Board of Directors did not have a Compensation Committee in fiscal 1995.
All  deliberations with regard to executive  compensation were by the full Board
of Directors. Dr. Cooper,  the former President and  Chief Executive Officer  of
the  Company,  participated  as a  director  in these  deliberations.  Dr. Given
 
                                       43
<PAGE>
participated as  a director  in  deliberations and  voting  with regard  to  the
compensation  of  Drs.  Platika,  Snodgrass  and  Williams,  but  abstained from
deliberations and voting with regard to his own compensation.
 
STOCK PLANS
 
1992 STOCK OPTION PLAN
 
   
    The 1992  Stock  Option  Plan was  adopted  and  approved by  the  Board  of
Directors  in December 1992 and  by the stockholders of  the Company in February
1993. The plan was amended with the  approval of the Board of Directors and  the
stockholders  in September 1995 to increase the number of shares of Common Stock
available for  grant.  A total  of  500,000 shares  of  Common Stock  have  been
reserved for issuance under the 1992 Stock Option Plan, as amended. As of August
15,  1996, options to  purchase 6,675 shares  of Common Stock  granted under the
1992 Stock Option Plan had been exercised, options to purchase 331,625 shares of
Common Stock were outstanding and options  to purchase 161,700 shares of  Common
Stock  remained available  for grant.  The outstanding  options were  held by 37
individuals and were exercisable at a  weighted average exercise price of  $4.68
per  share. Outstanding options  to purchase an aggregate  of 32,500 shares were
held by employees who  are not officers  or directors of  the Company. The  1992
Stock  Option Plan will terminate in 2002, unless sooner terminated by the Board
of Directors.
    
 
   
    The Board of Directors currently administers the 1992 Stock Option Plan. The
Board has designated a Compensation Committee and intends to delegate to it  the
administration of the 1992 Stock Option Plan. Awards under the 1992 Stock Option
Plan  may consist of (i)  options to purchase Common  Stock that are designed to
qualify, under Section 422 of the Internal Revenue Code of 1986, as amended (the
"Code"), as  "incentive  stock  options" ("Incentive  Stock  Options")  or  (ii)
options  to purchase Common Stock that are  not described in Sections 422 or 423
of the  Code ("Non-Qualified  Stock Options"  and, collectively  with  Incentive
Stock Options, "Options").
    
 
   
    The  Board of Directors  has discretion to grant  Incentive Stock Options to
employees and officers (including officers who are directors) of the Company and
Non-Qualified Stock Options to employees,  officers (including officers who  are
directors),  directors, independent contractors and  consultants of the Company.
The Board may set the terms  of such grants, subject to applicable  restrictions
in  the 1992 Stock Option Plan. Incentive Stock Option grants are subject to the
following limitations: (i)  the term of  any Incentive Stock  Option may not  be
longer  than ten  years, provided  that the term  of any  Incentive Stock Option
granted to an individual possessing more  than 10% of the combined voting  power
of  the Company  or an affiliate  (a "10% Holder")  may not be  longer than five
years; (ii) the aggregate fair market  value of all shares underlying  Incentive
Stock  Options granted  to an  individual that  first become  exercisable in any
calendar year may not exceed $100,000; and (iii) the exercise price of Incentive
Stock Options may  not be  less than  the fair  market value  of the  underlying
shares  on the  grant date,  provided that the  exercise price  of any Incentive
Stock Option granted  to a  10% Holder may  not be  less than 110%  of the  fair
market  value  of the  underlying  shares on  the  grant date.  With  respect to
Non-Qualified Stock Options, the Board has discretion to grant such Options with
an exercise price below the fair market value of the Common Stock. As of  August
15, 1996, no such below-market grants had been made.
    
 
    During an optionee's lifetime, an Option is exercisable only by the optionee
and  no Option may be transferred by the optionee other than by will or the laws
of descent and distribution. An optionee whose relationship with the Company  or
any related corporation ceases for any reason (other than termination because of
death  or total  disability) may exercise,  in the  three-month period following
such cessation (unless such Options terminate or expire sooner by their  terms),
or such longer period as determined by the Board, that portion of the optionee's
Options  that is  exercisable at the  time of  such cessation. In  the event the
optionee dies or becomes totally disabled, the Options vested as of the date  of
death or total disability may be exercised prior to the earlier of such Option's
specified  expiration date or one year from  the date of the optionee's death or
disability.
 
                                       44
<PAGE>
    Unexercised Options granted under the 1992 Stock Option Plan terminate  upon
the occurrence of certain events, including a dissolution, liquidation or merger
or  consolidation  of the  Company in  which  the Company  is not  the surviving
corporation. All  outstanding Options  vest and  become immediately  exercisable
prior  to the effective time of any such  event. In a merger or consolidation in
which the Company is the surviving corporation, Options will be deemed to  apply
to the numbers of shares to which the holders thereof prior to such merger would
be entitled. The converted Options would continue to vest in accordance with the
vesting schedule set by the Board for such Options.
 
    The  Board of  Directors may  amend the 1992  Stock Option  Plan, insofar as
permitted by  law, with  respect to  any  shares of  Common Stock  reserved  for
issuance but not yet subject to Options. Shares subject to Options granted under
the  1992 Stock Option Plan that have  lapsed or terminated may again be subject
to Options granted under the 1992 Stock Option Plan. Furthermore, the Board  may
offer  to exchange new Options for existing  Options, with the shares subject to
the existing Options being again available for grant under the 1992 Stock Option
Plan.
 
1996 STOCK INCENTIVE PLAN
 
   
    The 1996 Stock Incentive Plan (the "1996 Plan") was adopted and approved  by
the  Board of Directors  in May 1996 and  will be presented  for approval by the
stockholders of the Company  prior to the  closing of the  Offering. A total  of
850,000  shares of Common Stock  have been reserved for  issuance under the 1996
Plan. As of  August 15, 1996,  no options issued  under the 1996  Plan had  been
exercised,  options to purchase 275,000 shares  of Common Stock were outstanding
and options to purchase  575,000 shares of Common  Stock remained available  for
grant.  Outstanding  options  under  the  1996 Plan  were  held  by  three Named
Executive Officers and were exercisable at an exercise price of $9.00 per share.
No options  were held  by  persons who  are not  officers  or directors  of  the
Company.  A total of 75,000 shares of Common Stock under the 1996 Plan have been
reserved for issuance to non-employee directors of Progenitor (other than  those
who  are employees of Interneuron) pursuant to director compensation policies to
be adopted by  Progenitor in the  future. The  1996 Plan will  terminate in  May
2006, unless sooner terminated by the Board of Directors.
    
 
    Upon  the adoption and approval of the  1996 Plan by the stockholders of the
Company, the Board of Directors will delegate administration of the 1996 Plan to
the Compensation Committee  (the "Committee").  Awards under the  1996 Plan  may
consist  of (i) Incentive Stock Options, (ii) Non-Qualified Stock Options, (iii)
the sale  or bonus  grant  of restricted  shares  of Common  Stock  ("Restricted
Stock"),  (iv) the grant of stock  appreciation rights ("SARs"), either alone or
together with Options, (v) the grant  of dividend equivalent rights measured  by
dividends  paid with respect to the Common Stock ("DERs"), and (vi) the grant of
any of the  abovementioned options, rights  or shares based  upon attainment  of
certain performance criteria ("Performance Shares").
 
   
    The Committee will have discretion to grant Options, Restricted Stock, SARs,
DERs  and Performance Shares to employees,  officers (including officers who are
directors of the Company),  directors and consultants  of the Company,  provided
that  only employees  and officers  of the  Company may  receive Incentive Stock
Options. The Committee may set the  terms of such grants, subject to  applicable
restrictions  in the 1996  Plan. Incentive Stock  Option and Non-Qualified Stock
Option grants are subject to the same  limitations under the 1996 Plan as  those
discussed  above for the  1992 Stock Option Plan.  With respect to Non-Qualified
Stock Options, the Committee will have discretion to grant such Options with  an
exercise price below the fair market value of the Common Stock. As of August 15,
1996, no such below-market grants had been made.
    
 
   
    Upon  certain changes  in control  of the  Company (as  defined in  the 1996
Plan), or  upon  the  merger  or  consolidation,  reverse  merger,  dissolution,
liquidation  or sale of all  or substantially all of  the assets of the Company,
all outstanding Options,  SARs, Restricted  Stock, DERs  and Performance  Shares
will,  unless  otherwise  determined  by the  plan  administrator,  become fully
vested, nonforfeitable  and  exercisable,  and  any  Restricted  Stock  will  be
released   from   all  restrictions   on   transfer  and   all   repurchase  and
    
 
                                       45
<PAGE>
forfeiture restrictions. Each Option,  SAR or DER  shall remain exercisable  for
the  remaining term of the  Option, SAR or DER, except  that each Option, SAR or
DER shall  terminate as  of the  effective date  of a  merger or  consolidation,
reverse  merger, dissolution, liquidation or sale of all or substantially all of
the assets of the Company.
 
    The Board  of  Directors  may  amend  the  1996  Plan,  and  any  agreements
evidencing awards granted thereunder, at any time and for any reason, subject to
certain  restrictions  on  the  ability to  adversely  affect  awards previously
granted thereunder and to any legal requirement to obtain stockholder approval.
 
   
1996 EMPLOYEE STOCK PURCHASE PLAN
    
 
   
    The Company's 1996 Employee Stock Purchase Plan (the "Stock Purchase Plan"),
was approved by the Board of Directors and stockholders in August, 1996, and  is
intended  to qualify as an  "employee stock purchase plan"  under Section 423 of
the Code in order  to provide employees  of the Company  with an opportunity  to
purchase Common Stock through payroll deductions. An aggregate of 100,000 shares
of  the Company's Common Stock  have been reserved for  issuance under the Stock
Purchase Plan and available  for purchase thereunder,  subject to adjustment  in
the event of a stock split, stock dividend or other similar change in the Common
Stock or the capital structure of the Company. All employees of the Company (and
employees  of "subsidiary corporations" and "parent corporations" of the Company
(as defined by the Code) designated  by the administrator of the Stock  Purchase
Plan)  whose customary employment is  for more than five  months in any calendar
year and more than 20  hours per week are eligible  to participate in the  Stock
Purchase  Plan. Employees of Interneuron are  not expected to participate in the
Stock Purchase Plan. Non-employee directors, consultants, and employees  subject
to the rules or laws of a foreign jurisdiction that prohibit or make impractical
the  participation of such employees in the Stock Purchase Plan are not eligible
to participate in the Stock Purchase Plan.
    
 
   
    The Stock Purchase  Plan designates  Purchase Periods,  Accrual Periods  and
Exercise Dates. Purchase Periods are generally overlapping periods of 24 months.
A  Purchase Period will  initiate and additional  Purchase Periods will commence
each subsequent April 1 and October 1. The initial Purchase Period will begin on
the effective date of the  Stock Purchase Plan, which is  the date on which  the
Company  and  the Underwriters  agree  as to  the  pricing with  respect  to the
Offering, and end on September 30, 1998. Accrual Periods are generally six month
periods, with the initial Accrual Period commencing on the effective date of the
Stock Purchase Plan  and ending on  March 31, 1997.  Thereafter Accrual  Periods
will  commence each April  1 and October 1.  Exercise Dates are  the last day of
each Accrual  Period. In  the event  of a  merger of  the Company  with or  into
another  corporation, of the sale  of all or substantially  all of the assets of
the Company, or  certain other  transactions in  which the  stockholders of  the
Company  before the transaction own  less than 50% of  the total combined voting
power of the  Company's outstanding  securities following  the transaction,  the
administrator  of  the Stock  Purchase Plan  may elect  to shorten  the Purchase
Period then in progress.
    
 
   
    On the  first day  of  each Purchase  Period,  a participating  employee  is
granted a purchase right which is a form of option to be automatically exercised
on  the  forthcoming  Exercise Dates  within  the Purchase  Period  during which
deductions are to be made from the pay of participants (in accordance with their
authorizations) and credited to  their accounts under  the Stock Purchase  Plan.
When  the purchase right is exercised, the participant's withheld salary is used
to purchase shares of Common Stock of the Company. The price per share at  which
shares  of Common Stock are to be purchased under the Stock Purchase Plan during
any Accrual Period  is the lesser  of (a) 85%  of the fair  market value of  the
Common  Stock on the  date of the grant  of the option  (the commencement of the
Purchase Period) or (b) 85% of the fair market value of the Common Stock on  the
Exercise  Date (the last  day of an Accrual  Period). The participant's purchase
right is exercised  in this manner  on all  four Exercise Dates  arising in  the
Purchase  Period unless, on the first day of any Accrual Period, the fair market
value of the  Common Stock is  lower than the  fair market value  of the  Common
Stock  on  the  first day  of  the  Purchase Period.  If  so,  the participant's
participation in the original Purchase Period is terminated, and the participant
is automatically enrolled in the new Purchase Period effective the same date.
    
 
                                       46
<PAGE>
   
    Payroll deductions may range from 1% to 10% (in whole percentage increments)
of  a  participant's   regular  base  pay,   exclusive  of  overtime,   bonuses,
shift-premiums or commissions. Participants may not make direct cash payments to
their  accounts. The maximum number of shares of Common Stock which any employee
may purchase under  the Stock Purchase  Plan during an  Accrual Period is  5,000
shares.  Certain additional limitations on the  amount of Common Stock which may
be purchased during any calendar year are imposed by the Code.
    
 
   
    The Stock Purchase Plan will be administered by the Board of Directors or  a
commitee  designated by the Board, which will have the authority to terminate or
amend the Stock Purchase Plan (subject to specified restrictions) and  otherwise
to  administer the Stock Purchase Plan and  to resolve all questions relating to
the administration of the Stock Purchase Plan.
    
 
EMPLOYMENT AGREEMENT
 
    On January  3,  1993,  the  Company  entered  into  a  four-year  employment
agreement  with Dr.  Given. The  agreement provides  for an  initial annual base
salary of $175,000, reviewable  annually by the Board  of Directors, and  annual
bonuses based on the achievement of performance milestones as mutually agreed by
the Board of Directors and Dr. Given. Under the agreement, Dr. Given was granted
the  right  to  purchase  3%  of  the shares  of  Common  Stock  of  the Company
outstanding as of the  date of the  agreement, or 82,907  shares, at a  purchase
price  of $.02 per share. Such stock is  subject to a repurchase option in favor
of the Company, exercisable upon termination  of Dr. Given's employment for  any
reason,  that expires equally with respect to  one-fourth of such shares on each
anniversary date of the agreement beginning on the first anniversary date.
 
   
    Under the agreement, Dr. Given received the right to a $100,000 loan bearing
interest at 7% annually for the purchase of a home in Ohio. Upon the granting of
the loan, the Company waived the charging  of interest on the loan, and  certain
other  provisions of the agreement  relating to the loan,  and received from Dr.
Given an interest-free promissory note in the amount of $100,796 secured by  the
property purchased. The note requires Dr. Given to repay at least $60,796 of the
loan on or before April 1, 1997. Of this portion, $20,000 was forgiven effective
in  fiscal 1996 at the  approval of the Board  of Directors, and $40,796 remains
payable. The balance of $40,000 is payable  on or before April 15, 1997 or  upon
the  termination  of Dr.  Given's employment  and is  subject to  forgiveness in
$10,000 increments  upon  the  achievement of  certain  performance  milestones,
including a successful initial public offering of the Company's Common Stock. As
of June 30, 1996, the Company had forgiven, effective in fiscal 1996, $10,000 of
the  loan pursuant to this provision.  See "Certain Transactions -- Transactions
with Directors and Executive Officers."
    
 
    The agreement also  provides that,  during the  term of  the agreement  and,
unless  Dr.  Given  terminates  his  employment  for  cause  as  defined  in the
agreement,  for  a  period  of  two  years  after  termination  of  Dr.  Given's
employment, he will not compete with the Company, directly or indirectly. In the
event the Board of Directors terminates Dr. Given's employment without cause, as
defined in the agreement, he would be entitled to his base salary plus pro-rated
average  bonuses,  subject to  reduction  for compensation  received  from other
employment, for a period of six months from the date of termination.
 
                                       47
<PAGE>
                    STOCK OPTION GRANTS IN LAST FISCAL YEAR
 
    The following  table  contains information  concerning  the grant  of  stock
options  to the Named Executive Officers  during the fiscal year ended September
30, 1995.
 
<TABLE>
<CAPTION>
                                                                                                             POTENTIAL REALIZABLE
                                                                                                               VALUE AT ASSUMED
                                                  NUMBER OF      PERCENT OF                                 ANNUAL RATES OF STOCK
                                                 SECURITIES     TOTAL OPTIONS                               PRICE APPRECIATION FOR
                                                 UNDERLYING      GRANTED TO       EXERCISE                    OPTION TERM($)(3)
                                                   OPTIONS      EMPLOYEES IN        PRICE      EXPIRATION   ----------------------
                     NAME                        GRANTED(#)    FISCAL YEAR(1)   ($/SHARE)(2)      DATE          5%         10%
- ----------------------------------------------  -------------  ---------------  -------------  -----------  ----------  ----------
<S>                                             <C>            <C>              <C>            <C>          <C>         <C>
Douglass B. Given, M.D., Ph.D.................      50,000(4)        26.60%       $    6.00       9/14/05   $  188,668  $  478,123
                                                    45,000(5)        23.94             6.00       9/14/05      169,802     430,310
Doros Platika, M.D.(6)........................      32,500(5)        17.29             6.00       5/24/96           --          --
                                                     7,500(7)         4.00             6.00       8/24/96        2,121       4,242
 
H. Ralph Snodgrass, Ph.D......................      17,500(5)         9.31             6.00       9/14/05       66,034     167,343
                                                    12,500(8)         6.65             6.00       9/14/05       47,167     119,531
Stephen J. Williams, Ph.D.....................      17,500(5)         9.31             6.00       9/14/05       66,034     167,343
</TABLE>
 
- --------------
(1) Based on  an aggregate  of 188,000 options  granted to  employees in  fiscal
    1995.
 
(2) All options were granted at an exercise price equal to the fair market value
    of  the Common  Stock on the  date of grant,  as determined by  the Board of
    Directors.
 
(3) The potential realizable  value is based  on the term of  the option at  its
    time  of grant (ten  years, except for  options granted to  Dr. Platika (see
    footnotes (6) and (7)). It is calculated by assuming that the stock price on
    the date  of grant  appreciates  at the  indicated annual  rate,  compounded
    annually for the entire term of the option, and that the option is exercised
    and  sold on the  last day of its  term for the  appreciated stock price. No
    gain to the optionee is possible  unless the stock price increases over  the
    option term, which will benefit all stockholders.
 
(4)  Consists of options that vest equally  over three years on each anniversary
    of the date of grant, September 14, 1995.
 
(5) Consists of options that were under the terms of the original grant to  vest
    on the earlier of September 14, 2002 or a prior change in the control of the
    Company. On May 13, 1996, the Company's Board of Directors amended the terms
    of options to acquire an aggregate of 80,000 shares that had been granted to
    Drs.  Given, Snodgrass  and Williams  so that  they vest  equally over three
    years on each  anniversary of  the date of  grant, September  14, 1995.  See
    "Certain   Transactions  --   Transactions  with   Directors  and  Executive
    Officers."
 
(6) Dr. Platika's employment with the Company terminated effective as of May 24,
    1996, pursuant to a Separation Agreement and Release. Of the options granted
    during fiscal 1995,  those vested  as of  May 24,  1996, remain  exercisable
    until  August 24,  1996, and  all other  options granted  during fiscal 1995
    terminated effective May 24, 1996 in  accordance with the terms of the  1992
    Stock  Option Plan. See "Certain Transactions -- Transactions with Directors
    and Executive Officers."
 
(7) Consists of options that vested immediately on the date of grant,  September
    14, 1995.
 
(8)  Consists  of options  that vest  upon  the earliest  of the  achievement of
    performance milestones relating to the leptin receptor program or the  BFU-e
    growth factor program, or September 14, 2002.
 
                                       48
<PAGE>
                         FISCAL YEAR-END OPTION VALUES
 
    For  each  of  the  Named  Executive  Officers,  the  following  table shows
information about the value of unexercised options as of September 30, 1995.  No
options were exercised by the Named Executive Officers during fiscal 1995.
 
   
<TABLE>
<CAPTION>
                                                              NUMBER OF SECURITIES
                                                             UNDERLYING UNEXERCISED       VALUE OF UNEXERCISED
                                                               OPTIONS AT FISCAL        IN-THE-MONEY OPTIONS AT
                                                                  YEAR-END(#)            FISCAL YEAR-END($)(1)
                                                           --------------------------  --------------------------
                          NAME                             EXERCISABLE  UNEXERCISABLE  EXERCISABLE  UNEXERCISABLE
- ---------------------------------------------------------  -----------  -------------  -----------  -------------
<S>                                                        <C>          <C>            <C>          <C>
Douglass B. Given, M.D., Ph.D............................       4,125       107,375     $   8,250     $  24,750
Doros Platika, M.D.(2)...................................      23,750        53,750        84,750        94,750
H. Ralph Snodgrass, Ph.D.................................       8,333        41,667        34,331        34,669
Stephen J. Williams, Ph.D................................       5,000        32,500        10,000        30,000
</TABLE>
    
 
- --------------
(1)  Based on the fair market value of the Common Stock as of September 30, 1995
    ($6.00 per share),  minus the exercise  price, multiplied by  the number  of
    shares underlying the option.
 
(2) Dr. Platika's employment with the Company terminated effective as of May 24,
    1996,   pursuant  to  a  Separation  Agreement  and  Release.  See  "Certain
    Transactions -- Transactions with Directors and Executive Officers."
 
                                       49
<PAGE>
                              CERTAIN TRANSACTIONS
 
RELATIONSHIP WITH INTERNEURON
 
    Progenitor was incorporated in February 1992 as a majority-owned  subsidiary
of Interneuron and assumed all rights and obligations of Scimark Corp. under the
January  1992  research  and  licensing  agreement  with  Ohio  University.  See
"Business  --  License  Agreements   --  Ohio  University."  Upon   Progenitor's
organization,  Interneuron purchased 2,081,250 shares  of Common Stock for $.002
per share. Progenitor  also issued 112,500  and 56,250 shares  of Common  Stock,
respectively,  to Morris  Laster, M.D.,  a director  of the  Company, and Steven
Kanzer, then Assistant Secretary of the  Company, for a purchase price of  $.002
per  share. Lindsay Rosenwald, M.D.,  the Chairman of the  Board and a principal
stockholder of Interneuron,  was the Company's  President until September  1992,
and  was a director of  the Company until May 1996.  Dr. Rosenwald also owns the
Castle Group  Ltd.  ("Castle"), a  venture  capital  firm. Dr.  Laster  was  the
Company's  Chief Executive Officer until September  1992, and Dr. Laster and Mr.
Kanzer were and continue to be employees of Castle.
 
    From  Progenitor's  inception  through  December  1994,  Interneuron  funded
Progenitor's  operations through advances evidenced  by promissory notes payable
on demand and bearing interest at 1% over the prime rate. In December 1994, upon
the initial closing of  the private placement referred  to below, the  aggregate
amount of such advances of approximately $11.5 million, plus accrued interest of
approximately  $1.1 million, was  converted by Interneuron  into an aggregate of
2,020,496 shares of  Series A  Preferred Stock of  the Company  at a  conversion
price  of $6.25 per  share. These shares  will convert into  1,512,741 shares of
Common Stock upon the closing of the Offering. See "Description of Capital Stock
- -- Preferred Stock."
 
   
    Between December 1994 and July 1995, Progenitor issued and sold an aggregate
of 349,000 shares  of Series  B Preferred Stock  in a  private placement.  These
shares  will convert into 261,273 shares of Common Stock upon the closing of the
Offering. See "Description  of Capital  Stock -- Preferred  Stock." The  private
placement  was  a sale  of units,  each unit  consisting of  Series B  shares of
Preferred Stock  of the  Company,  shares of  preferred  stock of  Transcell,  a
subsidiary  of Interneuron, a put protection right from Interneuron and warrants
to purchase Interneuron's common stock.  The put protection right provides  that
on  the third anniversary  of the final  closing date of  the private placement,
holders of such Series B Preferred Stock  have the right to sell to  Interneuron
their  Series B Preferred Stock  of Progenitor at a  purchase price equal to the
purchase price of such shares in the private placement. The put protection right
will expire upon the closing of the Offering. Of the approximately $4.4  million
gross  proceeds of the private placement, Progenitor received approximately $1.6
million, net  of placement  agent fees  and Interneuron  received  approximately
$833,000 from the proceeds of the private placement as its consideration for the
issuance  of warrants for its common stock and the put protection right. Of this
amount, Interneuron loaned approximately $417,000 to Progenitor in exchange  for
a  convertible debenture dated March  31, 1995, bearing interest  at 1% over the
prime rate. The principal amount of this debenture and accrued interest  thereon
(approximately  $471,000 as of August 15, 1996), will automatically be converted
at the closing of the Offering into shares of Common Stock at a conversion price
equal to the initial public offering price. See "Description of Capital Stock --
Interneuron Convertible Debenture and Promissory Note."
    
 
    Paramount Capital, Inc. ("Paramount") acted  as the placement agent for  the
private  placement and D.H. Blair  & Co., Inc. ("Blair")  was a selected dealer.
Paramount is owned  by Dr.  Rosenwald. Progenitor  paid Paramount  approximately
$129,000  as its share  of placement agent fees.  Pursuant to Paramount's rights
under its  placement agent  agreement, designees  of Paramount  received in  the
private placement warrants to purchase an aggregate of 22,201 shares of Series B
Preferred  Stock (representing  the right  to purchase  16,619 shares  of Common
Stock following the closing of the Offering). Dr. Rosenwald received warrants to
purchase 12,274 of these  shares of Series B  Preferred Stock (representing  the
right  to purchase  9,189 shares  of Common Stock  following the  closing of the
Offering). Blair is  substantially owned by  family members of  J. Morton  Davis
(including members of Dr. Rosenwald's family), a principal
 
                                       50
<PAGE>
stockholder  of Interneuron. Blair received fees  for acting as selected dealer,
aggregating $45,094. Designees of Blair  also received in the private  placement
warrants  to purchase an aggregate of 12,700  shares of Series B Preferred Stock
(representing the right to purchase 9,507  shares of Common Stock following  the
closing of the Offering). All of these warrants are exercisable until five years
after  the closing of  the Offering at an  exercise price of  $9.18 per share of
Common Stock, and  pursuant to a  cashless exercise provision  may be  exercised
without  the need to  pay any cash.  See "Description of  Capital Stock -- Stock
Purchase Right and Warrants." The Company also agreed to indemnify Paramount and
Blair against certain  liabilities, including liabilities  under the  Securities
Act  in connection with the private placement. See "Description of Capital Stock
- -- Stock Purchase Right and Warrants."
 
   
    Since  March  1996,  Interneuron  has  continued  to  provide  advances   to
Progenitor.  These advances are  evidenced by a promissory  note dated March 31,
1996, in the principal amount of approximately $523,000, as updated from time to
time, payable on  the earlier of  five years from  the date of  the note or  the
closing  of the Offering.  Interneuron has agreed  to convert at  the closing of
this Offering  the entire  indebtedness  evidenced by  the note,  including  the
original  principal balance, additional advances from  April 1, 1996 through the
closing of the Offering, and all accrued interest (an aggregate of $2.2  million
of  principal  and  accrued interest  as  of  August 15,  1996)  into  shares of
Progenitor Common  Stock at  a  conversion price  equal  to the  initial  public
offering  price. See  "Description of  Capital Stock  -- Interneuron Convertible
Debenture and Promissory Note."
    
 
   
    Based on the amount owed by  Progenitor to Interneuron under the  promissory
note  as of August 15, 1996, and as  a result of the conversion upon the closing
of the  Offering of  the Series  A Preferred  Stock, convertible  debenture  and
promissory  note held by Interneuron, Interneuron  will own 3,820,134 shares, or
51.8% of Progenitor's outstanding Common Stock after closing of the Offering.
    
 
   
    During fiscal 1995, Interneuron paid  for certain Progenitor expenses  which
were  reimbursed  by Progenitor  at  cost. In  addition,  Interneuron guaranteed
Progenitor's office lease (which guarantee will be released upon the closing  of
the  Offering as to obligations  arising after the closing  of the Offering) and
its equipment leases.  Prior to  the closing of  the Offering,  the Company  and
Interneuron  intend to enter  into a tax allocation  agreement to provide, among
other things,  for  the payment  of  tax  liabilities, the  entitlement  to  tax
refunds,  and the allocation of responsibility  and cooperation in the filing of
tax returns. In addition,  the Company and Interneuron  intend to enter into  an
intercompany services agreement which will provide, among other things, for: the
participation  of the Company and its employees in certain programs administered
by Interneuron, at cost, such as  certain insurance programs; and the  provision
of certain services by Interneuron at Progenitor's request at agreed upon prices
in  areas such  as clinical  and regulatory  affairs, quality  control, finance,
administration,  human  resources  and   management  information  systems.   The
intercompany  services  agreement will  also provide  that in  the event  of any
future equity  offering by  the  Company, Interneuron  will  have the  right  to
purchase  (at the same  price and on the  same terms as  such equity offering) a
portion of the shares being offered so as to maintain its fully-diluted interest
in Progenitor  immediately prior  to such  equity offering,  subject to  certain
limitations.  The  intercompany services  agreement will  also provide  that all
future transactions between the Company and Interneuron must be on terms no less
favorable to the Company than could be obtained from unaffiliated third  parties
and must be approved or ratified by a majority of the independent members of the
Company's Board of Directors. As defined in the intercompany services agreement,
independent  directors are those  who are not  employees, officers, directors or
affiliates of, or  persons with  other material  financial interests  involving,
Interneuron, Progenitor or any of their respective affiliates.
    
 
   
    The  intercompany services  agreement will  also provide  to Interneuron the
right to nominate one designee for election to Progenitor's Board of  Directors,
for  so  long  as  Interneuron  reports  Progenitor's  financial  results  on  a
consolidated basis, on an equity basis or otherwise on a basis pursuant to which
a portion of Progenitor's results of operations appear in the financial  results
of  operations of Interneuron. After the  Offering, Interneuron will continue to
control the election  of directors  of the Company  and voting  with respect  to
matters   submitted   to   stockholders,   including   extraordinary   corporate
transactions such as  a merger  or sale of  substantially all  of the  Company's
assets. Interneuron's ownership of a
    
 
                                       51
<PAGE>
substantial  block  of  the Company's  voting  stock  could have  the  effect of
delaying or preventing sales of additional  securities of the Company or a  sale
of the Company or other change of control supported by the other stockholders of
the  Company. In addition, the  Company may be subject  to various risks arising
from Interneuron's influence over the  Company, including conflicts of  interest
relating  to new business opportunities that could  be pursued by the Company or
by Interneuron and its other affiliates, and significant corporate  transactions
for  which stockholder  approval is  required. See  "Risk Factors  -- Control of
Company By, and Potential Conflicts of Interest With, Interneuron."
 
    Interneuron has no obligation to invest any further funds in the Company  or
otherwise  provide funding  to the Company  after the Offering,  and the Company
does not expect  Interneuron to do  so. The Company  intends to seek  additional
funding  through public  or private equity  or debt  financing and collaborative
arrangements. There  can  be no  assurance  that additional  financing  will  be
available  when needed, or that, if  available, such financing will be available
on terms acceptable  to the Company.  See "Risk Factors  -- Need for  Additional
Capital; Uncertainty of Additional Funding."
 
    Interneuron has entered into a lock-up agreement which limits its ability to
sell  shares of the  Company's Common Stock during  the 365-day period following
the date  of  this  Prospectus.  See  "Shares  Eligible  for  Future  Sale"  and
"Underwriting."
 
THE OHIO UNIVERSITY FOUNDATION
 
   
    Upon   the  Company's  formation  in  February  1992,  The  Ohio  University
Foundation purchased 125,000 shares of Common Stock at a purchase price of $.002
per share,  and  Dr.  Thomas Wagner,  an  employee  of Ohio  University  and  an
affiliate  of The Ohio University Foundation, purchased 125,000 shares of Common
Stock at $.002  per share.  Pursuant to  certain antidilution  rights, The  Ohio
University  Foundation was  issued an additional  53,750 shares  of Common Stock
from fiscal  1992  through fiscal  1994.  Also,  in December  1994,  Dr.  Wagner
received  an  additional  53,750  shares of  Common  Stock  pursuant  to similar
antidilution provisions  contained in  a related  stock purchase  agreement.  In
February  1996, The  Ohio University  Foundation purchased  an additional 58,333
shares of Common Stock  for a purchase  price of $6.00 per  share pursuant to  a
stock purchase agreement. In the event the initial public offering price is less
than  $12.00  per share,  pursuant to  such stock  purchase agreement,  The Ohio
University Foundation will be  entitled to receive  additional shares of  Common
Stock  such  that the  effective price  per  share paid  by The  Ohio University
Foundation under the agreement  is equal to 50%  of the initial public  offering
price.  In connection  with such purchase,  the Company and  The Ohio University
Foundation amended certain provisions  of the 1992  stock purchase agreement  in
exchange  for which Progenitor granted The  Ohio University Foundation the right
to purchase 25,000 shares of Progenitor Common Stock at a price equal to 50%  of
the  initial public offering price. The Ohio University Foundation has agreed to
exercise such right to purchase 25,000 shares immediately prior to the  Offering
at a price of $6.00 per share.
    
 
   
    Ohio  University entered into license and sponsored research agreements with
the Company (or its predecessor) in January 1992 and April 1993. The April  1993
sponsored  research agreement terminated as of  June 30, 1996 upon completion of
the research thereunder.  Pursuant to  the initial license  agreement, The  Ohio
University  Foundation has  the right to  designate two  members of Progenitor's
Board of Directors until the completion of Progenitor's initial public offering.
Messrs. Axline and Peppers  are Trustees of The  Ohio University Foundation  and
serve  as The  Ohio University Foundation's  designees to  Progenitor's Board of
Directors. Under the Ohio University license and sponsored research  agreements,
Progenitor   paid  Ohio  University  an  aggregate  of  approximately  $570,000,
$246,000, $397,000 and  $109,000 in fiscal  1993, 1994, 1995,  and for the  nine
months  ended June 30,  1996, respectively. Ohio University  also is entitled to
receive royalties based on  any sales of licensed  products resulting from  such
arrangements.  Under  a consulting  agreement with  Dr.  Wagner entered  into in
February 1992,  Progenitor  paid Dr.  Wagner  consulting fees  of  approximately
$93,000,  $93,000, $113,000 and $45,000 during  fiscal 1993, 1994, 1995, and for
the nine months  ended June  30, 1996,  respectively. See  "Business --  License
Agreements."
    
 
                                       52
<PAGE>
TRANSACTIONS WITH DIRECTORS AND EXECUTIVE OFFICERS
 
    Dr.  Cooper served as the Company's President from September 1992 until June
1994. In September 1992, the Company loaned Dr. Cooper $150,000 to assist him in
purchasing a new home in the state  of Ohio. In October 1993, Dr. Cooper  repaid
the  loan in  full. Pursuant  to Dr.  Cooper's employment  agreement, Dr. Cooper
purchased 133,681  shares of  Common Stock  at $.02  per share,  subject to  the
Company's right to repurchase such shares over a three-year period. In May 1993,
upon Dr. Cooper's appointment as president of Interneuron, the repurchase option
was  modified  at  the  approval  of the  Board  of  Directors  and  the Company
repurchased 74,267 of Dr. Cooper's shares.
 
   
    On January 3, 1993,  the Company entered into  an employment agreement  with
Dr.  Given. Under the agreement, Dr. Given received the right to a $100,000 loan
bearing interest at 7%  annually for the  purchase of a home  in Ohio. Upon  the
granting  of the loan, the Company waived  the charging of interest on the loan,
and certain other provisions of the agreement relating to the loan, and received
from Dr.  Given an  interest-free  promissory note  in  the amount  of  $100,796
secured by the property purchased. The note requires Dr. Given to repay at least
$60,796  of the loan  on or before April  1, 1997. Of  this portion, $20,000 was
forgiven effective in fiscal 1996 at the approval of the Board of Directors, and
$40,796 remains payable. The  balance of $40,000 is  payable on or before  April
15,  1997 or upon  the termination of  Dr. Given's employment  and is subject to
forgiveness in $10,000  increments upon the  achievement of certain  performance
milestones,  including  a successful  initial public  offering of  the Company's
Common Stock. As of June 30, 1996, the Company had forgiven, effective in fiscal
1996, $10,000 of  the loan pursuant  to this provision.  Upon completion of  the
Offering,  an additional $10,000 of  the loan will be  forgiven pursuant to this
provision. See "Management -- Employment Agreement."
    
 
   
    The Company provided Dr. Williams with  a $55,000 down payment loan for  the
purchase of a home in Ohio upon the commencement of his employment in June 1994.
This  loan  is evidenced  by a  promissory  note executed  in fiscal  1995 which
accrues interest at 9% annually and is secured by Dr. Williams' home. Under  the
terms  of the promissory note,  $40,000 of this loan,  plus accrued interest, is
subject to forgiveness by the Board of Directors upon the achievement of certain
performance milestones. Pursuant  to this  arrangement, the  Board of  Directors
approved  forgiveness  effective in  fiscal 1996  of $20,000  of the  loan, plus
associated accrued interest.  The Board of  Directors also approved  forgiveness
effective  in fiscal 1996 of  an additional $8,000 of  the loan, plus associated
accrued interest,  in  lieu  of  a salary  increase.  The  balance  of  $30,674,
including  accrued  interest  as of  June  30, 1996,  remains  outstanding. Upon
completion of the Offering, an additional  $10,000 of the loan, plus  associated
accrued interest, will be forgiven. In addition, the Company loaned Dr. Williams
$21,448 in fiscal 1995. This amount was repaid in May 1996.
    
 
   
    Effective  as of  May 24,  1996, Dr.  Doros Platika's  employment terminated
pursuant to  a  Separation  Agreement  and Release  (the  "Release")  among  the
Company,  Dr.  Platika and  Interneuron. The  Release  obligates Dr.  Platika to
provide services to the Company in a consulting capacity for a minimum of twenty
hours per month  for the six-month  period following May  24, 1996. Dr.  Platika
also  agreed not to compete with the Company for a period of two years after his
termination. The Release also contains  arrangements with respect to loans  made
by the Company to Dr. Platika and certain stock options to acquire securities of
the Company and Interneuron. Prior to termination, the Company had made loans to
Dr.  Platika that had  a balance of  $216,426, including accrued  interest as of
July 23, 1996, which amount reflects the forgiveness effective in fiscal 1996 of
$26,424 of such loans previously approved by the Board of Directors. Pursuant to
the Release, an additional $120,000 of this balance was forgiven subject to  Dr.
Platika's  payment to the Company of  withholding payments required with respect
thereto and with respect to the loans to Dr. Platika previously forgiven by  the
Company  effective in fiscal 1996. The  remaining balance of $96,426, along with
applicable withholding payments, was  paid by Dr. Platika  as of July 23,  1996.
The  Company  will incur  a charge  to operations  equal to  the amount  of loan
forgiveness in connection with  the Release. Prior to  the Release, the  Company
had  granted Dr. Platika options to purchase  a total of 77,500 shares of Common
Stock, at  exercise prices  ranging from  $0.20 to  $6.00 per  share. Of  these,
options  to purchase  a total  of 23,750 shares  of Common  Stock had previously
vested. The
    
 
                                       53
<PAGE>
   
Release provides for the vesting as of June 1, 1996 of options to purchase 6,875
shares of Common Stock at $0.20 per share and the vesting as of June 15, 1996 of
options to acquire 2,500 shares of Common  Stock at $4.00 per share. All of  Dr.
Platika's  other unvested options  were canceled pursuant to  the Release. As of
August 15,  1996, Dr.  Platika held  options exercisable  for 33,125  shares  of
Common  Stock, which options will  expire on August 24,  1996 in accordance with
the terms of the  1992 Stock Option  Plan. Dr. Platika  has tendered notices  of
exercise  and payment for the  exercise of all of  these options effective as of
August  23,  1996.  In  connection  with  the  Release,  Interneuron  agreed  to
accelerate  vesting of  stock options  to purchase  2,500 shares  of Interneuron
Common Stock at a price  per share of $8.75,  which options were exercisable  by
Dr.  Platika on or prior to August 24,  1996. As of August 15, 1996, Dr. Platika
had exercised all of these Interneuron options.
    
 
   
    The Company  has  granted  stock  options to  its  directors  and  executive
officers  on several occasions since the beginning  of fiscal 1993, all of which
vest over a four-year period from the date of grant, except as indicated  below.
In  fiscal  1993, Dr.  Snodgrass received  options to  purchase 5,000  shares of
Common Stock at an exercise  price of $0.20 per  share, and options to  purchase
5,000 shares of Common Stock at an exercise price of $2.00 per share.
    
 
    During  fiscal 1994, Mr. Sharrock received  options to purchase 2,500 shares
of Common Stock at an exercise price  of $4.00 per share, which vest over  three
years.  Also in fiscal  1994, the Company granted  Drs. Cooper, Given, Snodgrass
and Williams options  to purchase  8,500, 16,500,  10,000 and  20,000 shares  of
Common Stock, respectively, at an exercise price of $4.00 per share.
 
    In  September 1995, the Company granted options to Drs. Given, Snodgrass and
Williams to  purchase 45,000,  17,500  and 17,500  shares, respectively,  at  an
exercise  price of $6.00  per share, which  originally were intended  to vest on
September 14, 2002. These options were amended by the Board of Directors on  May
13, 1996, so that one-third of such options vest on each anniversary date of the
date  of grant. In September  1995, the Company granted  to Dr. Given options to
purchase an additional 50,000  shares at an exercise  price of $6.00 per  share,
which  also vest over three years from the  date of grant. In September 1995 the
Company also  granted to  Dr. Snodgrass  options to  purchase 12,500  shares  of
Common  Stock,  all  of which  vest  upon  the earliest  of  the  achievement of
performance milestones  relating to  the leptin  receptor program  or the  BFU-e
growth factor program, or September 14, 2002.
 
    On  February 21,  1996, each of  Messrs. Axline, Haig,  Peppers and Sharrock
received options to purchase 7,500 shares  of Common Stock at an exercise  price
of $6.00 per share.
 
    All  of the  option grants  described above were  made pursuant  to the 1992
Stock Option Plan.
 
   
    On May 13, 1996, in connection with the Board of Directors' adoption of  the
Company's  1996 Stock  Incentive Plan, Drs.  Given, Snodgrass  and Williams were
granted options, which vest over three  years, to purchase 100,000, 100,000  and
75,000  shares of Common Stock, respectively, at  an exercise price of $9.00 per
share.
    
 
INSIDER TRANSACTIONS
 
    The Company has adopted  a policy that all  future transactions between  the
Company  and  its executive  officers, directors  and  other affiliates  must be
approved by a majority  of the disinterested members  of the Company's Board  of
Directors,  and must be on terms no less  favorable to the Company than could be
obtained from unaffiliated third parties. In addition, this policy requires that
any loans  by  the  Company  to  its  executive  officers,  directors  or  other
affiliates  be for  bona fide business  purposes only. A  determination of which
directors are disinterested with respect to a particular transaction will depend
upon the totality  of circumstances  including whether the  directors possess  a
direct  or indirect  material interest  in the  transaction or  in another party
involved in the transaction.
 
                                       54
<PAGE>
                             PRINCIPAL STOCKHOLDERS
 
   
    The following  table sets  forth  certain information  regarding  beneficial
ownership  of the Company's Common Stock as  of August 15, 1996, and as adjusted
to reflect the sale of the shares  of Common Stock being offered hereby, by  (i)
each stockholder who is known by the Company to own beneficially more than 5% of
the  Company's outstanding Common Stock, (ii)  each director and Named Executive
Officer of the  Company and (iii)  all directors and  executive officers of  the
Company as a group.
    
 
   
<TABLE>
<CAPTION>
                                                                                     PERCENTAGE BENEFICIALLY
                                                                        NUMBER OF            OWNED(2)
                                                                         SHARES     --------------------------
                                                                       BENEFICIALLY   PRIOR TO       AFTER
BENEFICIAL OWNER                                                        OWNED(1)      OFFERING      OFFERING
- ---------------------------------------------------------------------  -----------  ------------  ------------
<S>                                                                    <C>          <C>           <C>
Glenn L. Cooper, M.D.(3) ............................................   3,885,298         79.6%         52.6%
 One Ledgemont Center
 99 Hayden Avenue
 Lexington, Massachusetts 02173
Interneuron Pharmaceuticals, Inc. ...................................   3,820,134         78.3          51.8
 One Ledgemont Center
 99 Hayden Avenue
 Lexington, Massachusetts 02173
The Ohio University Foundation (4) ..................................     262,083          5.4           3.6
 102 Research and Technology Center
 Athens, Ohio 45701
Morris Laster, M.D...................................................     112,500          2.3           1.5
Douglass B. Given, M.D., Ph.D. (5)...................................     122,824          2.5           1.7
H. Ralph Snodgrass, Ph.D. (6)........................................      19,583        *             *
Stephen J. Williams, Ph.D. (7).......................................      15,833        *             *
David B. Sharrock (8)................................................       1,667        *             *
Robert P. Axline.....................................................          --        *             *
Alexander M. Haig, Jr................................................          --        *             *
Jerry P. Peppers.....................................................          --        *             *
                                                                        4,157,705         83.8          55.7
All executive officers and directors as a group
 (9 persons) (9).....................................................
</TABLE>
    
 
- ------------------
*   Less than one percent.
 
(1)  To the Company's  knowledge, except as  indicated in the  footnotes to this
    table and subject to applicable community property laws, each of the persons
    named in this table has sole voting and investment power with respect to all
    shares of Common Stock indicated opposite such person's name.
 
   
(2) Percentage of beneficial  ownership is based on  4,877,936 shares of  Common
    Stock  outstanding as  of August  15, 1996,  and 7,377,936  shares of Common
    Stock  outstanding  after  completion  of  this  Offering,  reflecting   the
    conversion  of  the  convertible  debenture  and  promissory  note  held  by
    Interneuron and all outstanding shares of Preferred Stock into Common  Stock
    and  the  purchase by  The Ohio  University Foundation  of 25,000  shares of
    Common Stock pursuant to  a stock purchase  right. See "Capitalization"  and
    "Description  of Capital Stock." Shares of  Common Stock subject to options,
    warrants and  convertible notes  currently  exercisable or  convertible,  or
    exercisable  or convertible  within 60 days  of August 15,  1996, are deemed
    outstanding for computing  the percentage  of the person  or entity  holding
    such  securities but are not deemed outstanding for computing the percentage
    of any other person or entity.
    
 
   
(3) Includes 3,820,134 shares held by Interneuron, options exercisable for 4,250
    shares of Common Stock held by Dr. Cooper and options exercisable for  1,500
    shares  of Common Stock held by Dr.  Cooper's wife. Dr. Cooper is President,
    Chief Executive Officer and a director of Interneuron. Dr. Cooper  disclaims
    beneficial ownership of the shares held by Interneuron.
    
 
(4) Includes a stock purchase right for 25,000 shares of Common Stock.
 
   
(5) Includes 82,907 shares held by a limited partnership of which Dr. Given is a
    general partner and options exercisable for 39,917 shares of Common Stock.
    
 
   
(6) Includes options exercisable for 19,583 shares of Common Stock.
    
 
   
(7) Includes options exercisable for 15,833 shares of Common Stock.
    
 
   
(8) Includes options exercisable for 1,667 shares of Common Stock.
    
 
   
(9)  Includes  options  exercisable  for  82,750  shares  of  Common  Stock. See
    footnotes 3, 5, 6, 7 and 8 above.
    
 
                                       55
<PAGE>
                          DESCRIPTION OF CAPITAL STOCK
 
    The  Company's Certificate of Incorporation, as amended (the "Certificate of
Incorporation")  currently  authorizes  42,000,000  shares  of  capital   stock,
consisting  of 39,000,000 shares of Common Stock,  Class A, $.001 par value, and
3,000,000 shares of  Preferred Stock,  $.01 par  value. In  connection with  the
Offering,  the  Company's  Certificate  of  Incorporation  will  be  amended and
restated (the "Restated Certificate of  Incorporation"). Upon completion of  the
Offering,  the Restated Certificate of Incorporation will authorize the issuance
of 44,000,000 shares of capital stock, consisting of 39,000,000 shares of Common
Stock, par value $.001 per share,  and 5,000,000 shares of Preferred Stock,  par
value  $.001 per share. Set forth below is a description of the capital stock of
the Company.
 
COMMON STOCK
 
   
    As of August 15, 1996, assuming the conversion of all outstanding shares  of
Preferred  Stock and the  convertible debenture and  promissory note into Common
Stock, and the exercise of the stock purchase right described below, there  were
4,877,936  shares of Common  Stock issued and  outstanding held of  record by 55
stockholders, 606,625  shares of  Common  Stock issuable  upon the  exercise  of
outstanding  stock options and  26,126 shares of Common  Stock issuable upon the
exercise of outstanding warrants.
    
 
    The holders  of Common  Stock are  entitled to  one vote  per share  on  all
matters  submitted to a vote of stockholders  and are not entitled to cumulative
voting rights with respect to the election of directors. Accordingly, holders of
a majority of the  shares of Common  Stock entitled to vote  in any election  of
directors  may  elect all  of the  directors standing  for election.  Holders of
Common Stock are entitled to receive ratably  such dividends, if any, as may  be
declared  by the  Board of  Directors out  of funds  legally available therefor,
subject to  preferences that  may  be applicable  to any  outstanding  Preferred
Stock.  In the event of  liquidation, dissolution or winding  up of the Company,
holders of  Common  Stock  are entitled  to  share  ratably in  all  net  assets
remaining  after payment  of liabilities and  the liquidation  preference of any
outstanding Preferred  Stock.  Holders  of  Common  Stock  have  no  preemptive,
subscription, redemption, conversion or other subscription rights, and there are
no  sinking  fund  provisions  applicable to  the  Common  Stock.  All currently
outstanding shares of  Common Stock are,  and the shares  of Common Stock  being
issued  and sold in the Offering will be, duly authorized, validly issued, fully
paid and nonassessable.
 
PREFERRED STOCK
 
   
    The Company currently has outstanding 2,020,496 shares of Series A Preferred
Stock and  349,000  shares  of  Series  B  Preferred  Stock.  Such  shares  will
automatically convert into Common Stock upon consummation of this Offering. Both
the  Series  A and  Series B  Preferred Stock  have antidilution  and conversion
adjustment provisions that  will increase or  decrease the number  of shares  of
Common  Stock outstanding  as of August  15, 1996  above or below  the number of
shares set forth herein and will increase or decrease the number of shares  used
in  calculations for purposes of, among other things, dilution to new investors,
shares held by  certain principal stockholders,  shares subject to  registration
rights and shares eligible for future sale, in the event that the initial public
offering  price of the Common Stock offered hereby, is less than or greater than
$12.00 per share, as the case may be. See "Dilution," "Principal  Stockholders,"
"-- Registration Rights," and "Shares Eligible for Future Sale."
    
 
    The  actual number  of shares  of Common  Stock issuable  to each  holder of
Preferred Stock upon  conversion of the  Series A and  Series B Preferred  Stock
will  equal the product of  (a) the number of shares  of Preferred Stock held by
such holder multiplied  by (b) the  greater of (x)  one or (y)  a fraction,  the
numerator of which is $12.50 and the denominator of which is .6957 multiplied by
the  initial public offering  price of the  Common Stock offered  hereby. At the
assumed initial public offering price of  $12.00 per share, 1,774,014 shares  of
Common Stock will issue upon conversion of the Preferred Stock.
 
                                       56
<PAGE>
    Following  completion of the Offering and  the conversion of all outstanding
shares of Preferred  Stock, the Board  of Directors will  have the authority  to
issue from time to time up to 5,000,000 shares of Preferred Stock in one or more
series   and  to  fix  the   powers,  designations,  preferences  and  relative,
participating, optional  or other  rights  thereof, including  dividend  rights,
conversion  rights, voting rights, redemption terms, liquidation preferences and
the number of shares constituting each such series, without any further vote  or
action  by the  Company's stockholders.  The issuance  of Preferred  Stock could
adversely affect the rights of holders of Common Stock and could have the effect
of delaying, deferring  or preventing a  change in control  of the Company.  The
Company has no present plans to issue any shares of Preferred Stock.
 
STOCK PURCHASE RIGHT AND WARRANTS
 
    Pursuant  to a Stock Purchase  Agreement entered into on  March 27, 1992, as
amended on February 26, 1996, the Company granted The Ohio University Foundation
the right to purchase  up to 25,000 shares  of Common Stock in  the event of  an
initial public offering, merger or other similar corporate transaction involving
Progenitor, at a price equal to 50% of the assumed initial public offering price
per  share or other per share  consideration. The Ohio University Foundation has
agreed to exercise such right in full prior to the closing of the Offering.  See
"Certain Transactions -- The Ohio University Foundation."
 
   
    As  of  June  30,  1996,  there were  warrants  outstanding  to  purchase an
aggregate of 26,126 shares  of Common Stock  at an exercise  price of $9.18  per
share.  The  warrants also  contain a  cashless exercise  right that  allows the
holder to receive the number  of shares of Common  Stock subject to the  warrant
multiplied  by a fraction, the numerator of  which is the difference between the
then current  per share  market price  of the  Common Stock  and $9.18  and  the
denominator  of which is the  then current per share  market price of the Common
Stock. These warrants  were issued  in connection  with a  private placement  of
Preferred  Stock  for which  Paramount, an  affiliate  of Interneuron,  acted as
placement agent. See  "Certain Transactions --  Relationship with  Interneuron."
The  warrants expire five years  from the date of  this Offering. Upon automatic
conversion  of  the   outstanding  Preferred  Stock   in  connection  with   the
consummation of this Offering, all such warrants will be converted into warrants
to  purchase shares of  Common Stock. The  number of shares  of Common Stock for
which such warrants  are exercisable  is subject  to adjustment  if the  initial
public offering price of the Common Stock offered hereby is less than or greater
than  $12.00 per  share in  the same  manner and  according to  the same formula
described above  for  the  conversion of  the  Company's  currently  outstanding
Preferred  Stock. See "-- Preferred Stock." The  warrants do not confer upon the
holder thereof  any  voting or  preemptive  rights, or  any  other rights  as  a
stockholder  of Progenitor  prior to exercise.  Upon exercise  of such warrants,
holders of the  underlying shares of  Common Stock will  be entitled to  certain
registration rights with respect to such shares. See "-- Registration Rights."
    
