LEUKOSITE INC
S-3, 1999-12-03
PHARMACEUTICAL PREPARATIONS
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<PAGE>




              AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION
                              ON DECEMBER 3, 1999
                         REGISTRATION NO. 333-_________


                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549

                                   -----------

                                    FORM S-3

                      AND POST-EFFECTIVE AMENDMENT NO. 1 TO
                      REGISTRATION STATEMENT NO. 333-85413,
                        POST-EFFECTIVE AMENDMENT NO. 2 TO
                     REGISTRATION STATEMENT NO. 333-76173 AND
                        POST-EFFECTIVE AMENDMENT NO. 4 TO
                      REGISTRATION STATEMENT NO. 333-65701


                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                                   -----------

                                 LEUKOSITE, INC.
             (Exact name of registrant as specified in its charter)

<TABLE>

<S>                                  <C>                                <C>
         DELAWARE                             2834                         04-3173859
(State or other jurisdiction of      (Primary Standard Industrial       (I.R.S. Employer
incorporation or organisation)       Classification Code Numbers)       Identification No.)

</TABLE>

                                215 FIRST STREET
                               CAMBRIDGE, MA 02142
                                 (617) 621-9350
               (Address, including zip code, and telephone number,
                 including area code, of registrant's principal
                               executive offices)

                                   -----------

                                 WITH COPIES TO:

CHRISTOPHER K. MIRABELLI, PH.D.                      JUSTIN P. MORREALE, ESQ.
CHAIRMAN OF THE BOARD OF DIRECTORS                   JULIO E. VEGA, ESQ.
LEUKOSITE, INC.                                      Bingham Dana LLP
215 First Street                                     150 Federal Street
Cambridge, MA 02142                                  Boston, MA 02110
(617) 621-9350                                       (617) 951-8000

            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

                                   -----------

         APPROXIMATE DATE OF COMMENCEMENT PROPOSED SALE TO THE PUBLIC:

<PAGE>

         FROM TIME TO TIME AFTER THIS REGISTRATION STATEMENT BECOMES EFFECTIVE.

         If the only securities being registered on this form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. / /

         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, check the following box. /X/

         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, check the following box and list the Securities
Act registration statement number of the earlier effective registration
statement or the same offering. / /

         If delivery of the  prospectus  is expected to be made  pursuant to
Rule 434, please check the following box. / /

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
- ---------------------------------------------------------------------------------------------------------------------------

                               PROPOSED               PROPOSED
                               MAXIMUM                MAXIMUM                   AGGREGATE        AMOUNT OF
TITLE OF SECURITIES            AMOUNT TO BE           AGGREGATE PRICE           OFFERING         REGISTRATION
    TO BE REGISTERED           REGISTERED(1)          PER UNIT (2)              PRICE (2)        FEE

- ---------------------------------------------------------------------------------------------------------------------------
<S>                            <C>                    <C>                       <C>              <C>

Common Stock,
par value $.01 per share            631,295                $37.59             $23,730,379           $6,264.82

- ---------------------------------------------------------------------------------------------------------------------------
</TABLE>

         (1) The total amount of selling shares listed in the prospectus is
8,140,667. A Registration Statement filed on October 15, 1998 registered
7,071,810 shares, of which 5,085,354 shares are being carried forward as of the
date hereof and are covered by the combined prospectus contained herein. A
registration fee of $14,874.49 was paid on October 15, 1998. A second

<PAGE>

Registration Statement declared effective on August 6, 1999, registered an
additional 935,625 shares, of which 748,500 are being carried forward as of the
date hereof and are covered by the combined prospectus contained herein. A
registration fee of $4,033.00 was paid on April 13, 1999. A third Registration
Statement declared effective on November 9, 1999, registered an additional
1,675,518 shares, all of which are being carried forward as of the date hereof
and are covered by the combined prospectus contained herein. A registration Fee
of $8,909.00 was paid on August 17, 1999. The number of new shares to be
registered under this Registration Statement is 631,295.

         (2) Estimated solely to determine the registration fee. Calculated in
accordance with Rule 457(c), based on the offering of up to 631,295 shares at a
purchase price of $37.59 per share, which is the average of the high and low
sale prices reported in the consolidated reporting system of the Nasdaq National
Market on November 26, 1999. It is not known how many shares will be purchased
under this Registration Statement or at what price such shares will be
purchased.

         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 WHICH 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 SECTION 8(A), MAY
DETERMINE.


<PAGE>

                                   PROSPECTUS

         THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED.
THESE SECURITIES SHALL NOT BE SOLD UNTIL THE REGISTRATION STATEMENT FILED WITH
THE SECURITIES AND EXCHANGE COMMISSION IS EFFECTIVE. THIS PROSPECTUS IS NOT AN
OFFER TO SELL THESE SECURITIES AND IT IS NOT SOLICITING AN OFFER TO BUY THESE
SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED.

                             DATED DECEMBER 3, 1999

                                8,140,667 SHARES

                                 LEUKOSITE, INC.
                                  COMMON STOCK

         Selling stockholders identified in this prospectus may sell up to
8,140,667 shares of common stock of LeukoSite, Inc. LeukoSite will not receive
any of the proceeds from the sale of shares by the selling stockholders.
LeukoSite's common stock is listed on the Nasdaq National Market under the
symbol "LKST". On November 26, 1999, the closing sale price of the common stock,
as reported on the Nasdaq National Market, was $38.25 per share.

              INVESTING IN THE COMMON STOCK INVOLVES A HIGH DEGREE
                OF RISK. SEE "RISK FACTORS," BEGINNING ON PAGE 4.

         NEITHER THE  SECURITIES  AND  EXCHANGE  COMMISSION  NOR ANY STATE
SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES, OR
DETERMINED IF THIS PROSPECTUS IS TRUTHFUL OR COMPLETE. ANY REPRESENTATION TO THE
CONTRARY IS A CRIMINAL OFFENSE.

         The selling stockholders may sell the shares of common stock described
in this prospectus in public or private transactions, on or off the National
Market System of the Nasdaq Stock Market, at prevailing market prices, or at
privately negotiated prices. The selling stockholders may sell shares directly
to purchasers or through brokers or dealers. Brokers or dealers may receive
compensation in the form of discounts, concessions or commissions from the
selling stockholders. More information is provided in the section titled "Plan
of Distribution."

                The date of this prospectus is December 3, 1999


<PAGE>

                       WHERE YOU CAN GET MORE INFORMATION

         We are a reporting company and file annual, quarterly and current
reports, proxy statements and other information with the SEC. You may read and
copy these reports, proxy statements and other information at the SEC's public
reference rooms in Washington, DC, New York, NY and Chicago, IL. You can request
copies of these documents by writing to the SEC and paying a fee for the copying
cost. Please call the SEC at 1-800-SEC-0330 for more information about the
operation of the public reference rooms. Our SEC filings are also available at
the SEC's Web site at "http://www.sec.gov". In addition, you can read and copy
our SEC filings at the office of the National Association of Securities Dealers,
Inc. at 1735 K Street, Washington, DC 20006.

         The SEC allows us to "incorporate by reference" information that we
file with them, which means that we can disclose important information to you by
referring you to those other documents. The information incorporated by
reference is an important part of this prospectus, and information that we file
later with the SEC will automatically update and supersede this information. We
incorporate by reference the documents listed below and any future filings we
will make with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Securities
Exchange Act of 1934:

         --Annual Report on Form 10-K/A for the year ended December 31, 1998.

         --Quarterly Reports on Form 10-Q filed May 12, 1999, August 12, 1999,
           and November 5, 1999.

         --Current Reports on Form 8-K filed January 5, 1999, February 26, 1999,
           April 6, 1999, April 27, 1999, June 24, 1999, August 3, 1999,
           September 3, 1999, and October 21, 1999.

         --The description of the common stock contained in LeukoSite's
           Registration Statement on Form 8-A filed with the SEC under the
           Securities Exchange Act of 1934.

         --You may request a copy of these filings at no cost, by writing,
           telephoning or e-mailing us at the following address:

                                 LeukoSite, Inc.
                                215 First Street
                               Cambridge, MA 02142
                            Attn: Investor Relations
                                 (617) 621-9350
                            [email protected]

         This prospectus is part of a Registration Statement we filed with the
SEC. You should rely only on the information incorporated by reference or
provided in this prospectus. No one else is authorized to provide you with
different information. We are not making an offer of these securities in any
state where the offer is not permitted. You should not assume that the
information in this prospectus is accurate as of any date other than the date on
the front of this document.


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<PAGE>

FORWARD-LOOKING STATEMENTS

         This prospectus contains forward-looking statements within the meaning
of Section 27A of the Securities Act of 1933 and Section 21E of the Securities
Exchange Act of 1934, including statements regarding LeukoSite's proposed merger
with a subsidiary of Millennium Pharmaceuticals, Inc., drug development
programs, clinical trials, receipt of regulatory approval, capital needs,
intellectual property, expectations and intentions.

         Forward-looking statements necessarily involve risks and uncertainties,
and LeukoSite's actual results could differ materially from those anticipated in
the forward-looking statements due to a number of factors, including those set
forth below under "Risk Factors" and elsewhere in this prospectus. The factors
set forth below under "Risk Factors" and other cautionary statements made in
this prospectus should be read and understood as being applicable to all related
forward-looking statements wherever they appear in this prospectus. We undertake
no obligation to update publicly any forward-looking statements for any reason,
even if new information becomes available or other events occur in the future.



                                       3
<PAGE>

RISK FACTORS

         INVESTING IN  LEUKOSITE'S  COMMON STOCK IS VERY RISKY.  YOU SHOULD BE
ABLE TO BEAR A COMPLETE LOSS OF YOUR INVESTMENT. YOU SHOULD CAREFULLY CONSIDER
THE FOLLOWING FACTORS, IN ADDITION TO THE OTHER INFORMATION IN THIS PROSPECTUS.

         IF CAMPATH (Registered Trademark) IS NOT APPROVED FOR SALE OF IF
SCHERING AG DOES NOT SUCCESSFULLY MARKET CAMPATH (Registered Trademark) ON OUR
BEHALF, OUR ANTICIPATED FUTURE REVENUE TARGETS WILL NOT BE ACHIEVED.

         We have only one product in the process of being reviewed by the FDA
for approval, our CAMPATH (Registered Trademark) monoclonal antibody, and that
review is in the early stages. There can be no assurance that the FDA or any
foreign governmental agency will approve CAMPATH(Registered Trademark) for
commercial sale on a timely basis or at all. The failure of CAMPATH (Registered
Trademark) to be approved by FDA and foreign governmental agencies on a timely
basis would have a material adverse effect on our business, financial condition
and results of operations.

         We have no experience with commercial sales and marketing. We will rely
solely upon Schering AG and its U.S. affiliate, Berlex Laboratories, for the
marketing, distribution and sale of CAMPATH (Registered Trademark) in the United
States and Europe. We have no plans to directly market CAMPATH (Registered
Trademark). Our right to share in the profits for U.S. sales of CAMPATH
(Registered Trademark) or to receive a royalty on sales of CAMPATH (Registered
Trademark) outside the U.S. is dependent upon the marketing and sales activities
of Schering and Berlex. We can make no assurances that there will be any profits
on sales of CAMPATH (Registered Trademark) in the U.S. In the event that there
are losses resulting from the marketing of CAMPATH (Registered Trademark) in the
U.S., LeukoSite will bear one-third of those losses.

         Our only source of revenues from product sales, if any, for the next
several years is likely to be from sales of CAMPATH (Registered Trademark);
however, we cannot be certain that CAMPATH (Registered Trademark) will be
approved for commercial sale or accepted in the United States or in any foreign
markets. A number of factors may affect the rate and level of market acceptance
of CAMPATH (Registered Trademark), including:

      -the perception by physicians and other members of the health care
       community of its safety and efficacy or that of competing products, if
       any;

      -the effectiveness of Berlex's sales and marketing efforts in the United
       States and the effectiveness of Schering's sales and marketing efforts in
       Europe;

      -the marketing and continued development of competing drugs;


                                       4
<PAGE>

      -unfavorable publicity concerning CAMPATH (Registered Trademark) or
       comparable drugs;

      -its price relative to other drugs or competing treatments;

      -the availability of third party reimbursement; and

      -regulatory developments related to the manufacture or continued use of
       CAMPATH (Registered Trademark).

         WE RELY ON BOEHRINGER INGLEHEIM AS OUR SOLE SOURCE MANUFACTURER OF
CAMPATH (Registered Trademark) AND OUR ABILITY TO GENERATE REVENUES IN THE
FUTURE WILL BE ADVERSELY AFFECTED IF WE ARE UNABLE TO OBTAIN SUFFICIENT
QUANTITIES OF CAMPATH (Registered Trademark) FROM THEM.

         We have an agreement with Boehringer Ingleheim for the production of
CAMPATH (Registered Trademark) for our clinical trials and for any commercial
sales. If Boehringer Ingleheim were not able to produce sufficient quantities of
CAMPATH (Registered Trademark) or if we were required to transfer manufacturing
processes of CAMPATH (Registered Trademark) to other third-party manufacturers,
then we could experience significant delays in supply. We have no experience in
manufacturing and we lack the facilities and personnel to manufacture CAMPATH
(Registered Trademark) and to produce an adequate supply to meet future
requirements. The loss of Boehringer Ingleheim as our contract manufacturer for
CAMPATH (Registered Trademark) or its inability to meet our requirements of
supply of CAMPATH (Registered Trademark) would have a material adverse effect on
our business, financial condition or results of operations.

         OUR DRUG CANDIDATES MAY NOT PROVE TO BE SAFE AND EFFECTIVE IN HUMAN
CLINICAL TRIALS.

         We are currently testing three monoclonal antibodies and three small
molecule products in human clinical trials. Clinical trials of drug candidates
involve the testing of potential therapeutic agents in humans to determine
whether the drug candidates are safe and effective and, if so, to what degree.
Many drugs in human clinical trials fail to demonstrate the desired safety and
efficacy characteristics. Drugs in later stages of clinical development may fail
to show the desired safety and efficacy traits despite having progressed through
initial human testing. The clinical trials of any of our drug candidates may not
be successful which may prevent us from commercializing the drug, substantially
impairing our business, financial condition and results of operations.


                                       5
<PAGE>

         OUR DRUG CANDIDATES ARE SUBJECT TO GOVERNMENTAL REGULATION AND PRODUCT
APPROVALS.

         Our products currently under development are subject to extensive and
rigorous regulation by the federal government, principally the FDA, and by state
and local governments. If we market these products abroad, foreign governments
may also impose export/import requirements and other restrictive regulations. We
must complete all appropriate regulatory clearance processes before
commercializing a product, which is lengthy and expensive. We cannot be sure
that we can obtain necessary regulatory approvals on a timely basis, if at all,
for any of the products we are currently developing, and all of the following
could have a material adverse effect on our business, financial condition and
results of operations

     --   significant delays in obtaining or failing to obtain required
          approvals

     --   loss of previously obtained approvals

     --   failing to comply with existing or future regulatory requirements

         Complying with FDA regulatory requirements applicable to product
development and obtaining FDA approval can take a number of years, involves the
expenditure of substantial resources and is uncertain. Many products that
initially appear promising ultimately do not reach the market because they are
found to be unsafe or ineffective or cannot meet the FDA's other regulatory
requirements. Moreover, it is possible that the current regulatory framework
could change or additional regulations could arise at any stage during our
product development, which may affect our ability to obtain approval as
anticipated, delay the submission or review of an application, or require
additional expenditures by LeukoSite.

         All of LeukoSite's product candidates will require FDA and foreign
government approvals for commercialization, none of which have been obtained.
LeukoSite and ILEX Oncology, our joint venture partner for the development of
CAMPATH (Registered Trademark), are required to file a Biologics Licensing
Application with the FDA before beginning commercialization of CAMPATH
(Registered Trademark) in the United States and must also file for marketing
approval from other jurisdictions. We are not certain when, independently or
with our collaborative partners, we will submit any marketing applications for
our other monoclonal antibodies or small molecule antagonists under development.
We cannot guarantee that any studies will demonstrate that the products are safe
and effective for their intended uses, or that the FDA will grant required
approval on a timely basis, or at all, for CAMPATH (Registered Trademark) or
other product for any studied indications.

         Government regulations may cause delays in LeukoSite's marketing of
products for a considerable or indefinite time, which could impose costly
procedural requirements upon LeukoSite's activities. While we attempt to comply
with such applicable government regulations, larger companies or companies more
experienced in regulatory



                                       6
<PAGE>

affairs may obtain a competitive advantage over us. Delays in obtaining
governmental regulatory approval could adversely affect our marketing strategy
as well as our ability to generate revenue from commercial sales. Our inability
to obtain marketing approval of our products on a timely basis, or at all, would
have a material adverse effect on our business, financial condition and results
of operations.

         WE ARE IN THE EARLY STAGES OF PRODUCT DEVELOPMENT.

         Many of LeukoSite's research and development programs are at an early
stage of development. The FDA has not approved any of our product candidates. We
have limited experience in conducting preclinical and clinical trials.
Furthermore, even if we receive initially positive preclinical trial results,
such results do not mean that similar results will be obtained in the later
stages of drug development, such as additional preclinical trials or human
clinical testing. All of our potential drug candidates are prone to the risks of
failure inherent in pharmaceutical product development, including the
possibility that none of our drug candidates will or can

         --be safe and effective

         --otherwise meet applicable regulatory standards

         --receive the necessary regulatory marketing approvals

         --develop into commercially viable drugs

         --be manufactured or produced economically and on a large scale

         --be successfully marketed

         --be reimbursed by government or private consumers

         --achieve customer acceptance

         In addition, third parties may preclude us from marketing our drugs
through enforcement of their proprietary rights. Or, third parties may succeed
in marketing equivalent or superior drug products. Our failure to develop safe,
commercially viable drugs would have a material adverse effect on our business,
financial condition and results of operations.

         IF OUR COLLARATIVE PARTNERS DO NOT ACTIVELY SEEK TO COMMERCIALIZE DRUG
CANDIDATES RESULTING FROM THEIR COLLABORATION WITH US, OUR REVENUES WILL SUFFER.

         A key element of LeukoSite's strategy is to accelerate certain of its
drug discovery and development programs and to fund its capital requirements, in
part, through collaboration agreements with major pharmaceutical companies. We
currently have



                                       7
<PAGE>

collaboration agreements with Warner-Lambert Company, Roche Bioscience, Kyowa
Hakko Kogyo, Ltd. and Genentech, Inc., Schering AG, and Hoechst Marion Roussel.
Warner-Lambert, Roche, Kyowa and Hoechst Marion Roussel have the right, but not
the obligation, to conduct preclinical and clinical trials of the compounds
developed during their collaboration with us and to commercialize any drug
candidates resulting from their collaboration with us. Genentech has the right,
but not the obligation, to conduct Phase III clinical trials of and to
commercialize our LDP-02 monoclonal antibody product. Thus, the collaboration
agreements allow our collaborative partners significant discretion in electing
whether to pursue the development of any potential drug candidates. As a result,
we cannot control the amount and timing of the resources dedicated by our
collaborative partners to their respective collaborations with us.

         This also means that LeukoSite's right to receive revenues under the
collaboration agreements for drug development milestones or royalties,
co-promotion rights or profit-sharing on sales is dependent largely upon the
activities and the development, manufacturing and marketing resources and
abilities of its collaborative partners. As such,

         --our partners may not pursue the  development  and  commercialization
           of compounds  resulting from their collaboration with us

         --any development or commercialization may not be successful even if
           our partners pursued such efforts

         --we may not derive substantial or any royalty or product sales revenue
           from our collaborations

         Moreover, certain drug candidates discovered by LeukoSite may be
competitive with our partners' drugs or drug candidates. Accordingly, it is
possible that our collaborative partners will choose not to proceed with the
development of our drug candidates or that they will pursue their existing or
alternative technologies in preference to our drug candidates. We advise you
that

         --our interests may not always coincide with those of our collaborative
           partners

         --some of our collaborative partners could independently develop or
           develop with third parties drugs which compete with ours

         --disagreements with our partners over rights to technology or other
           proprietary interests might occur, leading to delays in research or
           in the development and commercialization of certain product
           candidates (such disputes could also require or result in litigation
           or arbitration, which is time-consuming and expensive)



                                       8
<PAGE>

         IF OUR COLLABORATIVE PARTNERS TERMINATE OUR AGREEMENTS WITH THEM, OUR
ABILITY TO FUND OUR RESEARCH OPERATIONS AND CLINICAL TRIALS WILL SUFFER.

         LeukoSite relies on its collaborative partners to fund a substantial
portion of its research operations and clinical trials. Although each of the
collaboration agreements may be extended past its current term, we cannot be
sure that these contracts will be extended or renewed, or that any renewal, if
made, will be on terms favorable to us.

         In short, we cannot guarantee that any of the collaboration agreements
will remain in effect for its expected term. If any of the collaborative
partners terminates or breaches its agreement with LeukoSite, or fails to
conduct its collaborative activities in a timely manner, then the development or
commercialization of any drug candidate or research program with such partner
could be delayed or terminated. Alternatively, we may have to devote unexpected
and unbudgeted additional resources to such development or commercialization,
all of which could have a material adverse effect on our business, financial
condition and results of operations.

         OUR SIGNIFICANT EXPENSES MAY CAUSE US TO CONTINUE TO INCUR FUTURE
LOSSES.

         LeukoSite has incurred a net operating loss every year since it was
incorporated in May 1992, and had an accumulated deficit of approximately $68.8
million through September 30, 1999. LeukoSite expects to incur significant
additional operating losses over the next several years and expects cumulative
losses to increase substantially due to expanded research and development
efforts, preclinical and clinical trials and commercialization expenses. In
2000, we expect that our only revenues will come primarily from milestone
payments and any other amounts received under existing and future collaboration
agreements, if any. It is possible that we may not be able to

         -successfully commercialize any of our products

         -establish any additional collaborative relationships on terms
          acceptable to us

         -maintain the current collaboration agreements in effect

         -achieve the milestones that are required for us to receive funds from
          our current collaborative partners

         LeukoSite's ability to generate revenue or achieve profitability is
dependent in part on its and its collaborative partners' ability to complete the
development of drug candidates successfully, to obtain regulatory approvals for
drug candidates and to manufacture and commercialize any resulting drugs. We
cannot provide assurance that we will successfully identify, develop,
commercialize, manufacture and market any products, obtain required regulatory
approvals or achieve profitability.



                                       9
<PAGE>

         WE HAVE SIGNIFICANT DEVELOPMENT COSTS AND ARE UNCERTAIN AS TO THE
AVAILABILITY OF FUTURE FUNDING.

         LeukoSite will require substantial additional funds in order to finance
its drug discovery and development programs, fund operating expenses, pursue
regulatory clearances, and prosecute and defend its intellectual property
rights. We depend heavily upon our collaborative partners for research and
clinical trials funding and we cannot be sure that revenues from product sales
or our existing collaboration agreements will provide the necessary funding to
meet our operating expenses. In the event that the merger of LeukoSite and
Millennium is not consummated, LeukoSite will have to seek additional funding
through public or private financing or collaboration or other arrangements with
collaborative partners. The raising of additional funds through the issuance of
equity securities may result in further dilution to our existing stockholders.
We cannot be sure that additional financing will be available, in the first
instance, from any sources or, even if available, that such funds will be
available on acceptable terms.

         WE CANNOT BE CERTAIN THAT WE WILL OBTAIN SUFFICIENT PATENT PROTECTION,
OR THAT ANY SUCH PATENTS SO OBTAINED WILL PROVIDE SUFFICIENT PROTECTION AGAINST
COMPETITIVE PRODUCTS OR PROCESSES.

         LeukoSite's success will depend in part on its ability to obtain United
States and foreign patent protection for its drug candidates and processes,
preserve its trade secrets, and operate without infringing the proprietary
rights of third parties. We place considerable importance on obtaining patent
protection for significant new technologies, products and processes. Legal
standards relating to the validity of patents covering pharmaceutical and
biotechnological inventions, and the scope of claims made under such patents,
are still developing. Our patent position is highly uncertain and involves
complex legal and factual questions. We cannot be certain that the named
applicants or inventors of the subject matter covered by our patent applications
or patents (whether directly owned by us or licensed to us) were the first to
invent or the first to file patent applications for such inventions. Third
parties may challenge, infringe upon, circumvent or seek to invalidate existing
or future patents owned by or licensed to us. A court or other agency with
jurisdiction may find our patents unenforceable. Even if we have valid patents,
these patents still may not provide sufficient protection against competitive
products or other commercially valuable products or processes.

         If a third party claims the same or overlapping subject matter as we
have claimed in a United States patent application or patent, then we may decide
or be required to participate in interference proceedings in the United States
Patent and Trademark Office (PTO) in order to determine who invented the subject
matter first. If we lost such an interference proceeding, then we would be
deprived of the patent protection we previously sought or obtained. Indeed,
regardless of whether we win or lose in such proceedings, we would still incur
substantial costs.



                                      10
<PAGE>

         In addition to patent protection, LeukoSite relies on trade secrets,
proprietary know-how, and confidentiality provisions in agreements with our
collaborative partners, employees and consultants to protect our intellectual
property. We also rely on invention assignment provisions in agreements with
employees and certain consultants. It is possible that these agreements could be
breached or that we might not have adequate remedies for any such breaches.
Third parties may learn of or independently discover our trade secrets,
proprietary know-how and intellectual property, which could have a material
adverse effect on our business, financial condition and results of operations.

         LeukoSite's product candidates LDP-01, LDP-02 and CAMPATH (Registered
Trademark) are humanized monoclonal antibodies. We are aware that both the PTO
and certain foreign governments have issued patents to third parties which
relate to certain humanized antibodies, products useful for making humanized
antibodies, and processes for making and using humanized antibodies. We may
choose to seek or be required to seek licenses under certain of these patents.

         We are also aware of third party applications in the United States and
abroad relating to certain humanized monoclonal antibodies, products useful for
making humanized antibodies, and processes for making and using humanized
antibodies. LeukoSite may choose to seek or be required to seek licenses under
some or all of the patents which might issue from these patent applications.

         THERE IS SIGNIFICANT AND WIDESPREAD LITIGATION IN THE PHARMACEUTICAL
AND BIOTECHNOLOGY INDUSTRY REGARDING PATENTS AND PROPRIETARY RIGHTS AND OUR
BUSINESS AND RESULTS OF OPERATIONS COULD BE ADVERSELY AFFECTED IF WE BECOME
INVOLVED IN SUCH LITIGATION.

         There is significant and widespread litigation in the pharmaceutical
and biotechnology industry regarding patents and proprietary rights. LeukoSite
may need to assert claims of infringement, enforce its patents, protect trade
secrets, know-how or other intellectual property rights, or determine the scope
or validity of proprietary rights of third parties. Conversely, we may need to
defend against claims of infringement by third parties. We cannot guarantee that
any of our patents will ultimately be held valid or that our efforts to assert
or defend any patents, trade secrets, know-how or other intellectual property
rights would be successful. Similarly, we cannot guarantee that our products or
processes will not be held to infringe the patents or other intellectual
property rights of others. Uncertainties emanating from the initiation and
continuation of any patent or related litigation could have a material adverse
effect on our business, financial condition and results of operations.

         The expenses of intellectual property litigation or other similar
proceedings would be likely to be substantial, and could have a material adverse
effect on LeukoSite's business, financial condition and results of operations.
An adverse outcome in such litigation or proceeding could subject LeukoSite to
significant liabilities or require LeukoSite to cease certain activities. If any
of our present or future products or processes



                                       11
<PAGE>

is alleged or determined to infringe upon the patents or impermissibly use the
intellectual property of others, we may choose or be required to obtain licenses
from third parties under their patents or proprietary rights. We cannot
guarantee that we will be able to obtain those licenses on acceptable terms, if
at all. In such event, we would be severely restricted or prohibited from the
development, manufacture and sale of our drug candidates.

         IF OUR COMPETITIORS SUCCEED IN DEVELOPING OR LICENSING TECHNOLOGIES OR
FUTURE DRUG PRODUCTS, OUR TECHNOLOGY AND FUTURE DRUG PRODUCTS COULD BECOME
OBSOLETE AND NONCOMPETITIVE.

         The biotechnology and pharmaceutical industries are intensely
competitive. LeukoSite has many competitors both in the United States and
abroad, including major, multinational pharmaceutical and chemical companies,
specialized biotechnology firms and universities and other research
institutions. Many of our competitors have greater financial and other
resources, such as larger research and development staffs and more effective
marketing and manufacturing organizations. Our competitors may succeed in
developing or licensing on an exclusive basis technologies and drugs that are
more effective or less costly than any which we are currently developing, which
could render our technology and future drug products obsolete and
noncompetitive. It is possible for our competitors to obtain FDA or other
regulatory approvals for drug candidates before we can. In general, companies
that begin commercial sale of their drugs before their competitors have a
significant competitive advantage in the marketplace, including the ability to
obtain certain patent and FDA marketing exclusivity rights that would delay our
ability to market certain products. Even if our drugs or drug products are
approved for sale, we cannot assure our ability to compete successfully with
competitors' existing products or products under development.

         WE RELY ON CONTRACT MANUFACTURERS AND LACK MANUFACTURING EXPERIENCE
OURSELVES.

         In addition to relying on Boehringer Ingleheim as the sole manufacturer
of CAMPATH (Registered Trademark), LeukoSite depends on third parties to
manufacture its product candidates and is aware of only a limited number of
manufacturers which it believes has the ability and capability to manufacture
its drug candidates for preclinical and clinical trials. If we were required to
transfer manufacturing processes to other third-party manufacturers, then we
could experience significant delays in supply. If, at any time, we are unable to
maintain, develop or contract for manufacturing capabilities on acceptable
terms, then our ability to conduct preclinical and clinical trials with our drug
candidates will be adversely affected, resulting in delays in the submission of
drug candidates for regulatory approvals. We have no experience in manufacturing
and we currently lack the facilities and personnel to manufacture products in
accordance with Good Manufacturing Practices as prescribed by the FDA or to
produce an adequate supply of compounds to meet future requirements for
preclinical and clinical trials.



                                       12
<PAGE>

         RAPID TECHNOLOGICAL CHANGE COULD RENDER PRODUCTS OBSOLETE.

         Biotechnology and related pharmaceutical technology have undergone and
are subject to rapid and significant change. LeukoSite expects that the
technologies associated with biotechnology research and development will
continue along this rapid path. Our success will depend in large part on our
ability to maintain a competitive position in the rapidly changing environment.
Because of the rapid changes in technology, our compounds, products or processes
may become obsolete before we can recover the expenses incurred in developing
such compounds, products or processes. We cannot assure that we can maintain our
technological competitiveness.

         WE DEPEND ON KEY PERSONNEL.

         We believe that our ability to successfully implement our business
strategy is highly dependent on our management and scientific team. None of our
executive officers has employment agreements with us. Losing the services of one
or more of these individuals might hinder our ability to achieve our development
objectives. We are highly dependent on our ability to hire and retain qualified
scientific and technical personnel. The competition for these employees is
intense. We cannot be sure that we can continue to hire and retain the qualified
personnel needed for our business. Loss of the services of or the failure to
recruit key scientific and technical personnel could adversely affect our
business, operating results and financial condition.

         WE HAVE NOT DECLARED ANY DIVIDENDS.

         We have never declared or paid cash dividends. We do not intend to
declare or pay any cash dividends in the foreseeable future.

                                    LEUKOSITE

         LeukoSite is a biotechnology company developing proprietary monoclonal
antibody and small molecule drugs to treat patients with cancer and
inflammatory, autoimmune and viral diseases. The mailing address and telephone
number of our principal executive office is 215 First Street, Cambridge, MA
02142 and (617) 621-9350.

                               RECENT DEVELOPMENTS

         On October 14, 1999 LeukoSite signed an Agreement and Plan of Merger
(the "Merger Agreement") with Millennium Pharmaceuticals, Inc. and ANM, Inc., a
wholly owned subsidiary of Millennium. Under the terms of the Merger Agreement,
ANM, Inc. will merger with and into LeukoSite, whereby LeukoSite will become a
wholly owned subsidiary of Millennium (the "Merger"). Each LeukoSite stockholder
will receive for each share of Leukosite stock 0.4296 of Millennium Common
Stock, par value $.001 per share. The Merger Agreement and Merger are subject
to, among other things, LeukoSite stockholder approval.



                                       13
<PAGE>

         On July 20, 1999 LeukoSite raised approximately $14.4 million in a
private placement of its common stock with two institutional investors,
HealthCare Ventures V, L.P. and Perseus Capital, LLC, at a price per share of
$9.70, for an aggregate of 1,487,548 shares of common stock.

         On July 19, 1999 LeukoSite acquired by merger all of the issued and
outstanding capital stock of ProScript, Inc. and, in connection therewith,
issued an aggregate of 187,970 shares of common stock and paid initially
$411,719 in cash.

         On July 1, 1998 LeukoSite raised approximately $11.8 million in a
private placement of common stock. LeukoSite issued approximately 1,970,000
shares of Common Stock.

         On February 11, 1999 LeukoSite acquired by merger all of the issued and
outstanding capital stock of CytoMed, Inc. through the issuance initially of
935,625 shares of LeukoSite's Series A Convertible Preferred Stock, which
automatically converted into 935,625 shares of common stock as of May 25, 1999.
An additional 631,295 shares of common stock were issued on November 30, 1999.
These shares were issued to former CytoMed shareholders as additional merger
consideration when a milestone payment was received by LeukoSite.

