CERUS CORP, 10-K, 1998-03-06

CERUS CORP
10-K, 1998-03-06
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)

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SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM 10-K

[X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE
SECURITIES EXCHANGE ACT OF 1934
FOR THE FISCAL YEAR ENDED DECEMBER 31, 1997

[ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF
THE SECURITIES EXCHANGE ACT OF 1934
COMMISSION FILE NUMBER 0-21937

CERUS CORPORATION
(Exact name of registrant as specified in its charter)

DELAWARE 68-0262011
(State or other jurisdiction of (IRS Employer Identification
incorporation or organization) Number)
2525 STANWELL DR., SUITE 300 94520
CONCORD, CALIFORNIA (Zip Code)
(Address of principal executive
offices)

(510) 603-9071
(Registrant's telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:
NONE

Securities registered pursuant to Section 12(g) of the Act:
COMMON STOCK, PAR VALUE $.001 PER SHARE
(Title of Class)

Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes X No

Indicate by check mark if disclosure of delinquent filers pursuant to
Item 405 of Regulation S-K is not contained herein, and will not be contained,
to the best of registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10 - K. [ ]

The approximate aggregate market value of the Common Stock held by
non-affiliates of the registrant, based upon the closing price of the Common
Stock reported on the Nasdaq National Market on February 27, 1998, was
$84,215,505.

As of February 28, 1998, there were 9,228,497 shares of the registrant's
common stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Certain portions of the registrant's definitive proxy statement, to be filed not
later than 120 days after December 31, 1997 in connection with the registrant's
1998 Annual Meeting of Stockholders, is incorporated by reference into Part III
of this Form 10-K.

================================================================================

<PAGE> 2

TABLE OF CONTENTS

<TABLE>
<CAPTION>
PAGE
<S> <C> <C>
PART I

Item 1. Business....................................................................... 1

Item 2. Properties..................................................................... 20

Item 3. Legal Proceedings.............................................................. 20

Item 4. Submission of Matters to a Vote of Security Holders............................ 20

PART II

Item 5. Market for the Registrant's Common Equity and Related Stockholder Matters...... 21

Item 6. Selected Financial Data........................................................ 22

Item 7. Management's Discussion and Analysis of Financial Condition and Results of
Operations..................................................................... 23

Item 8. Financial Statements and Supplemental Data..................................... 26

Item 9. Changes in and Disagreements with Accountants on Accounting and Financial
Disclosure..................................................................... 26

PART III

Item 10. Directors and Executive Officers of the Registrant............................. 27

Item 11. Executive Compensation......................................................... 27

Item 12. Security Ownership of Certain Beneficial Owners and Management................. 27

Item 13. Certain Relationships and Related Transactions................................. 27

PART IV

Item 14. Exhibits, Financial Statement Schedules and Reports on Form 8-K................ 27
</TABLE>

<PAGE> 3

PART I

This report contains forward-looking statements within the meaning
Section 21E of the Securities Exchange Act of 1934 which are subject to the
"safe harbor" created by those sections. These forward-looking statements
include, but are not limited to, statements concerning the Company's plans to
continue development of its current product candidates; conduct clinical trials
with respect to its product candidates; seek regulatory approvals; address
certain markets; engage third-party manufacturers to supply its clinical trial
and commercial requirements; continue to rely on a third party for a marketing,
sales and distribution capability; and evaluate additional product candidates
for subsequent clinical and commercial development. These forward-looking
statements may be found under the captions "Business" and "Management's
Discussion and Analysis of Financial Condition and Results of Operations."
Forward-looking statements not specifically described above also may be found in
these and other sections of this report. Actual results could differ materially
from those discussed in the forward-looking statements as a result of certain
factors, including those discussed herein.

ITEM 1. BUSINESS

OVERVIEW

Cerus Corporation ("Cerus" or the "Company") is developing systems
designed to improve the safety of blood transfusions by inactivating infectious
pathogens in blood components (platelets, plasma and red blood cells) used for
transfusion and inhibiting the leukocyte activity that is responsible for
certain adverse immune and other transfusion-related reactions. Preclinical
studies conducted by the Company have indicated the ability of its systems to
inactivate a broad array of viral and bacterial pathogens that may be
transmitted in blood component transfusions and to inhibit leukocyte activity.
The Company believes that, as a result of the mechanism of action of its
proprietary technology, its systems also have the potential to inactivate many
new pathogens before they are identified and before tests have been developed to
detect their presence in the blood supply. Because the Company's systems are
being designed to inactivate rather than merely test for pathogens, these
systems also have the potential to reduce the risk of transmission of pathogens
that would remain undetected by testing.

The Company has completed four Phase 1 and Phase 2 clinical trials of
its platelet pathogen inactivation system in healthy subjects, and a Phase 2c
pilot patient study currently is underway. The Company has completed a Phase 1
clinical trial of its plasma pathogen inactivation system in healthy subjects,
with a Phase 2 study in healthy subjects currently underway. The Company's red
blood cell pathogen inactivation system is in preclinical development.

The Company's product development and commercialization programs are
being conducted pursuant to two agreements (the "Agreements") with Baxter
Healthcare Corporation ("Baxter") providing for development, manufacture and
marketing of pathogen inactivation systems for platelets, plasma and red blood
cells. The Agreements provide for Baxter and the Company to share development
expenses, for Baxter's exclusive right and responsibility to market the systems
worldwide and for the Company to receive a share of the gross profits from the
sale of the systems.

BACKGROUND

Blood transfusions are required to treat a variety of medical
conditions, including anemia, low blood volume, surgical bleeding, trauma,
acquired and congenital bleeding disorders and chemotherapy-induced blood
deficiencies. Worldwide, over 90 million whole blood donations occur each year.
Approximately 39 million of those donations occur in North America, Western
Europe and Japan, the major geographical markets for the Company's products. The
Company estimates the combined production in these regions of platelets, FFP and
red blood cells in 1995 to have been approximately 4 million, 9 million and 31
million, respectively.

Whole blood is composed of plasma, the liquid portion of blood
containing essential clotting proteins, and three cellular blood components:
platelets, red blood cells and white blood cells (leukocytes). Platelets are
essential to coagulation, while red blood cells carry oxygen to tissues and
carbon dioxide to the lungs. Leukocytes play a

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critical role in immune and other defense systems, but can cause harmful immune
transfusion-related reactions in, or transmit disease to, transfusion
recipients.