 
REGISTRATION RIGHTS
 
    Pursuant  to Investors' Rights Agreements (the "Investors' Agreements"), the
holders of  261,273 shares  of Common  Stock (the  "Registrable Securities")  or
their   transferees  are  entitled  to  certain   rights  with  respect  to  the
registration of such shares under the Securities Act. Pursuant to the Investors'
Agreements, subject to  certain exceptions  and limitations, the  holders of  at
least  50% of the Registrable Securities may require, on one occasion during the
four-year period commencing  12 months after  the closing of  the Offering  (the
"Registration  Period"), that the  Company use its best  efforts to register the
Registrable Securities for  public resale. During  the Registration Period,  the
holders of the Registrable Securities may also require the Company (but not more
than  twice  in  any  calendar year)  to  register  all or  a  portion  of their
Registrable Securities on  Form S-3 under  the Securities Act  when use of  such
form  becomes available to the Company;  provided, among other limitations, that
the anticipated  aggregate offering  price, net  of underwriting  discounts  and
commissions,  will  exceed  $500,000  or the  number  of  shares  of Registrable
Securities exceeds 20,000, whichever  has a greater value.  In addition, in  the
event
 
                                       57
<PAGE>
the Company elects to register any Common Stock under the Securities Act, either
for  its own account or for the  account of any other stockholders, the Company,
on two such occasions during the Registration Period, is required to notify, and
subject to certain marketing  and other limitations, is  required to include  in
such registration the Registrable Securities of holders requesting registration.
The  holders of 26,126 shares of Common  Stock issuable, after completion of the
Offering,  upon  exercise  of  outstanding  warrants  are  entitled  to  similar
registration rights with respect to the registration of the underlying shares on
a Form S-3 or in the event the Company files a registration statement during the
Registration  Period pursuant  to the  terms of  the warrants.  All registration
expenses of any such registration are to be borne by the Company and all selling
expenses relating to Registrable  Securities are to be  borne by the holders  of
the  securities being registered. See "Certain Transactions -- Relationship with
Interneuron."
 
INTERNEURON CONVERTIBLE DEBENTURE AND PROMISSORY NOTE
 
    On March 31, 1995, the Company issued a convertible debenture in the  amount
of  $387,968 to Interneuron, and procured an additional advance of $28,651 under
such debenture on June 30, 1995. The debenture is convertible immediately  prior
to  the consummation of  this Offering into  a number of  shares of Common Stock
equal to the outstanding  principal amount and any  accrued interest divided  by
the  initial public offering price  of the Common Stock,  plus a cash payment in
lieu of fractional shares.
 
   
    Interneuron has provided  and continues  to provide  advances to  Progenitor
evidenced  by a promissory note dated March 31, 1996, in the principal amount of
approximately $523,000, as updated from time to time, payable on the earlier  of
five  years  from  the  date  of  the note  or  the  closing  of  this Offering.
Interneuron has  agreed  to  convert  the indebtedness  evidenced  by  the  note
(approximately  $2.2  million  as  of  August  15,  1996),  including additional
advances from April  1, 1996  through the closing  of the  Offering and  accrued
interest  thereon, into shares of Common Stock  upon the closing of the Offering
at a conversion price equal to  the initial public offering price. See  "Certain
Transactions -- Relationship with Interneuron."
    
 
DELAWARE ANTI-TAKEOVER LAW AND CERTAIN CHARTER PROVISIONS
 
    The  Company is  subject to  the provisions of  Section 203  of the Delaware
General Corporation Law ("DGCL"), an anti-takeover law. In general, the  statute
prohibits  a  publicly-held Delaware  corporation from  engaging in  a "business
combination" with an "interested stockholder" for a period of three years  after
the   date  of  the  transaction  in  which  the  person  became  an  interested
stockholder, unless the business combination is, or the transaction in which the
person became an interested stockholder was, approved in a prescribed manner  or
another  prescribed exemption applies. For purposes  of Section 203, a "business
combination" is  defined  broadly to  include  a  merger, asset  sale  or  other
transaction  resulting in a financial benefit  to the interested stockholder. In
general, an "interested stockholder" is  a person who, together with  affiliates
and  associates, owns (or within the three  years prior to such transaction, did
own) 15% or more of the corporation's voting stock.
 
    In addition, certain  provisions of  the Company's  Restated Certificate  of
Incorporation  may have the  effect of preventing,  discouraging or delaying any
change in control  of Progenitor.  The authorization  of undesignated  Preferred
Stock makes it possible for the Board of Directors to issue Preferred Stock with
voting  or other  rights or  preferences that  could impede  the success  of any
attempt to change control of the Company. See "-- Preferred Stock."
 
LIMITATION OF LIABILITY
 
    Section 145  ("Section  145") of  the  DGCL provides  a  detailed  statutory
framework covering indemnification of officers and directors against liabilities
and  expenses arising out of legal proceedings brought against them by reason of
their being or having been directors or officers. Section 145 generally provides
that a director  or officer of  a corporation  (i) shall be  indemnified by  the
corporation for all expenses of
 
                                       58
<PAGE>
such  legal  proceedings  when he  is  successful  on the  merits,  (ii)  may be
indemnified by the corporation  for the expenses,  judgments, fines and  amounts
paid  in settlement of such proceedings (other  than a derivative suit), even if
he is not successful on the merits, if he acted in good faith and in a manner he
reasonably believed  to be  in  or not  opposed to  the  best interests  of  the
corporation,  and, with  respect to  any criminal  action or  proceeding, had no
reasonable cause  to  believe  his  conduct  was  unlawful,  and  (iii)  may  be
indemnified  by the corporation for the expenses of a derivative suit (a suit by
a stockholder alleging a breach by a director  or officer of a duty owed to  the
corporation),  even if he is  not successful on the merits,  if he acted in good
faith and in a manner he reasonably believed to be in or not opposed to the best
interests of the corporation. No indemnification may be made under clause  (iii)
above,  however, if the director or officer is adjudged liable for negligence or
misconduct in  the  performance of  his  duties  to the  corporation,  unless  a
corporation  determines that, despite such adjudication,  but in view of all the
circumstances, he is entitled to indemnification. The indemnification  described
in  clauses (ii)  and (iii)  above may  be made  only upon  a determination that
indemnification is proper because  the applicable standard  of conduct has  been
met. Such a determination may be made by a majority of a quorum of disinterested
directors,  independent legal counsel, the stockholders  or a court of competent
jurisdiction.
 
   
    The Company's Restated  Certificate of Incorporation  will provide that  the
Company  shall indemnify to the  fullest extent permitted by  Section 145, as it
now exists or as  amended, all persons whom  it may indemnify pursuant  thereto.
The Company has entered into agreements to indemnify its directors and executive
officers,  in addition to indemnification provided  for in the Company's charter
documents. These agreements, among other things, provide for the indemnification
of  the  Company's  directors  and  executive  officers  for  certain   expenses
(including attorneys' fees), judgments, fines and settlement amounts incurred by
any  such person in any action or proceeding,  including any action by or in the
right of the Company,  arising out of  such person's services  as a director  or
executive  officer of the  Company, any subsidiary  of the Company  or any other
company or enterprise to which such  person provides services at the request  of
the  Company  to the  fullest extent  permitted by  applicable law.  The Company
believes that  these  provisions  and  agreements will  assist  the  Company  in
attracting  and retaining qualified persons to  serve as directors and executive
officers.
    
 
    Section 102(b)(7)  of the  DGCL  permits a  corporation  to provide  in  its
certificate  of incorporation  that a director  of the corporation  shall not be
personally liable to the  corporation or its  stockholders for monetary  damages
for  breach of fiduciary  duty as a  director, except for  liability (i) for any
breach of the director's duty of loyalty to the corporation or its stockholders,
(ii) for  acts or  omissions not  in  good faith  or which  involve  intentional
misconduct  or a knowing violation of law,  (iii) under Section 174 of the DGCL,
or (iv) for any transaction from which the director derived an improper personal
benefit. The Company's  Restated Certificate of  Incorporation will provide  for
the  elimination of  personal liability  of a  director for  breach of fiduciary
duty, as permitted by Section 102(b)(7) of the DGCL.
 
    The Underwriting Agreement provides for indemnification by the  Underwriters
under  certain circumstances of  directors, officers and  controlling persons of
the  Company  against  certain  liabilities,  including  liabilities  under  the
Securities Act.
 
    Prior  to  the  closing  of  the Offering,  the  Company  intends  to obtain
liability insurance  insuring  the  Company's  officers  and  directors  against
liabilities that they may incur in such capacities.
 
    The  Investors' Agreements provide for cross-indemnification of stockholders
of the  Company  whose  shares  with  registration  rights  are  included  in  a
registration  under the  Securities Act,  and of  the Company,  its officers and
directors for certain liabilities arising in connection with such registration.
 
TRANSFER AGENT AND REGISTRAR
 
    Continental Stock  Transfer  &  Trust  Company has  been  appointed  as  the
transfer agent and registrar for the Company's Common Stock.
 
                                       59
<PAGE>
                        SHARES ELIGIBLE FOR FUTURE SALE
 
    Prior  to the Offering, there has not  been any public market for the Common
Stock and there can  be no assurance  that a significant  public market for  the
Common  Stock will  be developed  or be sustained  after the  Offering. Sales of
substantial amounts of Common Stock in the public market after the Offering,  or
the  possibility  of such  sales  occurring, could  adversely  affect prevailing
market prices for the Common Stock or the future ability of the Company to raise
capital through an offering of equity securities.
 
   
    After the Offering, the  Company will have  outstanding 7,377,936 shares  of
Common  Stock (7,752,936  shares if  the Underwriters'  over-allotment option is
exercised in full). Of these shares, the 2,500,000 shares offered hereby will be
freely tradable in the  public market without  restriction under the  Securities
Act, unless such shares are held by "affiliates" of the Company, as that term is
defined in Rule 144 under the Securities Act.
    
 
   
    The  remaining 4,877,936 shares of  Common Stock outstanding upon completion
of the Offering will be "restricted securities" as that term is defined in  Rule
144  ("Restricted Shares").  The Restricted Shares  were issued and  sold by the
Company in private  transactions in reliance  upon exemptions from  registration
under  the Securities Act.  Restricted Shares may  be sold in  the public market
only  if  they  are  registered  or  if  they  qualify  for  an  exemption  from
registration  under the Securities Act, including an exemption under Rule 144 or
701, which are summarized below.
    
 
   
    Pursuant to "lock-up"  agreements, all of  the Company's executive  officers
and  directors and certain  stockholders, who collectively  hold 902,541 of such
Restricted Shares, have agreed not to  offer, sell, contract to sell, grant  any
option  to purchase or otherwise dispose of any  such shares for a period of 180
days from  the date  of this  Prospectus without  the prior  written consent  of
Vector Securities International, Inc. Interneuron will hold 3,820,134 Restricted
Shares  and has  agreed pursuant to  a lock-up  agreement not to  offer, sell or
otherwise dispose of any of its Restricted Shares for a period of 365 days  from
the  date  of  this  Prospectus  without the  prior  written  consent  of Vector
Securities International, Inc.  The Company  has also  agreed that  it will  not
offer,  sell or otherwise dispose of Common Stock  for a period of 180 days from
the date of this Prospectus, other than pursuant to existing stock option plans,
without the prior written consent of Vector Securities International, Inc.  Upon
termination  of such lock-up agreements,  approximately 409,413 and 3,593,591 of
the Restricted Shares will be eligible for immediate sale beginning 181 days and
366 days, respectively, after the date of this Prospectus, in the public  market
subject  to certain volume, manner of sale  and other limitations under Rule 144
and approximately  385,450  of  such  Restricted Shares  will  be  eligible  for
immediate  sale 181  days after the  date of this  Prospectus without limitation
under Rule 144(k).
    
 
    The Securities and Exchange Commission  has recently proposed amendments  to
Rule  144 and Rule  144(k) that would  permit resale of  restricted shares under
Rule 144 after  a one-year, rather  than a two-year  holding period, subject  to
compliance  with the other  provisions of Rule  144, and would  permit resale of
restricted shares by non-affiliates under  Rule 144(k) after a two-year,  rather
than  a three-year holding  period. Adoption of such  amendments could result in
resale of restricted shares  sooner than would  be the case  under Rule 144  and
Rule 144(k) as currently in effect.
 
   
    Following the expiration of such lock-up periods, certain shares issued upon
exercise  of options granted by the Company prior to the date of this Prospectus
will also be available for sale in the public market pursuant to Rule 701  under
the  Securities Act. Rule  701 permits resales  of such shares  in reliance upon
Rule 144 but without compliance with certain restrictions, including the holding
period requirement,  imposed under  Rule  144. In  general,  under Rule  144  as
currently  in effect, beginning on             , 1996 (90 days after the date of
this Prospectus),  a  person  (or  persons  whose  shares  of  the  Company  are
aggregated)  who has beneficially owned Restricted Shares for at least two years
(including the holding period of any prior owner who is not an affiliate of  the
Company)  would be entitled  to sell within  any three-month period  a number of
shares that  does  not  exceed the  greater  of  (i) one  percent  of  the  then
outstanding  shares  of Common  Stock  (approximately 73,779  shares immediately
after the Offering),  or (ii) the  average weekly trading  volume of the  Common
Stock  during the four  calendar weeks preceding  the filing of  a Form 144 with
respect  to   such  sale.   Sales   under  Rule   144   are  also   subject   to
    
 
                                       60
<PAGE>
certain  manner  of sale  and  notice requirements  and  to the  availability of
current public information about the Company. Under Rule 144(k), a person who is
not deemed to have been  an affiliate of the Company  at any time during the  90
days  preceding a sale and who has  beneficially owned the shares proposed to be
sold for at least three years (including  the holding period of any prior  owner
who  is not an affiliate of the Company) is entitled to sell such shares without
complying with  the manner  of sale,  public information,  volume limitation  or
notice provisions of Rule 144.
 
   
    As  of August  15, 1996, options  to purchase  a total of  606,625 shares of
Common Stock were outstanding  under the Company's stock  option plans. Of  such
shares,  approximately 508,625  shares are subject  to lock-up  agreements for a
period of 180 days  from the date  of this Prospectus  and the remaining  98,000
shares will be available for sale in the public market 90 days after the date of
this Prospectus pursuant to Rule 701. As of August 15, 1996, 736,700 shares were
available for future option grants under such plans.
    
 
   
    The  Company  intends  to file  after  the  effective date  of  the Offering
Registration Statements on Form S-8 to register an aggregate of 1,443,325 shares
of Common Stock  reserved for issuance  under its 1992  Stock Option Plan,  1996
Stock  Incentive Plan and  1996 Employee Stock  Purchase Plan. Such Registration
Statements will become effective automatically upon filing. Shares issued  under
the  foregoing plans,  after the filing  of the Registration  Statements on Form
S-8, may be sold in the open market, subject, in the case of certain holders, to
the Rule 144 limitations applicable to affiliates, the above-referenced  lock-up
agreements and vesting restrictions imposed by the Company.
    
 
    After the closing of the Offering, holders of an aggregate of 261,273 shares
of  Common Stock issued upon the conversion  of Preferred Stock will be entitled
to certain rights  with respect  to the registration  of such  shares under  the
Securities  Act.  In  addition,  the 26,126  shares  issuable  upon  exercise of
outstanding warrants  have  similar  registration rights  during  the  four-year
period commencing 12 months after consummation of the Offering. See "Description
of Capital Stock -- Registration Rights."
 
                                       61
<PAGE>
                                  UNDERWRITING
 
    Subject  to  the terms  and conditions  of  the Underwriting  Agreement, the
underwriters (the  "Underwriters")  named  below,  for  whom  Vector  Securities
International,  Inc.,  Tucker Anthony  Incorporated  and Genesis  Merchant Group
Securities are acting as representatives (the "Representatives"), have severally
agreed to purchase,  subject to  the terms  and conditions  of the  Underwriting
Agreement, and the Company has agreed to sell to the Underwriters, the following
respective number of shares of Common Stock.
 
<TABLE>
<CAPTION>
UNDERWRITERS                                                                           NUMBER OF SHARES
- -------------------------------------------------------------------------------------  -----------------
<S>                                                                                    <C>
Vector Securities International, Inc.................................................
Tucker Anthony Incorporated..........................................................
Genesis Merchant Group Securities....................................................
 
                                                                                             --------
  Total..............................................................................       2,500,000
                                                                                             --------
                                                                                             --------
</TABLE>
 
    The Underwriting Agreement provides that the obligations of the Underwriters
are  subject  to  certain conditions  precedent,  including the  absence  of any
material adverse change  in the Company's  business and the  receipt of  certain
certificates,  opinions  and  letters  from  the  Company  and  its  counsel and
independent auditors. The nature  of the Underwriters'  obligation is such  that
they  are committed to purchase all shares of Common Stock offered hereby if any
of such shares are purchased.
 
    The Underwriters propose to offer the  shares of Common Stock to the  public
at  the offering  price set forth  on the cover  page of this  Prospectus and to
certain dealers at such price  less a concession not in  excess of $         per
share.  The  Underwriters may  allow to  selected dealers  and such  dealers may
reallow a concession  not in  excess of  $          per share  to certain  other
dealers.  After the initial public  offering of the shares  of Common Stock, the
offering price and other selling terms may be changed by the Representatives.
 
    The Company has granted  to the Underwriters an  option, exercisable at  any
time  during the 30-day period after the date of this Prospectus, to purchase up
to an additional 375,000 shares of  Common Stock at the initial public  offering
price  set  forth  on  the  cover page  of  this  Prospectus,  less underwriting
discounts and commissions. The Underwriters may exercise such option solely  for
the  purpose  of  covering  over-allotments,  if  any,  in  connection  with the
Offering. To  the extent  such option  is exercised,  each Underwriter  will  be
obligated,  subject to  certain conditions,  to purchase  approximately the same
percentage of such additional shares as the  number of shares set forth next  to
such  Underwriter's name  in the  preceding table bears  to the  total number of
shares listed in the table.
 
    The offering of the shares is made for delivery when, as and if accepted  by
the  Underwriters and subject  to prior sale and  to withdrawal, cancellation or
modification of the Offering without notice. The Underwriters reserve the  right
to reject an order for the purchase of shares in whole or in part.
 
    At  the request of the Company, the Underwriters have reserved 50,000 shares
for sale to employees, directors and other persons and entities associated  with
the  Company. The number of shares available for sale to the general public will
be reduced to the extent  that the reserved shares  are purchased by persons  or
entities  designated by the Company. Any  reserved shares that are not purchased
by persons  or  entities  designated by  the  Company  will be  offered  by  the
Underwriters  to the general  public on the  same basis as  other shares offered
hereby.
 
    The Company  has  agreed  to  indemnify  the  Underwriters  against  certain
liabilities, including liabilities under the Securities Act, or to contribute to
payments that the Underwriters may be required to make in respect thereof.
 
                                       62
<PAGE>
    The  executive officers, directors and certain  employees of the Company and
other stockholders have  agreed that they  will not, without  the prior  written
consent of Vector Securities International, Inc., offer, sell, contract to sell,
grant any option to purchase or otherwise dispose of any shares of Common Stock,
options or warrants to acquire shares of Common Stock or securities exchangeable
for  or convertible into  shares of Common Stock  for a period  of 180 days (365
days in the case of Interneuron) after the date of this Prospectus. The  Company
has  agreed  that it  will  not, without  the  prior written  consent  of Vector
Securities International, Inc., offer, sell, contract to sell, grant any  option
to  purchase or  otherwise dispose  of any  shares of  Common Stock,  options or
warrants to acquire  shares of Common  Stock or securities  exchangeable for  or
convertible  into shares of Common Stock for a period of 180 days after the date
of this Prospectus, except for securities  issued under its stock option  plans.
See "Shares Eligible for Future Sale."
 
    Prior to the Offering, there has been no public market for the Common Stock.
Consequently,  the initial public offering price  for the shares of Common Stock
included in the Offering will be determined by negotiations between the  Company
and  the Representatives. Among the factors considered in determining such price
will be the history of and prospects for the Company's business and the industry
in which it competes, an assessment of the Company's management and the  present
state  of  the  Company's  development,  its  past  and  present  operations and
financial performance, the  prospects for  future earnings of  the Company,  the
present  state of  the Company's  discovery programs,  the current  state of the
economy in the United States and the  current level of economic activity in  the
industry  in which the Company competes and in related or comparable industries,
and the  current  prevailing  condition in  the  securities  markets,  including
current  market valuations of  publicly traded companies  that are comparable to
the Company.
 
    In February 1996, the Company engaged Vector Securities International,  Inc.
as  its  primary financial  advisor  for a  period  of one  year  with automatic
six-month extensions,  unless terminated  in accordance  with the  terms of  the
agreement,  to provide  certain financial advisory  services to  the Company. As
compensation  for   such   services,   the  Company   paid   Vector   Securities
International,  Inc. a  non-refundable retainer  fee of  $75,000 to  be credited
against  additional   advisory  fees   payable   upon  completion   of   certain
transactions.
 
                                 LEGAL MATTERS
 
    The  validity of the issuance  of the shares of  Common Stock offered hereby
and certain matters relating to the Offering will be passed upon for the Company
by Morrison &  Foerster LLP,  San Francisco, California.  Certain legal  matters
relating  to the Offering will  be passed upon for  the Underwriters by Skadden,
Arps, Slate, Meagher & Flom, Chicago, Illinois.
 
                                    EXPERTS
 
    The financial statements of Progenitor,  Inc. (a Development Stage  Company)
as  of September 30, 1994 and 1995 and for each of the three years in the period
ended September  30,  1995,  and for  the  period  from May  8,  1992  (date  of
inception)  to September 30, 1995, appearing in this Prospectus and Registration
Statement  have  been   audited  by  Coopers   &  Lybrand  L.L.P.,   independent
accountants, as set forth in their report thereon appearing elsewhere herein and
in   this  Registration  Statement,  which  includes  an  explanatory  paragraph
regarding the Company's ability to continue as a going concern, and are included
in reliance upon such report given upon the authority of such firm as experts in
accounting and auditing.
 
    The statements  in  this Prospectus  under  the captions  "Risk  Factors  --
Uncertainty  of  Patents  and  Proprietary  Rights,"  "Business  -- Progenitor's
Functional Genomics Approach," "Business  -- Progenitor's Proprietary  Discovery
Technologies,"  "Business --  Progenitor's Discovery Programs"  and "Business --
Patents and Proprietary Rights"  relating to patent  matters have been  reviewed
and  approved by  Pennie & Edmonds,  New York,  New York, patent  counsel to the
Company, and have been included herein in reliance upon the review and  approval
by such firm as experts in patent law.
 
                                       63
<PAGE>
                             ADDITIONAL INFORMATION
 
    The  Company  has  filed  with the  Securities  and  Exchange  Commission, a
Registration Statement  on Form  S-1, including  amendments thereto,  under  the
Securities  Act with respect to the Common Stock offered hereby. This Prospectus
does not contain all of the information set forth in the Registration  Statement
and  the exhibits  and schedules filed  therewith. For  further information with
respect to the Company and  such Common Stock, reference  is hereby made to  the
Registration  Statement  and  to  the exhibits  and  schedules  filed therewith.
Statements contained in this Prospectus  regarding the contents of any  contract
or other document referred to are not necessarily complete, and in each instance
reference  is made to  the copy of such  contract or other  document filed as an
exhibit to the Registration  Statement, each such  statement being qualified  in
all  respects by such reference. Copies of the Registration Statement, including
the exhibits  and schedules  thereto, may  be inspected  without charge  at  the
principal  office of the Securities and Exchange Commission at 450 Fifth Street,
N.W, Room 1024, Washington, D.C. 20549, and at the following regional offices of
the Securities  and  Exchange  Commission: Midwest  Regional  Office,  500  West
Madison Street, Suite 1400, Chicago, Illinois 60661-2511; and Northeast Regional
Office,  Seven  World Trade  Center, New  York,  New York  10048. Copies  can be
obtained at prescribed rates from the Public Reference Section of the Commission
at 450 Fifth Street, N.W, Room 1024, Washington, D.C. 20549.
 
    The Company  intends  to  distribute  to  its  stockholders  annual  reports
containing  financial statements  audited by its  independent public accountants
and will make available copies of quarterly reports for the first three quarters
of each fiscal year containing unaudited financial information.
 
                                       64
<PAGE>
                         INDEX TO FINANCIAL STATEMENTS
 
<TABLE>
<CAPTION>
                                                                                                               PAGE
                                                                                                             ---------
<S>                                                                                                          <C>
Report of Independent Accountants..........................................................................        F-2
Balance Sheets.............................................................................................        F-3
Statements of Operations...................................................................................        F-4
Statements of Stockholders' Deficit........................................................................        F-5
Statements of Cash Flows...................................................................................        F-6
Notes to the Financial Statements..........................................................................        F-7
</TABLE>
 
                                      F-1
<PAGE>
                       REPORT OF INDEPENDENT ACCOUNTANTS
 
Board of Directors and Stockholders of
Progenitor, Inc.
 
We  have  audited  the  accompanying  balance  sheets  of  Progenitor,  Inc.  (a
Development Stage Company) as  of September 30, 1994  and 1995, and the  related
statements  of operations, stockholders'  deficit, and cash  flows for the years
ended September 30, 1993,  1994 and 1995,  and for the period  from May 8,  1992
(date  of inception) to  September 30, 1995. These  financial statements are the
responsibility of the Company's management. Our responsibility is to express  an
opinion on these financial statements based on our audits.
 
We   conducted  our  audits  in  accordance  with  generally  accepted  auditing
standards. Those standards require that we plan and perform the audit to  obtain
reasonable assurance about whether the financial statements are free of material
misstatement.  An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also  includes
assessing  the  accounting principles  used  and significant  estimates  made by
management, as well as evaluating the overall financial statement  presentation.
We believe that our audits provide a reasonable basis for our opinion.
 
In  our opinion, the  financial statements referred to  above present fairly, in
all material respects, the financial position of Progenitor, Inc. (a Development
Stage Company)  as of  September  30, 1994  and 1995,  and  the results  of  its
operations  and its cash flows for the  years ended September 30, 1993, 1994 and
1995, and for the period from May  8, 1992 (date of inception) to September  30,
1995, in conformity with generally accepted accounting principles.
 
The  accompanying financial statements  have been prepared  assuming the Company
will continue  as a  going concern.  As discussed  in Note  1 to  the  financial
statements,  the  Company is  in the  development stage.  The Company's  lack of
revenues and its  need for  additional financing  to fund  its operations  raise
substantial doubt about its ability to continue as a going concern. Management's
plans  in regard to  these matters are  also described in  Note 1. The financial
statements do not include any adjustments that might result from the outcome  of
this uncertainty.
 
                                          COOPERS & LYBRAND L.L.P.
 
Columbus, Ohio
June 5, 1996
 
                                      F-2
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                                 BALANCE SHEETS
 
                                     ASSETS
 
   
<TABLE>
<CAPTION>
                                                                       SEPTEMBER 30,                      PRO FORMA
                                                                  ------------------------   JUNE 30,     JUNE 30,
                                                                     1994         1995         1996         1996
                                                                  -----------  -----------  -----------  -----------
<S>                                                               <C>          <C>          <C>          <C>
                                                                                            (UNAUDITED)  (UNAUDITED)
Current assets:
  Cash and cash equivalents.....................................  $     9,544  $ 1,173,743   $  28,020    $ 178,020
  Accounts receivable...........................................           --      193,898     187,764      187,764
  Accounts receivable -- parent.................................           --      131,600          --           --
  Prepaid expenses and other current assets.....................        3,000       22,618     624,310      624,310
                                                                  -----------  -----------  -----------  -----------
    Total current assets........................................       12,544    1,521,859     840,094      990,094
                                                                  -----------  -----------  -----------  -----------
Property and equipment, at cost:
  Equipment.....................................................      908,788    1,063,602   1,086,562    1,086,562
  Leasehold improvements........................................      121,173           --          --           --
                                                                  -----------  -----------  -----------  -----------
                                                                    1,029,961    1,063,602   1,086,562    1,086,562
    Less accumulated depreciation...............................     (268,030)    (409,120)   (598,542)    (598,542)
                                                                  -----------  -----------  -----------  -----------
                                                                      761,931      654,482     488,020      488,020
Notes receivable officers, net..................................      202,096      218,734      72,222       72,222
                                                                  -----------  -----------  -----------  -----------
    Total assets................................................  $   976,571  $ 2,395,075   $1,400,336   $1,550,336
                                                                  -----------  -----------  -----------  -----------
                                                                  -----------  -----------  -----------  -----------
 
                                       LIABILITIES AND STOCKHOLDERS' DEFICIT
Current liabilities:
  Accounts payable..............................................  $   173,166  $   232,656   $ 397,425    $ 397,425
  Accrued expenses..............................................      679,394    1,343,718     879,588      879,588
  Capital lease obligation -- current...........................      147,907      214,485     245,718      245,718
                                                                  -----------  -----------  -----------  -----------
    Total current liabilities...................................    1,000,467    1,790,859   1,522,731    1,522,731
                                                                  -----------  -----------  -----------  -----------
Note payable -- parent..........................................   10,453,193           --   1,769,387           --
Convertible debenture -- parent.................................           --      436,740     465,963           --
Accrued interest -- parent......................................      871,585           --          --           --
Capital lease obligation........................................      441,976      268,382     172,333      172,333
                                                                  -----------  -----------  -----------  -----------
      Total liabilities.........................................   12,767,221    2,495,981   3,930,414    1,695,064
                                                                  -----------  -----------  -----------  -----------
Commitments and contingencies
Stockholders' deficit:
  Preferred stock, Series A, $.01 par value: 2,120,000 shares
   authorized; 2,020,496 shares issued and outstanding as of
   September 30, 1995 and June 30, 1996.........................           --       20,205      20,205           --
  Preferred stock, Series B, $.01 par value: 880,000 shares
   authorized; 349,000 shares issued and outstanding as of
   September 30, 1995 and June 30, 1996.........................           --        3,490       3,490           --
  Common stock, Class A, $.001 par value: 39,000,000 shares
   authorized; 2,568,668, 2,789,271, 2,852,779 and 4,838,072
   (pro forma) shares issued and outstanding as of September 30,
   1993, 1994 and 1995, and June 30, 1996, respectively.........        2,569        2,789       2,853        4,838
  Common stock, Class B, $.001 par value: 1,000,000 shares
   authorized; 250,000 shares issued and outstanding as of
   September 30, 1994...........................................          250           --          --           --
  Additional paid-in capital....................................        5,094   14,546,640  14,897,701   17,304,761
  Deficit accumulated during development stage..................  (11,798,563) (14,674,030) (17,454,327) (17,454,327)
                                                                  -----------  -----------  -----------  -----------
    Total stockholders' deficit.................................  (11,790,650)    (100,906) (2,530,078)    (144,728)
                                                                  -----------  -----------  -----------  -----------
    Total liabilities and stockholders' deficit.................  $   976,571  $ 2,395,075   $1,400,336   $1,550,336
                                                                  -----------  -----------  -----------  -----------
                                                                  -----------  -----------  -----------  -----------
</TABLE>
    
 
    The accompanying notes are an integral part of the financial statements.
 
                                      F-3
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                            STATEMENTS OF OPERATIONS
 
   
<TABLE>
<CAPTION>
                                                                      MAY 8, 1992                             MAY 8, 1992
                                                                       (DATE OF      NINE MONTHS ENDED JUNE     (DATE OF
                                    YEARS ENDED SEPTEMBER 30,        INCEPTION) TO            30,              INCEPTION)
                              -------------------------------------  SEPTEMBER 30,  ------------------------  TO JUNE 30,
                                 1993         1994         1995          1995          1995         1996          1996
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
<S>                           <C>          <C>          <C>          <C>            <C>          <C>          <C>
                                                                                    (UNAUDITED)  (UNAUDITED)  (UNAUDITED)
Revenue                       $        --  $        --  $ 2,821,386   $ 2,821,386    $2,602,372   $1,149,570  $  3,970,956
Operating expenses:
  Research and
   development..............    3,116,062    4,112,991    4,227,959    12,231,899    3,269,871    2,658,472     14,890,371
  General and
   administrative...........    1,339,086    1,274,896    1,116,652     3,995,433      857,043    1,167,275      5,162,708
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
    Total operating
     expenses...............    4,455,148    5,387,887    5,344,611    16,227,332    4,126,914    3,825,747     20,053,079
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
Interest expense capital
 lease......................           --       44,257       62,945       107,202       51,054       48,188        155,390
Interest expense parent.....      245,391      603,581      289,297     1,160,882      269,175       55,932      1,216,814
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
    Net loss................  $(4,700,539) $(6,035,725) $(2,875,467)  $(14,674,030) ($1,844,771) ($2,780,297) $(17,454,327)
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
                              -----------  -----------  -----------  -------------  -----------  -----------  ------------
Pro forma net loss per
 share......................                            $     (0.63)                              $   (0.58)
                                                        -----------                              -----------
                                                        -----------                              -----------
Pro forma weighted-average
 shares outstanding.........                              4,536,481                               4,780,787
                                                        -----------                              -----------
                                                        -----------                              -----------
</TABLE>
    
 
    The accompanying notes are an integral part of the financial statements.
 
                                      F-4
<PAGE>
   
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                      STATEMENTS OF STOCKHOLDERS' DEFICIT
          FROM MAY 8, 1992 (DATE OF INCEPTION) TO SEPTEMBER 30, 1995,
            AND (UNAUDITED) FOR THE NINE MONTHS ENDED JUNE 30, 1996
    
   
<TABLE>
<CAPTION>
                                                               PREFERRED STOCK                            COMMON STOCK
                                                ----------------------------------------------  ---------------------------------
                                                       SERIES A                SERIES B                CLASS A           CLASS B
                                                ----------------------  ----------------------  ----------------------  ---------
                                                 SHARES      AMOUNT      SHARES      AMOUNT      SHARES      AMOUNT      SHARES
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
<S>                                             <C>        <C>          <C>        <C>          <C>        <C>          <C>
Balance, May 8, 1992 (inception)
  Issued in May 1992 at $.002 per share.......         --   $      --          --   $      --   2,412,950   $   2,413          --
  Issued in May 1992 at $.001 per share.......         --          --          --          --          --          --     250,000
  Net loss....................................         --          --          --          --          --          --          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
Balance, September 30, 1992...................         --          --          --          --   2,412,950       2,413     250,000
  Issued in December 1992 and January 1993 at
   $.000 per share under anti-dilution
   provisions.................................         --          --          --          --      13,397          13          --
  Issued in December 1992 and January 1993 at
   $.02 per share.............................         --          --          --          --     216,588         217          --
  Repurchased at $.02 per share...............         --          --          --          --     (74,267)        (74)         --
  Net loss....................................         --          --          --          --          --          --          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
Balance, September 30, 1993...................         --          --          --          --   2,568,668       2,569     250,000
  Net loss....................................         --          --          --          --          --          --          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
Balance, September 30, 1994...................         --          --          --          --   2,568,668       2,569     250,000
                                                                                                ---------  -----------  ---------
  Issued preferred stock at $6.25 for
   conversion of debt to equity...............  2,020,496      20,205          --          --          --          --          --
  Conversion of Class B common to Class A
   common under anti-dilution provisions......         --          --          --          --     178,750         179    (250,000)
  Issued in December 1994 at $.000 per share
   under anti-dilution provisions.............         --          --          --          --      40,353          40          --
  Stock options exercised at $.20 per share...         --          --          --          --       1,500           1          --
  Issued preferred stock in December-April at
   $4.47 per share, net of offering costs.....         --          --     349,000       3,490          --          --          --
  Net loss....................................         --          --          --          --          --          --          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
Balance, September 30, 1995...................  2,020,496      20,205     349,000       3,490   2,789,271       2,789          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
  Stock options exercised at $.20-$2.00 per
   share......................................         --          --          --          --       5,175           5          --
  Issued common stock in February 1996 at
   $6.00 per share............................         --          --          --          --      58,333          59          --
  Net loss....................................         --          --          --          --          --          --          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
Balance, June 30, 1996 (Unaudited)............  2,020,496   $  20,205     349,000   $   3,490   2,852,779   $   2,853          --
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
                                                ---------  -----------  ---------  -----------  ---------  -----------  ---------
 
<CAPTION>
 
                                                                            DEFICIT
                                                                          ACCUMULATED
                                                                          DURING THE
                                                              PAID-IN     DEVELOPMENT
                                                  AMOUNT      CAPITAL        STAGE         TOTAL
                                                -----------  ----------  -------------  -----------
<S>                                             <C>          <C>         <C>            <C>
Balance, May 8, 1992 (inception)
  Issued in May 1992 at $.002 per share.......   $      --   $    2,413   $        --   $     4,826
  Issued in May 1992 at $.001 per share.......         250           --            --           250
  Net loss....................................          --           --    (1,062,299)   (1,062,299)
                                                       ---   ----------  -------------  -----------
Balance, September 30, 1992...................         250        2,413    (1,062,299)   (1,057,223)
  Issued in December 1992 and January 1993 at
   $.000 per share under anti-dilution
   provisions.................................          --          (13)           --            --
  Issued in December 1992 and January 1993 at
   $.02 per share.............................          --        4,105            --         4,322
  Repurchased at $.02 per share...............          --       (1,411)           --        (1,485)
  Net loss....................................          --           --    (4,700,539)   (4,700,539)
                                                       ---   ----------  -------------  -----------
Balance, September 30, 1993...................         250        5,094    (5,762,838)   (5,754,925)
  Net loss....................................          --           --    (6,035,725)   (6,035,725)
                                                       ---   ----------  -------------  -----------
Balance, September 30, 1994...................         250        5,094   (11,798,563)  (11,790,650)
                                                       ---   ----------  -------------  -----------
  Issued preferred stock at $6.25 for
   conversion of debt to equity...............          --   12,607,895            --    12,628,100
  Conversion of Class B common to Class A
   common under anti-dilution provisions......        (250)     161,751            --       161,680
  Issued in December 1994 at $.000 per share
   under anti-dilution provisions.............          --      214,960            --       215,000
  Stock options exercised at $.20 per share...          --          299            --           300
  Issued preferred stock in December-April at
   $4.47 per share, net of offering costs.....          --    1,556,641            --     1,560,131
  Net loss....................................          --           --    (2,875,467)   (2,875,467)
                                                       ---   ----------  -------------  -----------
Balance, September 30, 1995...................          --   14,546,640   (14,674,030)     (100,906)
                                                       ---   ----------  -------------  -----------
  Stock options exercised at $.20-$2.00 per
   share......................................          --        1,120            --         1,125
  Issued common stock in February 1996 at
   $6.00 per share............................          --      349,941            --       350,000
  Net loss....................................          --           --    (2,780,297)   (2,780,297)
                                                       ---   ----------  -------------  -----------
Balance, June 30, 1996 (Unaudited)............   $      --   $14,897,701  $(17,454,327) $ 2,530,078
                                                       ---   ----------  -------------  -----------
                                                       ---   ----------  -------------  -----------
</TABLE>
    
 
    The accompanying notes are an integral part of the financial statements.
 
                                      F-5
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                            STATEMENTS OF CASH FLOWS
 
   
<TABLE>
<CAPTION>
                                                                    MAY 8, 1992                             MAY 8, 1992
                                                                     (DATE OF      NINE MONTHS ENDED JUNE     (DATE OF
                                   YEARS ENDED SEPTEMBER 30,       INCEPTION) TO            30,              INCEPTION)
                               ----------------------------------  SEPTEMBER 30,  ------------------------   TO JUNE 30
                                  1993        1994        1995         1995          1995         1996          1996
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
<S>                            <C>         <C>         <C>         <C>            <C>          <C>          <C>
                                                                                  (UNAUDITED)  (UNAUDITED)  (UNAUDITED)
Cash flows from operating
 activities:
  Net loss...................  $(4,700,539) $(6,035,725) $(2,875,467)  $(14,674,030) ($1,844,771) ($2,780,297) ($17,454,327)
  Adjustments to reconcile
   net loss to net cash used
   in operating activities:
    Depreciation and
     amortization............     193,539     289,340     262,263       749,668      199,508      216,790       966,458
    Gain on sale of
     equipment...............          --          --          --            --           --      (30,729)      (30,729)
    Noncash expense for anti-
     dilution stock
     issuances...............          --          --     376,680       376,680           --           --       376,680
    Changes in operating
     assets and liabilities:
      Notes receivable
       officers, net.........      16,408     (66,146)    (16,638)     (218,734)     (76,448)     146,512       (72,222)
      Accounts receivable....          --          --    (193,898)     (193,898)     (64,633)       6,134      (187,764)
      Accounts receivable --
       parent................          --          --    (131,600)     (131,600)          --      131,600            --
      Prepaid expenses and
       other current
       assets................      (8,526)      7,000     (19,618)      (22,618)     (33,283)    (601,692)     (624,310)
      Accounts payable.......    (177,065)     59,847      59,490       232,656      (97,242)     164,770       397,426
      Accrued expenses.......     279,992     274,529     664,324     1,343,718      910,832     (464,130)      879,588
      Accrued interest --
       parent................     245,391     603,581     261,350     1,132,935      269,175       29,223     1,162,158
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
    Cash used in operating
     activities..............  (4,150,800) (4,867,574) (1,613,114)  (11,405,223)    (736,862)  (3,181,819)  (14,587,042)
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
Cash flows from investing
 activities:
  Purchase of property and
   equipment.................    (571,419)   (294,623)   (154,814)   (1,404,150)    (140,293)     (19,599)   (1,423,749)
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
    Cash used in investing
     activities..............    (571,419)   (294,623)   (154,814)   (1,404,150)    (140,293)     (19,599)   (1,423,749)
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
Cash flows from financing
 activities:
  Proceeds from note payable
   -- parent.................   4,695,371   4,570,771   1,041,972    11,495,165    1,034,147    1,769,387    13,264,552
  Proceeds from convertible
   debenture -- parent.......          --          --     436,740       436,740      407,068           --       436,740
  Proceeds from issuance of
   stock, net................       2,837          --   1,560,431     1,568,344    1,523,980      351,125     1,919,469
  Proceeds from sale
   leaseback.................          --     662,602      87,771       750,373       87,771      117,325       867,698
  Principal payments on
   capital lease
   obligation................          --     (72,719)   (194,787)     (267,506)    (133,229)    (182,142)     (449,648)
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
    Cash provided by
     financing activities....   4,698,208   5,160,654   2,932,127    13,983,116    2,919,737    2,055,695    16,038,811
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
    Net (decrease) increase
     in cash and cash
     equivalents.............     (24,011)     (1,543)  1,164,199     1,173,743    2,042,582   (1,145,723)       28,020
Cash and cash equivalents,
 beginning of period.........      35,098      11,087       9,544            --        9,544    1,173,743            --
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
    Cash and cash
     equivalents, end of
     period..................  $   11,087  $    9,544  $1,173,743   $ 1,173,743    $2,052,126   $  28,020    $   28,020
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
                               ----------  ----------  ----------  -------------  -----------  -----------  ------------
 
Supplemental disclosure of
 cash flow information:
  Cash paid for interest,
   net.......................  $       --  $   22,937  $   84,265   $   107,202
                               ----------  ----------  ----------  -------------
                               ----------  ----------  ----------  -------------
Supplemental schedule of
 noncash investing and
 financing activities:
</TABLE>
    
 
      In  1995, the  parent company  converted debt  of $11,495,165  and accrued
      interest of $1,132,935 into 2,020,496  shares of Series A preferred  stock
      (see Note 11).
 
    The accompanying notes are an integral part of the financial statements.
 
                                      F-6
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
1.  ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES:
 
    A.   ORGANIZATION:  Progenitor, Inc.  (the Company), a Delaware Corporation,
is a functional genomics company engaged in the discovery, characterization  and
validation  of novel genes, receptors and  related proteins as therapeutic leads
and targets for the treatment of major diseases.
 
    B.  BASIS OF PRESENTATION:  The accompanying financial statements have  been
prepared  on a going-concern basis, which contemplates the realization of assets
and the  satisfaction of  liabilities  in the  normal  course of  business.  The
financial   statements  do   not  include   any  adjustments   relating  to  the
recoverability and classification of recorded  asset amounts or the amounts  and
classification  of liabilities  that might  be necessary  should the  Company be
unable to continue as a going concern.
 
    During the  year ended  September 30,  1995, the  Company arranged  for  the
financing of its operating activities by borrowing approximately $1,458,000 from
its  parent  company,  Interneuron  Pharmaceuticals,  Inc.  ("Interneuron"),  by
obtaining a $2,500,000 licensing fee from Chiron Corporation ("Chiron"), and  by
raising  approximately $1,560,000 from a private placement offering. Significant
additional research and development activities, clinical testing, and regulatory
approvals must be completed before commercial sales, if any, will commence.  The
Company  is actively  pursuing research  and development  grants and negotiating
equity  and  corporate  partnership  arrangements  to  fund  its  research   and
development activities.
 
    C.     PROPERTY  AND   EQUIPMENT:    Depreciation   is  computed  using  the
straight-line method over the estimated useful lives of the depreciable  assets.
Equipment  leased  under capital  leases  is amortized  using  the straight-line
method over  the  lease term.  Leasehold  improvements are  amortized  over  the
estimated  useful life  of the  asset or  lease term,  whichever is  the shorter
period. Maintenance  and  repairs are  charged  to expense  as  incurred,  while
renewals  and  improvements  are capitalized.  Equipment  includes  $707,972 and
$795,743 of  equipment  under  capital lease  and  accumulated  amortization  of
$83,924 and $298,741 as of September 30, 1994 and 1995, respectively.
 
    D.   REVENUE  RECOGNITION:  The  Company recognizes  revenue under strategic
alliances as certain  agreed upon milestones  are achieved or  license fees  are
earned.
 
    E.   RESEARCH  AND DEVELOPMENT  COSTS:   All costs  related to  research and
development are expensed as incurred.
 
    F.  CASH AND CASH EQUIVALENTS:  For purposes of the statement of cash flows,
cash and  cash  equivalents  consist  of  cash  in  banks,  highly  liquid  debt
instruments  and money market funds with  original maturities of three months or
less.
 
    G.   INTERIM  FINANCIAL  STATEMENTS  (UNAUDITED):    The  interim  financial
statements   reflect  all  adjustments,  consisting  only  of  normal  recurring
accruals, which are, in the opinion of the Company's management, necessary for a
fair presentation of the  financial position and results  of operations for  the
periods  presented.  Revenues  and  expenses  for  any  interim  period  are not
necessarily indicative of results for a full year.
 
   
    H.  PRO  FORMA PRESENTATION (UNAUDITED):   The pro  forma unaudited  balance
sheet  as  of  June  30,  1996 reflects  (a)  the  automatic  conversion  of all
outstanding shares of Preferred Stock into  an aggregate of 1,774,014 shares  of
Common  Stock, (b)  the conversion of  the convertible  debenture and promissory
note held by Interneuron into an aggregate of 186,279 shares of Common Stock and
(c) the purchase by  the Ohio University Foundation  of 25,000 shares of  Common
Stock  at a price  of $6.00 per share  pursuant to a  stock purchase right. Such
conversions will occur upon the closing of the Company's proposed initial public
offering ("IPO") of common stock.
    
 
                                      F-7
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
1.  ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES: (CONTINUED)
   
    I.  PRO FORMA  NET INCOME PER  SHARE (UNAUDITED):   Pro forma unaudited  net
income  per share is  computed using the  weighted-average number of outstanding
shares of common stock and common stock equivalents, assuming conversion of  all
outstanding  Preferred Stock, the convertible debenture and promissory note held
by Interneuron into common stock (as of their original date of issuance),  which
will  occur  upon  completion  of  the  Company's  proposed  IPO.  Common  stock
equivalents  are   excluded  from   the  computation   when  their   effect   is
anti-dilutive;  however,  pursuant to  the  requirements of  the  Securities and
Exchange Commission ("SEC"),  common stock equivalent  shares relating to  stock
options  and warrants (using the treasury stock  method and an assumed IPO price
of $12.00 per  share) issued  during the 12-month  period prior  to the  initial
filing  of IPO are  included for all  periods presented whether  or not they are
anti-dilutive. Historical earnings  per share  have not  been presented  because
such  amounts are not meaningful due to  the significant change in the Company's
capital structure that will occur in connection with the Company's proposed IPO.
    
 
    J.   RECLASSIFICATIONS:   Certain reclassifications  have been  made to  the
prior year's financial statements to conform to the current-year presentation.
 
    K.  USE OF ESTIMATES:  The preparation of financial statements in conformity
with  generally  accepted  accounting  principles  requires  management  to make
estimates and  assumptions  that  affect  the reported  amounts  of  assets  and
liabilities  and disclosure of contingent assets  and liabilities at the date of
the financial  statements and  the  reported amounts  of revenues  and  expenses
during the reporting period. Actual results could differ from those estimates.
 
    L.    STOCK  SPLIT:   In  May  1996,  the Board  of  Directors  authorized a
one-for-two reverse stock split on Class A common shares effective prior to  the
effective  date of the  proposed IPO. All  references to Class  A common shares,
underlying stock options and warrants and  per share data have been restated  to
reflect the reverse stock split.
 
2.  ACCRUED EXPENSES:
    Accrued expenses consist of the following:
 
<TABLE>
<CAPTION>
                                                                         1994         1995
                                                                      ----------  ------------
<S>                                                                   <C>         <C>
Sponsored research..................................................  $  494,855  $    438,794
Chiron..............................................................          --       701,296
Other...............................................................     184,539       203,628
                                                                      ----------  ------------
                                                                      $  679,394  $  1,343,718
                                                                      ----------  ------------
                                                                      ----------  ------------
</TABLE>
 
3.  INCOME TAXES:
    No  income tax provision or benefit has been provided for federal income tax
purposes as the Company has incurred losses since inception. As of September 30,
1995, net  deferred tax  assets totaled  approximately $5,688,000  on total  net
operating  loss carryforwards  of approximately  $13,050,000 and  tax credits of
approximately $468,000 that  expire on various  dates through 2009.  Due to  the
uncertainty  surrounding the  realization of  these favorable  tax attributes in
future tax returns, all of the net deferred tax assets have been fully offset by
a valuation allowance.
 
4.  STOCK OPTIONS AND WARRANTS:
 
    A.  STOCK OPTIONS:  Under the  Company's Stock Option Plan adopted in  1992,
incentive  stock  options and  nonqualified stock  options  may be  granted. The
number of Class A common shares
 
                                      F-8
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
4.  STOCK OPTIONS AND WARRANTS: (CONTINUED)
authorized and reserved for  issuance is 500,000.  The outstanding options  vest
over  a period of three to four years. As of September 30, 1994 and 1995, 32,356
and 81,695  stock options  were exercisable,  respectively. Options  granted  to
stockholders with 10% or greater ownership expire after five years.
 
    Stock option activity is summarized below:
 
<TABLE>
<CAPTION>
                                                                       NUMBER OF     OPTION
                                                                        SHARES        PRICE
                                                                      -----------  -----------
<S>                                                                   <C>          <C>
Outstanding at September 30, 1992...................................          --            --
  Granted...........................................................     104,700   $ 0.20-4.00
  Forfeited.........................................................         250          0.20
                                                                      -----------
Outstanding at September 30, 1993...................................     104,450     0.20-4.00
  Granted...........................................................      75,875          4.00
  Forfeited.........................................................       1,700     0.20-4.00
                                                                      -----------
Outstanding at September 30, 1994...................................     178,625     0.20-4.00
  Granted...........................................................     192,250     4.00-6.00
  Forfeited.........................................................      20,472     0.20-4.00
  Exercised.........................................................       1,500          0.20
                                                                      -----------
Outstanding at September 30, 1995...................................     348,903     0.20-6.00
                                                                      -----------
                                                                      -----------
</TABLE>
 
    In  September  1995, the  Company issued  112,500  stock options  to certain
executives. These options  vest in  September 2002. An  additional 12,500  stock
options were issued that vest upon the achievement of certain milestones.
 
    The  Company issued 43,250 stock options to certain employees at an exercise
price of $6.00 per share. In May  1996, the Company amended the terms of  80,000
stock  options by changing  the vesting period  to three years  and 12,500 stock
options by changing the vesting period to four years.
 
    In December 1995,  the Financial  Accounting Standards  Board (FASB)  issued
Statement  of Financial  Accounting Standards  ("SFAS") No.  123, ACCOUNTING FOR
STOCK-BASED  COMPENSATION,  which  changes  the  measurement,  recognition   and
disclosure  standards for stock-based  compensation. The Company  will adopt the
disclosure requirements of SFAS No. 123 in  fiscal year 1997, but will elect  to
continue to measure compensation cost following present accounting rules.
 
   
    In May 1996, the Company adopted the 1996 Stock Incentive Plan (the "Plan").
The  number of common  shares authorized and available  for issuance is 850,000.
Under the  Plan,  incentive stock  options,  nonqualified stock  options,  stock
appreciation  rights and stock grants may be granted. In May 1996, 275,000 stock
options were granted to officers  of the Company at  an exercise price of  $9.00
per share.
    
 
    B.    WARRANTS:   In  June  1995, the  Company  issued to  designees  of the
Placement Agent,  which is  an  affiliate of  the  parent company,  warrants  to
purchase  a total of 34,901 shares of  Series B convertible preferred stock. The
warrants  were  issued  in  conjunction  with  the  private  placement  offering
discussed  in Note  10. The warrants  are exercisable  at a price  of $6.875 per
share and  expire on  the  earlier of  (i) five  years  from an  initial  public
offering  of the Company's common stock, or (ii) June 30, 2005. The Company paid
the Placement Agent approximately $129,000 as its share of placement agent fees.
 
5.  COMMITMENTS:
    The Company  has  entered  into  various  operating  leases  for  furniture,
fixtures, and equipment which expire through the year 1998.
 
                                      F-9
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
5.  COMMITMENTS: (CONTINUED)
    In  April 1994, the  Company entered into a  sale-lease back equipment lease
financing agreement with  a leasing company  providing for funding  of up to  an
aggregate of $2,200,000 for equipment purchased prior to June 30, 1995. The book
value  of the assets leased under this arrangement totaled $795,743, and the net
asset value of the equipment totaled  $750,373. During the year ended  September
30,  1994, the  Company recorded  and deferred  a loss  on the  leased assets of
$45,370, which it is amortizing over the  life of the lease. The lease is  being
treated as a capital lease and is guaranteed by Interneuron.
 