                                 USE OF PROCEEDS

         LeukoSite will not receive any proceeds from the sale of the shares of
common stock offered by the selling stockholders hereunder.

                              SELLING STOCKHOLDERS

         The Selling Stockholders covered by this prospectus are persons who
received LeukoSite common stock in connection with (one or more of the
following) (1) the private placement of LeukoSite's common stock which occurred
on July 1, 1998, (2) the acquisition (by merger) by LeukoSite of CytoMed, Inc.,
(3) the acquisition (by merger) by LeukoSite of ProScript, Inc., and/or (4) the
private placement of LeukoSite's common stock which occurred on July 20, 1999
and also includes persons who were entitled to have shares registered pursuant
to piggyback registration rights previously granted by LeukoSite to such
persons.

         1998 Private Placement. Under a Registration Rights Agreement dated
July 1, 1998 among LeukoSite and certain selling stockholders, we agreed to
register the LeukoSite common stock sold to those selling stockholders in the
private placement and to use our best efforts to keep the Registration Statement
effective for two years, or until all of the shares are sold under the
Registration Statement, whichever comes first.



                                       14
<PAGE>

         CytoMed Merger. Under an Agreement and Plan of Merger and
Reorganization dated January 4, 1999 among LeukoSite, LeukoSite Merger
Corporation, a wholly-owned subsidiary of LeukoSite, and CytoMed, Inc., we
agreed to register the LeukoSite common stock to be issued as consideration for
the merger of CytoMed with and into LeukoSite Merger Corporation for the
accounts of the former shareholders of CytoMed. We also agreed to use our best
efforts to keep the Registration Statement effective for two years, or until all
of the shares are sold under the Registration Statement, whichever comes first.

         ProScript Merger. Under an Agreement and Plan of Merger and
Reorganization dated June 22, 1999 among LeukoSite, ProScript Acquisition Co., a
wholly-owned subsidiary of LeukoSite, ProScript, Inc., HealthCare Ventures III,
L.P. and HealthCare Ventures IV, L.P., the shares of LeukoSite common stock
issued in connection therewith were required to be registered upon written
notice to LeukoSite or as a piggyback on any other registration statement being
filed by the Company.

         1999 Private Placement. Under two separate Registration Rights
Agreements each dated July 20, 1999 between LeukoSite and each of Perseus
Capital LLC and HealthCare Ventures V, L.P., we agreed to register the LeukoSite
common stock issued in connection with the private placement and to use our best
efforts to keep the Registration Statement effective for two years, or until all
of the shares are sold under the Registration Statement, whichever comes first.

         Our registration of the shares of common stock hereunder does not
necessarily mean that the selling stockholders will sell all or any of the
shares. The following tables set forth certain information regarding the
beneficial ownership of the common stock as of November 3, 1999, by each of the
selling stockholders. The estimated information provided in the tables below
with respect to each selling stockholder, however, has not been obtained
recently from all such selling stockholders and is based only on estimations by
the Company to the best of its knowledge. Except as otherwise disclosed below,
none of the selling stockholders has, or within the past three years has had,
any position, office or other material relationship with the Company. Because
the selling stockholders may sell all or some portion of the shares of common
stock beneficially owned by them, only an estimate (assuming each selling
stockholder sells all of its shares offered hereby) can be given as to the
number of shares of common stock that will be beneficially owned by the selling
stockholders after this offering. In addition, the selling stockholders may have
sold, transferred or otherwise disposed of, or may sell, transfer or otherwise
dispose of, at any time or from time to time since the date on which they last
provided the information regarding the shares of common stock beneficially owned
by them, all or a portion of the shares of common stock beneficially owned by
them in transactions exempt from the registration requirements of the Securities
Act of 1933. Selling stockholders have not provided updated information to us
regarding the shares of common stock beneficially owned by them.



                                       15
<PAGE>

                              SELLING STOCKHOLDERS


<TABLE>
<CAPTION>

                                                                               SHARES BENEFICIALLY
                                                                               OWNED AFTER OFFERING
                                                                             -------------------------
                            SHARES BENEFICIALLY    NUMBER OF SHARES
NAME AND ADDRESS            OWNED PRIOR TO         BEING OFFERED
OF BENEFICIAL OWNER         OFFERING (1)
                                                                             NUMBER    PERCENTAGE
- --------------------------  ---------------------  ----------------------    ------    ---------------
<S>                         <C>                       <C>                     <C>       <C>
Abrams, Larry                          1,320                 1,320              0               *
   24 Central Park South
   New York, NY  10019

Atlas Venture Fund II, L.P.           74,615                74,615              0               *
   222 Berkeley Street
   Boston, MA 02116
   Attn: Jean-Francois Formela

Atlas Venture Europe Fund B.V.        60,131                60,131              0               *
   P. O. Box 5225
   1410 AE NAARDEN
   The Netherlands
   Attn: Hans Bosman

Beck, Thomas R.                        1,050                 1,050              0               *
   345 Silver Hill Road
   Concord, MA 01742

Biotechnology Development             51,291                51,291              0               *
   Fund, L.P.
   575 High Street, Suite 201
    Palo Alto, CA 94301
   Attn: Virginia Leung

The Family Trust f/b/o James M. Casty     12                    12              0               *
   c/o Mr. James M. Casty
   Robin Lane
   Alpine, NJ  07620

</TABLE>



                                       16
<PAGE>

<TABLE>
<CAPTION>
                                                                               SHARES BENEFICIALLY
                                                                               OWNED AFTER OFFERING
                                                                             -------------------------
                            SHARES BENEFICIALLY    NUMBER OF SHARES
NAME AND ADDRESS            OWNED PRIOR TO         BEING OFFERED
OF BENEFICIAL OWNER         OFFERING (1)
                                                                             NUMBER    PERCENTAGE
- --------------------------  ---------------------  ----------------------    ------    ---------------
<S>                         <C>                       <C>                     <C>       <C>

The Family Trust f/b/o Lee S. Casty       44                    44              0               *
   c/o Mr. James M. Casty
   Robin Lane
   Alpine, NJ  07620

The Family Trust f/b/o Ronald G. Casty     8                     8              0               *
   c/o Mr. James M. Casty
   Robin Lane
   Alpine, NJ  07620

The Family Trust f/b/o Scott R. Casty     12                    12              0               *
   c/o Mr. James M. Casty
   Robin Lane
   Alpine, NJ  07620

Chiron Corporation                    87,039                87,039              0               *
   4560 Horton Street
   Emeryville, CA  94608

CIP Capital, L.P.                     59,454                59,454              0               *
   Bldg. 300
   435 Devon Park Drive
   Wayne, PA 19087
   Attn: Joseph Jackson

Deutsche Vermogens                   100,706               100,706              0               *
   Bildungsgesellschaft mbH
   Feldbergstr. 22
   60323 Frankfurt am Main
   Germany
   Attn: Berndt Ubach-Utermohl

Everest Trust                         16,334                16,334              0               *
   c/o Rho Asset Management Co.
   767 Fifth Avenue, 43rd Floor
   New York, NY  10153

Fisher, Richard A                        524                   524              0               *
   c/o UCB Research Inc.
   840 Memorial Drive
   Cambridge, MA 02139

Four Partners                         33,334                33,334              0               *
   667 Madison Avenue
   7th Floor
   New York, New York 10021

</TABLE>



                                       17
<PAGE>

<TABLE>
<CAPTION>

                                                                               SHARES BENEFICIALLY
                                                                               OWNED AFTER OFFERING
                                                                             -------------------------
                            SHARES BENEFICIALLY    NUMBER OF SHARES
NAME AND ADDRESS            OWNED PRIOR TO         BEING OFFERED
OF BENEFICIAL OWNER         OFFERING (1)
                                                                             NUMBER    PERCENTAGE
- --------------------------  ---------------------  ----------------------    ------    ---------------
<S>                         <C>                       <C>                     <C>       <C>

Gateway Venture                       37,187                37,187              0               *
     Partners III L.P.
   8000 Maryland Avenue, Suite 1190
   St. Louis, MO  63105
   Attn: C.E. Anagnostopoulos, Ph.D.

Goldman Sachs & Co.                  166,667               166,667              0               *
   One New York Plaza
   New York, New York 10004

HealthCare Ventures and
       Affiliated Entities         1,653,523             1,644,524          8,999               *
   44 Nassau Street
   Princeton, NJ  08542

Hudson Trust                          14,104                14,104              0               *
   47 Hulfish Street Suite 420
   Princeton, NJ 08542
   Attn: Scott Ciccone

Kisner, Daniel                         5,444                 5,444              0               *
   1849 Montgomery Avenue
   Cardiff, California 92007

Lombard Odier & Cie                  425,325               425,325              0               *
   Toedistrasse 36
   CH8027
   Zurich, Switzerland

New Day Investment
      Partnership                    111,111               111,111              0               *
   6690 LaJolla Scenic South
   LaJolla, California 92037

New York Life Insurance              162,036               162,036              0               *
        Company
   51 Madison Avenue, 2nd Floor
   New York, NY 10010
   Attn: Richard F. Drake, Room 207
             2nd Floor South,
             Home Office Building

Todd Noonan                              500                   500              0               *
   International Creative
   Management, Inc.
   40 West 57th Street, 18th Floor
   New York, New York 10019

Oracle Strategic Partners, L.P.      230,816               230,816              0               *
   712 5th Avenue, 45th Floor
   New York, NY 10019
   Attn: Norman Schleifer

</TABLE>



                                       18
<PAGE>

<TABLE>
<CAPTION>

                                                                               SHARES BENEFICIALLY
                                                                               OWNED AFTER OFFERING
                                                                             -------------------------
                            SHARES BENEFICIALLY    NUMBER OF SHARES
NAME AND ADDRESS            OWNED PRIOR TO         BEING OFFERED
OF BENEFICIAL OWNER         OFFERING (1)
                                                                             NUMBER    PERCENTAGE
- --------------------------  ---------------------  ----------------------    ------    ---------------
<S>                         <C>                       <C>                     <C>       <C>

Peretz Family Investments            124,757(3)            115,758          8,999               *
   20 Larchwood Drive
   Cambridge, MA 02138

Perseus Capital, LLC               1,447,595(4)          1,447,595              0               *
   The Army and Navy Club Building
   1627 I Street NW
   Suite 610
   Washington, DC 20006

Rho Management Co. Inc. and
   Affiliated Entities               563,001               563,001              0               *
   767 Fifth Avenue
   New York, NY  10153

Roche Finance Ltd                    269,901               269,901              0               *
   c/o Hoffman-La Roche, Ltd.
   124 Grensacherstrasse
   CH-4002 Basel
   Switzerland

Norma Sarofim                             80                    80              0               *
   778 Park Avenue
   New York, NY  10021

Schildkrout, Elliot & Barbara          7,777                 7,777              0               *
   45 Monadanock Road
   Newton, MA  02167

Schroders PLC and
   Affiliated Entities               878,625(6)            445,542        433,083               2.9%
   120 Cheapside
   London EC2V 6DS
   ENGLAND

Springer, Timothy                    775,547(7)            759,714         15,833               *
   Center for Blood Research
   200 Longwood Avenue
   Boston, Massachusetts 02115

Springer Family Trust                134,067               134,067              0               *
   245 Walcott Road
   Chestnut Hill, Massachusetts

Springer, Dr. Asa & Patricia          11,111                11,111              0               *
   3221 Diablo Trail
   Shingle Springs, CA  95682

</TABLE>



                                       19
<PAGE>

<TABLE>
<CAPTION>

                                                                               SHARES BENEFICIALLY
                                                                               OWNED AFTER OFFERING
                                                                             -------------------------
                            SHARES BENEFICIALLY    NUMBER OF SHARES
NAME AND ADDRESS            OWNED PRIOR TO         BEING OFFERED
OF BENEFICIAL OWNER         OFFERING (1)
                                                                             NUMBER    PERCENTAGE
- --------------------------  ---------------------  ----------------------    ------    ---------------
<S>                         <C>                       <C>                     <C>       <C>

S.R. One Ltd                         222,222               222,222              0               *
   200 Barr Harbor Drive
   Suite 250
   Four Tower Bridge
   West Conshohocken, PA 19428-2977

Stiefel Laboratories Ltd.             54,712                54,712              0               *
   (Ireland)
   Finisklin Industrial Estate
   Sligo, Ireland
   Attn: Thomas J. Crowley

Walsh, Christopher                    19,364(8)              9,145         10,219               *
   Harvard Medical School
   45 Shattuck Street
   Boston, Massachusetts 02115

Warner-Lambert Company               618,466               618,466              0               *
   201 Tabor Road
   Morris Plains, New Jersey 07950

Weiss Peck & Greer LLC and
   Affiliated Entities                71,111(9)             71,111              0               *
   One New York Plaza
   New York, New York 10004

Woodrich, Richard H.                     588                   588              0               *
   15 Edmunds Road.
   Wellesley Hills, MA 02481

WPG-Farber Present                    43,681                43,681              0               *
       Fund, L.P.
   One New York Plaza
   NewYork, NY 10004-1950
   Attn: Anthony Avicolli

WPG-Farber Present                     2,788                 2,788              0               *
         Overseas, Ltd.
   One New York Plaza
   New York, NY 10004-1950
   Attn: Anthony Avicolli

WPG-Present QP Fund, L.P.              4,820                 4,820              0               *
   One New York Plaza
   New York, NY 10004-1950
   Attn: Anthony Avicolli

YK Capital, L. P.                     83,000(10)            75,000          8,000               *
   509 Rochampton Road
   Hillsborough, California 94010

</TABLE>



                                       20
<PAGE>

*        Less than 1% of the outstanding shares of common stock (including the
         shares being registered hereunder).

(1)      The shares owned, and the shares included in the total number of shares
         outstanding, have been adjusted, and the percentage owned has been
         computed, in accordance with Rule 13d-3(d)(1) under the Securities
         Exchange Act of 1934, as amended, and includes options, to the extent
         called for by such rule, with respect to shares of Common Stock that
         can be exercised within 60 days of November 3, 1999. The inclusion
         herein of any shares as beneficially owned does not constitute an
         admission of beneficial ownership of those shares. Except as set forth
         in the footnotes below, such shares are beneficially owned with sole
         investment and sole voting power.

(2)      Includes shares held by HealthCare Ventures II, L.P., HealthCare
         Ventures III, L.P., HealthCare Ventures IV, L.P. and HealthCare
         Ventures V, L.P., Dr. James Cavanaugh, a director of the Company, is a
         general partner of the general partner of each of the foregoing listed
         HealthCare entities. Includes shares issued in connection with the July
         1998 private placement. HealthCare Ventures III, L.P. and HealthCare
         Ventures IV, L.P. were also represented on the Board of Directors of
         CytoMed, Inc. by Mark Leschly. Includes the following shares issued in
         connection with the CytoMed transaction: (a) 160,163 shares to
         HealthCare Ventures III, L.P. and (b) 47,597 shares issued to
         HealthCare Ventures IV, L.P. Includes 145,301 shares issued to
         HealthCare Ventures III, L.P. and 42,669 shares issued to HealthCare
         Ventures IV, L.P. in connection with the acquisition of ProScript, and
         456,620 shares issued to HealthCare Ventures V, L.P. in connection with
         the 1999 private placement. Includes 8,999 shares of Common Stock which
         HealthCare Ventures LLC has the right to acquire within 60 days of
         November 3, 1999 upon the exercise of stock options.

(3)      Dr. Martin Peretz, a director of LeukoSite, is a general partner of the
         Peretz Family Investments. Includes 8,999 shares of Common Stock which
         Dr. Peretz has the right to acquire within 60 days of November 3, 1999
         upon the exercise of stock options.

(4)      Includes  416,667 shares issued in connection  with the July 1998
         Private  Placement and 1,030,928  shares issued in connection with the
         July 1999 Private Placement.

(5)      Includes 548,307 shares issued in connection with the July 1998 private
         placement and, with respect to Rho Management Trust II, 14,694 shares
         issued at the closing in connection with the CytoMed transaction.

(6)      Includes shares held by Schroder Ventures International Life Sciences
         Fund L.P. 1 ("Schroder 1"), Schroder Ventures International Life
         Sciences



                                       21
<PAGE>

         Fund L.P.2 ("Schroder 2"), Schroder Ventures International Life
         Sciences Fund Trust (the "Schroder Trust"), Schroders Incorporated and
         Schroder Ventures International Life Sciences Co-Investment Scheme (the
         "Co-Investment Scheme"). Includes the following shares issued in
         connection with the CytoMed transaction: (a) 97,259 shares issued at
         the closing to Schroder 1; (b) 21,613 shares issued at the closing to
         Schroder 2; (c) 34,235 shares issued at the closing to the Schroder
         Trust; and (d) 768 shares issued at the closing to the Co-Investment
         Scheme. Also includes 8,999 shares of Common Stock which Schroders PLC
         has the right to acquire within 60 days of November 3, 1999 upon the
         exercise of stock options. Schroders PLC was represented on the Board
         of Directors of CytoMed, Inc. until January 1, 1999 by Barbara Piette
         and is currently represented on the LeukoSite Board of Directors by
         Kate Bingham.

(7)      Includes 15,833 shares of Common Stock which Dr. Springer has the right
         to acquire within 60 days of November 3, 1999 upon the exercise of
         stock options. Dr. Springer is a director of LeukoSite.

(8)      Includes 10,219 shares of Common Stock which Dr. Walsh has the right to
         acquire within 60 days of November 3, 1999 upon the exercise of stock
         options. Dr. Walsh is a director of LeukoSite.

(9)      Includes shares held by WPG Life Sciences Fund, L.P. and WPG
         Institutional Life Sciences, L.P. See also WPG-Farber Present Fund,
         L.P., WPG-Farber Present Overseas, Ltd. and WPG-Present QP Fund, L.P.

(10)     Dr. Yasunori Kaneko, a director of LeukoSite, is a general partner of
         YK Capital, L.P. Includes 8,000 shares of Common Stock which Dr. Kaneko
         has the right to acquire within 60 days of November 3, 1999 upon the
         exercise of stock options.

                              PLAN OF DISTRIBUTION

      The shares of common stock may be sold from time to time by the selling
stockholders in one or more transactions at fixed prices, at market prices at
the time of sale, at varying prices determined at the time of sale or at
negotiated prices. The selling stockholders may offer their shares of common
stock in one or more of the following transactions:

     --on any national securities exchange or quotation service on which the
       common stock may be listed or quoted at the time of sale, including the
       Nasdaq National Stock Market,

     --in the over-the-counter market,

     --in private transactions,



                                       22
<PAGE>

     --through options,

     --by pledge to secure debts and other obligations, or

     --a combination of any of the above transactions.

         If required, we will distribute a supplement to this prospectus to
describe material changes in the terms of the offering. The supplement will set
forth the aggregate number of shares of common stock being offered and the terms
of such offering, including the name or names of the broker/dealers or agents,
any discounts, commissions and other terms constituting compensation from the
selling stockholders and any discounts, commissions or concessions allowed or
reallowed to be paid to broker/dealers.

         The shares of common stock described in this prospectus may be sold
from time to time directly by the selling stockholders. Alternatively, the
selling stockholders may from time to time offer shares of common stock to or
through broker/dealers or agents. The selling stockholders and any
broker/dealers or agents that participate in the distribution of the shares of
common stock may be deemed to be "underwriters" within the meaning of the
Securities Act of 1933. Any profits on the resale of shares of common stock and
any compensation received by any underwriter, broker/dealer or agent may be
deemed to be underwriting discounts and commissions under the Securities Act of
1933.

         Any shares covered by this prospectus which qualify for sale pursuant
to Rule 144 under the Securities Act of 1933 may be sold under Rule 144 rather
than pursuant to this prospectus. The selling stockholders may not sell all of
the shares. The selling stockholders may transfer, devise or gift such shares by
other means not described in this prospectus.

         To comply with the securities laws of certain jurisdictions the common
stock must be offered or sold only through registered or licensed brokers or
dealers. In addition, in certain jurisdictions, the common stock may not be
offered or sold unless they have been registered or qualified for sale or an
exemption is available and complied with.

         Under applicable rules and regulations under the Securities Exchange
Act of 1934, any person engaged in a distribution of the common stock offered
hereby may not simultaneously engage in market-making activities with respect to
the common stock for a specified period prior to the start of the distribution.
In addition, each selling stockholder and any other person participating in a
distribution will be subject to the Securities Exchange Act of 1934, including
Regulation M, which may limit the timing of purchases and sales of common stock
by the selling stockholders or any such other person. These factors may affect
the marketability of the common stock and the ability of brokers or dealers to
engage in market-making activities.



                                       23
<PAGE>

         All expenses of this registration will be paid by LeukoSite. These
expenses include the SEC's filing fees and fees under state securities or "blue
sky" laws. The selling stockholders will pay all underwriting discounts and
selling commissions, if any.

                                  LEGAL MATTERS

         Bingham Dana LLP, Boston, Massachusetts will give its opinion that the
shares offered in this prospectus have been validly issued and are fully paid
and non-assessable. Justin P. Morreale, a partner at Bingham Dana LLP, is the
Secretary of LeukoSite. Other attorneys at Bingham Dana LLP own a total of
approximately 1,600 shares of common stock.

                                     EXPERTS

         The consolidated financial statements of LeukoSite as of December 31,
1997 and 1998, and for each of the three years in the period ended December 31,
1998, incorporated by reference into this prospectus and this Registration
Statement, have been audited by Arthur Andersen LLP, independent public
accountants, as indicated in their report with respect thereto, and are included
herein in reliance upon the authority of said firm as experts in giving said
report.

         WE HAVE NOT AUTHORIZED ANY DEALER, SALESPERSON OR OTHER PERSON TO GIVE
ANY INFORMATION OR TO MAKE ANY REPRESENTATIONS NOT CONTAINED IN THIS PROSPECTUS
OR ANY PROSPECTUS SUPPLEMENT. YOU MUST NOT RELY ON ANY UNAUTHORIZED INFORMATION.
THIS PROSPECTUS IS NOT AN OFFER OF THESE SECURITIES IN ANY STATE WHERE AN OFFER
IS NOT PERMITTED. THE INFORMATION IN THIS PROSPECTUS IS CURRENT AS OF
DECEMBER 2, 1999 (UNLESS OTHERWISE INDICATED HEREIN). YOU SHOULD NOT ASSUME
THAT THIS PROSPECTUS IS ACCURATE AS OF ANY OTHER DATE.



                                       24
<PAGE>

         TABLE OF CONTENTS

                                                  PAGE
                                                  ----

Where You Can Get More Information                  2
Forward-looking Statements                          3
Risk Factors                                        4
LeukoSite                                          13
Recent Developments                                13
Use of Proceeds                                    14
Selling Stockholders                               14
Plan of Distribution                               22
Legal Matters                                      24
Experts                                            24






                                8,140,667 SHARES

                                 LEUKOSITE, INC.

                                  COMMON STOCK

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

                                   PROSPECTUS

                                December 3, 1999

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



<PAGE>


                                     PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS


ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

         The expenses in connection with the issuance and distribution of the
securities being registered are set forth in the following table (all amounts
except the registration fee and the listing fee are estimated):

<TABLE>

<S>                                                     <C>
SEC Registration Fee                                      $6,597.00
Nasdaq National Market Listing Fees                      $12,625.00
Legal Fees and Expenses                                 $200,000.00
Accountants' Fees and Expenses                            $1,500.00
Miscellaneous Costs                                         $300.00

         Total                                          $221,022.00

</TABLE>


         All expenses in connection with the issuance and distribution of the
securities being offered shall be borne by the Company.

ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS

         Section 145 of the Delaware General Corporation Law empowers a Delaware
corporation to indemnify its officers and directors and certain other persons to
the extent and under the circumstances set forth therein.

         The Restated Certificate of Incorporation and the Amended and Restated
By-Laws of the Company, copies of which are filed herein as Exhibit 3.3 and 3.4,
provide for advancement of expenses and indemnification of officers and
directors of the Registrant and certain other persons against liabilities and
expenses incurred by any of them in certain stated proceedings and under certain
stated conditions to the fullest extent permissible under Delaware law.

         Each of the Registration Rights Agreements, dated as of July 1, 1998
and July 20, 1999 and the Agreement and Plan of Merger and Reorganization, dated
January 4, 1999, and the Agreement and Plan of Merger and Reorganization, dated
June 22, 1999 provides for indemnification by the Registrant of each of the
selling stockholders against certain liabilities under the Securities Act of
1933, the Securities Exchange Act of 1934, state securities laws or otherwise,
and provides for indemnification by the selling stockholders of the Registrant
and its directors, its officers and certain control persons against certain
liabilities under the Securities Act of 1933, the Securities Exchange Act of
1934, state securities laws or otherwise.



                                      II-1
<PAGE>

ITEM 16. EXHIBITS

EXHIBITS
- --------
   *3.3   Restated Certificate of Incorporation of the Registrant
   *3.4   Amended and Restated By-Laws of the Registrant, as amended to date
    4.1   Specimen certificate for shares of common stock issued in connection
          with the CytoMed Merger
    5     Opinion of Bingham Dana LLP
   10.1   Agreement and Plan of Merger and Reorganization, dated January 4, 1999
   23.1   Consent of Bingham Dana LLP (included in Exhibit 5)
   23.2   Consent of Arthur Andersen LLP


- --------
*        Incorporated by reference from the Registrant's Registration Statement
         on Form S-1 (Registration No. 333-30213).


ITEM 17. UNDERTAKINGS

         The undersigned registrant hereby undertakes:

         (1) To file, during any period in which offers or sales are being made
pursuant to this Registration Statement, a post-effective amendment to this
Registration Statement to include any material information with respect to the
plan of distribution not previously disclosed in this Registration Statement or
any material change to such information in this Registration Statement;

         (2) That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment 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 the initial bona
fide offering thereof.

         (3) To remove from registration by means of a post-effective amendment
any of the securities being registered which remain unsold at the termination of
the offering.

         The undersigned registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act of 1933, each filing of the
registrant's annual report pursuant to Section 13(a) or 15 (d) of the Securities
Exchange Act of 1934 (and, where applicable, each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the registration statement shall be
deemed to be a new registration statement relating to the



                                      II-2

<PAGE>

securities offered therein, and the offering of such securities at that time
shall be deemed to be the initial BONA FIDE offering thereof.

         Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Registrant pursuant to the foregoing provisions described in Item 15 above,
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, 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.
















                                      II-3
<PAGE>


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant, LeukoSite, Inc., certifies that it has reasonable grounds to
believe that it meets all of the requirements for filing on Form S-3 and has
duly caused this Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Cambridge, Commonwealth
of Massachusetts, on this 3 day of December, 1999.


                                       LEUKOSITE, INC.



                                       /s/ Christopher K. Mirabelli
                                       -----------------------------------
                                       Christopher K. Mirabelli
                                       CHAIRMAN OF THE BOARD OF DIRECTORS,
                                       PRESIDENT AND CHIEF EXECUTIVE OFFICER


                                POWER OF ATTORNEY

         Each person whose signature appears below hereby appoint each of
Christopher K. Mirabelli and Augustine Lawlor severally, acting alone and
without the other, his/her true and lawful attorney-in-fact with the authority
to execute in the name of each such person, any and all amendments (including
without limitation, post-effective amendments) to this Registration Statement on
Form S-3, to sign any and all additional registration statements relating to the
same offering of securities as this Registration Statement that are filed
pursuant to Rule 462(b) of the Securities Act, and to file such registration
statements with the Securities and Exchange Commission, together with any
exhibits thereto and other documents therewith, necessary or advisable to enable
the Registrant to comply with the Securities Act, and any rules, regulations and
requirements of the Securities and Exchange Commission in respect thereof, which
amendments may make such other changes in the Registration Statement as the
aforesaid attorney-in-fact executing the same deems appropriate.

         Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the dates indicated:



                                      II-4
<PAGE>


<TABLE>
<CAPTION>

       SIGNATURE                                 TITLE                                  DATE
       ---------                                 -----                                  ----
<S>                                 <C>                                                 <C>

                                    Chairman of the Board of Directors, President,      December 3, 1999
/s/ Christopher K. Mirabelli        Chief and Executive Officer (Principal
- --------------------------------    Executive Officer)
Christopher K. Mirabelli


                                    Senior Vice President, Corporate                    December 3, 1999
/s/ Augustine Lawlor                Development, Chief Operating and Financial
- --------------------------------    Office (Principal Financial and Accounting Officer)
Augustine Lawlor


                                    Director                                            December 3, 1999
/s/ Kate Bingham
- --------------------------------
Kate Bingham


                                    Director                                            December 3, 1999
/s/ James Cavanaugh
- --------------------------------
James Cavanaugh


                                    Director                                            December 3, 1999
/s/ Yasunori Kaneko
- --------------------------------
Yasunori Kaneko


                                    Director                                            December 3, 1999
/s/ Martin Peretz
- --------------------------------
Martin Peretz


                                    Director                                            December 3, 1999
/s/ Mark Skaletsky
- --------------------------------
Mark Skaletsky


                                    Director                                            December 3, 1999
/s/ Timothy A. Springer
- --------------------------------
Timothy A. Springer


                                    Director                                            December 3, 1999
/s/ Christopher T. Walsh
- --------------------------------
Christopher T. Walsh

</TABLE>



                                      II-5
<PAGE>


                                  EXHIBIT INDEX

EXHIBITS

   *3.3   Restated Certificate of Incorporation of the Registrant
   *3.4   Amended and Restated By-Laws of the Registrant, as amended to date
    4.1   Specimen certificate for shares of common stock issued in connection
          with the CytoMed Merger
    5     Opinion of Bingham Dana LLP
   10.1   Agreement and Plan of Merger and Reorganization, dated January 4, 1999
   23.1   Consent of Bingham Dana LLP (included in Exhibit 5)
   23.2   Consent of Arthur Andersen LLP


- --------
*        Incorporated by reference from the Registrant's Registration Statement
         on Form S-1 (Registration No. 333-30213).




<PAGE>


                                   EXHIBIT 4.1

         NUMBER                                                 SHARES

                                 LeukoSite Inc.

              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE
                                             SEE REVERSE FOR CERTAIN DEFINITIONS
                                                               CUSIP 52728R 10 2

       THIS CERTIFIES THAT            SPECIMEN




       is the owner of   XXXX

       FULLY PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK, $.01 PAR VALUE, OF

                                 LeukoSite, Inc.

(hereinafter called the Corporation, 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 or accompanied by a proper
assignment. This Certificate and the shares represented by this Certificate are
issued and shall be subject to the laws of the State of Delaware and to the
provisions of the Certificate of Incorporation and the By-Laws of the
Corporation as amended from time to time (copies of which are on file at the
principal office of the Corporation and the Transfer Agent), to all of which the
holder of this Certificate by acceptance hereof assents.

This Certificate is not valid until countersigned by the Transfer Agent and
registered by the Registrar.

IN WITNESS WHEREOF, the Corporation has caused the facsimile signatures of its
duly authorized officers and its facsimile seal to be hereunto affixed.

Dated:

                                 LEUKOSITE, INC.
                                      1992
                                    DELAWARE

                  TREASURER                         PRESIDENT


<PAGE>


                                 LeukoSite, Inc.

The Corporation is authorized to issue more than one class of stock. Upon
written request the Corporation will furnish without charge to each stockholder
a copy of the powers, designations, preferences and relative, participating,
optional or other special rights of each class of stock or series thereof and
the qualifications, limitations or restrictions of such preferences and/or
rights.

THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE OFFERED, SOLD, ASSIGNED,
PLEDGED, TRANSFERRED OR OTHERWISE DISPOSED OF EXCEPT (I) PURSUANT TO AN
EFFECTIVE REGISTRATION STATEMENT UNDER SAID ACT, (II) PURSUANT TO AN AVAILABLE
EXEMPTION FROM REGISTRATION UNDER SAID ACT AND, IF REQUESTED, BY THE COMPANY,
UPON DELIVERY OF AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY
THAT THE PROPOSED TRANSFER IS EXEMPT FROM SAID ACT OR (III) PURSUANT TO THE
RESALE PROVISIONS OF RULE 144.

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                UNIF GIFT MIN ACT _____ Custodian
TEN ENT - as tenants by the entireties         under Uniform Gift to Minors Act
JT TEN - as joint tenants with right of survivorship
and not as tenants in common
COM PROP - as community property


     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

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

Shares of the common 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

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




<PAGE>




                                    EXHIBIT 5



                         [ Bingham Dana LLP Letterhead ]



                               December 2, 1999

LeukoSite, Inc.
215 First Street
Cambridge, Massachusetts 02142


Ladies and Gentlemen:

         We have acted as counsel to LeukoSite, Inc., a Delaware corporation
(the "Company"), in connection with the registration under the Securities Act of
1933, as amended (the "Act"), of 631,295 shares (the "Shares") of the Company's
Common Stock, $0.01 par value per share, to be offered by certain stockholders
of the Company (the "Selling Stockholders"), pursuant to a Registration
Statement on Form S-3, filed by the Company with the Securities and Exchange
Commission on December 2, 1999.

         As such counsel, we have reviewed the corporate proceedings taken by
the Company with respect to the authorization of the issuance of the Shares. We
have also examined and relied upon originals or copies, certified or otherwise
authenticated to our satisfaction, of such corporate records, documents,
agreements or other instruments of the Company. As to all matters of fact
(including factual conclusions and characterizations and descriptions of
purpose, intention or other state of mind) we have entirely relied upon
certificates of officers of the Company, and have assumed, without independent
inquiry, the accuracy of those certificates.