Patients requiring transfusions typically are treated with the specific
blood component required for their particular deficiency, except in cases of
rapid, massive blood loss, in which whole blood may be transfused. Platelets
often are used to treat cancer patients following chemotherapy or organ
transplantation. Red blood cells frequently are administered to patients with
trauma or surgical bleeding, acquired chronic anemia or genetic disorders, such
as sickle cell anemia. Plasma used for transfusions is stored in frozen form and
is referred to as fresh frozen plasma, or FFP. FFP generally is used to control
bleeding. Plasma also can be separated, or "fractionated," into different parts
that are used to expand blood volume, fight infections or treat diseases such as
hemophilia.

Despite recent improvements in donor screening and in the testing and
processing of blood, patients receiving transfusions of blood components face a
number of significant risks from blood contaminants, as well as adverse immune
and other transfusion-related reactions induced by leukocytes. Viruses such as
hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus (HIV),
cytomegalovirus (CMV) and human T-cell lymphotropic virus (HTLV) can present
life-threatening risks. In addition, bacteria, the most common agents of
transfusion-transmitted disease, can cause complications such as sepsis, which
can result in serious illness or death. Although donor screening and diagnostic
testing of donated blood have been successful in reducing the incidence of
transmission of many pathogens, diagnostic testing has a number of limitations,
such as the inability of most tests to detect pathogens prior to the generation
of antibodies, ineffectiveness in detecting genetic variants of viruses, and the
risk of human error. In addition, emerging or unidentified pathogens for which
no tests exist represent a threat to the blood supply. Because of the continuing
risk of transmission of serious diseases through transfusion of contaminated
blood components from both known and unknown pathogens, together with the
limitations of current approaches to providing a safe blood supply, there
remains a need for an approach to blood-borne pathogen inactivation that is
safe, easy to implement and cost-effective.

TECHNOLOGY AND PRODUCTS

The Company is developing pathogen inactivation systems employing its
proprietary small molecule compounds, which act by preventing the replication of
nucleic acid (DNA or RNA). Platelets, FFP and red blood cells do not contain
nuclear DNA or RNA. When the inactivation compounds are introduced into the
blood components for treatment, they cross bacterial cell walls or viral
membranes, then move into the interior of the nucleic acid structure. When
subsequently activated by an energy source, such as light, the compounds bind to
the nucleic acid of the viral or bacterial pathogen, preventing replication of
the nucleic acid. A virus, bacteria or other pathogenic cell must replicate in
order to cause infection. The Cerus compounds react in a similar manner with the
nucleic acid in leukocytes. This interaction inhibits the leukocyte activity
that is responsible for certain adverse immune and other transfusion-related
reactions. These compounds are designed to react with nucleic acid only during
the pathogen inactivation process and not after the treated blood component is
transfused. The systems are also designed to reduce the amount of unbound, or
residual, inactivation compound and breakdown products of the inactivation
process prior to transfusion.

CLINICAL DEVELOPMENT

The Company believes that, in deciding whether a pathogen inactivation
system is safe and effective, the United States Food and Drug Administration
(the "FDA") and foreign regulatory authorities are likely to take into account
whether it adversely affects the therapeutic efficacy of blood components as
compared to the therapeutic efficacy of blood components not treated with the
system, and that the FDA will weigh the system's safety, including potential
toxicities of the inactivation compounds, and other risks against the benefits
of using the system in a blood supply that has become safer in recent years. No
assurance can be given that any of the Company's development programs will be
successfully completed, that any further investigational new drug application
("IND") or investigational device exemption application ("IDE") will become
effective or that additional clinical trials will be allowed by the FDA or other
regulatory authorities, that clinical trials will commence or be completed as
anticipated, that required United States or foreign regulatory approvals will be
obtained on a timely basis, if at all, or that any products for which approval
is obtained will be commercially successful.

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<PAGE> 5

Based on discussions with the FDA, the Company believes that it will be
required to provide data from human clinical trials to demonstrate the safety of
treated blood components and their therapeutic comparability to untreated
components, but that only data from in vitro and animal studies, not data from
human clinical disease transmission studies, will be required to demonstrate the
system's efficacy in inactivating pathogens. In light of these criteria, the
Company's clinical trial programs are different from typical Phase 1, Phase 2
and Phase 3 clinical studies. There can be no assurance, however, that the
Company's program for demonstrating safety and efficacy will ultimately be
acceptable to the FDA or that the FDA will continue to believe that this
clinical plan is appropriate. See "Additional Business Risks - Uncertainty
Associated with Clinical and Preclinical Testing" and " -- Government
Regulation."

PRODUCTS IN DEVELOPMENT

The Company is developing treatment systems to inactivate infectious
pathogens in platelets, FFP and red blood cells and to inactivate leukocytes to
reduce the risk of certain adverse transfusion-related reactions. The following
table identifies the Company's product development programs:

<TABLE>
<CAPTION>
THERAPEUTIC CERUS PRODUCT IN INACTIVATION DEVELOPMENT
PROGRAM INDICATION DEVELOPMENT COMPOUND STATUS
- -------------------- ------------------ -------------------- ---------------- ------------------
<S> <C> <C> <C> <C>
Platelets Surgery, cancer Platelet Pathogen S-59 Phases 1a, 1b,
chemotherapy, Inactivation System 2a and 2b
transplantation, Clinical Trials
bleeding completed
disorders
Phase 2c
Clinical Trial
commenced in
November 1997

Plasma (FFP) Surgery, FFP Pathogen S-59 Phase 1 Clinical
transplantation, Inactivation System Trial completed
bleeding
disorders Phase 2 Clinical
Trial commenced
in January 1998

Red Blood Cells Surgery, Red Blood Cell S-303 Preclinical
transplantation, Pathogen Development;
anemia, cancer Inactivation lead compound
chemotherapy, System selected
trauma
</TABLE>

PLATELET PROGRAM

Platelets are cellular components of blood that are an essential part of
the clotting mechanism. Platelets facilitate blood clotting and wound healing by
adhering to damaged blood vessels and to other platelets. Platelet transfusions
are used to prevent or control bleeding in platelet-deficient (thrombocytopenic)
patients, such as those undergoing cancer chemotherapy or organ transplant.
Transfusion units of platelets are obtained either by combining the platelets
from four to six whole blood donations (pooled random donor platelets), or in an
automated procedure in which a therapeutic dose of platelets is obtained from a
single donor (apheresis or single donor platelets).

The Company's platelet pathogen inactivation system applies a technology
that combines light and the Company's proprietary inactivation compound, S-59,
which is a synthetic small molecule from a class of compounds known as
psoralens. S-59 was selected from over 100 psoralen derivatives synthesized by
the Company, following preclinical studies conducted by the Company to assess
safety and ability to inactivate pathogens and leukocytes while preserving
platelet function.