    In  November 1994, the Company entered  into a one-year lease for laboratory
and administrative space that expires in  December 1995. The lease provides  for
monthly  rental payments of approximately $10,900.  The Company has extended the
lease through 1996. The Company has the  option to extend the lease on a  yearly
basis  for 1997.  The minimum rental  commitments under these  agreements are as
follows:
 
<TABLE>
<CAPTION>
                                                                     OPERATING   CAPITAL LEASE
YEARS ENDING SEPTEMBER 30,                                             LEASES     OBLIGATION
- -------------------------------------------------------------------  ----------  -------------
<S>                                                                  <C>         <C>
1996...............................................................  $  174,679   $   258,699
1997...............................................................      16,138       258,699
1998...............................................................      11,783        29,466
1999...............................................................      10,331            --
2000...............................................................       3,444            --
                                                                     ----------  -------------
Total lease payments...............................................  $  216,375       546,864
                                                                     ----------
                                                                     ----------
Less amount representing interest..................................                   (63,997)
                                                                                 -------------
Present value of future lease payments.............................                   482,867
Less current portion...............................................                  (214,485)
                                                                                 -------------
Noncurrent portion of capital lease obligation.....................               $   268,382
                                                                                 -------------
                                                                                 -------------
</TABLE>
 
    Rent expense approximated  $97,000, $140,000 and  $186,000 during the  years
ended  September 30,  1993, 1994  and 1995,  respectively, and  $514,000 for the
period May 8, 1992 (date of inception) through September 30, 1995.
 
6.  RELATED-PARTY TRANSACTIONS:
    Under employment agreements  with certain executives,  the Company  advanced
loans  to assist in purchasing  new homes. As of  September 30, 1995, there were
loans to three executives for a total of $359,744. The first loan of $100,796 is
interest-free,  with  $60,796  due  upon  the  earlier  of  April  1997  or  the
termination of the officer's employment. The remaining balance is to be forgiven
upon  the achievement of specified milestones. The second loan of $182,500 bears
interest at 7% per annum, with $142,500 due upon the earlier of the sale of  the
officer's  existing home, June 1997, or termination of the officer's employment.
The remaining  balance is  to  be forgiven  upon  the achievement  of  specified
milestones.  During 1995, loans totaling $76,448 were made to a third executive,
$21,448 of  which  is non-interest-bearing  and  was  repaid in  May  1996.  The
remaining loans bear interest at 9% per annum, with $15,000 due upon the earlier
of  March 1999, or the  termination of the officer's  employment. The balance of
$40,000 is to be forgiven upon the achievement of specified milestones.
 
    The Company has recorded $81,200 and  $141,010 as of September 30, 1994  and
1995,  respectively,  as  a  note  receivable  reserve  in  anticipation  of the
potential forgiveness of certain loan amounts.
 
                                      F-10
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
7.  CONSULTING AGREEMENTS:
    The Company has entered into various consulting agreements which range  from
one  to three  years and  are subject  to renewals,  whereby outside consultants
provide scientific advice and administrative  services to the Company.  Payments
to  consultants made during 1993, 1994 and 1995, totaled approximately $203,500,
$309,000 and $243,000,  respectively, and $914,000  for the period  May 8,  1992
(date  of inception) through September 30, 1995. Of these amounts, approximately
$181,000, $190,000 and $177,400 represented payments to certain stockholders  in
1993, 1994 and 1995, respectively, and $707,400 for the period May 8, 1992 (date
of inception) through September 30, 1995.
 
8.  LICENSE AND RESEARCH AGREEMENTS:
    The  Company  entered  into a  license  agreement and  a  sponsored research
agreement with Ohio  University in  January 1992,  certain terms  of which  were
amended  in October 1993. The license agreement grants the Company the exclusive
worldwide license to patent and other rights to yolk sac stem cells and  related
technologies  in exchange for  royalties based on  sales. The research agreement
requires the Company to  fund specified minimum levels  of research and  related
expenses, as well as any additional costs approved in advance by the Company.
 
    In  addition,  the Company  agreed to  issue 5%  of its  equity to  The Ohio
University Foundation and agreed to preserve this percentage ownership  position
until  the parent company's  total investment in  the Company is  at least $10.0
million or the date of an IPO  by the Company. The $10.0 million investment  was
achieved  during 1995, thus the percentage ownership position no longer needs to
be preserved. Until an  initial public offering of  the Company is  consummated,
The Ohio University Foundation was entitled to increase its interest to 6.25% by
purchasing  additional equity at a  price equal to 50%  of the offering price of
common stock in any such initial public offering. This provision was canceled in
February 1996, at which time The Ohio University Foundation entered into a stock
purchase agreement  with  the Company  pursuant  to which  The  Ohio  University
Foundation  purchased  58,333 shares  of common  stock  for $350,000  ($6.00 per
share). If the IPO price is less  than $12.00 per share, additional shares  will
be  issued until The Ohio University Foundation has paid a maximum of 50% of the
IPO price.  Additionally,  a  stock  purchase  right  was  issued  to  The  Ohio
University  Foundation to purchase 25,000  shares of the common  stock at 50% of
the IPO price.
 
    The license  agreement also  contains certain  requirements related  to  the
management  and  operation  of  the Company,  including  the  nomination  of two
designees of The  Ohio University Foundation  to the Board  of Directors of  the
Company.  The Castle  Group, Ltd.  ("Castle"), which  is controlled  by a former
director of  the  Company  and  a  principal  stockholder  of  Interneuron,  has
unconditionally  guaranteed to Ohio University  the performance of the Company's
obligations under the license  agreement until the earlier  of five years or  an
initial  public offering by the Company.  Certain employees of Castle own common
stock of the Company.
 
    In April 1993,  the Company entered  into a second  license agreement and  a
sponsored  research agreement with Ohio University pursuant to which the Company
agreed to fund research relating to the T7T7 gene delivery system, developing an
active cell membrane transport system. The license agreement grants the  Company
the exclusive worldwide license to all patent and other rights derived from this
and related technologies in exchange for royalties based on sales.
 
    In  February 1994, the Company entered  into a license agreement with Albert
Einstein College  of Medicine  of Yeshiva  University ("AECOM").  The  agreement
grants  the  Company the  exclusive worldwide  license to  all patent  and other
rights from  research done  on retroviral  vectors by  AECOM in  exchange for  a
license fee and royalties based on sales.
 
                                      F-11
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
8.  LICENSE AND RESEARCH AGREEMENTS: (CONTINUED)
    In  September  1994,  the  Company entered  into  a  license  agreement with
Wisconsin Alumni Research Foundation ("WARF"). The agreement grants the  Company
a  nonexclusive license to certain  patents developed by WARF  in exchange for a
license fee, maintenance fees, and royalties based on sales.
 
    In November  1994, the  Company  was awarded  a  competitive grant  of  $2.0
million  through the Advanced Technology Program  ("ATP") of the U.S. Department
of Commerce. The funds will be received over a three-year period commencing June
1, 1995.
 
    In March  1995,  the  Company  entered  into  a  license  and  collaboration
agreement  with Chiron. As required by the agreement, an initial cash payment of
$2.5 million was paid by  Chiron to the Company in  April 1995. The Company  has
committed  to reimburse Chiron the start-up manufacturing costs incurred related
to this agreement up to $750,000. Chiron paid $500,000 to the Company in January
1996, for  continued  research funding.  The  agreement also  calls  for  future
payments contingent upon the achievement of certain milestones.
 
    In  May  1995, the  Company entered  into a  sponsored research  and license
agreement with  Novo Nordisk,  through its  subsidiary, ZymoGenetics,  Inc.  The
agreement  calls  for research  and  license fees  to  be paid  to  the Company,
contingent upon certain conditions and the meeting of certain milestones.
 
   
    Additionally, the  Company  has  entered  into  various  sponsored  research
agreements  with varying terms  up to two  years in length.  The total sponsored
research expense  was  $882,217,  $890,000  and $601,103  for  the  years  ended
September  30, 1993, 1994 and 1995,  respectively, and $2,690,680 for the period
from May 8,  1992 (date of  inception) through September  30, 1995. Payments  to
Ohio  University for sponsored research totaled $485,480, $245,888 and $398,064,
for the  years  ended September  30,  1993,  1994 and  1995,  respectively,  and
$1,281,132  for the period May 8, 1992 (date of inception) through September 30,
1995. Amounts owed to Ohio University  for sponsored research were $424,401  and
$215,600 at September 30, 1994 and 1995, respectively. In addition, at September
30,  1995, the Company had commitments  to fund additional sponsored research of
approximately $824,000, including a commitment of $52,390 to Ohio University.
    
 
9.  COMMON STOCK:
    The Company is authorized  to issue two classes  of shares of common  stock,
designated Class A and Class B. Shares of the Company's Class B common stock are
convertible,  at any time  at the option of  the holder, into  shares of Class A
common stock. The  conversion ratio is  subject to adjustment  based on  several
factors, including the issuance of additional Class A shares.
 
    Holders  of Class B  shares are entitled to  pro rata dividend, liquidation,
and voting rights based on the number of Class A shares into which such Class  B
shares  are convertible. Class  B shares are automatically  converted to Class A
shares upon the receipt by the Company of capital contributions of $10.0 million
in aggregate amount from  the date of incorporation.  When this was achieved  in
1995,  all Class B shares were converted into  a total of 357,500 Class A common
shares.
 
10. PREFERRED STOCK:
    In  December  1994,   the  Company's   Board  of   Directors  approved   the
authorization  of 2,120,000 shares  of Series A  and 880,000 shares  of Series B
preferred stock. These preferred shares are  convertible into shares of Class  A
common  stock and have preferential rights in terms of dividends and liquidation
over common stock.  Shares of preferred  stock have voting  rights equal to  the
number of shares of their common stock equivalent.
 
                                      F-12
<PAGE>
                                PROGENITOR, INC.
                         (A DEVELOPMENT STAGE COMPANY)
                       NOTES TO THE FINANCIAL STATEMENTS
 
10. PREFERRED STOCK: (CONTINUED)
    Shares  of Series  A preferred  stock are  convertible, at  any time  at the
option of  the  holder,  into  shares  of Class  A  common  stock.  The  initial
conversion  ratio is based on  a Series A price  of $6.25, subject to adjustment
based on several factors. Series A preferred shares are automatically  converted
upon a qualified public offering.
 
    Through  July 7,  1995, the  Company has issued  349,000 shares  of Series B
preferred stock in connection with private placements. The private placement was
a sale  of units,  each unit  consisting of  shares of  preferred stock  of  the
Company,  shares  of  preferred  stock  of  another  subsidiary  of Interneuron,
Transcell Technologies, Inc., and a  put protection right from Interneuron.  The
put protection right provides that on the third anniversary of the final closing
date  of the private placement, the owner has the right to sell to Interneuron a
percentage of the preferred stock of the Company that is deemed to be  illiquid,
as  defined in the agreement. The Company received approximately $1,560,000, net
of offering costs,  as its  share of the  proceeds from  the private  placement.
Shares of Series B preferred stock are convertible, at any time at the option of
the holder, into shares of Class A common stock. The initial conversion ratio is
based  on a  Series B  price of  $6.25, subject  to adjustment  based on several
factors. Series B preferred shares are automatically converted upon a  qualified
public offering.
 
    Shares of authorized common stock have been reserved for the exercise of all
convertible preferred stock outstanding.
 
11. NOTE PAYABLE TO THE PARENT COMPANY:
   
    The note payable to the parent company, Interneuron, bore interest at a rate
of  1% over the prime lending rate (7  3/4% prime plus 1% at September 30, 1994)
and was payable on demand. Periodic advances were made available under this note
at the discretion of  Interneuron. In January 1995,  the outstanding balance  on
the Note Payable -- parent of $11,495,165 and accrued interest of $1,132,935 was
converted into 2,020,496 shares of Series A preferred stock.
    
 
    In  March 1996, the Company  entered into a promissory  note with the parent
company, bearing interest at a rate of 1% over the prime lending rate. The  note
is  due on the  earlier of March  31, 2001 or  the closing of  an initial public
offering.
 
    Since the inception of the Company, Interneuron has paid for certain Company
expenses which were reimbursed by the Company at cost.
 
12. CONVERTIBLE DEBENTURE-PARENT:
    In March 1995, the  Company entered into  a convertible debenture  agreement
with  IPI, at a rate of  1% over the prime lending  rate. The prime lending rate
was 8.75%  as of  September 30,  1995. Principal  and interest  are due  at  the
earlier  of five years  from the final  closing date or  upon a qualified public
offering as defined in the agreement. The debenture is convertible, at any  time
at the option of the holder, into shares of Class A common stock. The conversion
price  is equal to the fair market value of  the common stock at the time of the
conversion. The debenture  is automatically  converted upon  a qualified  public
offering.
 
13. EMPLOYEE BENEFITS:
    Employees  of the  Company are  eligible to  participate in  the Interneuron
Pharmaceuticals, Inc.  401(k) Savings  Plan under  which employees  may defer  a
portion  of  their  annual  compensation. Company  contributions  to  the 401(k)
Savings Plan may be made on a discretionary basis. As of September 30, 1995,  no
Company contributions have been made.
 
                                      F-13
<PAGE>
[Two  color photographs showing the following: 1. The location of the human B219
leptin receptor gene  on human  chromosome lp32; and  2. Staining  of the  Del-1
protein  in the endothelial cells  of blood vessels in a  human tumor grown in a
mouse.]
<PAGE>
- --------------------------------------------
                                    --------------------------------------------
- --------------------------------------------
                                    --------------------------------------------
 
    NO  DEALER,  SALES  REPRESENTATIVE  OR ANY  OTHER  PERSON  IS  AUTHORIZED IN
CONNECTION WITH ANY OFFERING MADE HEREBY TO GIVE ANY INFORMATION OR TO MAKE  ANY
REPRESENTATION  NOT CONTAINED HEREIN AND, IF  GIVEN OR MADE, SUCH INFORMATION OR
REPRESENTATION MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED BY THE  COMPANY
OR  THE UNDERWRITERS. THIS PROSPECTUS DOES NOT  CONSTITUTE AN OFFER TO SELL OR A
SOLICITATION OF AN OFFER TO BUY ANY SECURITY OTHER THAN THE COMMON STOCK OFFERED
HEREBY, NOR DOES IT CONSTITUTE AN OFFER TO SELL OR A SOLICITATION OF AN OFFER TO
BUY ANY OF THE COMMON STOCK OFFERED HEREBY TO ANY PERSON IN ANY JURISDICTION  IN
WHICH IT IS UNLAWFUL TO MAKE SUCH AN OFFER OR SOLICITATION. NEITHER THE DELIVERY
OF  THIS PROSPECTUS  NOR ANY SALE  MADE HEREUNDER SHALL  UNDER ANY CIRCUMSTANCES
CREATE ANY IMPLICATION  THAT THERE  HAS BEEN  NO CHANGE  IN THE  AFFAIRS OF  THE
COMPANY  SINCE  THE DATE  HEREOF  OR THAT  THE  INFORMATION CONTAINED  HEREIN IS
CORRECT AS OF ANY DATE SUBSEQUENT TO THE DATE HEREOF.
 
                            ------------------------
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                     PAGE
                                                   ---------
<S>                                                <C>
Prospectus Summary...............................          3
Risk Factors.....................................          5
Use of Proceeds..................................         17
Dividend Policy..................................         17
Capitalization...................................         18
Dilution.........................................         19
Selected Financial Data..........................         20
Management's Discussion and Analysis of Financial
  Condition and Results of Operations............         21
Business.........................................         24
Management.......................................         40
Certain Transactions.............................         48
Principal Stockholders...........................         53
Description of Capital Stock.....................         54
Shares Eligible for Future Sale..................         58
Underwriting.....................................         60
Legal Matters....................................         61
Experts..........................................         61
Additional Information...........................         62
Index to Financial Statements....................        F-1
</TABLE>
 
                            ------------------------
 
    UNTIL               , 1996 (25 DAYS AFTER THE DATE OF THIS PROSPECTUS),  ALL
DEALERS EFFECTING TRANSACTIONS IN THE COMMON STOCK, WHETHER OR NOT PARTICIPATING
IN  THIS  DISTRIBUTION, MAY  BE REQUIRED  TO  DELIVER A  PROSPECTUS. THIS  IS IN
ADDITION TO THE  OBLIGATION OF DEALERS  TO DELIVER A  PROSPECTUS WHEN ACTING  AS
UNDERWRITERS AND WITH RESPECT TO THEIR UNSOLD ALLOTMENTS OR SUBSCRIPTIONS.
 
                                2,500,000 SHARES
                                     [LOGO]
                                  COMMON STOCK
 
                              -------------------
 
                                   PROSPECTUS
 
                              -------------------
 
                     Vector Securities International, Inc.
 
                                 Tucker Anthony
                                  Incorporated
 
                             Genesis Merchant Group
                                    Securities
 
                                           , 1996
 
- --------------------------------------------
                                    --------------------------------------------
- --------------------------------------------
                                    --------------------------------------------
<PAGE>
                                    PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 13.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION
 
    The  following  table  sets  forth  all  expenses,  other  than underwriting
discounts and commissions, payable by the Registrant in connection with the sale
of the Common Stock being registered. All the amounts shown are estimates except
for the SEC registration fee, the NASD filing fee and the Nasdaq listing fee.
 
<TABLE>
<S>                                                                 <C>
SEC Registration Fee..............................................  $  12,888
NASD Filing Fee...................................................      4,238
Nasdaq National Market Listing Fee................................     38,971
Printing and engraving expenses...................................      *
Legal fees and expenses...........................................      *
Accounting fees and expenses......................................      *
Blue sky fees and expenses........................................     15,000
Transfer agent and registrar fees.................................      *
Miscellaneous.....................................................      *
                                                                    ---------
    Total.........................................................  $ 850,000
                                                                    ---------
                                                                    ---------
</TABLE>
 
- --------------
*   To be supplied by amendment.
 
ITEM 14.  INDEMNIFICATION OF OFFICERS AND DIRECTORS
 
    Section 145 ("Section 145") of the Delaware General Corporation Law ("DGCL")
provides a detailed statutory framework covering indemnification of officers and
directors against  liabilities and  expenses arising  out of  legal  proceedings
brought  against  them by  reason of  their  being or  having been  directors or
officers. Section  145  generally provides  that  a  director or  officer  of  a
corporation (i) shall be indemnified by the corporation for all expenses of such
legal  proceedings when he is successful on  the merits, (ii) may be indemnified
by the  corporation for  the  expenses, judgments,  fines  and amounts  paid  in
settlement of such proceedings (other than a derivative suit), even if he is not
successful  on  the  merits, if  he  acted in  good  faith  and in  a  manner he
reasonably believed  to be  in  or not  opposed to  the  best interests  of  the
corporation,  and, with  respect to  any criminal  action or  proceeding, had no
reasonable cause  to  believe  his  conduct  was  unlawful,  and  (iii)  may  be
indemnified  by the corporation for the expenses of a derivative suit (a suit by
a stockholder alleging a breach by a director  or officer of a duty owed to  the
corporation),  even if he is  not successful on the merits,  if he acted in good
faith and in a manner he reasonably believed to be in or not opposed to the best
interests of the corporation. No indemnification may be made under clause  (iii)
above,  however, if the director or officer is adjudged liable for negligence or
misconduct in  the  performance of  his  duties  to the  corporation,  unless  a
corporation  determines that, despite such adjudication,  but in view of all the
circumstances, he is entitled to indemnification. The indemnification  described
in  clauses (ii)  and (iii)  above may  be made  only upon  a determination that
indemnification is proper because  the applicable standard  of conduct has  been
met. Such a determination may be made by a majority of a quorum of disinterested
directors,  independent legal counsel, the stockholders  or a court of competent
jurisdiction. The  Company's  Certificate  of Incorporation  provides  that  the
Company  shall indemnify to the  fullest extent permitted by  Section 145, as it
now exists or as amended, all persons whom it may indemnify pursuant thereto.
 
    Section 102(b)(7)  of the  DGCL  permits a  corporation  to provide  in  its
Certificate  of Incorporation  that a director  of the corporation  shall not be
personally liable to the  corporation or its  stockholders for monetary  damages
for  breach of fiduciary  duty as a  director, except for  liability (i) for any
breach of the director's duty of loyalty to the corporation or its stockholders,
(ii) for  acts or  omissions not  in  good faith  or which  involve  intentional
misconduct  or  a knowing  violation  of law,  (iii)  under Section  174  of the
 
                                      II-1
<PAGE>
DGCL, or (iv) for  any transaction from which  the director derived an  improper
personal  benefit. The Company's  Certificate of Incorporation  provides for the
elimination of personal liability of a director for breach of fiduciary duty, as
permitted by Section 102(b)(7) of the DGCL.
 
   
    Section 7  of the  Form  of Underwriting  Agreement,  filed as  Exhibit  1.1
hereto, contains certain provisions relating to indemnification.
    
 
    Prior  to  the  closing  of  the Offering,  the  Company  intends  to obtain
liability insurance  insuring  the  Company's  officers  and  directors  against
liabilities that they may incur in such capacities.
 
   
    The  Company  has entered  into agreements  to  indemnify its  directors and
executive officers, in addition to indemnification provided for in the Company's
charter documents.  These  agreements,  among  other  things,  provide  for  the
indemnification  of the Company's  directors and executive  officers for certain
expenses (including attorneys'  fees), judgments, fines  and settlement  amounts
incurred by any such person in any action or proceeding, including any action by
or  in the  right of  the Company, arising  out of  such person's  services as a
director or executive officer of the  Company, any subsidiary of the Company  or
any  other company or enterprise  to which such person  provides services at the
request of the Company  to the fullest extent  permitted by applicable law.  The
Company believes that these provisions and agreements will assist the Company in
attracting  and retaining qualified persons to  serve as directors and executive
officers.
    
 
    The Investors' Agreements provide for cross-indemnification of  stockholders
of  the  Company  whose  shares  with  registration  rights  are  included  in a
registration under the  Securities Act,  and of  the Company,  its officers  and
directors for certain liabilities arising in connection with such registration.
 
    See also the undertakings set out in response to Item 17 herein.
 
ITEM 15.  RECENT SALES OF UNREGISTERED SECURITIES.
 
    Since  January  1,  1993, the  Company  has  issued and  sold  the following
unregistered securities:
 
    (1) In 1993, the Company (a) sold 82,907 shares of Common Stock to Dr. Given
       for $.02 per share pursuant to the terms of his employment agreement, (b)
       issued 11,400 shares of  Common Stock to  The Ohio University  Foundation
       without  additional consideration pursuant to certain antidilution rights
       contained in a stock purchase agreement with the Company and (c) issued a
       certificate for 14,854 shares of Common  Stock to Dr. Cooper in  exchange
       for  certificates  for  89,121  shares  of  Common  Stock  pursuant  to a
       repurchase of  Common Stock  in connection  with the  termination of  Dr.
       Cooper's employment agreement with the Company.
 
    (2)  In 1994, the Company  (a) issued 178,750 shares  of Common Stock to Dr.
       Thomas Wagner upon the conversion of  the shares of Class B Common  Stock
       held  by Dr. Wagner and  (b) issued 40,353 shares  of Common Stock to The
       Ohio University Foundation without  additional consideration pursuant  to
       certain  antidilution rights contained in a stock purchase agreement with
       the Company.
 
    (3) Between December  1994 and  July 1995, the  Company issued  and sold  an
       aggregate  of  349,000  shares of  Series  B Preferred  Stock  to certain
       persons and  entities  for  $4.48  per share.  In  connection  with  such
       transaction,  the Company  issued warrants  to purchase  22,627 shares of
       Series B Preferred  Stock to  designees of Paramount  Capital, Inc.,  the
       placement  agent for  such transaction,  and warrants  to purchase 12,274
       shares of Series  B Preferred  Stock to designees  of D.H.  Blair &  Co.,
       Inc.,  selected dealer for  such transaction, pursuant  to rights of such
       entities under agreements with the Company.
 
    (4) In December 1994, upon the initial  closing of the issuance and sale  of
       Series  B Preferred Stock  described in paragraph  (3) above, in exchange
       for the cancellation of  an aggregate of  approximately $12.6 million  of
       debt  owed by  the Company  to Interneuron,  the Company  issued and sold
       2,020,496 shares of Series A Preferred Stock to Interneuron for $6.25 per
       share.
 
                                      II-2
<PAGE>
    (5) In 1996, the  Company issued (a)  58,333 shares of  Common Stock to  The
       Ohio  University Foundation pursuant to  a Stock Purchase Agreement dated
       as of February 26, 1996, for $6.00  per share, (b) issued and sold  6,625
       shares  of Common Stock  for $0.20 per share  to certain former employees
       pursuant to the exercise  of stock options granted  under the 1992  Stock
       Option  Plan and (c) issued and sold  50 shares of Common Stock for $2.00
       per share to a former employee pursuant to the exercise of stock  options
       granted under the 1992 Stock Option Plan.
 
    (6)  Since January 1, 1993, the  Company granted stock options to employees,
       consultants,  directors,  officers  and  affiliates  of  the  Company  as
       described  below. From  February 1 to  June 1, 1993,  the Company granted
       stock options under the 1992 Stock  Option Plan covering an aggregate  of
       82,450 shares of Common Stock at an exercise price of $0.20 per share. On
       June  21, 1993,  the Company granted  stock options under  the 1992 Stock
       Option Plan covering an aggregate of 14,250 shares of Common Stock at  an
       exercise  price of  $2.00 per  share. From June  2, 1993  to December 31,
       1994, the Company granted stock options under the 1992 Stock Option  Plan
       covering  an aggregate  of 84,375 shares  of Common Stock  at an exercise
       price of $4.00 per share.  From March 1, 1995  to February 21, 1996,  the
       Company  granted stock options under the  1992 Stock Option Plan covering
       an aggregate of 235,000  shares of Common Stock  at an exercise price  of
       $6.00 per share. On May 13, 1996, the Company granted stock options under
       the  1996 Stock Incentive Plan covering an aggregate of 275,000 shares of
       Common Stock at an exercise price of $9.00 per share.
 
    The sales and  issuances of Common  Stock in the  transactions described  in
paragraphs  (1), (2) and (5) above other  than pursuant to the exercise of stock
options were deemed  to be  exempt from  registration under  the Securities  Act
pursuant to Section 4(2) thereof.
 
    The  issuance and sale of  the Series B Preferred  Stock in the transactions
described in paragraph (3) were deemed to be exempt from registration under  the
Securities  Act pursuant to Section 4(2) of the Securities Act and/or Regulation
D promulgated thereunder.
 
    The issuance of the warrants in the transactions described in paragraph  (3)
was  deemed to be exempt from registration  under the Securities Act pursuant to
Section 4(2) thereof.
 
    The issuance and  sale of the  Series A Preferred  Stock in the  transaction
described  in paragraph (4) were deemed to be exempt from registration under the
Securities Act pursuant to Section 4(2) thereof.
 
    The issuances and sales  of Common Stock pursuant  to the exercise of  stock
options  described in paragraph  (5) were deemed to  be exempt from registration
under the Securities Act by virtue  of Rule 701 promulgated thereunder, or  were
deemed to be exempt pursuant to Section 4(2) thereof.
 
    With  respect  to the  grant of  stock options  described in  paragraph (6),
exemption from registration  under the  Securities Act was  unnecessary in  that
none  of such transactions involved a "sale"  of securities as such term is used
in Section 2(3) of the Securities Act.
 
ITEM 16.  EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.
 
    (A) EXHIBITS.
 
   
<TABLE>
<C>        <S>
      1.1  Form of Underwriting Agreement.
      3.1  Form of Amended and Restated Certificate of Incorporation of the Company.
    **3.2  Amended and Restated Bylaws of the Company.
      4.1  Specimen Stock Certificate of the Company.
      4.2  Reference is made to Exhibits 3.1 and 3.2.
    **5.1  Opinion of Morrison & Foerster LLP.
</TABLE>
    
 
                                      II-3
<PAGE>
   
<TABLE>
<C>        <S>
     10.1  Form of  Indemnification  Agreement entered  into  between the  Company  and  its
           directors and executive officers.
   **10.2  The Company's 1992 Stock Option Plan.
   **10.3  Form of Incentive Stock Option Agreement under the 1992 Stock Option Plan.
   **10.4  Form of Non-Qualified Stock Option Agreement under the 1992 Stock Option Plan.
     10.5  The Company's 1996 Stock Incentive Plan and form of Stock Option Agreement.
   **10.6  Form  of Investors' Rights Agreement, entered into among the Company, Interneuron
           Pharmaceuticals, Inc.,  Transcell  Technologies, Inc.,  and  the holders  of  the
           Company's Preferred Stock, Series B.
 */**10.7  License  Agreement, dated as of  January 28, 1992, by  and between Scimark Corp.,
           The Castle Group Ltd. and Ohio University, as amended October 15, 1993.
 */**10.8  Sponsored Research  Agreement, dated  January 31,  1992, by  and between  Scimark
           Corp.  and  Ohio University,  as  amended October  15,  1993, February  16, 1994,
           November 16, 1994 and November 22, 1995.
 */**10.9  License Agreement, dated as of April 1, 1993, by and between the Company and Ohio
           University.
  **10.11  License Agreement, dated  as of  June 8,  1994, by  and between  the Company  and
           Associated Universities, Inc.
*/**10.12  Standard  License Agreement, dated  as of September  1, 1994, by  and between the
           Company and the Wisconsin Alumni Research Foundation, as amended June 2, 1995.
*/**10.13  License and Collaboration Agreement, dated as  of March 31, 1995, by and  between
           the Company and Chiron Corporation, as amended April 10, 1996.
*/**10.14  Sponsored Research and License Agreement, dated as of May 1, 1995, by and between
           the Company and Novo Nordisk A/S, as amended January 17, 1996 and March 17, 1996.
*/**10.15  License  Agreement, dated  as of July  17, 1995,  by and between  the Company and
           Vanderbilt University.
*/**10.16  License Agreement, dated as of May 30, 1996, by and between the Company and AMRAD
           Developments PTY Ltd.
  **10.17  Lease Agreement, dated as of November 1994, by and between the Company and Thomas
           R. Eggers.
  **10.18  Lease, Service and Affiliation  Agreement, entered into as  of February 1995,  by
           and between the Company and The Ohio State University.
  **10.19  Employment  Agreement,  dated January  3, 1993,  by and  between the  Company and
           Douglass B. Given.
   +10.20  Form of Intercompany Services Agreement, dated as of June  , 1996, by and between
           the Company and Interneuron Pharmaceuticals, Inc.
    10.21  Form of Tax Allocation Agreement,  dated as of June   , 1996, by and between  the
           Company and Interneuron Pharmaceuticals, Inc.
    10.22  The Company's 1996 Employee Stock Purchase Plan.
     23.1  Consent of Coopers & Lybrand L.L.P.
   **23.2  Consent of Pennie & Edmonds.
   **23.3  Consent of Morrison & Foerster LLP (included in Exhibit 5.1).
   **24.1  Power of Attorney.
   **27    Financial Data Schedule.
</TABLE>
    
 
                                      II-4
<PAGE>
- --------------
   
*   Documents for which confidential treatment has been requested.
    
 
**  Exhibit previously filed.
 
    (B) FINANCIAL STATEMENT SCHEDULES.
 
    None.
 
    Schedules  not  listed  above  have  been  omitted  because  the information
required to be set forth therein is not applicable or is shown in the  financial
statements or notes thereto.
 
ITEM 17.  UNDERTAKINGS.
 
    The  undersigned registrant hereby undertakes to provide to the Underwriters
at the closing  specified in  the Underwriting Agreement,  certificates in  such
denominations  and registered in  such names as required  by the Underwriters to
permit prompt delivery to each purchaser.
 
    Insofar as indemnification for liabilities arising under the Securities  Act
may  be  permitted  to  directors,  officers  and  controlling  persons  of  the
registrant pursuant to  the provisions  described in Item  14, the  Underwriting
Agreement,  or otherwise, the registrant has been advised that in the opinion of
the Securities and  Exchange Commission such  indemnification is against  public
policy  as expressed in the Securities  Act and is, therefore, unenforceable. In
the event that a claim for indemnification against such liabilities (other  than
the  payment  by the  registrant of  expenses  incurred or  paid by  a director,
officer or controlling person of the registrant in the successful defense of any
action,  suit,  or  proceeding)  is  asserted  by  such  director,  officer   or
controlling person in connection with the securities being registered hereunder,
the  registrant will, unless in  the opinion of its  counsel the matter has been
settled by controlling precedent, submit to a court of appropriate  jurisdiction
the  question whether  such indemnification  by it  is against  public policy as
expressed in the Securities Act and  will be governed by the final  adjudication
of such issue.
 
    The undersigned registrant undertakes that:
 
        (1)  For purposes of determining any liability under the Securities Act,
    the information omitted  from the form  of prospectus filed  as part of  the
    Registration  Statement in reliance upon Rule 430A and contained in the form
    of prospectus filed by the registrant  pursuant to Rule 424(b)(1) or (4)  or
    497(h)  under  the  Securities  Act  shall  be  deemed  to  be  part  of the
    Registration Statement as of the time it was declared effective.
 
        (2) For the purpose  of determining any  liability under the  Securities
    Act,  each post-effective amendment that contains a form of prospectus shall
    be deemed to  be a  new registration  statement relating  to the  securities
    offered  therein, and the offering of such  securities at that time shall be
    deemed to be in the initial bona fide offering thereof.
 
                                      II-5
<PAGE>
                                   SIGNATURES
 
   
    Pursuant  to the requirements of the  Securities Act of 1933, the Registrant
has duly caused this Amendment to the Registration Statement to be signed on its
behalf by the undersigned, thereunto duly  authorized, in the City of  Columbus,
State of Ohio, on August 16, 1996.
    
 
                                          PROGENITOR, INC.
 
                                          By:        /s/ DOUGLASS B. GIVEN
 
                                             -----------------------------------
                                               Douglass B. Given, M.D., Ph.D.
                                             PRESIDENT, CHIEF EXECUTIVE OFFICER
                                                         AND DIRECTOR
 
    Pursuant   to  the  requirements  of  the   Securities  Act  of  1933,  this
Registration  Statement  has  been  signed  by  the  following  persons  in  the
capacities and on the dates indicated:
 
   
<TABLE>
<CAPTION>
                      SIGNATURE                                         TITLE                         DATE
- ------------------------------------------------------  -------------------------------------  ------------------
 
<C>                                                     <S>                                    <C>
                /s/ DOUGLASS B. GIVEN
     -------------------------------------------        President, Chief Executive Officer      August 16, 1996
            Douglass B. Given, M.D., Ph.D.               and Director
 
                /s/ DAVID B. BITTNER*
     -------------------------------------------        Acting Chief Financial Officer          August 16, 1996
                   David B. Bittner
 
                /s/ ROBERT P. AXLINE*
     -------------------------------------------        Director                                August 16, 1996
                   Robert P. Axline
 
                 /s/ GLENN L. COOPER*
     -------------------------------------------        Director                                August 16, 1996
                 Glenn L. Cooper M.D.
 
             /s/ ALEXANDER M. HAIG, JR.*
     -------------------------------------------        Director                                August 16, 1996
                Alexander M. Haig, Jr.
 
                  /s/ MORRIS LASTER*
     -------------------------------------------        Director                                August 16, 1996
                 Morris Laster, M.D.
 
                /s/ JERRY P. PEPPERS*
     -------------------------------------------        Director                                August 16, 1996
                   Jerry P. Peppers
 
                /s/ DAVID B. SHARROCK*
     -------------------------------------------        Director                                August 16, 1996
                  David B. Sharrock
 
         *By:          /S/ DOUGLASS B. GIVEN
     -------------------------------------------
            Douglass B. Given, M.D., Ph.D.
                   ATTORNEY-IN-FACT
</TABLE>
    
 
                                      II-6
<PAGE>
                                 EXHIBIT INDEX
 
   
<TABLE>
<CAPTION>
 EXHIBIT
   NO.                                                 EXHIBIT                                                PAGE
- ----------  ----------------------------------------------------------------------------------------------  ---------
<C>         <S>                                                                                             <C>
      1.1   Form of Underwriting Agreement................................................................
      3.1   Form of Amended and Restated Certificate of Incorporation of the Company......................
    **3.2   Amended and Restated Bylaws of the Company....................................................
      4.1   Specimen Stock Certificate of the Company.....................................................
      4.2   Reference is made to Exhibits 3.1 and 3.2.....................................................
    **5.1   Opinion of Morrison & Foerster LLP............................................................
     10.1   Form of Indemnification Agreement entered into between the Company and its directors and
            executive officers............................................................................
   **10.2   The Company's 1992 Stock Option Plan..........................................................
   **10.3   Form of Incentive Stock Option Agreement under the 1992 Stock Option Plan.....................
   **10.4   Form of Non-Qualified Stock Option Agreement under the 1992 Stock Option
            Plan..........................................................................................
     10.5   The Company's 1996 Stock Incentive Plan and form of Stock Option Agreement....................
   **10.6   Form of Investors' Rights Agreement, entered into among the Company, Interneuron
            Pharmaceuticals, Inc., Transcell Technologies, Inc., and the holders of the Company's
            Preferred Stock, Series B.....................................................................
 */**10.7   License Agreement, dated as of January 28, 1992, by and between Scimark Corp., The Castle
            Group Ltd. and Ohio University, as amended October 15, 1993...................................
 */**10.8   Sponsored Research Agreement, dated January 31, 1992, by and between Scimark Corp. and Ohio
            University, as amended October 15, 1993, February 16, 1994, November 16, 1994 and November 22,
            1995..........................................................................................
 */**10.9   License Agreement, dated as of April 1, 1993, by and between the Company and Ohio
            University....................................................................................
   **10.11  License Agreement, dated as of June 8, 1994, by and between the Company and Associated
            Universities, Inc.............................................................................
 */**10.12  Standard License Agreement, dated as of September 1, 1994, by and between the Company and the
            Wisconsin Alumni Research Foundation, as amended June 2, 1995.................................
 */**10.13  License and Collaboration Agreement, dated as of March 31, 1995, by and between the Company
            and Chiron Corporation, as amended April 10, 1996.............................................
 */**10.14  Sponsored Research and License Agreement, dated as of May 1, 1995, by and between the Company
            and Novo Nordisk A/S, as amended January 17, 1996 and March 17, 1996..........................
 */**10.15  License Agreement, dated as of July 17, 1995, by and between the Company and Vanderbilt
            University....................................................................................
 */**10.16  License Agreement, dated as of May 30, 1996, by and between the Company and AMRAD Developments
            PTY Ltd.......................................................................................
   **10.17  Lease Agreement, dated as of November 1994, by and between the Company and Thomas R.
            Eggers........................................................................................
   **10.18  Lease, Service and Affiliation Agreement, entered into as of February 1995, by and between the
            Company and The Ohio State University.........................................................
   **10.19  Employment Agreement, dated January 3, 1993, by and between the Company and Douglass B.
            Given.........................................................................................
</TABLE>
    
<PAGE>
   
<TABLE>
<CAPTION>
 EXHIBIT
   NO.                                                 EXHIBIT                                                PAGE
- ----------  ----------------------------------------------------------------------------------------------  ---------
     10.20  Form of Intercompany Services Agreement, dated as of June  , 1996, by and between the Company
            and Interneuron Pharmaceuticals, Inc..........................................................
<C>         <S>                                                                                             <C>
     10.21  Form of Tax Allocation Agreement, dated as of June  , 1996, by and between the Company and
            Interneuron Pharmaceuticals, Inc..............................................................
     10.22  The Company's 1996 Employee Stock Purchase Plan...............................................
     23.1   Consent of Coopers & Lybrand L.L.P............................................................
   **23.2   Consent of Pennie & Edmonds...................................................................
   **23.3   Consent of Morrison & Foerster LLP (included in Exhibit 5.1)..................................
   **24.1   Power of Attorney.............................................................................
   **27     Financial Data Schedule.......................................................................
</TABLE>
    
 
- --------------
   
*   Documents for which confidential treatment has been requested.
    
 
**  Exhibit previously filed.


<PAGE>


                                   2,500,000 Shares

                                   PROGENITOR, INC.

                                     Common Stock


                            FORM OF UNDERWRITING AGREEMENT


                                                                 August __, 1996


VECTOR SECURITIES INTERNATIONAL, INC.
TUCKER ANTHONY INCORPORATED
GENESIS MERCHANT GROUP SECURITIES

     As Representatives of the Several Underwriters

c/o  VECTOR SECURITIES INTERNATIONAL, INC.
     1751 Lake Cook Road, Suite 350
     Deerfield, Illinois  60015

Ladies and Gentlemen:

         Progenitor, Inc., a Delaware corporation (the "Company"), proposes to
issue and sell an aggregate of 2,500,000 shares of its common stock, par value
$.001 per share, (the "Initial Securities") to the several Underwriters named in
Schedule I hereto (the "Underwriters") for whom Vector Securities International,
Inc. ("Vector"), Tucker Anthony Incorporated  and Genesis Merchant Group
Securities are acting as representatives (collectively, the "Representatives").
In addition, solely for the purpose of covering over-allotments, the Company
proposes to grant to the several Underwriters, upon the terms and conditions set
forth in Section 2 hereof, an option to purchase up to an additional 375,000
shares of Common Stock of the Company (the "Option Securities").  The Initial
Securities and the Option Securities are hereinafter collectively referred to as
the "Securities."  The Company's common stock, par value $.001 per share,
including the Securities, is hereinafter referred to as the "Common Stock."

         The Company and the Underwriters agree that up to 50,000 shares of 
the Securities to be purchased by the Underwriters (the "Reserved 
Securities") shall be reserved for sale by the Underwriters to certain 
eligible employees, directors and other persons and entities having business 
relationships with the Company, as part of the distribution of the Securities 
by the Underwriters, subject to the terms of this Agreement, the applicable 
rules, regulations and interpretations of the National Association of 
Securities Dealers, Inc. and all other applicable laws, rules and 
regulations.  To the extent that such Reserved Securities are not so 
purchased by such eligible employees, directors and other persons and 
entities having business relationships with the Company, such Reserved 
Securities may be offered to the public as part of the public offering 
contemplated hereby.

         The Company wishes to confirm as follows its agreements with you and
the other Underwriters on whose behalf you are acting in connection with the
several purchases by the Underwriters of the Securities:

         1.  REGISTRATION STATEMENT AND PROSPECTUS.  The Company has prepared
and filed with the Securities and Exchange Commission (the "Commission") a
registration statement on Form S-1 (No. 333-5369) covering the registration of
the Securities under the Securities Act of 1933, as amended (the "1933 Act"),
including the related preliminary prospectus, or prospectuses, and either (A)
has

<PAGE>

prepared and filed, prior to the effective date of such registration statement,
an amendment to such registration statement, including a final prospectus or (B)
if the Company has elected to rely upon Rule 430A ("Rule 430A") of the rules and
regulations of the Commission under the 1933 Act (the "1933 Act Regulations"),
will prepare and file a prospectus, in accordance with the provisions of Rule
430A and Rule 424(b) ("Rule 424(b)") of the 1933 Act Regulations, promptly after
execution and delivery of this Agreement.  Additionally, if the Company has
elected to rely upon Rule 434 ("Rule 434") of the 1933 Act Regulations, the
Company will prepare and file a term sheet (a "Term Sheet") in accordance with
the provisions of Rule 434 and Rule 424(b), promptly after execution and
delivery of this Agreement.  The information, if any, included in such
prospectus or in such Term Sheet, that was omitted from such registration
statement at the time it became effective but that is deemed to be part of such
registration statement at the time it becomes effective (a) pursuant to
paragraph (b) of Rule 430A, is referred to herein as the "Rule 430A
Information," or (b) pursuant to paragraph (d) of Rule 434, is referred to
herein as the "Rule 434 Information."  Each prospectus used before the time such
registration statement became effective, and any prospectus that omitted, as
applicable, the Rule 430A Information or the Rule 434 Information that was used
after effectiveness and prior to the execution and delivery of this Agreement is
herein called a "preliminary prospectus."  Such registration statement,
including the exhibits thereto, at the time it became effective and including,
if applicable, the Rule 430A Information or the Rule 434 Information, is herein
called the "Registration Statement."  Any registration statement filed pursuant
to Rule 462(b) of the 1933 Act Regulations is herein referred to as the "Rule
462(b) Registration Statement," and after such filing the term Registration
Statement shall include the Rule 462(b) Registration Statement.  The final
prospectus in the form first furnished to the Underwriters for use in connection
with the offering of the Securities is herein referred to as the "Prospectus."
If Rule 434 is relied upon, the term "Prospectus" shall refer to the preliminary
prospectus last furnished to the Underwriters in connection with the offering of
the Securities, together with the Term Sheet, and all references to the date of
the Prospectus shall mean the date of the Term Sheet.  For purposes of this
Agreement, all references to the Registration Statement, any preliminary
prospectus, the Prospectus or any Term Sheet or any amendment or supplement to
any of the foregoing shall be deemed to include the copy, if any, filed with the
Commission pursuant to its Electronic Data Gathering, Analysis and Retrieval
system ("EDGAR").

         2.  AGREEMENTS TO SELL AND PURCHASE.  Upon the basis of the
representations, warranties and agreements contained herein and subject to all
the terms and conditions set forth herein, the Company hereby agrees to issue
and sell to each Underwriter and each Underwriter agrees, severally and not
jointly, to purchase from the Company, at a purchase price of $[        ] per
share (the

                                          2

<PAGE>

"Purchase Price Per Share"), the number of Initial Securities set forth in
Schedule I opposite the name of such Underwriter under the column "Number of
Initial Securities to be Purchased from the Company" (or such number of Initial
Securities increased as set forth in Section 10 hereof).

         Upon the basis of the representations, warranties and agreements
contained herein and subject to all the terms and conditions set forth herein,
the Company hereby grants an option (the "Over-Allotment Option") to the
Underwriters to purchase from the Company, at the Purchase Price Per Share, up
to an aggregate of 375,000 Option Securities.  Option Securities may be
purchased solely for the purpose of covering over-allotments made in connection
with the offering of the Securities.  Such option shall expire at 5:00 P.M.,
Chicago time, on the 30th day after the date of this Agreement (or, if such 30th
day shall be a Saturday or Sunday or a holiday, on the next business day
thereafter when the New York Stock Exchange is open for trading).  Such over-
allotment option may be exercised at any time or from time to time until its
expiration.  Upon any exercise of the Over-Allotment Option, each Underwriter,
severally and not jointly, agrees to purchase from the Company that proportion
of the total number of Option Securities as is equal to the percentage of
Initial Securities that such Underwriter is purchasing from the Company (or such
number of Initial Securities increased as set forth in Section 10 hereof),
subject to such adjustments as you may determine to avoid fractional shares.

         3.  TERMS OF PUBLIC OFFERING.  The Company has been advised by you
that the Underwriters propose to make a public offering of the Securities as
soon after the Registration Statement and this Agreement have become effective
as in your judgment is advisable and initially to offer the Securities upon the
terms set forth in the Prospectus.

         4.  DELIVERY OF THE SECURITIES AND PAYMENT THEREFOR.  Delivery to the
Underwriters of and payment for the Initial Securities shall be made at the
office of Skadden, Arps, Slate, Meagher & Flom, 333 West Wacker Drive, Suite
2100, Chicago, Illinois  60606, at 9:00 A.M., Chicago time, on the third
(fourth, if the pricing occurs after 4:30 p.m. (Eastern Time) on any given day)
business day after the date hereof (unless postponed in accordance with the
provisions of Section 10 hereof) (the "Closing Date").  The place of closing for
the Initial Securities and the Closing Date may be varied by agreement among you
and the Company.

         Delivery to the Underwriters of and payment for any Option Securities
to be purchased by the Underwriters shall be made at the aforementioned office
of Skadden, Arps, Slate, Meagher & Flom at such time on such date (an "Option
Closing Date"), which may be the same as the Closing Date but shall in no event
be earlier than the Closing Date nor earlier than two nor later than


                                          3

<PAGE>

ten business days after the giving of the notice hereinafter referred to, as
shall be specified in a written notice from you on behalf of the Underwriters to
the Company of the Underwriters' determination to purchase a number, specified
in such notice, of Option Securities.  The place of closing for any Option
Securities and the Option Closing Date for such Option Securities may be varied
by agreement between you and the Company.

         Certificates for the Initial Securities and for any Option Securities
to be purchased hereunder shall be registered in such names and in such
denominations as you shall request by written notice (it being understood that a
facsimile transmission shall be deemed written notice) prior to 9:30 A.M.,
Chicago time, on the second business day preceding the Closing Date or any
Option Closing Date, as the case may be.  Such certificates shall be made
available to you in Chicago, Illinois or New York, New York, as requested by you
in the aforesaid notice, for inspection and packaging not later than 9:30 A.M.,
Chicago time, on the business day next preceding the Closing Date or an Option
Closing Date, as the case may be.  The certificates evidencing the Initial
Securities and any Option Securities to be purchased hereunder shall be
delivered to you on the Closing Date or the Option Closing Date, as the case may
be, against payment of the purchase price therefor by certified or official bank
check or checks payable in New York Clearing House (next day) funds to the order
of the Company.  It is understood that each Underwriter has authorized you, for
its account, to accept delivery of, acknowledge receipt of, and make payment of
the purchase price for, the Initial Securities and the Option Securities, if
any, which it has agreed to purchase.  Vector, individually and not as
representative of the Underwriters, may (but shall not be obligated to) make
payment of the purchase price for the Initial Securities or the Option
Securities, if any, to be purchased by any Underwriter whose check has not been
received by the Closing Date or the Option Closing Date, as the case may be, but
such payment shall not relieve such Underwriter from its obligations hereunder.

         5.  AGREEMENTS OF THE COMPANY.  The Company covenants and agrees with
the several Underwriters as follows:

              a.  The Company will notify the Representatives immediately, and
confirm the notice in writing, (i) of the effectiveness of the Registration
Statement and any amendment thereto, (ii) of the receipt of any comments from
the Commission, (iii) of any request by the Commission for any amendment to the
Registration Statement or any amendment or supplement to the Prospectus or for
additional information, (iv) of the issuance by the Commission of any stop order
suspending the effectiveness of the Registration Statement or the suspension of
qualification of the Securities for offering or sale in any jurisdiction or the
initiation of any proceedings for such purpose and (v) during the period when
the Prospectus is required to be delivered under the

                                          4

<PAGE>

1933 Act or Securities Exchange Act of 1934, as amended (the "1934 Act"), of any
change, or any event or occurrence which could result in such a change, in the
Company's condition, financial or otherwise, or the earnings, business affairs
or business prospects of the Company or the happening of any event, including
the filing of any information, documents or reports pursuant to the 1934 Act,
that makes any statement of a material fact made in the Registration Statement
or the Prospectus (as then amended or supplemented) untrue or which requires the
making of any additions to or changes in the Registration Statement or the
Prospectus in order to state a material fact required by the 1933 Act or the
1933 Act Regulations to be stated therein or necessary in order to make the
statements therein not misleading, or of the necessity to amend or supplement
the Prospectus to comply with the 1933 Act, the 1933 Act Regulations or any
other law.  The Company shall use its best efforts to prevent the issuance of
any stop order or order suspending the qualification or exemption of the
Securities under any state securities or Blue Sky laws, and, if at any time the
Commission shall issue any stop order suspending the effectiveness of the
Registration Statement, or any state securities commission or other regulatory
authority shall issue an order suspending the qualification or exemption of the
Securities under any state securities or Blue Sky laws, the Company shall use
every reasonable effort to obtain the withdrawal or lifting of such order at the
earliest possible time.

              b.  The Company will give the Underwriters notice of its
intention to prepare or file any amendment to the Registration Statement
(including any post-effective amendment), any Rule 462(b) Registration
Statement, any Term Sheet or any amendment or supplement to the Prospectus
(including any revised prospectus or Term Sheet and preliminary prospectus which
the Company proposes for use by the Underwriters in connection with the offering
of the Securities which differs from the prospectus on file at the Commission at
the time the Registration Statement becomes effective, whether or not such
revised prospectus or Term Sheet and preliminary prospectus is required to be
filed pursuant to Rule 424(b)), whether pursuant to the 1933 Act, the 1934 Act
or otherwise, will furnish the Underwriters with copies of any Rule 462(b)
Registration Statement, Term Sheet, amendment or supplement a reasonable amount
of time prior to such proposed filing or use, as the case may be, and will not
file any such Rule 462(b) Registration Statement, Term Sheet, amendment or
supplement or use any such prospectus to which the Underwriters or counsel for
the Underwriters shall object.

              c.  The Company has furnished or will deliver to the Underwriters
and their counsel, without charge, as many signed and conformed copies of the
Registration Statement as originally filed and of each amendment thereto
(including exhibits filed therewith or incorporated by reference therein) as the
Underwriters may reasonably request.  If applicable, the copies of the
Registration

                                          5

<PAGE>

Statement and each amendment thereto furnished to the Underwriters will be
identical to the electronically transmitted copies thereof filed with the
Commission pursuant to EDGAR, except to the extent permitted by Regulation S-T.

              d.  The Company will furnish to each Underwriter, without charge,
from time to time during the period when the Prospectus is required to be
delivered under the 1933 Act or the 1934 Act, such number of copies of the
Prospectus (as amended or supplemented) as such Underwriter may reasonably
request for the purposes contemplated by the 1933 Act, the 1934 Act, the 1933
Act Regulations or the rules and regulations of the Commission under the 1934
Act (the "1934 Act Regulations").  If applicable, the Prospectus and any
amendments or supplements thereto furnished to the Underwriters will be
identical to the electronically transmitted copies thereof filed with the
Commission pursuant to EDGAR, except to the extent permitted by Regulation S-T.

              e.  The Company will comply with the 1933 Act and the 1933 Act
Regulations so as to permit the completion of the distribution of the Securities
as contemplated in this Agreement and in the Prospectus.  If at any time when a
prospectus is required by the 1933 Act, the 1934 Act, the 1933 Act Regulations
or the 1934 Act Regulations to be delivered in connection with sales of the
Securities, any event shall occur or condition shall exist as a result of which
it is necessary, in the opinion of counsel for the Underwriters or for the
Company, to amend the Registration Statement or amend or supplement the
Prospectus in order that the Prospectus will not include any untrue statements
of a material fact or omit to state a material fact necessary in order to make
the statements therein not misleading in the light of the circumstances existing
at the time it is delivered to a purchaser, or if it shall be necessary, in the
opinion of such counsel, at any such time to amend the Registration Statement or
amend or supplement the Prospectus in order to comply with the requirements of
the 1933 Act or the 1933 Act Regulations, the Company will promptly prepare and
file with the Commission, subject to Section 5(b) of the 1933 Act, such
amendment or supplement as may be necessary to correct such statement or
omission or to make the Registration Statement or the Prospectus comply with
such requirements and the Company will furnish to the Underwriters such number
of copies of such amendment or supplement as the Underwriters may reasonably
request.

              f.  During the period of five years hereafter, the Company will
furnish to you (i) as soon as available, a copy of each report of the Company
mailed to stockholders or filed with the Commission or the Nasdaq National
Market ("NASDAQ"), and (ii) from time to time such other information concerning
the Company as you may request.