         We have assumed the genuineness of all signatures, the conformity to
the originals of all documents reviewed by us as copies, the authenticity and
completeness of all original documents reviewed by us in original or copy form
and the legal competence of each individual executing a document. We have also
assumed that the registration requirements of the Act and all applicable
requirements of state laws regulating the sale of securities will have been duly
satisfied.

         With respect to our opinion set forth below with respect to the Shares,
we have assumed that the Company has received the specified purchase price or
other consideration therefor set forth in that certain Agreement and Plan of
Merger and Reorganization, dated January 4, 1999.

         This opinion is limited solely to the Delaware General Corporation Law
as applied by courts located in the State of Delaware.



<PAGE>

LeukoSite, Inc.
December 2, 1999
Page 2


         Subject to the foregoing, it is our opinion that the Shares have been
duly authorized, validly issued and fully paid and are non-assessable.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement.


                                       Very truly yours,

                                       /s/ Bingham Dana LLP

                                       Bingham Dana LLP





<PAGE>


                                                                    EXHIBIT 10.1



                AGREEMENT AND PLAN OF MERGER AND REORGANIZATION

         This Agreement and Plan of Merger and Reorganization dated as of
January 4, 1999 (this "Agreement"), is by and among LeukoSite, Inc., a Delaware
corporation ("LeukoSite"), LeukoSite Merger Corporation, a Delaware corporation
that is a wholly owned subsidiary of LeukoSite ("Merger Sub"), and CytoMed,
Inc., a Delaware corporation (the "Company").

         WHEREAS, the parties desire that Merger Sub be merged with and into the
Company (the "Merger"), subject to the terms and conditions set forth in this
Agreement.

         NOW, THEREFORE, in consideration of the foregoing premises and the
mutual agreements, covenants, representations and warranties hereinafter set
forth, the parties hereto agree as follows:

         1.    DEFINITIONS.

         1.1.  CERTAIN  DEFINED  TERMS.  As used in this  Agreement,  the
following terms have the following respective meanings:

         "Affiliate" means, with respect to any person, any other person (i)
that directly or indirectly, through one or more intermediaries, controls, is
controlled by, or is under common control with, such person or (ii) who is a
family member or relative of such person. When used with reference to the
Company, the term "Affiliate" includes the Stockholders.

         "Affiliated Group" has the meaning ascribed to it in Section 1504 of
the Code, and in addition includes any analogous combined, consolidated or
unitary group, as defined under any applicable state, local, or foreign income
Tax law.

         "Aggregate Contingent Consideration Payments" means the Contingent
Third Party Payments, the LeukoSite Contingent Milestone Payments and the
Contingent Partner Licensing Payments.

         "Approved Payments" means the Company's expenditures, payments,
expenses, costs or Indebtedness set forth in Section 10.2 to the Disclosure
Schedule.

         "Code" means the United States Internal Revenue Code of 1986, as
amended.

         "Company Common Stock" means the Company's common stock, par value
$0.01 per share.



<PAGE>
                                       2


         "Company Intellectual Property" shall mean that Intellectual Property
owned by, or licensed to, the Company that is set forth on Section 7.10 of the
Disclosure Schedule.

         "Company Preferred Stock" means any or all, as the context may require
or allow, of the Company Series I Preferred Stock, the Company Series II
Preferred Stock, the Company Series III Preferred Stock, the Company Series V
Preferred Stock, the Company Series VI Preferred Stock and the Company Series
VII Preferred Stock.

         "Company Series I Preferred Stock" means the Company's Series I
Convertible Preferred Stock, par value $.01 per share.

         "Company Series II Preferred Stock" means the Company's Series II
Convertible Preferred Stock, par value $.01 per share.

         "Company Series III Preferred Stock" means the Company's Series III
Convertible Preferred Stock, par value $.01 per share.

         "Company Series V Preferred Stock" means the Company's Series V
Convertible Preferred Stock, par value $.01 per share.

         "Company Series VI Preferred Stock" means the Company's Series VI
Convertible Preferred Stock, par value $.01 per share.

         "Company Series VII Preferred Stock" means the Company's Series VII
Convertible Preferred Stock, par value $.01 per share.

         "Company Registered Intellectual Property" means those United States,
international and foreign: (a) patents and patent applications (including
provisional applications) and all reissues, divisions, renewals, extensions,
provisions, continuations, foreign counterparts, and continuations-in-part
thereof, in each case that are listed in Section 7.10 of the Disclosure
Schedule; (b) registered trademarks, registered service marks, applications to
register trademarks or service marks, intent-to-use applications, or other
registrations or applications related to trademarks or service marks, in each
case that are listed in Section 7.10 of the Disclosure Schedule; and (c)
registered copyrights and applications for copyright registration, in each case
that are listed on Section 7.10 of the Disclosure Schedule.

         "Company Stock" means, collectively, the Company Common Stock and the
Company Preferred Stock.

         "CytoMed Programs" means, collectively, (i) the Company's ongoing
proprietary internal research and development program related to the compound



<PAGE>
                                       3


CMI-977 and related compounds, (ii) the Company's ongoing proprietary internal
research and development program related to the compound CMI-392 and related
compounds, and (iii) the Company's ongoing proprietary internal research and
development program related to complement mediated disease.

         "Damages" means all damages, losses, claims, demands, actions, causes
of action, suits, litigations, arbitrations, liabilities, costs, and expenses,
including court costs and the reasonable fees and expenses of legal counsel.

         "Designated Preferred Stockholders" means the Stockholders whose
signatures are set forth on the signature pages to the Designated Preferred
Stockholders Agreement.

         "Designated Preferred Stockholders Agreement" means the Designated
Preferred Stockholders Agreement, dated of even date herewith, among LeukoSite
and the Designated Preferred Stockholders.

         "Drug Development Program" means a drug development program conducted
by LeukoSite, its Affiliates or sublicensees, at no cost to the Company, for
pre-clinical and clinical development, regulatory approval, and
commercialization of a Product Candidate that was included in a CytoMed Program.

         "Exchange Act" means the Securities Exchange Act of 1934, as amended,
and the rules and regulations of the SEC thereunder, as in effect as of the
relevant time of reference.

         "Excluded Indebtedness" means all Indebtedness that is identified in
Section 3.7 of the Disclosure Schedule as "Excluded Indebtedness".

         "First Commercial Sale" means the first sale for end use or consumption
of a Product Candidate in a country after required approvals have been granted
by the governing regulatory authority in such country.

         "FDA" means the United States Food and Drug Administration.

         "Included Additional Assets" means the fixed assets, prepaid expenses
and accounts receivable that are identified in Section 3.7 of the Disclosure
Schedule as "Included Additional Assets."

         "Indebtedness," as applied to any person, means (a) all indebtedness of
such person for borrowed money, whether current or funded, or secured or
unsecured, (b) all indebtedness of such person for the deferred purchase price
of property or services represented by a note or other security, (c) all
indebtedness of such person created or arising under any conditional sale or
other title



<PAGE>
                                       4


retention agreement (even if the rights and remedies of the seller or lender
under such agreement in the event of default are limited to repossession or sale
of specific property), (d) all indebtedness of such person secured by a purchase
money mortgage or other Lien to secure all or part of the purchase price of
property subject to such mortgage or other Lien, (e) all accounts payable, notes
payable and accrued expenses of such person, (f) all indebtedness or liabilities
of such person that would be required to be reflected on a balance sheet or
referred to in the notes thereto in accordance with generally accepted
accounting principles, (g) all indebtedness, liabilities or obligations of such
person that are identified in Section 3.7 of the Disclosure Schedule as
"Indebtedness", (h) all other obligations of such person under leases that have
been or must be, in accordance with generally accepted accounting principles,
recorded as capital leases in respect of which such person is liable as lessee,
(i) any liability of such person in respect of banker's acceptances or letters
of credit, and (j) all indebtedness referred to in clauses (a), (b), (c), (d),
(e), (f), (g), (h) or (i) above that is directly or indirectly guaranteed by
such person or which such person has agreed (contingently or otherwise) to
purchase or otherwise acquire or in respect of which such person has otherwise
assured a creditor against loss.

         "Intellectual Property" shall mean any or all of the following and all
rights in, arising out of, or associated therewith: (a) all United States,
international and foreign patents and applications thereof and all reissues,
divisions, renewals, extensions, provisions, continuations and
continuations-in-part thereof; (b) all inventions (whether patentable or not),
invention disclosures, improvements, drug candidates, trade secrets, proprietary
information, know how, technology, technical data and customer lists, and all
documentation relating to any of the foregoing; (c) all copyrights, copyright
registrations and applications therefor, and all other rights corresponding
thereto throughout the world; (d) all industrial designs and any registration
and applications therefor throughout the world; (e) all trade names, logos,
common law trademarks and service marks, trademark and service mark registration
and applications therefor throughout the world; (f) all databases and data
collections and all rights therein throughout the world; and (g) any similar or
equivalent rights to any of the foregoing anywhere in the world.

         "knowledge," when used to qualify a representation or warranty in this
Agreement, has the following meaning: Where a representation or warranty is made
to the best of the Company's knowledge, or with a similar qualification, the
Company will be conclusively deemed to have knowledge of any matter with respect
to which the Company's chief executive, operating, scientific and/or financial
officers and/or Vice President, Clinical Development has actual knowledge after
conducting a reasonable investigation. Where a representation or warranty is
made to the best of LeukoSite's or Merger Sub's knowledge, or with a similar
qualification, LeukoSite and Merger Sub will be conclusively deemed to have
knowledge of any matter with respect to which LeukoSite's or



<PAGE>
                                       5


Merger Sub's chief executive, scientific, and/or financial officers has actual
knowledge after conducting a reasonable investigation.

         "LeukoSite Common Stock" means the common stock, par value $0.01 per
share, of LeukoSite.

         "LeukoSite Preferred Stock" means the preferred stock, par value $0.01
per share, of LeukoSite.

         "LeukoSite Series A Preferred Stock" means the Series A Convertible
Preferred Stock, par value $0.01 per share, of LeukoSite, the terms, rights,
preferences and privileges of which shall be those set forth in EXHIBIT A
hereto.

         "LeukoSite Stock" means, at the relevant time of reference thereto, (i)
LeukoSite Series A Preferred Stock or (ii) in the event that, on or prior to
such time, there has been a mandatory conversion of all issued and outstanding
shares of LeukoSite Series A Preferred Stock into shares of LeukoSite Common
Stock in accordance with the terms of the LeukoSite Series A Preferred Stock,
the LeukoSite Common Stock.

         "LeukoSite Stock Plans" means, collectively, LeukoSite's Amended and
Restated 1993 Stock Option Plan and LeukoSite's 1997 Employee Stock Purchase
Plan.

         "Liens" means any and all liens, claims, mortgages, security interests,
pledges, options, rights of first offer or refusal, charges, encumbrances,
limitations on voting rights, and restrictions on transfer of any kind, except
(i) in the case of references to securities, those arising under applicable
securities laws solely by reason of the fact that such securities were issued
pursuant to exemptions from registration under such securities laws, (ii)
mechanic's, materialmen's and similar liens, (iii) liens for Taxes not yet due
and payable and (iv) liens arising under worker's compensation, unemployment
insurance, social security, retirement and similar legislation.

         "Material Adverse Effect" means, with reference to any person, any
material adverse effect on the condition (financial or otherwise), operations,
business, assets (including intangible assets), rights, liabilities, obligations
or prospects of such person, or on such person's ability to consummate the
transactions hereby contemplated.

         "Merger Common Shares" means, collectively, (i) shares of LeukoSite
Common Stock issued by LeukoSite pursuant to the Merger and (ii) shares of
LeukoSite Common Stock issued by LeukoSite upon conversion of any and all
LeukoSite Series A Preferred Stock issued by LeukoSite pursuant to the Merger.



<PAGE>
                                       6


         "Merger Consideration" means the Merger Shares, the Contingent Third
Party Payments, the LeukoSite Contingent Milestone Payments and the Contingent
Partner Licensing Payments.

         "Merger Conversion Shares" means shares of LeukoSite Common Stock
issued by LeukoSite upon conversion of any and all LeukoSite Series A Preferred
Stock issued by LeukoSite pursuant to the Merger.

         "Merger Shares" means the Aggregate Base  Consideration  Shares,  the
Aggregate Subsequent Consideration Shares, the Milestone Shares and the Merger
Conversion Shares.

         "NDA" means a New Drug Application filed with the FDA or its
equivalent, or any corresponding application filed in any country other than the
United States.

         "Net Cash Balance" means (a) the sum of (i) cash, cash equivalents and
marketable securities (with maturities less than 180 days) and (ii) Included
Additional Assets, MINUS (b) all Indebtedness other than Excluded Indebtedness.

         "person" (regardless of whether capitalized) means any natural person,
entity, or association, including without limitation any corporation,
partnership, limited liability company, government (or agency or subdivision
thereof), trust, joint venture or proprietorship.

         "Product Candidate" shall mean any product or compound for the
diagnosis, prophylaxis or treatment of human disease.

         "PTO" means the United States Patent and Trademark Office.

         "SEC" means the United States Securities and Exchange Commission.

         "Securities Act" means the Securities Act of 1933, as amended, and the
rules and regulations of the SEC thereunder, as in effect as of the relevant
time of reference.

         "Shen  Consulting  Agreement"  means the Consulting  Agreement,  dated
as of January 1, 1992, between the Company and T.Y. Shen.

         "Stockholders" means the stockholders of the Company.

         "Subsidiary" or "Subsidiaries" means, with respect to any person, any
corporation a majority (by number of votes) of the outstanding shares of any
class or classes of which will at the time be owned by such person or by a
Subsidiary of such person, if the holders of the shares of such class or classes
(a)



<PAGE>
                                       7


are ordinarily, in the absence of contingencies, entitled to vote for the
election of a majority of the directors (or persons performing similar
functions) of the issuer thereof, even though the right so to vote has been
suspended by the happening of such a contingency, or (b) are at the time
entitled, as such holders, to vote for the election of a majority of the
directors (or persons performing similar functions) of the issuer thereof,
whether or not the right so to vote exists by reason of the happening of a
contingency.

         "Tax" or "Taxes" means any federal, state, local, or foreign income,
gross receipts, franchise, estimated, alternative minimum, add-on minimum,
sales, use, transfer, registration, value added, excise, natural resources,
severance, stamp, occupation, premium, windfall profit, environmental, customs,
duties, real property, personal property, capital stock, intangibles, social
security, unemployment, disability, payroll, license, employee or other tax or
levy of any kind whatsoever, including any interest, penalties, or additions to
tax in respect of the foregoing.

         "Tax Return" means any return, declaration, report, claim for refund,
information return, or other document filed or required to be filed (including
any related or supporting estimates, elections, schedules, statements, or
information filed or required to be filed) in connection with the determination,
assessment or collection of any Tax or the administration of any laws,
regulations or administrative requirements relating to any Tax.

         "UCB" means, collectively, UCB Research, Inc., a Delaware corporation,
UCB Farchim, S.A., a Swiss corporation, and UCB S.A., a Belgian corporation.

         "UCB Agreement" means the Asset Purchase Agreement, dated as of October
23, 1998, between UCB and the Company.

         "Unaudited Closing Net Cash Balance" means the Unaudited Signing Net
Cash Balance as adjusted by (a) the mutual agreement of LeukoSite and the
Company for (i) unrecorded liabilities, (ii) the Company's UCB transaction
retention program, and (iii) adjustments related to the accruals for tax
liabilities, the incentive bonus program, severance program, audit and closing
costs, if any, and (b) subtracting any and all expenditures, payments, accrued
expenses, costs or Indebtedness incurred, made or accrued by the Company during
the period from the date of this Agreement to and including the Closing (but
excluding (i) Approved Payments and (ii) any and all of such expenditures,
payments, accrued expenses, costs or Indebtedness that are approved in writing
by at least one member of the Transition Committee that is a representative of
LeukoSite in accordance with the provisions of Section 10.2 hereof).

         1.2. TERMS  DEFINED  ELSEWHERE.  The  following  terms are defined
herein in the sections identified below:



<PAGE>
                                       8

<TABLE>
<CAPTION>

   Term                             Section                    Term                             Section
   ----                             -------                    ----                             -------
<S>                                 <C>                     <C>                                 <C>

Aggregate Base Consideration                                Incidental Shares                   6.1(c)
  Shares                            3.7(c)                  Indemnification Agreement           13.13
Aggregate Subsequent                                        Indemnified                         14.2(b)
  Consideration Shares              3.8(a)                  IRS                                 7.14(b)
Agreement                           Preamble                LeukoSite                           Preamble
Audited Closing Balance                                     LeukoSite Contingent
  Sheet                             3.7(d)                    Milestone Payment                 3.8(c)
Audited Signing Balance                                     LeukoSite Indemnified Party         14.2(b)
  Sheet                             3.7(d)                  LeukoSite R&D Programs              3.8(g)
Audited Closing Net Cash                                    LeukoSite's SEC Reports             9.5
Balance                             3.7(d)                  Material Contract                   7.18
Audited Signing Net Cash                                    Merger                              2
Balance                             3.7(d)                  Merger Certificate
Blocking Third Party Patent         3.8(c)                  Merger Sub                          Preamble
CERCLA                              7.15(b)                 Milestone Shares                    3.8(c)
Certificate                         4.1                     NMS                                 17.6
Claim Notice                        14.4(b)                 November 30, 1998
Claimed Amount                      14.4(b)                 Balance Sheet                       7.7
Closing                             2                       PBGC                                7.14(d)(ii)
Closing Date                        2                       Partner                             3.5(c)
Company                             Preamble                Piggyback Notice                    6.1(b)
Company Indemnified Party           14.1                    Qualified Holders                   6.1(c)
Company Options                     5                       RCRA                                7.15(b)
Company Warrants                    5                       Registering Stockholders            6.1(a)
Complementary Technology            3.8(c)                  Response Notice                     14.4(c)
Contingent Partner                                          Restricted Period                   15.3
  Licensing Payment                 3.8(d)                  SARA                                7.15(b)
Contingent Third Party                                      Stockholders' Representatives       4.10(a)
  Payment                           3.8(b)                  Stockholders Registration
DGCL                                3.1                     Statement                           6.1(a)
Dissenting Shares                   3.6(c)                  Surviving Corporation               3.1
Effective Period                    6.1(a)                  Subsequent UCB Payment              3.8(a)
Effective Time                      2                       Suspension Period                   6.2(a)
Employee Benefit Plan               7.14(a)                 Transition Committee                10.2
Environmental Laws                  7.15(b)                 Unaudited Closing Balance
EPA                                 7.15(c)                   Sheet                             3.7(b)
ERISA                               7.14(c)                 Unaudited Signing Balance
Escrow Agreement                    4.3                     Sheet                               3.7(a)
Escrowed Securities                 4.3                     Unaudited Signing Net Cash
Hazardous Substances                7.15(c)                 Balance                             3.7(a)
Holder Inclusion Notice             6.1(b)

</TABLE>

         2. CLOSING. Subject to the other provisions of this Agreement, the
closing of the transactions contemplated under this Agreement (the "Closing")
will be held at the offices of Bingham Dana LLP, 150 Federal Street, Boston,
Massachusetts 02110, as soon as is reasonably practicable following satisfaction
or waiver of the conditions set forth in Sections 11 through 13 (the date on
which the Closing actually occurs is hereinafter referred to as the "Closing
Date"). On the Closing Date, Merger Sub and the Company will execute a



<PAGE>
                                       9


Certificate of Merger, substantially in the form of the attached EXHIBIT B (the
"Merger Certificate"), and will file it with the Delaware Secretary of State in
order to cause the Merger to be effected in accordance with the laws of the
State of Delaware. The Merger will be effective upon the filing of the Merger
Certificate (the "Effective Time"). For all purposes, all of the document
deliveries and other actions to occur at the Closing will be conclusively
presumed to have occurred at the same time, immediately before the Effective
Time.

         3.   EFFECT OF MERGER. At the Effective Time, automatically and without
further action:

         3.1. SURVIVING CORPORATION. Merger Sub will be merged with and into the
Company and the separate existence of Merger Sub will cease. The Company will
continue in existence as the surviving corporation in the Merger (the "Surviving
Corporation"). The effect of the Merger will be as provided in the applicable
provisions of the Delaware General Corporation Law (the "DGCL"). Without
limiting the generality of the foregoing, and subject thereto, except as
otherwise provided herein, all of the property, rights, privileges, powers, and
franchises of Merger Sub and the Company, respectively, will vest in the
Surviving Corporation, and all of the debts, liabilities, and duties of Merger
Sub and the Company, respectively, will become the debts, liabilities, and
duties of the Surviving Corporation.

         3.2  CERTIFICATE OF INCORPORATION. The Certificate of Incorporation of
the Surviving Corporation shall be the same as the Certificate of Incorporation
of the Merger Sub immediately prior to the Effective Time, except that the name
of the corporation set forth therein shall be changed to the name of the
Company.

         3.3  BY-LAWS. The by-laws of the Surviving Corporation shall be the
same as the by-laws of the Merger Sub immediately prior to the Effective Time,
except that the name of the corporation set forth therein shall be changed to
the name of the Company.

         3.4. DIRECTORS AND OFFICERS. From and after the Effective Time, the
respective officers and members of the Board of Directors of the Surviving
Corporation will consist of those persons named as such in the Merger
Certificate, each such person to hold office, subject to the applicable
provisions of the Certificate of Incorporation and the by-laws of the Surviving
Corporation, until the next annual meeting of directors or stockholders, as the
case may be, of the Surviving Corporation and until his or her successor is duly
elected or appointed and qualified.



<PAGE>
                                       10


         3.5. CONVERSION OF MERGER SUB'S SHARES. Each share of the common stock,
par value $0.01 per share, of Merger Sub that was issued and outstanding
immediately before the Effective Time will be converted into and become one
share of the common stock, par value $ 0.01 per share, of the Surviving
Corporation.

         3.6.     CANCELLATION OF COMPANY STOCK; DISSENTING SHARES.

                  (a) CANCELLATION OF COMPANY STOCK. At the Effective Time, each
         share of Company Stock issued and outstanding immediately before the
         Effective Time (other than any Dissenting Shares (as defined in Section
         3.6(c) below) and other than any shares of Company Stock held directly
         or indirectly by the Company) will be cancelled and, subject to the
         provisions of Sections 3.6(c), 4.3 and 4.6 hereof, each Stockholder
         shall have the right to receive, in lieu of all shares of Company Stock
         held by such Stockholder that will be so cancelled, (i) that number of
         shares of LeukoSite Stock representing the percentage of the Aggregate
         Base Consideration Shares to which such Stockholder may be entitled, if
         any, in accordance with the provisions of SCHEDULE A hereto, (ii) that
         number of shares of LeukoSite Stock representing the percentage of the
         Aggregate Subsequent Consideration Shares to which such Stockholder may
         be entitled, if any, in accordance with the provisions of SCHEDULE A
         hereto (it being understood that any such right of such Stockholder to
         receive such number of shares of LeukoSite Stock is a contingent right
         that is dependent, among other things, on whether LeukoSite is required
         to issue any Aggregate Subsequent Consideration Shares pursuant to
         Section 3.8(a) hereof), (iii) that number of shares of LeukoSite Stock
         representing the percentage of the Milestone Shares to which such
         Stockholder may be entitled, if any, in accordance with the provisions
         of SCHEDULE A hereto (it being understood that any such right of such
         Stockholder to receive such number of shares of LeukoSite Stock is a
         contingent right that is dependent, among other things, on whether
         LeukoSite is required to issue any Milestone Shares pursuant to Section
         3.8(c) hereof), and (iv) cash payments each equal to the percentage of
         any Aggregate Contingent Consideration Payment to which such
         Stockholder may be entitled, if any, in accordance with the provisions
         of SCHEDULE A hereto (it being understood that any such right of such
         Stockholder to receive any such cash payment is a contingent right that
         is dependent, among other things, on whether LeukoSite is required to
         pay any Aggregate Contingent Consideration Payment pursuant to Sections
         3.8(b), 3.8(c), 3.8(d), 3.8(e) or 3.8(f) hereof). Notwithstanding
         anything in this Section 3.6(a) or in SCHEDULE A hereto to the
         contrary, no fractional shares of LeukoSite Stock shall be issued in
         connection with the Merger, but cash payments shall be made in lieu of
         such fractional shares pursuant to, and in accordance with, the
         provisions of Section 4.6 hereof.



<PAGE>
                                       11


                  (b) CANCELLATION OF TREASURY STOCK, ETC. At the Effective
         Time, each share of Company Stock held directly or indirectly by the
         Company will be canceled and will cease to exist, and no payment will
         be made with respect thereto.

                  (c) DISSENTING SHARES. Each share of Company Stock that,
         immediately before the Effective Time, was held by any person who has
         duly exercised the appraisal rights afforded to dissenting stockholders
         pursuant to Section 262 of the DGCL (such shares, collectively,
         "Dissenting Shares") will not entitle the holder thereof to receive the
         consideration referred to in Section 3.6(a) hereof. Instead, the
         holders of Dissenting Shares will be entitled to receive payment of the
         appraised value of such shares in accordance with the provisions of
         such Section 262, except that all Dissenting Shares held by
         Stockholders who withdraw, fail to perfect, or otherwise lose their
         appraisal rights with respect to Dissenting Shares will thereupon be
         deemed to entitle the holder thereof to receive the consideration
         referred to in Section 3.6(a) hereof. In the event that any Stockholder
         exercises his, her or its appraisal rights pursuant to Section 262 of
         the DGCL and LeukoSite makes any payment to such Stockholder in respect
         of his, her or its Dissenting Shares (regardless of whether such
         payment represents the appraised value of such Dissenting Shares as
         determined pursuant to a judicial proceeding or represents amounts paid
         by LeukoSite in settlement of such appraisal rights with the written
         consent of the Stockholders' Representatives), then LeukoSite shall be
         entitled to reduce the aggregate amount of consideration payable to the
         Stockholders pursuant to and in connection with the Merger by an amount
         equal to the sum of any such payment made by LeukoSite to such
         Stockholder in respect of his, her or its Dissenting Shares PLUS the
         aggregate amount of reasonable attorneys' fees and expenses incurred by
         LeukoSite in connection with any judicial proceeding or settlement
         discussions or negotiations resulting from the exercise of appraisal
         rights by such Stockholder, and such Stockholder's share of the Merger
         Consideration on SCHEDULE A shall be allocated pro rata among the other
         Stockholders in the respective tranche. Any such reduction in the
         aggregate amount of consideration payable by LeukoSite to the
         Stockholders shall be accomplished by LeukoSite making a claim against
         the Escrowed Securities pursuant to, and in accordance with, the
         provisions of the Escrow Agreement and/or by LeukoSite exercising its
         set-off rights pursuant to Section 14.5(b) hereof against any future
         payment owed by LeukoSite to the Stockholders in connection with the
         Merger. LeukoSite shall not settle any claims for appraisal rights with
         respect to Dissenting Shares without the consent of the Stockholders'
         Representatives, which consent shall not be unreasonably withheld or
         delayed.



<PAGE>
                                       12


         3.7.     AGGREGATE BASE CONSIDERATION.

                  (a) UNAUDITED SIGNING BALANCE SHEET. Section 3.7(a) of the
         Disclosure Schedule sets forth the unaudited balance sheet of the
         Company as of the date hereof (the "Unaudited Signing Balance Sheet")
         and a calculation of the Net Cash Balance as of the date hereof (the
         "Unaudited Signing Net Cash Balance"), together with a certificate
         signed by the Chief Financial Officer of the Company certifying (i)
         that the Unaudited Signing Balance Sheet was prepared in accordance
         with generally accepted accounting principles, consistently applied,
         except for the absence of footnotes and subject to adjustments
         consisting of normal year-end accruals, the effect of which, both
         individually and in the aggregate, is not material, (ii) that the
         Unaudited Signing Balance Sheet fairly and accurately presents the
         financial condition of the Company as of the date hereof, and (iii) as
         to the calculation of the Unaudited Signing Net Cash Balance. The
         Unaudited Signing Balance Sheet shall have been prepared in
         consultation with LeukoSite and LeukoSite's representatives after
         LeukoSite and LeukoSite's representatives have had access (consistent
         with the provisions reflected in Section 10.1) to financial information
         and personnel relevant to the preparation of the Unaudited Signing
         Balance Sheet. The parties shall use their good faith efforts to
         resolve any disagreements between them concerning the Unaudited Signing
         Balance Sheet.

                  (b) UNAUDITED CLOSING BALANCE SHEET. On the Closing Date, the
         Company shall deliver to LeukoSite an unaudited balance sheet of the
         Company as of the Closing Date (the "Unaudited Closing Balance Sheet")
         and a calculation of the Unaudited Closing Net Cash Balance, together
         with a certificate signed by the Chief Financial Officer of the Company
         certifying (i) that the Unaudited Closing Balance Sheet was prepared in
         accordance with generally accepted accounting principles, consistently
         applied, except for the absence of footnotes and subject to adjustments
         consisting of normal year-end accruals, the effect of which, both
         individually and in the aggregate, is not material, (ii) that the
         Unaudited Closing Balance Sheet fairly and accurately presents the
         financial condition of the Company as of the Closing Date, and (iii) as
         to the calculation of the Unaudited Closing Net Cash Balance. The
         Unaudited Closing Balance Sheet shall have been prepared in
         consultation with LeukoSite and LeukoSite's representatives after
         LeukoSite and LeukoSite's representatives have had access (consistent
         with the provisions reflected in Section 10.1) to financial information
         and personnel relevant to the preparation of the Unaudited Closing
         Balance Sheet. The parties shall use their good faith efforts to
         resolve any



<PAGE>
                                       13


         disagreements between them concerning the Unaudited Closing Balance
         Sheet.

                  (c) AGGREGATE BASE CONSIDERATION SHARES. The aggregate number
         of shares of LeukoSite Stock that LeukoSite shall issue at the
         Effective Time to the Stockholders (other than holders of Dissenting
         Shares), in accordance with their respective interests as determined
         pursuant to Section 3.6(a), pursuant to the Merger (the "Aggregate Base
         Consideration Shares") shall be equal to the quotient obtained by
         dividing (i) the product of 1.25 and the Unaudited Closing Net Cash
         Balance by (ii) $11.88 (such amount to be proportionately adjusted to
         reflect stock splits, stock dividends, reverse stock splits, and other
         recapitalizations, reorganizations, and similar events affecting
         LeukoSite Common Stock and occurring after the date of this Agreement
         but prior to the Effective Time).

                  (d) AUDITED BALANCE SHEETS. LeukoSite shall have the right,
         exercisable at any time during the period commencing on the Closing
         Date and ending with the completion of LeukoSite's first audit after
         the Closing Date, to have an independent certified public accounting
         firm of national reputation prepare an audited balance sheet of the
         Company as of the date hereof (the "Audited Signing Balance Sheet"), an
         audited balance sheet as of the Closing Date (the "Audited Closing
         Balance Sheet"), an audited calculation of the Net Cash Balance as of
         the date hereof (the "Audited Signing Net Cash Balance") and an audited
         calculation of the Unaudited Closing Net Cash Balance (the "Audited
         Closing Net Cash Balance"). The Audited Signing Balance Sheet and the
         Audited Closing Balance Sheet shall be prepared in accordance with
         generally accepted accounting principles, consistently applied, and
         shall fairly and accurately present the financial condition of the
         Company as of the respective dates thereof. In the event that the
         Audited Closing Net Cash Balance will be the basis for an adjustment in
         the number of Aggregate Base Consideration Shares pursuant to Section
         3.7(e), then a copy of the Audited Signing Balance Sheet, the Audited
         Closing Balance Sheet, the Audited Signing Net Cash Balance and the
         Audited Closing Net Cash Balance shall be made available to the
         Stockholders' Representatives.