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<PAGE> 6
When illuminated, S-59 undergoes a specific and irreversible chemical
reaction with nucleic acid. This chemical reaction renders the genetic material
of a broad array of pathogens and cells incapable of replication. A virus,
bacteria or other pathogenic cell must replicate in order to cause infection. A
similar reaction with leukocyte nucleic acid inhibits the leukocyte activity
that is responsible for certain adverse immune and other transfusion-related
reactions. Most of the S-59 is converted to breakdown products during and after
the inactivation reaction. Studies conducted by the Company with preclinical
models have indicated that, following transfusion, the unbound S-59 and its
unbound breakdown products are rapidly metabolized and excreted. As a further
safety measure, the system under development employs a removal process designed
to reduce the amount of residual S-59 and unbound breakdown products prior to
transfusion (the S-59 reduction device or "SRD").

The Company's platelet pathogen inactivation system, developed with
Baxter, has been designed for use in the blood center setting. The system
consists of a disposable processing set, containing the S-59 compound and the
SRD, and an illumination device to deliver light to initiate the inactivation
reaction. The Company believes that, in order to manufacture the SRD for its
platelet pathogen inactivation system on a commercial scale, it will need to
modify the SRD configuration and the related manufacturing process. The Company
currently is pursuing such modification. There can be no assurance that use of a
reconfigured SRD will not cause the Company to have to conduct additional
clinical studies or otherwise to experience delays in the approval process.

Human clinical trials of the platelet pathogen inactivation system are
currently being pursued by the Company. Baxter is the sponsor of such trials. To
date, the Company has completed studies in healthy subjects that have
demonstrated the safety and tolerability and the recovery and lifespan of
platelets treated with the platelet pathogen inactivation system.

Based on the results of its Phase 2a clinical trial, the Company
submitted a protocol to the FDA for a Phase 3 randomized clinical study of
treated apheresis platelets in approximately 100 patients requiring platelet
transfusion. The Company reviewed this protocol with the FDA and agreed to
perform a pilot study in 15 patients prior to initiating the larger Phase 3
trial. This Phase 2c trial, currently underway, is a double blind, controlled
cross-over study in which double dose platelet transfusions are given to
thrombocytopenic patients and bleeding time correction and post-transfusion
platelet count increment are measured. The results of this pilot Phase 2c
clinical trial, given its small size, cannot satisfactorily be evaluated
statistically. Thus, non-statistically significant variations in bleeding times,
or other measures of the trial, may result in the FDA requiring additional
patients to be enrolled in the Phase 2c trial. Due to the nature of the trial,
its implementation and its assessment of bleeding times, enrollment of a
significant number of additional patients would be impracticable to accomplish
on a timely basis and could significantly delay completion of this trial and, as
a result, commencement of a Phase 3 clinical trial in the United States. This
Phase 2c trial currently is not expected to be completed until at least the
third quarter of 1998. In addition, there can be no assurance that, upon
completion of the pilot study, the FDA will permit initiation of a Phase 3 trial
in the United States. The Company has submitted a protocol to the ethical
committees in five European countries for a Phase 3 clinical trial of treated
apheresis and pooled random donor platelets in approximately 120 patients
requiring platelet transfusion. Approval to proceed has been obtained for four
of the five study sites, but patient enrollment has not yet commenced. The
primary endpoint in these Phase 3 studies will be the increase in
post-transfusion platelet count adjusted for platelet dose and patient size (the
"corrected count increment"). The Phase 3 European clinical trial is a
randomized study designed to assess the therapeutic efficacy of platelets
treated with the pathogen inactivation system for apheresis platelets and pooled
random donor platelets. The Phase 3 United States clinical trial is being
designed to assess the therapeutic efficacy of platelets treated with the
pathogen inactivation system for apheresis platelets, not pooled random donor
platelets. If the Company decides to seek FDA approval of the platelet pathogen
inactivation system for use in treating pooled random donor platelets, the
Company may be required by the FDA to conduct additional clinical studies.

FFP PROGRAM

Plasma is a noncellular component of blood that contains coagulation
factors and is essential for maintenance of intravascular volume. Plasma is
either separated from collected units of whole blood or collected directly by
apheresis. The collected plasma is then packaged and frozen to preserve the
coagulation factors. Some of the frozen plasma is made available for
fractionation, while some is designated for use as FFP. FFP is a source of all
blood clotting factors except platelets and is used to control bleeding in
patients who require clotting factors, such as

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patients undergoing transplants or other extensive surgical procedures, patients
with chronic liver disease or certain genetic clotting factor deficiencies.

The Company's pathogen inactivation system for FFP will use the same
S-59 psoralen compound and an SRD and illumination device similar to those being
used by the Company in its clinical trials for its platelet pathogen
inactivation system. The FFP pathogen inactivation system under development has
been designed for use in the blood center setting and is compatible with plasma
collected either manually or by apheresis.

In vitro studies conducted by the Company to date have indicated the
efficacy of the FFP pathogen inactivation system for the inactivation in FFP of
a broad array of viral pathogens. Because of the mechanism of action of its FFP
pathogen inactivation system, the Company believes that its system may also
inactivate protozoans and inhibit leukocyte activity. Although bacterial
contamination in FFP is typically not as significant a problem as in platelets,
the Company believes that the FFP pathogen inactivation system will inactivate
bacteria at the levels typically found in FFP. To date, the Company has
conducted no studies on protozoans or to detect inhibition of leukocyte activity
in FFP and only limited studies on bacteria in FFP, and there can be no
assurance that the Company's FFP pathogen inactivation system would effectively
inactivate protozoans, leukocytes or bacteria. The Company has assessed the
impact of S-59 photochemical treatment on the function of plasma proteins.
Plasma derived from whole blood or apheresis must be frozen within six to eight
hours of collection to meet the standard as "fresh frozen plasma." After
freezing, plasma may be stored for up to one year, thawed once, and must be
transfused within four hours of thawing. The Company has measured the in vitro
coagulation function activity of various clotting factors in FFP after
photochemical treatment, SRD treatment, freezing and thawing. These in vitro
results are not necessarily indicative of coagulation function that may be
obtained in vivo, and there can be no assurance that the FDA or foreign
regulatory authorities would view such levels of coagulation function as
adequate.