                                          6

<PAGE>

              g.  The Company will use its best efforts, in cooperation with
counsel to the Underwriters, to qualify the Securities for offering and sale
under the applicable securities or Blue Sky laws of such states and other
jurisdictions of the United States as the Representatives may designate and to
maintain such qualifications in effect for a period of not less than one year
from the later of the effective date of the Registration Statement and any Rule
462(b) Registration Statement; PROVIDED, HOWEVER, that the Company shall not be
obligated to qualify as a foreign corporation in any jurisdiction in which it is
not so qualified.  In each jurisdiction in which the Securities have been so
qualified, the Company will file such statements and reports as may be required
by the laws of such jurisdiction to continue such qualification in effect for a
period of not less than one year from the later of the effective date of the
Registration Statement and any Rule 462(b) Registration Statement.

              h.  The Company will make generally available to its security
holders as soon as practicable, but not later than 45 days after the close of
the period covered thereby, an earnings statement (in form complying with the
provisions of Rule 158 of the 1933 Act Regulations) covering a twelve-month
period beginning not later than the first day of the Company's fiscal quarter
next following the "effective date" (as defined in said Rule 158) of the
Registration Statement.

              i.  The Company will use the net proceeds received by it from the
sale of the Securities in the manner specified in the Prospectus under "Use of
Proceeds."

              j.  If, at the time that the Registration Statement becomes
effective, any Rule 430A Information or Rule 434 Information shall have been
omitted therefrom, then immediately following the execution of this Agreement,
the Company will prepare, and file or transmit for filing with the Commission in
accordance with Rule 430A or Rule 434 and Rule 424(b), copies of a Prospectus or
Term Sheet containing such Rule 430A Information and Rule 434 Information,
respectively, or, if required by Rule 430A, a post-effective amendment to the
Registration Statement (including an amended Prospectus), containing such Rule
430A Information.

              k.  If the Company elects to rely upon Rule 462(b), the Company
shall both file a Rule 462(b) Registration Statement with the Commission in
compliance with Rule 462(b) and pay the applicable fees in accordance with Rule
111 of the 1933 Act Regulations by the earlier of (i) 10:00 P.M. Eastern Time on
the date hereof and (ii) the time confirmations are sent or given, as specified
by Rule 462(b)(2).

              l.  The Company, during the period when the Prospectus is
required to be delivered under the 1933 Act or the 1934 Act, will file all
documents required to be filed with the


                                          7

<PAGE>

Commission pursuant to Section 13, 14 or 15 of the 1934 Act within the time
periods required by the 1934 Act and the 1934 Act Regulations.

              m.  During a period of 180 days from the date of the Prospectus,
the Company will not, without the prior written consent of Vector, (i) offer,
pledge, sell, contract to sell, sell any option or contract to purchase,
purchase any option or contract to sell, grant any option, right or warrant to
purchase or otherwise transfer or dispose of, directly or indirectly, any share
of Common Stock or any securities convertible into or exercisable or
exchangeable for Common Stock or file any registration statement under the 1933
Act with respect to any of the foregoing or (ii) enter into any swap or any
other agreement or any transaction that transfers, in whole or in part, directly
or indirectly, the economic consequence of ownership of the Common Stock,
whether any such swap or transaction described in clause (i) or (ii) above is to
be settled by delivery of Common Stock or such other securities, in cash or
otherwise.  The foregoing sentence shall not apply to (A) the Securities to be
sold hereunder, (B) any shares of Common Stock issued by the Company upon the
exercise of an option or warrant or the conversion of any security outstanding
on the date hereof and referred to in the Prospectus, (C) any shares of Common
Stock issued or options to purchase Common Stock granted pursuant to existing
employee benefit plans of the Company referred to in the Prospectus or (D) any
shares of Common Stock issued pursuant to any non-employee director stock plan.

              n.  The Company has furnished or will furnish to you "lock-up"
letters, in form and substance satisfactory to you, signed by each of its
current officers and directors and each of its stockholders designated by you.

              o.  The Company will supply the Underwriters with copies of all
correspondence to and from, and all documents issued to and by, the Commission
in connection with the registration of the Securities under the 1933 Act.

              p.  Prior to the Closing Date, the Company shall furnish to the
Underwriters, as soon as they have been prepared, copies of any unaudited
interim financial statements of the Company, for any periods subsequent to the
periods covered by the financial statements appearing in the Registration
Statement and the Prospectus.

              q.  Prior to the Closing Date, the Company will issue no press
release or other communications directly or indirectly and hold no press
conference with respect to the Company, the condition, financial or otherwise,
or the earnings, business affairs or business prospects of the Company, or the
offering of the Securities, without the prior written consent of the
Representatives unless in the judgment of the Company and its

                                          8

<PAGE>

counsel, and after notification to the Representatives, such press release or
communication is required by law.

              r.  The Company will comply with all provisions of Florida H.B.
1771, codified as Section 517.075 of the Florida statutes, and all regulations
promulgated thereunder relating to issuers doing business with Cuba.

              s.  The Company has not taken, nor will it take, directly or
indirectly, any action designed to, or that might reasonably be expected to,
cause or result in stabilization or manipulation of the price of the Common
Stock to facilitate the sale or resale of the Securities.

              t.  The Company will use its best efforts to maintain the
quotation of the Common Stock (including the Securities) on NASDAQ and will file
with NASDAQ all documents and notices required by NASDAQ of companies that have
securities that are traded in the over-the-counter market and quotations for
which are reported by NASDAQ.

         6.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  The Company
represents and warrants to each Underwriter that:

              a.  When the Registration Statement, any Rule 462(b) Registration
Statement and any post-effective amendment thereto becomes effective, at the
date of the Prospectus, if different, and at the Closing Date and the Option
Closing Date, as the case may be, the Registration Statement, the Rule 462(b)
Registration Statement and any amendments and supplements thereto complied or
will comply in all material respects with the requirements of the 1933 Act and
the 1933 Act Regulations and did not and will not contain any untrue statement
of a material fact or omit to state a material fact required to be stated
therein or necessary to make the statements therein not misleading.  The
Prospectus and any supplements or amendments thereto will not at the date of the
Prospectus, at the date of any such supplements or amendments, or at the Closing
Date or the Option Closing Date, if any, include an untrue statement of a
material fact or omit to state a material fact necessary in order to make the
statements therein, in the light of the circumstances under which they were
made, not misleading.  If Rule 434 is used, the Company will comply with the
requirements of Rule 434 and the Prospectus shall not be "materially different,"
as such term is used in Rule 434, from the Prospectus included in the
Registration Statement at the time it became effective.  The representations and
warranties in this subsection shall not apply to statements in or omissions from
the Registration Statement or Prospectus relating to any Underwriter made in
reliance upon and in conformity with information furnished to the Company in
writing by or on behalf of any Underwriter, through you expressly for use in the
Registration Statement or Prospectus.  The Company has not distributed any
offering materials

                                          9

<PAGE>

in connection with the offering or sale of the Securities other than the
Registration Statement, the preliminary prospectus, the Prospectus, the Term
Sheet, if applicable, or any other materials, if any, permitted by the 1933 Act
or the 1933 Act Regulations.

              b.  Each preliminary prospectus and the prospectus filed as part
of the Registration Statement as originally filed or as part of any amendment
thereto, or filed pursuant to Rule 424 under the 1933 Act, complied when so
filed in all material respects with the 1933 Act Regulations and, if applicable,
each preliminary prospectus and the Prospectus delivered to the Underwriters for
use in connection with this offering was identical to the electronically
transmitted copies thereof filed with the Commission pursuant to EDGAR, except
to the extent permitted by Regulation S-T.

              c.  The accountants who certified the financial statements
included in the Registration Statement are independent public accountants as
required by the 1933 Act and the 1933 Act Regulations.

              d.  The financial statements included in the Registration
Statement and the Prospectus present fairly the financial position of the
Company as of the dates indicated and the results of its operations for the
periods specified; except as otherwise stated in the Registration Statement,
said financial statements have been prepared in conformity with generally
accepted accounting principles applied on a consistent basis; and no supporting
schedules are required to be included in the Registration Statement.  The
summary and selected financial information and data set forth in the Prospectus
are prepared on an accounting basis consistent with such financial statements.

              e.  Since the respective dates as of which information is given
in the Registration Statement and the Prospectus, except as otherwise stated
therein, (i) there has been no material adverse change or any development
involving a prospective material adverse change in or affecting the condition,
financial or otherwise, or in the earnings, business affairs or business
prospects of the Company, whether or not arising in the ordinary course of
business, (ii) there have been no transactions entered into by the Company,
other than those in the ordinary course of business, which are material with
respect to the Company, and (iii) there has been no dividend or distribution of
any kind declared, paid or made by the Company on any class of its capital
stock.  The Company has no material contingent obligations which are not
specifically disclosed in the Company's financial statements that are included 
in the Registration Statement.

              f.  The Company has been duly incorporated and is validly
existing as a corporation in good standing under the laws of the State of
Delaware with corporate power and authority to own, lease and operate its
properties and to conduct its business as

                                          10

<PAGE>

described in the Prospectus and to enter into and perform its obligations under
this Agreement; and the Company is duly qualified as a foreign corporation to
transact business and is in good standing in each jurisdiction in which such
qualification is required, whether by reason of the ownership or leasing of
property or the conduct of business, except where the failure to so qualify
would not, singly or in the aggregate, have a material adverse effect on the
condition, financial or otherwise, or the earnings, business affairs or business
prospects of the Company.

              g.  The Company does not own, directly or indirectly, any shares
of stock or any other equity or long-term debt securities of any corporation or
have any equity interest in any firm, partnership, joint venture, association or
other entity.

              h.  The authorized, issued and outstanding capital stock of the
Company is as set forth in the Prospectus under "Capitalization" (except for
subsequent issuances, if any, pursuant to this Agreement or pursuant to
reservations, agreements, employee or director benefit plans or the exercise of
convertible securities referred to in the Prospectus); the shares of issued and
outstanding capital stock of the Company have been duly authorized and validly
issued and are fully paid and non-assessable and have not been issued in
violation of or are not otherwise subject to any preemptive or other similar
rights; the Securities have been duly authorized for issuance and sale to the
Underwriters pursuant to this Agreement and, when issued and delivered by the
Company pursuant to this Agreement against payment of the consideration set
forth herein, will be validly issued and fully paid and non-assessable; the
certificates evidencing the Securities are in due and proper form under Delaware
law; the authorized capital stock of the Company, including the Securities,
conforms to all statements relating thereto contained in the Prospectus; and the
issuance of the Securities is not subject to preemptive or other similar rights.
There are no outstanding subscriptions, options, warrants, convertible or
exchangeable securities or other rights granted to or by the Company to purchase
shares of Common Stock or other securities of the Company and there are no
commitments, plans or arrangements to issue any shares of Common Stock or any
security convertible into or exchangeable for Common Stock, in each case other
than as described in the Prospectus.

              i.  Except as disclosed in the Registration Statement and except
as would not, singly or in the aggregate, reasonably be expected to have a
material adverse effect on the condition, financial or otherwise, or the
earnings, business affairs or business prospects of the Company, (A) the Company
is in compliance with all applicable Environmental Laws, (B) the Company has all
permits, authorizations and approvals required under any applicable
Environmental Laws and is in compliance with the requirements of such permits,
authorizations and approvals, (C) there are no pending or, to the best knowledge
of the Company,


                                          11

<PAGE>

threatened Environmental Claims against the Company and (D) under applicable
law, there are no circumstances with respect to any property or operations of
the Company that are reasonably likely to form the basis of an Environmental
Claim against the Company.

              For purposes of this Agreement, the following terms shall have
the following meanings:  "Environmental Law" means any United States (or other
applicable jurisdiction's) Federal, state, local or municipal statute, law,
rule, regulation, ordinance, code, policy or rule of common law and any judicial
or administrative interpretation thereof, including any judicial or
administrative order, consent decree or judgement, relating to the environment,
health, safety or any chemical, material or substance, exposure to which is
prohibited, limited or regulated by any governmental authority.  "Environmental
Claims" means any and all administrative, regulatory or judicial actions, suits,
demands, demand letters, claims, liens, notices of noncompliance or violation,
investigations or proceedings relating in any way to any Environmental Law.

              j.  The Company is not in violation of its charter or in default
in the performance or observance of any material obligation, agreement, covenant
or condition contained in any contract, indenture, mortgage, loan agreement,
deed, trust, note, lease, sublease, voting agreement, voting trust, or other
instrument or agreement to which the Company is a party or by which it may be
bound, or to which any of the property or assets of the Company is subject; and
the execution, delivery and performance of this Agreement and the consummation
of the transactions contemplated herein and compliance by the Company with its
obligations hereunder have been duly authorized by all necessary corporate
action and will not conflict with or constitute a breach of, or default under,
or result in the creation or imposition of any lien, charge or encumbrance upon
any property or assets of the Company pursuant to, any contract, indenture,
mortgage, loan agreement, deed, trust, note, lease, sublease, voting agreement,
voting trust or other instrument or agreement to which the Company is a party or
by which it may be bound, or to which any of the property or assets of the
Company is subject, nor will such action result in any violation of the
provisions of the charter or bylaws of the Company or any applicable statute,
law, rule, regulation, ordinance, decision, directive or order.

              k.  No labor dispute with the employees of the Company exists or,
to the best knowledge of the Company, is imminent; and the Company is not aware
of any existing or imminent labor disturbance by the employees of any of its
principal suppliers, manufacturers or contractors which might, singly or in the
aggregate, be expected to result in any material adverse change in the
condition, financial or otherwise, or in the earnings, business affairs or
business prospects of the Company.


                                          12

<PAGE>


              l.  There is no action, suit or proceeding before or by any court
or governmental agency or body, domestic or foreign, now pending, or, to the
knowledge of the Company, threatened, against or affecting the Company, which is
required to be disclosed in the Registration Statement (other than as disclosed
therein), or which, singly or in the aggregate, might result in any material
adverse change in the condition, financial or otherwise, or in the earnings,
business affairs or business prospects of the Company, or which, singly or in
the aggregate, might materially and adversely affect the properties or assets
thereof or which might materially and adversely affect the consummation of this
Agreement; all pending legal or governmental proceedings to which the Company is
a party or of which any of its property or assets is the subject which are not
described in the Registration Statement, including ordinary routine litigation
incidental to the business, are, considered in the aggregate, not material; and
there are no contracts or documents of the Company which are required to be
filed as exhibits to the Registration Statement by the 1933 Act or by the 1933
Act Regulations which have not been so filed.

              m.  Except with respect to the Protest filed with the United
States Patent and Trademark Office ("PTO") as described in the Prospectus, the
Company owns or is licensed to use all patents, patent applications, inventions,
trademarks, trade names, applications for registration of trademarks, service
marks, service mark applications, copyrights, know-how, manufacturing processes,
formulae, trade secrets, licenses and rights in any thereof and any other
intangible property and assets (herein called the "Proprietary Rights") which
are material to the business of the Company as now conducted and as proposed to
be conducted, in each case as described in the Prospectus.  The description of
the Proprietary Rights in the Prospectus is correct in all material respects and
fairly and correctly describes the Company's rights with respect thereto.
Except with respect to the Protest filed with the PTO as described in the
Prospectus, the Company does not have any knowledge of, and the Company has not
given or received any notice of, any pending conflicts with or infringement of
the rights of others with respect to any Proprietary Rights or with respect to
any license of Proprietary Rights.  Except with respect to the Protest filed
with the PTO as described in the Prospectus, no action, suit, arbitration, or
legal, administrative or other proceeding, or investigation is pending, or, to
the best knowledge of the Company, threatened, which involves any Proprietary
Rights and is material to the business of the Company as now conducted and as
proposed to be conducted, in each case as described in the Prospectus.  The
Company is not subject to any judgment, order, writ, injunction or decree of any
court or any Federal, state, local, foreign or other governmental department,
commission, board, bureau, agency or instrumentality, domestic or foreign, or
any arbitrator, and has not entered into and is not a party to any contract
which restricts or impairs the use of any such Proprietary Rights in a manner
which would have a material adverse effect on


                                          13

<PAGE>

the use of any of the Proprietary Rights.  To the best knowledge of the Company,
no Proprietary Rights used by the Company, and no services or products sold by
the Company, conflict with or infringe upon any proprietary rights available to
any third party.  The Company has not received written notice of any pending
conflict with or infringement upon such third-party proprietary rights.  The
Company has not entered into any consent, indemnification, forbearance to sue or
settlement agreement with respect to Proprietary Rights other than in the
ordinary course of business.  Except as specifically disclosed in the
Prospectus, no claims have been asserted by any person with respect to the
validity of the Company's ownership or right to use the Proprietary Rights and,
to the best knowledge of the Company, there is no reasonable basis for any such
claim to be successful.  The Proprietary Rights are valid and enforceable and no
registration relating thereto has lapsed, expired or been abandoned or cancelled
or is the subject of cancellation or other adversarial proceedings, and all
applications therefore are pending and are in good standing.  The Company has
complied, in all material respects, with its contractual obligations relating to
the protection of the Proprietary Rights used pursuant to licenses.  To the best
knowledge of the Company, no person is infringing on or violating the
Proprietary Rights owned or used by the Company.

              n.  No registration, authorization, approval, qualification or
consent of any court or governmental authority or agency is necessary in
connection with the offering, issuance or sale of the Securities hereunder,
except such as may be required under the 1933 Act or the 1933 Act Regulations or
state securities or Blue Sky laws (or such as may be required by the National
Association of Securities Dealers, Inc. ("NASD")).

              o.  The Company possesses and is operating in compliance with all
licenses, certificates, consents, authorities, approvals and permits
(collectively, "permits") from all state, Federal, foreign and other regulatory
agencies or bodies necessary to conduct the business now operated by it, and the
Company has not received any notice of proceedings relating to the revocation or
modification of any such permit or any circumstance which would lead it to
believe that such proceedings are reasonably likely which, singly or in the
aggregate, if the subject of an unfavorable decision, ruling or finding, would
materially and adversely affect the condition, financial or otherwise, or the
earnings, business affairs or business prospects of the Company.

              p.  This Agreement has been duly executed and delivered by the
Company and constitutes a valid and binding obligation of the Company,
enforceable against the Company in accordance with its terms, except as rights
to indemnity and contribution hereunder may be limited by Federal or state
securities laws or the public policy underlying such laws.


                                          14

<PAGE>


              q.  Except as described in the Prospectus, there are no persons
with registration or other similar rights to have any securities registered
pursuant to the Registration Statement or otherwise registered by the Company
under the 1933 Act.

              r.  No order preventing or suspending the use of any preliminary
prospectus has been issued and no proceedings for that purpose are pending,
threatened, or, to the knowledge of the Company, contemplated by the Commission;
and to the best knowledge of the Company, no order suspending the offering of
the Securities in any jurisdiction designated by the Underwriters pursuant to
Section 5(g) of this Agreement has been issued and, to the best knowledge of the
Company, no proceedings for that purpose have been instituted or threatened or
are contemplated.

              s.  The Company has good and marketable title to its properties,
free and clear of all material security interests, mortgages, pledges, liens,
charges, encumbrances, claims and equities of record.  The properties of the
Company are, in the aggregate, in good repair (reasonable wear and tear
excepted), and suitable for their respective uses.  Any real properties held
under lease by the Company are held by it under valid, subsisting and
enforceable leases with such exceptions as are not material and do not interfere
with the conduct of the business of the Company.

              t.  The Company maintains a system of internal accounting
controls sufficient to provide reasonable assurances that (i) transactions are
executed in accordance with management's general or specific authorization, (ii)
transactions are recorded as necessary to permit preparation of financial
statements in conformity with generally accepted accounting principles and to
maintain accountability for assets, (iii) access to assets is permitted only in
accordance with management's general or specific authorization, and (iv) the
recorded accountability for assets is compared with the existing assets at
reasonable intervals and appropriate action is taken with respect to any
differences.

              u.  The Company has conducted and is conducting its business in
compliance with all applicable Federal, state, local and foreign statutes, laws,
rules, regulations, ordinances, codes, decisions, decrees, directives and
orders, except where the failure to do so would not, singly or in the aggregate,
have a material adverse effect on the condition, financial or otherwise, or on
the earnings, business affairs or business prospects of the Company.

              v.  To the best of the Company's knowledge, neither the Company
nor any employee or agent of the Company has made any payment of funds of the
Company or received or retained any funds in violation of any law, rule or
regulation, which payment, receipt or retention of funds is of a character
required to be disclosed in the Prospectus.


                                          15

<PAGE>

              w.  The Company is not now, and after sale of the Securities to
be sold by it hereunder and application of the net proceeds from such sale as
described in the Prospectus under the caption "Use of Proceeds" will not be, an
"investment company" within the meaning of the Investment Company Act of 1940,
as amended.

              x.  All offers and sales of capital stock of the Company prior to
the date hereof were at all relevant times duly registered or exempt from the
registration requirements of the 1933 Act and were duly registered or subject to
an available exemption from the registration requirements of the applicable
state securities or Blue Sky laws.

              y.  The Company has complied with all provisions of Florida H.B.
1771, codified as Section 517.075 of the Florida statutes, and all regulations
promulgated thereunder relating to issuers doing business with Cuba.

              z.  The Common Stock is registered pursuant to Section 12(g) of
the 1934 Act.  The Securities have been duly authorized for quotation on NASDAQ.
The Company has taken no action designed to, or likely to have the effect of,
terminating the registration of the Common Stock under the 1934 Act or delisting
the Common Stock from NASDAQ, nor has the Company received any notification that
the Commission or NASDAQ is contemplating terminating such registration or
listing.

              aa.  Neither the Company  nor, to its knowledge, any of its
officers, directors or affiliates has taken, and at the Closing Date and at any
later Option Closing Date, neither the Company nor, to its knowledge, any of its
officers, directors or affiliates will have taken, directly or indirectly, any
action which has constituted, or might reasonably be expected to constitute, the
stabilization or manipulation of the price of sale or resale of the Securities.

              bb.  The Company maintains insurance of the types and in amounts
adequate for its business and consistent with insurance coverage maintained by
similar companies in similar business, including but not limited to, insurance
covering product liability and real and personal property owned or leased
against theft, damage, destruction, acts of vandalism and all other risks
customarily insured against, all of which insurance is in full force and effect.

              cc.  The Company has filed all material tax returns required to
be filed, which returns are true and correct in all material respects, and the
Company is not in default in the payment of any taxes, including penalties and
interest, assessments, fees and other charges, shown thereon due or otherwise
assessed, other than those being contested in good faith and for which adequate


                                          16

<PAGE>

reserves have been provided or those currently payable without interest which
were payable pursuant to said returns or any assessments with respect thereto.

              dd.  Except as described in the Prospectus, to the best of the
Company's knowledge, there are no rulemaking or similar proceedings before The
United States Food and Drug Administration or comparable Federal, state, local
or foreign government bodies which involve or affect the Company, which, if the
subject of an action unfavorable to the Company, could involve a prospective
material adverse change in or effect on the condition, financial or otherwise,
or in the earnings, business affairs or business prospects of the Company.

              ee.  The Company has not received any communication (whether
written or oral) relating to the termination or threatened termination or
modification or threatened modification of any material consulting, licensing,
marketing, research and development, cooperative or any similar agreement,
including, without limitation, the collaborative research and license agreements
listed under the sections of the Prospectus entitled, "Business--Strategic
Collaboration Agreements" and "Business--License Agreements."  Each such
collaborative and licensing agreement is in effect substantially as described in
such sections of the Prospectus.

              ff.  To the knowledge of the Company, if any full-time employee
identified in the Prospectus has entered into any non-competition, non-
disclosure, confidentiality or other similar agreement with any party other than
the Company or any subsidiary, such employee is neither in violation thereof nor
is expected to be in violation thereof as a result of the business conducted or
expected to be conducted by the Company as described in the Prospectus or such
person's performance of his obligations to the Company; and the Company has not
received written notice that any consultant or scientific advisor of the Company
is in violation of any non-competition, non-disclosure, confidentiality or
similar agreement.

         7.  INDEMNIFICATION AND CONTRIBUTION.

              a.  The Company agrees to indemnify and hold harmless (i) each
Underwriter and (ii) each person, if any, who controls any Underwriter within
the meaning of Section 15 of the 1933 Act (any of the persons referred to in
this clause (ii) being hereinafter referred to as a "controlling person") and
(iii) the respective directors, officers, partners and employees of any of the
Underwriters or any controlling person (any person referred to in clause (i),
(ii) or (iii) may hereinafter be referred to as an "Indemnified Person") to the
fullest extent lawful, from and against any and all losses, claims, damages,
liabilities and expenses whatsoever (including, without limitation, all
reasonable


                                          17

<PAGE>

costs of pursuing, investigating and defending any claim, suit or action or any
investigation or proceeding by any governmental agency or body, commenced or
threatened, including the reasonable fees and expenses of counsel to any
Indemnified Person), directly or indirectly, caused by, related to, based upon
or arising out of or in connection with any untrue statement or alleged untrue
statement of a material fact contained in the Registration Statement or any
amendment thereto, including the Rule 430A Information and Rule 434 Information,
if applicable, or any omission or alleged omission to state therein a material
fact required to be stated therein or necessary to make the statements therein
not misleading or caused by, related to, based upon, arising out of or in
connection with any untrue statement or alleged untrue statement of a material
fact contained in any preliminary prospectus or the Prospectus (or any amendment
or supplement thereto) or any omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein, in the light of the circumstances under which they were made, not
misleading, except insofar as such losses, claims, damages, liabilities or
expenses arise out of or are based upon any untrue statement or omission or
alleged untrue statement or omission which has been made therein or omitted
therefrom in reliance upon and in conformity with the information relating to
such Underwriter furnished in writing to the Company by or on behalf of any
Underwriter through you expressly for use in connection therewith; PROVIDED,
HOWEVER, that the indemnification contained in this paragraph a. with respect to
any preliminary prospectus shall not inure to the benefit of any Underwriter (or
related Indemnified Person) on account of any such loss, claim, damage,
liability or expense arising from the sale of the Securities by such Underwriter
to any person if a copy of the Prospectus shall not have been delivered or sent
to such person within the time required by the 1933 Act or the 1933 Act
Regulations, and the untrue statement or alleged untrue statement or omission or
alleged omission of a material fact contained in such preliminary prospectus was
corrected in the Prospectus (or any amendment or supplement thereto), provided
that the Company has delivered the Prospectus to the several Underwriters in
requisite quantity on a timely basis to permit such delivery or sending.

              b.  If any action, suit or proceeding shall be brought against
any Indemnified Person in respect of which indemnity may be sought against the
Company, such Indemnified Person shall promptly notify the parties against whom
indemnification is being sought (the "indemnifying parties"), and such
indemnifying parties shall assume the defense thereof, including the employment
of counsel and payment of all fees and expenses.  Such Indemnified Person shall
have the right to employ separate counsel in any such action, suit or proceeding
and to participate in the defense thereof, but the fees and expenses of such
counsel shall be at the expense of such Indemnified Person unless (i) the
indemnifying parties have agreed in writing to pay


                                          18

<PAGE>

such fees and expenses, (ii) the indemnifying parties have failed to assume the
defense and employ counsel or (iii) the named parties to any such action, suit,
investigation or proceeding (including any impleaded parties) include both such
Indemnified Person and the indemnifying parties and representation of such
Indemnified Person and any indemnifying party by the same counsel would, in the
reasonable judgment of the Indemnified Person, be inappropriate due to actual or
potential differing interests between them (in which case the indemnifying party
shall not have the right to assume the defense of such action, suit or
proceeding on behalf of such Indemnified Person).  It is understood, however,
that the indemnifying parties shall, in connection with any one such action,
suit or proceeding or separate but substantially similar or related actions,
suits or proceedings in the same jurisdiction arising out of the same general
allegations or circumstances, be liable for the reasonable fees and expenses of
only one separate firm of attorneys (in addition to any local counsel) at any
time for all such Indemnified Persons not having actual or potential differing
interests with you or among themselves, which firm shall be designated in
writing by Vector, and that all such fees and expenses shall be reimbursed as
they are incurred.  The indemnifying parties shall not be liable for any
settlement of any such action, suit or proceeding effected without their written
consent, which consent shall not be unreasonably withheld, but if settled with
such written consent, or if there be a final judgment for the plaintiff in any
such action, suit or proceeding, the indemnifying parties agree to indemnify and
hold harmless any Indemnified Person, to the extent provided in the preceding
paragraph, from and against any loss, claim, damage, liability or expense by
reason of such settlement or judgment.

              c.  Each Underwriter agrees, severally and not jointly, to
indemnify and hold harmless the Company, its directors, its officers who sign
the Registration Statement and any person who controls the Company within the
meaning of Section 15 of the 1933 Act, to the same extent as the foregoing
indemnity from the Company to each Indemnified Person, but only with respect to
information relating to such Underwriter furnished in writing by or on behalf of
such Underwriter through you expressly for use in the Registration Statement,
the Prospectus or any preliminary prospectus, or any amendment or supplement
thereto.  If any action, suit, investigation or proceeding shall be brought
against the Company, any of its directors, any such officer or any such
controlling person based on the Registration Statement, the Prospectus or any
preliminary prospectus, or any amendment or supplement thereto, and in respect
of which indemnity may be sought against any Underwriter pursuant to this
paragraph (c), such Underwriter shall have the rights and duties given to the
Company by paragraph (b) above, and the Company, its directors, any such officer
and any such controlling person shall have the rights and duties given to the
Indemnified Persons by paragraph (a) above.  The indemnity and contribution
obligations of the Underwriters set


                                          19

<PAGE>

forth in this Section 7 shall be in addition to any liability or obligation the
Underwriters may otherwise have to the Company.

              d.  If the indemnification provided for in this Section 7 is
unavailable to, or insufficient to hold harmless, an indemnified party under
paragraphs (a) or (c) hereof in respect of any losses, claims, damages,
liabilities or expenses referred to therein, then each indemnifying party, in
lieu of indemnifying such indemnified party, shall contribute to the amount paid
or payable by such indemnified party as a result of such losses, claims,
damages, liabilities or expenses (i) in such proportion as is appropriate to
reflect the relative benefits received by the Company on the one hand and the
Underwriters on the other hand from the offering of the Securities or (ii) if
the allocation provided by clause (i) above is not permitted by applicable law
or judicial determination, in such proportion as is appropriate to reflect not
only the relative benefits referred to in clause (i) above but also the relative
fault of the Company on the one hand and the Underwriters on the other hand, as
well as any other relevant equitable considerations.  The relative benefits
received by the Company on the one hand and the Underwriters on the other hand
shall be deemed to be in the same proportion as the total net proceeds from the
offering (before deducting expenses) received by the Company bear to the total
underwriting discounts and commissions received by the Underwriters, in each
case as set forth in the table on the cover page of the Prospectus or, if Rule
434 is used, the corresponding location on the Term Sheet.  The relative fault
of the Company on the one hand and the Underwriters on the other hand shall be
determined by reference to, among other things, whether the untrue or alleged
untrue statement of a material fact or the omission or alleged omission to state
a material fact relates to information supplied by the Company on the one hand
or by the Underwriters on the other hand and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission or any failure of the nature referred to in Section 7 f 
hereof.  The indemnity and contribution obligations of the Company set forth
herein shall be in addition to any liability or obligation the Company may
otherwise have to any Indemnified Person.

              e.  The Company and the Underwriters agree that it would not be
just and equitable if contribution pursuant to this Section 7 were determined by
a pro rata allocation (even if the Underwriters were treated as one entity for
such purpose) or by any other method of allocation that does not take account of
the equitable considerations referred to in the immediately preceding paragraph.
The amount paid or payable by an indemnified party as a result of the losses,
claims, damages, liabilities and expenses referred to in the immediately
preceding paragraph shall be deemed to include, subject to the limitations set
forth above, any legal or other expenses reasonably incurred by such indemnified
party in connection with investigating any claim or defending any such action,
suit or proceeding.  Notwithstanding the provisions of this


                                          20

<PAGE>

Section 7, no Underwriter (or any of its related Indemnified Persons) shall be
required to contribute (whether pursuant to subsection (a) or (c) or otherwise)
any amount in excess of the underwriting discount applicable to the Securities
underwritten by such Underwriter.  No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the 1933 Act) shall be
entitled to contribution from any person who was not guilty of such fraudulent
misrepresentation.  The Underwriters' obligations to contribute pursuant to this
Section 7 are several in proportion to the respective numbers of Securities set
forth opposite their names in Schedule I hereto (or such numbers of Securities
increased as set forth in Section 10 hereof) and not joint.

              f.  The Company agrees to indemnify and hold harmless each 
Indemnified Person to the fullest extent lawful, from and against any and all 
losses, claims, damages, liabilities and expenses whatsoever (including, 
without limitation, all reasonable costs of pursuing, investigating and 
defending any claim, suit or action or any investigation or proceeding by any 
governmental agency or body, commenced or threatened, including the 
reasonable fees and expenses of counsel to any Indemnified Person), directly 
or indirectly, caused by, related to, based upon or arising out of or in 
connection with the failure of eligible employees, directors and other 
persons and entities having business relationships with the Company to pay 
for and accept delivery of Reserved Securities which were subject to a 
properly confirmed agreement to purchase.

              g.  No indemnifying party shall, without the prior written
consent of the Indemnified Person, effect any settlement of any pending or
threatened action, suit or proceeding in respect of which any Indemnified Person
is or could have been a party and indemnity could have been sought hereunder by
such Indemnified Person, unless such settlement includes an unconditional
release of such Indemnified Person from all liability on claims that are the
subject matter of such action, suit or proceeding.

              h.  Any losses, claims, damages, liabilities or expenses for
which an indemnified party is entitled to indemnification or contribution under
this Section 7 shall be paid by the indemnifying party to the indemnified party
as such losses, claims, damages, liabilities or expenses are incurred.  The
indemnity and contribution agreements contained in this Section 7 and the
representations and warranties of the Company set forth in this Agreement shall
remain operative and in full force and effect, regardless of (i) any
investigation made by or on behalf of any Indemnified Person, the Company, its
directors or officers or any person controlling the Company, (ii) acceptance of
any Securities and payment therefor hereunder and (iii) any termination of this
Agreement.

         8.  CONDITIONS OF UNDERWRITERS' OBLIGATIONS.  The several obligations
of the Underwriters to purchase the Initial Securities hereunder are subject to
the following conditions:

              a.  The Registration Statement, including any Rule 462(b)
Registration Statement, shall have become effective on the date hereof; no stop
order suspending the effectiveness of the Registration Statement shall have been
issued under the 1933 Act or proceedings therefor initiated or threatened by the
Commission.  If the Company has elected to rely upon Rule 430A, Rule 430A
Information previously omitted from the effective Registration Statement
pursuant to Rule 430A shall have been transmitted to the Commission for filing
pursuant to Rule 424(b) within the prescribed time period and the Company shall
have provided evidence satisfactory to the Underwriters of such timely filing,
or a post-effective amendment providing such information shall have been


                                          21

<PAGE>

promptly filed and declared effective in accordance with the requirements of
Rule 430A.  If the Company has elected to rely upon Rule 434, a Term Sheet shall
have been transmitted to the Commission for filing pursuant to Rule 424(b)
within the prescribed time period.

              b.  The Underwriters shall have received:

(i)  The favorable opinion, dated as of the Closing Date, of Morrison & Foerster
         LLP, counsel for the Company, in form and substance satisfactory to
         counsel for the Underwriters, to the effect that:

              A.  The Company has been duly incorporated and is validly
         existing as a corporation in good standing under the laws of the State
         of Delaware.

              B.  The Company has corporate power and authority to conduct its
         business as described in the Registration Statement and the Prospectus
         and to enter into and perform its obligations under this Agreement.

              C.  To the best of their knowledge and information, the Company
         is duly qualified as a foreign corporation to transact business and is
         in good standing in each jurisdiction in which such qualification is
         required, except to the extent that the failure to be so qualified or
         be in good standing would not have a material adverse effect on the
         Company.

              D.  The authorized, issued and outstanding capital stock of the
         Company is as set forth in the Prospectus under "Capitalization"
         (except for subsequent issuances, if any, pursuant to reservations,
         agreements, employee or director benefit plans or the exercise of
         convertible securities referred to in the Prospectus), excluding Pro 
         Forma and Pro Forma As Adjusted information, and the shares of issued
         and outstanding capital stock of the Company, including the Common
         Stock, have been duly authorized and validly issued and are fully 
         paid and non-assessable and, to their knowledge and information, have
         not been issued in violation of or are not otherwise subject to any
         preemptive rights or other similar rights.


                                          22

<PAGE>


              E.  The Securities have been duly authorized and, upon delivery
         to the Underwriters against payment therefor in accordance with the
         terms of this Agreement, will be validly issued, fully paid and non-
         assessable; and the issuance of the Securities is not subject to
         preemptive rights.

              F.  To the best of their knowledge and information, except as
         described in the Prospectus, there are no outstanding options,
         warrants or other rights granted to or by the Company to purchase
         shares of Common Stock or other securities of the Company and there
         are no commitments, plans or arrangements to issue any shares of
         Common Stock or other securities.

              G.  This Agreement has been duly authorized, executed and
         delivered by the Company and constitutes the legal, valid and binding
         obligation of the Company.

              H.  At the time the Registration Statement became effective and
         at the Closing Date, the Registration Statement (other than the
         financial statements, and related notes thereto, and other financial
         information included therein, as to which no opinion need be rendered)
         complied as to form in all material respects with the requirements of
         the 1933 Act and the 1933 Act Regulations.

              I.  The form of certificate used to evidence each of the
         Securities is in due and proper form and complies with all applicable
         statutory requirements of Delaware law.

              J.  To the best of their knowledge and information, there are no
         legal or governmental proceedings pending or threatened which are
         required to be disclosed in the Registration Statement other than
         those disclosed therein, and all pending legal or governmental
         proceedings to which the Company is a party or to which any of its
         property is subject which are not described in the Registration


                                          23

<PAGE>

         Statement, including ordinary routine litigation incidental to the
         business, are, considered in the aggregate, not material.

              K.  The information in the Prospectus under "Risk Factors--
         Shares Eligible for Future Sale; Registration Rights; Possible Adverse
         Effect on Stock Price," "Management--Stock Plans," "Management--
         Directors' Compensation," "Management--Employment Agreement,"
         "Description of Capital Stock" and "Shares Eligible for Future Sale"
         to the extent that it constitutes matters of law, summaries of legal
         matters, documents or proceedings, or legal conclusions, has been
         reviewed by them and is correct in all material respects and fairly
         and correctly presents the information called for with respect thereto.

              L.  To the best of their knowledge and information, there is no
         agreement, contract or other document of a character required to be
         described or referred to in the Registration Statement or to be filed
         as an exhibit thereto other than those described or referred to
         therein or filed as exhibits thereto, the descriptions thereof or
         references thereto are correct; and to the best of their knowledge and
         information, no default exists in the due performance or observance of
         any material obligation, agreement, covenant or condition contained in
         any material contract, indenture, mortgage, loan agreement, deed,
         trust, note, lease, sublease, voting trust, voting agreement or other
         instrument or agreement of the Company.

              M.  No authorization, approval, consent or order of any court or
         governmental authority or agency is required in connection with the
         offering, issuance or sale of the Securities to the Underwriters,
         except such as may be required under the 1933 Act or the 1933 Act
         Regulations or state securities or Blue Sky laws or such as may be
         required by the


                                          24

<PAGE>

         NASD; and the execution, delivery and performance of this Agreement
         and the consummation of the transactions contemplated herein and the
         compliance by the Company with its obligations hereunder will not
         conflict with or constitute a breach of, or default under, or result
         in the creation or imposition of any lien, charge or encumbrance upon
         any property or assets of the Company pursuant to, any contract,
         indenture, mortgage, loan agreement, note, deed, trust, lease,
         sublease, voting trust, voting agreement or other instrument or
         agreement to which the Company is a party or by which it may be bound,
         or to which any of the property or assets of the Company is subject,
         nor will such action result in any violation of the provisions of the
         charter or bylaws of the Company, or any applicable statute, law,
         rule, regulation, ordinance, code, decision, directive or order.

              N.  Except as described in the Prospectus, to the best of their
         knowledge and information, there are no persons with registration or
         other similar rights to have any securities registered pursuant to the
         Registration Statement or otherwise registered by the Company under
         the 1933 Act.

              O.  The Company is not an "investment company" or a company
         "controlled" by an "investment company" within the meaning of the
         Investment Company Act of 1940, as amended.

              P.  To the best of their knowledge and information, the Company
         is in compliance with, and conducts its business in conformity with,
         all applicable laws and regulations relating to the operation of its
         business as described in the Registration Statement, except to the
         extent that any failure so to comply or conform would not have a
         material adverse effect upon the business or condition, financial or
         otherwise, of the Company.

              Q.  The Registration Statement has become effective under the
         1933 Act; any


                                          25

<PAGE>

         required filing of the Prospectus, and any supplements thereto or the
         Term Sheet, pursuant to Rule 424(b) and if applicable, Rule 434, has
         been made in the manner and within the time period required; and to
         their best knowledge and information, no stop order suspending the
         effectiveness of the Registration Statement or any part thereof has
         been issued and no proceedings therefor have been instituted or are
         pending or contemplated under the 1933 Act.

      In rendering such opinion, such counsel may rely (i) on the opinion of
      Pennie & Edmonds, patent counsel to the Company, given pursuant to Section
      8(b)(ii) hereof, (ii) as to matters of local law, on opinions of local
      counsel, and (iii) as to matters of fact, on certificates of officers of
      the Company and of governmental officials, in which case their opinion is
      to state that they are so doing and that the Underwriters are justified in
      relying on such opinions of certificates, and copies of said opinions of
      certificates are to be attached to the opinion.

(ii)  The favorable opinion, dated as of the Closing Date, of Pennie & Edmonds,
      patent counsel for the Company, in form and substance satisfactory to
      counsel for the Underwriters, to the effect that:

         A.   The statements in the Prospectus relating to United States 
patent matters, under the captions "Risk Factors - Uncertainty of Patents and 
Proprietary Rights"; "Business - Progenitor's Functional Genomics Approach"; 
"Business - Progenitor's Proprietary Discovery Technologies''; Business - 
Progenitor's Discovery Programs"; and "Business -Patents and Proprietary 
Rights", insofar as such statements constitute matters of law, legal 
conclusions, or summaries of legal matters or proceedings, are correct in all 
material respects and present fairly the information purported to be shown.

         B.   With respect to the United States patent applications referred to
in the Registration Statement which are listed in Schedules E and G, the
sections of the Registration Statement entitled "Risk Factors - Uncertainty of
Patents and Proprietary Rights";  "Business - Progenitor's Functional Genomics
Approach"; "Business - Progenitor's Proprietary Discovery Technologies"; 
Business - Progenitor's Discovery Programs"; and
"Business - Patents and Proprietary Rights", at the time the Registration
Statement became effective, did not contain any untrue statement of material
fact or omit to state a material fact required to be stated therein or necessary
to make the statements therein, not misleading.

         C.   With respect to the United States patent applications referred to
in the Prospectus which are listed in Schedules E and G, the sections of the
Prospectus entitled "Risk Factors - Uncertainty of Patents and Proprietary
Rights"; "Business - Progenitor's Functional Genomics Approach"; "Business -
Progenitor's Proprietary Discovery Technologies"; "Business - Progenitor's
Discovery Programs"; and "Business - Patents and Proprietary Rights", as of this
Closing Date, do not contain any untrue statement of material fact or omit to
state a material fact necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading.

         D.   To the best of such counsel's knowledge, except as described in
the Prospectus, and with the exception of proceedings before the U.S. Patent and
Trademark Office, there are no pending, or threatened, legal or governmental
proceedings relating to U.S. Patent No. 5,032,407, or to any U.S. patent
application referred


                                          26

<PAGE>



to in the Prospectus which is listed in Schedules E and G.

         E.   To the best of such counsel's knowledge, the License Agreements
listed in Schedule I grant the Company rights in the U.S. patents and patent
applications referred to in the Prospectus which are listed in Schedules D and
G, and such License Agreements are validly binding and enforceable under federal
case law relating to the licensing of patent rights.

         F.   To the best of such counsel's knowledge, the Company owns the
U.S. patent applications referred to in the Prospectus which are listed in
Schedule E.

         G.   To the best of such counsel's knowledge, except as described in
the Prospectus, no third party has any rights to U.S. Patent No. 5,032,407, or
to any U.S. patent application referred to in the Prospectus which is listed in
Schedules E and G.

         H.   To the best of such counsel's knowledge, no interference has been
declared or provoked with respect to U.S. Patent No. 5,032,407, or with respect
to any U.S. patent application referred to in the Prospectus which is listed in
Schedules E and G.

         I.   To the best of such counsel's knowledge, there have been no
inventorship challenges with respect to U.S. Patent No. 5,032,407, or with
respect to any U.S. patent application referred to in the Prospectus which is
listed in Schedules E and G.

         J.   To the best of such counsel's knowledge, no third party is
infringing U.S. Patent No. 5,032,407.

         K.   To the best of such counsel's knowledge, the Company has not
received any notice challenging the Company's rights to U.S. Patent No.
5,032,407, or to any U.S. patent application referred to in the Prospectus
which is listed in Schedules E and G.

         L.   To the best of such counsel's knowledge, the Company has not
received any notice challenging the validity or enforceability of U.S. Patent
No. 5,032,407.


                                          27

<PAGE>

         M.   While there can be no guarantee that any particular patent
application will issue as a patent, each of the U.S. patent aplications referred
to in the Prospectus which is listed in Schedules E and G was properly filed,
and is being properly and diligently prosecuted, in the U.S. Patent and
Trademark Office.

         N.   To the best of such counsel's knowledge, without any searches
specifically having been conducted, or having been required to have been
conducted, for the purpose of rendering such counsel's opinion, while there can
be no guarantee that any particular patent application will issue as a patent,
each of the U.S. patent applications referred to in the Prospectus which is
listed in Schedules E and G discloses patentable subject matter.

         O.   To the best of such counsel's knowledge, no liens have been
recorded against the Company with respect to any U.S. patent application
referred to in the Prospectus which is listed in Schedule E.

         P.   to the best of such counsel's knowldege, no claim has been
asserted against the Company relating to the potential infringement of, or
conflict with, any patents, trademarks copyrights, trade secrets, or proprietary
rights, of others.

         Q.   While there can be no assurance that any of the Company's U.S.
patent applications relating to certain leptin receptors will issue as patents,
or that any such patent, if issued, would be broad enough to cover leptin
receptors of Millennium or others, there is a reasonable basis for the Company's
continued efforts in seeking the broadest allowable claims from the U.S. Patent
and Trademark Office, including claims broad enough to cover leptin receptors of
Millennium or others.

         R.   To the best of such counsel's knowledge, for each U.S. patent
application listed in Schedules E and G, all information known, to date, to be
"material to patentability", as defined in 37 C.F.R. Section 1.56(b), has been
disclosed, or will be disclosed pursuant to 37 C.F.R. Section 1.97, to the U.S.
Patent and Trademark Office.


                                          28

<PAGE>


(iii)  The favorable opinion, dated as of the Closing Date, of Skadden, Arps,
         Slate, Meagher & Flom, counsel for the Underwriters with respect to
         the issuance and sale of the Securities, the Registration Statement
         and the Prospectus and such other related matters as the Underwriters
         shall reasonably request.

(iv)   In giving their opinions required by subsections (b)(i) and (b)(iii),
         respectively, of this Section 8, Morrison & Foerster LLP and Skadden,
         Arps, Slate, Meagher & Flom shall each additionally state that nothing
         has come to their attention that leads them to believe that the
         Registration Statement (except for financial statements, and related
         notes thereto, and other financial information included therein, as to
         which counsel need make no statement), at the time it became
         effective, contained an untrue statement of a material fact or omitted
         to state a material fact required to be stated therein or necessary to
         make the statements therein not misleading or that the Prospectus
         (except for financial statements, and related notes thereto, and other
         financial information included therein, as to which counsel need make
         no statement), as of its date (unless the term "Prospectus" refers to
         a prospectus which has been provided to the Underwriters by the
         Company for use in connection with the offering of the Securities
         which differs from the Prospectus on file at the Commission at the
         time the Registration Statement becomes effective, in which case at
         the time it is first provided to the Underwriters for such use) or at
         the Closing Date or the Option Closing Date, as the case may be,
         included or includes an untrue statement of a material fact or omitted
         or omits to state a material fact necessary in order to make the
         statements therein, in the light of the circumstances under which they
         were made, not misleading.

              c.  (i) There shall not have been, since the date hereof or since
the respective dates as of which information is given in the Registration
Statement and the Prospectus, any material adverse change or any development
involving a prospective material adverse change in or affecting the condition,
financial or otherwise, or in the earnings, business affairs or business
prospects of the Company, whether or not arising in the ordinary course of
business, (ii) the representations and warranties of the Company in Section 6
hereof shall be true and correct with the same force and effect as though
expressly made at and as of the Closing


                                          29

<PAGE>

Date, except to the extent that any such representation or warranty relates to a
specific date, (iii) the Company shall have complied in all material respects
with all agreements and satisfied all conditions on its part to be performed or
satisfied at or prior to the Closing Date, (iv) no stop order suspending the
effectiveness of the Registration Statement has been issued and no proceedings
for that purpose have been initiated or threatened by the Commission and (v) the
Representatives shall have received a certificate, dated the Closing Date and
signed by the President or any Vice President and the chief financial or
accounting officer of the Company to the effect set forth in clauses (i), (ii),
(iii) and (iv) above.

              d.  At the time of the execution of this Agreement, the
Underwriters shall have received from Coopers & Lybrand L.L.P. a letter dated
such date, in form and substance satisfactory to the Underwriters, together with
signed or reproduced copies of such letter for each of the other Underwriters
containing statements and information of the type ordinarily included in
accountants' "comfort letters" to underwriters with respect to the financial
statements and certain financial information contained in the Registration
Statement and the Prospectus.

              e.  The Underwriters shall have received from Coopers & Lybrand
L.L.P. a letter, dated as of the Closing Date, to the effect that they reaffirm
the statements made in the letter furnished pursuant to subsection (d) of this
Section, except that the specified date referred to shall be a date not more
than three business days prior to the Closing Date.

              f.  The Securities shall have been approved for quotation on
NASDAQ.

              g.  In the event that the Underwriters exercise their option
provided in Section 2 hereof to purchase all or any portion of the Option
Securities, the representations and warranties of the Company contained herein
and the statements in any certificates furnished by the Company hereunder shall
be true and correct as of the Option Closing Date and, at the relevant Option
Closing Date, the Underwriters shall have received:

                        (1)  A certificate, dated such Option
         Closing Date, of the President or any Vice President
         of the Company and of the chief financial or accounting
         officer of the Company confirming that the certificate
         delivered at the Closing Date pursuant to Section 8 (c)
         hereof remains true and correct as of such Option
         Closing Date.

                        (2) The favorable opinion of Morrison &
         Foerster LLP, in form and substance


                                          30

<PAGE>

         satisfactory to counsel for the Underwriters, dated
         such Option Closing Date, relating to the Option
         Securities to be purchased on such Option Closing Date
         and otherwise to the same effect as the opinion required
         by Sections 8 (b)(i) and 8 (b)(iv) hereof.

                        (3)  The favorable opinion of Pennie & Edmonds,
         in form and substance satisfactory to counsel for the
         Underwriters, dated such Option Closing Date to the same
         effect as the opinion required by Section 8(b)(ii) hereof.

                        (4)  The favorable opinion of Skadden, Arps,
         Slate, Meagher & Flom, counsel for the Underwriters,
         dated such Option Closing Date, relating to the Option
         Securities to be purchased on such Option Closing Date and
         otherwise to the same effect as the opinion required by
         Sections 8 (b)(iii) and 8 (b)(iv) hereof.

                        (5)  A letter from Coopers & Lybrand L.L.P.
         in form and substance satisfactory to the Underwriters
         and dated such Option Closing Date, substantially the
         same in form and substance as the letter furnished to the
         Underwriters pursuant to Section 8(e) hereof, except
         that the "specified date" in the letter furnished
         pursuant to this Section 8(g)(5) shall be a date not
         more than three business days prior to such Option
         Closing Date.

              h.  At the date of this Agreement, the Underwriters shall have
received lock-up agreements in form and substance satisfactory to the
Underwriters by the persons listed on Schedule II hereto.

              i.  Counsel for the Underwriters shall have been furnished with
such documents and opinions as they may reasonably request for the purpose of
enabling them to pass upon the issuance and sale of the Securities as herein
contemplated and related proceedings, or in order to evidence the accuracy of
any of the representations or warranties or the fulfillment of any of the
conditions herein contained; and all proceedings taken by the Company in
connection with the issuance and sale of the Securities as herein contemplated
shall be satisfactory in form and substance to the Underwriters and counsel for
the Underwriters.

              j.  The NASD shall not have raised any objection with respect to
the fairness and reasonableness of the underwriting terms and arrangements.