                  (e) ADJUSTMENT TO AGGREGATE BASE CONSIDERATION SHARES. In the
         event that the Unaudited Closing Net Cash Balance exceeds the Audited
         Closing Net Cash Balance, then the number of Aggregate Base
         Consideration Shares shall be reduced by a number of shares of
         LeukoSite Stock equal to the quotient obtained by dividing (i) the
         product of 1.25 and the amount by which the Unaudited Closing Net Cash
         Balance exceeds the Audited Closing Net Cash Balance by (ii) $11.88
         (such amount to be proportionately adjusted to reflect stock splits,
         stock dividends, reverse



<PAGE>
                                       14


          stock splits, and other recapitalizations, reorganizations, and
          similar events affecting LeukoSite Common Stock and occurring after
          the date of this Agreement). In the event that the Audited Closing Net
          Cash Balance exceeds the Unaudited Closing Net Cash Balance, then the
          number of Aggregate Base Consideration Shares shall be increased by a
          number of shares of LeukoSite Stock equal to the quotient obtained by
          dividing (i) the product of 1.25 and the amount by which the Audited
          Closing Net Cash Balance exceeds the Unaudited Closing Net Cash
          Balance by (ii) $11.88 (such amount to be proportionately adjusted to
          reflect stock splits, stock dividends, reverse stock splits, and other
          recapitalizations, reorganizations, and similar events affecting
          LeukoSite Common Stock and occurring after the date of this
          Agreement). If the number of Aggregate Base Consideration Shares
          increases as a result of any adjustment pursuant to this Section
          3.7(e), the increased number of shares shall be allocated among the
          Stockholders (other than holders of Dissenting Shares) in accordance
          with their respective interests as provided on SCHEDULE A, and
          LeukoSite shall deliver (A) to the Escrow Agent, to be held in escrow
          pursuant to the provisions of Section 4.3 hereof and the Escrow
          Agreement, a stock certificate registered in the name of each
          Stockholder that is entitled to a portion of such increased number of
          shares, which stock certificate shall represent twenty percent (20%)
          of the portion of such increased number of shares that is allocated to
          such Stockholder, and (B) to each Stockholder a stock certificate,
          registered in the name of such Stockholder, representing the balance
          of the portion of such increased number of shares allocated to such
          Stockholder. If the number of Aggregate Base Consideration Shares is
          reduced as a result of any adjustment pursuant to this Section 3.7(e),
          the correct number of shares for each Stockholder shall be
          recalculated by allocating such smaller number of Aggregate Base
          Consideration Shares among the Stockholders (other than holders of
          Dissenting Shares) in accordance with their respective interests as
          determined pursuant to Section 3.6(a), and LeukoSite shall have the
          right to recover any excess number of shares of LeukoSite Stock
          previously issued by LeukoSite to the Stockholders in connection with
          the Merger by, at LeukoSite's option, (i) making a claim against the
          Escrowed Securities pursuant to, and in accordance with, the
          provisions of the Escrow Agreement, and/or (ii) exercising its set-off
          rights pursuant to Section 14.5(b) hereof against any future payment
          owed by LeukoSite to the Stockholders in connection with the Merger.



<PAGE>
                                       15


         3.8.     AGGREGATE SUBSEQUENT CONSIDERATION.

                  (a) AGGREGATE SUBSEQUENT CONSIDERATION SHARES. In the event
         that LeukoSite or the Surviving Corporation shall receive payment from
         UCB pursuant to Section 4.2(b) of the UCB Agreement (the "Subsequent
         UCB Payment") of up to $6,000,000, LeukoSite will issue to the
         Stockholders, at the time specified below in this Section 3.8(a), an
         additional number of shares of LeukoSite Stock (the "Aggregate
         Subsequent Consideration Shares") equal to the quotient obtained by
         dividing (i) the product of 1.25 and the amount of the Subsequent UCB
         Payment actually received by LeukoSite or the Surviving Corporation
         (less any adjustment for taxes pursuant to Section 3.8(h)) by (ii)
         $11.88 (such amount to be proportionately adjusted to reflect stock
         splits, stock dividends, reverse stock splits, and other
         recapitalizations, reorganizations, and similar events affecting
         LeukoSite Common Stock and occurring after the date of this Agreement
         but prior to the issuance of the Aggregate Subsequent Consideration
         Shares pursuant to this Section 3.8(a)). The Aggregate Subsequent
         Consideration Shares shall be allocated among the Stockholders (other
         than those who are holders of Dissenting Shares who shall not be
         entitled to receive any portion of the Aggregate Subsequent
         Consideration Shares) in accordance with their respective interests as
         determined pursuant to Section 3.6(a). Within thirty (30) days after
         receiving the Subsequent UCB Payment, LeukoSite shall cause its
         transfer agent to issue to each Stockholder a stock certificate or
         stock certificates representing the portion, if any, of the Aggregate
         Subsequent Consideration Shares to which such Stockholder is entitled.

                  (b) CONTINGENT THIRD PARTY PAYMENTS. In the event that,
         subsequent to the date hereof, LeukoSite or the Surviving Corporation
         shall receive any payment (a "Contingent Third Party Payment") under
         (i) Sections 4.2(c), (d) or (e) of the UCB Agreement, which Sections
         provide, in the aggregate, for up to $6,000,000 in milestone payments
         to the Company, or (ii) Section 4.1 of the License Agreement between
         the Company and Stiefel Laboratories, Inc. ("Stiefel"), which Section
         provides for a license fee of $1,000,000 payable to the Company upon
         execution of the License Agreement by Stiefel, then, subject to the
         provisions of Section 3.8(e), LeukoSite shall, within thirty (30) days
         of the receipt of any such Contingent Third Party Payment, make payment
         of such Contingent Third Party Payment (less any adjustment for taxes
         pursuant to Section 3.8(h)) to the Stockholders (other than holders of
         Dissenting Shares) in accordance with their respective interests as
         determined pursuant to Section 3.6(a).



<PAGE>
                                       16


                  (c) LEUKOSITE CONTINGENT MILESTONE PAYMENTS. If a CytoMed
         Program conducted internally by LeukoSite, its Affiliates or its
         sublicensees (other than a Partner pursuant to Section 3.8(d)) as a
         Drug Development Program yields a Product Candidate which achieves the
         drug development milestones set forth in the table below (whether such
         milestones are achieved by LeukoSite, its Affiliates or its
         sublicensees (other than a Partner pursuant to Section 3.8(d)), then,
         subject to the provisions of Section 3.8(e), LeukoSite shall make
         payment and/or delivery to the Stockholders (other than holders of
         Dissenting Shares), in accordance with their respective interests as
         determined pursuant to Section 3.6(a), of the consideration set forth
         in the table below (a "LeukoSite Contingent Milestone Payment") within
         sixty (60) days of the occurrence of the drug development milestones
         set forth in the table below; PROVIDED, HOWEVER, that, except as
         provided below, LeukoSite shall be obligated to pay consideration for
         each drug development milestone only once, regardless of how many
         Product Candidates achieve such drug development milestone and
         regardless of where in the world such drug development milestone is
         achieved. If (a) LeukoSite reasonably determines that (i) a third party
         patent covers the manufacture, use or sale of a Product Candidate (a
         "Blocking Third Party Patent") or (ii) a patented or proprietary
         complementary technology owned by a third party is necessary for
         LeukoSite's clinical development of a Product Candidate (a
         "Complementary Technology"), and (b) LeukoSite in-licenses such
         Blocking Third Party Patent or Complementary Technology pursuant to
         terms requiring LeukoSite to make milestone payments to such third
         party upon the achievement of any drug development milestones, then
         fifty percent (50%) of the amount of any milestone payment that
         LeukoSite is required to pay in connection with such in-licensed
         Blocking Third Party Patent or Complementary Technology shall be offset
         against the milestone payments that LeukoSite is required to pay
         pursuant to this Section 3.8(c) with respect to such Product Candidate,
         PROVIDED THAT the aggregate amount of all such offsets with respect to
         any of such milestone payments shall in no event exceed fifty percent
         (50%) of any of such milestone payments. In the event that there has
         been an offset against a milestone payment pursuant to the preceding
         sentence, the balance of the scheduled milestone payment not paid as a
         result of such offset shall remain payable if and when a subsequent
         Product Candidate achieves the applicable drug development milestone
         (subject to the offset provided for in the preceding sentence).



<PAGE>
                                       17

<TABLE>
<CAPTION>

         --------------------------------------------------   --------------------------------------------------
                               EVENT                                               PAYMENT
         --------------------------------------------------   --------------------------------------------------
         <S>                                                  <C>

         Completion of a successful and acceptable Phase                         $1,500,000
         II study and the determination by LeukoSite to       and 84,175 shares of LeukoSite Stock (subject to
         commence a pivotal Phase III study                   proportional adjustment for stock splits, stock
                                                              dividends, recapitalizations and the like affecting
                                                              LeukoSite Common Stock and occurring after the date
                                                              of this Agreement but prior to the issuance of such
                                                              shares pursuant to this Section 3.8(c)), or such
                                                              lesser number of shares as may have a Fair Market
                                                              Value (as defined in SCHEDULE A) as of the date of
                                                              issuance of $4,000,000 (the "Milestone Shares")

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

         Completion of a successful and acceptable Phase                         $5,000,000
         III study and decision by LeukoSite to prepare
         and file an NDA

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

         Filing of NDA                                                           $1,000,000

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

         Approval of NDA                                                         $3,000,000

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

         First Commercial Sale                                                   $6,000,000

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

</TABLE>


                  (d) CONTINGENT PARTNER LICENSING PAYMENTS. If LeukoSite
         determines, in its sole discretion, to license, transfer or sell a
         Product Candidate to a third party which is not an Affiliate of
         LeukoSite (a "Partner") for use in the treatment of asthma, skin,
         opthalmic or gastro-intestinal disease or complement mediated
         inflammation in cardiovascular disease or organ transplantation, and
         such Product Candidate was being developed by the Company to treat such
         medical indications, then, subject to the provisions of Section 3.8(e),
         LeukoSite shall make payment to the Stockholders (other than holders of
         Dissenting Shares), in accordance with their respective interests as
         determined pursuant to Section 3.6(a), of an amount equal to
         twenty-five percent (25%) of the license fees, milestone payments or
         royalties received by LeukoSite from the Partner in respect of such
         Product Candidate (a "Contingent Partner Licensing Payment"). Any
         payment that LeukoSite is required to make pursuant to this Section
         3.8(d) shall be made within thirty (30) days following LeukoSite's
         receipt of consideration from the Partner. Consideration received by
         LeukoSite from a Partner that is not



<PAGE>
                                       18


         in the form of cash shall be valued by LeukoSite's Board of Directors
         in good faith as of the date of receipt of such consideration by
         LeukoSite.

                  (e) ROYALTY PAYMENTS TO DR. SHEN. Notwithstanding anything in
         this Agreement (including, without limitation, this Section 3.8)
         expressed or implied to the contrary, LeukoSite shall reduce the Merger
         Consideration required to be paid or delivered to the Stockholders
         pursuant to this Agreement relating to a Contingent Third Party Payment
         or any Product Candidate included in a CytoMed Program by any amounts
         which LeukoSite or the Surviving Corporation are obligated or become
         obligated to pay to T.Y. Shen under the Shen Consulting Agreement in
         respect of any Contingent Third Party Payment or any Product Candidate
         included in a CytoMed Program.

                  (f) MAXIMUM PAYMENT. Notwithstanding anything in this Section
         3.8 expressed or implied to the contrary, (A) in no event shall the
         cumulative aggregate amount or value of consideration that LeukoSite
         shall be required to provide to the Stockholders (other than holders of
         Dissenting Shares) pursuant to Sections 3.8(c) and/or 3.8(d) (after
         giving effect to any and all reductions to such consideration that may
         be required pursuant to Section 3.8(e) above) exceed the sum of
         $16,500,000 plus the Milestone Shares; PROVIDED, HOWEVER, that such
         cumulative aggregate amount or value of consideration shall be
         $17,500,000 in the event that no Milestone Shares have been issued at
         the time such cumulative aggregate amount or value of consideration
         exceeds $16,500,000, (B) in no event shall LeukoSite issue Milestone
         Shares to the Stockholders if such cumulative aggregate amount or value
         of consideration has already exceeded $16,500,000 prior to the issuance
         of any Milestone Shares and (C) in no event shall LeukoSite issue
         Milestone Shares to the Stockholders if and to the extent that (i) the
         number of such Milestone Shares is subject to reduction pursuant to
         Section 3.8(e) above or (ii) the Fair Market Value (as defined on
         SCHEDULE A) of such Milestone Shares on the date of their issuance
         (after giving effect to any and all reductions to the number of such
         Milestone Shares that may be required pursuant to Section 3.8(e) above)
         exceeds $4,000,000. Consideration from a Partner that is not in the
         form of cash shall be valued by LeukoSite's Board of Directors in good
         faith as of the date of receipt of such consideration by LeukoSite.

                  (g) CYTOMED PROGRAMS. LeukoSite represents and warrants that,
         as of the date of this Agreement and based upon the information
         available to it as of such date, it intends to continue the development
         and commercialization of Product Candidates included in the CytoMed
         Programs. However, it is agreed by the Company and LeukoSite that, from
         and after the date hereof, the CytoMed Programs shall be evaluated by
         LeukoSite in the context of the overall research and development



<PAGE>
                                       19


         programs undertaken from time to time by LeukoSite (the "LeukoSite R&D
         Programs"). In making determinations concerning whether, when and/or in
         what manner to develop, market or commercialize any Product Candidate
         or any other compound included in any CytoMed Program from and after
         the date hereof, LeukoSite shall use the same criteria that it applies
         in making such or similar evaluations and determinations concerning the
         LeukoSite R&D Programs. Specifically, and without limiting the
         generality of the foregoing sentence, LeukoSite shall take into account
         its available financial resources and personnel, LeukoSite's
         commitments and obligations to its corporate partners, the ease of, and
         the timeframe for, obtaining regulatory approval, the potential
         therapeutic benefits of the drug candidate, the level of competition in
         the marketplace for the drug candidate, the relative costs of
         pre-clinical and clinical development of any Product Candidate or any
         compound in a CytoMed Program as compared with LeukoSite's other drug
         development candidates, the results and data obtained in any
         pre-clinical or clinical trials, and the relative potential economic
         returns to LeukoSite from the development, sale, marketing or other
         commercialization of any Product Candidate or any compound in a CytoMed
         Program as compared to any of LeukoSite's other drug development
         candidates. After making a thorough evaluation utilizing the criteria
         described above, LeukoSite may continue, modify, postpone or terminate
         any CytoMed Program or the development and commercialization of any
         Product Candidate. The Stockholders' Representatives shall have the
         right to obtain information about the status of the CytoMed Programs
         pursuant to Section 9.15 hereof.

                  (h) REDUCTION FOR ADDITIONAL TAX LIABILITY. To the extent that
         any of the payments to be received by LeukoSite pursuant to Sections
         3.8(a) or (b) will result (i) in an additional ultimate Tax liability
         (other than an "alternative minimum tax" Tax liability) of LeukoSite
         despite reasonable tax planning by LeukoSite which shall include
         without limitation maximizing the benefits of filing consolidated
         returns, preserving and maximizing the prompt use of any available net
         operating loss and credit carryforwards of the Company, and maximizing
         the tax benefits available to LeukoSite by virtue of paying tax on and
         making payments with respect to the Subsequent UCB Payment or the
         Contingent Third Party Payments, or (ii) in "alternative minimum tax"
         Tax liability of LeukoSite, LeukoSite shall be entitled to retain the
         amount of the Subsequent UCB Payment and the Contingent Third Party
         Payments necessary to pay such Tax liability and shall reduce on a
         dollar for dollar basis (i) in the case of Section 3.8(a), the amount
         of Subsequent UCB Payment used to determine the number of Aggregate
         Subsequent Consideration Shares issued to the Stockholders or (ii) in
         the case of Section 3.8(b), the Contingent Third Party Payments paid to
         the Stockholders.



<PAGE>
                                       20


         4.   PROCEDURES; ESCROWED SECURITIES.

         4.1. CERTIFICATES. After the Effective Time, stock certificates (each,
a "Certificate," and collectively, the "Certificates") representing shares of
Company Stock that, pursuant to the provisions of Section 3.6(a) above, entitle
the holder thereof to receive therefor shares of LeukoSite Stock or other Merger
Consideration pursuant to the Merger, will be conclusively deemed to represent
the right to receive such shares of LeukoSite Stock or other Merger
Consideration.

         4.2. EXCHANGE OF CERTIFICATES. As promptly as practicable after the
Effective Time, LeukoSite or its transfer agent for LeukoSite Stock will send to
each Stockholder transmittal materials for use in exchanging their Certificates
for certificates for the shares of LeukoSite Stock or such other Merger
Consideration to which such Stockholder may be entitled as determined in
accordance with the provisions of this Agreement. Upon surrender of a
Certificate to LeukoSite or its transfer agent, as the case may be, together
with a duly executed letter of transmittal and any other reasonably required
documents, the holder of such Certificate will be entitled to receive (subject
to the escrow arrangements referred to in Section 4.3), in exchange for such
Certificate, a certificate or certificates for the number of shares of LeukoSite
Stock or such other Merger Consideration to which such holder may be entitled
(as determined in accordance with the provisions of this Agreement), and such
Certificate will be canceled.

         4.3. ESCROWED SECURITIES. Notwithstanding any other provision of this
Agreement to the contrary, at the Closing, LeukoSite, the Stockholders'
Representatives and the Escrow Agent will execute and deliver an Escrow
Agreement in the form attached hereto as EXHIBIT C (the "Escrow Agreement"),
pursuant to which LeukoSite shall deliver to the Escrow Agent stock certificates
representing twenty percent (20%) of the Aggregate Base Consideration Shares to
be issued to the Stockholders (the "Escrowed Securities"), to be held in escrow
pursuant to the terms of the Escrow Agreement until either (i) December 31,
1999, if but only if on or prior to December 31, 1999 there has not been a Claim
against the Escrowed Securities pursuant to the terms of this Agreement and the
Escrow Agreement or any exercise by LeukoSite of its right of set-off pursuant
to the terms of this Agreement, or (ii) the second anniversary of the Closing
Date, if on or prior to December 31, 1999 there has been a Claim against the
Escrowed Securities pursuant to the terms of this Agreement and the Escrow
Agreement or any exercise by LeukoSite of its right of set-off pursuant to the
terms of this Agreement. Notwithstanding anything in this Section 4.3 to the
contrary, a claim for an adjustment in the Aggregate Base Consideration Shares
pursuant to Section 3.7(e) that is made on or prior to December 31, 1999 shall
not be taken into account in determining whether the Escrowed Securitites



<PAGE>
                                       21


should be held in escrow under the Escrow Agreement beyond December 31, 1999.
Notwithstanding anything in this Agreement expressed or implied to the contrary,
any Merger Conversion Shares issued upon conversion of shares of LeukoSite
Series A Preferred Stock held in escrow pursuant to this Agreement (including,
without limitation, this Section 4.3) or the Escrow Agreement shall also be held
in escrow pursuant to, and in accordance with, the provisions of this Agreement
(including, without limitation, this Section 4.3) and the Escrow Agreement to
the same extent and on the same basis as such shares of LeukoSite Series A
Preferred Stock, and any reference in this Agreement to the term "ESCROWED
SECURITIES" shall be deemed to include any and all of such Merger Conversion
Shares.

         4.4. DISTRIBUTIONS. No dividend or other distribution payable after the
Effective Time with respect to LeukoSite Stock will be paid to the holder of any
unsurrendered Certificate until the holder thereof surrenders such Certificate,
at which time such holder will receive all dividends and distributions, without
interest thereon, previously payable but withheld from such holder pursuant
hereto.

         4.5. NO TRANSFERS. After the Effective Time, no transfers of shares of
Company Stock will be made in the stock transfer books of the Company. If, after
the Effective Time, Certificates are presented (for transfer or otherwise) to
the Surviving Corporation or its transfer agent for Company Stock, they will be
canceled and exchanged for the shares of LeukoSite Stock or other Merger
Consideration deliverable in respect thereof as determined in accordance with
this Agreement (or returned to the presenting person, if such Certificate
represents Dissenting Shares).

         4.6. NO FRACTIONAL SHARES. In lieu of the issuance of fractional shares
of LeukoSite Stock, cash adjustments will be paid (without interest) to the
Stockholders in respect of any fractional share of LeukoSite Stock that would
otherwise be issuable to them and the amount of such cash adjustments will be
determined by multiplying each relevant holder's fractional interest by $11.88
(such amount to be proportionately adjusted to reflect stock splits, stock
dividends, reverse stock splits, and other recapitalizations, reorganizations,
and similar events affecting LeukoSite Common Stock and occurring after the date
of this Agreement). For purposes of determining whether, and in what amounts, a
particular Stockholder would be entitled to receive cash adjustments under this
section, shares held of record by such holder and represented by two or more
Certificates will be aggregated.

         4.7. TERMINATION OF RIGHTS. After the Effective Time, holders of
Company Stock will cease to be, and will have no rights as, stockholders of the
Company, other than (i) in the case of shares other than Dissenting Shares, the
rights to receive the Merger Consideration and/or payments made in lieu of



<PAGE>
                                       22


fractional shares, as provided in this Agreement, and (ii) in the case of
Dissenting Shares, the rights afforded to the holders thereof under Section 262
of the DGCL.

         4.8. ABANDONED PROPERTY. Neither LeukoSite nor the Company nor any
other person will be liable to any holder or former holder of shares of Company
Stock for any shares, or any dividends or other distributions with respect
thereto, properly delivered to a public official pursuant to applicable
abandoned property, escheat, or similar laws.

         4.9. LOST CERTIFICATES, ETC. In the event that any Certificate has been
lost, stolen, or destroyed, then upon receipt of appropriate evidence as to such
loss, theft, or destruction, and to the ownership of such Certificate by the
person claiming such Certificate to be lost, stolen, or destroyed, and the
receipt by LeukoSite or its transfer agent for LeukoSite Stock of appropriate
and customary indemnification, LeukoSite or such transfer agent will issue in
exchange for such lost, stolen, or destroyed Certificate the shares of LeukoSite
Stock and the fractional share payment, if any, deliverable in respect thereof
as determined in accordance with this Agreement.

         4.10 STOCKHOLDERS' REPRESENTATIVES.

                  (a) In order to efficiently administer the transactions
         contemplated hereby, including (i) the waiver of any condition to the
         obligations of the Stockholders to consummate the transactions
         contemplated hereby, (ii) any adjustment in the number of Aggregate
         Base Consideration Shares pursuant to Section 3.7(e), (iii) the ability
         to consent, approve and agree on behalf of the Stockholders to any
         adjustment or change in the Unaudited Closing Net Cash Balance that may
         be agreed upon by LeukoSite and the Company, (iv) the defense and/or
         settlement of any claims for which the Stockholders may be required to
         indemnify LeukoSite and/or the Surviving Corporation pursuant to
         Section 14 below or for which LeukoSite shall have the right to make a
         claim against the Escrowed Securities pursuant to this Agreement and
         the Escrow Agreement or the right of set-off pursuant to this
         Agreement, (v) the ability, subject to and upon the terms and
         conditions set forth in Section 9.14 hereof, to take all action
         necessary against UCB in connection with breaches of payment
         obligations by UCB under the UCB Agreement, and (vi) the orderly
         distribution of Merger Consideration from LeukoSite to the
         Stockholders, the Stockholders hereby designate Richard Sherman and
         Joel Liffman, acting jointly, as their representatives (in such
         capacity, the "Stockholders' Representatives").



<PAGE>
                                       23


                  (b) The Stockholders hereby authorize the Stockholders'
         Representatives, acting jointly, (i) to make all decisions on behalf of
         the Stockholders relating to any adjustment in the number of Aggregate
         Base Consideration Shares pursuant to Section 3.7(e), (ii) to make all
         decisions and grant all consents and approvals on behalf of the
         Stockholders relating to any adjustments or changes to the Unaudited
         Closing Net Cash Balance that have been agreed upon by LeukoSite and
         the Company, (iii) to take all action necessary in connection with the
         waiver of any condition to the obligations of the Stockholders to
         consummate the transactions contemplated hereby, or the defense and/or
         settlement of any claims for which the Stockholders may be required to
         indemnify LeukoSite, the Merger Sub and/or the Surviving Corporation
         pursuant to Section 14 below or for which LeukoSite shall have the
         right to make a claim against the Escrowed Securities pursuant to this
         Agreement and the Escrow Agreement or the right of set-off pursuant to
         this Agreement, (iv) subject to and upon the terms and conditions set
         forth in Section 9.14 hereof, to take all action necessary against UCB
         in connection with breaches of payment obligations by UCB under the UCB
         Agreement, (v) to determine the Stockholders to whom consideration from
         LeukoSite shall be distributed, the amount of consideration to be so
         distributed, and the address of such Stockholders, (vi) to give and
         receive all notices required to be given under this Agreement and the
         Escrow Agreement, and (vii) to take any and all additional action as is
         contemplated to be taken by or on behalf of the Stockholders by the
         terms of this Agreement or the Escrow Agreement. In order for any
         action, consent, approval or determination taken or made by the
         Stockholders' Representatives to be valid, binding and enforceable, it
         must be taken or made by joint action of both Stockholders'
         Representatives. Neither of the Stockholders' Representatives shall
         have any power or authority to take any action individually without the
         other, and, in the event that either of the Stockholders'
         Representatives takes any action individually without the other, such
         action shall not be binding or of any force or effect whatsoever.

                  (c)      In the event that:

                           (i) Richard Sherman, or his substitute as one of the
                  Stockholders' Representatives, dies, becomes unable to perform
                  his responsibilities hereunder or resigns from such position,
                  the Stockholders holding, immediately prior to the Closing, a
                  majority of the combined voting power of the Company Stock
                  shall select another representative to fill such vacancy and
                  such substituted representative shall be deemed to a
                  Stockholders' Representative for all purposes of this
                  Agreement and the documents delivered pursuant hereto.



<PAGE>
                                       24


                           (ii) Joel Liffman, or his substitute as one of the
                  Stockholders' Representatives, dies, becomes unable to perform
                  his responsibilities hereunder or resigns from such position,
                  the Stockholders holding, immediately prior to the Closing, a
                  majority of the shares of Company Series VII Preferred Stock
                  shall select another representative to fill such vacancy and
                  such substituted representative shall be deemed to a
                  Stockholders' Representative for all purposes of this
                  Agreement and the documents delivered pursuant hereto.

                  (d) All decisions and actions by the Stockholders'
         Representatives, including without limitation any agreement between the
         Stockholders' Representatives and LeukoSite relating to the defense or
         settlement of any claims for which the Stockholders may be required to
         indemnify LeukoSite, Merger Sub and/or the Surviving Corporation
         pursuant to Section 14 below or for which LeukoSite shall have the
         right to proceed against the Escrowed Securities pursuant to this
         Agreement and the Escrow Agreement or the right of set-off pursuant to
         this Agreement, shall be binding upon all of the Stockholders and no
         Stockholder shall have the right to object, dissent, protest or
         otherwise contest the same.

                  (e) By virtue of the adoption of this Agreement and the
         approval of the Merger by the Stockholders at a meeting of Stockholders
         (or by written consent in lieu of a meeting) pursuant to, and in
         accordance with, the applicable provisions of the DGCL, each
         Stockholder (regardless of whether or not such Stockholder votes in
         favor of the adoption of this Agreement and the approval of the Merger
         at such meeting or by written consent) that is not a holder of
         Dissenting Shares hereby agrees that:

                           (i) LeukoSite shall be able to rely conclusively on
                  the joint instructions and decisions of the Stockholders'
                  Representatives as to the settlement of any claims for
                  indemnification by LeukoSite, Merger Sub and/or the Surviving
                  Corporation pursuant to Section 14 below or for which
                  LeukoSite shall have the right to make a claim against the
                  Escrowed Securities pursuant to this Agreement and the Escrow
                  Agreement or the right of set-off pursuant to this Agreement,
                  or as to any other actions required or permitted to be taken
                  by the Stockholders' Representatives hereunder or under the
                  Escrow Agreement, and no party hereunder shall have any cause
                  of action against LeukoSite to the extent LeukoSite has relied
                  upon the joint instructions or decisions of the Stockholders'
                  Representatives;



<PAGE>
                                       25


                           (ii) all actions, decisions and instructions of the
                  Stockholders' Representatives shall be conclusive and binding
                  upon all of the Stockholders and no Stockholder shall have any
                  cause of action against either of the Stockholders'
                  Representatives for any action taken, decision made or
                  instruction given by the Stockholders' Representatives, acting
                  jointly, under this Agreement, except for fraud or willful
                  breach of this Agreement by the Stockholders' Representatives;

                           (iii) the provisions of this Section 4.10 are
                  independent and severable, are irrevocable and coupled with an
                  interest and shall be enforceable notwithstanding any rights
                  or remedies that any Stockholder may have in connection with
                  the transactions contemplated by this Agreement;

                           (iv) remedies available at law for any breach of the
                  provisions of this Section 4.10 are inadequate; therefore,
                  LeukoSite, Merger Sub and/or the Surviving Corporation shall
                  be entitled to temporary and permanent injunctive relief
                  without the necessity of proving damages if either LeukoSite,
                  Merger Sub and/or the Surviving Corporation brings an action
                  to enforce the provisions of this Section 4.10; and

                           (v) the provisions of this Section 4.10 shall be
                  binding upon the executors, heirs, legal representatives,
                  personal representatives, successor trustees, and successors
                  of each Stockholder, and any references in this Agreement to a
                  Stockholder or the Stockholders shall mean and include the
                  successors to the Stockholder's rights hereunder, whether
                  pursuant to testamentary disposition, the laws of descent and
                  distribution or otherwise.

                  (f) All fees and expenses incurred by the Stockholders'
         Representatives shall be paid by the Stockholders (other than holders
         of Dissenting Shares) in proportion to their ownership of Company
         Stock.

         4.11. EFFECT OF STOCKHOLDER APPROVAL OF MERGER. Subject to the
provisions of the last sentence of this Section 4.11, the adoption of this
Agreement and the approval of the Merger by the Stockholders at a meeting of
Stockholders (or by written consent in lieu of a meeting) pursuant to, and in
accordance with, the applicable provisions of the DGCL shall be deemed to
constitute approval by each Stockholder individually (regardless of whether or
not such Stockholder votes in favor of the adoption of this Agreement and the
approval of the Merger at such meeting or by written consent), to the same
extent as if such Stockholder were a party to this Agreement, of (i) all of the
provisions of this Agreement that pertain to the Stockholders, that impose



<PAGE>
                                       26


liabilities, obligations or burdens on the Stockholders (including, without
limitation, the indemnification provisions of Section 14 hereof) or that limit
the rights of the Stockholders (including, without limitation, with respect to
the right of the Stockholders to receive all or any portion of the Merger
Consideration), (ii) the appointment of the Stockholders' Representatives, (iii)
the grant to the Stockholders' Representatives of all of the powers, rights and
privileges contemplated under this Agreement (including, without limitation,
Section 4.10 hereof), (iv) the provisions of this Agreement concerning the
replacement and substitution of either of the Stockholders' Representatives, (v)
the Escrow Agreement and all of the arrangements relating thereto, including,
without limitation, the placement of the Escrowed Securities in escrow and the
appointment of the Escrow Agent pursuant to the Escrow Agreement, (vi) the
provisions of this Agreement that authorize LeukoSite to make a claim or proceed
against the Escrowed Securities held in escrow pursuant to the Escrow Agreement,
(vii) the provisions of this Agreement that authorize LeukoSite to exercise any
right of set-off (including, without limitation, the provisions of Section
14.5(b) hereof) and (viii) any and all provisions of this Agreement that
contemplate, authorize or provide for any increase, reduction or other
adjustment in the Merger Consideration payable to the Stockholders pursuant to
the Merger (including, without limitation, any provisions of this Agreement that
specify or provide a procedure for determining or implementing any such
increase, reduction or other adjustment in the Merger Consideration).
Notwithstanding the foregoing, the provisions of this Section 4.11 shall not
apply to those Stockholders that duly exercise the appraisal rights afforded to
dissenting stockholders pursuant to Section 262 of the DGCL.

         5. STOCK OPTIONS AND WARRANTS. Prior to the Effective Time, the Company
and its Board of Directors shall (i) take all actions necessary to effect the
exercise and/or termination of each option to purchase Company Stock ("Company
Options"), whether issued under one of the Company's option plans or otherwise,
and (ii) use commercially reasonable efforts to cause each holder of a warrant
to purchase Company Stock outstanding at any time prior to the Effective Time
(the "Company Warrants") to exercise or agree to the termination of the warrant
in full prior to the Effective Time. LeukoSite will not assume any Company
Option not exercised prior to the Effective Time.

6.       REGISTRATION AND LOCK-UP OF LEUKOSITE COMMON STOCK.

         6.1      REGISTRATION OF SHARES.

                  (a) LeukoSite shall file with the SEC, on or before the 60th
         day following the Closing Date, a registration statement on Form S-3
         (or on Form S-1 if LeukoSite does not qualify for Form S-3) covering
         the resale to the public by the Stockholders who hold or may hold
         Merger Common Shares (the "Registering Stockholders"), of the Merger
         Common Shares



<PAGE>
                                       27


         (the "Stockholder Registration Statement"). LeukoSite shall use its
         best efforts to cause the Stockholder Registration Statement to be
         declared effective by the SEC as soon as practicable following the
         filing thereof and to remain effective until the second anniversary of
         the Closing Date or such earlier time as all of the Merger Common
         Shares covered by the Stockholder Registration Statement have been
         sold pursuant thereto (the "Effective Period"). Thereafter LeukoSite
         shall be entitled to withdraw the Stockholder Registration Statement
         and the Stockholders shall have no further right to offer or sell any
         of the Merger Common Shares pursuant to the Stockholders Registration
         Statement (or any prospectus pursuant thereto). The shares subject to
         the Stockholder Registration Statement shall not be underwritten
         unless LeukoSite shall otherwise consent in its sole discretion.