The Company has completed a clinical study in healthy subjects that has
demonstrated the safety and tolerability of FFP treated with the pathogen
inactivation system as well as the comparability of post-transfusion coagulation
factors between subjects transfused with treated and untreated FFP. A Phase 2
clinical trial commenced in January 1998 and is presently underway at three
trial sites. In this study, 30 healthy subjects will donate plasma, with
one-half being prepared and frozen as standard FFP and one-half being treated
with the Company's pathogen inactivation system and frozen as S-59 FFP. After
plasma collection, subjects will be treated with an oral anticoagulant to reduce
the levels of clotting factors II, VII, IX, and X. Following anticoagulant
therapy, subjects will be transfused with a therapeutic dose of either standard
FFP or S-59 FFP in random order. Following transfusion, the levels of clotting
factors II, VII, IX, and X will be measured and compared between S-59 and
standard FFP transfusions. The Phase 2 trial is designed to serve as a
transitional therapeutic efficacy study into a Phase 3 trial to evaluate the
therapeutic efficacy of S-59 FFP for several major therapeutic indications,
including chronic liver disease with minor surgery, liver transplant surgery,
and thrombotic thrombocytopenic purpura with multiple whole blood volume plasma
exchange. While the Company has presented this clinical trial plan to the FDA,
there can be no assurance that the FDA will concur with this trial plan.

RED BLOOD CELL PROGRAM

Red blood cells are essential components of blood that carry oxygen to
tissues and carbon dioxide to the lungs. Red blood cells may be transfused as a
single treatment in surgical and trauma patients with active bleeding or on a
repeated basis in patients with acquired anemia or genetic disorders, such as
sickle cell anemia, or in connection with chemotherapy.

The Company has developed a system for pathogen inactivation in red
blood cells using a compound that binds to nucleic acid in a manner similar to
that of S-59-based systems, but does not require light. The Company's method for
inactivating pathogens in red blood cells is based on a proprietary ALE
compound, S-303, a small molecule synthesized by the Company. The selection of
S-303 was based on preclinical studies of over 100 ALE compounds synthesized by
the Company to assess safety, stability and ability to inactivate pathogens,
while preserving red blood cell survival and function.

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<PAGE> 8

In vitro studies by the Company have indicated the efficacy of the ALE
process for the inactivation of a broad array of viral and bacterial pathogens
with preservation of red blood cell function. Because of the mechanism of action
of its red blood cell ALE treatment system, the Company believes that its system
may also inactivate protozoans and inhibit leukocyte function. However, the
Company has conducted no studies on protozoans or to detect inhibition of
leukocyte activity in red blood cells, and there can be no assurance that the
Company's red blood cell system would be effective to inactivate protozoans or
leukocytes. The Company is currently conducting good laboratory practice (GLP)
toxicology and pathogen inactivation validation studies on its red blood cell
pathogen inactivation system.

The Company has not filed to commence a Phase 1 clinical trial in red
blood cells. There can be no assurance as to whether Phase 1 trials, if
commenced, will be successful or as to the timing of these studies or the
acceptance of the design of these or any later studies by the FDA.

FUTURE PRODUCT DEVELOPMENT

The Company believes that the technology it has developed for treatment
of platelets, FFP and red blood cells may have application in treating other
blood products, including plasma fractions, such as Factor VIII and Factor IX
clotting factors, and recombinant equivalents of plasma derivatives. The Company
also believes that the compounds and processes it has developed for inactivation
of pathogens and leukocytes may have other medical applications in which
reactions with nucleic acid may serve to prevent or control the activities of
cells or microorganisms.

ALLIANCE WITH BAXTER

The Agreements with Baxter provide for the development, manufacture and
marketing of pathogen inactivation systems for platelets, FFP and red blood
cells. The Agreements generally provide for Baxter and the Company to share
development expenses equally, subject to mutually agreed budgets established
from time to time, and for Baxter's exclusive right and responsibility to market
the systems worldwide. Under the Agreements, the Company is to receive between
26.8% and 30.7% of revenues from sales of inactivation system disposables for
platelets after deducting from such revenues the amount by which Baxter's and
the Company's cost of goods for the inactivation system disposables exceeds
certain dollar amounts specified in the agreement (the "Premium"). The
percentage of Premium to be received by the Company will be determined on the
basis of the market price of the disposables; in no event, however, will the
amount to be received per inactivation system disposable be less than $8.50,
plus 2.2% of the Premium, nor more than $20.00, plus 2.2% of the Premium. For
red blood cells and FFP, the Company and Baxter are to share equally in gross
profits from sales of inactivation system disposables, after deducting from such
gross profits a specified percentage allocation to be retained by the marketing
party for marketing and administrative expenses. However, the revenue sharing
under this agreement is subject to adjustment upon the occurrence of certain
events, including any adjustments in the relative sharing by the parties of
development expenses. For red blood cells and FFP, the Company and Baxter are
also to receive their respective costs of goods for compounds and components
supplied for inactivation system disposables and the depreciation of certain
instruments used in the systems. For platelets, red blood cells and FFP, Baxter
will retain revenues from the sales of any related instruments, such as the
illumination devices used to activate S-59. The Company is obligated to supply
the inactivation compound for the systems, with Baxter supplying the remaining
components. Through December 31, 1997, Baxter paid the Company up-front license
fees and milestone and development payments totaling $14.8 million and invested
$17.5 million in the capital stock of the Company. Baxter currently owns
1,457,830 shares of the Company's common stock, or approximately 15.9% of the
Company's common stock currently outstanding. Baxter is obligated to make
additional equity investments, at 120% of the market price at the time of each
investment, subject to the achievement of certain milestones as follows: (i)
either $5 million, upon the achievement of both (a) the mutual determination by
the Company and Baxter that there is sufficient data to conclude that Phase 3
platelet trials are likely to satisfy specified criteria (the "Interim Platelet
Determination") and (b) the filing of a regulatory application with the FDA to
begin a Phase 1 study under the red blood cell program or comparable filing in
Europe under such program, or separate equity investments of $2 million upon the
Interim Platelet Determination, and $3 million upon the approval of a regulatory
application by the FDA under the red blood cell program or comparable approval
in Europe under such program; and (ii) $5 million, upon the achievement of both
(a) the approval by the FDA to commence a Phase 3 study in the United States or
comparable approval in

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Europe under the red blood cell program and (b) the approval by the FDA of an
application to market products developed under the platelet program or
comparable approval in Europe under such program.