                                          31

<PAGE>


              k.  Any certificate or document signed by any officer of the
Company and delivered to you, as Representatives of the Underwriters, or to
counsel for the Underwriters, shall be deemed a representation and warranty by
the Company to each Underwriter as to the statements made therein.

              l.  If any condition specified in this Section 8 shall not have
been fulfilled when and as required to be fulfilled, this Agreement, or, in the
case of any condition to the purchase of Option Securities, on an Option Closing
Date which is after the Closing Date, the obligations of the several
Underwriters to purchase the relevant Option Securities, may be terminated by
the Representatives by notice to the Company at any time at or prior to Closing
Date or such an Option Closing Date as the case may be, and such termination
shall be without liability of any party to any other party except as provided in
Section 9 and except that Sections 6 and 7 shall survive any such termination
and remain in full force and effect.

         9.  EXPENSES.  The Company agrees to pay the following costs and
expenses and all other costs and expenses incident to the performance by it of
its obligations hereunder:  (i) the preparation, printing or reproduction, and
filing with the Commission of the Registration Statement (including financial
statements and exhibits thereto), each preliminary prospectus, the Prospectus,
and each amendment or supplement to any of them; (ii) the printing (or
reproduction) and delivery (including postage, air freight and charges for
counting and packaging) of such copies of the Registration Statement, each
preliminary prospectus, the Prospectus, and all amendments or supplements to any
of them as may be reasonably requested for use in connection with the offering
and sale of the Securities; (iii) the preparation, printing, authentication,
issuance and delivery of certificates for the Securities, including any stamp
taxes in connection with the original issuance and sale of the Securities; (iv)
the printing (or reproduction) and delivery of this Agreement, the preliminary
and supplemental Blue Sky Memoranda and all other agreements or documents
printed (or reproduced) and delivered in connection with the original issuance
and sale of the Securities; (v) the registration of the Common Stock under the
1934 Act and the quotation of the Securities on NASDAQ; (vi) the registration or
qualification of the Securities for offer and sale under the securities or Blue
Sky laws of the several states as provided in Section 5(g) hereof (including the
reasonable fees, expenses and disbursements of counsel for the Underwriters
relating to the preparation, printing or reproduction, and delivery of the
preliminary and supplemental Blue Sky Memoranda and such registration and
qualification); (vii) the filing fees and the reasonable fees and expenses of
counsel for the Underwriters incident to securing any required review by the
NASD; (viii) the fees and expenses of the Company's accountants and the fees
and


                                          32


<PAGE>

expenses of counsel (including local and special counsel) for the Company; 
and (ix) all costs and expenses of the Underwriters, including the fees and 
disbursements of counsel for the Underwriters, in connection with matters 
related to the Reserved Securities which are designated by the Company for 
sale to employees, directors and other persons and entities having a business 
relationship with the Company.

         If this Agreement shall terminate or shall be terminated after
execution pursuant to any provisions hereof (otherwise than pursuant to the
second paragraph of Section 10 or pursuant to clauses (ii), (iii), (iv) and (v)
of Section 11 hereof) or if this Agreement shall be terminated by the
Underwriters because of any failure or refusal on the part of the Company to
comply, in any material respect, with the terms or fulfill, in any material
respect, any of the conditions of this Agreement, the Company agrees to
reimburse the Representatives for all reasonable out-of-pocket expenses
(including reasonable fees and expenses of counsel for the Underwriters)
incurred by you in connection herewith.

         10.  EFFECTIVE DATE OF AGREEMENT.  This Agreement shall become
effective: (i) upon the execution and delivery hereof by or on behalf of the
parties hereto; or (ii) if, at the time this Agreement is executed and
delivered, it is necessary for the Registration Statement or a post-effective
amendment thereto to be declared effective before the offering of the Securities
may commence, when notification of the effectiveness of the Registration
Statement or such post-effective amendment has been released by the Commission.
Until such time as this Agreement shall have become effective, it may be
terminated by the Company, by notifying you, or by you, as Representatives of
the several Underwriters, by notifying the Company.

         If one or more of the Underwriters shall fail on the Closing Date to
purchase the Initial Securities which it or they are obligated to purchase under
this Agreement (the "Defaulted Securities"), the Representatives shall have the
right, within 24 hours thereafter, to make arrangements for one or more of the
non-defaulting Underwriters, or any other underwriters, to purchase all, but not
less than all, of the Defaulted Securities in such amounts as may be agreed upon
and upon the terms herein set forth; if, however, the Representatives shall not
have completed such arrangements within such 24-hour period, then:

              a.  if the number of Defaulted Securities does not exceed 10% of
the number of Initial Securities, the non-defaulting Underwriters shall be
obligated to purchase the full amount thereof in the proportions that their
respective underwriting obligations hereunder bear to the underwriting
obligations of all non-defaulting Underwriters, or

              b.  if the number of Defaulted Securities exceeds 10% of the
number of Initial Securities, this Agreement shall terminate without liability
on the part of any non-defaulting Underwriter or the Company.


                                          33

<PAGE>


         No action taken pursuant to this Section shall relieve any defaulting
Underwriter from liability in respect of its default.

         In the event of any such default which does not result in a
termination of this Agreement, either the Representatives or the Company shall
have the right to postpone the Closing Date for a period not exceeding seven
days in order to effect any required changes in the Registration Statement or
Prospectus or in any other documents or arrangements.  As used herein, the term
"Underwriter" includes any person substituted for an Underwriter under this
Section 10.

         Any notice under this Section 10 may be given by telegram, telecopy or
telephone but shall be subsequently confirmed by letter.

         11.  TERMINATION OF AGREEMENT.  The Underwriters may terminate this
Agreement, by notice to the Company, at any time at or prior to the Closing Date
or Option Closing Date, as the case may be, (i) if there has been, since the
date of this Agreement or since the respective dates as of which information is
given in the Registration Statement, any material adverse change or any
development involving a prospective material adverse change in or affecting the
condition, financial or otherwise, or in the earnings, business affairs or
business prospects of the Company, whether or not arising in the ordinary course
of business, (ii) if there has occurred any change in the financial markets in
the United States or elsewhere or any outbreak of hostilities or escalation
thereof or other calamity or crisis the effect of which is such as to make it,
in your judgement, impracticable or inadvisable to market the Securities or to
enforce contracts for the sale of the Securities, (iii) if trading in the Common
Stock has been suspended by the Commission, or if trading generally on the
American Stock Exchange, the New York Stock Exchange or in the over-the-counter
markets has been suspended, or minimum or maximum prices for trading have been
fixed, or maximum ranges for prices for securities have been required, by such
exchange or markets or by order of the Commission or any other governmental
authority, or if a banking moratorium has been declared by either Federal, New
York or Illinois authorities, (iv) the enactment, publication, decree or other
promulgation of any Federal or state statute, regulation, rule or order of any
court or other governmental authority which in your judgement materially and
adversely affects or may materially or adversely affect the business or
operations of the Company or (v) the taking of any action by any Federal, state
or local government or agency in respect of its monetary or fiscal affairs which
in your judgement has a material adverse effect on the securities markets in the
United States, and would in your judgement make it impracticable or inadvisable
to market the Securities or to enforce any contract for the sale thereof.
Notice


                                          34

<PAGE>

of such termination may be given by telegram, telecopy or telephone and shall be
subsequently confirmed by letter.

              a.  If this Agreement is terminated pursuant to this Section 11,
such termination shall be without liability of any party to any other party
except as provided in Section 9 and provided further that Sections 6 and 7 shall
survive such termination and remain in full force and effect.

         12.  INFORMATION FURNISHED BY THE UNDERWRITERS.  The statements set
forth in the last paragraph on the cover page, the stabilization legend on the
inside front cover page, and the statements under the caption "Underwriting" in
any preliminary prospectus and in the Prospectus constitute the only information
furnished by or on behalf of the Underwriters through you as such information is
referred to in Sections 5(a) and 7 hereof.

         13.  MISCELLANEOUS.  Except as otherwise provided in Sections 5, 10
and 11 hereof, notice given pursuant to any provision of this Agreement shall be
in writing and shall be delivered (i) if to the Company at the office of the
Company at 1507 Chambers Road, Columbus, Ohio 43212, Attention: Douglass B.
Given, President and Chief Executive Officer; or (ii) if to you, as
Representatives of the several Underwriters, care of Vector Securities
International, Inc., 1751 Lake Cook Road, Suite 350, Deerfield, Illinois 60015,
Attention:  Syndicate Department.

         14.  APPLICABLE LAW; COUNTERPARTS.   This Agreement shall be governed
by and construed in accordance with the laws of the State of Illinois applicable
to contracts made and to be performed within the State of Illinois.  This
Agreement may be signed in various counterparts which together constitute one
and the same instrument.  If signed in counterparts, this Agreement shall not
become effective unless at least one counterpart hereof shall have been executed
and delivered on behalf of each party hereto.

         15.  SUCCESSORS.  This Agreement has been and is made solely for the
benefit of the several Underwriters, the Company, its directors and officers,
the other persons referred to in Section 7 hereof and their respective
successors and assigns, to the extent provided herein, and no other person shall
acquire or have any right under or by virtue of this Agreement.  Neither the
term "successor" nor the term "successors and assigns" as used in this Agreement
shall include a purchaser from any Underwriter of any of the Securities in his
status as such purchaser.


                                          35

<PAGE>

         Please confirm that the foregoing correctly sets forth the agreement
among the Company and the several Underwriters.

                                       Very truly yours,

                                       PROGENITOR, INC.



                                       By: ____________________________________
                                           President and Chief
                                           Executive Officer

Confirmed as of the date first
above mentioned on behalf of
themselves and the other several
Underwriters named in Schedule I
hereto.

VECTOR SECURITIES INTERNATIONAL, INC.
TUCKER ANTHONY INCORPORATED
GENESIS MERCHANT GROUP SECURITIES

   As Representatives of the Several Underwriters

By VECTOR SECURITIES INTERNATIONAL, INC.


By: __________________________________
         Vice President


                                          36

<PAGE>

                                      SCHEDULE I


                                   PROGENITOR, INC.









                                                                     NUMBER OF
                                                                     INITIAL
                                                                     SECURITIES
                                                                     PURCHASED
   UNDERWRITER                                                       FROM THE
                                                                     COMPANY
Vector Securities                                                   
International, Inc. . . .

Tucker Anthony
Incorporated . . . .  . .

Genesis Merchant Group
Securities. . . . . .











Total


                                          37

<PAGE>

   
                       RESTATED CERTIFICATE OF INCORPORATION OF
                                   PROGENITOR, INC.
    


   
       Douglass B. Given hereby certifies that:
    
   
       1.      The name of this corporation is Progenitor, Inc. and the date of
filing of the original Certificate of Incorporation of this corporation with the
Secretary of State of the State of Delaware is February 25, 1992.
    
   
       2.      He is the duly elected and acting President of Progenitor, Inc.,
a Delaware corporation.
    
   
       3.      This Restated Certificate of Incorporation has been duly
approved and adopted by the Stockholders of this Corporation in accordance with
the provisions of Sections 228, 242, and 245 of the General Corporation Law of
the State of Delaware.
    
   
       4.      The Certificate of Incorporation of this corporation is hereby
restated to read as follows:
    

                                          "I

       The name of the Corporation is Progenitor, Inc. (the "Corporation").

                                          II

       The address of the registered office of the Corporation in the State of
Delaware is the Corporation Trust Center, 1209 Orange Street, in the City of
Wilmington, County of New Castle, and the name of its registered agent at that
address is The Corporation Trust Company.

                                         III

       The purpose of the Corporation is to engage in any lawful act or
activity for which a corporation may be organized under the General Corporation
Law of the State of Delaware.

                                          IV

   
       The total number of shares of all classes of stock that the Corporation
is authorized to issue is Forty-Seven Million (47,000,000) shares, consisting of
Thirty-Nine Million (39,000,000) shares of Common Stock with a par value of
$.001 per share, Three Million (3,000,000) shares of Preferred Stock, with a par
value of $.01 per share, and Five Million (5,000,000) shares of Preference Stock
("Additional Preferred Stock") with a par value of $.001 per share.


                                          1

<PAGE>

The rights, preferences, privileges and restrictions granted to and imposed upon
such classes of shares are set forth below in this Article.
    

       A.      COMMON STOCK.

               1.      DIVIDEND RIGHTS.  Subject to the prior rights of holders
of all classes of stock at the time outstanding having prior rights as to
dividends, the holders of the Common Stock shall be entitled to receive, when
and as declared by the Board of Directors, out of any assets of the Corporation
legally available therefor, such dividends as may be declared from time to time
by the Board of Directors.

   
               2.      LIQUIDATION RIGHTS.  Upon the liquidation, dissolution
or winding up of the Corporation, the assets of the corporation shall be
distributed ratably among holders of Common Stock in proportion to the amount of
such stock owned by each such holder, subject to any liquidation rights of any
then outstanding Preference Shares (as defined in Article IV(C)below).
    
               3.      REDEMPTION.  The Common Stock is not redeemable.

               4.      VOTING RIGHTS.  The holder of each share of Common Stock
shall have the right to one vote, shall be entitled to notice of any
shareholders' meeting in accordance with the Bylaws of this Corporation, except
as otherwise provided herein, and shall be entitled to vote upon such matters
and in such manner as may be provided by law.

   
       B.      PREFERRED STOCK.  The Preferred Stock shall be divided into two
series, designated Series A Convertible Preferred Stock (the "Series A Preferred
Stock") and Series B Convertible Preferred Stock (the "Series B Preferred
Stock").  The number of shares of Series A Preferred Stock and the rights,
preferences, privileges and restrictions granted to and imposed thereon shall be
as set forth in Exhibit A attached hereto, and the number of shares of Series B
Preferred Stock and the rights, preferences, privileges and restrictions granted
to and imposed thereon shall be as set forth in Exhibit B attached hereto;
PROVIDED, HOWEVER, that upon the conversion of the shares of such series of
Preferred Stock into shares of Common Stock in accordance with the terms of
such Exhibits, no share or shares of Series A or Series B Preferred Stock shall
be reissued, and all such shares shall be canceled, retired and eliminated from
the shares that the Corporation shall be authorized to issue.
    
   
       C.      ADDITIONAL PREFERRED STOCK.  The Additional Preferred Stock
authorized by this Certificate of Incorporation may be issued from time to time
in series.  The Board of Directors is hereby authorized to fix or alter the
rights, preferences, privileges, and restrictions granted to or imposed upon any
series of Additional Preferred Stock (including the dividend rights, conversion
rights, voting rights, terms of redemption, liquidation preferences and sinking
fund terms thereof), and the number of shares constituting any such series and
the designation thereof.


                                          2

<PAGE>

Subject to compliance with applicable protective voting rights which have been
or may be granted to the Series A and Series B Preferred Stock, or Additional
Preferred Stock or series thereof (collectively, "Preference Shares") in
Certificates of Designation or the Corporations's Certificate of Incorporation
("Protective Provisions"), but notwithstanding any other rights of the
Preference Shares or any series thereof, the rights, privileges, preferences,
and restrictions of any such additional series may be subordinated to, PARI
PASSU with (including, without limitation, inclusion in provisions with respect
to liquidation and acquisition preferences, redemption, and/or approval of
matters by vote or written consent) or senior to any of those of any present or
future class or series of Preference Shares or Common Stock.  Subject to the
compliance with applicable Protective Provisions, the Board of Directors is also
authorized to increase or decrease the number of shares of any series prior or
subsequent to the issue of that series, but not below the number of shares of
such series then outstanding.  In case the number of shares of any series shall
be so decreased, the shares constituting such decrease shall resume the status
which they had prior to the adoption of the resolution originally fixing the
number of shares of such series.
    
   
       Upon restatement of the Certificate of Incorporation as set forth
herein, each authorized share of Common Stock of the Corporation issued and
outstanding prior to such restatement shall be automatically reclassified,
without any action by the holder thereof, into one-half (1/2) of one share of
fully-paid and nonassessable Common Stock.  No fractional shares of Common Stock
shall be issued upon such reclassification.  Instead of any fractional share of
Common Stock that would otherwise be issuable upon such reclassification, the
Corporation shall pay cash to the holder thereof equal to the product of such
fraction multiplied by the fair market value of one share of Common Stock after
such reclassification, as determined by the Board of Directors of the
Corporation in good faith exercising reasonable business judgment.
    

                                          V

       A.      To the fullest extent permitted by Delaware statutory or
decisional law, as amended or interpreted, no director of the Corporation shall
be personally liable to the Corporation or its stockholders for monetary damages
for breach of fiduciary duty as a director.  This Article V does not affect the
availability of equitable remedies for breach of fiduciary duties.

       B.      Any repeal or modification of this Article V shall be
prospective and shall not affect the rights under this Article V in effect at
the time of the alleged occurrence of any act or omission to act giving rise to
liability or indemnification.

                                          VI

       The Corporation shall, to the fullest extent permitted by Section 145 of
the General Corporation Law of the State of Delaware, as amended from time to
time, indemnify all persons whom it may indemnify pursuant thereto.


                                          3

<PAGE>

                                         VII

       For the management of the business and for the conduct of the affairs of
the Corporation, and in further definition, limitation and regulation of the
powers of the Corporation, of its directors and of its stockholders or any class
thereof, as the case may be, it is further provided that:

       A.      The management of the business and the conduct of the affairs of
the Corporation shall be vested in its Board of Directors.  The number of
directors which shall constitute the whole Board of Directors shall be fixed by
the Board of Directors in the manner provided in the Bylaws.

   
       B.      The Board of Directors may from time to time make, amend,
supplement or repeal the Bylaws.
    

       C.      The Directors of the Corporation need not be elected by written
ballot unless the Bylaws so provide.

   
                                         VIII
    

       Whenever a compromise or arrangement is proposed between this
Corporation and its creditors or any class of them and/or between this
Corporation and its stockholders or any class of them, any court of equitable
jurisdiction within the State of Delaware may, on the application in a summary
way of this Corporation or of any creditor or stockholder thereof, or on the
application of any receiver or receivers appointed for this Corporation under
the provisions of Section 291 of Title 8 of the Delaware Code or on the
application of trustees in dissolution or of any receiver or receivers appointed
for this Corporation under the provisions of Section 279 of Title 8 of the
Delaware Code order a meeting of the creditors or class of creditors, and/or of
the stockholders or class of stockholders of this Corporation, as the case may
be, to be summoned in such manner as the said court directs.  If a majority in
number representing three-fourths in value of the creditors or class of
creditors, and/or of the stockholders or class of stockholders of this
Corporation, as the case may be, agree to any compromise or arrangement and to
any reorganization of this Corporation as a consequence of such compromise or
arrangement, the said compromise or arrangement and the said reorganization
shall, if sanctioned by the court to which the said application has been made,
be binding on all the creditors or class of creditors, and/or on all the
stockholders or class of stockholders, of this Corporation, as the case may be,
and also on this Corporation.

                                          IX



       The Corporation reserves the right to amend, alter, change or repeal any
provision contained in this Certificate of Incorporation, in the manner now or
hereafter prescribed by statute, and all rights conferred upon the stockholders
herein are granted subject to this right."

                                         ****


                                          4

<PAGE>

   
    
   
IN WITNESS WHEREOF, Progenitor, Inc. has caused this Restated Certificate of
Incorporation to be signed by the President on this _____ day of August, 1996.
    


                                       PROGENITOR, INC.



                                       By:
                                           ----------------------------------
                                               Douglass B. Given, President
   
    


                                          5

<PAGE>

                                      EXHIBIT A

                       DESCRIPTION OF SERIES A PREFERRED STOCK

       SECTION 1. DESIGNATION OF SERIES; RANK.

       (a)     2,120,000 shares of Preferred Stock shall be designated
"Series A Convertible Preferred Stock"  (the "SERIES A PREFERRED STOCK").

       (b)     With respect to the payments of dividends, the Series A
Preferred Stock shall rank on a parity with the Series B Preferred Stock and
senior to the Common Stock.  With respect to the distribution of assets upon
liquidation, dissolution, or winding up, the Series A Stock shall rank on a
parity with the Series B Preferred Stock and senior to the Common Stock.


       SECTION 2. DIVIDENDS.  The holders of the shares of Series A Preferred
Stock shall be entitled to receive dividends out of funds legally available
therefor, when, as and if declared by the Board of Directors of the Corporation
in its discretion; provided, however, that no dividends shall be declared or
paid on the Common Stock during any final year unless the Board of Directors
during such fiscal year shall have declared and set aside for payment a dividend
on the Series A Preferred Stock.

       SECTION 3. CONVERSION.  The holders of the shares of the Series A
Preferred Stock shall have conversion rights as follows:

       (a)     CONVERSION PRIVILEGE.  Subject to Section 3(f), each share of
Series A Preferred Stock shall be convertible, at the option of the holder
thereof, at any time after the date of issuance of such shares, into such number
of duly authorized, fully paid and non-assessable shares of Common Stock at the
Series A Conversion Price at the time in effect for such shares (the "SERIES A
CONVERSION PRICE").  The initial Series A Conversion Price shall be $6.25,
subject to adjustment as set forth in Sections 3(d) and 3(e).

       (b)     AUTOMATIC CONVERSION.  In the event of (A) a Qualified Public
Offering (hereinafter defined) of the Corporation; or (B) the receipt by the
Corporation of notice from a majority of the holders of Series A Preferred Stock
electing to convert their shares, each share of Series A Preferred Stock shall
be automatically converted at the closing of the Qualified Public Offering or
the Transaction or upon receipt of such notice, without any action by the holder
thereof, into duly authorized, fully paid and non-assessable shares of Common
Stock at the then applicable Series A Conversion Price, subject to adjustment as
provided in Sections 3(d) and 3(e), plus cash in lieu of fractional shares.  The
Corporation shall make no payment or adjustment on the account of any accrued
and unpaid dividends on the Series A Preferred Stock upon surrender for
conversion.  A "QUALIFIED PUBLIC OFFERING" means an underwritten public offering
of Common Stock registered under the Securities Act of 1933, as amended, in
which the aggregate proceeds to the Corporation, net of underwriting discounts
and commissions, equal or exceed $7,500,000.


                                          1

<PAGE>

       (c)     MECHANICS OF CONVERSION.  Before any holder of shares of
Preferred Stock shall be entitled to convert such shares into Common Stock, such
holder shall surrender the certificate or certificates therefor, duly endorsed,
at the principal executive offices of the Corporation or of the transfer agent
therefor, if any, and shall give written notice to the Corporation that such
holder elects to convert all or part of the shares represented by the
certificate or certificates and shall state in writing therein the name or names
in which such holder wishes the certificate or certificates for Common Stock to
be issued.  The Corporation shall, as soon as practicable thereafter, issue and
deliver to such holder or to such holder's nominee or nominees, a certificate or
certificates for the number of full shares of Common Stock to which such holder
shall be entitled as aforesaid, together with cash in lieu of any fraction of a
share as provided in Section 3(h).  If surrendered certificates for Preferred
Stock are converted only in part, the Corporation will issue and deliver to the
holder, or to such holder's nominee or nominees, a new certificate or
certificates representing the remaining unconverted shares of Preferred Stock. 
Shares of Preferred Stock shall be deemed to have been converted as of the date
of the surrender of such shares for conversion as provided above, and the person
or persons entitled to receive the Common Stock issuable upon conversion shall
be treated for all purposes as the record holder or holders of such Common Stock
as of the date of conversion.

       (d)     CONVERSION PRICE ADJUSTMENTS FOR SERIES A PREFERRED STOCK.  The
Series A Conversion Price shall be subject to adjustment from time to time as
follows (the adjustments referred to in Subsections 3(d)(i) and (ii) shall be
referred to as a "MINIMUM RETURN ADJUSTMENT"):

       (i)     If at any time after the last closing of the offering and sale
of shares of Series A Preferred Stock pursuant to the Corporation's Confidential
Term Sheet dated November 7, 1994, as supplemented (the "Final Closing Date"),
the Corporation:

               (A)     completes an underwritten initial public offering of its
       securities (a "Terminating IPO") in which it issues any shares of Common
       Stock or other securities or rights convertible into, or entitling the
       holder thereof to receive directly or indirectly, additional shares of
       Common Stock ("Common Stock Equivalents"), or

               (B)     consummates a merger or consolidation in which more than
       fifty percent (50%) of the voting power of the Corporation is
       transferred, or a sale or other disposition of all or substantially all
       of the assets of the Corporation (a "Corporate Transaction"),

       and, in the event of a Terminating IPO, the effective price per Common
       Stock Equivalent issued, or in the event of a Corporate Transaction, the
       fair market value of the stock, securities or other property to be
       received by the holders of Common Stock of the Corporation on a per
       share as-converted basis (including the Common Stock issuable to the
       holders of Series A Preferred Stock electing to convert and taking into
       account any Minimum Return Adjustment effected as a


                                          2

<PAGE>

       result of such transaction) (the "Per Share Price"), is less than (X)
       during the first year following the Final Closing Date, 135% of the then
       applicable Series A Conversion Price, (Y) during the second year
       following the Final Closing Date, subject to Quarterly Allocation (as
       defined in Subsection 3(d)(iii)), 170% of the then applicable Series A
       Conversion Price or (Z) after the second year following the Final
       Closing Date, subject to Quarterly Allocation, 205% of the then
       applicable Series A Conversion Price, then the Series A Conversion Price
       will be reduced (but not increased) to equal (A) 74.07% of the Per Share
       Price for issuances made during the first year following the Final
       Closing Date, (B) 58.82% of the Per Share Price for issuances made
       during the second year following the Final Closing Date and (C) 48.78%
       of the Per Share Price for issuances made after the second year
       following the Final Closing Date.

       (ii)    In the event that in connection with a Terminating IPO, the Per
Share Price is not readily ascertainable, the determination of the Per Share
Price of any Common Stock Equivalent shall be determined in good faith by the
Corporation's Board of Directors based upon an allocation of the proceeds of the
Subsequent Offering among the Common Stock Equivalents, considering the special
terms, rights or privileges or other securities incorporated or included in such
Subsequent Offering.  In the event that any holder of Series A Preferred Stock
disagrees with the determination of the Board of Directors, then for a period
commencing no earlier than 60 days and ending no later than 30 days prior to
commencement of the Terminating IPO, such holder shall have the right to convert
their shares of Series A Preferred Stock into the same type and class of
securities or other consideration comprising the Terminating IPO at a discount
to the per security offering of the Subsequent Offering equal to (i) 74.07% for
a Terminating IPO consummated during the first year following the Final Closing
Date, (ii) 58.82% for a Terminating IPO consummated during the second year
following the Final Closing Date, and (iii) 48.78% for a Terminating IPO
consummated after the second year following the Final Closing Date.  Such right
of conversion shall represent the sole and exclusive remedy of such holder with
respect to such Subsequent Offering.

       (iii)   Minimum Return Adjustments will not be made after the conversion
of the Series A Preferred Stock (a "Termination Event").  Minimum Return
Adjustments may be made more than once, but will never serve to increase the
Series A Preferred Conversion Price.  Commencing during the second year
following the Final Closing Date, Minimum Return Adjustments will be allocated
8.75% per quarter to reflect the quarter of the year in which the transaction
causing such Minimum Return Adjustment occurs ("Quarterly Allocation").

       (iv)    In no event shall the Series A Conversion Price be reduced to
less than $1.00, as adjusted for any stock splits, recapitalizations or similar
events.

       (e)     ADDITIONAL ADJUSTMENTS TO THE SERIES A CONVERSION PRICE.  The
Series A Conversion Rate shall be adjusted from time to time as follows:


                                          3

<PAGE>


       (i)     If the Corporation shall (A) pay a dividend or make a
distribution on its outstanding shares of Common Stock in share of its capital
stock (whether shares of its Common Stock or capital stock of any other class),
(B) subdivide its outstanding shares of Common Stock, (C) combine its
outstanding shares of Common Stock into a smaller number of shares or (D) issue
by reclassification of its shares of Common Stock any shares of capital stock of
the Corporation, the Series A Conversion Price in effect immediately prior to
such action shall be adjusted so that the holder of any shares of Series A
Preferred Stock thereafter surrendered for conversion shall be entitled to
receive the number of shares of capital stock of the Corporation which such
holder would have owned immediately following such action had such shares of
Preferred Stock been converted immediately prior thereto.  Upon the effective
date of any such dividend, distribution, subdivision, combination or
reclassification, an adjustment made pursuant to this Section 3(e)(i) shall
become effective retroactively as of the record date for any such dividend,
distribution, subdivision, combination or reclassification.

       (ii)    If the Corporation shall issue to holders of shares of its
outstanding Common Stock generally any rights, options or warrants entitling
them to subscribe for or purchase (A) shares of its Common Stock, (B) any assets
of the Corporation, (C) any securities of the Corporation (except its Common
Stock) or of any corporation other than the Corporation or (D) any rights,
options or warrants entitling them to subscribe for or to purchase any of the
foregoing securities, whether or not such rights, options or warrants are
immediately exercisable (collectively, a "DISTRIBUTION ON COMMON STOCK"), the
Corporation shall issue to the holders of its outstanding shares of Series A
Preferred Stock the Distribution on Common Stock to which they would have been
entitled if they had converted such shares of Series A Preferred Stock
immediately prior to the record date for the purpose of determining stockholders
entitled to receive such Distribution on Common Stock.

       (f)     DE MINIMIS CHANGES.  No adjustment in the Series A Conversion
Price shall be required unless such adjustment would require an increase or
decrease of at least $.05 in such Series A Conversion Price; provided, however,
that any adjustments which by reason of this Section 3(f) are not required to be
made shall be carried forward and taken into account in any subsequent
adjustment.  All calculations under this Section 3(f) shall be made to the
nearest cent or the nearest one hundredth of a share, as the case may be.

       (g)     NOTICE OF ADJUSTMENT.  Upon the occurrence of each adjustment or
readjustment of the Series A Conversion Price pursuant to this Section 3, the
Corporation, at its expense, shall promptly compute such adjustment or
readjustment in accordance with the terms hereof and prepare and furnish to each
holder of shares of Series A Preferred Stock a certificate setting forth such
adjustment or readjustment and the computations upon which it is based.  The
Corporation shall, upon the written request at any time of any holder of Series
A Preferred Stock, furnish or cause to be furnished to such holder a like
certificate setting forth (A) such adjustment and readjustment, (B) the Series A
Conversion Price in effect at such time and (C) the number of shares of


                                          4

<PAGE>

Common Stock and the amount, if any, of other property which at the time would
be received upon the conversion of a share of the Preferred Stock held by such
holder.

       (h)     NO FRACTIONAL SHARES TO BE ISSUED.  No fractional shares or
script representing fractional shares of Common Stock shall be issued upon
conversion of shares of Preferred Stock.  Instead of any fractional share of
Common Stock that would otherwise be issuable upon conversion of shares of
Series A Preferred Stock (or specified portions thereof), the Corporation shall
pay in cash to the holders of such Preferred Stock in respect of such fraction
of a share an amount equal to the same fraction of the fair market value per
share of the amount of Common Stock into which such shares of Preferred Stock
would otherwise be convertible, as determined by the Board of Directors of the
Corporation in good faith exercising reasonable business judgment.

       (i)     EFFECT OF SALE, MERGER OR CONSOLIDATION.  In the event of any
capital reorganization of the Corporation (other than a subdivision or
combination of shares of Common Stock set forth in Section 3(e)(i)),
reclassification (other than a change in par value) of the Common Stock,
conversion of the Common Stock into securities of another corporation, or a
Transaction (each such event being referred to as a "CAPITAL CHANGE"), a share
of Series A Preferred Stock shall be convertible after such Capital Change, upon
the terms and conditions specified herein, for the number of shares of stock or
other securities or property of the Corporation or of the corporation into which
shares of Common Stock are converted or resulting from such consolidation or
surviving such merger or to which such sale shall be made, as the case may be,
to which, at the time of such Capital Change, the shares of Common Stock
issuable upon conversion of such shares of Series A Preferred Stock would have
been entitled upon such Capital Change.  In any case, if necessary, the
provisions set forth in Section 3 with respect to the rights and interests of
the holders of Series A Preferred Stock shall be appropriately adjusted so as to
be reasonably applicable to any shares of stock or other securities or property
thereafter deliverable on the conversion of each such series.  The Corporation
shall not effect any consolidation, merger or sale resulting in a Capital Change
unless, prior to or simultaneously with the consummation thereof, any successor
corporation or corporation purchasing such assets shall assume, by written
instrument, the obligation to deliver to the holders of Series A Preferred Stock
such shares of stock, securities or assets as the holders of each Preferred
Stock may be entitled to receive upon conversion of the such stock in accordance
with the foregoing provisions and all the other obligations of the Corporation
hereunder.

       (j)     RESERVATION OF SHARES FOR ISSUANCE UPON CONVERSION.  The
Corporation shall at all times reserve and keep available out of its authorized
but unissued shares of Common Stock, solely for the purpose of issuance upon
conversion of Series A Preferred Stock as provided herein, such number of shares
of Common Stock as shall then be issuable upon the conversion of all outstanding
shares of Preferred Stock.  All shares of Common Stock which shall be so issued
upon conversion of the Series A Preferred Stock as herein provided shall, when
issued, be duly authorized, validly issued, fully paid and non-assessable, free
of all liens, claims and changes and not subject to preemptive rights.


                                          5

<PAGE>

       (k)     PAYMENT OF TAXES ON SHARES ISSUED UPON CONVERSION.  The issuance
of certificates of Common Stock upon conversion of shares of the Series A
Preferred Stock shall be made without charge to the converting holders for any
tax in respect of the issuance of such certificates and such certificates shall
be issued in the respective names of, or in such names as may be directed by,
the holders of the shares of the Preferred Stock so converted; provided,
however, that the Corporation shall not be required to pay any tax which may be
payable in respect of any transfer involved in the issuance and delivery of any
such certificate in a name other than the name in which the shares of the Series
A Preferred Stock so converted were registered, and the Corporation shall not be
required to issue or deliver such certificates unless or until the person or
persons requesting the issuance thereof shall have paid to the Corporation the
amount of such tax or shall have established to the satisfaction of the
Corporation that such tax has been paid.

       (l)     OTHER EVENTS.  If any event occurs as to which in the opinion of
the Board of Directors the provisions of this Section 3 would not fairly protect
the conversion rights of the holders of Series A Preferred Stock and/or the
rights of other stockholders of the Corporation in accordance with the intent
and principles of such provisions, then the Corporation's Board of Directors
may, in its discretion, adjust the application of such provisions, in accordance
with such intent and principles, so as to protect such conversion rights and/or
the rights of other stockholders of the Corporation, if applicable.

       (m)     NO IMPAIRMENT.  The Corporation will not, by amendment of this
Exhibit A or the Certificate of Incorporation or through any reorganization,
recapitalization, transfer of assets, consolidation, merger, dissolution, issue
or sale of securities or any other voluntary action, avoid or seek to avoid the
observance or performance of any of the terms to be observed or performed
hereunder by the Corporation with regard to the Series A Preferred Stock, but
will at all times in good faith assist in the carrying out of all the provisions
of this Section 3 and in the taking of all such action as may be necessary or
appropriate in order to protect the Conversion Rights of the holders of the
Series A Preferred Stock against impairment.

       SECTION 4. PREFERENCE ON LIQUIDATION.

       (a)     LIQUIDATION TRANSACTION; LIQUIDATION PREFERENCES.  In the event
of any voluntary or involuntary liquidation, dissolution or winding-up of the
Corporation or upon a Corporate Transaction (any such event being referred to as
a "LIQUIDATION TRANSACTION"), the holders of the Series A Preferred Stock shall
have the option to either (i) convert their shares into Common Stock of the
Corporation immediately prior to the Transaction, or (ii) be entitled to be paid
out of the assets of the Corporation available for distribution to its
stockholders (whether capital or surplus), or out of the proceeds thereof, an
amount in cash equal to $6.25 per share plus any accrued and unpaid dividends on
the Series A Preferred Stock (the "SERIES A LIQUIDATION PREFERENCE"), as
provided in this Section 4.


                                          6

<PAGE>

       (b)     ORDER OF PREFERENCE AND AMOUNT.  In the event of a Liquidation
Transaction, any payment or distribution of the assets of the Corporation
(whether capital or surplus) or the proceeds thereof, shall be made to set apart
in the following order of preference and amounts after payment or provision for
payment of the debts and other liabilities of the Corporation:

       (i)     the holders of the issued and outstanding shares of the Series A
Preferred Stock and the Series B Preferred Stock shall be entitled to receive
payment of the Series A Liquidation Preference and the Series B Liquidation
Preference on a PARI PASSU basis, as described below; and

       (ii)    if the amounts available to the holders of the issued and
outstanding shares of Series A Preferred Stock and Series B Preferred Stock are
not sufficient to pay the holders thereof in full the applicable preferential
amounts set forth in Section 4(a), then the amounts available for payment to
such holders shall be paid proportionately to the holders of each such series of
Preferred Stock as a group.

       (c)     ADDITIONAL DISTRIBUTIONS.  In the event the Liquidating
Transaction is not a Corporate Transaction, then after payment in full of the
preferential amounts set forth in Section 4(a), the remaining assets of the
Corporation legally available for distribution shall be distributed ratably on a
per share basis among the holders of shares of Common Stock, the Series A
Preferred Stock and the Series B Preferred Stock.

       (d)     CONSOLIDATION, MERGER OR SALE OF ASSETS.  Notwithstanding
anything to the contrary stated herein, a consolidation or merger of the
Corporation with or into any other corporation or corporations, or a sale,
conveyance or disposition of all or substantially all of the assets of the
Corporation or the effectuation by transactions in which the Corporation is not
the surviving corporation or in which more than 50% of the voting power of the
Corporation is disposed of, shall not be deemed to be a liquidation, dissolution
or winding up within the meaning of this Section 4, but shall instead be treated
pursuant to Subsection 3(d) hereof.

       SECTION 5. VOTING.

       (a)     GENERAL.  The holders of Series A Preferred Stock shall be
entitled to vote on all matters submitted to a vote of the holders of Common
Stock generally and to receive notice of all meetings of the stockholders. 
Unless otherwise required by applicable law, the holders of shares of Series A
Preferred Stock shall vote together with the holders of the Common Stock as
though part of that class and shall have the right to that number of votes equal
to the number of shares of Common Stock into which the shares of Series A
Preferred Stock are convertible on the applicable record date.

       (b)     PROTECTIVE PROVISIONS.

       (i)     So long as any shares of Series A Preferred Stock are
outstanding, this Corporation shall not without first obtaining the approval (by
vote or written consent, as


                                          7

<PAGE>

provided by law) of the holders of at least a majority of the then outstanding
shares of Series A Preferred Stock, voting separately as a class, (A) alter or
change the rights, preferences or privileges of the shares of such Series A
Preferred Stock so as to affect adversely the shares or (B) increase the
authorized number of shares of Series A Preferred Stock.

               SECTION 6. NOTICE.  Any notice required by these provisions to
be given to the holders of shares of Series A Preferred Stock shall be deemed
given if sent U.S. certified mail, return receipt requested and postage prepaid,
or by overnight courier and addressed to each holder of record at its address
appearing on the books of the Corporation.  The date of any such notice shall be
deemed to be the date of which it is received.


                                          8

<PAGE>

                                      EXHIBIT B

                       DESCRIPTION OF SERIES B PREFERRED STOCK

       SECTION 1. DESIGNATION OF SERIES; RANK.

       (a)     880,000 shares of Preferred Stock shall be designated "Series B
Convertible Preferred Stock"  (the "SERIES B PREFERRED STOCK").

       (b)     With respect to the payments of dividends, the Series B
Preferred Stock shall rank on a parity with the Series A Preferred Stock and
senior to the Common Stock.  With respect to the distribution of assets upon
liquidation, dissolution, or winding up, the Series B Stock shall rank on a
parity with the Series A Preferred Stock and senior to the Common Stock.

       SECTION 2. DIVIDENDS.  The holders of the shares of Series B Preferred
Stock shall be entitled to receive dividends out of funds legally available
therefor, when, as and if declared by the Board of Directors of the Corporation
in its discretion; provided, however, that no dividends shall be declared or
paid on the Common Stock during any final year unless the Board of Directors
during such fiscal year shall have declared and set aside for payment a dividend
on the Series B Preferred Stock.

       SECTION 3. CONVERSION.  The holders of the shares of the Series B
Preferred Stock shall have conversion rights as follows:

       (a)     CONVERSION PRIVILEGE.  Subject to Section 3(f), each share of
Series B Preferred Stock shall be convertible, at the option of the holder
thereof, at any time after the date of issuance of such shares, into such number
of duly authorized, fully paid and non-assessable shares of Common Stock at the
Series B Conversion Price at the time in effect for such shares (the "SERIES B
CONVERSION PRICE").  The initial Series B Conversion Price shall be $6.25,
subject to adjustment as set forth in Sections 3(d) and 3(e).

       (b)     AUTOMATIC CONVERSION.  In the event of (A) a Qualified Public
Offering (hereinafter defined) of the Corporation; or (B) the receipt by the
Corporation of notice from a majority of the holders of Series B Preferred Stock
electing to convert their shares, each share of Series B Preferred Stock shall
be automatically converted at the closing of the Qualified Public Offering or
the Transaction or upon receipt of such notice, without any action by the holder
thereof, into duly authorized, fully paid and non-assessable shares of Common
Stock at the then applicable Series B Conversion Price, subject to adjustment as
provided in Sections 3(d) and 3(e), plus cash in lieu of fractional shares.  The
Corporation shall make no payment or adjustment on the account of any accrued
and unpaid dividends on the Series B Preferred Stock upon surrender for
conversion.  A "QUALIFIED PUBLIC OFFERING" means an underwritten public offering
of Common Stock registered under the Securities Act of 1933, as amended, in
which the aggregate proceeds to the Corporation, net of underwriting discounts
and commissions, equal or exceed $7,500,000.


                                          1

<PAGE>

       (c)     MECHANICS OF CONVERSION.  Before any holder of shares of
Preferred Stock shall be entitled to convert such shares into Common Stock, such
holder shall surrender the certificate or certificates therefor, duly endorsed,
at the principal executive offices of the Corporation or of the transfer agent
therefor, if any, and shall give written notice to the Corporation that such
holder elects to convert all or part of the shares represented by the
certificate or certificates and shall state in writing therein the name or names
in which such holder wishes the certificate or certificates for Common Stock to
be issued.  The Corporation shall, as soon as practicable thereafter, issue and
deliver to such holder or to such holder's nominee or nominees, a certificate or
certificates for the number of full shares of Common Stock to which such holder
shall be entitled as aforesaid, together with cash in lieu of any fraction of a
share as provided in Section 3(h).  If surrendered certificates for Preferred
Stock are converted only in part, the Corporation will issue and deliver to the
holder, or to such holder's nominee or nominees, a new certificate or
certificates representing the remaining unconverted shares of Preferred Stock. 
Shares of Preferred Stock shall be deemed to have been converted as of the date
of the surrender of such shares for conversion as provided above, and the person
or persons entitled to receive the Common Stock issuable upon conversion shall
be treated for all purposes as the record holder or holders of such Common Stock
as of the date of conversion.

       (d)     CONVERSION PRICE ADJUSTMENTS FOR SERIES B PREFERRED STOCK.  The
Series B Conversion Price shall be subject to adjustment from time to time as
follows (the adjustments referred to in Subsections 3(d)(i) and (ii) shall be
referred to as a "MINIMUM RETURN ADJUSTMENT"):

       (i)     If at any time after the last closing of the offering and sale
of shares of Series B Preferred Stock pursuant to the Corporation's Confidential
Term Sheet dated November 7, 1994, as supplemented (the "Final Closing Date"),
the Corporation:

               (A)     completes an underwritten initial public offering of its
       securities (a "Terminating IPO") in which it issues any shares of Common
       Stock or other securities or rights convertible into, or entitling the
       holder thereof to receive directly or indirectly, additional shares of
       Common Stock ("Common Stock Equivalents"), or

               (B)     consummates a merger or consolidation in which more than
       fifty percent (50%) of the voting power of the Corporation is
       transferred, or a sale or other disposition of all or substantially all
       of the assets of the Corporation (a "Corporate Transaction"),

       and, in the event of a Terminating IPO, the effective price per Common
       Stock Equivalent issued, or in the event of a Corporate Transaction,
       the fair market value of the stock, securities or other property to be
       received by the holders of Common Stock of the Corporation on a per
       share as-converted basis (including the Common Stock issuable to the 
       holders of Series B Preferred Stock electing to convert and taking into
       account any Minimum Return Adjustment effected as a


                                          2

<PAGE>

       result of such transaction) (the "Per Share Price"), is less than (X)
       during the first year following the Final Closing Date, 135% of the then
       applicable Series B Conversion Price, (Y) during the second year
       following the Final Closing Date, subject to Quarterly Allocation (as
       defined in Subsection 3(d)(iii)), 170% of the then applicable Series B
       Conversion Price or (Z) after the second year following the Final
       Closing Date, subject to Quarterly Allocation, 205% of the then
       applicable Series B Conversion Price, then the Series B Conversion Price
       will be reduced (but not increased) to equal (A) 74.07% of the Per Share
       Price for issuances made during the first year following the Final
       Closing Date, (B) 58.82% of the Per Share Price for issuances made
       during the second year following the Final Closing Date and (C) 48.78%
       of the Per Share Price for issuances made after the second year
       following the Final Closing Date.

       (ii)    In the event that in connection with a Terminating IPO, the Per
Share Price is not readily ascertainable, the determination of the Per Share
Price of any Common Stock Equivalent shall be determined in good faith by the
Corporation's Board of Directors based upon an allocation of the proceeds of the
Subsequent Offering among the Common Stock Equivalents, considering the special
terms, rights or privileges or other securities incorporated or included in such
Subsequent Offering.  In the event that any holder of Series B Preferred Stock
disagrees with the determination of the Board of Directors, then for a period
commencing no earlier than 60 days and ending no later than 30 days prior to
commencement of the Terminating IPO, such holder shall have the right to convert
their shares of Series B Preferred Stock into the same type and class of
securities or other consideration comprising the Terminating IPO at a discount
to the per security offering of the Subsequent Offering equal to (i) 74.07% for
a Terminating IPO consummated during the first year following the Final Closing
Date, (ii) 58.82% for a Terminating IPO consummated during the second year
following the Final Closing Date, and (iii) 48.78% for a Terminating IPO
consummated after the second year following the Final Closing Date.  Such right
of conversion shall represent the sole and exclusive remedy of such holder with
respect to such Subsequent Offering.

       (iii)   Minimum Return Adjustments will not be made after the conversion
of the Series B Preferred Stock (a "Termination Event").  Minimum Return
Adjustments may be made more than once, but will never serve to increase the
Series B Preferred Conversion Price.  Commencing during the second year
following the Final Closing Date, Minimum Return Adjustments will be allocated
8.75% per quarter to reflect the quarter of the year in which the transaction
causing such Minimum Return Adjustment occurs ("Quarterly Allocation").

       (iv)    In no event shall the Series B Conversion Price be reduced to
less than $1.00, as adjusted for any stock splits, recapitalizations or similar
events.

       (e)     ADDITIONAL ADJUSTMENTS TO THE SERIES B CONVERSION PRICE.  The
Series B Conversion Rate shall be adjusted from time to time as follows:


                                          3

<PAGE>

       (i)     If the Corporation shall (A) pay a dividend or make a
distribution on its outstanding shares of Common Stock in share of its capital
stock (whether shares of its Common Stock or capital stock of any other class),
(B) subdivide its outstanding shares of Common Stock, (C) combine its
outstanding shares of Common Stock into a smaller number of shares or (D) issue
by reclassification of its shares of Common Stock any shares of capital stock of
the Corporation, the Series B Conversion Price in effect immediately prior to
such action shall be adjusted so that the holder of any shares of Series B
Preferred Stock thereafter surrendered for conversion shall be entitled to
receive the number of shares of capital stock of the Corporation which such
holder would have owned immediately following such action had such shares of
Preferred Stock been converted immediately prior thereto.  Upon the effective
date of any such dividend, distribution, subdivision, combination or
reclassification, an adjustment made pursuant to this Section 3(e)(i) shall
become effective retroactively as of the record date for any such dividend,
distribution, subdivision, combination or reclassification.

       (ii)    If the Corporation shall issue to holders of shares of its
outstanding Common Stock generally any rights, options or warrants entitling
them to subscribe for or purchase (A) shares of its Common Stock, (B) any assets
of the Corporation, (C) any securities of the Corporation (except its Common
Stock) or of any corporation other than the Corporation or (D) any rights,
options or warrants entitling them to subscribe for or to purchase any of the
foregoing securities, whether or not such rights, options or warrants are
immediately exercisable (collectively, a "DISTRIBUTION ON COMMON STOCK"), the
Corporation shall issue to the holders of its outstanding shares of Series B
Preferred Stock the Distribution on Common Stock to which they would have been
entitled if they had converted such shares of Series B Preferred Stock
immediately prior to the record date for the purpose of determining stockholders
entitled to receive such Distribution on Common Stock.

       (f)     DE MINIMIS CHANGES.  No adjustment in the Series B Conversion
Price shall be required unless such adjustment would require an increase or
decrease of at least $.05 in such Series B Conversion Price; provided, however,
that any adjustments which by reason of this Section 3(f) are not required to be
made shall be carried forward and taken into account in any subsequent
adjustment.  All calculations under this Section 3(f) shall be made to the
nearest cent or the nearest one hundredth of a share, as the case may be.

       (g)     NOTICE OF ADJUSTMENT.  Upon the occurrence of each adjustment or
readjustment of the Series B Conversion Price pursuant to this Section 3, the
Corporation, at its expense, shall promptly compute such adjustment or
readjustment in accordance with the terms hereof and prepare and furnish to each
holder of shares of Series B Preferred Stock a certificate setting forth such
adjustment or readjustment and the computations upon which it is based.  The
Corporation shall, upon the written request at any time of any holder of Series
B Preferred Stock, furnish or cause to be furnished to such holder a like
certificate setting forth (A) such adjustment and readjustment, (B) the Series B
Conversion Price in effect at such time and (C) the number of shares of


                                          4

<PAGE>

Common Stock and the amount, if any, of other property which at the time would
be received upon the conversion of a share of the Preferred Stock held by such
holder.

       (h)     NO FRACTIONAL SHARES TO BE ISSUED.  No fractional shares or
script representing fractional shares of Common Stock shall be issued upon
conversion of shares of Preferred Stock.  Instead of any fractional share of
Common Stock that would otherwise be issuable upon conversion of shares of
Series B Preferred Stock (or specified portions thereof), the Corporation shall
pay in cash to the holders of such Preferred Stock in respect of such fraction
of a share an amount equal to the same fraction of the fair market value per
share of the amount of Common Stock into which such shares of Preferred Stock
would otherwise be convertible, as determined by the Board of Directors of the
Corporation in good faith exercising reasonable business judgment.

       (i)     EFFECT OF SALE, MERGER OR CONSOLIDATION.  In the event of any
capital reorganization of the Corporation (other than a subdivision or
combination of shares of Common Stock set forth in Section 3(e)(i)),
reclassification (other than a change in par value) of the Common Stock,
conversion of the Common Stock into securities of another corporation, or a
Transaction (each such event being referred to as a "CAPITAL CHANGE"), a share
of Series B Preferred Stock shall be convertible after such Capital Change, upon
the terms and conditions specified herein, for the number of shares of stock or
other securities or property of the Corporation or of the corporation into which
shares of Common Stock are converted or resulting from such consolidation or
surviving such merger or to which such sale shall be made, as the case may be,
to which, at the time of such Capital Change, the shares of Common Stock
issuable upon conversion of such shares of Series B Preferred Stock would have
been entitled upon such Capital Change.  In any case, if necessary, the
provisions set forth in Section 3 with respect to the rights and interests of
the holders of Series B Preferred Stock shall be appropriately adjusted so as to
be reasonably applicable to any shares of stock or other securities or property
thereafter deliverable on the conversion of each such series.  The Corporation
shall not effect any consolidation, merger or sale resulting in a Capital Change
unless, prior to or simultaneously with the consummation thereof, any successor
corporation or corporation purchasing such assets shall assume, by written
instrument, the obligation to deliver to the holders of Series B Preferred Stock
such shares of stock, securities or assets as the holders of each Preferred
Stock may be entitled to receive upon conversion of the such stock in accordance
with the foregoing provisions and all the other obligations of the Corporation
hereunder.

       (j)     RESERVATION OF SHARES FOR ISSUANCE UPON CONVERSION.  The
Corporation shall at all times reserve and keep available out of its authorized
but unissued shares of Common Stock, solely for the purpose of issuance upon
conversion of Series B Preferred Stock as provided herein, such number of shares
of Common Stock as shall then be issuable upon the conversion of all outstanding
shares of Preferred Stock.  All shares of Common Stock which shall be so issued
upon conversion of the Series B Preferred Stock as herein provided shall, when
issued, be duly authorized, validly issued, fully paid and non-assessable, free
of all liens, claims and changes and not subject to preemptive rights.


                                          5

<PAGE>

       (k)     PAYMENT OF TAXES ON SHARES ISSUED UPON CONVERSION.  The issuance
of certificates of Common Stock upon conversion of shares of the Series B
Preferred Stock shall be made without charge to the converting holders for any
tax in respect of the issuance of such certificates and such certificates shall
be issued in the respective names of, or in such names as may be directed by,
the holders of the shares of the Preferred Stock so converted; provided,
however, that the Corporation shall not be required to pay any tax which may be
payable in respect of any transfer involved in the issuance and delivery of any
such certificate in a name other than the name in which the shares of the Series
B Preferred Stock so converted were registered, and the Corporation shall not be
required to issue or deliver such certificates unless or until the person or
persons requesting the issuance thereof shall have paid to the Corporation the
amount of such tax or shall have established to the satisfaction of the
Corporation that such tax has been paid.

       (l)     OTHER EVENTS.  If any event occurs as to which in the opinion of
the Board of Directors the provisions of this Section 3 would not fairly protect
the conversion rights of the holders of Series B Preferred Stock and/or the
rights of other stockholders of the Corporation in accordance with the intent
and principles of such provisions, then the Corporation's Board of Directors
may, in its discretion, adjust the application of such provisions, in accordance
with such intent and principles, so as to protect such conversion rights and/or
the rights of other stockholders of the Corporation, if applicable.

       (m)     NO IMPAIRMENT.  The Corporation will not, by amendment of this
Exhibit B or the Certificate of Incorporation or through any reorganization,
recapitalization, transfer of assets, consolidation, merger, dissolution, issue
or sale of securities or any other voluntary action, avoid or seek to avoid the
observance or performance of any of the terms to be observed or performed
hereunder by the Corporation with regard to the Series B Preferred Stock, but
will at all times in good faith assist in the carrying out of all the provisions
of this Section 3 and in the taking of all such action as may be necessary or
appropriate in order to protect the Conversion Rights of the holders of the
Series B Preferred Stock against impairment.