                  (b) From and after the date hereof and prior to the expiration
         of the Effective Period, whenever LeukoSite proposes to file a
         registration statement relating to an offering in which LeukoSite
         proposes to sell shares of LeukoSite Common Stock for its own account
         (other than registration statements on Form S-4 or Form S-8 or any
         successor form for securities to be offered in a transaction of the
         type contemplated by Rule 145 under the Securities Act or to employees
         or consultants of LeukoSite pursuant to any employee benefit plan), it
         will, prior to such filing, give at least 20 days' written notice to
         all Registering Stockholders of its intention to do so (subject to the
         limitations set forth in paragraph (d) below) (the "Piggyback Notice")
         and, upon the written request of one or more Registering Stockholders
         given within ten days after the LeukoSite Piggyback Notice is given
         (which request shall state the intended method of disposition of such
         Merger Common Shares) (the "Holder Inclusion Notice"), LeukoSite shall
         use its best efforts to cause all Merger Common Shares which LeukoSite
         has been requested by such Registering Stockholder or Registering
         Stockholders to register to be registered under the Securities Act to
         the extent necessary to permit their sale or other disposition in
         accordance with the intended methods of distribution specified in the
         Holder Inclusion Notice; provided, that (i) LeukoSite shall have the
         right to postpone or withdraw any registration effected pursuant to
         this Section 6.1(b) hereof without obligation to any Registering
         Stockholder, (ii) the number of Merger Common Shares proposed to be
         sold by any such Registering Stockholder is at least twenty-five
         percent (25%) of the total number of Merger Common Shares then held by
         such Registering Stockholder.

                  (c) In connection with any offering under Section 6.1(b)
         hereof involving an underwriting, LeukoSite shall not be required to
         include any Merger Common Shares in such underwriting unless the
         holders thereof accept the terms of the underwriting as agreed upon
         between LeukoSite



<PAGE>
                                       28


          and the underwriter(s) of such offering. If in the opinion of the
          managing underwriter(s) of such offering the registration of all, or
          part of, the shares of LeukoSite Common Stock (the "Incidental
          Shares") which the Registering Stockholders have requested to be
          included pursuant to Section 6.1(b) hereof and/or which other holders
          of shares of LeukoSite Common Stock or other securities of LeukoSite
          entitled to include shares of LeukoSite Common Stock in such
          registration have requested to be included (collectively, the
          "Qualified Holders") would materially and adversely affect the success
          of such public offering or the price that would be received for any
          shares of LeukoSite Common Stock offered in the offering, then,
          notwithstanding anything in this Section 6 to the contrary, LeukoSite
          shall be required to include in the underwriting only that number of
          such shares, if any, which the managing underwriter(s) believe(s) may
          be sold without causing such adverse effect. If a registration
          pursuant to this Section 6 hereof involves an underwritten offering
          and the managing underwriter shall advise LeukoSite in writing that,
          in its opinion, the number of shares of LeukoSite Common Stock
          requested by the Qualified Holders to be included in such registration
          is likely to affect materially and adversely the success of the public
          offering or the price that would be received for any shares of
          LeukoSite Common Stock offered in such offering, then, notwithstanding
          anything in this Section 6 to the contrary, LeukoSite shall only be
          required to include in such registration to the extent of the number
          of shares of LeukoSite Common Stock which LeukoSite is so advised can
          be sold in such offering, (i) first, the number of shares of LeukoSite
          Common Stock proposed to be included in such registration for the
          account of LeukoSite and/or any stockholders of LeukoSite that have
          exercised demand registration rights in accordance with the
          priorities, if any, then existing among LeukoSite and/or such
          stockholders of LeukoSite with demand registration rights, and (ii)
          second, the shares of LeukoSite Common Stock requested to be included
          in such registration by all other stockholders of LeukoSite
          (including, without limitation, the Registering Stockholders), PRO
          RATA among such other stockholders (including, without limitation, the
          Registering Stockholders) on the basis of the number of shares of
          LeukoSite Common Stock that each of them requested to be included in
          such registration.

                  (d) Notwithstanding anything in this Section 6 to the
          contrary, LeukoSite shall not be required to provide any advance
          notice to Registering Stockholders in connection with any offering
          under this Section 6.1 involving an underwriting if LeukoSite has been
          informed in writing that in the opinion of the managing underwriter(s)
          the inclusion of any Incidental Shares in such offering would
          materially and adversely affect the success of the offering or the
          price that would be received for any shares of LeukoSite Common Stock
          offered in the offering. In such



<PAGE>
                                       29


         event, LeukoSite will provide written notice to all Registering
         Stockholders containing a copy of such managing underwriter's(s')
         opinion, which notice need not be given prior to the filing of the
         applicable registration statement.

         6.2      LIMITATIONS ON REGISTRATION RIGHTS.

                  (a) Notwithstanding anything in this Section 6 to the
         contrary, if the Company shall furnish to the Registering Stockholders
         a certificate signed by the President or Chief Executive Officer of
         LeukoSite stating that the Board of Directors of LeukoSite has made the
         good faith determination (i) that continued use by the Registering
         Stockholders of the Stockholder Registration Statement filed by
         LeukoSite for purposes of effecting offers or sales of Merger Common
         Shares pursuant thereto would require, under the Securities Act and the
         rules and regulations promulgated thereunder, premature disclosure in
         the registration statement (or the prospectus relating thereto) of
         material, nonpublic information concerning LeukoSite, its business or
         prospects or any proposed material transaction involving LeukoSite,
         (ii) that such premature disclosure would be materially adverse to
         LeukoSite, its business or prospects or any such proposed material
         transaction or would make the successful consummation by LeukoSite of
         any such material transaction significantly less likely and (iii) that
         it is therefore essential to suspend the use by the Registering
         Stockholders of such Stockholder Registration Statement (and the
         prospectus relating thereto) for purposes of effecting offers or sales
         of Merger Common Shares pursuant thereto, then the right of the
         Registering Stockholders to use such Stockholder Registration Statement
         (and the prospectus relating thereto) for purposes of effecting offers
         or sales of Merger Common Shares pursuant thereto shall be suspended
         for a period (the "Suspension Period") of not more than 90 days after
         delivery by the Company of the certificate referred to above in this
         Section 6.2(a). During the Suspension Period, none of the Registering
         Stockholders shall offer or sell any Merger Common Shares pursuant to
         or in reliance upon such Stockholder Registration Statement (or the
         prospectus relating thereto). LeukoSite agrees that, as promptly as
         practicable after the consummation, abandonment or public disclosure of
         the event or transaction that caused LeukoSite to suspend the use of
         the Registration Statement (and the prospectus relating thereto)
         pursuant to this Section 6.2(a), LeukoSite will provide the Registering
         Stockholders with revised prospectuses, if required, and will notify
         the Registering Stockholders of their ability to effect offers or sales
         of Merger Common Shares pursuant to or in reliance upon such
         Stockholder Registration Statement.


<PAGE>

                                       30


                  (b) LeukoSite agrees that no other holder of LeukoSite Stock
         seeking to resell shares of LeukoSite Common Stock pursuant to a shelf
         registration statement on Form S-3 will be permitted to sell shares of
         LeukoSite Common Stock pursuant to such shelf registration statement
         during a Suspension Period. LeukoSite shall not be required to disclose
         to the Registering Stockholders the reasons for requiring a suspension
         of sales hereunder, and the Registering Stockholders shall not disclose
         to any third party the existence of any such suspension.

                  (c) If LeukoSite suspends the Stockholder Registration
         Statement or requires the Stockholders to cease sales of shares
         pursuant to Section 6.2(a) above, LeukoSite shall, as promptly as
         practicable following the termination of the circumstance which
         entitled LeukoSite to do so, take such actions as may be necessary to
         reinstate the effectiveness of the Stockholder Registration Statement
         and/or give written notice to all Registering Stockholders authorizing
         them to resume sales pursuant to the Stockholder Registration
         Statement. If as a result thereof the prospectus included in the
         Stockholder Registration Statement has been amended to comply with the
         requirements of the Securities Act, LeukoSite shall enclose such
         revised prospectus with a notice to Registering Stockholders given
         pursuant to this Section 6.2(c).

         6.3      REGISTRATION PROCEDURES.

                  (a) In connection with the filing by LeukoSite of the
         Stockholder Registration Statement, LeukoSite shall furnish to each
         Registering Stockholder a copy of the prospectus, including a
         preliminary prospectus, in conformity with the requirements of the
         Securities Act. Subject to Section 6.2 hereof, LeukoSite shall prepare
         and file with the SEC such amendments and supplements to the
         Stockholder Registration Statement and the prospectus used in
         connection with such Stockholder Registration Statement as may be
         reasonably necessary to keep such Stockholder Registration Statement
         effective and to comply with the provisions of the Securities Act with
         respect to the disposition of all Merger Common Shares pursuant to such
         Stockholder Registration Statement until the earlier of (i) such time
         as all such Merger Common Shares have been disposed of, (ii) such time
         as such Merger Common Shares are eligible for sale pursuant to Rule 144
         (without being subject to volume limitations), or (iii) the second
         anniversary of the Closing Date. LeukoSite shall furnish to each
         Registering Stockholder a copy of any amendment or supplement to such
         Stockholder Registration Statement or prospectus prior to filing the
         same with the SEC, and shall not file any such amendment or supplement
         to which any such requesting Registering Stockholder shall reasonably
         have objected to in writing prior to the filing thereof on the



<PAGE>
                                       31


         grounds that such amendment or supplement contains a material
         inaccuracy with respect to the description of such Registering
         Stockholder.

                  (b) If LeukoSite has delivered preliminary or final
         prospectuses to the Registering Stockholders and after having done so
         the prospectus is amended or supplemented to comply with the
         requirements of the Securities Act as described in Section 6.3(a)
         hereof, LeukoSite shall promptly notify the Registering Stockholders
         and, if requested by LeukoSite, the Registering Stockholders shall
         immediately cease making offers or sales of shares under the
         Stockholder Registration Statement and return all prospectuses to
         LeukoSite. LeukoSite shall promptly provide the Registering
         Stockholders with revised prospectuses and, following receipt of the
         revised prospectuses, the Registering Stockholders shall be free to
         resume making offers and sales under the Stockholder Registration
         Statement.

                  (c) LeukoSite shall furnish to each requesting Registering
         Stockholder such number of conformed copies of the Stockholder
         Registration Statement and of each such amendment and supplement
         thereto (in each case including all exhibits thereto), such number of
         copies of the prospectus included in such Stockholder Registration
         Statement (including each preliminary prospectus) and such number of
         documents, if any, incorporated by reference in such Stockholder
         Registration Statement or prospectus, as such requesting Registering
         Stockholder may reasonably request.

                  (d) LeukoSite shall use its best efforts to register or
         qualify the Merger Common Shares covered by the Stockholder
         Registration Statement under the securities or "blue sky" laws of such
         states as the Registering Stockholders shall reasonably request;
         PROVIDED, HOWEVER, that LeukoSite shall not be required in connection
         with this paragraph (b) to qualify as a foreign corporation or execute
         a general consent to service of process in any jurisdiction.

                  (e) LeukoSite shall pay the expenses incurred by it in
         complying with its obligations under this Section 6, including all
         registration and filing fees, exchange listing fees, fees and expenses
         of counsel for LeukoSite, and fees and expenses of accountants for
         LeukoSite, but excluding (i) any brokerage fees, selling commissions or
         underwriting discounts incurred by the Registering Stockholders in
         connection with sales under the Stockholder Registration Statement and
         (ii) the fees and expenses of any counsel retained by Registering
         Stockholders.



<PAGE>
                                       32


         6.4 REQUIREMENTS OF COMPANY STOCKHOLDERS. LeukoSite shall not be
required to include any Merger Common Shares in the Stockholder Registration
Statement unless:

                  (a) the Registering Stockholder owning such shares furnishes
         to LeukoSite in writing such information regarding such Registering
         Stockholder and the proposed sale of Merger Common Shares by such
         Registering Stockholder as LeukoSite may reasonably request in writing
         in connection with the Stockholder Registration Statement or as shall
         be required in connection therewith by the SEC or any state securities
         law authorities;

                  (b) such Registering Stockholder shall have provided to
LeukoSite its written agreement:

                           (i) to indemnify LeukoSite and each of its directors
                  and officers under the circumstances and substantially in the
                  form set forth in Section 6.5(b) hereof; and

                           (ii) From the Closing Date to the second anniversary
                  of the Closing Date, each Registering Stockholder which holds
                  or owns (at the time of the written request of LeukoSite or
                  managing underwriter referred to below in this Section 6.4(b)
                  or at any time during the 90 day period commencing on the
                  effective date of the registration statement relating to such
                  underwritten public offering of LeukoSite Common Stock) of
                  record or beneficially (within the meaning of Section 13(d) of
                  the Exchange Act and the rules and regulations promulgated
                  thereunder) Merger Common Shares hereby agrees that, at the
                  written request of LeukoSite or any managing underwriter of
                  any underwritten public offering of LeukoSite Common Stock,
                  such Registering Stockholder shall not, without the prior
                  written consent of LeukoSite or such managing underwriter,
                  sell, make any short sale of, loan, grant any option for the
                  purchase of, pledge, encumber, or otherwise dispose of, or
                  exercise any registration rights with respect to, any Merger
                  Common Shares during the 90 day period commencing on the
                  effective date of the registration statement relating to such
                  underwritten public offering of LeukoSite Common Stock;
                  provided that no Registering Stockholder shall be obligated to
                  enter into such lock-up agreement described in this Section
                  6.4(b)(ii) unless all executive officers and directors of
                  LeukoSite enter into similar agreements. In order to enforce
                  the foregoing covenant, LeukoSite may impose stop transfer
                  instructions with respect to the Merger Common Shares of each
                  Registering Stockholder (and the shares or securities of every
                  other person subject to the foregoing restriction)



<PAGE>
                                       33


                  until the end of such reasonable and customary period, and
                  the Registering Stockholders agree to enter into a customary
                  agreement with the underwriters of such offering reflecting
                  the lock-up agreement set forth herein.

                  (c) Each Stockholder hereby agrees that, without the prior
         written consent of LeukoSite, such Stockholder shall not sell, make any
         short sale of, loan, grant any option for the purchase of, pledge,
         encumber, or otherwise dispose of any Merger Common Shares during the
         180 day period commencing on the Closing Date.

         6.5 INDEMNIFICATION. In the event that any Merger Common Shares of the
Registering Stockholders are included in a registration statement pursuant to
this Agreement:

                  (a) To the fullest extent permitted by law, LeukoSite will
         indemnify and hold harmless each Registering Stockholder, any
         underwriter (as defined in the Securities Act) for LeukoSite, and each
         officer, director, fiduciary, employee, member, general partner and
         limited partner (and affiliates thereof) of such Registering
         Stockholder or such underwriter, each broker or other person acting on
         behalf of such Registering Stockholder and each person, if any, who
         controls such Registering Stockholder or such underwriter within the
         meaning of the Securities Act, against any losses, claims, damages or
         liabilities, joint or several, to which they may become subject under
         the Securities Act or otherwise, insofar as such losses, claims,
         damages or liabilities (or actions in respect thereof) arise out of or
         are based upon any untrue or alleged untrue statement of any material
         fact contained in such registration statement, including any
         preliminary prospectus or final prospectus contained therein or any
         amendments or supplements thereto, or arise out of or are based upon
         the 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 any violation by LeukoSite of the Securities
         Act or state securities or blue sky laws applicable to LeukoSite and
         leading to action or inaction required of LeukoSite in connection with
         such registration or qualification under such Securities Act or state
         securities or blue sky laws; and will reimburse on demand such
         Registering Stockholder, such underwriter, such broker or other person
         acting on behalf of such Registering Stockholder or such officer,
         director, fiduciary, employee, member, general partner, limited
         partner, affiliate or controlling person for any legal or other
         expenses reasonably incurred by any of them in connection with
         investigating or defending any such loss, claim, damage, liability or
         action, subject to the provisions of Section 6.5(c); PROVIDED, HOWEVER,
         that the indemnity agreement contained in this Section 6.5(a) shall not
         apply to amounts paid in settlement of any such



<PAGE>
                                       34


         loss, claim, damage, liability or action if such settlement is
         effected without the consent of LeukoSite (which consent shall not be
         unreasonably withheld), nor shall LeukoSite be liable in any such case
         for any such loss, damage, liability or action to the extent that it
         arises out of or is based upon an untrue statement or alleged untrue
         statement or omission made in connection with such registration
         statement, preliminary prospectus, final prospectus, or amendments or
         supplements thereto, in reliance upon and in conformity with written
         information furnished expressly for use in connection with such
         registration by the Registering Stockholders, any underwriter for them
         or controlling person with respect to them.

                  (b) To the fullest extent permitted by law, each Registering
         Stockholder will indemnify and hold harmless LeukoSite, each of its
         directors, each of its officers who have signed such registration
         statement, each person, if any, who controls LeukoSite within the
         meaning of the Securities Act, any underwriter for LeukoSite (within
         the meaning of the Securities Act), and all other Registering
         Stockholders against any losses, claims, damages or liabilities to
         which LeukoSite or any such director, officer, controlling person, or
         underwriter may become subject to, under the Securities Act or
         otherwise, insofar as such losses, claims, damages or liabilities (or
         actions in respect thereto) arise out of or are based upon any untrue
         or alleged untrue statement of any material fact contained in such
         registration statement, including any preliminary prospectus or final
         prospectus contained therein or any amendments or supplements thereto,
         or arise out of or are based upon the omission or alleged omission to
         state therein a material fact required to be stated therein or
         necessary to make the statements therein not misleading, in each case
         to the extent that such untrue statement or alleged untrue statement or
         omission or alleged omission was made in such registration statement,
         preliminary prospectus, final prospectus, or amendments or supplements
         thereto, in reliance upon and in conformity with written information
         furnished by such Registering Stockholder expressly for use in
         connection with such registration; and such Registering Stockholder
         will reimburse any legal or other expenses reasonably incurred by
         LeukoSite or any such director, officer, controlling person,
         underwriter or other Registering Stockholder in connection with
         investigating or defending any such loss, claim, damage, liability or
         action, subject to the provisions of Section 6.5(c), PROVIDED, HOWEVER,
         that the maximum amount of liability of each Registering Stockholder
         hereunder shall be limited to the proceeds (net of underwriting
         discounts and commissions, if any) actually received by such
         Registering Stockholder from the sale of Merger Common Shares covered
         by such registration statement, and PROVIDED, FURTHER, HOWEVER, that
         the indemnity agreement contained in this Section 6.5(b) shall not
         apply to amounts paid in settlement of any such loss, claim, damage,
         liability or



<PAGE>
                                       35


         action if such settlement is effected without the consent
         of those Registering Stockholder(s) against which the request for
         indemnity is being made (which consent shall not be unreasonably
         withheld).

                  (c) Promptly after receipt by an indemnified party under this
         Section 6.5 of notice of the commencement of any action, such
         indemnified party will, if a claim in respect thereof is to be made
         against any indemnifying party under this Section 6.5, notify the
         indemnifying party in writing of the commencement thereof and the
         indemnifying party shall have the right to participate in and, to the
         extent the indemnifying party desires, jointly with any other
         indemnifying party similarly noticed, to assume at its expense the
         defense thereof with counsel mutually satisfactory to the parties;
         PROVIDED, HOWEVER, that, if any indemnified party shall have reasonably
         concluded that there may be one or more legal defenses available to
         such indemnified party which are different from or additional to those
         available to the indemnifying party, or that such claim or litigation
         involves or could have an effect upon matters beyond the scope of the
         indemnity agreement provided in this Section 6.5, the indemnifying
         party shall not have the right to assume the defense of such action on
         behalf of such indemnified party, and such indemnifying party shall
         reimburse such indemnified party and any person controlling such
         indemnified party for the fees and expenses of counsel retained by the
         indemnified party which are reasonably related to the matters covered
         by the indemnity agreement provided in this Section 6.5. Subject to the
         foregoing, an indemnified party shall have the right to employ separate
         counsel in any such action and to participate in the defense thereof
         but the fees and expenses of such counsel shall not be at the expense
         of the indemnifying party. The failure to notify an indemnifying party
         promptly of the commencement of any such action, if materially
         prejudicial to his ability to defend such action, shall relieve such
         indemnifying party of any liability to the indemnified party under this
         Section 6.5, but the omission so to notify the indemnifying party will
         not relieve him of any liability which the indemnifying party may have
         to any indemnified party otherwise other than under this Section 6.5.

                  (d) Notwithstanding anything in this Section 6 to the
         contrary, if, in connection with an underwritten public offering,
         LeukoSite, the Registering Stockholders and the underwriters enter into
         an underwriting or purchase agreement relating to such offering which
         contains provisions covering indemnification among the parties, then
         the indemnification provision of this Section 6.5 shall be deemed
         inoperative for purposes of such offering.

         6.6 RULE 144. LeukoSite shall comply with the requirements of Rule
144(c) under the Securities Act, as such Rule may be amended from time to time



<PAGE>
                                       36


(or any similar rule or regulation hereafter adopted by the SEC), regarding the
availability of current public information to the extent required to enable each
Registering Stockholder to sell Merger Common Shares without registration under
the Securities Act pursuant to the resale provisions of Rule 144 (or any similar
rule or regulation). Upon the request of a Registering Stockholder, LeukoSite
will deliver to such Registering Stockholder a written statement as to whether
it has complied with such requirements and, upon a Registering Stockholder's
compliance with the applicable provisions of Rule 144, will take such action as
may be required (including, without limitation, causing legal counsel to issue
an appropriate opinion) to cause its transfer agent to effectuate any transfer
of Merger Common Shares properly requested by such Registering Stockholder, in
accordance with the terms and conditions of Rule 144.

         6.7.     SECURITIES LAWS TRANSFER RESTRICTIONS, LEGENDS.

                  (a) No Stockholder shall sell, assign, pledge, transfer or
         otherwise dispose or encumber any of those Merger Shares received by
         it, except (i) pursuant to the Stockholder Registration Statement or
         other effective registration statement under the Securities Act, (ii)
         pursuant to an available exemption from registration under the
         Securities Act and applicable state securities laws and, if requested
         by LeukoSite, upon delivery by such Stockholder of an opinion of
         counsel of such Stockholder reasonably satisfactory to LeukoSite to the
         effect that the proposed transfer is exempt from registration under the
         Securities Act and applicable state securities law or (iii) pursuant to
         the resale provisions of Rule 144 (or any similar rule or regulation).
         Any transfer or purported transfer in violation of this Section 6.7(a)
         shall be voidable by LeukoSite. LeukoSite shall not be required or
         obligated to register any transfer of the Merger Shares in violation of
         this Section 6.7(a). LeukoSite may, and may instruct any transfer agent
         for LeukoSite Stock, to place such stop transfer orders as may be
         required on the transfer books of LeukoSite in order to ensure
         compliance with the provisions of this Section 6.7(a).

                  (b) To the extent applicable, each certificate or other
         document evidencing any of the Merger Shares shall be endorsed with the
         legend set forth below, and each Stockholder covenants that, except to
         the extent such restrictions are waived by LeukoSite, it shall not
         transfer the shares represented by any such certificate without
         complying with the restrictions on transfer described in this Agreement
         and the legends endorsed on such certificate:

         "THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
         UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE OFFERED,
         SOLD, ASSIGNED, PLEDGED, TRANSFERRED OR OTHERWISED DISPOSED OF EXCEPT



<PAGE>
                                       37


         (I) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER SAID ACT,
         (II) PURSUANT TO AN AVAILABLE EXEMPTION FROM REGISTRATION UNDER SAID
         ACT AND, IF REQUESTED BY THE COMPANY, UPON DELIVERY OF AN OPINION OF
         COUNSEL REASONABLE SATISFACTORY TO THE COMPANY THAT THE PROPOSED
         TRANSFER IS EXEMPT FROM SAID ACT OR (III) PURSUANT TO THE RESALE
         PROVISIONS OF RULE 144."

         7.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

         The Company hereby represents and warrants to LeukoSite and Merger Sub
as follows, subject in each case to such exceptions as are specifically
contemplated by this Agreement or as are set forth in the attached Disclosure
Schedule.

         7.1. INCORPORATION; AUTHORITY. The Company is a corporation duly
organized, validly existing, and in good standing under the laws of the State of
Delaware and has all requisite corporate power and authority to own or lease and
operate its properties and to carry on its business as now conducted. The
Company has delivered to LeukoSite complete and correct copies of its
Certificate of Incorporation and by-laws, in each case with all amendments
thereto, which Certificate of Incorporation and by-laws are in full force and
effect.

         7.2. AUTHORIZATION AND ENFORCEABILITY. The Company has all requisite
corporate power to enter into the Agreement and to consummate the transactions
contemplated hereby. The execution and delivery of this Agreement and the
consummation of the transactions contemplated hereby have been duly authorized
by all necessary corporate action on the part of the Company, subject only to
the approval of the Merger and this Agreement by the Company's stockholders. The
Board of Directors of the Company has (i) approved this Agreement and the
transactions contemplated hereby, (ii) determined that the Merger is in the best
interests of the stockholders of the Company and is on terms that are fair to
such stockholders, and (iii) recommended that the stockholders to the Company
approve this Agreement and the Merger. This Agreement has been duly executed and
delivered by the Company and constitutes the valid and binding obligation of the
Company, enforceable in accordance with its terms except (i) as limited by
applicable bankruptcy, insolvency, reorganization, moratorium and other laws of
general application affecting enforcement of creditors' rights generally and
(ii) as limited by laws relating to the availability of specific performance,
injunctive relief or other equitable remedies. On or prior to the Closing, the
Escrow Agreement will be duly executed and delivered by the Stockholders'
Representatives, and the Escrow Agreement, when duly executed and delivered by
the Stockholders' Representatives, shall constitute the valid and binding
obligation of the



<PAGE>
                                       38


Stockholders' Representatives and each Stockholder, enforceable in accordance
with its terms except (i) as limited by applicable bankruptcy, insolvency,
reorganization, moratorium and other laws of general application affecting
enforcement of creditors' rights generally and (ii) as limited by laws relating
to the availability of specific performance, injunctive relief or other
equitable remedies. The Designated Preferred Stockholder Agreement has been duly
executed and delivered by Designated Preferred Stockholders and constitutes the
valid and binding obligation of the Designated Preferred Stockholders,
enforceable in accordance with its terms except (i) as limited by applicable
bankruptcy, insolvency, reorganization, moratorium and other laws of general
application affecting enforcement of creditors' rights generally and (ii) as
limited by laws relating to the availability of specific performance, injunctive
relief or other equitable remedies. The combined voting power of the shares of
Company Stock held by the Designated Preferred Stockholders is such that the
affirmative vote (whether at a meeting of stockholders of the Company or by
written consent in lieu of a meeting) of all shares of Company Stock held by the
Designated Preferred Stockholders in favor of the adoption of this Agreement and
the approval of the Merger would be sufficient to constitute the required
stockholder approval thereof pursuant to, and in accordance with, the terms of
the Company's Certificate of Incorporation, the Company's by-laws and the DGCL.

         7.3. GOVERNMENTAL AND OTHER THIRD-PARTY CONSENTS, NON-CONTRAVENTION,
ETC. Except for the filing of the Merger Certificate and except as described in
Section 7.3 of the Disclosure Schedule, no consent, approval, or authorization
of or registration, designation, declaration, or filing with any governmental
authority, federal or other, or any other person, is required on the part of the
Company in connection with the execution, delivery, and performance of this
Agreement or the consummation of the Merger and the other transactions
contemplated hereby. Except as described in Section 7.3 of the Disclosure
Schedule, the execution, delivery, and performance of this Agreement and the
consummation of such transactions will not violate (a) any provision of the
Company's Certificate of Incorporation or by-laws, (b) any order, judgment,
injunction, award or decree of any court or state or federal governmental or
regulatory body applicable to the Company, or (c) any judgment, decree, order,
statute, rule, regulation, agreement, instrument, or other obligation to which
the Company is a party or by or to which it or any of its assets is bound or
subject.

         7.4. CAPITALIZATION. The authorized and outstanding capital stock and
other securities of the Company are as set forth in Section 7.4 of the
Disclosure Schedule. All of such outstanding shares of capital stock of the
Company are duly authorized, validly issued, fully paid and non-assessable, and
all of such outstanding shares and other securities are owned of record as set
forth in Section 7.4 of the Disclosure Schedule, and were issued in compliance
with all applicable laws, including securities laws, and all applicable
preemptive or



<PAGE>
                                       39


similar rights of any person. The Company is not aware of any person who has a
valid right to rescind any purchase of any shares of the Company's capital stock
or other securities.

         There are no agreements or other obligations to which the Company is a
party or by which it is bound to purchase or sell, and other than as set forth
in Section 7.4 of the Disclosure Schedule, no convertible or exchangeable
securities, options, warrants or other rights to acquire from the Company any
shares of its capital stock or other securities. Section 7.4 of the Disclosure
Schedule sets forth the name of each person who holds any option, warrant or
other right to acquire shares of the Company's capital stock, the number and
type of shares subject to such option or right, the per-share exercise price
payable therefor and, in the case of warrants, the priority and amount of
consideration to be payable upon exercise thereof after the Merger.

         7.5. QUALIFICATION. The Company is duly qualified and in good standing
as a foreign corporation in all jurisdictions in which the character of its
owned or leased properties or the nature of its activities makes such
qualification necessary, except for such failures to be so qualified or in good
standing as would not, either individually or in the aggregate, be reasonably
likely to have a Material Adverse Effect on the Company.

         7.6. SUBSIDIARIES.  The Company  does not have any  Subsidiaries  or
own any legal and/or beneficial interests in or to any other business enterprise
or other person.

         7.7. FINANCIAL STATEMENTS.

                  (a) Included in Section 7.7 of the Disclosure Schedule are
         copies of (i) the audited balance sheets of the Company as of the last
         day of December in each of the years 1995 through 1997, inclusive, and
         the related audited statements of income and retained earnings and cash
         flows, respectively, of the Company, for the fiscal years ended on such
         dates, certified by PriceWaterhouseCoopers LLP, independent public
         accountants, and (ii) the unaudited balance sheet of the Company as of
         November 30, 1998, and the related unaudited statements of income and
         retained earnings and cash flows, respectively, of the Company, for the
         eleven-month period ended on such date (such balance sheet as of
         November 30, 1998, the "November 30, 1998 Balance Sheet"). Each of such
         financial statements and the Unaudited Signing Balance Sheet have been
         prepared in accordance with generally accepted accounting principles
         applied on a basis consistent with prior periods; each of such balance
         sheets and the Unaudited Signing Balance Sheet presents fairly and
         accurately in all material respects the financial condition of the
         Company as of its respective date; and each of such statements of
         income and



<PAGE>
                                       40


         retained earnings and cash flows, respectively, presents fairly and
         accurately in all material respects the results of operations and
         retained earnings, or cash flows, as the case may be, of the Company
         for the period covered thereby; in each case, subject, with respect to
         the unaudited financial statements referred to in clause (ii) of this
         section and with respect to the Unaudited Signing Balance Sheet, to
         the absence of footnote disclosure and to normal, recurring
         end-of-period adjustments, the effect of which, both individually and
         in the aggregate, is not and will not be material.

                  (b) When delivered to LeukoSite at the Closing, the Unaudited
         Closing Balance Sheet will have been prepared in accordance with
         generally accepted accounting principles applied on a basis consistent
         with prior periods; the Unaudited Closing Balance Sheet will present
         fairly and accurately in all material respects the financial condition
         of the Company as of the Closing Date, subject to the absence of
         footnote disclosure and to normal, recurring end-of-period adjustments,
         the effect of which, both individually and in the aggregate, is not and
         will not be material.

         7.8. ABSENCE OF CERTAIN CHANGES. Since November 30, 1998, except as
disclosed in Section 7.8 of the Disclosure Schedule there has not been any: (i)
change in the assets, liabilities, sales, income, or business of the Company or
in its relationships with suppliers, customers, or lessors, other than changes
that were both in the ordinary course of business and have not caused, either in
any case or in the aggregate, a Material Adverse Effect on the Company; (ii)
acquisition or disposition by the Company of any material asset or property;
(iii) damage, destruction or loss, whether or not covered by insurance,
materially and adversely affecting, either in any case or in the aggregate, the
business or any material property of the Company; (iv) declaration, setting
aside or payment of any dividend or any other distributions in respect of any
shares of capital stock of the Company; (v) issuance of any shares of the
capital stock of the Company or any direct or indirect redemption, purchase, or
other acquisition by the Company of any such capital stock; (vi) loss of the
services of any officer or key employee or consultant, or any increase in the
compensation, pension, or other benefits payable or to become payable by the
Company to any of its officers or key employees or consultants, or any bonus
payments or arrangements made to or with any of them; (vii) forgiveness or
cancellation of any debts or claims by the Company or any waivers of any rights;
(viii) entry by the Company into any transaction with any of its Affiliates;
(ix) incurrence by the Company of any obligations or liabilities, whether
absolute, accrued, contingent or otherwise (including without limitation
liabilities as guarantor or otherwise with respect to obligations of others),
other than obligations and liabilities incurred in the ordinary course of
business with persons other than Affiliates of the Company; (x) incurrence or
imposition of any Lien on any of the assets, tangible or



<PAGE>
                                       41


intangible, of the Company; or (xi) discharge or satisfaction by the Company of
any Lien or payment by the Company of any obligation or liability (fixed or
contingent) other than (A) current liabilities included in the November 30, 1998
Balance Sheet, (B) current liabilities to persons other than Affiliates of the
Company incurred since November 30, 1998 in the ordinary course of business, and
(C) current liabilities incurred in connection with the transactions
contemplated hereby and disclosed in Section 7.8 of the Disclosure Schedule.