Baxter has agreed that it will not at any time, nor will it permit any
of its affiliates to, own capital stock of the Company having 20.1% or more of
the outstanding voting power of the Company. Such restrictions on stock
purchases will not apply in the event a third party makes a tender offer for a
majority of the outstanding voting securities of the Company or if the Board of
Directors of the Company determines to liquidate or sell to a third party
substantially all of the assets or a majority of the voting securities of the
Company or to approve a merger or consolidation in which the Company's
stockholders will not own a majority of the voting securities of the surviving
entity.

In March 1998, the Company and Baxter entered into an amendment to one
of the Agreements providing that, to the extent the approved spending for 1998
for the red blood cell project exceeds $7.3 million, Cerus will fund all
expenses for the red blood cell project in 1998 in excess of such amount, up to
the amount of the approved budget. To compensate Cerus for such excess
expenditures, Baxter will fully fund the first expenditures under the approved
budget for the red blood cell project for 1999 in an amount equal to such excess
expenditures, after which the parties shall equally share the expenses of the
red blood cell project. If there is for any reason not an approved budget for
the red blood cell project for 1999, Baxter will fully fund the first
expenditures for 1999 under the approved budget for such other Cerus-Baxter
program or programs as Cerus shall designate in an amount equal to the Cerus
1998 excess expenditures. If by July 1, 1999, however, there is not an approved
budget for such other Cerus-Baxter program or programs that is at least equal to
such excess expenditures, Baxter will promptly pay to Cerus one-half of the
amount by which the excess expenditures exceed the amount of expenditures to be
funded by Baxter. Cerus anticipates that the expenditures for 1998 for the FFP
program will exceed the previously approved budget. Cerus and Baxter are
discussing each company's level of funding in 1998 for the FFP program. There
can be no assurance that the parties will agree on a budget that would permit
the FFP program to proceed in accordance with the Company's plans.

Baxter has certain discretion in decisions concerning the development
and marketing of pathogen inactivation systems. There can be no assurance that
Baxter will not elect to pursue alternative technologies or product strategies
or that its corporate interests and plans will remain consistent with those of
the Company. The Company is aware that Baxter is developing an alternative
pathogen inactivation system for FFP, based on a compound known as methylene
blue.

The Agreements contain restrictions on the Company's ability to develop
and market pathogen inactivation systems for blood components outside the
Agreements. The Company is entitled, however, to enter into development and
licensing agreements with third parties for pathogen inactivation technology for
plasma derivatives and recombinant equivalents of plasma derivatives. Such
development and licensing agreements are free of any rights of Baxter, except
that the Company must offer Baxter the right to license such technology on terms
no less favorable than the terms offered to other plasma derivative
manufacturers.

The development programs under the Agreements may be terminated by
Baxter or the Company on 90 days' notice. If either party so terminates as to a
program, the other party will gain exclusive development and marketing rights to
the program, and the terminating party's sharing in program revenues will be
reduced significantly. See "Additional Business Risks - Reliance on Baxter."

MANUFACTURING AND SUPPLY

The Company has in the past utilized, and intends to continue to
utilize, third parties to manufacture and supply the psoralen and ALE
inactivation compounds for its systems and to rely on Baxter to supply system
components for use in clinical trials and for the potential commercialization of
its products in development. The Company has no experience in manufacturing
products for commercial purposes and does not have any manufacturing facilities.
Consequently, the Company is dependent on contract manufacturers for the
production of compounds and on Baxter for other system components for
development and commercial purposes.

Under the Agreements, the Company is responsible for developing and
delivering its proprietary compounds for effecting pathogen inactivation to
Baxter for incorporation into the final system configuration. Baxter is
responsible for manufacturing or supplying the disposable units, such as blood
storage containers and

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related tubing, as well as any device associated with the inactivation process.
This arrangement applies both to the current supply for clinical trials and, if
applicable regulatory approvals are obtained, the future commercial supply. In
order to provide the inactivation compounds for its platelet and FFP pathogen
inactivation systems, the Company has contracted with two manufacturing
facilities for large-scale synthesis of S-59, although only one currently is
performing such synthesis and currently has a stock of compound sufficient to
support the anticipated remaining clinical trials planned for the platelet and
FFP pathogen inactivation systems. The Company has not contracted with a
manufacturer to produce large-scale quantities of S-303. There can be no
assurance that the Company will be able to contract for the manufacturing of
products and compounds for its pathogen inactivation systems in the future on
reasonable terms, if at all.

The Company purchases certain key components of its compounds from a
limited number of suppliers. While the Company believes that there are
alternative sources of supply for such components, establishing additional or
replacement suppliers for any of the components in the Company's compounds, if
required, may not be accomplished on a timely basis and could involve
significant additional costs. See "Additional Business Risks - Reliance on Third
Party Manufacturing; Dependence on Key Suppliers."

MARKETING, SALES AND DISTRIBUTION

If appropriate regulatory approvals are received, Baxter will be
responsible for the marketing, sales and distribution of the Company's pathogen
inactivation systems for blood components worldwide. The Company does not
currently maintain, nor does it intend to develop, its own marketing and sales
organization but instead expects to rely on Baxter to market and sell its
pathogen inactivation systems. There can be no assurance that the Company will
be able to maintain its relationship with Baxter or that such marketing
arrangements will result in payments to the Company. Revenues to be received by
the Company through any marketing and sales arrangement with Baxter will be
dependent on Baxter's efforts, and there can be no assurance that the Company
will benefit from Baxter's present or future market presence or that such
efforts will otherwise be successful. If the Agreements were terminated or if
Baxter's marketing efforts were unsuccessful, the Company's business, financial
condition and results of operations would be materially adversely affected.

COMPETITION

The Company expects to encounter competition in the sale of products it
may develop. If regulatory approvals are received, the Company's products may
compete with other approaches to blood safety currently in use, as well as with
future products developed by biotechnology and pharmaceutical companies,
hospital supply companies, national and regional blood centers, and certain
governmental organizations and agencies. Many companies and organizations that
may be competitors or potential competitors have substantially greater financial
and other resources than the Company and may have greater experience in
preclinical testing, human clinical trials and other regulatory approval
procedures. The Company's ability to compete successfully will depend, in part,
on its ability to develop proprietary products, develop and maintain products
that reach the market first, are technologically superior to and/or are of lower
cost than other products on the market, attract and retain scientific personnel,
obtain patent or other proprietary protection for its products and technologies,
obtain required regulatory approvals, and manufacture, market and sell any
product that it develops. In addition, other technologies or products may be
developed that have an entirely different approach or means of accomplishing the
intended purposes of the Company's products, or that might render the Company's
technology and products uncompetitive or obsolete. Furthermore, there can be no
assurance that the Company's competitors will not obtain patent protection or
other intellectual property rights that would limit the Company's ability to use
the Company's technology or commercialize products that may be developed.