       SECTION 4. PREFERENCE ON LIQUIDATION.

       (a)     LIQUIDATION TRANSACTION; LIQUIDATION PREFERENCES.  In the event
of any voluntary or involuntary liquidation, dissolution or winding-up of the
Corporation or upon a Corporate Transaction (any such event being referred to as
a "LIQUIDATION TRANSACTION"), the holders of the Series B Preferred Stock shall
have the option to either (i) convert their shares into Common Stock of the
Corporation immediately prior to the Transaction, or (ii) be entitled to be paid
out of the assets of the Corporation available for distribution to its
stockholders (whether capital or surplus), or out of the proceeds thereof, an
amount in cash equal to $6.25 per share plus any accrued and unpaid dividends on
the Series B Preferred Stock (the "SERIES B LIQUIDATION PREFERENCE"), as
provided in this Section 4.


                                          6

<PAGE>

       (b)     ORDER OF PREFERENCE AND AMOUNT.  In the event of a Liquidation
Transaction, any payment or distribution of the assets of the Corporation
(whether capital or surplus) or the proceeds thereof, shall be made to set apart
in the following order of preference and amounts after payment or provision for
payment of the debts and other liabilities of the Corporation:

       (i)     the holders of the issued and outstanding shares of the Series A
Preferred Stock and the Series B Preferred Stock shall be entitled to receive
payment of the Series A Liquidation Preference and the Series B Liquidation
Preference on a PARI PASSU basis, as described below; and 

       (ii)    if the amounts available to the holders of the issued and
outstanding shares of Series A Preferred Stock and Series B Preferred Stock are
not sufficient to pay the holders thereof in full the applicable preferential
amounts set forth in Section 4(a), then the amounts available for payment to
such holders shall be paid proportionately to the holders of each such series of
Preferred Stock as a group.

       (c)     ADDITIONAL DISTRIBUTIONS.  In the event the Liquidating
Transaction is not a Corporate Transaction, then after payment in full of the
preferential amounts set forth in Section 4(a), the remaining assets of the
Corporation legally available for distribution shall be distributed ratably on a
per share basis among the holders of shares of Common Stock, the Series A
Preferred Stock and the Series B Preferred Stock.

       (d)     CONSOLIDATION, MERGER OR SALE OF ASSETS.  Notwithstanding
anything to the contrary stated herein, a consolidation or merger of the
Corporation with or into any other corporation or corporations, or a sale,
conveyance or disposition of all or substantially all of the assets of the
Corporation or the effectuation by transactions in which the Corporation is not
the surviving corporation or in which more than 50% of the voting power of the
Corporation is disposed of, shall not be deemed to be a liquidation, dissolution
or winding up within the meaning of this Section 4, but shall instead be treated
pursuant to Subsection 3(d) hereof.

       SECTION 5. VOTING.

       (a)     GENERAL.  The holders of Series B Preferred Stock shall be
entitled to vote on all matters submitted to a vote of the holders of Common
Stock generally and to receive notice of all meetings of the stockholders. 
Unless otherwise required by applicable law, the holders of shares of Series B
Preferred Stock shall vote together with the holders of the Common Stock as
though part of that class and shall have the right to that number of votes equal
to the number of shares of Common Stock into which the shares of Series B
Preferred Stock are convertible on the applicable record date.

       (b)     PROTECTIVE PROVISIONS.

       (i)     So long as any shares of Series B Preferred Stock are
outstanding, this Corporation shall not without first obtaining the approval (by
vote or written consent, as


                                          7

<PAGE>

provided by law) of the holders of at least a majority of the then outstanding
shares of Series B Preferred Stock, voting separately as a class, (A) alter or
change the rights, preferences or privileges of the shares of such Series B
Preferred Stock so as to affect adversely the shares or (B) increase the
authorized number of shares of Series B Preferred Stock.

       SECTION 6. NOTICE.  Any notice required by these provisions to be given
to the holders of shares of Series B Preferred Stock shall be deemed given if
sent U.S. certified mail, return receipt requested and postage prepaid, or by
overnight courier and addressed to each holder of record at its address
appearing on the books of the Corporation.  The date of any such notice shall be
deemed to be the date of which it is received.

                                         8

<PAGE>


PROGENITOR, INC.

INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

Number           Shares
- ------           ------

SEE REVERSE FOR
CERTAIN DEFINITIONS

CUSIP 743188 10 4


THIS CERTIFIES THAT



is the owner of




FULLY PAID AND NON-ASSESSABLE SHARES OF THE  COMMON  STOCK, PAR VALUE $.001 PER
SHARE, OF

                                   PROGENITOR, INC.

transferable on the books of the Corporation by the holder hereof in person or
by duly authorized attorney upon surrender of this certificate properly
endorsed.

  This certificate is not valid unless countersigned and registered by the
Transfer Agent and  Registrar.

  WITNESS the facsimile seal of the Corporation and the facsimile signatures of
its duly authorized officers.

Dated:

/s/ Gavin B. Grover
SECRETARY

/s/ Douglass B. Given
PRESIDENT

[SEAL]

COUNTERSIGNED AND REGISTERED:

CONTINENTAL  STOCK TRANSFER & TRUST COMPANY

(JERSEY CITY, NJ)

TRANSFER AGENT

AND REGISTRAR

BY

AUTHORIZED OFFICER

<PAGE>

    The Company will furnish to any shareholder upon request and without charge
a full statement of the designation, relative rights, preferences and
limitations of the shares of each class authorized to be issued  and the
designation, relative rights, preferences and limitations of each series of
preferred shares which the Company is authorized to issue so far as the same
have been fixed, and the authority of the Board of Directors of the Company to
designate and fix the relative rights, preferences and limitations of other
series.


    The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:


TEN COM - as tenants in common

TEN ENT - as tenants by the entireties

JT TEN - as joint tenants with right of
         survivorship and not as tenants
         in common


UNIF GIFT MIN ACT  --         Custodian
                      (Cust)             (Minor)
                      under Uniform Gifts to Minors
                      Act
                            (State)
    Additional abbreviations may also be used though not in the above list.


FOR VALUE RECEIVED,   HEREBY SELL, ASSIGN AND TRANSFER UNTO

PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE



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   PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE:

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SHARES OF THE CAPITAL STOCK REPRESENTED BY THE WITHIN  CERTIFICATE, AND DO
HEREBY IRREVOCABLY CONSTITUTE AND APPOINT                             ATTORNEY
TO TRANSFER THE SAID STOCK ON THE BOOKS OF THE WITHIN NAMED  CORPORATION WITH
FULL POWER OF SUBSTITUTION IN THE PREMISES.


DATED
      ------------------------


                              -------------------------------------------------
                   NOTICE:   THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND
                             WITH THE NAME AS WRITTEN UPON THE FACE OF THE
                             CERTIFICATE IN EVERY PARTICULAR, WITHOUT
                             ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.
Signature(s) Guaranteed:


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THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION
(BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH
MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO
S.E.C. RULE 17Ad-15.


<PAGE>
                              INDEMNIFICATION AGREEMENT
   

         THIS AGREEMENT is entered into, effective as of August 9, 1996 by 
and between Progenitor, Inc., a Delaware corporation (the "Company"), and 
______________("Indemnitee").

    
         WHEREAS, it is essential to the Company to retain and attract as
directors and officers the most capable persons available; 

         WHEREAS, Indemnitee is a director and/or officer of the Company;

         WHEREAS, both the company and Indemnitee recognize the increased risk
of litigation and other claims currently being asserted against directors and
officers of corporations; and 

         WHEREAS, in recognition of Indemnitee's need for substantial
protection against personal liability in order to enhance Indemnitee's continued
and effective service to the Company, and in order to induce Indemnitee to
provide services to the Company as a director and /or officer, the Company
wishes to provide in this Agreement for the indemnification of and the advancing
of expenses to Indemnitee to the fullest extent (whether partial or complete)
permitted by Delaware law and as set forth in this Agreement, and, to the extent
insurance is maintained, for the coverage of Indemnitee under the Company's
directors' and officers' liability insurance policies.

         NOW, THEREFORE, in consideration of the above premises and of
Indemnitee's continuing to serve the Company directly or, at its request, with
another enterprise, and intending to be legally bound hereby, the parties agree
as follows:
   
         1.   CERTAIN DEFINITIONS:

              (a)  BOARD:  the Board of Directors of the Company.

              (b)  CHANGE IN CONTROL:  shall be deemed to have occurred if (i)
any "person" (as such term is used in Sections 13(d) and 14(d) of the Securities
Exchange Act of 1934, as amended (the "Act")), other than Interneuron
Pharmaceuticals, Inc. ("Interneuron"), a stockholder of Interneuron who receives
stock in the Company in substantially the same proportion as Interneuron, a
trustee or other fiduciary holding securities under an employee benefit plan of
the Company or a corporation owned directly or indirectly by the stockholders of
the Company or Interneuron in substantially the same proportions as their
ownership of stock of the Company or Interneuron, respectively (collectively
"excluded persons"), is or becomes the "Beneficial Owner" (as defined in Rule
13d-3 under the Act), directly or indirectly, of securities of the Company
representing 30% or more of the total voting power represented by the Company's
then outstanding Voting Securities, or (ii) during any period of two consecutive
years, individuals who at the beginning of such period constitute the Board and
any new director whose election by the Board or nomination for election by the
Company's stockholders was approved by a vote of at least two-thirds (2/3) of
the directors then still in office who either were
    


                                          1

<PAGE>

   

directors at the beginning of the period or whose election or nomination for
election was previously so approved, cease for any reason to constitute a
majority of the Board, or (iii) the stockholders of the Company approve a merger
or consolidation of the Company with any other corporation, other than
Interneuron, other than a merger or consolidation that would result in the
Voting Securities of the Company outstanding immediately prior thereto
continuing to represent (either by remaining outstanding or by being converted
into Voting Securities of the surviving entity) at least 50% of the total voting
power represented by the Voting Securities of the Company or such surviving
entity outstanding immediately after such merger or consolidation, or (iv) the
stockholders of the Company approve a plan of complete liquidation of the
Company or an agreement for the sale or disposition by the Company (in one
transaction or a series of transactions) of all or substantially all of the
Company's assets.

              (c)  EXPENSES:  any expense, liability, or loss, including
attorneys' fees, judgments, fines, ERISA excise taxes and penalties, amounts
paid or to be paid in settlement, any interest, assessments, or other charges
imposed thereon, and any federal, state, local, or foreign taxes imposed as a
result of the actual or deemed receipt of any payments under this Agreement,
paid or incurred in connection with investigating, defending, being a witness
in, or participating in (including on appeal), or preparing for any of the
foregoing in, any Proceeding relating to any Indemnifiable Event.

              (d)  INDEMNIFIABLE EVENT:  any event or occurrence that takes
place either prior to or after the effective date of this Agreement, related to
the fact that Indemnitee is or was a director or an officer of the Company, or
while a director or officer is or was serving at the request of the Company as a
director, officer, employee, trustee, agent, or fiduciary of another foreign or
domestic corporation, partnership, joint venture, employee benefit plan, trust,
or other enterprise, or was a director, officer, employee, or agent of a foreign
or domestic corporation that was a predecessor corporation of the Company or of
another enterprise at the request of such predecessor corporation, or related to
anything done or not done by Indemnitee in any such capacity.
    
              (e)  INDEPENDENT COUNSEL:  the person or body appointed in
connection with Section 3.
   
              (f)  POTENTIAL CHANGE IN CONTROL:  shall be deemed to have
occurred if (i) the Company enters into an agreement or arrangement, the
consummation of which would result in the occurrence of a Change in Control;
(ii) any person (including the Company) publicly announces an intention to take
or to consider taking actions that, if consummated, would constitute a Change in
Control; (iii) any person (other than an Excluded Person) who is or becomes the
Beneficial Owner, directly or indirectly, of securities of the Company
representing 10% or more of the combined voting power of the Company's then
outstanding Voting
    

<PAGE>
   
Securities, increases his beneficial ownership of such securities by 5% or more
over the percentage so owned by such person on the date hereof, or (iv) the
Board adopts a resolution to the effect that, for purposes of this Agreement, a
Potential Change in Control has occurred.

              (g)  PROCEEDING:  (i) any threatened, pending, or completed
action, suit, or proceeding, whether civil, criminal, administrative,
investigative, or other; or (ii) any inquiry, hearing, or investigation, whether
conducted by the Company or any other party, that Indemnitee in good faith
believes might lead to the institution of any such action, suit, or proceeding.

              (h)  REVIEWING PARTY:  the person or body appointed in accordance
with Section 3.


              (i)  VOTING SECURITIES:  any securities of the Company that vote
generally in the election of directors.
    

   
         2.   AGREEMENT TO INDEMNIFY.

              (a)  GENERAL AGREEMENT.  In the event Indemnitee was, is, or
becomes a party to or witness or other participant in, or is threatened to be
made a party to or witness or other participant in, a Proceeding by reason of
(or arising in part out of) an Indemnifiable Event, the Company shall indemnify
Indemnitee from and against any and all Expenses to the fullest extent permitted
by law, as the same exists or may hereafter be amended or interpreted (but in
the case of any such amendment or interpretation, only to the extent that such
amendment or interpretation permits the Company to provide broader
indemnification rights than were permitted prior thereto).  The parties hereto
intend that this Agreement shall provide for indemnification in excess of that
expressly permitted by statute, including, without limitation, any
indemnification provided by the Company's Certificate of Incorporation, its
bylaws, vote of its stockholders or disinterested directors, or applicable law.

              (b)  INITIATION OF PROCEEDING.  Notwithstanding anything in this
Agreement to the contrary, Indemnitee shall not be entitled to indemnification
pursuant to this Agreement in connection with any Proceeding initiated by
Indemnitee against the Company or any director or officer of the Company unless
(i) the Company has joined in or the Board has consented to the initiation of
such Proceeding; (ii) the Proceeding is one to enforce indemnification rights
under Section 5; or (iii) the Proceeding is instituted after a Change in Control
and Independent Counsel has approved its initiation.

              (c)  EXPENSE ADVANCES.  If so requested by Indemnitee, the
Company shall advance (within ten business days of such request) any and all
Expenses to Indemnitee (an "Expense Advance"); provided that such request shall
be accompanied by reasonable evidence of the expenses incurred by indemnitee and
that, if and to the extent that the Reviewing Party determines that Indemnitee
would not be permitted to be so indemnified under applicable law, the Company
shall be entitled to be reimbursed by Indemnitee (who hereby agrees to reimburse
the Company) for all such amounts theretofore paid.
    


                                          3
<PAGE>


If Indemnitee has commenced legal proceedings in a court of competent
jurisdiction to secure a determination that Indemnitee should be indemnified
under applicable law, as provided in Section 4, any determination made by the
Reviewing Party that Indemnitee would not be permitted to be indemnified under
applicable law shall not be binding and Indemnitee shall not be required to
reimburse the Company for any Expense Advance until a final judicial
determination is made with respect thereto (as to which all rights of appeal
therefrom have been exhausted or have lapsed).

   
         (d)  MANDATORY INDEMNIFICATION.  Notwithstanding any other provision
of this Agreement (other than Section 2(f) below), to the extent that Indemnitee
has been successful on the merits in defense of any Proceeding relating in whole
or in part to an Indemnifiable Event or in defense of any issue or matter
therein, Indemnitee shall be indemnified against all Expenses incurred in
connection therewith.
    
         (e)  PARTIAL INDEMNIFICATION.  If Indemnitee is entitled under any
provision of this Agreement to indemnification by the Company for some or a
portion of Expenses, but not, however, for the total amount thereof, the Company
shall nevertheless indemnify Indemnitee for the portion thereof to which
Indemnitee is entitled.

         (f)  PROHIBITED INDEMNIFICATION.  No indemnification pursuant to this
Agreement shall be paid by the Company on account of any Proceeding in which
judgment is rendered against Indemnitee for an accounting of profits made from
the purchase or sale by Indemnitee of securities of the Company pursuant to the
provisions of Section 16(b) of the Act or similar provisions of any federal,
state or local laws.
   
    3.   REVIEWING PARTY.  Prior to any Change in Control, the Reviewing Party
shall be any appropriate person or body consisting of a member or members of the
Board or any other person or body appointed by the Board who is not a party to
the particular Proceeding with respect to which Indemnitee is seeking
indemnification; after a Change in Control, the Reviewing Party shall be the
Independent Counsel referred to below.  With respect to all matters arising
after a Change in Control (other than a Change in Control approved by a majority
of the directors on the Board who were directors immediately prior to such
Change in Control) concerning the rights of Indemnitee to indemnity payments and
Expense Advances under this Agreement or any other agreement or under applicable
law or the Company's Certificate of Incorporation or Bylaws now or hereafter in
effect relating to indemnification for Indemnifiable Events, the Company shall
seek legal advice only from Independent Counsel selected by Indemnitee and
approved by the Company and who has not otherwise performed services for the
Company or the Indemnitee (other than in connection with indemnification
matters) within the last five years.  The Independent Counsel shall not include
any person who, under the applicable standards of professional conduct then
prevailing, would have a conflict of interest in representing either the Company
or Indemnitee in an action to determine Indemnitee's rights under this
Agreement.  Such counsel, among other things, shall render its written opinion
to the Company and Indemnitee as to whether and to what
    
                                          4

<PAGE>

extent the Indemnitee should be permitted to be indemnified under applicable
law.  The Company agrees to pay the reasonable fees of the Independent Counsel
and to indemnify fully such counsel against any and all expenses (including
attorney's fees), claims, liabilities, loss, and damages arising out of or
relating to this Agreement or the engagement of Independent Counsel pursuant
hereto.

   
    4.   INDEMNIFICATION PROCESS AND APPEAL.

         (a)  SUIT TO ENFORCE RIGHTS.  Regardless of any action by the
Reviewing Party, if Indemnitee has not received full indemnification within 60
days after making a request in accordance with Section 2(c), Indemnitee shall
have the right to enforce its indemnification rights under this Agreement by
commencing litigation, in any appropriate court having subject matter
jurisdiction thereof and in which venue is proper, seeking an intial
determination by the court or challenging any determination by the Reviewing
Party or any aspect thereof, provided, however, that such 60-day period shall be
extended for a reasonable time, not to exceed another 60 days, if the reviewing
party in good faith requires additional time for the obtaining or evaluating of
documentation and information relating thereto.  The Company hereby consents to
service of process and to appear in any such proceeding.  Any determination by
the Reviewing Party not challenged by the Indemnitee shall be binding on the
Company and Indemnitee.  The remedy provided for in this Section 4 shall be in
addition to any other remedies available to Indemnitee in law or equity.
    
         (b)  DEFENSE TO INDEMNIFICATION, BURDEN OF PROOF, AND PRESUMPTIONS.
It shall be a defense to any action brought by Indemnitee against the Company to
enforce this Agreement (other than an action brought to enforce a claim for
Expenses incurred in defending a Proceeding in advance of its final disposition
where the required undertaking has been tendered to the Company) that it is not
permissible under applicable law for the Company to indemnify Indemnitee for the
amount claimed.  In connection with any such action or any determination by the
Reviewing Party or otherwise as to whether Indemnitee is entitled to be
indemnified hereunder, the burden of proving such a defense or determination
shall be on the Company.  Neither the failure of the Reviewing Party or the
Company (including its Board, independent legal counsel, or its stockholders) to
have made a determination prior to the commencement of such action by Indemnitee
that indemnification of the claimant is proper under the circumstances because
Indemnitee has met the standard of conduct set forth in applicable law, nor an
actual determination by the Reviewing Party or Company (including its Board,
independent legal counsel, or its stockholders) that the Indemnitee had not met
such applicable standard of conduct, shall be a defense to the action or create
a presumption that the Indemnitee has not met the applicable standard of
conduct.  For purposes of this Agreement, the termination of any claim, action,
suit, or proceeding, by judgment, order, settlement (whether with or without
court approval), conviction, or upon a plea of nolo contendere, or its
equivalent,
                                          5

<PAGE>

shall not create a presumption that Indemnitee did not meet any particular
standard of conduct or have any particular belief or that a court has determined
that indemnification is not permitted by applicable law.

   
    5.   INDEMNIFICATION FOR EXPENSES INCURRED IN ENFORCING RIGHTS.  The
Company shall indemnify Indemnitee against any and all Expenses and, if
requested by Indemnitee, shall (within ten business days of such request),
advance such Expenses to Indemnitee, that are incurred by Indemnitee in
connection with any claim asserted against or covered action brought by
Indemnitee for
    
         (i)  indemnification of Expenses or Expense Advances by the Company
under this Agreement or any other agreement or under applicable law or the
Company's Certificate of Incorporation or Bylaws now or hereafter in effect
relating to indemnification for Indemnifiable Events, and/or

         (ii)  recovery under directors' and officers' liability insurance
policies maintained by the Company, regardless of whether Indemnitee ultimately
is determined to be entitled to such indemnificaiton, Expense Advances, or
insurance recovery, as the case may be.

    6.   NOTIFICATION AND DEFENSE OF PROCEEDING.

         (a)  NOTICE.  Promptly after receipt by Indemnitee of notice of the
commencement of any Proceeding, Indemnitee shall, if a claim in respect thereof
is to be made against the Company under this Agreement, notify the Company of
the commencement thereof; but the omission so to notify the Company will not
relieve the Company from any liability that it may have to Indemnitee, except as
provided in Section 6(c).

         (b)  DEFENSE.  With respect to any Proceeding as to which Indemnitee
notifies the Company of the commencement thereof, the Company shall be entitled
to participate in the Proceeding at its own expense and except as otherwise
provided below, to the extent the Company so wishes, it may assume the defense
thereof with counsel reasonably satisfactory to Indemnitee.  After notice from
the Company to Indemnitee of its election to assume the defense of any
Proceeding, the Company shall not be liable to Indemnitee under this Agreement
or otherwise for any Expenses subsequently incurred by Indemnitee in connection
with the defense of such Proceeding other than reasonable costs of investigation
or as otherwise provided below.  Indemnitee shall have the right to employ his
or her own legal counsel in such Proceeding, but all Expenses related thereto
incurred after notice from the Comapny of its assumption of the defense shall be
at Indemnitee's expense unless:  (i) the employment of legal counsel by
Indemnitee has been authorized by the Company, (ii) Indemnitee has reasonable
determined that there may be a conflict of interest between Indemnitee and the
Company in the defense of the Proceeding, (iii) after a Change in Control, the
employment of counsel by Indemnitee has been approved by the Independent
Counsel, or (iv) the Company shall not in fact have employed counsel to assume
the defense of such Proceeding,in each of which case all Expenses of the
Proceeding shall be borne by the Company.  The Company shall not be entitled

                                          6

<PAGE>

to assume the defense of any Proceeding brought by or on behalf of the Company
or as to which Indemnitee shall have made the determination provided for in (ii)
above.

                                          7
<PAGE>
   
              (c)     SETTLEMENT OF CLAIMS. The Company shall not be liable 
to indemnify Indemnitee under this Agreement or otherwise for any amounts 
paid in settlement of any Proceeding effected without the Company's written 
consent, provided, however, that if a Change in Control has occurred, the 
Company shall be liable for indemnification of Indemnitee for amounts paid in 
settlement if the Independent Counsel has approved the settlement. The 
Company shall not settle any Proceeding in any manner that would impose any 
penalty or limitation on Indemnitee without Indemnitee's written consent. The
Company shall not be liable to indemnify the Indemnitee under this Agreement 
with regard to any judicial award if the Company was not given a reasonable and
timely opportunity, at its expense, to participate in the defense of such 
action; the Company's liability hereunder shall not be excused if participation
in the Proceeding by the Company was barred by this Agreement.
    
   
         7.   NON-EXCLUSIVITY. The rights of Indemnitee hereunder shall be 
in addition to any other rights Indemnitee may have under the Company's 
Certificate of Incorporation, Bylaws, applicable law, or otherwise. To the 
extent that a change in applicable law (whether by statute or judicial 
decision) permits greater indemnification by agreement than would be afforded 
currently under
    


                                       8
<PAGE>

the Company's Certificate of Incorporation, Bylaws, applicable law, or this 
Agreement, it is the intent of the parties that Indemnitee enjoy by this 
Agreement the greater benefits so afforded by such change.
   
         8.   LIABILITY INSURANCE. To the extent the Company maintains an 
insurance policy or policies providing directors' and officers' liability 
insurance, Indemnitee shall be covered by such policy or policies, in 
accordance with its or their terms, to the maximum extent of the coverage 
available for any Company director or officer.
    
   
         9.   AMENDMENT OF THIS AGREEMENT. No supplement, modification, or 
amendment of this Agreement shall be binding unless executed in writing by 
both of the parties hereto. No waiver of any of the provisions of this 
Agreement shall operate as a waiver of any other provisions hereof (whether or 
not similar), nor shall such waiver constitute a continuing waiver. Except as 
specifically provided herein, no failure to exercise or any delay in 
exercising any right or remedy hereunder shall constitute a waiver thereof.
    
   
         10.  SUBROGATION. In the event of payment under this Agreement, the 
Company shall be subrogated to the extent of such payment to all of the 
rights of recovery of Indemnitee, who shall execute all papers required and 
shall do everything that may be necessary to secure such rights, including 
the execution of such documents necessary to enable the Company effectively 
to bring suit to enforce such rights.
    

                                       9
<PAGE>
   
         11.  NO DUPLICATION OF PAYMENTS. The Company shall not be liable 
under this Agreement to make any payment in connection with any claim made 
against Indemnitee to the extent Indemnitee has otherwise received payment 
(under any insurance policy, Bylaw, or otherwise) of the amounts otherwise 
INDEMNIFIABLE hereunder.
    
   
         12.  BINDING EFFECT. This Agreement shall be binding upon and inure 
to the benefit of and be enforceable by the parties hereto and their 
respective successors (including any direct or indirect successor by 
purchase, merger, consolidation, or otherwise to all or substantially all of 
the business and/or assets of the Company), assigns, spouses, heirs, and 
personal and legal representatives. The indemnification provided under this 
Agreement shall continue as to Indemnitee for any action taken or not taken 
while serving in an indemnified capacity pertaining to an Indemnifiable Event 
even though he or she may have ceased to serve in such capacity at the time 
of any Proceeding.
    
   
         13.  SEVERABILITY. If any provision (or portion thereof) of this 
Agreement shall be held by a court of competent jurisdiction to be invalid, 
void, or otherwise unenforceable, the remaining provisions shall remain 
enforceable to the fullest extent permitted by law. Furthermore, to the 
fullest extent possible, the provisions of this Agreement (including, without 
limitation, each portion of this Agreement containing any provision held to 
be invalid, void, or otherwise unenforceable, that is not itself invalid, 
void, or unenforceable) shall be construed so as to give effect to the intent 
manifested by the provision held invalid, void, or unenforceable.
    
   
         14.  GOVERNING LAW. This Agreement shall be governed by and 
construed and enforced in accordance with the laws of the State of Delaware 
applicable to contracts made and to be performed in such State without giving 
effect to the principles of conflicts of laws.
    
   
         15.  NOTICES. All notices, demands, and other communications 
required or permitted hereunder shall be made in writing and shall be deemed 
to have been duly given if delivered by hand, against receipt, or mailed, 
postage prepaid, certified or registered mail, return receipt requested, and 
addressed to the Company at:
    
              Progenitor, Inc.
              1507 Chamber Road
              Columbus, Ohio 43212
              Attention: President


                                       10
<PAGE>

              Notice of change of address shall be effective only when given 
in accordance with this Section. All notices complying with this Section 
shall be deemed to have been received on the date of delivery or on the third 
business day after mailing.
   
         16.  COUNTERPARTS. This Agreement may be executed in one or more 
counterparts, each of which shall be deemed an original, but all of which 
together shall constitute one and the same instrument.
    
         IN WITNESS WHEREOF, the parties hereto have duly executed and 
delivered this Agreement as of the day specified above.


                                       PROGENITOR, INC.



                                       By:
                                          --------------------------------

                                       Title:
                                             -----------------------------

                                       INDEMNITEE:



                                       -----------------------------------
                                       [Indemnitee]


                                      11

<PAGE>
                                                                   Exhibit 10.5


                                PROGENITOR, INC.

                            1996 STOCK INCENTIVE PLAN

     1.   PURPOSES OF THE PLAN.  The purposes of this Stock Incentive Plan are
to attract and retain the best available personnel for positions of substantial
responsibility, to provide additional incentive to Employees, Directors and
Consultants of the Company and its Subsidiaries and to promote the success of
the Company's business.

     2.   DEFINITIONS.  As used herein, the following definitions shall apply:

          (a)  "ADMINISTRATOR" means the Board or any of the Committees
appointed to administer the Plan.

          (b)  "AFFILIATE" and "ASSOCIATE" shall have the respective meanings
ascribed to such terms in Rule 12b-2 promulgated under the Exchange Act.

          (c)  "APPLICABLE LAWS" means the legal requirements relating to the
administration of stock incentive plans, if any, under applicable provisions of
federal securities laws, state corporate and securities laws, the Code, and the
rules of any applicable stock exchange or national market system.

          (d)  "AWARD" means the grant of an Option, SAR, Dividend Equivalent
Right, Restricted Stock, Performance Unit, Performance Share, or other right or
benefit under the Plan.

          (e)  "AWARD AGREEMENT" means the written agreement evidencing the
grant of an Award executed by the Company and the Grantee, including any
amendments thereto.

          (f)  "BOARD" means the Board of Directors of the Company.

          (g)  "CHANGE IN CONTROL" shall mean a change in ownership or control
of the Company effected through either of the following transactions:

               (i)  the direct or indirect acquisition by any person or related
group of persons (other than an acquisition from or by the Company or by a
Company-sponsored employee benefit plan or by a person that directly or
indirectly controls, is controlled by, or is under common control with, the
Company) of beneficial ownership (within the meaning of Rule 13d-3 of the
Exchange Act) of securities possessing more than fifty percent (50%) of the
total combined voting power of the Company's outstanding securities pursuant to
a tender or exchange offer made directly to the Company's stockholders which a
majority of the Continuing Directors who are not Affiliates or Associates of the
offeror do not recommend such stockholders to accept, or

               (ii) a change in the composition of the Board over a period of
thirty-six (36) months or less such that a majority of the Board members
(rounded up to the next whole


                                        1
<PAGE>


number) ceases, by reason of one or more contested elections for Board
membership, to be comprised of individuals who are Continuing Directors.

          (h)  "CODE" means the Internal Revenue Code of 1986, as amended.

          (i)  "COMMITTEE" means any committee appointed by the Board to
administer the Plan.

          (j)  "COMMON STOCK" means the common stock of the Company, as adjusted
in accordance with the provisions of Section 10, below.

          (k)  "COMPANY" means Progenitor, Inc., a Delaware corporation.

          (l)  "CONSULTANT" means any person who is engaged by the Company or
any Parent or Subsidiary to render consulting or advisory services and is
compensated for such services.

          (m)  "CONTINUING DIRECTORS" shall mean members of the Board who either
(i) have been Board members continuously for a period of at least thirty-six
(36) months or (ii) have been Board members for less than thirty-six (36) months
and were elected or nominated for election as Board members by at least a
majority of the Board members described in clause (i) who were still in office
at the time such election or nomination was approved by the Board.

          (n)  "CONTINUOUS STATUS AS AN EMPLOYEE, DIRECTOR OR CONSULTANT" means
that the employment, director or consulting relationship with the Company, any
Parent, or Subsidiary, is not interrupted or terminated.  Continuous Status as
an Employee, Director or Consultant shall not be considered interrupted in the
case of (i) any leave of absence approved by the Company or (ii) transfers
between locations of the Company or between the Company, its Parent, any
Subsidiary, or any successor.  A leave of absence approved by the Company shall
include sick leave, military leave, or any other personal leave approved by an
authorized representative of the Company.  For purposes of Incentive Stock
Options, no such leave may exceed 90 days, unless reemployment upon expiration
of such leave is guaranteed by statute or contract.

          (o)  "CORPORATE TRANSACTION" means any of the following stockholder-
approved transactions to which the Company is a party:

               (i)  a merger or consolidation in which the Company is not the
surviving entity, except for a transaction the principal purpose of which is to
change the state in which the Company is incorporated,

               (ii) the sale, transfer or other disposition of all or
substantially all of the assets of the Company (including the capital stock of
the Company's subsidiary corporations) in connection with complete liquidation
or dissolution of the Company, or


                                        2
<PAGE>


               (iii)     any reverse merger in which the Company is the
surviving entity but in which securities possessing more than fifty percent
(50%) of the total combined voting power of the Company's outstanding securities
are transferred to a person or persons different from those who held such
securities immediately prior to such merger.

          (p)  "DIRECTOR" means a member of the Board.

          (q)  "DIVIDEND EQUIVALENT RIGHT" means a right entitling the Grantee
to compensation measured by dividends paid with respect to Common Stock.

          (r)  "EMPLOYEE" means any person, including Officers and Directors,
employed by the Company or any Parent or Subsidiary of the Company.  The payment
of a director's fee by the Company shall not be sufficient to constitute
"employment" by the Company.

          (s)  "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

          (t)  "FAIR MARKET VALUE" means, as of any date, the value of Common
Stock determined as follows:

               (i)  Where there exists a public market for the Common Stock, the
Fair Market Value shall be (A) the closing sales price for a Share for the last
market trading day prior to the time of the determination (or, if no sales were
reported on that date, on the last trading date on which sales were reported) on
the New York Stock Exchange, the Nasdaq National Market or the principal
securities exchange on which the Common Stock is listed for trading, whichever
is applicable or (B) if the Common Stock is not traded on any such exchange or
national market system, the average of the closing bid and asked prices of a
Share on the Nasdaq Small Cap Market, in each case, as reported in THE WALL
STREET JOURNAL or such other source as the Administrator deems reliable; or

               (ii) In the absence of an established market of the type
described in (i), above, for the Common Stock, the Fair Market Value thereof
shall be determined by the Administrator in good faith, and such determination
shall be conclusive and binding on all persons.

          (u)  "GRANTEE" means an Employee, Director or Consultant who receives
an Award under the Plan.

          (v)  "INCENTIVE STOCK OPTION" means an Option intended to qualify as
an incentive stock option within the meaning of Section 422 of the Code.

          (w)  "NON-QUALIFIED STOCK OPTION" means an Option not intended to
qualify as an Incentive Stock Option.


                                        3
<PAGE>


          (x)  "OFFICER" means a person who is an officer of the Company within
the meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

          (y)  "OPTION" means a stock option granted pursuant to the Plan.

          (z)  "OPTIONED STOCK" means the Common Stock subject to an Option or
other Award.

          (aa) "PARENT" means a "parent corporation," whether now or hereafter
existing, as defined in Section 424(e) of the Code.

          (bb) "PERFORMANCE SHARES" means Shares or an Award denominated in
Shares which may be earned in whole or in part upon attainment of performance
criteria established by the Administrator.

          (cc) "PERFORMANCE UNITS" means monetary awards which may be earned in
whole or in part upon attainment of performance criteria established by the
Administrator.

          (dd) "PLAN" means this 1996 Stock Incentive Plan.

          (ee) "RESTRICTED STOCK" means Shares issued under the Plan to the
Grantee for such consideration, if any, and subject to such restrictions on
transfer, rights of first refusal, repurchase provisions, forfeiture provisions,
and other terms and conditions as established by the Administrator.

          (ff) "RULE 16b-3" means Rule 16b-3 promulgated under the Exchange Act
or any successor thereto.

          (gg) "SAR" means a stock appreciation right entitling the Grantee to
Shares or cash compensation measured by appreciation in the value of Common
Stock.

          (hh) "SHARE" means a share of the Common Stock.

          (ii) "SUBSIDIARY" means a "subsidiary corporation," whether now or
hereafter existing, as defined in Section 424(f) of the Code.

          (jj) "SUBSIDIARY DISPOSITION" means the disposition by the Company of
its equity holdings in any subsidiary corporation effected by a merger or
consolidation involving that subsidiary corporation, the sale of all or
substantially all of the assets of that subsidiary corporation or the Company's
sale or distribution of substantially all of the outstanding capital stock of
such subsidiary corporation.

     3.   STOCK SUBJECT TO THE PLAN.

          (a)  Subject to the provisions of Section 10, below, the maximum
aggregate number of Shares which may be issued pursuant to all Awards (including
Incentive Stock


                                        4

<PAGE>

   
Options) is 1,700,000 Shares (determined as of May 13, 1996, the date of
approval of the Plan by the Board), of which 150,000 Shares are allocated
exclusively for Awards to Directors. The Shares may be authorized, but
unissued, or reacquired Common Stock.
    
          (b)  If an Award expires or becomes unexercisable without having been
exercised in full, or is surrendered pursuant to an Award exchange program, or
if any unissued Shares are retained by the Company upon exercise of an Award in
order to satisfy the exercise price for such Award or any withholding taxes due
with respect to such Award, such unissued or retained Shares shall become
available for future grant or sale under the Plan (unless the Plan has
terminated).  Shares that actually have been issued under the Plan pursuant to
an Award shall not be returned to the Plan and shall not become available for
future distribution under the Plan, except that if unvested Shares are
forfeited, or repurchased by the Company at their original purchase price, such
Shares shall become available for future grant under the Plan.

     4.   ADMINISTRATION OF THE PLAN.

          (a)  PLAN ADMINISTRATOR.

               (i)  ADMINISTRATION WITH RESPECT TO DIRECTORS AND OFFICERS. 
With respect to grants of Awards to Directors or Employees who are also Officers
or Directors of the Company, the Plan shall be administered by (A) the Board or
(B) a Committee designated by the Board, which Committee shall be constituted in
such a manner as to satisfy the Applicable Laws and to permit such grants and
related transactions under the Plan to be exempt from Section 16(b) of the
Exchange Act in accordance with Rule 16b-3.  Once appointed, such Committee
shall continue to serve in its designated capacity until otherwise directed by
the Board.

               (ii) ADMINISTRATION WITH RESPECT TO CONSULTANTS AND OTHER
EMPLOYEES.  With respect to grants of Awards to Employees or Consultants who are
neither Directors nor Officers of the Company, the Plan shall be administered by
(A) the Board or (B) a Committee designated by the Board, which committee shall
be constituted in such a manner as to satisfy the Applicable Laws.  Once
appointed, such Committee shall continue to serve in its designated capacity
until otherwise directed by the Board.  The Board may authorize one or more
Officers to grant such Awards and may limit such authority by requiring that
such Awards must be reported to and ratified by the Board or a Committee within
six (6) months of the grant date, and if so ratified, shall be effective as of
the grant date.

          (b)  POWERS OF THE ADMINISTRATOR.  Subject to Applicable Laws, the
provisions of the Plan (including any other powers given to the Administrator
hereunder) and except as otherwise provided by the Board, the Administrator
shall have the authority, in its discretion:

               (i)  to select the Employees, Directors and Consultants to whom
Awards may from time to time be granted hereunder;

               (ii) to determine whether and to what extent Awards are granted
hereunder;

                                       5

<PAGE>


               (iii)     to determine the number of Shares to be covered by each
Award granted hereunder;

               (iv) to approve forms of Award Agreement for use under the Plan;

               (v)  to determine the terms and conditions of any Award granted
hereunder;

               (vi) to amend the terms of any outstanding Award granted under
the Plan including a reduction in the exercise price (or base amount on which
appreciation is measured) of any Award to reflect a reduction in the Fair Market
Value of the Common Stock since the grant date of the Award, provided that any
amendment that would adversely affect the Grantee's rights under an outstanding
Award shall not be made without the Grantee's written consent;

               (vii)     to construe and interpret the terms of the Plan and
Awards granted pursuant to the Plan; and

               (viii)    to take such other action, not inconsistent with the
terms of the Plan, as the Administrator deems appropriate.

          (c)  EFFECT OF ADMINISTRATOR'S DECISION.  All decisions,
determinations and interpretations of the Administrator shall be final and
binding on the Grantees and any other holders of Awards intended by the
Administrator to be affected thereby.

     5.   ELIGIBILITY.  Awards other than Incentive Stock Options may be granted
to Employees, Directors and Consultants.  Incentive Stock Options may be granted
only to Employees.  An Employee, Director or Consultant who has been granted an
Award may, if otherwise eligible, be granted additional Awards.  Awards may be
granted to such Employees of the Company and its subsidiaries who are residing
in foreign jurisdictions as the Administrator in its sole discretion may
determine from time to time.  The Administrator may establish additional terms,
conditions, rules or procedures to accommodate the rules or laws of applicable
foreign jurisdictions and to afford Grantees favorable treatment under such
laws; provided, however, that no Award shall be granted under any such
additional terms, conditions, rules or procedures with terms or conditions which
are inconsistent with the provisions of the Plan.

     6.   TERMS AND CONDITIONS OF AWARDS.

          (a)  TYPE OF AWARDS.  The Administrator is authorized under the Plan
to award any type of arrangement to an Employee, Director or Consultant that is
not inconsistent with the provisions of the Plan and that by its terms involves
or might involve the issuance of (i) Shares, (ii) an Option, a SAR or similar
right with an exercise or conversion privilege at a fixed or variable price
related to the Common Stock and/or the passage of time, the occurrence of one or
more events, or the satisfaction of performance criteria or other conditions, or
(iii) any other security with the value derived from the value of the Common
Stock. Such awards include, without limitation, Options, SARs, sales or bonuses
of Restricted Stock, Dividend Equivalent


                                        6
<PAGE>


Rights, Performance Units or Performance Shares, and an Award may consist of one
such security or benefit, or two or more of them in any combination or
alternative.

          (b)  DESIGNATION OF AWARD.  Each Award shall be designated in the
Award Agreement.  In the case of an Option, the Option shall be designated as
either an Incentive Stock Option or a Non-Qualified Stock Option.  However,
notwithstanding such designation, to the extent that the aggregate Fair Market
Value of Shares subject to Options designated as Incentive Stock Options which
become exercisable for the first time by a Grantee during any calendar year
(under all plans of the Company or any Parent or Subsidiary) exceeds $100,000,
such excess Options, to the extent of the Shares covered thereby in excess of
the foregoing limitation,  shall be treated as Non-Qualified Stock Options.  For
this purpose, Incentive Stock Options shall be taken into account in the order
in which they were granted, and the Fair Market Value of the Shares shall be
determined as of the date the Option with respect to such Shares is granted.

          (c)  CONDITIONS OF AWARD.  Subject to the terms of the Plan, the
Administrator shall determine the provisions, terms, and conditions of each
Award including, but not limited to, the Award vesting schedule, repurchase
provisions, rights of first refusal, forfeiture provisions, form of payment
(cash, Shares, or other consideration) upon settlement of the Award, payment
contingencies, and satisfaction of any performance criteria.  The performance
criteria established by the Administrator may be based on any one of, or
combination of, increase in share price, earnings per share, total shareholder
return, return on equity, return on assets, return on investment, net operating
income, cash flow, revenue, economic value added, personal management
objectives, or other measure of performance selected by the Administrator.
Partial achievement of the specified criteria may result in a payment or vesting
corresponding to the degree of achievement as specified in the Award Agreement.

          (d)  TERM OF AWARD.  The term of each Award shall be the term stated
in the Award Agreement, provided, however, that the term of an Incentive Stock
Option shall be no more than ten (10) years from the date of grant thereof.
However, in the case of an Incentive Stock Option granted to a Grantee who, at
the time the Option is granted, owns stock representing more than ten percent
(10%) of the voting power of all classes of stock of the Company or any Parent
or Subsidiary, the term of the Incentive Stock Option shall be five (5) years
from the date of grant thereof or such shorter term as may be provided in the
Award Agreement.

          (e)  TRANSFERABILITY OF AWARDS.  Incentive Stock Options may not be
sold, pledged, assigned, hypothecated, transferred, or disposed of in any manner
other than by will or by the laws of descent or distribution and may be
exercised, during the lifetime of the Grantee, only by the Grantee.  Other
Awards shall be transferable to the extent provided in the Award Agreement.

          (f)  TIME OF GRANTING AWARDS.  The date of grant of an Award shall for
all purposes be the date on which the Administrator makes the determination to
grant such Award, or such other date as is determined by the Administrator.
Notice of the grant determination shall


                                        7
<PAGE>


be given to each Employee, Director or Consultant to whom an Award is so granted
within a reasonable time after the date of such grant.

     7.   AWARD EXERCISE OR PURCHASE PRICE, CONSIDERATION, TAXES AND RELOAD
     OPTIONS.

          (a)  EXERCISE OR PURCHASE PRICE.  The exercise or purchase price, if
any, for an Award shall be as follows:

               (i)   In the case of an Incentive Stock Option:

                     (A) granted to an Employee who, at the time of the grant of
such Incentive Stock Option owns stock representing more than 10% of the voting
power of all classes of stock of the Company or any Parent or Subsidiary, the
per Share exercise price shall be not less than 110% of the Fair Market Value
per Share on the date of grant.

                     (B) granted to any Employee other than an Employee
described in the preceding paragraph, the per Share exercise price shall be not
less than 100% of the Fair Market Value per Share on the date of grant.

               (ii)  In the case of a Non-Qualified Stock Option, the per Share
exercise price shall be not less than 85% of the Fair Market Value per Share on
the date of grant unless otherwise determined by the Administrator.

               (iii) In the case of other Awards, such price as is determined
by the Administrator.

          (b)  CONSIDERATION.  Subject to Applicable Laws, the consideration to
be paid for the Shares to be issued upon exercise or purchase of an Award
including the method of payment, shall be determined by the Administrator (and,
in the case of an Incentive Stock Option, shall be determined at the time of
grant).  In  addition to any other types of consideration the Administrator may
determine, the Administrator is authorized to accept as consideration for Shares
under the Plan the following:

               (i)    cash;

               (ii)   check;

               (iii)  delivery of Grantee's promissory note with such recourse,
interest, security, and redemption provisions as the Administrator in its
discretion determines as appropriate;

               (iv)   surrender of  Shares (including withholding of Shares
otherwise deliverable upon exercise of the Award) which have a Fair Market Value
on the date of surrender equal to the aggregate exercise price of the Shares as
to which said Award shall be exercised (but only to the extent that such
exercise of the Award would not result in an accounting compensation charge with
respect to the Shares used to pay the exercise price unless otherwise determined
by the Administrator);


                                        8
<PAGE>


               (v)    delivery of a properly executed exercise notice together
with such other documentation as the Administrator and the broker, if
applicable, shall require to effect an exercise of the Award and delivery to the
Company of the sale or loan proceeds required to pay the exercise price; or

               (vi)   any combination of the foregoing methods of payment.

In making its determination as to the type of consideration to accept, the
Administrator shall consider if acceptance of such consideration may be
reasonably expected to benefit the Company.

          (c)  TAXES.  No Shares shall be delivered under the Plan to any
Grantee or other person until such Grantee or other person has made arrangements
acceptable to the Administrator for the satisfaction of federal, state, and
local income and employment tax withholding obligations, including, without
limitation, obligations incident to the receipt of Shares or the disqualifying
disposition of Shares received on exercise of an Incentive Stock Option. Upon
exercise of an Award, the Company shall withhold from Grantee an amount
sufficient to satisfy such tax obligations.

          (d)  RELOAD OPTIONS.  In the event the exercise price or tax
withholding of an Option is satisfied by the Company or the Grantee's employer
withholding Shares otherwise deliverable to the Grantee, the Administrator may
issue the Grantee an additional Option, with terms identical to the Award
Agreement under which the Option was exercised, but at an exercise price as
determined by the Administrator in accordance with the Plan.

     8.   EXERCISE OF AWARD.

          (a)  PROCEDURE FOR EXERCISE; RIGHTS AS A SHAREHOLDER.

               (i)    Any Award granted hereunder shall be exercisable at such
times and under such conditions as determined by the Administrator under the
terms of the Plan and specified in the Award Agreement.

               (ii)   An Award shall be deemed to be exercised when written
notice of such exercise has been given to the Company in accordance with the
terms of the Award by the person entitled to exercise the Award and full payment
for the Shares with respect to which the Award is exercised has been received by
the Company.  Until the issuance (as evidenced by the appropriate entry on the
books of the Company or of a duly authorized transfer agent of the Company) of
the stock certificate evidencing such Shares, no right to vote or receive
dividends or any other rights as a shareholder shall exist with respect to
Optioned Stock, notwithstanding the exercise of an Option or other Award.  The
Company shall issue (or cause to be issued) such stock certificate promptly upon
exercise of the Award.  No adjustment will be made for a dividend or other right
for which the record date is prior to the date the stock certificate is issued,
except as provided in the Award Agreement or Section 10, below.


                                        9
<PAGE>


          (b)  EXERCISE OF AWARD FOLLOWING TERMINATION OF EMPLOYMENT, DIRECTOR
OR CONSULTING RELATIONSHIP.

               (i)    An Award may not be exercised after the termination date
of such Award set forth in the Award Agreement and may be exercised following
the termination of a Grantee's Continuous Status as an Employee, Director or
Consultant only to the extent provided in the Award Agreement.

               (ii)   Where the Award Agreement permits a Grantee to exercise an
Award following the termination of the Grantee's Continuous Status as an
Employee, Director or Consultant for a specified period, the Award shall
terminate to the extent not exercised on the last day of the specified period or
the last day of the original term of the Award whichever occurs first.

               (iii)  Any Award designated as an Incentive Stock Option to the
extent not exercised within the time permitted by law for the exercise of
Incentive Stock Options following the termination of a Grantee's Continuous
Status as an Employee, Director or Consultant shall convert automatically to a
Non-Qualified Stock Option and thereafter shall be exercisable as such to the
extent exercisable by its terms for the period specified in the Award Agreement.

          (c)  BUYOUT PROVISIONS.  The Administrator may at any time offer to
buy out for a payment in cash or Shares, an Award previously granted, based on
such terms and conditions as the Administrator shall establish and communicate
to the Grantee at the time that such offer is made.

     9.   CONDITIONS UPON ISSUANCE OF SHARES.

     (a)  Shares shall not be issued pursuant to the exercise of an Award unless
the exercise of such Award and the issuance and delivery of such Shares pursuant
thereto shall comply with all Applicable Laws, and shall be further subject to
the approval of counsel for the Company with respect to such compliance.

     (b)  As a condition to the exercise of an Award, the Company may require
the person exercising such Award to represent and warrant at the time of any
such exercise that the Shares are being purchased only for investment and
without any present intention to sell or distribute such Shares if, in the
opinion of counsel for the Company, such a representation is required by any
Applicable Laws.

     10.  ADJUSTMENTS UPON CHANGES IN CAPITALIZATION.  Subject to any required
action by the shareholders of the Company, the number of Shares covered by each
outstanding Award, and the number of Shares which have been authorized for
issuance under the Plan but as to which no Awards have yet been granted or which
have been returned to the Plan, as well as the price per share of Common Stock
covered by each such outstanding Award, shall be proportionately adjusted for
any increase or decrease in the number of issued shares of Common Stock
resulting from a stock split, reverse stock split, stock dividend, combination
or reclassification of the



                                       10
<PAGE>


Common Stock, or any other similar event resulting in an increase or decrease in
the number of issued shares of Common Stock.  Such adjustment shall be made by
the Administrator, and its determination in that respect shall be final, binding
and conclusive.  Except as expressly provided herein, no issuance by the Company
of shares of stock of any class, or securities convertible into shares of stock
of any class, shall affect, and no adjustment by reason hereof shall be made
with respect to, the number or price of Shares subject to an Award.

     11.  CORPORATE TRANSACTIONS/CHANGES IN CONTROL/SUBSIDIARY DISPOSITIONS.

   
          (a)  Should any Corporate Transaction occur while an Grantee's
Continuous Status as an Employee, Director or Consultant has not terminated,
then each outstanding Award held by such Grantee, shall become fully vested 
and exercisable and be released from any restrictions on transfer and 
repurchase or forfeiture rights, immediately prior to the specified effective 
date of such Corporate Transaction, for all of the Shares at the time
represented by such Award and may be exercised with respect to any or all of 
such Shares represented by such Award.  Effective upon the consummation of the
Corporate Transaction, all outstanding Awards under the Plan shall terminate 
unless assumed by the successor company or its Parent.
    

          (b)  Should a Change in Control (other than a Change in Control which
is also a Corporate Transaction) occur while an Grantee's Continuous Status as
an Employee, Director or Consultant has not terminated, then each outstanding
Award held by such Grantee, unless otherwise determined by the Administrator,
shall become fully vested and exercisable and be released from any restrictions
on transfer and repurchase or forfeiture rights, immediately prior to the
specified effective date of such Change in Control, for all of the Shares at the
time subject to such Award and may be exercised with respect to any or all of
such Shares represented by such Award.  Each such Award shall remain so
exercisable until the expiration or sooner termination of the applicable Award
term.

          (c)  Should a Subsidiary Disposition occur while an Grantee's
Continuous Status as an Employee, Director or Consultant with the subsidiary
corporation involved in such Subsidiary Disposition has not terminated, then
each outstanding Award held by such Grantee, unless otherwise determined by the
Administrator, shall become fully vested and exercisable and be released from
any restrictions on transfer and repurchase or forfeiture rights, immediately
prior to the specified effective date of such Subsidiary Disposition, for all of
the Shares at the time subject to such Award and may be exercised with respect
to any or all of such Shares represented by such Award.  Each such Award shall
remain so exercisable until the expiration or sooner termination of the Award
term.

          (d)  The portion of any Incentive Stock Option accelerated under this
Section 11 in connection with a Corporate Transaction, Change in Control or
Subsidiary Disposition shall remain exercisable as an Incentive Stock Option
under the Code only to the extent the $100,000 dollar limitation of
Section 422(d) of the Code is not exceeded.  To the extent such dollar
limitation is exceeded, the accelerated excess portion of such Option shall be
exercisable as a Non-Qualified Stock Option.


                                       11
<PAGE>


     12.  TERM OF PLAN.  The Plan shall become effective upon the earlier to
occur of its adoption by the Board or its approval by the shareholders of the
Company.  It shall continue in effect for a term of ten (10) years unless sooner
terminated.

     13.  AMENDMENT, SUSPENSION OR TERMINATION OF THE PLAN.

          (a)  The Board may at any time amend, suspend or terminate the Plan.
To the extent necessary and desirable to comply with Applicable Laws, the
Company shall obtain shareholder approval of any Plan amendment in such a manner
and to such a degree as required.