         7.9. PROPERTIES AND ASSETS. The Company has good and marketable title
or leasehold title, as the case may be, to all of its assets and properties that
it purports to own or lease, including without limitation all those reflected in
the unaudited balance sheet referred to in clause (ii) of Section 7.7(a) hereof
(except for properties or assets sold, consumed, or otherwise disposed of in the
ordinary course of business since November 30, 1998), all free and clear of
Liens on the Company's interest therein. All such properties and assets are in
good condition and repair, reasonable wear-and-tear excepted, and are, and as of
the Closing Date will be, adequate and sufficient to carry on the business of
the Company as presently conducted. Section 7.9(a) of the Disclosure Schedule
sets forth a complete and correct list of all capital assets of the Company.

         The Company does not own any real property. The Company has not
received any notice that either the whole or any portion of any real property
leased by it is to be condemned, requisitioned, or otherwise taken by any public
authority or is to be the subject of any public improvements that may result in
special assessments against or otherwise affect such real property. Section
7.9(b) of the Disclosure Schedule sets forth a complete and correct description
of all leases of real property to which the Company is a party. Complete and
correct copies of all such leases have been delivered to LeukoSite. Each such
lease is valid and subsisting and no event or condition exists that constitutes,
or after notice or lapse of time or both could constitute, a default thereunder
by the Company, or to the best of its knowledge, any other person. The leasehold
interests of the Company are subject to no Lien, and the Company is in quiet
possession of the properties covered by such leases.

         7.10.    INTELLECTUAL PROPERTY.

                  (a) Section 7.10(a) of the Disclosure Schedule lists all inter
         partes proceedings or actions known to the Company before any court or
         tribunal (including the PTO or equivalent authority anywhere in the
         world) related to any Company Intellectual Property. To the best of the
         Company's knowledge, no Company Intellectual Property is the subject of
         any inter partes proceeding or outstanding decree, order, judgment,
         agreement, or stipulation restricting in any manner the use, transfer,
         or licensing thereof by the Company or any of its Subsidiaries, or
         which may



<PAGE>
                                       42


         affect the validity, use or enforceability of such Company Intellectual
         Property.

                  (b) With respect to each item of Company Registered
         Intellectual Property, necessary registration, maintenance and renewal
         fees in connection with such Company Registered Intellectual Property
         have been made and all necessary documents and certificates in
         connection with such Company Registered Intellectual Property have been
         filed with the relevant patent authorities in the United States for the
         purposes of maintaining such Company Registered Intellectual Property
         and no information material to patentability under applicable law has
         been withheld from the examining office that would constitute fraud or
         inequitable conduct.

                  (c) The Company owns and has good and exclusive title or the
         Company exclusively licenses, in each case free and clear of any Lien,
         all Company Registered Intellectual Property listed on Section 7.10(c)
         of the Disclosure Schedule (for purposes of this Section 7.10(c), joint
         ownership with third parties of such Company Registered Intellectual
         Property constitutes "good and exclusive title").

                  (d) To the extent that any work, invention, or material has
         been developed or created by a third party for the Company, the Company
         and each of its Subsidiaries has a written agreement with such third
         party with respect thereto and the Company has obtained ownership of,
         and is the exclusive owner of, or has a valid license to use, all
         Company Intellectual Property in such work, material or invention by
         operation of law or by valid assignment or by agreement, as the case
         may be.

                  (e) Except as set forth on Schedule 7.10(e) of the Disclosure
         Schedule, the Company has not transferred ownership of, or granted any
         license with respect to, any Company Intellectual Property to any third
         party. Section 7.10(e) of the Disclosure Schedule lists all contracts,
         licenses and agreements to which the Company is a party that are
         currently in effect (i) with respect to Company Intellectual Property
         licensed or offered to any third party; or (ii) pursuant to which a
         third party has licensed or transferred any Company Intellectual
         Property to the Company.

                  (f) To the best of the Company's knowledge, the contracts,
         licenses and agreements listed on Section 7.10(e) of the Disclosure
         Schedule are in full force and effect. The consummation of the
         transactions contemplated by this Agreement will neither violate nor
         result in the breach, modification, cancellation, termination, or
         suspension of such contracts, licenses and agreements listed on Section



<PAGE>
                                       43


         7.10(e) of the Disclosure Schedule. The Company is in material
         compliance with, and has not materially breached any term any of such
         contracts, licenses and agreements listed on Section 7.10(e) of the
         Disclosure Schedule and, to the knowledge of the Company, all other
         parties to such contracts, licenses and agreements listed on Section
         7.10(e) of the Disclosure Schedule are in compliance with, and have not
         breached any term of, such contracts, licenses and agreements. To the
         best of the Company's knowledge, following the Closing Date, the
         Surviving Corporation will be permitted to exercise all of the
         Company's rights under the contracts, licenses and agreements listed on
         Section 7.10(e) of the Disclosure Schedule to the same extent the
         Company would have been able to had the transaction contemplated by
         this Agreement not occurred and without the payment of any additional
         funds other than ongoing fees, royalties or payments which the Company
         would otherwise be required to pay.

                  (g) To the best of the Company's knowledge, Section 7.10(g) of
         the Disclosure Schedule lists all contracts, licenses and agreements
         between the Company and any third party wherein or whereby the Company
         has agreed to, or assumed, any obligation or duty to warrant,
         indemnify, hold harmless or otherwise assume or incur any obligation or
         liability with respect to the infringement or misappropriation by the
         Company of any third party's Intellectual Property.

                  (h) The Company (including its executive officer, directors
         and, to the best of the Company's knowledge, employees) has not
         received notice from any third party that the operation of its business
         or any act, product, drug candidate or service of the Company,
         infringes or misappropriates the Intellectual Property of any third
         party or constitutes unfair competition or trade practices under the
         laws of any jurisdiction.

                  (i) To the best of the Company's knowledge, (i) no Person has
         nor is infringing or misappropriating any Company Intellectual Property
         and (ii) there have been, and are, no claims asserted against the
         Company or against any licensee of the Company with respect to the
         Company Intellectual Property.

                  (j) The Company maintains reasonable security measures for the
         preservation of the secrecy and proprietary nature of such of the
         Company Intellectual Property as constitute trade secrets or other
         confidential information. To the best of the Company's knowledge, no
         officer, director, employee, or consultant of the Company is obligated
         under or bound by any agreement or instrument, or any judgment, decree,
         or order of any court of administrative agency, that (i) conflicts or
         may conflict with his agreements and obligations to use his best
         efforts to promote the interest



<PAGE>
                                       44


         of the Company, (ii) conflicts or may conflict with the business or
         operations of the Company, or (iii) restricts or may restrict the use
         or disclosure of any information that may be useful to the company.

         7.11. INDEBTEDNESS. At the date hereof, the Company has no Indebtedness
outstanding except as set forth in Section 7.11 of the Disclosure Schedule. The
Company is not in default with respect to any outstanding Indebtedness or any
agreement, instrument, or other obligation relating thereto and no such
Indebtedness or any agreement, instrument or other obligation relating thereto
purports to limit the issuance of any securities by the Company, or (except as
set forth in Section 7.11 of the Disclosure Schedule) the operation of its
businesses. Complete and correct copies of all agreements, instruments, and
other obligations (including all amendments, supplements, waivers, and consents)
relating to any Indebtedness of the Company have been furnished to LeukoSite.

         7.12. ABSENCE OF UNDISCLOSED LIABILITIES. Except to the extent (a)
reflected or reserved against in the November 30, 1998 Balance Sheet, or (b)
described in Section 7.12 of the Disclosure Schedule, the Company does not have
any liabilities or obligations of any nature, whether accrued, absolute,
contingent, or otherwise (including, without limitation, liabilities, as
guarantor or otherwise, in respect of obligations of others) that would be
required to be reflected or reserved against in a balance sheet prepared in
accordance with generally accepted accounting principles or referred to in the
notes thereto.

         7.13.    TAXES.

                  (a) ELECTIONS. All material elections with respect to Taxes
         (including, without limitation, any elections under Sections 108(b)(5),
         338(g), 565, 936(a) or 936(e) of the Code or Treasury Regulation
         Section 1.1502-20(g) or Treasury Regulation Section 1.1502-32(f)(2) as
         in effect prior to August 12, 1994) affecting the Company have been
         provided to LeukoSite in the Tax Returns.

                  (b) FILING OF TAX RETURNS AND PAYMENT OF TAXES. The Company
         has timely filed all Tax Returns required to be filed by it, each such
         Tax Return has been prepared in compliance with all applicable laws and
         regulations, and all such Tax Returns are true and accurate in all
         respects. All Taxes due and payable by the Company have been paid, and
         the Company will not be liable for any additional Taxes in respect of
         any taxable period ending on or before the Closing Date in an amount
         that exceeds the corresponding reserve for unpaid Taxes, if any,
         reflected in the Unaudited Closing Balance Sheet. The Company has
         delivered or made available to LeukoSite true and complete copies of
         all Tax Returns filed by or with respect to it with respect to taxable
         periods ended on or



<PAGE>
                                       45


         after December 31, 1992, and all relevant material documents and
         information with respect thereto in the possession of the Company, its
         tax advisers and its auditors, including without limitation
         examination reports and statements of deficiencies assessed against or
         agreed to by the Company with respect thereto.

                  (c) AUDIT HISTORY. With respect to each taxable period of the
         Company ended on or before December 31, 1992, either such taxable
         period has been audited by the relevant taxing authority or the time
         for assessing or collecting Tax with respect to each such taxable
         period has closed and such taxable period is not subject to review by
         any relevant taxing authority.

                  (d) DEFICIENCIES. No deficiency or proposed adjustment in
         respect of Taxes that has not been settled or otherwise resolved has
         been asserted or assessed by any taxing authority against the Company.

                  (e) LIENS. There are no Liens for Taxes (other than current
         Taxes not yet due and payable) on the assets of the Company.

                  (f) EXTENSIONS TO STATUTE OF LIMITATIONS FOR ASSESSMENT OF
         TAXES. The Company does not currently have in effect any consent to
         extend the time in which any Tax may be assessed or collected by any
         taxing authority.

                  (g) EXTENSIONS OF THE TIME FOR FILING TAX RETURNS. The Company
         has not requested or been granted an extension of the time for filing
         any Tax Return to a date on or after the Closing Date.

                  (h) PENDING PROCEEDINGS. There is no action, suit, taxing
         authority proceeding, or audit with respect to any Tax now in progress,
         pending, or to the best of the Company's knowledge, threatened, against
         or with respect to (i) the Company, or (ii) any Affiliated Group with
         respect to a taxable period during which the Company was a member of
         such Affiliated Group.

                  (i) NO FAILURES TO FILE TAX RETURNS. No claim has ever been
         made by a taxing authority in a jurisdiction where the Company does not
         pay Tax or file Tax Returns that the Company is or may be subject to
         Taxes assessed by such jurisdiction.

                  (j) MEMBERSHIP IN AFFILIATED GROUPS, ETC. The Company has
         never been a member of any Affiliated Group, or filed or been included
         in a combined, consolidated, or unitary Tax Return.



<PAGE>
                                       46


                  (k) ADJUSTMENTS UNDER SECTION 481. The Company will not be
         required, as a result of a change in method of accounting for any
         period ending on or before the Closing Date other than as a result of
         the transactions contemplated by the Agreement, to include any
         adjustment under Section 481(c) of the Code (or any similar or
         corresponding provision or requirement under any Tax law) in taxable
         income for any period ending on or after the Closing Date.

                  (l) TAX SHARING, ALLOCATION, OR INDEMNITY AGREEMENTS. The
         Company is not a party to or bound by any Tax sharing or allocation
         agreement or has any current or potential contractual obligation to
         indemnify any other person with respect to Taxes.

                  (m) WITHHOLDING TAXES. The Company has withheld and paid all
         Taxes required to have been withheld and paid by it in connection with
         amounts paid or owing to any employee, creditor, independent
         contractor, or other person.

                  (n) FOREIGN PERMANENT ESTABLISHMENTS AND BRANCHES. Except as
         set forth in Section 7.13(n) of the Disclosure Schedule, the Company
         does not have a permanent establishment in any foreign country, as
         defined in the relevant tax treaty between the United States of America
         and such foreign country, and does not otherwise operate or conduct
         business through any branch in any foreign country.

                  (o) U.S. REAL PROPERTY HOLDING CORPORATION. The Company is not
         and has not been a United States real property holding corporation
         within the meaning of Code Section 897(c)(2), during the applicable
         period specified in Code Section 897(c)(1)(A)(ii).

                  (p) SAFE HARBOR LEASE PROPERTY. None of the property owned or
         used by the Company is subject to a tax benefit transfer lease executed
         in accordance with Section 168(f)(8) of the Internal Revenue Code of
         1954, as amended by the Economic Recovery Tax Act of 1981.

                  (q) TAX-EXEMPT USE PROPERTY. None of the property owned by the
         Company is "tax-exempt use property" within the meaning of Section
         168(h) of the Code.

                  (r) SECURITY FOR TAX-EXEMPT OBLIGATIONS. None of the assets of
         the Company directly or indirectly secures any indebtedness, the
         interest on which is tax-exempt under Section 103(a) of the Code, and
         the Company is not directly or indirectly an obligor or a guarantor
         with respect to any such indebtedness.



<PAGE>
                                       47


                  (s) SECTION 341(f) CONSENT. The Company has not filed a
         consent under Code Section 341(f) concerning collapsible corporations.

                  (t) PARACHUTE PAYMENTS. The Company has not made any payments,
         is not obligated to make any payments, and is not a party to any
         agreement that under certain circumstances could obligate it to make
         any payments, that will not be deductible under Code Sections 162(m) or
         280G.

         7.14.    EMPLOYEE BENEFIT PLANS.

                  (a) Except as described in Section 7.14(a) of the Disclosure
         Schedule, the Company does not now maintain or contribute to, and has
         not in the current or preceding six calendar years maintained or
         contributed to, any pension, profit-sharing, deferred compensation,
         bonus, stock option, share appreciation right, severance, group or
         individual health, dental, medical, life insurance, survivor benefit,
         or similar plan, policy, or arrangement, whether formal or informal,
         for the benefit of any director, officer, consultant or employee,
         whether active or terminated, of the Company. Each of the arrangements
         set forth in Section 7.14(a) of the Disclosure Schedule is hereinafter
         referred to as an "Employee Benefit Plan," except that any such
         arrangement that is a multi-employer plan will be treated as an
         Employee Benefit Plan only for purposes of Sections 7.14(d)(iv), (vi),
         and (viii) and 7.14(g) below.

                  (b) The Company has delivered or made available to LeukoSite
         true, correct, and complete copies of each Employee Benefit Plan, and
         with respect to each such Plan (i) any associated trust, custodial,
         insurance, or service agreements, (ii) any annual report, actuarial
         report, or disclosure materials (including specifically any summary
         plan descriptions) submitted to any governmental agency or distributed
         to participants or beneficiaries thereunder in the current calendar
         year or any of the six preceding calendar years, and (iii) the most
         recently received Internal Revenue Service ("IRS") determination
         letters and any governmental advisory opinions or rulings.

                  (c) To the best of the Company's knowledge, each Employee
         Benefit Plan is and has heretofore been maintained and operated in
         material compliance with the terms of such Plan and with the
         requirements prescribed (whether as a matter of substantive law or as
         necessary to secure favorable tax treatment) by any and all statutes,
         governmental or court orders, and governmental rules or regulations in
         effect from time to time, including, but not limited to, the Employee
         Retirement Income Security Act of 1974, as amended ("ERISA"), and the
         Code, and applicable to such Plan. Each Employee Benefit Plan that is




<PAGE>
                                       48


         intended to qualify under Section 401(a) of the Code and each trust
         forming part of an Employee Benefit Plan which is intended to qualify
         under Section 501(c)(9) of the Code is specifically so identified in
         Section 7.14(a) of the Disclosure Schedule and has been determined by
         the IRS to be so qualified, and to the best of the Company's knowledge,
         nothing has occurred since the date of the last such determination as
         to each such Plan or trust that has resulted or is likely to result in
         the revocation of such determination as to such Plan or trust, other
         than such failures as may be corrected without expenditure of more than
         $10,000.

                  (d) (i) There is no pending, or to the best of the Company's
         knowledge, threatened, legal action, proceeding, or investigation,
         other than routine claims for benefits, concerning any Employee Benefit
         Plan, or to the best of the Company's knowledge, any fiduciary or
         service provider thereof, and to the best of the Company's knowledge,
         there is no basis for any such legal action, proceeding, or
         investigation.

                           (ii) No liability (contingent or otherwise) to the
                  Pension Benefit Guaranty Corporation ("PBGC") or any
                  multi-employer plan has been incurred by the Company or any of
                  its ERISA affiliates (other than insurance premiums satisfied
                  in due course).

                           (iii) No reportable event, or event or condition that
                  presents a material risk of termination by the PBGC, has
                  occurred with respect to any Employee Benefit Plan, or any
                  retirement plan of an ERISA affiliate of the Company, which is
                  subject to Title IV of ERISA.

                           (iv) To the best of the Company's knowledge, no
                  Employee Benefit Plan nor any party in interest with respect
                  thereto, has engaged in a prohibited transaction that could
                  subject the Company directly or indirectly to liability under
                  Section 409 or 502(i) of ERISA or Section 4975 of the Code.

                           (v) No communication, report, or disclosure has been
                  made that, at the time made, did not reflect accurately in all
                  material respects the terms and operations of any Employee
                  Benefit Plan.

                           (vi) No Employee Benefit Plan provides welfare
                  benefits subsequent to termination of employment to employees
                  or their beneficiaries (except to the extent required by
                  applicable state insurance laws and Title I, Part 6 of ERISA),
                  other than (A) coverage mandated by applicable law, (B)
                  benefits the full cost of which is borne by the current or
                  former employees (or their



<PAGE>
                                       49


                  beneficiaries), and (C) benefits that have already been
                  satisfied in full.

                           (vii) No benefits due under any Employee Benefit Plan
                  have been forfeited subject to the possibility of
                  reinstatement (which possibility would still exist at or after
                  the Closing) except as required by applicable law.

                           (viii) The Company has not undertaken to maintain any
                  Employee Benefit Plan for any period of time and each such
                  Plan is terminable at the sole discretion of the Company,
                  subject only to such constraints as may be imposed by
                  applicable law.

                  (e) With respect to each Employee Benefit Plan for which a
         separate fund of assets is or is required to be maintained, full
         payment has been made of all amounts that the Company is required,
         under the terms of each such Plan, to have paid as contributions to
         that Plan as of the end of the most recently ended plan year of that
         Plan, and no accumulated funding deficiency (as defined in Section 302
         of ERISA and Section 412 of the Code), whether or not waived, exists
         with respect to any such Plan. The current value of the assets of each
         such Employee Benefit Plan, as of the end of the most recently ended
         plan year of that Plan, exceeded the current value of all accrued
         benefits under that Plan.

                  (f) The execution of this Agreement and the consummation of
         the transactions contemplated hereby will not result in any payment
         (whether of severance pay or otherwise) becoming due from any Employee
         Benefit Plan to any current or former director, officer, consultant, or
         employee of the Company or result in the vesting, acceleration of
         payment, or increases in the amount of any benefit payable to or in
         respect of any such current or former director, officer, consultant, or
         employee. No representation or warranty is made as to the foregoing
         with respect to actions taken by LeukoSite after the Closing with
         respect to the Employee Benefit Plans.

                  (g) No Employee Benefit Plan is a multi-employer plan.

                  (h) For purposes of this Section 7.14, "multi-employer plan,"
         "party in interest," "current value," "accrued benefit," "reportable
         event," and "benefit liability" have the same meaning assigned such
         terms under Sections 3, 4043(b) or 4001(a) of ERISA, and "ERISA
         affiliate" means any entity that under Section 414 of the Code is
         treated as a single employer with the Company.



<PAGE>
                                       50


         7.15.    SAFETY  AND  ENVIRONMENTAL  MATTERS.  Except as set forth in
Section  7.15 of the  Disclosure Schedule:

                  (a) None of the activities carried on by the Company at any
         plants, offices, or properties in or on which the Company operates are
         in violation of any zoning, health, or safety law or regulation,
         including without limitation the Occupational Safety and Health Act of
         1970, as amended, excluding only such violations as will not, either
         individually or in the aggregate, have a Material Adverse Effect on the
         Company.

                  (b) Neither the Company, nor to the best of the Company's
         knowledge, any operator of any real property presently or formerly
         owned, leased, or operated by the Company is in violation or alleged
         violation of any judgment, decree, order, law, license, rule or
         regulation pertaining to environmental matters, including without
         limitation the Resource Conservation and Recovery Act ("RCRA"), the
         Comprehensive Environmental Response, Compensation and Liability Act of
         1980, as amended ("CERCLA"), the Superfund Amendments and
         Reauthorization Act of 1986 ("SARA"), the Federal Clean Water Act, the
         Federal Clean Air Act, the Toxic Substances Control Act, and applicable
         federal, state, foreign, and local statutes, regulations, ordinances,
         orders, and decrees relating to health, safety, or the environment (all
         of the foregoing, collectively, "Environmental Laws"), excluding only
         such violations as will not, either individually or in the aggregate,
         have a Material Adverse Effect on the Company.

                  (c) The Company has not received notice from any third party,
         including without limitation any federal, state, foreign, or local
         governmental authority, that (i) the Company has been identified by the
         United States Environmental Protection Agency (the "EPA") as a
         potentially responsible party under CERCLA with respect to a site
         listed on the National Priorities List, 40 C.F.R. Part 300 Appendix B
         (1986); (ii) any hazardous waste as defined by 42 U.S.C. Section
         6903(5), any hazardous substance as defined by 42 U.S.C. Section
         9601(14), any pollutant or contaminant as defined by 42 U.S.C. Section
         9601(33) or any toxic substance, oil, or hazardous material or other
         chemical or substance regulated by any Environmental Laws
         (collectively, "Hazardous Substances") that the Company has generated,
         transported, handled, used, or disposed of has been found at any site
         at which a federal, state, foreign, or local agency or other third
         party has conducted or has ordered that the Company conduct a remedial
         investigation, removal, or other response action pursuant to any
         Environmental Law; or (iii) the Company is or will be a named party to
         any claim, action, cause of action, complaint (contingent or
         otherwise), or legal or administrative proceeding arising out of any
         third party's



<PAGE>
                                       51


         incurrence of costs, expenses, losses, or damages of any kind
         whatsoever in connection with the release of Hazardous Substances.

                  (d) (i) No portion of any real property presently or formerly
         owned, leased, or operated by the Company has been used by the Company,
         or to the best of the Company's knowledge, by any other person, to
         handle, use, manufacture, transport, store, or dispose of Hazardous
         Substances except in accordance in all material respects with
         applicable Environmental Laws; and no underground tank or other
         underground storage receptacle for Hazardous Substances used by the
         Company is located on any real property presently owned, leased, or
         operated by the Company, or to the best of the Company's knowledge, any
         real property formerly owned, leased, or operated by it; (ii) in the
         course of the activities conducted by the Company and to the best of
         the Company's knowledge, without investigation, those of any other
         operators of any real property presently or formerly owned, leased, or
         operated by the Company, no Hazardous Substances have been generated,
         stored, or used on such properties except in accordance with applicable
         Environmental Laws; (iii) to the best of the Company's knowledge, there
         have been no releases (I.E. any past or present releasing, spilling,
         leaking, pumping, pouring, emitting, emptying, discharging, injecting,
         escaping, disposing, or dumping) or threatened releases of Hazardous
         Substances by the Company on, upon, into, or from any real property
         presently or formerly owned, leased, or operated by the Company; (iv)
         to the best of the Company's knowledge, there have been no releases on,
         upon, from, or into any real property in the vicinity of any real
         property presently or formerly owned, leased, or operated by the
         Company that, through soil or groundwater contamination, have come to
         be located on, any of the real property presently or formerly owned,
         leased, or operated by the Company; and (v) to the extent required by
         applicable Environmental Laws, any Hazardous Substances that have been
         generated by the Company, or to the Company's actual knowledge, by any
         other person, on any real property presently or formerly owned, leased,
         or operated by the Company, have been transported offsite only by
         carriers having an identification number issued by the EPA and treated
         or disposed of only by treatment or disposal facilities having, to the
         Company's actual knowledge, valid permits as required under applicable
         Environmental Laws, which transporters and facilities, to the Company's
         actual knowledge, have been and are operating substantially in
         compliance with such permits and applicable Environmental Laws.

                  (e) No real property presently owned, leased, or operated by
         the Company, and to the best of the Company's knowledge, no real
         property formerly owned, leased, or operated by the Company, and as a
         result of



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                                       52


         the present or past activities of the Company, is subject to any
         Environmental Law requiring the performance of any Hazardous
         Substances site assessment, the removal or remediation of any
         Hazardous Substances, the giving of notice to any governmental agency
         or other person, or the recording and/or delivery to any governmental
         agency or other person of any environmental disclosure statement or
         document, by reason of, or as a condition to the effectiveness of, the
         Merger and/or any other transaction contemplated hereby.

         7.16. LABOR RELATIONS. The Company is and has been in compliance in all
material respects with all federal and state laws respecting employment and
employment practices, terms and conditions of employment, wages and hours, and
nondiscrimination in employment, and is not and has not been engaged in any
unfair labor practice. There is no charge or proceeding pending, or to the best
of the Company's knowledge, threatened, against the Company alleging unlawful
discrimination in employment practices or unfair labor practice before any court
or agency, including without limitation the National Labor Relations Board.
There is no labor strike, dispute, work slow-down, or work stoppage pending, or
to the best of the Company's knowledge, threatened against or involving the
Company. No one has petitioned within the last five years or is now petitioning
for union representation of any of the employees of the Company. No grievance or
arbitration proceeding arising out of or under any collective bargaining
agreement is pending against the Company and no claim therefor has been
asserted. None of the employees of the Company is covered by any collective
bargaining agreement, and no collective bargaining agreement is currently being
negotiated by the Company. The Company has not experienced any work stoppage or
other material labor difficulty during the last five years.

         7.17. LITIGATION. No litigation, arbitration, action, suit, proceeding,
or investigation (whether conducted by any judicial or regulatory body,
arbitrator, or other person) is pending (as evidenced by the Company's receipt
of service of process or other written notice of such pendency), or to the best
of the Company's knowledge, threatened, against the Company, nor is there any
basis therefor known to the Company.

         7.18. CONTRACTS. Section 7.18 of the Disclosure Schedule sets forth a
complete and accurate list of all "Material Contracts" to which the Company is a
party or by or to which it or any of its assets or properties is bound or
subject. As used in this Agreement, the term "Material Contract" means every
agreement or understanding of any kind, written or oral, that is legally
enforceable by or against or otherwise binding on the Company and which is
material to the Company's business, and specifically includes without
limitation: (a) agreements with any current or former officer, director,
employee, consultant, or stockholder, or any partnership, corporation, joint
venture, or any other entity in which any such person has an interest;
(b) agreements with any



<PAGE>
                                       53


labor union or association representing any employee; (c) agreements for the
provision of services by or to the Company; (d) bonds or other security
agreements provided by any party in connection with the business of the Company;
(e) agreements for the purchase or other acquisition or the sale or other
disposition of assets or properties (other than in the ordinary course of
business), or for the grant to any person of any preferential rights to purchase
any such assets or properties; (f) joint venture agreements relating to the
assets, properties, or business of the Company or by or to which it or any of
its assets or properties is bound or subject; (g) agreements under which the
Company agrees to indemnify any party, to share tax liability of any party, or
to refrain from competing with any party; (h) agreements with regard to
Indebtedness, including, without limitation, any indenture or other agreements
in connection with issuances of bonds, debentures or other debt securities by
the Company and any agreements in connection with bank financings by the
Company; (i) any agreement, contract, commitment, transaction or series of
transaction for any purpose other than in the ordinary course of the Company's
business relating to capital expenditures or commitments or long-term
obligations; (j) any purchase order or contract for the purchase of raw
materials; (k) any distribution, joint marketing or development agreement; (l)
any assignment, license or other agreement with respect to any form of
intangible property; (m) any research collaboration agreement; (n) any
agreements relating to venture capital and other equity financings by the
Company; (o) any stockholder agreements or other agreements with any of the
Stockholders pertaining to the shares of Company Stock held by them or their
rights as stockholders of the Company; and (p) any voting trust or voting
agreements among the Stockholders.

         All of the contracts listed in Section 7.18 of the Disclosure Schedule
are in full force and effect, and neither the Company, nor to the best of the
Company's knowledge, any other party thereto, is in default under or material
breach of any of the material terms thereof, nor does any event or condition
exist that after notice or lapse of time or both could constitute a default
thereunder or material breach thereof on the part of the Company, or to the best
of the Company's knowledge, any other party thereto. No approval or consent of
any person that has not already been obtained and listed in Section 7.18 of the
Disclosure Schedule is needed in order that the contracts listed in Section 7.18
of the Disclosure Schedule continue in full force and effect following the
consummation of the Merger and the other transactions contemplated hereby, and
no such contract includes any provision, the effect of which may be to terminate
(or give rise to a right of termination under) such contract, to enlarge or
accelerate any obligations of the Company thereunder, or to give additional
rights to any other person, as a result of the consummation of the Merger or the
other transactions contemplated hereby. The Company has delivered or made
available to LeukoSite true, correct, and complete copies of all such Material
Contracts, including all amendments, modifications, and supplements thereto.



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                                       54


         7.19. POTENTIAL CONFLICTS OF INTEREST. No officer, director, or, to
best of the Company's knowledge, stockholder of the Company (a) owns, directly
or indirectly, any interest (excepting not more than 5% stock holdings for
investment purposes in securities of publicly held and traded companies) in, or
is an officer, director, employee, or consultant of, any person that furnishes
or sells services, drug candidates or products that the Company furnishes or
sells or proposes to furnish or sell or is a lessor, lessee, customer, or
supplier of the Company; (b) owns, directly or indirectly, in whole or in part
(other than solely as a result of his or its ownership of Company Stock), any
tangible or intangible property that the Company is using or the use of which is
necessary for the business of the Company; or (c) to the best of the Company's
knowledge, has any cause of action or other claim whatsoever against, or owes
any amount to, the Company, except for claims in the ordinary course of
business, such as for accrued vacation pay, accrued benefits under Employee
Benefit Plans, and similar matters and agreements.

         7.20. INSURANCE. Section 7.20 of the Disclosure Schedule lists the
policies of products liability, theft, fire, liability, worker's compensation,
life, property and casualty, and other insurance owned or held by the Company.
Such policies of insurance are of the kinds, cover such risks, and are in such
amounts and with such deductibles and exclusions, as are consistent with prudent
business practice for companies in the Company's line of business and of a
similar size and location. All such policies are in full force and effect; are
sufficient for compliance by the Company with all requirements of law and of all
agreements to which the Company is a party; are valid, outstanding, and
enforceable policies and provide that they will remain in full force and effect
through the respective dates set forth in the Disclosure Schedule; and will not
in any way be affected by, or terminate or lapse as a result of the consummation
of, the transactions contemplated by this Agreement.

         7.21. BANK ACCOUNTS, SIGNING AUTHORITY, POWERS OF ATTORNEY. Section
7.21 of the Disclosure Schedule sets forth a complete and accurate list of all
bank, brokerage, and other accounts, and all safe-deposit boxes, of the Company
and the persons with signing or other authority to act with respect thereto.
Except as so listed, the Company does not have any account or safe deposit box
in any bank, and no person has any power, whether singly or jointly, to sign any
checks on behalf of the Company, to withdraw any money or other property from
any bank, brokerage, or other account of the Company, or to act under any agency
or power of attorney granted by the Company at any time for any purpose. Section
7.21 of the Disclosure Schedule also sets forth the names of all persons
authorized to borrow money or sign notes on behalf of the Company.

         7.22. RELATIONSHIPS WITH SUPPLIERS AND LICENSORS. No current supplier
to the Company has notified the Company of an intention to terminate



<PAGE>
                                       55


or substantially alter its existing business relationship with the Company, nor
has any licensor under a license agreement with the Company notified the Company
of an intention to terminate or substantially alter the Company's rights under
such license, which termination or alteration would have a Material Adverse
Effect on the Company.

         7.23. EMPLOYMENT OF OFFICERS, EMPLOYEES. The name and current annual
salary and other compensation payable by the Company to each exempt non-hourly
employee whose current total annual compensation or estimated compensation from
the Company (including but not limited to wages, salary, commissions, normal
bonus, profit sharing, deferred compensation, and other extra compensation) are
as set forth in Section 7.23 of the Disclosure Schedule. Except to the extent
otherwise disclosed in Section 7.23 of the Disclosure Schedule, none of the
current or former officers, directors, employees or consultants of the Company
is a party to, or the beneficiary of, any agreement, plan or arrangement that
provides for any payment (whether of severance pay or otherwise) becoming due to
such current or former officer, director, employee or consultant upon
termination of his or her relationship with the Company or as a result of the
Merger, or that provides for the vesting, acceleration of payment, or increases
in the amount of any benefit payable to or in respect of such current or former
director, officer, consultant, or employee upon termination of his or her
relationship with the Company or as a result of the Merger.

         7.24. MINUTE BOOKS. The minute books of the Company made available to
LeukoSite for inspection accurately record therein all material actions taken by
its Board of Directors, all committees thereof, and its stockholders.

         7.25. BROKERS. No finder, broker, agent, or other intermediary has
acted for or on behalf of the Company in connection with the negotiation,
preparation, execution, or delivery of this Agreement or the consummation of the
Merger or the other transactions contemplated hereby.