Several companies are developing technologies which are, or in the
future may be, the basis for products that will directly compete with or reduce
the market for the Company's pathogen inactivation systems. A number of
companies are specifically focusing on alternative strategies for pathogen
inactivation or removal in various blood components. Although no commercial
processes are currently available to eliminate or inactivate pathogens in
platelets and red blood cells, a number of pathogen inactivation methods are
used commercially in Europe for FFP, including treatment with solvent-detergent
or methylene blue. Because the solvent-detergent process combines hundreds of
units of plasma into large pools, there is increased risk of transmission of
pathogens not inactivated by the process, such as parvovirus B19. In December
1996, the Blood Products Advisory Committee, an advisory panel

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to the FDA, unanimously recommended that solvent-detergent be approved for use
in treating FFP. Although recommendations of advisory committees are not
binding, unanimous recommendations generally are followed by the FDA. If
approved by the FDA, the treatment of FFP by solvent-detergent may become a
widespread practice prior to any commercialization of the Company's FFP pathogen
inactivation system, making such commercialization more difficult. Other groups
are developing synthetic blood product substitutes or products to stimulate the
growth of platelets. If any of these technologies is successfully developed, it
could have a material adverse effect on the Company's business, financial
condition and results of operations.

The Company believes that the primary competitive factors in the market
for pathogen inactivation systems will include the breadth and effectiveness of
pathogen inactivation processes, ease of use, the scope and enforceability of
patent or other proprietary rights, product price, product supply and marketing
and sales capability. In addition, the length of time required for products to
be developed and to receive regulatory and, in some cases, reimbursement
approval are important competitive factors. The Company believes it competes
favorably with respect to these factors, although there can be no assurance that
it will be able to continue to do so. The biopharmaceutical field is
characterized by rapid and significant technological changes. Accordingly, the
Company's success will depend in part on its ability to respond quickly to
medical and technological changes through the development and introduction of
new products. Product development involves a high degree of risk, and there can
be no assurance that the Company's product development efforts will result in
any commercially successful products.

Under the Agreements, Baxter has reserved the right to market competing
products not within the field of psoralen or ALE inactivation. Baxter is
conducting several independent product development efforts in blood collection
and processing that may improve blood component quality and safety. The Company
is aware that Baxter is developing an alternative pathogen inactivation system
for FFP, based on methylene blue. The development and commercialization of the
Company's pathogen inactivation systems could be materially adversely affected
by competition with Baxter or by Baxter's election to pursue alternative
strategies or technologies in lieu of those of the Company. See "Additional
Business Risks -- Rapid Technological Change; Significant Competition."

PATENTS, LICENSES AND PROPRIETARY RIGHTS

The Company's success depends in part on its ability to obtain patents,
to protect trade secrets, to operate without infringing upon the proprietary
rights of others and to prevent others from infringing on the proprietary rights
of the Company. The Company's policy is to seek to protect its proprietary
position by, among other methods, filing United States and foreign patent
applications related to its proprietary technology, inventions and improvements
that are important to the development of its business. As of December 31, 1997,
the Company owned 33 issued or allowed United States patents and 14 issued or
allowed foreign patents. The Company's patents expire at various dates between
2003 and 2015. In addition, the Company has 29 pending United States patent
applications and has filed 26 corresponding patent applications under the Patent
Cooperation Treaty, three of which are currently pending in Europe, Japan,
Australia and Canada. Proprietary rights relating to the Company's planned and
potential products will be protected from unauthorized use by third parties only
to the extent that they are covered by valid and enforceable patents or are
effectively maintained as trade secrets. There can be no assurance that any
patents owned by, or licensed to, the Company will afford protection against
competitors or that any pending patent applications now or hereafter filed by,
or licensed, to the Company will result in patents being issued. In addition,
the laws of certain foreign countries do not protect the Company's intellectual
property rights to the same extent as do the laws of the United States.

The patent positions of biopharmaceutical companies involve complex
legal and factual questions and, therefore, their enforceability cannot be
predicted with certainty. There can be no assurance that any of the Company's
patents or patent applications, if issued, will not be challenged, invalidated
or circumvented, or that the rights granted thereunder will provide proprietary
protection or competitive advantages to the Company against competitors with
similar technology. Furthermore, there can be no assurance that others will not
independently develop similar technologies or duplicate any technology developed
by the Company. Because of the extensive time required for development, testing
and regulatory review of a potential product, it is possible that, before any of
the Company's products can be commercialized, any related patent may expire or
remain in existence for only a short period following commercialization, thus
reducing any advantage of the patent, which could adversely affect the

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<PAGE> 12

Company's ability to protect future product development and, consequently, its
operating results and financial position.

Because patent applications in the United States are maintained in
secrecy until patents issue and since publication of discoveries in the
scientific or patent literature often lag behind actual discoveries, the Company
cannot be certain that it was the first to make the inventions covered by each
of its issued or pending patent applications or that it was the first to file
for protection of inventions set forth in such patent applications. There can be
no assurance that the Company's planned or potential products will not be
covered by third-party patents or other intellectual property rights, in which
case continued development and marketing of such products would require a
license under such patents or other intellectual property rights. There can be
no assurance that such required licenses will be available to the Company on
acceptable terms, if at all. If the Company does not obtain such licenses, it
could encounter delays in product introductions while it attempts to design
around such patents, or could find that the development, manufacture or sale of
products requiring such licenses is foreclosed. Litigation may be necessary to
defend against or assert such claims of infringement, to enforce patents issued
to the Company, to protect trade secrets or know-how owned by the Company or to
determine the scope and validity of the proprietary rights of others. In
addition, interference proceedings declared by the United States Patent and
Trademark Office may be necessary to determine the priority of inventions with
respect to patent applications of the Company. Litigation or interference
proceedings could result in substantial costs to and diversion of effort by the
Company, and could have a material adverse effect on the Company's business,
financial condition and results of operations. There can be no assurance that
these efforts by the Company would be successful.

The Company is a licensee under a worldwide exclusive license agreement
with Miles, Inc. and Diamond Scientific Corporation with respect to two United
States patents covering inventions pertaining to psoralen-based photochemical
decontamination treatment of whole blood or blood components and four United
States patents relating to vaccines, as well as related foreign patents. Whether
the Company's psoralen-based pathogen inactivation systems practice either of
the photochemical decontamination patents depends on an interpretation of the
scope of the patent claims. If such systems practice such patents, the license
provides for Cerus to make milestone payments and pay royalties on revenues
Cerus receives from sales of such systems. The license also calls for minimum
annual royalty payments in order to maintain certain exclusive rights. The
manner in which any such milestone payments and royalties would be shared by
Baxter, if at all, has not been determined.