          (b)  No Award may be granted during any suspension or after
termination of the Plan.

          (c)  Any amendment, suspension or termination of the Plan shall not
affect Awards already granted, and such Awards shall remain in full force and
effect as if the Plan had not been amended, suspended or terminated, unless
mutually agreed otherwise between the Grantee and the Administrator, which
agreement must be in writing and signed by the Grantee and the Company.

     14.  RESERVATION OF SHARES.

          (a)  The Company, during the term of the Plan, will at all times
reserve and keep available such number of Shares as shall be sufficient to
satisfy the requirements of the Plan.

          (b)  The inability of the Company to obtain authority from any
regulatory body having jurisdiction, which authority is deemed by the Company's
counsel to be necessary to the lawful issuance and sale of any Shares hereunder,
shall relieve the Company of any liability in respect of the failure to issue or
sell such Shares as to which such requisite authority shall not have been
obtained.

     15.  NO EFFECT ON TERMS OF EMPLOYMENT.  The Plan shall not confer upon any
Grantee any right with respect to continuation of employment or consulting
relationship with the Company, nor shall it interfere in any way with his or her
right or the Company's right to terminate his or her employment or consulting
relationship at any time, with or without cause.

     16.  SHAREHOLDER APPROVAL.  Continuance of the Plan with respect to the
grant of Incentive Stock Options shall be subject to approval by the
shareholders of the Company within twelve (12) months before or after the date
the Plan is adopted.  Such shareholder approval shall be obtained in the degree
and manner required under Applicable Laws.


                                       12
<PAGE>


                      PROGENITOR, INC. 1996 STOCK INCENTIVE PLAN

                                STOCK OPTION AGREEMENT

I.     NOTICE OF STOCK OPTION GRANT

       Optionee's Name and Address:
                                       -----------------------------------

                                       -----------------------------------

                                       -----------------------------------

       You have been granted an option to purchase shares of Common Stock of
the Company, subject to the terms and conditions of the Plan and this Option
Agreement, as follows:

       Grant Number
                                       -----------------------------------
       Date of Grant
                                       -----------------------------------
       Vesting Commencement Date
                                       -----------------------------------
       Exercise Price per Share        $
                                        ----------------------------------
       Total Number of Shares Granted
                                       -----------------------------------
       Total Exercise Price            $
                                       -----------------------------------
       Type of Option:                           Incentive Stock Option
                                       ------
                                                 Non-Qualified Stock Option
                                       ------
       Term/Expiration Date:
                                       -----------------------------------

VESTING SCHEDULE:

       Subject to other limitations set forth in this Agreement, this Option
may be exercised, in whole or in part, in accordance with the following
schedule:


TERMINATION PERIOD:

       This Option may be exercised for THREE (3) months after termination of
the Optionee's employment or consulting relationship, or such longer period as
may be applicable upon death or disability of Optionee as provided in the
Agreement.  In the event of the Optionee's change in status from Employee to
Consultant or Consultant to Employee, this Option Agreement shall remain in
effect; provided, however, that in the event of a change in status from Employee
to Consultant, Optionee's Incentive Stock Option shall cease to be treated as an
Incentive Stock Option and shall be treated as a Non-Qualified Stock Option on
the ninety-first (91st) day

                                          1

<PAGE>

following such change in status.  In no event shall this Option be exercised
later than the Term/Expiration Date as provided above.


                                          2

<PAGE>

II.    AGREEMENT

       1.      GRANT OF OPTION.  Progenitor, Inc., a Delaware corporation (the
"Company"), hereby grants to the Optionee named in the Notice of Stock Option
Grant (the "Optionee"), an option (the "Option") to purchase the total number of
shares of Common Stock (the "Shares") set forth in the Notice of Stock Option
Grant, at the exercise price per share set forth in the Notice of Stock Option
Grant (the "Exercise Price") subject to the terms, definitions and provisions of
the Company's 1996 Stock Incentive Plan (the "Plan") adopted by the Company,
which is incorporated herein by reference.  Unless otherwise defined herein, the
terms defined in the Plan shall have the same defined meanings in this Option
Agreement.

       If designated in the Notice of Stock Option Grant as an Incentive Stock
Option, this Option is intended to qualify as an Incentive Stock Option as
defined in Section 422 of the Code.  Nevertheless, to the extent that it exceeds
the $100,000 rule of Section 422(d) of the Code, this Option shall be treated as
a Non-Qualified Stock Option.

       2.      EXERCISE OF OPTION.

               (a)     RIGHT TO EXERCISE.  This Option shall be exercisable
during its term in accordance with the Vesting Schedule set out in the Notice of
Stock Option Grant and with the applicable provisions of the Plan and this
Option Agreement.  In the event of termination of Optionee's Continuous Status
as an Employee, Director or Consultant, this Option shall be exercisable in
accordance with the applicable provisions of the Plan and this Option Agreement.
This Option shall be subject to the provisions of Section 11 of the Plan
relating to the exercisability or termination of the Option in the event of a
Corporate Transaction, Change in Control or Subsidiary Disposition.

               (b)     METHOD OF EXERCISE.  This Option shall be exercisable
only by delivery of an Exercise Notice (attached as Exhibit A) which shall state
the election to exercise the Option, the whole number of Shares in respect of
which the Option is being exercised, such other representations and agreements
as to the holder's investment intent with respect to such Shares and such other
provisions as may be required by the Administrator.  Such Exercise Notice shall
be signed by the Optionee and shall be delivered in person or by certified mail
to the Secretary of the Company accompanied by payment of the Exercise Price.
The Option shall be deemed to be exercised upon receipt by the Company of such
written notice accompanied by the Exercise Price.

               No Shares will be issued pursuant to the exercise of the Option
unless such issuance and such exercise shall comply with all Applicable Laws.
Assuming such compliance, for income tax purposes, the Shares shall be
considered transferred to the Optionee on the date on which the Option is
exercised with respect to such Shares.

               (c)     TAXES.  No Shares will be issued to the Optionee or
other person pursuant to the exercise of the Option until the Optionee or other
person has made arrangements


                                          3

<PAGE>

acceptable to the Administrator for the satisfaction of foreign, federal, state
and local income and employment tax withholding obligations.

       3.      METHOD OF PAYMENT.  Payment of the Exercise Price shall be by
any of the following, or a combination thereof, at the election of the Optionee;
provided, however, that such exercise method does not then violate an Applicable
Law:

               (a)     cash;

               (b)     check;

               (c)     [SURRENDER OF SHARES OF COMMON STOCK OF THE COMPANY
(INCLUDING WITHHOLDING OF SHARES OTHERWISE DELIVERABLE UPON EXERCISE OF THIS
OPTION) WHICH HAVE A FAIR MARKET VALUE ON THE DATE OF SURRENDER EQUAL TO THE
EXERCISE PRICE OF THE SHARES AS TO WHICH THE OPTION IS BEING EXERCISED (BUT ONLY
TO THE EXTENT THAT SUCH EXERCISE OF THE OPTION WOULD NOT RESULT IN AN ACCOUNTING
COMPENSATION CHARGE WITH RESPECT TO THE SHARES USED TO PAY THE EXERCISE PRICE
UNLESS OTHERWISE DETERMINED BY THE ADMINISTRATOR); OR

               (d)     DELIVERY OF A PROPERLY EXECUTED EXERCISE NOTICE TOGETHER
WITH SUCH OTHER DOCUMENTATION AS THE ADMINISTRATOR AND THE BROKER, IF
APPLICABLE, SHALL REQUIRE TO EFFECT AN EXERCISE OF THE OPTION AND DELIVERY TO
THE COMPANY OF THE SALE OR LOAN PROCEEDS REQUIRED TO PAY THE EXERCISE PRICE].

       [ADD ANY ADDITIONAL EXERCISE METHODS, SUCH AS RECOURSE LOAN]

       4.      RESTRICTIONS ON EXERCISE.  This Option, if an Incentive Stock
Option, may not be exercised until such time as the Plan has been approved by
the stockholders of the Company.  In addition, this Option may not be exercised
if the issuance of the Shares subject to the Option upon such exercise would
constitute a violation of any Applicable Laws.

       5.      TERMINATION OF RELATIONSHIP.  In the event the Optionee's
Continuous Status as an Employee, Director or Consultant terminates, the
Optionee may, to the extent otherwise so entitled at the date of such
termination (the "Termination Date"), exercise this Option during the
Termination Period set out in the Notice of Stock Option Grant.  Except as
provided in Sections 6 and 7, below, to the extent that the Optionee was not
entitled to exercise this Option on the Termination Date, or if the Optionee
does not exercise this Option within the Termination Period, the Option shall
terminate.

       6.      DISABILITY OF OPTIONEE.  In  the Optionee's Continuous Status as
an Employee, Director or Consultant terminates as a result of his or her
disability, the Optionee may, but only within twelve (12) months from the
Termination Date (and in no event later than the Term/Expiration Date), exercise
the Option to the extent otherwise entitled to exercise it on the Termination
Date; provided, however, that if such disability is not a "disability" as such
term is defined in Section 22(e)(3) of the Code and the Option is an Incentive
Stock Option, such Incentive Stock Option shall cease to be treated as an
Incentive Stock Option and shall be treated as a Non-Qualified Stock Option on
the ninety-first (91st) day following the Termination Date.  To the extent that
the Optionee was not entitled to exercise the Option on the Termination Date,


                                          4

<PAGE>

or if the Optionee does not exercise such Option to the extent so entitled
within the time specified herein, the Option shall terminate.

       7.      DEATH OF OPTIONEE.  In the event of the Optionee's death, the
Option may be exercised at any time within twelve (12) months following the date
of death (and in no event later than the Term/Expiration Date), by the
Optionee's estate or by a person who acquired the right to exercise the Option
by bequest or inheritance, but only to the extent the Optionee could exercise
the Option at the date of death.

       8.      TRANSFERABILITY OF OPTION.  This Option, if an Incentive Stock
Option, may not be transferred in any manner otherwise than by will or by the
laws of descent or distribution and may be exercised during the lifetime of the
Optionee only by the Optionee.  This Option, if a Non-Qualified Stock Option,
may be transferred by the Optionee in a manner and to the extent acceptable to
the Administrator as evidenced by a writing signed by the Company and the
Optionee.  The terms of this Option shall be binding upon the executors,
administrators, heirs and successors of the Optionee.

       9.      TERM OF OPTION.  This Option may be exercised only within the
term set out in the Notice of Stock Option Grant, and may be exercised during
such term only in accordance with the Plan and the terms of this Option
Agreement.

   
       10.     TAX CONSEQUENCES.  Set forth below is a brief summary as of the
date of this Option Agreement of some of the federal tax consequences of 
exercise of this Option and disposition of the Shares.  THIS SUMMARY IS 
NECESSARILY INCOMPLETE, AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO 
CHANGE.  OPTIONEE SHOULD CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION 
OR DISPOSING OF THE SHARES.
    

   
               (a)     EXERCISE OF INCENTIVE STOCK OPTION.  If this Option
qualifies as an Incentive Stock Option, there will be no regular federal income
tax liability upon the exercise of the Option, although the excess, if any, 
of the Fair Market Value of the Shares on the date of exercise over the 
Exercise Price will be treated as an adjustment to the alternative minimum 
tax for federal tax purposes and may subject the Optionee to the alternative 
minimum tax in the year of exercise.
    

               (b)     EXERCISE OF INCENTIVE STOCK OPTION FOLLOWING DISABILITY.
If the Optionee's Continuous Status as an Employee, Director or Consultant
terminates as a result of disability that is not total and permanent disability
as defined in Section 22(e)(3) of the Code, to the extent permitted on the date
of termination, the Optionee must exercise an Incentive Stock Option within 90
days of such termination for the Incentive Stock Option to be qualified as an
Incentive Stock Option.

   
               (c)     EXERCISE OF NON-QUALIFIED STOCK OPTION.  There may be a
regular federal income tax liability upon the exercise of a Non-Qualified 
Stock Option.  The Optionee will be treated as having received compensation 
income (taxable at ordinary income tax rates) equal to the excess, if any, of 
the Fair Market Value of the Shares on
    

                                          5

<PAGE>

the date of exercise over the Exercise Price.  If Optionee is an Employee or a
former Employee, the Company will be required to withhold from Optionee's
compensation or collect from Optionee and pay to the applicable taxing
authorities an amount in cash equal to a percentage of this compensation income
at the time of exercise, and may refuse to honor the exercise and refuse to
deliver Shares if such withholding amounts are not delivered at the time of
exercise.

   
               (d)     DISPOSITION OF SHARES.  In the case of a Non-Qualified
Stock Option, if Shares are held for at least one year, any gain realized on
disposition of the Shares will be treated as long-term capital gain for federal
income tax purposes.  In the case of an Incentive Stock Option, if Shares 
transferred pursuant to the Option are held for at least one year after 
receipt of the Shares and are disposed of at least two years after the Date 
of Grant, any gain realized on disposition of the Shares also will be treated 
as long-term capital gain for federal income tax purposes.  If Shares 
purchased under an Incentive Stock Option are disposed of within such 
one-year or two-year periods, any gain realized on such disposition will be 
treated as compensation income (taxable at ordinary income rates) to the 
extent of the difference between the Exercise Price and the lesser of (i) the 
Fair Market Value of the Shares on the date of exercise, or (ii) the sale 
price of the Shares.
    

   
       11.     ENTIRE AGREEMENT: GOVERNING LAW.  The Plan is incorporated
herein by reference.  The Plan and this Option Agreement constitute the entire
agreement of the parties with respect to the subject matter hereof and supersede
in their entirety all prior undertakings and agreements of the Company and the
Optionee with respect to the subject matter hereof, and may not be modified
adversely to the Optionee's interest except by means of a writing signed by the
Company and Optionee.  This agreement is governed by Delaware law except for
that body of law pertaining to conflict of laws.
    

       12.     HEADINGS.  The captions used in this Option are inserted for
convenience and shall not be deemed a part of this Option for construction or
interpretation.


                                          6

<PAGE>

       13.     INTERPRETATION.  Any dispute regarding the interpretation of
this Option Agreement shall be submitted by the Optionee or by the Company
forthwith to the Board or the Administrator that administers the Plan, which
shall review such dispute at its next regular meeting.  The resolution of such
dispute by the Board or the Administrator shall be final and binding on all
persons.

                                       Progenitor, Inc.,
                                       a Delaware corporation
                                       By:
                                          -----------------------------------

                                       Its:
                                           ----------------------------------

OPTIONEE ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES PURSUANT TO THE
OPTION HEREOF IS EARNED ONLY BY CONTINUING CONSULTANCY OR EMPLOYMENT AT THE WILL
OF THE COMPANY (NOT THROUGH THE ACT OF BEING HIRED, BEING GRANTED THIS OPTION OR
ACQUIRING SHARES HEREUNDER).  OPTIONEE FURTHER ACKNOWLEDGES AND AGREES THAT
NOTHING IN THIS AGREEMENT, NOR IN THE COMPANY'S 1996 STOCK INCENTIVE PLAN WHICH
IS INCORPORATED HEREIN BY REFERENCE, SHALL CONFER UPON OPTIONEE ANY RIGHT WITH
RESPECT TO CONTINUATION OF EMPLOYMENT OR CONSULTANCY BY THE COMPANY, NOR SHALL
IT INTERFERE IN ANY WAY WITH OPTIONEE'S RIGHT OR THE COMPANY'S RIGHT TO
TERMINATE OPTIONEE'S EMPLOYMENT OR CONSULTANCY AT ANY TIME, WITH OR WITHOUT
CAUSE.

       Optionee acknowledges receipt of a copy of the Plan and represents that
he is familiar with the terms and provisions thereof, and hereby accepts this
Option Agreement subject to all of the terms and provisions thereof.  Optionee
has reviewed the Plan and this Option Agreement in their entirety, has had an
opportunity to obtain the advice of counsel prior to executing this Option
Agreement and fully understands all provisions of the Option Agreement.
Optionee hereby agrees to accept as binding, conclusive and final all decisions
or interpretations of the Administrator upon any questions arising under the
Plan or this Option Agreement.  Optionee further agrees to notify the Company
upon any change in the residence address indicated below.

Dated:                                 Signed:
      -----------------------------           -------------------------------
                                              Optionee

                                       Residence Address:

                                       --------------------------------------

                                       --------------------------------------

                                       --------------------------------------


                                          7

<PAGE>

                                      EXHIBIT A

                      PROGENITOR, INC. 1996 STOCK INCENTIVE PLAN

                                   EXERCISE NOTICE


Progenitor, Inc.
1507 Chambers Road
Columbus, OH  43212

Attention: Secretary

      1.     EXERCISE OF OPTION.  Effective as of today, ______________,
________________________________, the undersigned ("Optionee") hereby elects to
exercise Optionee's option to purchase ___________ shares of the Common Stock
(the "Shares") of Progenitor, Inc. (the "Company") under and pursuant to the
Company's 1996 Stock Incentive Plan (the "Plan") and the [  ] Incentive
[  ] Non-Qualified Stock Option Agreement dated ______________, ________ (the
"Option Agreement").

      2.     REPRESENTATIONS OF OPTIONEE.  Optionee acknowledges that Optionee
has received, read and understood the Plan and the Option Agreement and agrees
to abide by and be bound by their terms and conditions.

      3.     RIGHTS AS STOCKHOLDER.  Until the stock certificate evidencing
such Shares is issued (as evidenced by the appropriate entry on the books of the
Company or of a duly authorized transfer agent of the Company), no right to vote
or receive dividends or any other rights as a stockholder shall exist with
respect to the Optioned Stock, notwithstanding the exercise of the Option.  The
Company shall issue (or cause to be issued) such stock certificate promptly
after the Option is exercised.  No adjustment will be made for a dividend or
other right for which the record date is prior to the date the stock certificate
is issued, except as provided in Section 10 of the Plan.

      4.     DELIVERY OF PAYMENT.  Optionee herewith delivers to the Company
the full Exercise Price for the Shares.

      5.     TAX CONSULTATION.  Optionee understands that Optionee may suffer
adverse tax consequences as a result of Optionee's purchase or disposition of
the Shares.  Optionee represents that Optionee has consulted with any tax
consultants Optionee deems advisable in connection with the purchase or
disposition of the Shares and that Optionee is not relying on the Company for
any tax advice

      6.     TAXES.  Optionee agrees to satisfy all applicable federal, state
and local income and employment tax withholding obligations and [HEREWITH
DELIVERS TO THE COMPANY THE FULL AMOUNT OF SUCH OBLIGATIONS] OR [HAS MADE
ARRANGEMENTS ACCEPTABLE TO THE COMPANY TO SATISFY SUCH OBLIGATIONS.]  [OPTIONEE
ALSO AGREES, AS PARTIAL CONSIDERATION FOR THE DESIGNATION


                                          1

<PAGE>

OF THE OPTION AS AN INCENTIVE STOCK OPTION, TO NOTIFY THE COMPANY IN WRITING
WITHIN THIRTY (30) DAYS OF ANY DISPOSITION OF ANY SHARES ACQUIRED BY EXERCISE OF
THE OPTION IF SUCH DISPOSITION OCCURS WITHIN TWO (2) YEARS FROM THE GRANT DATE
OR WITHIN ONE (1) YEAR FROM THE DATE THE SHARES WERE TRANSFERRED TO OPTIONEE.
IF THE COMPANY IS REQUIRED TO SATISFY ANY FEDERAL, STATE OR LOCAL INCOME OR
EMPLOYMENT TAX WITHHOLDING OBLIGATIONS AS A RESULT OF SUCH AN EARLY DISPOSITION,
OPTIONEE AGREES TO SATISFY THE AMOUNT OF SUCH WITHHOLDING IN A MANNER THAT THE
ADMINISTRATOR PRESCRIBES.]

      7.     SUCCESSORS AND ASSIGNS.  The Company may assign any of its rights
under this Exercise Notice to single or multiple assignees, and this Agreement
shall inure to the benefit of the successors and assigns of the Company.  This
Exercise Notice shall be binding upon Optionee and his or her heirs, executors,
administrators, successors and assigns.

      8.     HEADINGS.  The captions used in this Agreement are inserted for
convenience and shall not be deemed a part of this Agreement for construction or
interpretation.

      9.     INTERPRETATION.  Any dispute regarding the interpretation of this
Exercise Notice shall be submitted by Optionee or by the Company forthwith to
the Company's Board of Directors or the Administrator that administers the Plan,
which shall review such dispute at its next regular meeting.  The resolution of
such a dispute by the Board or Administrator shall be final and binding on all
persons.

   
      10.    GOVERNING LAW; SEVERABILITY.  This Agreement shall be governed by
and construed in accordance with the laws of the State of Delaware excluding
that body of law pertaining to conflicts of law.  Should any provision of this
Agreement be determined by a court of law to be illegal or unenforceable, the
other provisions shall nevertheless remain effective and shall remain
enforceable.
    

      11.    NOTICES.  Any notice required or permitted hereunder shall be
given in writing and shall be deemed effectively given upon personal delivery or
upon deposit in the United States mail by certified mail, with postage and fees
prepaid, addressed to the other party at its address as shown below beneath its
signature, or to such other address as such party may designate in writing from
time to time to the other party.

      12.    FURTHER INSTRUMENTS.  The parties agree to execute such further
instruments and to take such further action as may be reasonably necessary to
carry out the purposes and intent of this Agreement.


                                          2

<PAGE>

      13.    ENTIRE AGREEMENT.  The Plan and the Option Agreement are
incorporated herein by reference.  This Exercise Notice, the Plan and the Option
Agreement constitute the entire agreement of the parties with respect to the
subject matter hereof and supersede in their entirety all prior undertakings and
agreements of the Company and Optionee with respect to the subject matter
hereof, and may not be modified adversely to the Optionee's interest except by
means of a writing signed by the Company and Optionee.

Submitted by:                          Accepted by:

OPTIONEE:                              PROGENITOR, INC.
                                       By:
                                          -----------------------------------

- -----------------------------------    Its:
(Signature)                                ----------------------------------


ADDRESS:                               ADDRESS:

___________________________________    1507 Chambers Road
___________________________________    Columbus, OH  43212


                                          3

<PAGE>

                             INTERCOMPANY AGREEMENT

     THIS INTERCOMPANY AGREEMENT ("Agreement"), is entered into on ________,
1996, to be effective as of the Effective Date (as defined herein), by and
between Interneuron Pharmaceuticals, Inc., a Delaware corporation
("Interneuron"), and Progenitor, Inc., a Delaware corporation ("Progenitor").

                                R E C I T A L S:

     A.   WHEREAS, Interneuron owns beneficially a substantial portion of the
shares of the capital stock of Progenitor.

     B.   WHEREAS, Progenitor is a development stage biotechnology company
engaged in the business of identifying genes, proteins and receptors and
developing related products for the treatment of various diseases, including
cancer, and such other activities as Progenitor may in the future engage.

     C.   WHEREAS, in connection with Progenitor's initial public offering, and
effective on the date a registration statement relating to such offering is
declared effective by the Securities and Exchange Commission (the "Effective
Date"), the parties desire (i) to set forth the terms and conditions under which
Progenitor may retain Interneuron to perform certain services (the "Services"),
(ii) to establish and maintain certain policies and procedures in connection
with Progenitor and (iii) to coordinate certain financial, corporate and other
activities, as set forth in this Agreement.

     NOW, THEREFORE, in consideration of the foregoing and the mutual
agreements, provisions and covenants contained in this Agreement, the parties
hereby agree as follows:

                                   ARTICLE I.



                              PROVISION OF SERVICES

SECTION 1.1.   TYPES OF SERVICES

     Progenitor hereby engages and retains Interneuron to provide the Services
set forth below from time to time as and to the extent reasonably requested by
Progenitor, and Interneuron hereby accepts and agrees to provide such Services,
upon the terms and conditions hereinafter set forth:

          (i)    executive and administrative;

          (ii)   regulatory, including such Services as are necessary or useful
     to assist Progenitor in meeting reporting requirements of regulatory
     agencies;


                                        1

<PAGE>

          (iii)  tax advice and services, including, without limitation,
     assistance in the preparation of federal, state, local and foreign tax
     returns;

          (iv)   auditing, accounting, payroll and bookkeeping advice and
     services, including services related to financial reporting and assistance
     in the preparation of financial statements relating to reporting
     requirements under the federal securities laws;

          (v)    financial advice and services, including, without limitation,
     assistance with respect to cash management, treasury and risk management;

          (vi)   human resources and personnel policies, including, without
     limitation, wage and salary, administrative, employee relations and
     administration of employee insurance plans, pension plans and other
     employee benefits plans;

          (vii)  assistance with marketing projects, consumer studies and other
     information gathering or promotional activities;

          (viii) purchasing services, and assistance in the purchase or leasing
     of equipment and supplies, including where possible and acceptable to
     Interneuron making available to Progenitor volume purchase discount
     arrangements and group rates for purchasing insurance and other supplies
     and services;

          (ix)   facilities services, including mail, telephone, supply, food
     service and employee services;

          (x)    management information, supplemental data processing,
     telecommunications, computer programming and other computer systems
     services; and

          (xi)   such other services, advice and assistance as may be reasonably
     requested by Progenitor and agreed to by Interneuron from time to time.

SECTION 1.2.   PERFORMANCE

     (a)  All Services to be provided by Interneuron hereunder shall be
performed at the request and under the general direction of Progenitor and
Interneuron shall not have any power to act independently on behalf of
Progenitor other than as specifically authorized hereunder or as requested from
time to time by Progenitor.  Neither Interneuron nor its employees, vendors or
suppliers shall be deemed to be agents, representatives, employees or servants
of Progenitor, except to the extent expressly provided pursuant to the authority
granted under this Agreement.

     (b)  The specified Services may be rendered by Interneuron or Interneuron's
other subsidiaries ("Other Subsidiaries"), affiliates or third parties, as
Interneuron shall reasonably determine.

     (c)  Interneuron shall determine its corporate facilities to be used in
rendering the Services and the individuals who will render such Services.


                                        2

<PAGE>

     (d)  Services provided to Progenitor hereunder shall be performed by those
employees of Interneuron who perform equivalent services for Interneuron and the
Other Subsidiaries in the normal course of their employment.  Accordingly,
Interneuron shall not be obligated to make available any Services to the extent
that doing so would unreasonably interfere with the performance by any employee
of Services for Interneuron or any of the Other Subsidiaries, or otherwise cause
an unreasonable burden to Interneuron.

     (e)  Nothing herein shall be deemed to restrict Interneuron or its
directors, officers or employees from engaging in any business other than that
contemplated herein, or from contracting with other parties, including, without
limitation, Other Subsidiaries of Interneuron for similar or different Services.

SECTION 1.3.   COMPENSATION

     (a)  Progenitor shall pay to Interneuron, with respect to the Services
performed by Interneuron hereunder, a pro-rata allocation of salaries (without
reference to any stock options or other compensation other than salary) of
Interneuron personnel, based upon actual time worked in connection with the
performance of the Services on behalf of Progenitor, plus a reasonable mark-up
(the "burden rate") to be calculated and agreed to by Interneuron and Progenitor
based on, among other factors, the cost of benefits, taxes, allocated equipment,
support costs and facility costs.  In the event the burden rate cannot be
mutually calculated or agreed to, a 35% burden rate will apply, PROVIDED that
the burden rate charged to Progenitor will not exceed any similar rate charged
for similar services to any other division of Interneuron or any other entity
(each, an "Interneuron Affiliate") that, directly or indirectly, controls, is
controlled by or is subject to common control with Interneuron, but not
including Progenitor.  Interneuron will not charge Progenitor for any allocation
of employee time incurred by Interneuron or Interneuron Affiliate employees in
performing obligations of Progenitor required by Interneuron pursuant to this
Agreement.

     (b)  Any reasonable out-of-pocket charges, including but not limited to
travel, and other direct costs incurred in providing Services to Progenitor (but
not including salaries of employees or any costs contemplated within the burden
rate) will be paid by Progenitor separately as out-of-pocket costs.  Interneuron
will not incur any out-of-pocket fees for professional services for the account
of Progenitor without the consent of Progenitor.

     (c)  Within thirty (30) days of each subsequent calendar month end,
Progenitor shall pay to Interneuron the amounts specified by Interneuron in
invoices submitted in such preceding month by Interneuron to Progenitor
specifying the amounts described above with respect to the Services provided
during the month in question, together with such documentation and detail
regarding such charges as Progenitor may reasonably request.

SECTION 1.4.   BOOKS AND RECORDS

     Interneuron shall keep accurate books and records with respect to the costs
and expenses incurred in connection with the Services, and Progenitor or its
auditors shall be permitted from


                                        3

<PAGE>

time to time upon reasonable notice to inspect the books and records with
respect to such costs and expenses.

                                   ARTICLE II.

                               OTHER COORDINATION

SECTION 2.1.   ADOPTION OF FINANCIAL POLICIES

     To the extent not already in place, Progenitor shall establish a set of
financial, accounting and corporate policies similar to those generally
established by companies comparable to Progenitor, tailored to Progenitor and
reasonably satisfactory to Interneuron.  Areas to be addressed by these policies
shall include (without limitation) the following:

          (i)    investment guidelines for cash and marketable securities;

          (ii)   levels of authorization and approval by management and the
     Board of Directors for purchases, contracts, check signing, wire transfers
     and capital commitments;

          (iii)  accrual and recognition of expenses;

          (iv)   depreciation;

          (v)    revenue recognition;

          (vi)   human resources, including termination of employment,
     discrimination and sexual harassment;

          (vii)  insider trading;

          (viii) stock option accounting (and FASB compliance); and

          (ix)   other accounting issues, including consolidation, maintaining
     adequate controls and preparation of statements in accordance with
     generally accepted accounting principles ("GAAP").

SECTION 2.2.   COORDINATION OF FINANCIAL REPORTING

     For so long as Interneuron reports Progenitor's financial results on a
consolidated basis, on an equity basis or otherwise on a basis pursuant to which
a portion of the results of operations of Progenitor appear in the financial
results of operations of Interneuron (the "Combined Reporting Period"), then:

     (a)  Progenitor shall use its best efforts to have its independent auditors
complete their review of Progenitor's quarterly financial statements within 15
business days of the end of the applicable quarter and their audit of
Progenitor's annual financial statements within 20 business


                                        4

<PAGE>

days of the end of the applicable fiscal year.  Progenitor will keep Interneuron
informed as to the timing and issues relating to such financial statements on an
ongoing basis and will provide Interneuron with its annual statements in draft
form no later than 40 days and in final form no later than 50 days after the end
of the applicable fiscal year.

     (b)  Without the prior consent of Interneuron, Progenitor will not change
its fiscal year end, except to coincide with any such change by Interneuron.

     (c)  Progenitor shall provide Interneuron with all financial and other
related information reasonably requested by Interneuron, Interneuron's auditors
or government agencies on a timetable to be agreed upon and made a part of this
Agreement as EXHIBIT A, as such Exhibit A may be amended from time to time by
agreement of the parties hereto, it being understood that such Exhibit A shall
be evidence of mutual agreement, and provided, however, that Progenitor shall
deliver to Interneuron drafts of annual operating plans, cash flow forecasts
and/or budgets, including monthly numbers by line item and categorized by
department, with supporting schedules or other information as may be reasonably
requested ("Plans"), for the following fiscal year no later than 30 days prior
to the beginning of such fiscal year and shall deliver the final forms of such
Plans to Interneuron no later than the beginning of such fiscal year, and that
Progenitor shall notify Interneuron in writing of any material changes to such
Plans as soon as they occur.

     (d)  Progenitor shall employ the same independent auditors as Interneuron
(subject to any required stockholder ratification), provided that such firm is
one of the ten largest independent auditing firms (based on audit employees) in
the United States.  If Progenitor requires the use of an independent auditing
firm outside of the United States, Progenitor shall employ the same or a related
firm, provided that if such a firm is not available, then Progenitor shall use a
firm which is reasonable satisfactory to Interneuron and its auditors.

     (e)  At Interneuron's request and expense, Interneuron's representatives
may perform financial reviews of Progenitor, on an approximately quarterly
basis, at a mutually convenient time at Progenitor's executive offices, for the
purpose of reviewing the following:

          (i)    bank reconciliations and cash investments;

          (ii)   payroll and employee benefits;

          (iii)  travel and entertainment expenses;

          (iv)   contracts; and

          (v)    other financial information reasonably requested by
     Interneuron.

At such time as Interneuron no longer reports Progenitor's results on a
consolidated basis, the parties will agree upon procedures to be applicable to
Progenitor in lieu of those set forth in Sections 2.2(a) through 2.2(e) on such
terms as may be reasonably necessary to enable Interneuron to comply with any
obligation to report Progenitor's results on an equity basis.


                                        5

<PAGE>

SECTION 2.3.   EMPLOYEE BENEFIT PLANS.  Interneuron and Progenitor may agree
from time to time to allow Progenitor's employees to participate in employee
benefit plans of Interneuron on the same terms and conditions as employees of
Interneuron or Interneuron Affiliates.  Progenitor shall pay to Interneuron the
costs of contribution and administration attributable to participating
Progenitor employees at rates to be agreed upon, but in all events no greater
than as charged to, and on substantially the same terms as made available to,
Interneuron divisions or Interneuron Affiliates.

SECTION 2.4.   INSURANCE, HEALTH AND WELFARE PLANS.

     (a)  Progenitor and Interneuron shall jointly determine minimum levels of
insurance coverage for Progenitor (including liability, property and casualty,
directors and officers, product liability, clinical liability, and key man
insurance) and, in any event, Progenitor shall maintain insurance coverage in
amounts comparable to that maintained by companies similar in size and business
to Progenitor and, to the extent practicable, with carriers having the highest
tier rating.  To the extent requested by Interneuron, Progenitor shall utilize
the same insurance broker as Interneuron with respect to its directors and
officers liability insurance coverage, unless such utilization will result in
increased cost or burden to Progenitor.

     (b)  Interneuron shall use reasonable efforts to assist Progenitor to
obtain the benefits of any available group pricing or group discounts for
property and casualty insurance, including workers' compensation, comprehensive
general liability, comprehensive automobile liability, all risk property
insurance and employee dishonesty coverage, through group rate coverage under
policies obtained by Interneuron.

     (c)  If agreed upon by Interneuron and Progenitor, Interneuron shall
provide the following health and welfare benefits coverage to Progenitor
employees on the same terms and conditions as provided to employees of
Interneuron or Interneuron Affiliates (except to the extent of state, regulatory
or other factors which cause variance in premium costs), but in any event at not
less than the cost to Interneuron:

          (i)    comprehensive health insurance, including medical and dental
     insurance, and covering active and retired employees;

          (ii)   life insurance;

          (iii)  accidental death or dismemberment;

          (iv)   long-term disability insurance; and

          (v)    travel accident insurance.

     (d)  Progenitor shall be billed for all such insurance and health and
welfare benefits coverage at rates to be agreed upon, but in all events no
greater than as charged to, and on substantially the same terms as made
available to, internal units of Interneuron and Interneuron Affiliates.


                                        6

<PAGE>

SECTION 2.5.   CASH MANAGEMENT SERVICES

     To the extent mutually agreed to, Interneuron shall make available to
Progenitor Interneuron's cash management program.

SECTION 2.6.   BOARD OF DIRECTORS

     For so long as Interneuron reports Progenitor's financial results on a
consolidated basis, on an equity basis or otherwise on a basis pursuant to which
a portion of the results of operations of Progenitor appear in the financial
results of operations of Interneuron, Progenitor shall nominate for election to
its Board of Directors a nominee designated by Interneuron.  Interneuron
recognizes that Progenitor intends to seek to have at least two Independent
Directors; however, nothing herein shall require Interneuron to vote for or take
any other action to ensure the election or retention of any particular
Independent Director.  "Independent Directors" shall be directors who are not
employees, officers, directors or affiliates of, or persons with a material
financial relationship with, Interneuron or Progenitor or any of their
respective affiliates (including any such relationship that would be required to
be disclosed pursuant to the disclosure requirements of Item 404 of
Regulation S-K as in effect from time to time (including any successor
provisions thereto)) and who shall qualify as "independent directors" for
purposes of the listing requirements of the Nasdaq National Market or of any
other national stock exchange or trading system on which Progenitor's securities
are listed or admitted for trading from time to time.

SECTION 2.7.   PUBLICITY

     (a)  Subject to subsection 2.7(c) below, Progenitor shall submit all press
releases and reports to be filed with the Securities and Exchange Commission
("SEC") to Interneuron in draft form at least four business days prior to
release or filing, as applicable.  Any comments by Interneuron to such release
or filing shall be transmitted to Progenitor within two business days prior to
any such release or filing, and Progenitor shall consider and utilize such
comments to the extent reasonably deemed appropriate.

     (b)  Subject to the same terms and conditions as subsection 2.7(a) above,
Interneuron shall submit to Progenitor any press releases or reports to be filed
with the SEC which refer to Progenitor (or portions thereof).

     (c)  In the event of the happening of any occurrence which requires a press
release within a time period which is not sufficient to follow the procedures
set forth in subsection 2.7(a) or 2.7(b) above, each party shall use its best
efforts to send the other party a draft release, and the other party shall use
its best efforts to review such release, as expeditiously as possible.

SECTION 2.8.   RIGHT TO PURCHASE SHARES

     Subject to the terms and conditions specified in this Agreement, Progenitor
hereby grants to Interneuron a right to purchase Shares (as hereinafter defined)
of Progenitor in connection with future issuances by Progenitor of its Shares
after Progenitor's initial public offering.  Each time Progenitor proposes to
offer (an "Offer") any shares of, or securities convertible into or


                                        7

<PAGE>

exchangeable for any shares of, any class of its capital stock ("Shares"),
Progenitor shall offer Shares to Interneuron in accordance with the following
provisions:

     (a)  Progenitor shall deliver a notice by certified mail or facsimile
confirmation requested ("Notice") to Interneuron stating (i) its bona fide
intention to offer such Shares, (ii) the number of such Shares to be offered,
and (iii) the price and terms, if any, upon which it proposes to offer such
Shares.

     (b)  By written notification received by Progenitor, within ten (10)
business days after receipt of the Notice, Interneuron may elect to purchase or
obtain, at the price and on the terms specified in the Notice, up to that
portion of such Shares as is necessary to preserve Interneuron's Fully Diluted
Equity Interest in Progenitor (calculated as hereinafter set forth) immediately
prior to the Offer, provided however that in the event of a firm commitment
underwritten offering (a "Qualified Public Offering") of Progenitor Shares,
Interneuron shall respond to the Notice within two business days prior to the
date on which a usual and customary number of preliminary prospectuses relating
to such offering are projected to be available and may provide that its election
to purchase Shares pursuant to this Section 2.8 is limited to a maximum purchase
price.  The Fully Diluted Equity Interest shall be calculated based on the
number of outstanding shares of Progenitor's common stock ("Common Stock") plus
the number of shares of Common Stock issuable upon conversion or exercise of
outstanding securities of Progenitor without the payment of additional
consideration (including options or warrants, other than options issued in
connection with employee benefit plans or services rendered by employees or
consultants), and giving effect to the Shares issued by Progenitor in connection
with the transaction giving rise to Interneuron's rights hereunder and the
Shares purchased by Interneuron hereunder.

     (c)  If all Shares referred to in the Notice which Interneuron is entitled
to purchase pursuant to Section 2.8(b) are not elected to be purchased as
provided in Section 2.8(b) hereof, Progenitor may, during the sixty (60) day
period following expiration of the period provided in Section 2.8(b) hereof,
offer the same number of Shares offered to Interneuron to any person or persons
at a price not less than, and upon terms no more favorable to the offeree than
those specified in the Notice.  In the event of any change in the number of
Shares offered in connection with a Qualified Public Offering, or in the price
or other terms of any other Offer, Progenitor shall provide a new notice to
Interneuron and the same procedures with respect to such revised Offer shall be
followed.  If Progenitor does not enter into an agreement for the sale of the
Shares within the specified period, or if such agreement is not consummated
within sixty (60) days of the execution thereof, the right provided hereunder
shall be deemed to be revived and such Shares shall not be offered unless first
reoffered to Interneuron in accordance herewith.

     (d)  In the event of a proposed offer or issuance by Progenitor of any
Shares in connection with employee benefit plans, services rendered by employees
or consultants, or the acquisition of another business or corporation so long as
such acquisition is not primarily a financing transaction (each, a "Transaction
Issuance"), the provisions of this Section 2.8 shall not be applicable to such
Transaction Issuance.



                                        8

<PAGE>

     (e)  If in connection with any future issuance of Shares by Progenitor for
consideration, the purchase price is not readily ascertainable, the purchase
price applicable to Interneuron's right to purchase Shares hereunder shall be
equal to the fair market value of Progenitor's Common Stock (the "Fair Market
Value") on the date of the issuance, as determined by the Board of Directors of
Progenitor (considering factors which would typically be considered in an
independent valuation of fair market value of a similar company); provided that,
in the event that Progenitor is a public company, Fair Market Value shall mean
the average of the closing sales prices on the Nasdaq National Market (or if not
so traded, the average of the closing bid and asked prices) of Progenitor's
Common Stock for the ten (10) business days immediately preceding the date of
the issuance.

SECTION 2.9.   MATERIAL TRANSACTIONS WITH INTERNEURON

     Except as contemplated by this Agreement or with respect to transactions
which are immaterial, Progenitor shall not enter into any contract, agreement or
transaction with Interneuron or any Interneuron Affiliate, unless such contract,
agreement or transaction is both on terms no less favorable to Progenitor than
could be obtained from unaffiliated third parties and approved by:  (i) majority
vote of the Independent Directors, or (ii) a majority of the shares of the
voting capital stock of Progenitor that are not held by Interneuron and
Interneuron Affiliates, voting separately as a class with a quorum of such
shares voting.

SECTION 2.10.  INTERPRETATION OF AGREEMENT, ETC.

     A majority of the Independent Directors shall have full and complete
authority on behalf of Progenitor to interpret the terms of and take other
actions with respect to this Agreement, including to negotiate with Interneuron
or to take such actions to enforce this Agreement as may be available under
applicable law.

SECTION 2.11.  OTHER COOPERATION

     Progenitor shall use its commercially reasonable efforts to fulfill all its
obligations and otherwise comply with any office or equipment leases which are
guaranteed by Interneuron and to obtain a release of such guaranty as soon as
practicable.  In the event Progenitor defaults under any of these leases and
Interneuron satisfies any obligation pursuant to the related guaranty, at
Interneuron's request, Progenitor shall, to the extent permitted under
Progenitor's contractual and legal commitments, assign and transfer to
Interneuron all of its right, title and interest to the lease and related
equipment or office space.


                                        9

<PAGE>

                                  ARTICLE III.

                        STANDARD OF CARE; INDEMNIFICATION

SECTION 3.1.   STANDARD OF CARE

     (a)  Interneuron makes no express or implied representations, warranties,
or guarantees relating to the Services or the quality or results of Services to
be performed under this Agreement.

     (b)  Nothing in this Agreement shall require Interneuron to provide or
develop additional support or to render any Service not provided for in this
Agreement, or in a manner or pursuant to methods different from the standard set
forth in Section 3.1(d), or, in performing Services hereunder, to make any
change or addition which will require capital expenditures.

     (c)  The duties of Interneuron under this Agreement are subject to
interpretation or discontinuance by Progenitor at any time and from time to
time, without incurring liability to Interneuron or any other person for any
loss, damage or expense which may result therefrom, for FORCE MAJEURE or other
causes beyond Interneuron's or Progenitor's control.

     (d)  Interneuron will use reasonable efforts to make the Services available
with substantially the same degree of care as it makes the same services
available for its own operations, but shall not be liable to Progenitor or any
other person for any loss, damage or expense which may result therefrom or from
Interneuron's changing its manner of rendering the Services if Interneuron deems
that such change is necessary to desirable in the conduct of its own operations.

     (e)  Interneuron and officers and employees of Interneuron who provide
Services to Progenitor shall not be liable to Progenitor or any third party,
including governmental agencies, for any claims, damages or expenses relating to
the Services provided pursuant to this Agreement except for willful malfeasance,
bad faith or gross negligence in the performance of Services hereunder and
Progenitor shall have the ultimate responsibility for all Services provided
herein.

     (f)  Interneuron shall not be liable to Progenitor for the consequences of
any failure or delay to perform any of its obligations under this Agreement
other than for damages arising from Interneuron's gross negligence or willful or
reckless misconduct; provided that it shall provide reasonably prompt notice to
Progenitor of such liability and the reasons therefor.

     (g)  Progenitor shall indemnify and hold harmless any Interneuron employee
who performs Services for Progenitor pursuant to this Agreement to the same
extent that Interneuron would indemnify such employee if the employee were to
perform such Services for Interneuron.

     (h)  Progenitor shall indemnify, defend and hold harmless Interneuron and
its officers and employees who perform Services hereunder from and against all
liabilities, claims, damages, losses and expenses (including, but not limited
to, reasonable attorneys fees and court costs) arising from any threatened,
pending or completed action, suit, claim, judgment or other


                                       10

<PAGE>

proceeding arising out of Interneuron's or any of its officer's or director's
performance of Services pursuant to this Agreement.

SECTION 3.2.   INDEMNIFICATION FOR SERVICES

     (a)  Interneuron will defend and hold harmless Progenitor and its employees
and agents from and against any and all claims, actions, proceedings, judgments,
expenses, damages and liabilities, including court costs and reasonable
attorneys fees (collectively, "Claims"), arising out of Interneuron's
performance of the Services provided hereunder (including Services provided by
Interneuron's other subsidiaries or affiliates or by third parties) due to
Interneuron's malfeasance, bad faith, gross negligence or breach of this
Agreement.

     (b)  Progenitor will indemnify and hold harmless Interneuron and its
employees and agents who perform Services for Progenitor pursuant to this
Agreement from and against any and all Claims arising out of Interneuron's
performance of the Services provided hereunder (including Services provided by
Interneuron's other subsidiaries or affiliates or by third parties), due to
Progenitor's malfeasance, bad faith, gross negligence or breach of this
Agreement.

SECTION 3.3.   INDEMNIFICATION FOR INTERNEURON LIABILITIES

     (a)  "Interneuron Liabilities" shall mean any liability or obligation
related to the past, present or future businesses, operations or assets of
Interneuron or any Interneuron Affiliates, including but not limited to all
liabilities and obligations, whether known or unknown, by reason of any
violation of or noncompliance with any federal, state, local or foreign law,
rule or regulation or any requirement of any governmental authority, including
without limitation any laws establishing an obligation to notify employees in
advance of facility closings or changes in control, occurring in connection
with, and to the extent relating to, the past, present or future assets,
businesses or operations of Interneuron or any Interneuron Affiliate.

     (b)  "Progenitor Liabilities" shall mean any liability or obligation
related to the past, present or future businesses, operations or assets of
Progenitor or any entity more than 50% of the capital stock of which is owned by
Progenitor, including but not limited to all liabilities and obligations,
whether known or unknown, by reason of any violation of or noncompliance with
any federal, state, local or foreign law, rule or regulation or any requirement
of any governmental authority, including without limitation any laws
establishing an obligation to notify employees in advance of facility closings
or changes in control, occurring in connection with, and to the extent relating
to, the past, present or future assets, businesses or operations of Progenitor
or any entity described above, PROVIDED, that Progenitor Liabilities shall not
include any such liabilities related to the business of Interneuron or the
property or assets owned by Interneuron.

     (c)  Each of Progenitor and Interneuron will defend and hold harmless the
other and its employees and agents from and against any and all Claims arising
in connection with or that otherwise result from, relate to or are attributable
to any of the Interneuron Liabilities in the case of indemnification by
Interneuron and the Progenitor Liabilities in the case of indemnification by
Progenitor, PROVIDED, that indemnification under this Agreement will not be
available for Claims which are already indemnified under the Tax Allocation
Agreement between the parties.


                                       11

<PAGE>

                                   ARTICLE IV.

                           RECORDS AND CONFIDENTIALITY

SECTION 4.1.   ACCESS TO RECORDS

     (a)  Subsequent to the effective date of this Agreement, each of Progenitor
and Interneuron may have in its possession or under its control (or the control
of persons or firms which have rendered services to or otherwise done business
with it) books, records, contracts, instruments, data and other information
(collectively, "Records") which may prove necessary or desirable to the other in
connection with the other's business or in connection with the other's rights
under this Agreement or under the Tax Allocation Agreement.  Accordingly,
subsequent to such date:

          (i)    Progenitor shall provide to Interneuron, and Interneuron shall
     provide to Progenitor, upon the other's written request, upon reasonable
     notice and at all reasonable times, full and complete access to (including
     access to persons or firms possessing information, and including electronic
     access in the case of computerized records) and duplication rights with
     respect to, any and all such Records relating to the other party as such
     other party may reasonably request and require in the conduct of its
     business, subject to confidentiality restrictions; and

          (ii)   Progenitor shall use its best efforts to make available to
     Interneuron, and Interneuron shall use its best efforts to make available
     to Progenitor, upon the other's written request, their respective officers,
     directors, employees and agents as witnesses to the extent that such
     persons may reasonably be required in connection with any legal,
     administrative or other proceedings in which Progenitor or Interneuron, as
     the case may be, may from time to time be involved.

     (b)  For purposes of this Agreement, "Records" shall include, without
limitation, information sought for audit, accounting, claims, litigation and tax
purposes, as well as for purposes for fulfilling disclosure and reporting
obligations under the federal securities laws.

     (c)  Neither party shall destroy or permit the destruction of (without
having first offered to deliver to the other) any such Records relating to the
other for the time period during which it would be required to retain such
Records pursuant to its standard document retention policy (and in any event not
less than any period required by applicable law).

     (d)  Each party shall cooperate with the other in a timely manner in any
administrative or judicial proceeding involving any matter affecting the
potential liability of either party hereunder.  Such cooperation will include,
without limitation, making available to the other party, during normal business
hours and upon reasonable notice, all books, records and information of such
other party, and all officers and employees, necessary or useful in connection
with any claim for indemnification hereunder or under the Tax Allocation
Agreement.



                                       12

<PAGE>

     (e)  The party providing Records or making available witnesses pursuant to
the preceding paragraph (a) shall be entitled to receive from the other party,
upon the presentation of invoices therefor, payment for its reasonable out-of-
pocket expenses incurred in connection therewith (but not the labor cost
thereof), but shall not be entitled to receive any other payment with respect
thereto other than a per diem reimbursement for appearing as a witness in
circumstances where the parties agree and in amounts that are agreed upon.

SECTION 4.2.   CONFIDENTIALITY

     (a)  Following termination of the Consolidated Reporting Period, each of
Interneuron and Progenitor (i) will treat confidentially all Confidential
Information (as defined below) of the other party, and (ii) will not disclose
any Confidential Information of the other party to any third party, other than
to its employees, officers, directors, agents and subcontractors with a need to
know such Confidential Information for the purposes for which it was provided.

     (b)  For purposes of this Agreement, "Confidential Information" of a party
shall mean confidential or proprietary information of that party disclosed by
that party to the other party and marked "confidential" or "proprietary",
PROVIDED, that Confidential Information shall not include any information which
(i) was known to the receiving party prior to its receipt from the other party
and not subject to another confidentiality agreement with or other obligation of
secrecy  to such other party, (ii) is now or later  becomes generally available
to the public other than as a result of a disclosure by the receiving party,
(iii) is received separately by the receiving party from a third party which is
not prohibited from disclosing such information by a legal, contractual or
fiduciary obligation to the other party, or (iv) is developed independently by
the receiving party.


                                   ARTICLE V.

                                  MISCELLANEOUS

SECTION 5.1.   COMPLETE AGREEMENT; CONSTRUCTION

     This Agreement shall constitute the entire agreement between the parties
with respect to the subject matter hereof and shall supersede all previous
negotiations, commitments and writings with respect to such subject matter.

SECTION 5.2.   RELATIONSHIP OF THE PARTIES

     For all purposes of this Agreement, Interneuron and Progenitor shall be
deemed to be independent entities and, anything in this Agreement to the
contrary notwithstanding, nothing herein shall be deemed to constitute
Interneuron and Progenitor as partners, joint venturers, co-owners, an
association or any entity separate and apart from each party itself, nor shall
this Agreement constitute any party hereto an employee or agent, legal or
otherwise, of the other party for any purposes whatsoever.  Neither party hereto
is authorized to make any statements or


                                       13

<PAGE>

representations behalf of the other party or in any way obligate the other
party, except as expressly authorized in writing by the other party.

SECTION 5.3.   GOVERNING LAW

     This Agreement shall be governed by and construed in accordance with the
laws of the State of Delaware, without regard to the principles of conflicts of
laws thereof.

SECTION 5.4.   NOTICES

     Except as otherwise set forth herein, all notices and other communications
hereunder shall be in writing and shall be delivered by hand or mailed by
registered or certified mail (return receipt requested) to the parties at the
following addresses (or at such other addresses for a party as shall be
specified by like notice) and shall be deemed given on the date on which such
notice is received:

                    To Interneuron:     One Ledgemont Center
                                        99 Hayden Avenue, Suite 340
                                        Lexington, MA  02173
                                        Attention:  Mark S. Butler, Esq.

                    To Progenitor:      1507 Chambers Road
                                        Columbus, OH 43212-1566
                                        Attention:  Douglass B. Given
                                        President and Chief
                                        Executive Officer

SECTION 5.5.   AMENDMENTS; WAIVERS

     This Agreement may not be modified or amended except by an agreement in
writing signed by the parties.

SECTION 5.6.   ASSIGNMENT

     This Agreement shall not be assignable, in whole or in part, directly or
indirectly, by either party hereto without the prior written consent of the
other, and any attempt to assign any rights or obligations arising under this
Agreement without such consent shall be void.

SECTION 5.7.   TERM AND TERMINATION

     The term of this Agreement shall commence with the Effective Date and
terminate, unless extended by agreement of the parties, upon the termination of
the Combined Reporting Period, unless earlier terminated:

          (i)    by mutual agreement of the parties, who may agree to terminate
     the Agreement in whole or in part;


                                       14

<PAGE>

          (ii)   in the event of material breach of this Agreement by one party,
     by the nonbreaching party, upon 60 days written notice to the other party;
     or

SECTION 5.8.   NO THIRD-PARTY BENEFICIARIES

     This Agreement is solely for the benefit of the parties hereto and should
not be deemed to confer upon third parties any remedy, claim, liability,
reimbursement, claim of action or other right in excess of those existing
without reference to this Agreement.