         7.26. COMPLIANCE WITH OTHER AGREEMENTS, LAWS, ETC. The Company has
complied with, and is in compliance with, (a) all laws, statutes, governmental
regulations and all judicial or administrative tribunal orders, judgments,
writs, injunctions, decrees or similar commands applicable to its business, (b)
all unwaived terms and provisions of all contracts, agreements and indentures to
which the Company is a party, or by which the Company or any of its properties
is subject, and (c) its Certificate of Incorporation and by-laws, respectively,
each as amended to date; in the case of the preceding clauses (a) and (b),
excepting only any such noncompliances that, both individually and in the
aggregate, have not resulted and will not result in any Material Adverse Effect
with respect to the Company. The Company has not been charged with, or to the
best of its knowledge, been under investigation with respect to, any



<PAGE>
                                       56


violation of any provision of any federal, state, or local law or administrative
regulation.

         7.27.    PERMITS, LICENSES, AND PROGRAMS; NO DEBARMENT.

                  (a) Section 7.27 of the Disclosure Schedule contains a
         complete and correct copy of (i) each pending application or
         registration for governmental approval and each governmental approval
         held by the Company to develop, manufacture, test (including, without
         limitation, preclinical tests and clinical trials), import, export,
         store, market and sell the Company's products or drug candidates, (ii)
         the most recent report by or on behalf of the FDA or any other
         governmental body involving or relating to any facility inspection of
         the Company's facilities, and (iii) a description of all ongoing
         proprietary internal research and development programs included in the
         CytoMed Programs. Except as are set forth in Section 7.27 of the
         Disclosure Schedule, (i) the Company possesses such governmental
         approvals from all governmental bodies including, without limitation,
         all FDA approvals, necessary to permit the operation of its business in
         the manner as the same is currently conducted, and to operate, own or
         occupy its properties, (ii) there have been no product recalls, field
         corrective activity, medical device reports, warning letters or
         administrative actions by the FDA or any other governmental body, and
         (iii) to the knowledge of the Company, (aa) there is no administrative
         action pending or threatened for the revocation of any such
         governmental approval and (bb) assuming the obtaining of the
         authorizations, consents, approvals and other actions listed in Section
         7.27 of the Disclosure Schedule, no governmental approvals and other
         actions listed in Section 7.27 of the Disclosure Schedule of the
         Disclosure Schedule, no governmental approval by any governmental body
         having jurisdiction over the operation of the Company's business,
         whether in whole or in part, will be revoked, or become ineffective or
         subject to revocation, as a consequence of the transactions
         contemplated by this Agreement.

                  (b) The Company (i) has not been debarred or received notice
         of action or threat of action with respect to its debarment under the
         provisions of the Generic Drug Enforcement Act of 1992, 31 U.S.C.
         Section 335(a) and (b), or (ii) to the best of the Company's knowledge,
         has used in any capacity the services of any individual, corporation,
         partnership or association which has been debarred under the provisions
         of the Generic Drug Enforcement Act of 1992, 21 U.S.C. Section 335(a)
         and (b).

         7.28. DISTRIBUTION OF MERGER CONSIDERATION. The Merger Consideration,
when distributed in accordance with the terms of this Agreement, will have been
distributed to the holders of Company Stock in accordance with the provisions of
the Company's Certificate of Incorporation in



<PAGE>
                                       57


effect immediately prior to the Effective Time and any other document or
agreement among the Company and such holders related to the distribution of the
Merger Consideration.

         7.29. DISCLOSURE. No representation or warranty of the Company in this
Agreement (including the exhibits and schedules hereto) or in any other
agreement, instrument, certificate, or other document delivered by the Company
in connection with this Agreement, the Merger, or any of the other transactions
contemplated hereby contains or will contain any untrue statement of a material
fact or omits or will omit to state a material fact required to be stated
therein or necessary to make the statements contained therein not false or
misleading.

         8.    REPRESENTATIONS AND WARRANTIES OF LEUKOSITE AND MERGER SUB.

         LeukoSite and Merger Sub hereby jointly and severally represent and
warrant to the Company as follows:

         8.1. INCORPORATION; AUTHORITY. Each of LeukoSite and Merger Sub is a
corporation duly organized, validly existing, and in good standing under the
laws of the State of Delaware and has all requisite corporate power and
authority to own or lease and operate its properties and to carry on its
business as now conducted. LeukoSite is duly qualified or licensed to conduct
its business and is in good standing as a foreign corporation in each
jurisdiction in which the failure to be so qualified would have, or would be
reasonably expected to have, a Material Adverse Effect on the Company.

         8.2. AUTHORIZATION AND ENFORCEABILITY. Each of LeukoSite and Merger Sub
has all requisite corporate power and authority (including due approval of its
Board of Directors) to enter into this Agreement and to consummate the
transactions contemplated hereby and thereby. This Agreement has been duly
executed and delivered by each of LeukoSite and Merger Sub and constitutes a
legal, valid, and binding obligation of each of them, enforceable against each
of them in accordance with its terms, except as enforceability may be subject to
the effect of any applicable bankruptcy, insolvency, fraudulent conveyance,
moratorium, reorganization, marshaling, or other similar laws or rules of law
affecting creditors' rights and remedies generally, and to general principles of
equity. On or prior to the Closing, the Escrow Agreement will be duly executed
and delivered by LeukoSite, and the Escrow Agreement, when duly executed and
delivered by LeukoSite, shall constitute the valid and binding obligation of
LeukoSite, enforceable in accordance with its terms, except as limited by
applicable bankruptcy, insolvency, reorganization, moratorium and other laws of
general application affecting enforcement of creditors' rights generally and as
limited also by laws relating to the availability of specific performance,
injunctive relief or other



<PAGE>
                                       58


equitable remedies. LeukoSite does not require any approval from its
stockholders in connection with this Agreement, the Escrow Agreement, the Merger
or any of the transactions contemplated hereby or thereby (including the
issuance of the Merger Shares), except that LeukoSite requires approval from a
majority of the outstanding shares of LeukoSite Common Stock present and
entitled to vote at a stockholders' meeting in order for any shares of LeukoSite
Series A Preferred Stock issued pursuant to the Merger to convert into shares of
LeukoSite Common Stock. None of the stockholders of LeukoSite or Merger Sub will
have any appraisal rights under Section 262 of the DGCL by reason of the
consummation of the Merger or the other transactions contemplated hereby.

         8.3. GOVERNMENTAL AND OTHER THIRD-PARTY CONSENTS, NON-CONTRAVENTION,
ETC. Except for (i) obtaining approval from the stockholders of LeukoSite with
respect to the conversion of shares of LeukoSite Series A Preferred Stock issued
pursuant to the Merger into shares of LeukoSite Common Stock, (ii) filing a
listing application for purposes of listing the Merger Conversion Shares in the
Nasdaq Stock Market and obtaining approval of such proposed listing, (iii) the
filing of the Merger Certificate and the Stockholder Registration Statement and
(iv) any filings required in order to comply with federal and state securities
laws that may be applicable to the issuance of the Merger Shares, no consent,
approval, or authorization of or registration, designation, declaration, or
filing with any governmental authority, federal or other, or any other person,
is required on the part of LeukoSite or Merger Sub in connection with this
Agreement, the Escrow Agreement, the Merger, or any of the other transactions
contemplated hereby (including the issuance of the Merger Shares). The
execution, delivery, and performance of this Agreement and the Escrow Agreement
and the filing of the Stockholders Registration Statement pursuant to Section 6
and the consummation of such transactions will not violate (a) any provision of
LeukoSite's or Merger Sub's Certificate of Incorporation or by-laws, (b) any
order, judgment, injunction, award or decree of any court or state or federal
governmental or regulatory body applicable to LeukoSite or Merger Sub, or (c)
any judgment, decree, order, statute, rule, regulation, agreement, instrument,
or other obligation to which LeukoSite or Merger Sub is a party or by or to
which either of them or any of their respective assets is bound or subject.

         8.4. MERGER SUB. Merger Sub has been organized for the specific purpose
of engaging in the Merger and the other transactions contemplated hereby and has
not incurred any liabilities, conducted any business, or entered into any
contracts or commitments, in each case except such as are in furtherance of or
incidental to such transactions.

         8.5. LEUKOSITE'S SEC STATEMENTS, REPORTS AND DOCUMENTS. Since August
15, 1997, LeukoSite has timely filed with the SEC all forms, reports,
registration statements, and documents required to be filed by it. LeukoSite has



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                                       59


delivered to the Company true and complete copies of (i) its Annual Report on
Form 10-K for its fiscal year ended December 31 1997, (ii) its proxy statements
relating to all meetings of its stockholders (whether annual or special) held
since August 15, 1997, and (iii) all other forms, reports (including without
limitation annual reports pursuant to Exchange Act rule 14a-3), registration
statements, and documents filed or required to be filed by it with, or provided
or required to be provided by it to, the SEC since August 15, 1997
(collectively, all of the foregoing documents, "LeukoSite's SEC Reports"). As of
their respective dates, LeukoSite's SEC Reports complied in all material
respects with all applicable requirements of the Securities Act and the Exchange
Act and the rules and regulations promulgated thereunder, and did 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, in
light of the circumstances under which they were made, not misleading. None of
LeukoSite's SEC Reports is required to be amended or supplemented as of the date
hereof. The financial statements (including any related notes) of LeukoSite
included in LeukoSite's SEC Reports were prepared in conformity with generally
accepted accounting principles applied on a consistent basis (except as
otherwise stated in the financial statements or, in the case of audited
statements, the related report of LeukoSite's independent certified public
accountants) and present fairly in all material respects the consolidated
financial position, results of operations, changes in stockholders' equity, and
cash flows, as applicable, of LeukoSite and its consolidated Subsidiaries as of
the dates and for the periods indicated; subject, in the case of unaudited
interim consolidated financial statements, to condensation, the absence of
footnote disclosure, and normal, recurring end-of-period adjustments, the effect
of which was not and will not be material.

         Except to the extent (a) reflected or reserved against in LeukoSite's
consolidated balance sheet as of September 30, 1998, included in its Quarterly
Report on Form 10-Q for its fiscal quarter ended on that date, or (b) incurred
with persons other than any Affiliate of LeukoSite in the ordinary course of
business after the date of such balance sheet, the Company does not have any
liabilities or obligations of any nature, whether accrued, absolute, contingent,
or otherwise (including without limitation liabilities, as guarantor or
otherwise, in respect of obligations of others) that would be required to be
reflected or reserved against in a balance sheet prepared in accordance with
generally accepted accounting principles or referred to in the notes thereto.

         8.6. CERTIFICATE OF INCORPORATION AND BY-LAWS. LeukoSite's Certificate
of Incorporation and by-laws set forth as Exhibits 3.1 through 3.4,
respectively, to LeukoSite's Registration Statement on Form S-1 (Registration
No. 333-30213), as declared effective under the Securities Act on August 15,
1997, are complete and correct copies thereof, and have not been amended since
the date of such filing. LeukoSite has previously provided to the Company a
complete and correct copy of the Certificate of Incorporation and by-laws of



<PAGE>
                                       60


Merger Sub, neither of which has been amended or restated. Such Certificates of
Incorporation and by-laws of LeukoSite and Merger Sub, respectively, are in full
force and effect. Neither LeukoSite nor Merger Sub is in violation of any
provisions of its Certificate of Incorporation or by-laws.

         8.7. CAPITALIZATION. The authorized capital of LeukoSite consists of
25,000,000 shares of LeukoSite Common Stock and 5,000,000 shares of LeukoSite
Preferred Stock. No shares of LeukoSite Preferred Stock are issued and
outstanding.

         As of December 24, 1998, (i) 11,923,670 shares of LeukoSite Common
Stock were issued and outstanding, all of which were duly authorized, validly
issued, fully paid and non-assessable, and (ii) options granted pursuant to the
LeukoSite Stock Plans to acquire up to an aggregate of not more than 1,359,447
shares of LeukoSite Common Stock were outstanding. Since that date, no shares of
LeukoSite Common Stock have been issued except upon exercise of options granted
under the LeukoSite Stock Plans.

         Except for stock options issued pursuant to the LeukoSite Stock Plans
and as set forth on Section 8.7 of the Disclosure Schedule, there are no
options, warrants, or other rights, agreements, arrangements, or commitments of
any character to which LeukoSite is a party or by which it is bound relating to
the issued or unissued shares of the capital stock of LeukoSite or any of its
Subsidiaries (including any agreement relating to the manner in which any of
such shares will be voted at any regular or special meeting of the stockholders
of LeukoSite) or obligating LeukoSite or any of its Subsidiaries to issue or
sell any shares of capital stock of, or other equity interests in, LeukoSite or
any of its Subsidiaries.

         Except as set forth on Section 8.7 of the Disclosure Schedule, there
are no outstanding contractual obligations of LeukoSite or any of its
Subsidiaries to repurchase, redeem, or otherwise acquire, or (except pursuant to
Section 6 hereof) to register any shares of any of them under the Securities
Act.

         Each outstanding share of the capital stock of each of LeukoSite's
Subsidiaries is duly authorized, validly issued, fully paid, and non-assessable,
owned by LeukoSite, and free and clear of all Liens.

         8.8. BROKERS. No finder, broker, agent, or other intermediary has acted
for or on behalf of LeukoSite or Merger Sub in connection with the negotiation,
preparation, execution, or delivery of this Agreement or the consummation of the
transactions contemplated hereby.

         8.9. OWNERSHIP OF COMPANY STOCK. Neither LeukoSite nor Merger Sub
beneficially owns, directly or indirectly, or is a party to any agreement



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                                       61


(other than this Agreement), arrangement, or understanding with respect to the
acquisition, holding, voting, or disposition of any shares of the capital stock
or other securities of the Company.

         8.10. LEGALITY OF MERGER SHARES. All of the Merger Shares have been
duly authorized and, when issued and delivered in accordance with the terms
hereof, will be validly issued, fully paid and non-assessable, and free of
preemptive rights.

         8.11. ABSENCE OF CERTAIN CHANGES. Since September 30, 1998, there has
not been any material adverse change in the assets, business, financial
condition, results of operations of LeukoSite and its Subsidiaries, taken as a
whole.

         8.12. DISCLOSURE. No representation or warranty of LeukoSite in this
Agreement (including the exhibits and schedules hereto) or in any other
agreement, instrument, certificate, or other document delivered by LeukoSite in
connection with this Agreement, the Merger, or any of the other transactions
contemplated hereby contains or will contain any untrue statement of a material
fact or omits or will omit to state a material fact required to be stated
therein or necessary to make the statements contained therein not false or
misleading.

         9.   MUTUAL COVENANTS.

         9.1. SATISFACTION OF CONDITIONS. Each of the parties will use its best
reasonable efforts to cause the satisfaction as promptly as possible, but in any
event by February 28, 1999, of the conditions contained in Sections 11 through
13 of this Agreement that impose obligations on it or require action on its part
or the part of any of its stockholders or Affiliates.

         9.2. ACCOUNTING  CONSEQUENCES.  It is intended by the parties hereto
that the Merger shall be accounted for as a purchase, not a pooling of
interests.

         9.3. BLUE SKY APPROVALS. LeukoSite will file all documents required to
obtain the Blue Sky permits and approvals, if any, required to carry out the
transactions contemplated by this Agreement (to the extent required prior to the
Effective Time), will pay all expenses incident thereto and will use its best
efforts to obtain such permits and approvals; PROVIDED, HOWEVER, that LeukoSite
shall not be required in connection with this Section 9.3 to qualify as a
foreign corporation or execute a general consent to service of process in any
jurisdiction.

         9.4. TAX MATTERS. The parties understand and agree that none of them is
making any representation or warranty with respect to the tax consequences of
this Agreement, the Merger or the other transactions contemplated hereby.



<PAGE>
                                       62


         9.5. FURTHER ASSURANCES. Subject to the terms and conditions set forth
in this Agreement, from time to time both before and after the Effective Time,
each of the parties will use his or its best reasonable efforts, as promptly as
is practicable, to take or cause to be taken all actions, and to do or cause to
be done all other things, as are necessary, proper, or advisable to consummate
and make effective the Merger and the other transactions contemplated hereby.

         9.6. STOCKHOLDER APPROVAL. The Company will take all steps necessary or
appropriate duly to call, give notice of, convene and hold a Stockholders
meeting, or otherwise obtain the necessary consents of Stockholders, as the case
may be, as soon as reasonably practicable for the purpose of adopting and
approving this Agreement and the transactions contemplated hereunder, and for
such other purposes as may be necessary or desirable. The Company will recommend
to its Stockholders the adoption and approval of this Agreement and the
transactions contemplated hereby and the other matters to be submitted to its
Stockholders in connection therewith, and the Company shall use all reasonable
efforts to obtain the necessary approvals by its Stockholders of this Agreement
and the transactions contemplated hereby. LeukoSite will take all steps
necessary or appropriate duly to call, give notice of, convene and hold its
annual (or a special) stockholders meeting, no later than May 31, 1999, for the
purpose, among other purposes, of proposing to the stockholders of LeukoSite
that they approve resolutions authorizing (i) the conversion of the shares of
LeukoSite Series A Preferred Stock issued pursuant to the Merger into shares of
LeukoSite Common and (ii) the issuance of any other Merger Shares issuable
pursuant to this Agreement in the form of LeukoSite Common Stock. LeukoSite will
recommend to its stockholders the adoption and approval of such resolutions
authorizing (i) the conversion of the shares of LeukoSite Series A Preferred
Stock issued pursuant to the Merger into shares of LeukoSite Common Stock and
(ii) the issuance of any other Merger Shares issuable pursuant to this Agreement
in the form of LeukoSite Common Stock. Prior to Closing, LeukoSite and the
Company shall use their best reasonable efforts to obtain irrevocable binding
commitments or proxies, in substantially the form of either EXHIBIT D-1 or D-2
attached hereto or such other form as may be acceptable to the Company,
representing at least an aggregate of sixty percent (60%) of the shares of
LeukoSite Common Stock outstanding at the Closing, to vote such shares of
LeukoSite Common Stock in favor of (i) the conversion of the shares of LeukoSite
Series A Preferred Stock issued pursuant to the Merger into shares of LeukoSite
Common Stock and (ii) the issuance of any other Merger Shares issuable pursuant
to this Agreement in the form of LeukoSite Common Stock.

         9.7. NASDAQ/NMS APPLICATION. Subject to obtaining the approval of the
stockholders of LeukoSite to (i) the conversion of the shares of LeukoSite
Series A Preferred Stock issued pursuant to the Merger into shares of LeukoSite
Common Stock and (ii) the issuance of any other Merger Shares issuable



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pursuant to this Agreement in the form of LeukoSite Common Stock, LeukoSite will
prepare and submit to the National Association of Securities Dealers, Inc. a
listing application covering all of the Merger Common Shares, and will use its
best reasonable efforts to cause all of the Merger Common Shares to be approved
for listing in the National Market System (the "NMS") of the National
Association of Securities Dealers, Inc., subject to official notice of issuance.

         9.8. DISSENTING SHARES. As promptly as practicable after any such
meeting of the Stockholders of the Company at which this Agreement and the
transactions contemplated hereunder are submitted to such Stockholders for
adoption and approval, the Company shall furnish LeukoSite with the name and
address of any dissenting stockholder and the number of Dissenting Shares.

         9.9. INTELLECTUAL PROPERTY. LeukoSite and the Company each agree that,
prior to the Merger, any and all Intellectual Property, including trade secrets,
created or developed by either party shall remain the exclusive property of the
party who created or developed such property, notwithstanding the sharing of
information prior to the Merger.

         9.10. PUBLIC DISCLOSURE. Between the date hereof and the Effective Time
of the Merger, neither the Company nor LeukoSite will furnish any communications
to the public generally if the subject matter thereof relates to the other party
or to the transactions contemplated under this Agreement, without the prior
approval of the other party as to the contents thereof, which approval shall not
be unreasonably withheld or delayed; PROVIDED, HOWEVER, that the foregoing
provisions of this Section 9.10 shall not apply with respect to any
communication that either party is required to release, furnish or send to
comply with such party's obligations under applicable law (in which case such
party shall use commercially reasonable efforts to provide a copy of such
communication to the other party for review, comment and approval within a
commercially reasonable period of time prior to the release, publication or
dissemination of such communication).

         9.11. CONSENTS. The Company shall use its best efforts to obtain the
consents, waivers and approvals under any of the Contracts as may be required in
connection with the Merger (all of such consents, waivers and approvals are set
forth in Disclosure Schedule), so as to preserve all rights of and benefits to
the Company thereunder.

         9.12. NOTIFICATION OF CERTAIN MATTERS.

                  (a) Between the date hereof and the Effective Time of the
         Merger, each of LeukoSite and the Company shall, upon obtaining
         knowledge of any of the following, promptly notify the other of:



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                           (i) any notice or other communication from any Person
                  alleging that the consent of such Person is or may be required
                  in connection with the Merger;

                           (ii) any actions, suits, claims, investigations or
                  other judicial proceedings known to its executive officers
                  commenced or threatened against such party or any of its
                  Subsidiaries which, if pending on the date of this Agreement,
                  would have been required to have been disclosed pursuant to
                  Section 7.17 or which relate to the consummation of the
                  Merger;

                           (iii) occurrence or non-occurrence of any other event
                  known to its executive officers which is likely to cause any
                  representation or warranty of such party contained in this
                  Agreement to be materially untrue or inaccurate at or prior to
                  the Effective Time; and

                           (iv) any failure of such party known to its executive
                  officers to comply with or satisfy any covenant, condition or
                  agreement to be complied with or satisfied by it hereunder.

                  (b) In addition to its obligations set forth in Section
         9.12(a), the Company shall promptly notify LeukoSite of any adverse
         determination or recommendation in connection with any governmental
         proceeding to license any of the Company's products and any report
         filed with the FDA regarding an unexpected fatal or life-threatening
         experience with respect to any such product.

                  (c) The delivery of any notice pursuant to this Section 9.12
         shall not limit or otherwise affect any remedies available to a party.

         9.13. COMPANY AUDITORS. The Company will use its best efforts to cause
its management and its independent auditors to facilitate on a timely basis (i)
the preparation of financial statements of the Company (including pro forma
financial statements if required) as required by LeukoSite to comply with
applicable SEC regulations and (ii) the review of the Company's audit work
papers for up to the past three years, including the examination of selected
interim financial statements and data.

         9.14 UCB AGREEMENT. Neither LeukoSite nor any of its Affiliates
(including, after the Closing Date, the Surviving Corporation) shall, directly
or indirectly terminate, modify, alter or otherwise amend Article IV, Section
5.2, Section 5.3 or Article XIII of the UCB Agreement or agree that UCB or any
of its Affiliates are entitled to any indemnification payment under the UCB
Agreement without the prior written consent of the Stockholders'



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                                       65


Representatives. LeukoSite and its Affiliates shall provide the Stockholders'
Representatives with a copy of any Claim Notice (as defined in the UCB
Agreement) it receives under the UCB Agreement within 15 days of receipt of such
notice. LeukoSite agrees that, in the event that the Subsequent UCB Payment is
not made by UCB on its due date pursuant to the UCB Agreement and LeukoSite
shall determine not to take action to enforce its legal rights thereunder, the
Stockholders' Representatives shall have the right to take any necessary action
against UCB to collect the Subsequent UCB Payment on behalf of LeukoSite. In the
event that the Stockholders' Representatives are entitled pursuant to the
provisions of the foregoing sentence to take action against UCB, the
Stockholders' Representatives shall have the right, on behalf of LeukoSite, to
settle any claims against UCB relating to the Subsequent UCB Payment with the
prior written consent of LeukoSite, which consent shall not be unreasonably
withheld or delayed.

         9.15. ACCESS TO DATA. The Stockholders' Representatives shall have the
right from and after the Closing Date to have reasonable access, upon request
and reasonable notice and during normal business hours, to the books, records
and accounts of LeukoSite and its Affiliates, and to the Chief Executive Officer
and the Chief Financial Officer of LeukoSite, for the limited purpose of
confirming the calculations made pursuant to Section 3.8 hereof and obtaining an
update concerning the status of the CytoMed Programs.

         9.16. EQUITY FINANCINGS. LeukoSite agrees that, prior to the conversion
of the shares of LeukoSite Series A Preferred Stock into shares of LeukoSite
Common Stock, LeukoSite will not issue shares of LeukoSite Common Stock or
LeukoSite Preferred Stock in an equity financing (other than in connection with
a public offering pursuant to a registration statement) without either (a)
obtaining irrevocable binding commitments or proxies from each purchaser in such
equity financing or such lesser number of such purchasers as may be required to
obtain stockholder approval in favor of (i) the conversion of the shares of
LeukoSite Series A Preferred Stock issued pursuant to the Merger into shares of
LeukoSite Common Stock and (ii) the issuance of any other Merger Shares issuable
pursuant to this Agreement in the form of LeukoSite Common Stock, or (b) the
prior written consent of the holders of a majority of the outstanding shares of
LeukoSite Series A Preferred Stock.

         10.   CONDUCT OF THE COMPANY'S BUSINESS PENDING THE CLOSING. From and
after the date of this Agreement and until the Closing, except as otherwise
specifically agreed by LeukoSite and the Company:

         10.1. FULL ACCESS. The Company will afford to LeukoSite and its
authorized representatives full access, upon request and reasonable notice and
during normal business hours, to all of the properties, books, records,
contracts, and documents of the Company, and a reasonable opportunity to make
such



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                                       66


investigations as LeukoSite desires to make, and will furnish or cause to be
furnished to LeukoSite and its authorized representatives all such information
with respect to the Company's affairs and businesses as LeukoSite reasonably
requests. No information or knowledge obtained in any investigation pursuant to
this Section 10.1 shall affect or be deemed to modify any representation or
warranty contained herein or the conditions of the parties to consummate the
Merger.

         10.2. ACTIVITIES PENDING THE CLOSING. The Company and LeukoSite will
form a transition committee (the "Transition Committee") to oversee the
operations of the Company pending the consummation of the Merger and to provide
LeukoSite with veto power over decisions concerning the Company's business,
finances and operations during the period commencing on the date hereof and
ending on the earlier of the Effective Time of the Merger or the termination of
this Agreement pursuant to Section 15. The Transition Committee will be composed
of representatives of the Company and one or more representatives of LeukoSite.
The Company agrees that, without the written consent of at least one member of
the Transition Committee that is a representative of LeukoSite (which written
consent may be obtained by having such member of the Transition Committee sign
minutes of meetings of the Transition Committee at which decisions concerning
the Company's business, finances and operations have been made), the Company
will not (i) except with respect to any Approved Payments or any Excluded
Indebtedness, make any expenditure, spend any money, accrue any expense, or
incur any costs, Indebtedness or other liability, including, without limitation,
in connection with any ongoing clinical trials or drug development programs or
in connection with any ongoing research collaborations with third parties, (ii)
initiate or agree to initiate any clinical trials, drug development programs, or
research collaborations with third parties, (iii) make any decisions,
determinations or evaluations concerning the Company's ongoing clinical trials,
drug development programs, or research collaborations with third parties
(including, without limitation, any decision to amend, change or modify any of
the Company's ongoing clinical trials, drug development programs, or research
collaborations with third parties), (iv) in-license or out-license any
intellectual property, technology or drug candidate, (v) make or institute any
new, unusual, or novel methods of manufacture, purchase, sale, lease,
management, accounting, or operation or take or permit to occur or exist any
action or circumstance referred to in Section 7.8 hereof. The Company will use
its best efforts to maintain its owned and leased properties in good operating
condition and repair and make all necessary renewals, additions, and
replacements thereto.

         10.3. NO DIVIDENDS, ISSUANCES, REPURCHASES, ETC. The Company will not
declare, set aside, or pay any dividends (whether in cash, shares of stock,
other property, or otherwise) on, or make any other distribution in respect of,
any shares of its capital stock or other securities, or issue, purchase, redeem,
or



<PAGE>
                                       67


otherwise acquire for value any shares of its capital stock or other securities.
The Company will not issue any shares of its capital stock or other securities
(including without limitation any options, warrants, or other rights to acquire
Company Stock), other than shares of Company Stock issued upon the due exercise
of vested Company Stock Options or Company Warrants listed in Section 7.4 of the
Disclosure Schedule (which exercises will be disclosed by the Company in a
supplement to the Disclosure Schedule pursuant to Section 10.13 hereof).

         10.4. NO COMPENSATION CHANGES. The Company will not increase the
compensation payable or to become payable to any of its officers, directors, key
employees, or agents, or increase any severance, bonus, insurance, pension, or
other benefit plan, payment, or arrangement made to, for, or with any such
officers, directors, key employees, or agents, nor will it effect any general or
uniform increase in the compensation payable or to become payable to its
employees or consultants, including without limitation any increase in the
benefits under any severance, bonus or pension plan or other contract or
commitment, except as described in Section 10.4 of the Disclosure Schedule. The
Company shall not pay any severance benefits to, enter into any contract,
agreement or arrangement to provide severance benefits to, or implement any
severance plan for the benefit of, any of the Company's officers, directors,
employees or consultants, except pursuant to any severance plan, contract or
arrangement described in Section 7.14 of the Disclosure Schedule.

         10.5. CONTRACTS AND COMMITMENTS. The Company will not enter into any
contract or commitment, or engage in any other transaction, other than as
contemplated by this Agreement.

         10.6. PURCHASE AND SALE OF CAPITAL ASSETS. The Company will not
purchase, lease as lessee, license as licensee, or otherwise acquire any
interest in, or sell, lease as lessor, license as licensor, or otherwise dispose
of any interest in, any capital asset(s).

         10.7. INSURANCE.  The Company will maintain the insurance referred to
on Section 7.20 of the Disclosure Schedule.

         10.8. PRESERVATION OF ORGANIZATION. The Company will use its best
reasonable efforts to preserve its business organization intact, to preserve for
the benefit of the Surviving Corporation its present business relationships with
its suppliers and customers and others having business relationships with it.

         10.9. NO DEFAULT. The Company will not take or omit to take any action,
or permit any action or omission to act, that would cause a default under or a
breach of any of its material contracts, commitments, or obligations.



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                                       68


         10.10. COMPLIANCE WITH LAWS. The Company will duly comply in all
material respects with all applicable laws, regulations, and orders.

         10.11. ADVICE OF CHANGE. The Company will promptly advise LeukoSite in
writing of any event or occurrence which results in or is reasonably likely to
result in a Material Adverse Effect.

         10.12. NO SHOPPING. The Company will not negotiate for, solicit,
discuss, negotiate, or enter into any agreement or understanding, whether or not
binding, with respect to the issuance, sale, or transfer of any of the capital
stock or any material portion of the assets of the Company or any merger or
other business combination of the Company, to or with any person other than
LeukoSite and Merger Sub.

         10.13. DISCLOSURE SUPPLEMENTS. From time to time before the Closing,
and in any event immediately before the Closing, each of LeukoSite and the
Company will promptly advise the other in writing of any matter hereafter
arising or becoming known to the disclosing person that, if existing, occurring,
or known at or before the date of this Agreement, would have been required to be
set forth or described in the Disclosure Schedule, or that is necessary to
correct any information in the Disclosure Schedule that is or has become
inaccurate. No such disclosure will be taken into account in determining whether
the conditions to (i) in the case of any such supplemental disclosure by
LeukoSite, the obligations of the Company, and (ii) in the case of any such
supplemental disclosure by the Company, the respective obligations of LeukoSite
and Merger Sub, to consummate the transactions contemplated by this Agreement
have been satisfied. If the Merger is consummated, then for purposes of the
indemnification provisions of this Agreement, such supplemental disclosures
pursuant to this Section 10.13 will be deemed to have been made as of the date
hereof, and no indemnification will be payable in respect thereof by reason of
the fact that such disclosure was not made on the date hereof.

         11. MUTUAL CONDITIONS TO THE PARTIES' OBLIGATIONS. The parties'
obligations to consummate the Merger are subject to the satisfaction (or waiver
by each such party, in its sole discretion) of each of the conditions set forth
in this section on or before the Closing Date. If the Merger is consummated,
such conditions will conclusively be deemed to have been satisfied or waived.

         11.1. STOCKHOLDER APPROVAL. This Agreement and the Merger shall have
been approved and adopted by the Stockholders of the Company by the requisite
vote under applicable law and the Company's Certificate of Incorporation.

         11.2. NO INJUNCTIONS OR RESTRAINTS. No temporary restraining order,
preliminary or permanent injunction, or other order issued by any court of



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                                       69


competent jurisdiction, or other legal restraint or prohibition preventing the
consummation of the Merger, will be in effect, and no petition or request for
any such injunction or other order will be pending.

         11.3. SECURITIES LAW COMPLIANCE. All filings necessary under federal
and state securities laws to permit the issuance and delivery to the
Stockholders of the shares of LeukoSite Common Stock issuable pursuant to the
Merger will have been made, and any authorizations in connection therewith from
all applicable securities regulatory authorities will have been obtained.

         11.4. PROCEEDINGS AND DOCUMENTS SATISFACTORY. All proceedings in
connection with the transactions contemplated by this Agreement and all
certificates and other documents delivered to such party pursuant to this
Agreement or in connection with the Closing will be reasonably satisfactory to
such party and its counsel.

         12. CONDITIONS TO THE COMPANY'S OBLIGATIONS. The obligations of the
Company to consummate the Merger are subject to the satisfaction (or waiver by
the Company, in its sole discretion) of each of the conditions set forth in this
section on or before the Closing Date. If the Merger is consummated, such
conditions will conclusively be deemed to have been satisfied or waived.