The Company may rely, in certain circumstances, on trade secrets to
protect its technology. However, trade secrets are difficult to protect. The
Company seeks to protect its proprietary technology and processes, in part, by
confidentiality agreements with its employees and certain contractors. There can
be no assurance that these agreements will not be breached, that the Company
will have adequate remedies for any breach, or that the Company's trade secrets
will not otherwise become known or be independently discovered by competitors.
To the extent that the Company's employees or its consultants or contractors use
intellectual property owned by others in their work for the Company, disputes
may also arise as to the rights in related or resulting know-how and inventions.

In August 1996, the Company received correspondence from Circadian
Technologies, Inc., an Australian entity, alleging that unspecified trade
secrets and know-how jointly owned by Circadian and the Auckland Division Cancer
Society of New Zealand were, without the consent of Circadian, used in the
development by the Cancer Society and the Company of unspecified compounds for
the Company's red blood cell program. Such claims do not relate to the Company's
platelet or FFP programs. In subsequent correspondence, Circadian has indicated
that it is seeking compensation in the form of royalties or a lump sum payment.
Based on its investigation of the matter to date, the Company does not believe
that the claims are meritorious. Any future litigation involving these
allegations, however, would be subject to inherent uncertainties, especially in
cases where complex technical issues are decided by a lay jury. There can be no
assurance that, if a lawsuit were commenced, it would not be decided against the
Company, which could have a material adverse effect upon the Company's business,
financial condition and results of operations.

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GOVERNMENT REGULATION

The Company and its products are comprehensively regulated in the United
States by the FDA and, in some instances, by state and local governments, and by
comparable governmental authorities in other countries. The FDA regulates drugs,
medical devices, and biologics under the Federal Food, Drug and Cosmetic Act and
other laws, including, in the case of biologics, the Public Health Service Act.
These laws and implementing regulations govern, among other things, the
development, testing, manufacturing, record keeping, storage, labeling
advertising, promotion and premarket clearance or approval of products subject
to regulation.

The Company believes its pathogen inactivation systems will be regulated
by the FDA as devices. It is also possible, however, that the FDA will decide to
regulate the pathogen inactivation systems as biologics, as drugs, as
combination products including drugs or biologics and one or more medical
devices, or as drugs or biologics with one or more medical devices (i.e., the
blood bags and light source) requiring separate approval or clearance. Whether
the FDA regulates the pathogen inactivation systems as devices or as one or more
of the other alternatives, it is likely that the FDA's Center for Biologics
Evaluation and Research will be principally responsible for regulating the
pathogen inactivation systems.

Before a medical device may be marketed in the United States, the FDA
must clear a pre-market notification (a "510(k)") or approve a pre-market
approval application ("PMA") for the product. Before a new drug may be marketed
in the United States, the FDA must approve an NDA for the product. Before a
biologic may be marketed in the United States, the FDA must approve a Biologic
License Application ("BLA"). Before a combination product can be marketed in the
United States, it must have an approved NDA, BLA or PMA, depending on which
statutory authority the FDA elects to use.

Despite the multiplicity of statutory and regulatory possibilities, the
steps required before approval are essentially the same whether the product is
ultimately regulated as a medical device, biologic, drug, a combination product,
or a combination thereof. The steps required before a medical device, drug or
biologic may be approved for marketing in the United States pursuant to a PMA,
BLA or NDA, respectively, generally include (i) preclinical laboratory and
animal tests, (ii) submission to the FDA of an investigational device exemption
("IDE") (for medical devices) or an IND (for drugs or biologics) for human
clinical testing, which must become effective before human clinical trials may
begin (iii) appropriate tests to show the product's safety, (iv) adequate and
well-controlled human clinical trials to establish the product's efficacy for
its intended indications, (v) submission to the FDA of a PMA, BLA or NDA, as
appropriate and (vi) FDA review of the PMA, BLA or NDA in order to determine,
among other things, whether the product is safe and effective for its intended
uses. In addition, the FDA inspects the facilities at which the product is
manufactured and will not approve the product unless compliance with current
Good Manufacturing Practices ("cGMP") requirements is satisfactory. The steps
required before a medical device may be cleared for marketing in the United
States pursuant to a 510(k) are generally the same, except that instead of
conducting tests to demonstrate safety and efficacy, data, including clinical
data if necessary, must be obtained to show that the product is substantially
equivalent to a legally marketed device, and the FDA must make a determination
of substantial equivalence rather than a determination that the product is safe
and effective.

The Company believes that, in deciding whether a pathogen inactivation
system is safe and effective, the FDA is likely to take into account whether it
adversely affects the therapeutic efficacy of blood components as compared to
the therapeutic efficacy of blood components not treated with the system, and
that the FDA will weigh the system's safety, including potential toxicities of
the inactivation compounds, and other risks against the benefits of using the
system in a blood supply that has become safer in recent years. There can be no
assurance that the FDA will not require further toxicology studies of the
Company's products.

Based on discussions with the FDA, the Company believes that it will be
required to provide data from human clinical studies to demonstrate the safety
of treated platelets and their therapeutic comparability to untreated platelets,
but that only data from in vitro and animal studies, not data from human
clinical studies, will be required to demonstrate the system's efficacy in
inactivating pathogens. In light of these criteria, the Company's clinical trial
programs for platelets and FFP will consist of studies that differ from the
usual Phase 1, Phase 2 and Phase 3 clinical studies.

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There can be no assurance, however, that these means of demonstrating
safety and efficacy will ultimately be acceptable to the FDA or that the FDA
will continue to believe that this clinical plan is appropriate. Moreover, even
if the FDA considers these means of demonstrating safety and efficacy to be
acceptable in principle, there can be no assurance that the FDA will find the
data submitted sufficient to demonstrate safety and efficacy. In particular,
although the Company anticipates that the FDA will consider in vitro and animal
data an appropriate means of demonstrating efficacy in pathogen inactivation,
there can be no assurance that the FDA will so conclude, and any requirement to
provide other than in vitro and animal data would adversely affect the timing
and could affect the success of the Company's efforts to obtain regulatory
approval.