SECTION 5.9.   ARBITRATION

     (a)  Any dispute, controversy, claim or question arising out of or relating
to this Agreement, or the breach thereof, shall be settled by arbitration in New
York, New York, in accordance with the rules then in effect of the American
Arbitration Association, and judgment upon the award rendered may be entered by
any court having jurisdiction thereof.

     (b)  Neither Interneuron nor Progenitor will cease its obligations under
this Agreement during any arbitration proceedings, except by mutual agreement.

SECTION 5.10.  TITLES AND HEADINGS

     Titles and headings to sections herein are inserted for convenience of
reference only and are not intended to be a part of or to affect the meaning of
or interpretation of this Agreement.

SECTION 5.11.  LEGAL ENFORCEABILITY

     Any provision of this Agreement which is prohibited or unenforceable shall,
as to such jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions hereof.

SECTION 5.12.  FURTHER ASSURANCES

     Subject to the terms and conditions hereof, each party agrees to use its
best efforts to do, or cause to be done, all things necessary, proper or
advisable under applicable laws and regulations to consummate the transactions
contemplated by this Agreement and carry out its obligations hereunder as
expeditiously as practicable, including, without limitation, the performance of
such further acts or the execution and delivery of any additional instruments or
documents as any party may reasonably request in order to carry out the purposes
of this Agreement and the transactions contemplated hereby.

SECTION 5.13.  COUNTERPARTS

     This Agreement may be executed simultaneously in two or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.



                                       15

<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed as of the date first above written.


                                        INTERNEURON PHARMACEUTICALS, INC.



                                        By:
                                                --------------------------------
                                          Name:
                                                --------------------------------
                                          Title:
                                                --------------------------------

                                        PROGENITOR, INC.



                                        By:
                                                --------------------------------
                                          Name:
                                                --------------------------------
                                          Title:
                                                --------------------------------


                                       16

<PAGE>

                               TAX ALLOCATION AGREEMENT

         THIS TAX ALLOCATION AGREEMENT ("Agreement") is dated as of ________,
1996 by and between Interneuron Pharmaceuticals, Inc. ("IPI") and Progenitor,
Inc. ("Progenitor").
                                 W I T N E S S E T H

         WHEREAS, IPI has been the common parent of an affiliated group of
corporations which has filed consolidated income tax returns in accordance with
the Internal Revenue Code of 1986, as amended (the "Code"), and the applicable
regulations thereunder (the "Regulations"), as well as the parent of a group of
corporations filing combined tax returns for state and local tax purposes; and

         WHEREAS, IPI's ownership interest in Progenitor has become less than
80% of the total voting power of and less than 80% of the total value of the
issued and outstanding stock of Progenitor; and

         WHEREAS, Progenitor, by virtue of the foregoing, is not eligible to
file consolidated income tax returns with IPI and is no longer a member of IPI's
affiliated group of corporations; and

         WHEREAS, IPI and Progenitor desire to define the method by which the
consolidated Federal income tax liability of the affiliated group for each
taxable year during which Progenitor was a part of IPI's consolidated income tax
returns should be allocated among the parties and the manner in which said
allocated liability will be paid for, to provide for the allocation and payment
of any refund arising from a carry back of losses or tax credits from subsequent
tax years, the compensation of any party for use of its losses or tax credits
and the participation and cooperation by Members of the Group (as defined
herein) in coordinating tax planning and in other matters relating to the
consolidated tax return of the Group; and

         WHEREAS, IPI and Progenitor desire to define the method by which tax
attributes of the affiliated group, including not by way of limitation, the Code
Section 382 limitations relating to net operating losses and capital loss
carryforwards, should be allocated and apportioned between IPI and Progenitor in
connection with Progenitor's departure from IPI's affiliated group and to
provide for payments with respect to ongoing state or local tax matters;

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements contained herein, the parties agree as follows:

         1.   DEFINITIONS

         For purposes of this Agreement, the terms set forth below shall have
the following meanings:


                                      1

<PAGE>


              (a) "Affiliate" shall mean, with respect to any entity, any other
entity who, directly or indirectly, controls, is controlled by or is subject to
common control with such entity.

              (b) "Effective Date" shall mean the date of the closing of the
Offering.

              (c) "ERISA" shall mean the Employee Retirement and Security Act of
1974, as amended.

              (d) "Group," with respect to any taxable year of IPI for which a
consolidated Federal income tax return is or was filed by IPI, or for which a
state or local income or franchise tax return is or was filed which includes the
activity of a related corporation (hereinafter referred to as a "State Unitary
Return"), shall mean all corporations included in such consolidated return or
State Unitary Return.  Each corporation included in the Group, other than IPI,
is sometimes referred to herein as a "Subsidiary," IPI and each Subsidiary are
sometimes referred to herein as "Members."

              (e) "IPI Plan Liabilities" shall mean any obligation or
liabilities relating to any Plan, or any trust or insurance policy related
thereto, administered, sponsored or maintained by IPI or any IPI Affiliate
(other than Progenitor) for any past, present or future employee of IPI, any IPI
Affiliate (other than Progenitor) or Progenitor, including without limitation
any liability for any minimum funding contributions under ERISA or the Code,
PROVIDED, that IPI Plan Liabilities shall not include obligations or liabilities
relating to any Plan, or any trust or insurance policy related thereto, to the
extent such obligations or liabilities relate to benefits accrued for past,
present or future employees of Progenitor that arise after the Effective Date,
unless attributable to the gross negligence or willful misconduct of IPI or an
Affiliate of IPI (other than Progenitor).

              (f) "Offering" shall mean the initial public offering of common
stock of Progenitor.

              (g) "Plans" shall mean (i) any "employee benefit plan" within the
meaning of Section 3(3) of ERISA, (ii) any profit sharing, pension, deferred
compensation, bonus, stock option or purchase, severance, retainer, consulting,
"cafeteria," accident and health, welfare or incentive plan, policy or
agreement, life insurance, accident and disability insurance, and any post-
employment benefits of any kind, whether legally binding or not, (iii) any plan
or policy providing for "fringe benefits" to officers, directors, employees or
agents, including, without limitation, vacation, paid holidays, personal leave,
family and medical leave, employee discount, educational benefit and similar
programs, and (iv) any employment, consulting, severance or indemnification
agreements or other agreements of any nature whatsoever between IPI or any of
its Affiliates, on the one hand, and any officer, director, employee or agent of
IPI or of any of IPI's Affiliates, on the other hand.

              (h) "Separate Return Tax Liability" as applied to any Member with
respect to a taxable year (or portion thereof) of such Member shall mean such
Member's tax liability computed, with the exceptions provided in
Section 1.1552-1(a)(2)(ii) of the Regulations, as if such Member had filed a
separate Federal income tax return or State Unitary Return for such


                                          2

<PAGE>


year, provided that the carryover for any tax attributed from a prior tax year
that is not available in determining the consolidated tax liability of the Group
for such taxable period (or portion thereof) shall be disregarded.

              (i) "Tax Liability of the Group" with respect to a taxable year
for which a consolidated Federal income tax return or State Unitary Return is
filed by IPI shall mean the Federal income tax or State Unitary Return liability
of the Group for such taxable year, including liability for alternative minimum
tax.

         2.   ALLOCATION OF FEDERAL TAX EXPENSE

         U.S. consolidated income tax returns including Progenitor as a Member
have been filed by IPI for the tax year ended September 30, 1992.  Progenitor
also was included in the consolidated income tax returns filed by IPI for a
portion of IPI's taxable year ending September 30, 1993.  The Tax Liability of
the Group for all taxable years in which Progenitor is or was included as a
Member for all or a portion thereof shall be allocated as follows:


              (a) The Tax Liability of the Group for a taxable year (or portion
thereof) shall initially be allocated to each Member in accordance with the
ratio which the Separate Return Tax Liability of such Member for such taxable
year (or portion thereof) bears to the total of the Separate Return Tax
Liabilities of all the Members of the Group for such taxable year (or portion
thereof).

              (b) An additional amount shall be allocated to each Member for a
taxable year (or portion thereof) equal to 100% of the excess, if any, of
(i) the Separate Return Tax Liability of such Member for such taxable year (or
portion thereof), over (ii) the portion of the Tax Liability of the Group for
such taxable year (or portion thereof) allocated to such Member in accordance
with paragraph 2(a), above.

              (c) The total of the additional amounts allocated to all Members
in accordance with paragraph 2(b), above (referred to herein as the
"Consolidated Return Tax Benefit") shall be allocated among and credited to the
Members in a manner which fairly reflects the income, deductions or credits to
which the Consolidated Return Tax Benefit is attributable.

              (d) The sum of (i) the amount allocated to a Member pursuant to
paragraph 2(a), above, plus (ii) the additional amount allocated to such Member
pursuant to paragraph 2(b), above, less (iii) the amount allocated to such
Member pursuant to paragraph 2(c), above, shall be deemed the Federal income tax
expense (or, where the amount allocated pursuant to paragraph 2(c), above,
exceeds the sum of the amounts allocated pursuant to paragraphs 2(a) and 2(b),
above, a refund of Federal income tax expense) of such Member for such taxable
year.

         3.   PAYMENT OF FEDERAL INCOME TAX EXPENSE

         For the part of the taxable year of IPI ending on the date that
Progenitor left the federal IPI Group:


                                          3

<PAGE>


              (a) IPI shall have the authority to pay in full the federal Tax
Liability of the Group for such taxable year and shall be entitled to obtain all
federal refunds or credits with respect to an overpayment of the federal Tax
Liability of the Group for such taxable year.

              (b) If the sum of the amounts allocated to Progenitor for such
portion of such taxable year pursuant to paragraphs 2(a) and 2(b), above,
exceeds the amount allocated to Progenitor for such period pursuant to
paragraph 2(c) above, Progenitor shall pay such excess to IPI.

              (c) If the amount allocated to Progenitor for such portion of such
taxable year pursuant to paragraph 2(c), above, exceeds the sum of the amounts
allocated to Progenitor for such period pursuant to paragraphs 2(a) and 2(b),
above, IPI shall pay such excess to Progenitor.

              (d) No payments shall be required to be made pursuant to
paragraph 3(b) or 3(c), above, until such time as the Tax Liability is paid.

         4. PRIOR TAX YEARS

         For each year in which Progenitor was a Member of the IPI Group, IPI
shall pay to Progenitor, immediately upon execution of this Agreement, an amount
equal to all amounts calculated pursuant to paragraph 3(c), above.  For each
year in which Progenitor was a member of the IPI Group, Progenitor shall pay to
IPI, immediately upon Progenitor leaving the IPI Group, an amount equal to all
amounts calculated pursuant to paragraph 3(b), above.

         5.   CARRYFORWARDS

         If part or all of an unused loss or tax credit is or has been
allocated to Progenitor pursuant to Regulation Section 1.1502-79 (including any
unused losses or tax credits that arise from the filing of an amended return or
from a recalculation or recomputation of such items after the date hereof), and
is carried forward to a year in which Progenitor files a separate return or a
consolidated return with another affiliated group, any refund or reduction in
tax liability arising from the carryforward shall be retained by Progenitor.  If
the election described in proposed Treasury Regulations Section 1.1502-95(c) (or
any analogous election described in final Treasury Regulations or future law)
becomes available, IPI shall make such election in a timely manner and shall, in
such election, apportion the amount of any consolidated Code Section 382
limitation to Progenitor in an amount equal to the 382 limitation that would
have been applicable to Progenitor as a standalone company.  In addition, IPI
shall allocate to Progenitor the maximum amount of any consolidated Code
Section 382 limitation permitted under current law that is necessary for
Progenitor to use any of its carryforwards.

         6. CARRYBACKS

         If any loss or credit of Progenitor is carried back to a year in which
Progenitor was a part of the IPI Group, any refund or reduction in tax liability
arising from the carryback shall be paid to Progenitor by IPI.


                                          4

<PAGE>


         7.   SUBSEQUENT ADJUSTMENTS

         If (i) the Tax Liability of the Group for a taxable year (or portion
thereof) during which Progenitor was a Member is changed or adjusted, and
(ii) such change or adjustment is part of a "determination," as that term is
defined in section 1313(a) of the Code or is otherwise a final decision,
disposition, or unappealable determination under state or local law, then the
allocations and payments made under this Agreement for such taxable year shall
be adjusted, in accordance with this Agreement, to conform to the Tax Liability
of the Group, as fixed by the final federal or state and local determination,
including interest thereon at the rate imposed by the Code or local law, as
appropriate, provided, however, that Progenitor shall not be obligated to make
any payments and shall not have any increased liability pursuant to this
paragraph 7 if Progenitor has not (i) been provided with copies of any filings
or reports or amended filings or amended reports that would affect or report or
alter the Tax Liability of the Group or any Member thereof  at least sixty days
in advance of the date on which any such filings or reports or amended filings
or amended reports are made and Progenitor gives its written consent and
approval to the filing of and the contents of such filings or reports or amended
filings or amended reports, (ii) been notified within 10 days after the
commencement of any audit or examination of any tax matter affecting the Tax
Liability of the Group or any Member thereof by any taxing authority and been
given copies of all correspondence, notices, reports and other materials with
respect to such audit or examination and approved all decisions, agreements,
pleadings, adjustments, settlements and compromises with respect to such audit
or examination or any litigation or controversy arising therefrom, (iii) and
otherwise been kept informed of and given the opportunity to consent to any
event, act, occurrence or change that would result in any change or adjustment
pursuant to this paragraph 7 and provided further that notwithstanding the
foregoing, amounts attributable to increased losses or credits being allocated
to Progenitor in connection with an amended return or a recalculation or
recomputation by Progenitor's accountants shall be paid to Progenitor
immediately upon the filing of such return or recalculation or recomputation
whether or not in connection with a determination or final decision,
disposition, or unappealable determination under applicable law.

         8. STATE TAX LIABILITY

         For every taxable period in which Progenitor is or was included in a
State Unitary Return that also includes or included IPI or is or was otherwise
included in a combined or group return including IPI for state, local or foreign
tax purposes, IPI shall pay Progenitor (i) the amount of any tax benefit enjoyed
by IPI or other member of such combined return or State Unitary Return as a
result of losses or credits or apportionment factors contributed by Progenitor
and (ii) the amount by which Progenitor's tax liability is greater than if
Progenitor had not been included in such combined return or State Unitary
Return.  For every such period, Progenitor shall pay IPI (i) the amount of any
tax benefit enjoyed by Progenitor as a result of losses or credits or
apportionment factors contributed by IPI or other member of such combined return
or State Unitary Return and (ii) the amount by which Progenitor's tax liability
is less than if Progenitor had not been included in such combined return or
State Unitary Return.


                                          5

<PAGE>


         9.   INDEMNITY

              (a)  IPI shall protect, defend, indemnify and hold harmless
Progenitor from any and all taxes (including without limitation any obligation
to contribute to the payment of any taxes determined on a consolidated, combined
or unitary basis with respect to a group of corporations that includes or
included Progenitor) which are resulting by reason of the several liability of
Progenitor pursuant to Treasury Regulations section 1.1502-6 or any analogous
state, local or foreign law or regulation or by reason of Progenitor having been
a member of any consolidated, combined or unitary group including IPI or
resulting from Progenitor ceasing to be a member of the IPI Group.  Nothing in
this paragraph shall be construed to require IPI to indemnify Progenitor for any
taxes or related interest or penalty liability attributable to any tax liability
of Progenitor that it would have had on a separate return basis if it had not
been a part of IPI's affiliated group.

              (b)  IPI shall protect, defend, indemnify and hold harmless
Progenitor from any and all claims, proceedings, investigations, inquiries,
losses, damages, demands, costs, expenses, penalties and liabilities (including
reasonable attorneys' fees) that result from, relate to or are attributable to
any of the IPI Plan Liabilities.

         10. DETERMINATIONS

         All determinations required hereunder for each taxable year shall be
made by mutual agreement of IPI and Progenitor with the advice of the
independent public accountants regularly engaged by IPI and Progenitor at the
time at which such determination is made.  If IPI and Progenitor and their
accountants cannot agree, then such matter shall be submitted to mediation
before a mutually agreeable mediator, which cost is to be borne equally by the
parties.  In the event mediation is unsuccessful in resolving the claim or
controversy, such claim or controversy shall be resolved by arbitration.
Arbitration under this Agreement shall be the exclusive remedy for all such
arbitrable claims. The parties agree that arbitration shall be held in or near
San Francisco, California, and shall be in accordance with the then-current
rules of the American Arbitration Association, before an arbitrator licensed to
practice law in California.  The arbitrator shall have authority to award or
grant both legal, equitable, and declaratory relief.  Such arbitration shall be
final and binding on the parties.



         11.  MISCELLANEOUS PROVISIONS

              (a) This Agreement has been made in and shall be construed and
enforced in accordance with the laws of the State of Delaware.

              (b) This Agreement shall be binding upon and inure to the benefit
of each party hereto and their respective successors and assigns, whether by
statutory merger, acquisition of assets, or otherwise.  This Agreement is solely
for the benefit of the parties hereto and should not be deemed to confer upon
third parties any remedy, claim, liability, reimbursement, claim of action or
other right in excess of those existing without reference to this Agreement.


                                          6

<PAGE>


              (c) All notices and other communications hereunder shall be in
writing and shall be delivered by hand or mailed by registered or certified mail
(return receipt requested) to the parties at the following addresses (or at such
other addresses for a party as shall be specified by like notice) and shall be
deemed given on the date on which such notice is received:

         To Interneuron:          One Ledgemont Center
                                  99 Hayden Avenue, Suite 340
                                  Lexington, MA  02173
                                  Attention:  Mark S. Butler, Esq.

         To Progenitor:           1507 Chambers Road
                                  Columbus, OH 43212-1566
                                  Attention:  _______________
                                              

              (d) Subject to the terms and conditions hereof, each party agrees
to use its best efforts to do, or cause to be done, all things necessary, proper
or advisable under applicable laws and regulations to consummate the
transactions contemplated by this Agreement and carry out its obligations
hereunder as expeditiously as practicable, including, without limitation, the
performance of such further acts or the execution and delivery of any additional
instruments or documents as any party may reasonably request in order to carry
out the purposes of this Agreement and the transactions contemplated hereby.

              (e) This Agreement may be executed simultaneously in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

              (f) Any dispute hereunder shall be resolved by arbitration in the
manner described in Section 10 hereof.

              (g) This Agreement contains the entire understanding of the
parties hereto with respect to the subject matter contained herein.

              (h) No alteration, amendment or modification of any of the terms
of this Agreement shall be valid unless made by an instrument signed in writing
by an authorized officer of each party hereto.  No rights under this Agreement
may be waived, except in writing by the party charged with such waiver.  No
waiver of any provision of this Agreement, in one or more instances, shall be
deemed to be, or construed as, a further or continuing waiver of such provision
or as a waiver of any other provision of this Agreement.

              (i) The headings of sections of this Agreement are inserted for
convenience only and shall not constitute a part hereof.




                                          7


<PAGE>


         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed on the date and year first above written.

                                            INTERNEURON PHARMACEUTICALS, INC.



                                             By:  
                                                ----------------------------
                                             Name: 
                                                  --------------------------
                                             Title: 
                                                   -------------------------
                                                     
                                                   -------------------------

                                            PROGENITOR, INC.



                                              By:  
                                              Name: 
                                                   -------------------------
                                              Title:  
                                                    ------------------------
                                                    
                                                    ------------------------


                                          8

<PAGE>

                                PROGENITOR, INC.


                        1996 EMPLOYEE STOCK PURCHASE PLAN


          The following constitute the provisions of the 1996 Employee Stock
Purchase Plan of Progenitor, Inc.

          1.   PURPOSE.  The purpose of the Plan is to provide employees of the
Company and its Designated Parents or Subsidiaries with an opportunity to
purchase Common Stock of the Company through accumulated payroll deductions.  It
is the intention of the Company to have the Plan qualify as an "Employee Stock
Purchase Plan" under Section 423 of the Code.  The provisions of the Plan,
accordingly, shall be construed so as to extend and limit participation in a
manner consistent with the requirements of that section of the Code.

          2.   DEFINITIONS.

          (a)  "ACCRUAL PERIOD" shall mean a period of approximately six months,
commencing on April 1 and October 1 of each year and terminating on the next
following September 30 or March 31, respectively; provided, however, that the
first Accrual Period shall commence on the Effective Date and shall end on
March 31, 1997.

          (b)  "BOARD" shall mean the Board of Directors of the Company.

          (c)  "CODE" shall mean the Internal Revenue Code of 1986, as amended.

          (d)  "COMMON STOCK" shall mean the common stock of the Company.

          (e)  "COMPANY" shall mean Progenitor, Inc., a Delaware corporation.

          (f)  "COMPENSATION" shall mean an Employee's base salary, commissions,
overtime, and bonuses from the Company or one or more Designated Parents or
Subsidiaries, including such amounts as are deferred by the Employee (i) under a
qualified cash or deferred arrangement described in Section 401(k) of the Code,
or (ii) to a plan qualified under Section 125 of the Code.  Compensation does
not include annual awards, other incentive payments, shift premiums, long-term
disability payments, worker's compensation, reimbursements or other expense
allowances, fringe benefits (cash or noncash), moving expenses, deferred
compensation, contributions (other than contributions described in the first
sentence) made on the Employee's behalf by the Company or one or more Designated
Parents or Subsidiaries under any employee benefit or welfare plan now or
hereafter established, and any other payments not specifically referenced in the
first sentence.

          (g)  "CORPORATE TRANSACTION" shall mean any of the following
stockholder-approved transactions to which the Company is a party:

<PAGE>

               (1)  a merger or consolidation in which the Company is not the
          surviving entity, except for a transaction the principal purpose of
          which is to change the state in which the Company is incorporated;

               (2)  the direct or indirect acquisition by any person or related
          group of persons (other than an acquisition from or by the Company or
          by a Company-sponsored employee benefit plan or by a person that
          directly or indirectly controls, is controlled by, or is under common
          control with, the Company) of beneficial ownership (within the meaning
          of Rule 13d-3 of the Exchange Act) of securities possessing more than
          fifty percent (50%) of the total combined voting power of the
          Company's outstanding securities;

               (3)  the sale, transfer or other disposition of all or
          substantially all of the assets of the Company (including the capital
          stock of the Company's subsidiary corporations) in connection with
          complete liquidation or dissolution of the Company; or

               (4)  any reverse merger in which the Company is the surviving
          entity but in which securities possessing more than fifty percent
          (50%) of the total combined voting power of the Company's outstanding
          securities are transferred to a person or persons different from those
          who held such securities immediately prior to such merger.

          (h)  "DESIGNATED PARENTS OR SUBSIDIARIES" shall mean the Parents or
Subsidiaries which have been designated by the Plan Administrator from time to
time in its sole discretion as eligible to participate in the Plan.

          (i)  "EFFECTIVE DATE" shall mean the date on which the Pricing
Committee of the Board agrees with the underwriters as to the price at which the
Common Stock will be offered to the public in the initial public offering of the
Common Stock.  However, should any Designated Subsidiary become a participating
company in the Plan after such date, then such entity shall designate a separate
Effective Date with respect to its employee-participants.

          (j)  "EMPLOYEE" shall mean any individual who is engaged in the
rendition of personal services to the Company or a Designated Parent or
Subsidiary for Compensation.  For purposes of the Plan, the employment
relationship shall be treated as continuing intact while the individual is on
sick leave or other leave of absence approved by the individual's employer.
Where the period of leave exceeds 90 days and the individual's right to
reemployment is not guaranteed either by statute or by contact, the employment
relationship will be deemed to have terminated on the 91st day of such leave.

          (k)  "ENROLLMENT DATE" shall mean the first day of each Purchase
Period.

          (l)  "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
amended.

          (m)  "EXERCISE DATE" shall mean the last day of each Accrual Period.


                                        2
<PAGE>


          (n)  "FAIR MARKET VALUE" shall mean, as of any date, the value of
Common Stock determined as follows:

               (1)  Where there exists a public market for the Common Stock, the
          Fair Market Value shall be (A) the closing sales price for a share of
          Common Stock for the last market trading day prior to the time of the
          determination (or, if no sales were reported on that date, on the last
          trading date on which sales were reported) on the stock exchange
          determined by the Administrator to be the primary market for the
          Common Stock or the Nasdaq National Market, whichever is applicable or
          (B) if the Common Stock is not traded on any such exchange or national
          market system, the average of the closing bid and asked prices of a
          share of Common Stock on the Nasdaq Small Cap Market for the day prior
          to the time of the determination (or, if no such prices were reported
          on that date, on the last date on which such prices were reported), in
          each case as reported in THE WALL STREET JOURNAL or such other source
          as the Plan Administrator deems reliable;

               (2)  In the absence of an established market of the type
          described in (1), above, for the Common Stock, and subject to (3),
          below, the Fair Market Value thereof shall be determined by the Plan
          Administrator in good faith; or

               (3)  On the Effective Date, the Fair Market Value shall be the
          price at which the Pricing Committee of the Board and the underwriters
          agree to offer Common Stock to the public in the initial public
          offering of the Common Stock, net of discounts and underwriting
          commissions.

          (o)  "PARENT" shall mean a "parent corporation," whether now or
hereafter existing, as defined in Section 424(a) of the Code.

          (p)  "PARTICIPANT" shall mean an Employee of the Company or Designated
Parent or Subsidiary who is actively participating in the Plan.

          (q)  "PLAN" shall mean this Employee Stock Purchase Plan.

          (r)  "PLAN ADMINISTRATOR" shall mean either the Board or a committee
of the Board that is responsible for the administration of the Plan.

          (s)  "PURCHASE PERIOD" shall mean a purchase period established
pursuant to paragraph 4 hereof.

          (t)  "PURCHASE PRICE" shall  mean an amount equal to 85% of the Fair
Market Value of a share of Common Stock on the Enrollment Date or on the
Exercise Date, whichever is lower.

          (u)  "RESERVES" shall mean the number of shares of Common Stock
covered by each option under the Plan which have not yet been exercised and the
number of shares of


                                        3
<PAGE>


Common Stock which have been authorized for issuance under the Plan but not yet
placed under option.

          (v)  "RULE 16b-3" shall mean Rule 16b-3 promulgated under the Exchange
Act or any successor thereto.

          (w)  "SUBSIDIARY" shall mean a "subsidiary corporation," whether now
or hereafter existing, as defined in Section 424(f) of the Code.

          3.   ELIGIBILITY.

          (a)  GENERAL.  Any individual who is an Employee on a given Enrollment
Date shall be eligible to participate in the Plan for the Purchase Period
commencing with such Enrollment Date.

          (b)  LIMITATIONS ON GRANT AND ACCRUAL.  Any provisions of the Plan to
the contrary notwithstanding, no Employee shall be granted an option under the
Plan (i) if, immediately after the grant, such Employee (taking into account
stock owned by any other person whose stock would be attributed to such Employee
pursuant to Section 424(d) of the Code) would own stock and/or hold outstanding
options to purchase stock possessing five percent (5%) or more of the total
combined voting power or value of all classes of stock of the Company or of any
Parent or Subsidiary of the Company, or (ii) which permits his or her rights to
purchase stock under all employee stock purchase plans of the Company and its
Parents or Subsidiaries to accrue at a rate which exceeds Twenty-Five Thousand
Dollars ($25,000) worth of stock (determined at the Fair Market Value of the
shares at the time such option is granted) for each calendar year in which such
option is outstanding at any time.  The determination of the accrual of the
right to purchase stock shall be made in accordance with Section 423(b)(8) of
the Code and the regulations thereunder.

          (c)  OTHER LIMITS ON ELIGIBILITY.  Notwithstanding subparagraph (a),
above, the following Employees shall not be eligible to participate in the Plan
for any relevant Purchase Period: (i) Employees whose customary employment is 20
or fewer hours or less per week; (ii) Employees whose customary employment is
for not more than 5 or fewer months in any calendar year; and (iii) Employees
who are subject to rules or laws of a foreign jurisdiction that prohibit or make
impractical the participation of such Employees in the Plan.

          4.   PURCHASE PERIODS.

          (a)  The Plan shall be implemented through overlapping or consecutive
Purchase Periods until such time as (i) the maximum number of shares of Common
Stock available for issuance under the Plan shall have been purchased or
(ii) the Plan shall have been sooner terminated in accordance with paragraph 19
hereof.  The maximum duration of a Purchase Period shall be twenty-seven (27)
months.  Initially, the Plan shall be implemented through overlapping Purchase
Periods of twenty-four (24) months' duration commencing each April 1 and
October 1 following the Effective Date (except that the initial Purchase Period
shall commence on the Effective Date and shall end on September 30, 1998).  The
Plan Administrator


                                        4
<PAGE>


shall have the authority to change the length of any Purchase  Period and the
length of Accrual Periods within any such Purchase Period subsequent to the
initial Purchase Period by announcement at least thirty (30) days prior to the
commencement of the Purchase Period and to determine whether subsequent Purchase
Periods shall be consecutive or overlapping.

          (b)  A Participant shall be granted a separate option for each
Purchase Period in which he/she participates.  The option right shall be granted
on the Enrollment Date and shall be automatically exercised in successive
installments on the Exercise Dates ending within the Purchase Period.

          (c)  An Employee may participate in only one Purchase Period at a
time.  Accordingly, except as provided in paragraph 4(d), an Employee who wishes
to join a new Purchase Period must withdraw from the current Purchase Period in
which he/she is participating and must also enroll in the new Purchase Period
prior to the Enrollment Date for that Purchase Period.

          (d)  If on the first day of any Accrual Period in a Purchase Period in
which a Participant is participating, the Fair Market Value of the Common Stock
is less than the Fair Market Value of the Common Stock on the Enrollment Date of
the Purchase Period (after taking into account any adjustment during the
Purchase Period pursuant to paragraph 18(a)), the Purchase Period shall be
terminated automatically and the Participant shall be enrolled automatically in
the new Purchase Period which has its first Accrual Period commencing on that
date, provided the Participant is eligible to participate in the Plan on that
date and has not elected to terminate participation in the Plan.

          (e)  Except as specifically provided herein, the acquisition of Common
Stock through participation in the Plan for any Purchase Period shall neither
limit nor require the acquisition of Common Stock by a Participant in any
subsequent Purchase Period.

          5.   PARTICIPATION.

          (a)  An eligible Employee may become a Participant in the Plan by
completing a subscription agreement authorizing payroll deductions in the form
of Exhibit A to this Plan and filing it with the Company's payroll office at
least fifteen (15) business days prior to the Enrollment Date for the Purchase
Period in which such participation will commence, unless a later time for filing
the subscription agreement is set by the Plan Administrator for all eligible
Employees with respect to a given Purchase Period.

          (b)  Payroll deductions for a Participant shall commence with the
first payroll period following the Enrollment Date and shall end on the last
complete payroll period during the Purchase Period, unless sooner terminated by
the Participant as provided in paragraph 10.

          6.   PAYROLL DEDUCTIONS.

          (a)  At the time a Participant files his/her subscription agreement,
he/she shall elect to have payroll deductions made during the Purchase Period in
an amount not exceeding ten percent (10%) of the Compensation which he/she
receives during the Purchase Period.


                                        5
<PAGE>


          (b)  All payroll deductions made for a Participant shall be credited
to his/her account under the Plan and will be withheld in whole percentages
only.  A Participant may not make any additional payments into such account.

          (c)  A Participant may discontinue his or her participation in the
Plan as provided in paragraph 10, or may decrease the rate of his/her payroll
deductions during the Purchase Period by completing or filing with the Company a
new subscription agreement authorizing a decrease in the payroll deduction rate.
The decrease in rate shall be effective with the first full payroll period
following ten (10) business days after the Company's receipt of the new
subscription agreement unless the Company elects to process a given change in
participation more quickly.  A Participant may increase the rate of his/her
payroll deductions for a future Purchase Period by filing with the Company a new
subscription agreement authorizing an increase in the payroll deduction rate
within ten (10) business days (unless the Company elects to process a given
change in participation more quickly) before the commencement of the upcoming
Purchase Period.  A Participant's subscription agreement shall remain in effect
for successive Purchase Periods unless terminated as provided in paragraph 10.
The Plan Administrator shall be authorized to limit the number of payroll
deduction rate changes during any Purchase Period.

          (d)  Notwithstanding the foregoing, to the extent necessary to comply
with Section 423(b)(8) of the Code and paragraph 3(b) herein, a Participant's
payroll deductions may be decreased to 0% at such time during any Accrual Period
which is scheduled to end during the current calendar year (the "Current Accrual
Period") that the aggregate of all payroll deductions which were previously used
to purchase stock under the Plan in a prior Accrual Period which ended during
that calendar year plus all payroll deductions accumulated with respect to the
Current Accrual Period equal $21,250.  Payroll deductions shall recommence at
the rate provided in such Participant's subscription agreement at the beginning
of the first Accrual Period which is scheduled to end in the following calendar
year, unless terminated by the Participant as provided in paragraph 10.

          7.   GRANT OF OPTION.  On the Enrollment Date, each Participant in
such Purchase Period shall be granted an option to purchase on each Exercise
Date of such Purchase Period (at the applicable Purchase Price) up to a number
of shares of the Common Stock determined by dividing such Participant's payroll
deductions accumulated prior to such Exercise Date and retained in the
Participant's account as of the Exercise Date by the applicable Purchase Price;
provided (i) that such purchase shall be subject to the limitations set forth in
paragraphs 3(b) and 12 hereof, and (ii) the maximum number of shares of Common
Stock a Participant shall be permitted to purchase in any Accrual Period shall
be 5,000 shares, subject to adjustment as provided in paragraph 18 hereof.
Exercise of the option shall occur as provided in paragraph 8, unless the
Participant has withdrawn pursuant to paragraph 10, and the option, to the
extent not exercised, shall expire on the last day of the Purchase Period.

          8.   EXERCISE OF OPTION.  Unless a Participant withdraws from the Plan
as provided in paragraph 10, below, his/her option for the purchase of shares
will be exercised automatically on each Exercise Date, and the maximum number of
full shares subject to the option shall be purchased for such Participant at the
applicable Purchase Price with the



                                        6
<PAGE>


accumulated payroll deductions in his/her account.  No fractional shares will be
purchased; any payroll deductions accumulated in a Participant's account which
are not sufficient to purchase a full share shall be carried over to the next
Purchase Period or returned to the Participant, if the Participant withdraws
from the Plan.  Any amount remaining in a Participant's account following the
purchase of shares on the Exercise Date which exceeds the cost of one full share
of Common Stock on the Exercise Date shall be returned to the Participant and
shall not be carried over to the next Purchase Period.  During a Participant's
lifetime, a Participant's option to purchase shares hereunder is exercisable
only by him/her.

          9.   DELIVERY.  Upon receipt of a request from a Participant after
each Exercise Date on which a purchase of shares occurs, the Company shall
arrange the delivery to such Participant, as appropriate, of a certificate
representing the shares purchased upon exercise of his/her option.

          10.  WITHDRAWAL; TERMINATION OF EMPLOYMENT.

          (a)  A Participant may withdraw all but not less than all the payroll
deductions credited to his/her account and not yet used to exercise his/her
option under the Plan at any time by giving written notice to the Company in the
form of Exhibit B to this Plan.  All of the Participant's payroll deductions
credited to his/her account will be paid to such Participant promptly after
receipt of notice of withdrawal, such Participant's option for the Purchase
Period will be automatically terminated, and no further payroll deductions for
the purchase of shares will be made during the Purchase Period.  If a
Participant withdraws from a Purchase Period, payroll deductions will not resume
at the beginning of the succeeding Purchase Period unless the Participant
delivers to the Company a new subscription agreement.

          (b)  Upon a Participant's ceasing to be an Employee for any reason or
upon termination of a Participant's employment relationship (as described in
paragraph 2(j)), the payroll deductions credited to such Participant's account
during the Purchase Period but not yet used to exercise the option will be
returned to such Participant or, in the case of his/her death, to the person or
persons entitled thereto under paragraph 14, and such Participant's option will
be automatically terminated.

          11.  INTEREST.  No interest shall accrue on the payroll deductions
credited to a Participant's account under the Plan.

          12.  STOCK.

          (a)  The maximum number of shares of Common Stock which shall be made
available for sale under the Plan shall be 200,000 shares (determined as of
August 9, 1996, the date of adoption of the Plan by the Board), subject to
adjustment upon changes in capitalization of the Company as provided in
paragraph 18.  If on a given Exercise Date the number of shares with respect to
which options are to be exercised exceeds the number of shares then available
under the Plan, the Plan Administrator shall make a pro rata allocation of the
shares remaining available for purchase in as uniform a manner as shall be
practicable and as it shall determine to be equitable.


                                        7
<PAGE>


          (b)  A Participant will have no interest or voting right in shares
covered by his/her option until such shares are actually purchased on the
Participant's behalf in accordance with the applicable provisions of the Plan.
No adjustment shall be made for dividends, distributions or other rights for
which the record date is prior to the date of such purchase.

          (c)  Shares to be delivered to a Participant under the Plan will be
registered in the name of the Participant or in the name of the Participant and
his/her spouse.

          13.  ADMINISTRATION.

          (a)  ADMINISTRATIVE BODY.  The Plan shall be administered by the Board
or a committee of members of the Board appointed by the Board.  The Board or its
committee shall have full and exclusive discretionary authority to construe,
interpret and apply the terms of the Plan, to determine eligibility and to
adjudicate all disputed claims filed under the Plan.  Every finding, decision
and determination made by the Board or its committee shall, to the full extent
permitted by law, be final and binding upon all persons.  Members of the Board
who are eligible Employees are permitted to participate in the Plan except to
the extent limited by subparagraph (b) of this paragraph 13.

          (b)  RULE 16b-3 LIMITATIONS.  Notwithstanding the provisions of
subparagraph (a), above, in the event that Rule 16b-3 provides specific
requirements for the administrators of plans of this type, the Plan shall be
administered only by such a body and in such a manner as shall comply with the
applicable requirements of Rule 16b-3.  Unless permitted by Rule 16b-3, no
discretion concerning decisions regarding the Plan shall be afforded to any
committee or person that is not "disinterested" as that term is used in Rule
16b-3.

          14.  DESIGNATION OF BENEFICIARY.

          (a)  Each Participant will file a written designation of a beneficiary
who is to receive any shares and cash, if any, from the Participant's account
under the Plan in the event of such Participant's death.  If a Participant is
married and the designated beneficiary is not the spouse, spousal consent shall
be required for such designation to be effective.

          (b)  Such designation of beneficiary may be changed by the Participant
(and his or her spouse, if any) at any time by written notice.  In the event of
the death of a Participant and in the absence of a beneficiary validly
designated under the Plan who is living at the time of such Participant's death,
the Company shall deliver such shares and/or cash to the executor or
administrator of the estate of the Participant, or if no such executor or
administrator has been appointed (to the knowledge of the Plan Administrator),
the Plan Administrator, in its discretion, may deliver such shares and/or cash
to the spouse or to any one or more dependents or relatives of the Participant,
or if no spouse, dependent or relative is known to the Plan Administrator, then
to such other person as the Plan Administrator may designate.

          15.  TRANSFERABILITY.  Neither payroll deductions credited to a
Participant's account nor any rights with regard to the exercise of an option or
to receive shares under the Plan may be assigned, transferred, pledged or
otherwise disposed of in any way (other than by will,


                                        8
<PAGE>


the laws of descent and distribution or as provided in paragraph 14 hereof) by
the Participant.  Any such attempt at assignment, transfer, pledge or other
disposition shall be without effect, except that the Plan Administrator may
treat such act as an election to withdraw funds from a Purchase Period in
accordance with paragraph 10.

          16.  USE OF FUNDS.  All payroll deductions received or held by the
Company under the Plan may be used by the Company for any corporate purpose, and
the Company shall not be obligated to segregate such payroll deductions.

          17.  REPORTS.  Individual accounts will be maintained for each
Participant in the Plan.  Statements of account will be given to Participants at
least annually, which statements will set forth the amounts of payroll
deductions, the Purchase Price, the number of shares purchased and the remaining
cash balance, if any.

          18.  ADJUSTMENTS UPON CHANGES IN CAPITALIZATION; CORPORATE
TRANSACTIONS.

          (a)  ADJUSTMENTS UPON CHANGES IN CAPITALIZATION.  Subject to any
required action by the stockholders of the Company, the Reserves, as well as the
Purchase Price, shall be proportionately adjusted for any increase or decrease
in the number of issued shares of Common Stock resulting from a stock split,
reverse stock split, stock dividend, combination or reclassification of the
Common Stock, or any other similar event resulting in an increase or decrease in
the number of issued shares of Common Stock.  Such adjustment shall be made by
the Plan Administrator, whose determination in that respect shall be final,
binding and conclusive.  Except as expressly provided herein, no issue by the
Company of shares of stock of any class, or securities convertible into shares
of stock of any class, shall affect, and no adjustment by reason thereof shall
be made with respect to, the number or price of shares of Common Stock subject
to an option.  The Plan Administrator may, if it so determines in the exercise
of its sole discretion, make provision for adjusting the Reserves, as well as
the price per share of Common Stock covered by each outstanding option, in the
event the Company effects one or more reorganizations, recapitalizations, rights
offerings or other increases or reductions of shares of its outstanding Common
Stock.

          (b)  CORPORATE TRANSACTIONS.  In the event of a proposed Corporate
Transaction, the Plan Administrator may elect to shorten the Purchase Period
then in progress by setting a new Exercise Date (the "New Exercise Date").  If
the Plan Administrator shortens the Purchase Period then in progress in the
event of a Corporate Transaction, the Plan Administrator shall notify each
Participant in writing, at least ten (10) days prior to the New Exercise Date,
that the Exercise Date for his/her option has been changed to the New Exercise
Date and that his/her option will be exercised automatically on the New Exercise
Date, unless prior to such date he/she has withdrawn from the Purchase Period as
provided in paragraph 10.  In the event of a proposed Corporate Transaction
(other than a Corporate Transaction described in Section 2(g)(2), above,) in
which the Plan Administrator elects not to shorten the Purchase Period, each
option under the Plan shall be assumed or an equivalent option shall be
substituted by such successor corporation or a parent or subsidiary of such
successor corporation.  For purposes of this subparagraph, an option granted
under the Plan shall be deemed to be assumed if, following the Corporate


                                        9
<PAGE>


Transaction, the option confers the right to purchase, for each share of Common
Stock subject to the option immediately prior to the Corporate Transaction, the
consideration (whether stock, cash or other securities or property) received in
the Corporate Transaction by holders of Common Stock for each share of Common
stock held on the effective date of the Corporate Transaction (and if such
holders were offered a choice of consideration, the type of consideration chosen
by the holders of a majority of the outstanding shares of Common Stock);
provided, however, that if such consideration received in the Corporate
Transaction was not solely common stock of the successor corporation or its
Parent, the Board may, with the consent of the successor corporation and the
Participant, provide for the consideration to be received upon exercise of the
option to be solely common stock of the successor corporation or its Parent
equal in fair market value to the per share consideration received by holders of
Common Stock in the Corporate Transaction.

          19.  AMENDMENT OR TERMINATION.

          (a)  The Plan Administrator may at any time and for any reason
terminate or amend the Plan.  Except as provided in paragraph 18, no such
termination can affect options previously granted, provided that a Purchase
Period may be terminated by the Plan Administrator on any Exercise Date if the
Plan Administrator determines that the termination of the Plan is in the best
interests of the Company and its stockholders.  Except as provided in paragraph
18, no amendment may make any change in any option theretofore granted which
adversely affects the rights of any Participant.  To the extent necessary to
comply with Rule 16b-3 or Section 423 of the Code (or any successor rule or
provision or any other applicable law or regulation), the Company shall obtain
stockholder approval in such a manner and to such a degree as required.

          (b)  Without stockholder consent and without regard to whether any
Participant rights may be considered to have been "adversely affected," the Plan
Administrator shall be entitled to change the Purchase Periods, limit the
frequency and/or number of changes in the amount withheld during Purchase
Periods, establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars, establish additional terms, conditions, rules
or procedures to accommodate the rules or laws of applicable foreign
jurisdictions, permit payroll withholding in excess of the amount designated by
a Participant in order to adjust for delays or mistakes in the Company's
processing of properly completed withholding elections, establish reasonable
waiting and adjustment periods and/or accounting and crediting procedures to
ensure that amounts applied toward the purchase of Common Stock for each
Participant properly correspond with amounts withheld from the Participant's
Compensation, and establish such other limitations or procedures as the Plan
Administrator determines in its sole discretion advisable and which are
consistent with the Plan.

          20.  NOTICES.  All notices or other communications by a Participant to
the Company under or in connection with the Plan shall be deemed to have been
duly given when received in the form specified by the Plan Administrator at the
location, or by the person, designated by the Plan Administrator for the receipt
thereof.

          21.  CONDITIONS UPON ISSUANCE OF SHARES.  Shares shall not be issued
with respect to an option unless the exercise of such option and the issuance
and delivery of such


                                       10
<PAGE>


shares pursuant thereto shall comply with all applicable provisions of law,
domestic or foreign, including, without limitation, the Securities Act of 1933,
as amended, the Exchange Act, the rules and regulations promulgated thereunder,
and the requirements of any stock exchange upon which the shares may then be
listed, and shall be further subject to the approval of counsel for the Company
with respect to such compliance.  As a condition to the exercise of an option,
the Company may require the Participant to represent and warrant at the time of
any such exercise that the shares are being purchased only for investment and
without any present intention to sell or distribute such shares if, in the
opinion of counsel for the Company, such a representation is required by any of
the aforementioned applicable provisions of law.  In addition, no options shall
be exercised or shares issued hereunder before the Plan shall have been approved
by stockholders of the Company as provided in paragraph 24.

          22.  TERM OF PLAN.  The Plan shall become effective upon the earlier
to occur of its adoption by the Board or its approval by the stockholders of the
Company.  It shall continue in effect for a term of ten (10) years unless sooner
terminated under paragraph 19.

          23.  ADDITIONAL RESTRICTIONS OF RULE 16b-3.  The terms and conditions
of options granted hereunder to, and the purchase of shares by, persons subject
to Section 16 of the Exchange Act shall comply with the applicable provisions of
Rule 16b-3.  This Plan shall be deemed to contain, such options shall contain,
and the shares issued upon exercise thereof shall be subject to, such additional
conditions and restrictions as may be required by Rule 16b-3 to qualify for the
maximum exemption from Section 16 of the Exchange Act with respect to Plan
transactions.

          24.  STOCKHOLDER APPROVAL.  Continuance of the Plan shall be subject
to approval by the stockholders of the Company within twelve (12) months before
or after the date the Plan is adopted.  If such stockholder approval is obtained
at a duly held stockholders' meeting, the Plan must be approved by a majority of
the votes cast at such stockholders' meeting at which a quorum representing a
majority of all outstanding voting stock of the Company is, either in person or
by proxy, present and voting on the Plan.  If such stockholder approval is
obtained by written consent, it must be obtained by the written consent of the
holders of a majority of all outstanding voting stock of the Company.  However,
approval at a meeting or by written consent may be obtained by a lesser degree
of stockholder approval if the Plan Administrator determines, in its discretion
after consultation with the Company's legal counsel, that such a lesser degree
of stockholder approval will comply with all applicable laws and will not
adversely affect the qualification of the Plan under Section 423 of the Code.

          25.  NO EMPLOYMENT RIGHTS.  The Plan does not, directly or indirectly,
create any right for the benefit of any employee or class of employees to
purchase any shares under the Plan, or create in any employee or class of
employees any right with respect to continuation of employment by the Company or
a Designated Subsidiary, and it shall not be deemed to interfere in any way with
such employer's right to terminate, or otherwise modify, an employee's
employment at any time.


                                       11
<PAGE>


          26.  EFFECT OF PLAN.  The provisions of the Plan shall, in accordance
with its terms, be binding upon, and inure to the benefit of, all successors of
each Participant, including, without limitation, such Participant's estate and
the executors, administrators or trustees thereof, heirs and legatees, and any
receiver, trustee in bankruptcy or representative of creditors of such
Participant.

          27.  APPLICABLE LAW.  The law of the State of Delaware will govern all
matters relating to this Plan except to the extent it is superseded by the laws
of the United States.


                                       12
<PAGE>

                                    EXHIBIT A

                                PROGENITOR, INC.
                        1996 EMPLOYEE STOCK PURCHASE PLAN
                             SUBSCRIPTION AGREEMENT


__        Original Application                    Enrollment Date:_____________
__        Change in Payroll Deduction Rate
__        Change of Beneficiary(ies)


          1.   I,________________________, hereby elect to participate in the
Progenitor, Inc. 1996 Employee Stock Purchase Plan (the "Employee Stock Purchase
Plan") and subscribe to purchase shares of the Company's Common Stock in
accordance with this Subscription Agreement and the Employee Stock Purchase
Plan.

          2.   I hereby authorize payroll deductions from each paycheck in the
amount of ____% of my Compensation on each payday (not to exceed 10%) during the
Purchase Period in accordance with the Employee Stock Purchase Plan.  (Please
note that no fractional percentages are permitted.)

          3.   I understand that the payroll deductions shall be accumulated for
the purchase of shares of Common Stock at the applicable Purchase Price
determined in accordance with the Employee Stock Purchase Plan.  I understand
that if I do not withdraw from a Purchase Period, any accumulated payroll
deductions will be used to automatically exercise my option.

          4.   I have received a copy of the complete "Progenitor, Inc. 1996
Employee Stock Purchase Plan." I understand that my participation in the
Employee Stock Purchase Plan is in all respects subject to the terms of the
Plan.  I understand that the grant of the option by the Company under this
Subscription Agreement is subject to obtaining stockholder approval of the
Employee Stock Purchase Plan.

          5.   Shares purchased for me under the Employee Stock Purchase Plan
should be issued in the name(s) of:

               _________________________________
               _________________________________

          6.   I understand that if I dispose of any shares received by me
pursuant to this Plan within 2 years after the Enrollment Date (the first day of
the Purchase Period during which I purchased such shares) or within 1 year after
the Exercise Date (the date I purchased such shares), I will be treated for
federal income tax purposes as having received ordinary income at the time of
such disposition in an amount equal to the excess of the fair market value of
the shares at the time such shares were delivered to me over the price which I
paid for the shares.  I HEREBY AGREE TO NOTIFY THE COMPANY IN WRITING WITHIN 30
DAYS AFTER THE DATE OF ANY SUCH DISPOSITION AND I

<PAGE>


WILL MAKE ADEQUATE PROVISION FOR FOREIGN, FEDERAL, STATE OR OTHER TAX
WITHHOLDING OBLIGATIONS, IF ANY WHICH ARISE UPON THE DISPOSITION OF THE COMMON
STOCK.  The Company may, but will not be obligated to, withhold from my
compensation the amount necessary to meet any applicable withholding obligation
including any withholding necessary to make available to the Company any tax
deductions or benefits attributable to sale or early disposition of Common Stock
by me.  If I dispose of such shares at any time after the expiration of the 2-
year and 1-year holding periods described above, I understand that I will be
treated for federal income tax purposes as having received income only at the
time of such disposition, and that such income will be taxed as ordinary income
only to the extent of an amount equal to the lesser of (1) the excess of the
fair market value of the shares at the time of such disposition over the
purchase price which I paid for the shares, or (2) 15% of the fair market value
of the shares on the first day of the Purchase Period.  The remainder of the
gain, if any, recognized on such disposition will be taxed as capital gain.  I
also understand that the foregoing income tax consequences are based on current
federal income tax law and that the Company is not responsible for advising me
of any changes in the applicable tax rules.

          7.   I hereby agree to be bound by the terms of the Employee Stock
Purchase Plan.  The effectiveness of this Subscription Agreement is dependent
upon my eligibility to participate in the Employee Stock Purchase Plan.

          8.   In the event of my death, I hereby designate the following as my
beneficiary(ies) to receive all payments and shares due me under the Employee
Stock Purchase Plan.

NAME: (Please print)     _______________________________________________________
                         (First)             (Middle)            (Last)

Relationship:            _______________________________________________________

Address:                 _______________________________________________________
                         _______________________________________________________
                         _______________________________________________________

Employee's Social
Security Number:         _______________________________________________________

Employee's Address:      _______________________________________________________

                         _______________________________________________________

                         _______________________________________________________

<PAGE>

I UNDERSTAND THAT THIS SUBSCRIPTION AGREEMENT SHALL REMAIN IN EFFECT THROUGHOUT
SUCCESSIVE PURCHASE PERIODS UNLESS TERMINATED BY ME

Employee's Signature:    _______________________________________________________

Dated:                   _______________________________________________________

Signature of spouse
if beneficiary is other
than spouse:             _______________________________________________________

Dated:                   _______________________________________________________

<PAGE>

                                    EXHIBIT B

                                PROGENITOR, INC.
                        1996 EMPLOYEE STOCK PURCHASE PLAN
                             SUBSCRIPTION AGREEMENT
                              NOTICE OF WITHDRAWAL


          The undersigned participant in the Purchase Period of the Progenitor,
Inc. 1996 Employee Stock Purchase Plan which began on _________________, 19___,
(the "Enrollment Date") hereby notifies the Company that he or she hereby
withdraws from the Purchase Period.  He or she hereby directs the Company to pay
to the undersigned as promptly as practicable all the payroll deductions
credited to his or her account with respect to such Purchase Period.  The
undersigned understands and agrees that his or her option for such Purchase
Period will be automatically terminated.  The undersigned understands further
that no further payroll deductions will be made for the purchase of shares in
the current Purchase Period and the undersigned shall be eligible to participate
in succeeding Purchase Periods only by delivering to the Company a new
Subscription Agreement.

Name and Address
of Participant:          _______________________________________________________

                         _______________________________________________________

                         _______________________________________________________

Signature:               _______________________________________________________

Date:                    _______________________________________________________

<PAGE>
                                                                    Exhibit 23.1


                        CONSENT OF INDEPENDENT ACCOUNTANTS

We consent to the inclusion in this registration statement on Form S-1 of our 
report, which includes an explanatory paragraph regarding the Company's 
ability to continue as a going concern, dated June 5, 1996 on our audits of 
the financial statements of Progenitor, Inc. (a Development Stage Company). 
We also consent to the reference to our firm under the caption "Experts."

                                       COOPERS & LYBRAND L.L.P.

Columbus, Ohio
August 15, 1996



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