         12.1. REPRESENTATIONS AND WARRANTIES. Each of the representations and
warranties made by LeukoSite and/or Merger Sub in or pursuant to this Agreement
or in any statement, certificate, or other document delivered to the Company or
the Stockholders in connection with this Agreement, the Merger, or any of the
other transactions contemplated hereby will have been true and correct in all
material respects when made and will be true and correct in all material
respects at and as of the Closing (in each case, except that any representation
or warranty that expressly includes a materiality standard will have been and be
true and correct in all respects, giving effect to such standard), subject only
to the effect of any activities or transactions occurring after the date hereof
and either expressly contemplated by this Agreement or consented to in writing
by the Company and except for representations and warranties made as of a
specific date, which shall be true and correct in all material respects as of
such date.

         12.2. COMPLIANCE WITH AGREEMENT. LeukoSite and Merger Sub will have
performed and complied in all material respects with all of their respective
obligations under this Agreement to be performed or complied with by them before
or at the Closing, including without limitation the execution and delivery of
all documents to be executed and delivered by any of them in connection with
this Agreement and/or the consummation of the Merger and the other transactions
contemplated hereby.



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                                       70


         12.3 MATERIAL ADVERSE DEVELOPMENT. There shall not have occurred any
event or occurrence which results in or would reasonably be likely to have a
Material Adverse Effect on LeukoSite.

         12.4. CLOSING CERTIFICATE. LeukoSite and Merger Sub will have executed
and delivered to the Company, at and as of the Closing, a certificate (without
qualification as to knowledge or materiality) certifying that the conditions
referred to in Sections 12.1, 12.2 and 12.3 have been satisfied.

         12.5. OPINION OF COUNSEL. Bingham Dana LLP, counsel to LeukoSite and
Merger Sub, will have delivered to the Company a written legal opinion addressed
to the Company, dated on and as of the Closing Date, and in a form reasonably
acceptable to the Company and its counsel.

         12.6. ESCROW AGREEMENT. LeukoSite and the Escrow Agent shall have
executed and delivered the Escrow Agreement.

         12.7. PROXIES. The Company and LeukoSite shall have obtained
irrevocable binding commitments or proxies, in substantially the form of either
EXHIBIT D-1 or D-2 attached hereto or such other form as may be acceptable to
the Company, representing at least a majority of the shares of LeukoSite Common
Stock outstanding prior to the Closing, to vote such shares of LeukoSite Common
Stock in favor of (i) the conversion of the shares of LeukoSite Series A
Preferred Stock issued pursuant to the Merger into shares of LeukoSite Common
Stock and (ii) the issuance of any other Merger Shares issuable pursuant to this
Agreement in the form of LeukoSite Common Stock.

         13. CONDITIONS TO LEUKOSITE'S AND MERGER SUB'S OBLIGATIONS. The
obligations of each of LeukoSite and Merger Sub, respectively, to consummate the
Merger are subject to the satisfaction (or waiver by LeukoSite, in its sole
discretion) of each of the conditions set forth in this section on or before the
Closing Date. If the Merger is consummated, such conditions will conclusively be
deemed to have been satisfied or waived.

         13.1. REPRESENTATIONS AND WARRANTIES. Each of the representations and
warranties made by the Company in or pursuant to this Agreement or in any
statement, certificate, or other document delivered to LeukoSite or Merger Sub
in connection with this Agreement, the Merger, or any of the other transactions
contemplated hereby will have been true and correct in all material respects
when made and will be true and correct in all material respects at and as of the
Closing (in each case, except that any representation or warranty that expressly
includes a materiality standard will have been and be true and correct in all
respects, giving effect to such standard), subject only to the effect of any
activities or transactions occurring after the date hereof and either expressly
contemplated by this Agreement or consented to in writing by LeukoSite and



<PAGE>
                                       71


except for representations and warranties made as of a specific date, which
shall be true and correct in all material respects as of such date.

         13.2. COMPLIANCE WITH AGREEMENT. The Company will have performed and
complied in all material respects with all of its respective obligations under
this Agreement to be performed or complied with by it before or at the Closing,
including without limitation the execution and delivery of all documents to be
executed and delivered by the Company (or the Stockholders) in connection with
this Agreement and/or the consummation of the Merger and the other transactions
contemplated hereby.

         13.3. MATERIAL ADVERSE DEVELOPMENT. There shall not have occurred any
event or occurrence which results in or would reasonably be likely to have a
Material Adverse Effect on the Company.

         13.4. CLOSING CERTIFICATE. The Company will have executed and delivered
to LeukoSite, at and as of the Closing, a certificate (without qualification as
to knowledge or materiality) certifying with respect to themselves that the
conditions referred to in Sections 13.1, 13.2 and 13.3 have been satisfied.

         13.5. OPINION OF COUNSEL. Hale and Dorr LLP, counsel to the Company,
will have delivered to LeukoSite a written legal opinion addressed to LeukoSite,
dated on and as of the Closing Date, and in a form reasonably satisfactory to
LeukoSite and its counsel.

         13.6. THIRD PARTY CONSENTS. LeukoSite shall have been furnished with
evidence satisfactory to it that the Company has obtained the consents,
approvals and waivers set forth in Sections 7.3 and 7.18 of the Disclosure
Schedule and any other consents, approvals and waivers that are necessary or
required as a result of the Merger to preserve all of the Company's rights and
benefits in its business, assets, properties, leases and contracts following the
Merger.

         13.7. COMPANY OPTIONS AND COMPANY WARRANTS. All of the Company Options
and Company Warrants (other than those Company Warrants exercisable for no
greater than 71,000 shares of Company Preferred Stock and 720,000 shares of
Company Common Stock) shall have been exercised or terminated immediately prior
to the Closing.

         13.8. RESIGNATION OF DIRECTORS AND OFFICERS. The directors and officers
of the Company in office immediately prior to the Effective Time shall have
resigned as directors and officers of the Surviving Corporation effective
immediately following the Effective Time.



<PAGE>
                                       72


         13.9. DISSENTERS' RIGHTS. Stockholders holding in the aggregate more
than fifteen per cent (15%) of the outstanding shares of the Company Stock shall
not have exercised appraisal, dissenters' or similar rights under applicable law
with respect to their shares of the Company Stock by virtue of the Merger.

         13.10. ESCROW AGREEMENT. The Stockholders' Representatives and the
Escrow Agent shall have executed and delivered the Escrow Agreement.

         13.11. DESIGNATED PREFERRED STOCKHOLDERS AGREEMENT. The Designated
Preferred Stockholders Agreement shall remain in full force and effect, and no
Designated Preferred Stockholder shall have taken any action to terminate or
rescind the Designated Preferred Stockholders Agreement.

         14.   INDEMNIFICATION.

         14.1. INDEMNIFICATION BY LEUKOSITE AND MERGER SUB. Subject to the
limitations set forth in Section 14.6 hereof, LeukoSite and Merger Sub, jointly
and severally, will indemnify, defend, and hold harmless the Stockholders (but
only if the Merger is consummated) and, if the Merger is not consummated, the
Company, and each of their respective directors, officers, employees, agents,
representatives and other Affiliates, in each case to the same extent as
LeukoSite and Merger Sub have agreed to indemnify the Stockholders or the
Company, as the case may be (all persons entitled to indemnification under this
Section 14.1 being hereinafter referred to as the "Company Indemnified
Parties"), from and against any and all Damages related to or arising, directly
or indirectly, out of or in connection with any breach by LeukoSite and/or
Merger Sub of any representation, warranty, covenant, agreement, obligation, or
undertaking made by LeukoSite and/or Merger Sub in this Agreement (including any
schedule or exhibit hereto), or any other agreement, instrument, certificate, or
other document delivered by or on behalf of LeukoSite and/or Merger Sub in
connection with this Agreement, the Merger, or any of the other transactions
contemplated hereby.

         14.2. INDEMNIFICATION BY THE COMPANY. Subject to the limitations set
forth in Section 14.6 hereof, if the Merger is not consummated the Company will
indemnify, defend, and hold harmless LeukoSite, Merger Sub and each of their
respective directors, officers, employees, agents, representatives and other
Affiliates, from and against any and all Damages related to or arising, directly
or indirectly, out of or in connection with any breach by the Company of any
representation, warranty, covenant, agreement, obligation, or undertaking made
by the Company in this Agreement (including any schedule or exhibit hereto), or
any other agreement, instrument, certificate, or other document delivered by or
on behalf of the Company in connection with this Agreement, the Merger, or any
of the other transactions contemplated hereby.



<PAGE>
                                       73


         14.3. INDEMNIFICATION BY THE STOCKHOLDERS. Subject to the limitations
set forth in Section 14.6 hereof, if the Merger is consummated the Stockholders,
jointly and severally, will indemnify, defend, and hold harmless LeukoSite, the
Surviving Corporation, and each of their respective directors, officers,
employees, agents, representatives and other Affiliates (all persons entitled to
indemnification under Section 14.2 and this Section 14.3 being hereinafter
referred to as the "LeukoSite Indemnified Parties", and, together with the
Company Indemnified Parties, the "Indemnified Parties"), from and against any
and all Damages related to or arising, directly or indirectly, out of or in
connection with:

                           (i) any breach by the Company of any representation,
                  warranty, covenant, agreement, obligation, or undertaking made
                  by the Company in this Agreement (including any schedule or
                  exhibit hereto), or any other agreement, instrument,
                  certificate, or other document delivered by or on behalf of
                  the Company in connection with this Agreement, the Merger, or
                  any of the other transactions contemplated hereby;

                           (ii) any claim for indemnification made by UCB
                  pursuant to the UCB Agreement or any breach by the Company of
                  any representation, warranty, covenant, agreement, obligation
                  or undertaking made by the Company in the UCB Agreement;

                           (iii) any claim for payment of the appraised value of
                  Dissenting Shares of Company Stock in accordance with the
                  provisions of Section 262 of the DGCL and Section 3.6(c) of
                  this Agreement and/or any and all costs, expenses and Damages
                  incurred by LeukoSite in connection with such claim,
                  including, without limitation, (1) any payment made by
                  LeukoSite pursuant to Section 3.6(c) hereof in connection with
                  any such claim (regardless of whether such payment represents
                  the appraised value of such Dissenting Shares as determined
                  pursuant to a judicial proceeding or represents amounts paid
                  by LeukoSite in settlement of such appraisal rights with the
                  consent of the Stockholders' Representatives) and (2) any and
                  all court costs and reasonable legal fees and disbursements
                  incurred by LeukoSite in connection with any litigation or
                  judicial proceeding and/or settlement relating to such claim;
                  or

                           (iv) any claim by LeukoSite that the Unaudited
                  Closing Net Cash Balance exceeds the Audited Closing Net Cash
                  Balance and any claim that the number of Aggregate Base
                  Consideration Shares should be reduced pursuant to Section
                  3.7(e) as a result of such excess.



<PAGE>
                                       74


         14.4.    CLAIMS.

                  (a) All claims for indemnification by an Indemnified Party
         pursuant to this Section 14 shall be made in accordance with the
         provisions of this Section 14 and, if applicable, the Escrow Agreement.

                  (b) If an Indemnified Party has incurred or suffered Damages
         for which it is entitled to indemnification under this Section 14, such
         Indemnified Party shall, prior to the expiration of the representation,
         warranty, covenant or agreement to which such claim relates, give
         prompt written notice of such claim (a "Claim Notice") to the
         Stockholders' Representatives, in the case of a claim by a LeukoSite
         Indemnified Party, or to LeukoSite, in the case of a claim by a Company
         Indemnified Party (the Stockholders or LeukoSite, as the case may be,
         the "Indemnifying Party"). Each Claim Notice shall state the amount of
         claimed Damages (the "Claimed Amount"), if known, and the basis for
         such claim.

                  (c) Within 20 days after delivery of a Claim Notice, the
         Indemnifying Party (who for purposes of this Section 14 shall be
         represented by the Stockholders' Representatives in the case of a claim
         by a LeukoSite Indemnified Party) shall provide to the Indemnified
         Party a written response (the "Response Notice") in which the
         Indemnifying Party shall: (i) agree that all of the Claimed Amount is
         owed to the Indemnified Party, (ii) agree that part, but not all, of
         the Claimed Amount (the "Agreed Amount") is owed to the Indemnified
         Party, or (iii) contest that any of the Claimed Amount is owed to the
         Indemnified Party. The Indemnifying Party may contest the payment of
         all or a portion of the Claimed Amount only based upon a good faith
         belief that all or such portion of the Claimed Amount does not
         constitute Damages for which the Indemnified Party is entitled to
         indemnification under this Section 14. If no Response Notice is
         delivered by the Indemnifying Party within such 20-day period, the
         Indemnifying Party shall be deemed to have agreed that all of the
         Claimed Amount is owed to the Indemnified Party.

                  (d) If the Indemnifying Party in the Response Notice agrees
         (or is deemed to have agreed) that all of the Claimed Amount is owed to
         the Indemnified Party, the Indemnifying Party shall owe to the
         Indemnified Party an amount equal to the Claimed Amount to be paid in
         the manner set forth in this Section 14. If the Indemnifying Party in
         the Response Notice agrees that part, but not all, of the Claimed
         Amount is owed to the Indemnified Party, the Indemnifying Party shall
         owe to the Indemnified Party an amount equal to the Agreed Amount set
         forth in such Response Notice to be paid in the manner set forth in
         this Section 14.



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                                       75


                  (e) The Indemnified Party shall give prompt written
         notification to the Indemnifying Party of the commencement of any
         action, suit or proceeding relating to a third party claim for which
         indemnification pursuant to this Section may be sought; provided,
         however, that no delay on the part of the Indemnified Party in
         notifying the Indemnifying Party shall relieve the Indemnifying Party
         of any liability or obligation hereunder except to the extent of any
         damage or liability caused by or arising out of such delay. Within 20
         days after delivery of such notification, the Indemnifying Party may,
         upon written notice thereof to the Indemnified Party, assume control of
         the defense of such action, suit or proceeding with counsel reasonably
         satisfactory to the Indemnified Party, provided (i) the Indemnifying
         Party acknowledges in writing to the Indemnified Party, on behalf of
         the Indemnifying Party, that any damages, fines, costs or other
         liabilities that may be assessed against the Indemnified Party in
         connection with such action, suit or proceeding constitute Damages for
         which the Indemnified Party shall be entitled to indemnification
         pursuant to this Section 14, (ii) the third party seeks monetary
         damages only, and (iii) an adverse resolution of the third party's
         claim would not have a material adverse effect on the goodwill or the
         reputation of the Indemnified Party or the business, operations or
         future conduct of the Indemnified Party. If the Indemnifying Party does
         not so assume control of such defense, the Indemnified Party shall
         control such defense. The party not controlling such defense may
         participate therein at its own expense; provided that if the
         Indemnifying Party assumes control of such defense and the Indemnified
         Party reasonably concludes that the Indemnifying parties and the
         Indemnified Party have conflicting interests or different defenses
         available with respect to such action, suit or proceeding, the
         reasonable fees and expenses of counsel to the Indemnified Party shall
         be considered "Damages" for purposes of this Agreement. The party
         controlling such defense shall keep the other party advised of the
         status of such action, suit or proceeding and the defense thereof and
         shall consider in good faith recommendations made by the other party
         with respect thereto. The Indemnified Party shall not agree to any
         settlement of such action, suit or proceeding without the prior written
         consent of the Indemnifying Party, which shall not be unreasonably
         withheld or delayed. The Indemnifying Party shall not agree to any
         settlement of or the entry of a judgment in any action, suit or
         proceeding without the prior written consent of the Indemnified Party,
         which shall not be unreasonably withheld (it being understood that it
         is reasonable to withhold such consent if, among other things, the
         settlement or the entry of a judgment (A) lacks a complete release of
         the Indemnified Party for all liability with respect thereto or (B)
         imposes any liability or obligation on the Indemnified Party).



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                                       76


         14.5     PAYMENT OF CLAIMS.

                  (a) An Indemnifying Party shall make payment of any portion of
         any Claimed Amount that such Indemnifying Party has agreed in a
         Response Notice that it owes to an Indemnified Party or that such
         Indemnifying Party is deemed to have agreed it owes to such
         Indemnifying Party pursuant to the provisions of Section 14.4(c)
         hereof, said payment to be made within thirty (30) days after such
         Response Notice is delivered by such Indemnifying Party or should have
         been delivered by such Indemnifying Party, as the case may be.

                  (b) Anything in this Agreement to the contrary
         notwithstanding, subject to the provisions of Section 14.6, LeukoSite
         may withhold and set-off against any Merger Consideration otherwise
         required to be paid or delivered to the Stockholders pursuant to this
         Agreement any amount as to which the Stockholders are obligated to
         indemnify LeukoSite pursuant to any provision of this Agreement.

         14.6.    LIMITATIONS OF LIABILITY.

                  (a) THRESHOLD. No Indemnifying Party will be required to
         indemnify an Indemnified Party hereunder with respect to any Damages
         arising on account of or related to any breach of a representation or
         warranty made by such Indemnifying Party pursuant to this Agreement
         until such time as the aggregate amount of Damages for which (i)
         LeukoSite, Merger Sub and their respective directors, officers,
         employees, representatives and other Affiliates, on the one hand, or
         (ii) the Company and its directors, officers, employees,
         representatives and other Affiliates, as the case may be, on the other
         hand, are otherwise entitled to indemnification pursuant to this
         Section 14 exceeds $50,000, whereupon such Indemnified Party will be
         entitled to indemnification for the full amount of all such Damages
         without regard to such threshold amount.

                  (b) LIMITED RECOURSE; MAXIMUM LIABILITY. Notwithstanding any
         other provision in this Agreement, all claims for indemnification by a
         LeukoSite Indemnified Party under this Section 14 shall be satisfied
         solely from the Escrowed Securities or by the right of set-off set
         forth in Section 14.5(b) above, and no Stockholder shall otherwise have
         any direct or indirect liability to any LeukoSite Indemnified Party.
         For purposes of this Section 14.6(b), the value of the shares of
         LeukoSite Stock issued to such Stockholder pursuant to the Merger and
         of the Merger Conversion Shares shall be conclusively deemed to be
         equal to be $11.88 per share of LeukoSite Common Stock (such dollar
         figure to be proportionately adjusted to reflect stock splits, stock
         dividends, reverse stock splits, and



<PAGE>
                                       77


         other recapitalizations, reorganizations and similar events affecting
         LeukoSite Common Stock and occuring after the date of this Agreement).

                  (c) TIME LIMIT. No Indemnifying Party will be liable for any
         Damages hereunder unless a written claim for indemnification is given
         by the Indemnified Party to the Indemnifying Party on or prior to the
         second anniversary of the Closing Date; PROVIDED, HOWEVER, that the
         foregoing provisions of this Section 14.6(c) shall not apply to any
         claim by LeukoSite for indemnification pursuant to clause (ii) of
         Section 14.3 hereof.

                  (d) TAX AND INSURANCE BENEFITS. The amount of any Damages
         otherwise payable to any Indemnified Party hereunder will be reduced
         (i) to the extent that such Indemnified Party actually realizes, by
         reason of such Damages, any tax benefit that is not offset by any
         corresponding adjustment of the tax attributes of such Indemnified
         Party or any of his or its assets (E.G., any tax deduction available to
         such Indemnified Party in respect of such Damages will not be deemed to
         result in a tax benefit to such Indemnified Party to the extent that
         such deduction results in a decrease in such Indemnified Party's tax
         basis in any securities or other assets), and (ii) by any insurance
         proceeds actually received by such Indemnified Party in respect
         thereof, to the extent that such reduction is permitted without
         reduction of the amount of such proceeds payable under the applicable
         insurance policy.

         Each Indemnified Party will use reasonable efforts to collect any
Damages from any available insurer before attempting to collect from the
Indemnifying Party at any time. If any Indemnified Party recovers any amount
from any insurer after payment to such Indemnified Party by one or more
Indemnifying Parties of all Damages suffered or incurred by such Indemnified
Party in respect of the matters to which such insurance payment relates, then
such Indemnified Party will promptly pay over to such Indemnifying Parties the
amount so recovered, to the extent not in excess of the amount previously paid
by such Indemnifying Party to such Indemnified Party in respect of such matter.

         14.7. SUBROGATION. An Indemnifying Party who indemnifies an Indemnified
Party pursuant to this Section 14 will, upon indefeasible payment in full of the
amount owed with respect to such matter pursuant to this Section 14, be
subrogated to the extent of such payment to the rights of such Indemnified Party
against all other persons in respect of the matter for which such
indemnification payment was made, to the extent permitted by applicable
insurance policies of such Indemnified Party, and upon such subrogation may
assert such rights against such other persons.



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                                       78


         14.8. EXCLUSIVE REMEDIES. The parties acknowledge and agree that their
sole and exclusive remedies in respect of any and all claims relating to any
breach or purported breach of any representation, warranty, covenant, agreement,
obligation, or undertaking contained in this Agreement (including any schedule
or exhibit hereto), or any other agreement, instrument, certificate, or other
document delivered by or on behalf of any party hereto in connection with this
Agreement, the Merger, or any of the other transactions contemplated hereby will
be pursuant to the indemnification provisions of this Section 14. No breach of
any such representation, warranty, covenant, agreement, obligation, or
undertaking will give rise to any right of any party hereto to rescind this
Agreement or any of the transactions contemplated hereby.

         14.9. APPLICABILITY. The provisions of this Section 14 will not apply
to claims for indemnification or contribution arising under or in connection
with Section 6 hereof and/or the Stockholder Registration Statement and the
other transactions contemplated by Section 6 hereof.

         15. RELEASES. If the Merger is consummated, then, effective as of the
Effective Time, each of the Stockholders, for himself or itself and his or its
heirs, legatees, successors, and assigns, hereby fully and irrevocably releases,
remises, and discharges the Surviving Corporation and its officers, directors,
employees, agents, representatives, successors, and assigns from any and all
Damages, regardless of whether known, unknown, or unknowable, and regardless of
whether absolute, contingent, or otherwise, and regardless of whether at law, in
equity, or otherwise, without limitation, whether now existing or arising in the
future, in each case to the extent based on actions, omissions, and/or events
occurring at or before the Effective Time, including without limitation all
rights to indemnification and/or contribution, but excluding Damages and rights
of indemnification arising expressly under this Agreement and claims for accrued
but unpaid salaries and reimbursable expenses (the aggregate amount of which
salaries and expenses does not exceed $50,000). Furthermore, each of such
releasing persons hereby irrevocably agrees not to sue, or to commence,
maintain, or aid in the prosecution of any litigation, arbitration, or other
action or proceeding against or adverse to any of such released persons, or
otherwise to seek any recourse against any of such released persons, in respect
of any matter hereby released or purported or attempted to be released.

         16.      TERMINATION.

                  (a) This Agreement may be terminated at any time before the
         Effective Time by agreement of LeukoSite and the Company,
         notwithstanding the approval of this Agreement and/or of the Merger by
         the stockholders of any party.



<PAGE>
                                       79


                  (b) If (i) any temporary restraining order, preliminary or
         permanent injunction, or other order issued by any court of competent
         jurisdiction, or other binding legal restraint or prohibition
         preventing the consummation of the Merger or the other transactions
         contemplated hereby is at any time in effect for a period of more than
         20 consecutive days, or (ii) the Closing does not occur on or before
         February 28, 1999, then either LeukoSite or the Company may terminate
         this Agreement by delivering written notice to the other at any time
         after the close of business on date such termination right arises
         hereunder, PROVIDED that such failure to close is not the result of a
         breach of this Agreement by the terminating party (including, in the
         case of any such termination by LeukoSite, any breach by Merger Sub, or
         in the case of any such termination by the Company, any breach by any
         of the Stockholders).

                  (c) Any termination of this Agreement will not affect the
         rights or obligations of any party arising, or based on actions or
         omissions occurring, before such termination. The provisions of Section
         1 ("Definitions"), Section 14 ("Indemnification"), this Section 16
         ("Termination") and Section
         17 ("General") will survive any termination of this Agreement.

         17.   GENERAL.

         17.1. COOPERATION. Each of the parties will cooperate with the others
and use its best reasonable efforts to prepare all necessary documentation, to
effect all necessary filings, and to obtain all necessary permits, consents,
approvals, and authorizations of all governmental bodies and other third parties
necessary to consummate the transactions contemplated by this Agreement.

         17.2. SURVIVAL OF PROVISIONS. The provisions of this Agreement,
including without limitation the representations and warranties of the parties,
and the provisions of the other documents executed and delivered in connection
with this Agreement, the Merger, and the other transactions contemplated hereby
will be deemed material, and, notwithstanding any investigation by or on behalf
of any other party, will be deemed to have been relied on by each other party,
and will survive the Closing and the consummation of the Merger and the other
transactions contemplated hereby until terminated or no longer in effect in
accordance with their respective terms, except that (i) the representations and
warranties made by the parties pursuant to this Agreement shall survive the
Closing and the consummation of the Merger and the other transactions
contemplated hereby until the second anniversary of the Closing Date and (ii)
the covenants set forth in Sections 9.14 and 9.15 shall survive the Closing and
the consummation of the Merger and the other transactions contemplated



<PAGE>
                                       80


hereby until such date as the payments set forth in Section 3.8(b) and Section
3.8(d), respectively, have been made.

         17.3. EXPENSES. LeukoSite, on the one hand, and the Company, on the
other hand, will be responsible for and will pay all of their own respective
expenses in connection with the negotiation and preparation of this Agreement
and the consummation of the Merger and the other transactions contemplated
hereby.

         17.4.    BENEFITS OF AGREEMENT; NO ASSIGNMENTS; NO THIRD-PARTY
BENEFICIARIES.

                  (a) This Agreement will bind and inure to the benefit of the
         parties hereto and their respective heirs, successors, and permitted
         assigns.

                  (b) No party will assign any rights or delegate any
         obligations hereunder without the consent of the other parties, other
         than in the case of LeukoSite, in connection with (i) a merger or
         consolidation of LeukoSite or (ii) a sale of the assets to which this
         transaction relates (provided that, in the event of such sale of
         assets, the buyer agrees in writing with the Stockholders'
         Representatives to be bound by the obligations of LeukoSite under this
         Agreement), and any attempt to do so will be void.

                  (c) Nothing in this Agreement is intended to or will confer
         any rights or remedies on any person other than the parties hereto and
         their respective heirs, successors, and permitted assigns, except as
         expressly provided in Section 13 hereof; PROVIDED HOWEVER, that the
         provisions in Section 3 concerning the issuance of the consideration
         for the Company Stock, the registration thereof pursuant to Section 6,
         the representations of LeukoSite and the Merger Sub set forth in
         Section 8, and the indemnification provisions in Section 14 are for the
         benefit of the Stockholders.

         17.5. NOTICES. All notices, requests, payments, instructions, or other
documents to be given hereunder will be in writing or by written
telecommunication, and will be deemed to have been duly given if (i) delivered
personally (effective upon delivery), (ii) mailed by registered or certified
mail, return receipt requested, postage prepaid (effective five business days
after dispatch), (iii) sent by a reputable, established courier service that
guarantees next business day delivery (effective the next business day), or (iv)
sent by telecopier followed within 24 hours by confirmation by one of the
foregoing methods (effective upon receipt of the telecopy in complete, readable
form), addressed as follows (or to such other address as the recipient party may
have furnished to the sending party for the purpose pursuant to this section):



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                                       81


                  (a) If to LeukoSite, Merger Sub, and/or (after the Effective
         Time), the Surviving Corporation to:

                  LeukoSite Inc.
                  215 First Street
                  Cambridge, MA  02142
                  Attention:  Christopher K. Mirabelli, Ph.D.
                  Telecopier No. (617) 621-9349

                  with a copy sent at the same time and by the same means to:

                  Justin P. Morreale, Esq.
                  Julio E. Vega, Esq.
                  Bingham Dana LLP
                  150 Federal Street
                  Boston, Massachusetts  02110
                  Telecopier No. (617) 951-8736

                  (b) If to the Company (before the Effective Time) to:

                  CytoMed, Inc.
                  840 Memorial Drive
                  Cambridge, MA  02139
                  Attention:  Richard H. Woodrich
                  Telecopier No. (617) 661-7364

                  If to the Company (after the Effective Time) or to the
Stockholders' Representatives to:

                  Richard Sherman
                  Q.E.D. Technologies
                  20 Valley Stream Parkway, Suite 265
                  Malverne, PA  19355-1457
                  Telecopier No. (610) 695-2517

                  Joel Liffman
                  Oracle Partners L.P.
                  712 Fifth Avenue
                  45th Floor
                  New York, NY  10019
                  Telecopier No. ______________



<PAGE>
                                       82


                  with a copy sent at the same time and by the same means to:

                  Steven D. Singer, Esq.
                  Virginia Kingsley Kapner, Esq.
                  Hale and Dorr LLP
                  60 State Street
                  Boston, MA  02109
                  Telecopier No. (617) 526-5000

         17.6. COUNTERPARTS. This Agreement may be executed by the parties in
separate counterparts, each of which when so executed and delivered will be an
original, but all of which together will constitute one and the same agreement.
In pleading or proving this Agreement, it will not be necessary to produce or
account for more than one such counterpart.

         17.7. CAPTIONS. The captions of sections or subsections of this
Agreement are for reference only and will not affect the interpretation or
construction of this Agreement.

         17.8. EQUITABLE RELIEF. Each of the parties hereby acknowledges that
any breach by him or it of his or its obligations under this Agreement would
cause substantial and irreparable damage to the parties, and that money damages
would be an inadequate remedy therefor, and accordingly, acknowledges and agrees
that each other party will be entitled to an injunction, specific performance,
and/or other equitable relief to prevent the breach of such obligations.

         17.9. CONSTRUCTION. The language used in this Agreement is the language
chosen by the parties to express their mutual intent, and no rule of strict
construction will be applied against any party.

         17.10. WAIVERS. No waiver of any breach or default hereunder will be
valid unless in a writing signed by the waiving party. No failure or other delay
by any party exercising any right, power, or privilege hereunder will be or
operate as a waiver thereof, nor will any single or partial exercise thereof
preclude any other or further exercise thereof or the exercise of any other
right, power, or privilege.

         17.11. ENTIRE AGREEMENT. This Agreement, together with the exhibits and
schedules hereto and the other agreements, instruments, certificates, and other
documents referred to herein as having been or to be executed and delivered in
connection with the transactions contemplated hereby, contains the entire
understanding and agreement among the parties, and supersedes any prior
understandings or agreements among them, or between or among any of them, with
respect to the subject matter hereof. Notwithstanding the foregoing,



<PAGE>
                                       83


the provisions of the Confidentiality Agreement dated as of October 16, 1998, by
and between the Company and LeukoSite, will survive the execution and delivery
of this Agreement and the consummation of the Merger.

         17.12. GOVERNING LAW. This Agreement will be governed by and
interpreted and construed in accordance with the internal laws of Commonwealth
of Massachusetts, as applied to contracts under seal made, and entirely to be
performed, within Massachusetts, and without reference to principles of
conflicts or choice of laws.

         17.13. AMENDMENT. This Agreement may not be amended, modified, or
supplemented except by a writing duly executed by LeukoSite, Merger Sub, the
Company and the Stockholder Representatives; PROVIDED however, that any
amendment effected subsequent to the time the Stockholders approve this
Agreement shall be subject to the provisions of the DGCL. Notwithstanding the
foregoing, SCHEDULE A to this Agreement may be amended solely by the Company and
the Stockholders Representatives, without the consent of LeukoSite or Merger
Sub, if such amendment is (a) consistent with the liquidation provisions of the
Company's Certificate of Incorporation and (b) would not result in the
Designated Preferred Stockholders having the ability to revoke the proxy granted
pursuant to Section 3 of the Designated Preferred Stockholders Agreement.


















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                                       84


         IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Agreement and Plan of Merger and Reorganization under seal as of the date first
above written.


LEUKOSITE:                             LEUKOSITE, INC.



                                       By    /s/ Christopher K. Mirabelli
                                          --------------------------------
                                          Name:  Christopher K. Mirabelli
                                          Title:  President


MERGER SUB:                            LEUKOSITE MERGER CORPORATION



                                       By    /s/ Christopher K. Mirabelli
                                          --------------------------------
                                          Name:  Christopher K. Mirabelli
                                          Title:  President


COMPANY:                               CYTOMED, INC.



                                       By    /s/ Richard H. Woodrich
                                          --------------------------------
                                          Name:  Richard H. Woodrich
                                          Title:  Executive Vice President and
                                                     and Chief Operating Officer




<PAGE>
                                       85


                             EXHIBITS AND SCHEDULES


Exhibits

         A.                Terms of LeukoSite Series A Preferred Stock

         B                 Merger Certificate

         C                 Escrow Agreement

         D-1               Voting Agreement

         D-2               Voting Agreement and Irrevocable Proxy



Schedules

Schedule A                 Distribution of Merger Consideration

Disclosure Schedules of the Company






<PAGE>





                                  EXHIBIT 23.2



                               ARTHUR ANDERSEN LLP



                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


As independent public accountants, we hereby consent to the incorporation by
reference in this registration statement of our report dated January 29, 1999
included in LeukoSite, Inc.'s Form 10-K for the year ended December 31, 1998
and to all references to our Firm included in this registration statement.


                                           /s/ Arthur Andersen LLP
                                           -----------------------
                                           Arthur Andersen LLP

Boston, Massachusetts
December 1, 1999




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