Even if regulatory approval or clearance is granted, it could include
significant limitations on the indicated uses for which a product could be
marketed. For example, the Company does not believe that it will be able to make
any labeling claims that the Company's pathogen inactivation systems may
inactivate any pathogens for which it does not have in vitro, and in certain
cases animal, data supporting such claims. The testing and approval/clearance
process requires substantial time, effort and financial resources, and is
generally lengthy, expensive and uncertain. The approval process is affected by
a number of factors, including the availability of alternative treatments and
the risks and benefits demonstrated in clinical trials. Additional animal
studies or clinical trials may be requested during the FDA review period and may
delay marketing approval. After FDA approval for the initial indications,
further clinical trials may be necessary to gain approval for the use of the
product for additional indications. The FDA may also require post-marketing
testing to monitor for adverse effects, which can involve significant expense.
Later discovery of previously unknown problems with a product may result in
restrictions on the product, including withdrawal of the product from the
market. In addition, the policies of the FDA may change, and additional
regulations may be promulgated which could prevent or delay regulatory approval
of the Company's planned products. There can be no assurance that any approval
or clearance will be granted on a timely basis, if at all. Any failure to obtain
or delay in obtaining such approvals or clearances, and any significant
limitation on their indicated uses, could have a material adverse effect on the
Company's business, financial condition and results of operations.

A medical device, biologic or drug, its manufacturer, and the holder of
the PMA or 510(k), BLA or NDA for the product are subject to comprehensive
regulatory oversight, both before and after approval or clearance is obtained.
Violations of regulatory requirements at any stage, including during the
preclinical and clinical testing process, during the approval/clearance process
or after the product is approved/cleared for marketing, could result in various
adverse consequences, including the FDA's requiring that a clinical trial be
suspended or halted, the FDA's delay in approving/clearing or refusing to
approve/clear a product, withdrawal of an approved/cleared product from the
market and the imposition of criminal penalties. For example, the holder of a
PMA or 510(k), BLA or NDA is required to report certain adverse reactions to the
FDA, and must comply with certain requirements concerning advertising and
promotional labeling for the product. Also, quality control and manufacturing
procedures must continue to conform to cGMP regulations after approval or
clearance, and the FDA periodically inspects manufacturing facilities to assess
compliance with cGMP. Accordingly, manufacturers must continue to expend time,
monies and efforts on regulatory compliance, including cGMP compliance. In
addition, new government requirements may be established that could delay or
prevent regulatory approval or clearance of the Company's products under
development or otherwise alter the applicable law. There can be no assurance
that the FDA will determine that the facilities and manufacturing procedures of
Baxter or any other third-party manufacturer of the Company's planned products
will conform to cGMP requirements.

In addition to the regulatory requirements applicable to the Company and
its products, there are also regulatory requirements applicable to the Company's
prospective customers, which are primarily entities that ship blood and blood
products in interstate commerce. Such entities are regulated by the FDA pursuant
to the Food, Drug and Cosmetic Act and the Public Health Service Act and
implementing regulations. Blood centers and others that ship blood and blood
products interstate will likely be required to obtain approved license
supplements from the FDA before shipping products processed with the Company's
pathogen inactivation systems. This requirement and/or FDA delays in approving
such supplements may deter some blood centers from using the Company's products,
and blood centers that do submit supplements may face disapproval or delays in
approval that could provide further disincentives to use of the systems. The
regulatory impact on potential customers could have a material adverse effect on
the Company's business, financial condition and results of operations.

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The Phase 3 European clinical trial is being designed to assess the
therapeutic efficacy of the platelet pathogen inactivation system for use in
treating apheresis platelets and pooled random donor platelets. The Phase 3
United States clinical trial is being designed to assess the therapeutic
efficacy of the platelet pathogen inactivation system for use in treating
apheresis platelets, not pooled random donor platelets, which represent 55% and
45% of the market, respectively. If the Company decides to seek FDA approval of
the platelet pathogen inactivation system for use in treating pooled random
donor platelets, the Company may be required by the FDA to conduct additional
clinical studies. In addition, there currently are three principal manufacturers
of automated apheresis collection equipment used in the United States, including
Baxter. The equipment of each manufacturer collect platelets into plastic
disposables designed for that equipment; thus, a pathogen inactivation system
designed for disposables used by one manufacturer will not necessarily be
compatible with other manufacturers' collection equipment. The Company intends
initially to seek FDA approval of a platelet pathogen inactivation system
configured for Baxter's aphersis collection equipment. If the Company determines
that compatibility with other equipment is desirable, it will need to develop
additional processing procedures. Although the Company believes that the FDA
would accept the clinical data from the original system for platelets collected
using other equipment and procedures and would require only limited additional
studies to show comparability, there can be no assurance that it would do so.

Because of the risk of bacterial growth, current FDA rules require that
platelets may not be stored for more than five days after collection from the
donor. The rules also require that pooled platelets be transfused within four
hours of pooling and, as a result, most pooling occurs at hospitals. However,
the Company's platelet pathogen inactivation system is being designed to be used
at blood centers, not at hospitals, and requires a processing time of
approximately eight hours. Therefore, in order for the Company's platelet
pathogen inactivation system to be effectively implemented and accepted at blood
centers as planned, the FDA-imposed limit on the time between pooling and
transfusion would need to be lengthened or eliminated for blood products treated
with the Company's systems, which are being designed to inactivate bacteria that
would otherwise contaminate pooled platelets. If the Company were to pursue the
pooled random donor platelet market, it would need to work with the FDA during
the approval/clearance process to obtain the necessary changes in these
limitations. There can be no assurance, however, that the FDA would change this
requirement and, if such a change were not made, the Company's business,
financial condition and results of operations would be materially adversely
affected.

The Company is developing a European investigational plan based on the
platelet and FFP treatment systems using S-59 being categorized as Class III
devices under European Union regulatory authorities. However, there can be no
assurance that this approach will be accepted by European authorities. The
European Union has promulgated rules that require that medical devices receive
by mid-1998 the right to affix the CE Mark, an international symbol of adherence
to quality assurance standards and compliance with applicable European medical
device directives. Failure to receive CE Mark certification will prohibit the
Company from selling its products in the European Union.

The Company is subject to federal, state and local laws, rules,
regulations and policies governing the use, generation, manufacture, storage,
air emission, effluent discharge, handling and disposal of certain materials,
biological specimens and wastes. There can be no assurance that the Company will
not be required to incur significant costs to comply with environmental and
health and safety regulations in the future. The Company's research and
development involves the controlled use of hazardous materials, including
certain hazardous chemicals and radioactive materials. Although the Company
believes that its safety procedures for handling and disposing of such materials
comply with the standards prescribed by state and federal regulations, the risk
of accidental contamination or injury from these materials cannot be eliminated.
In the event of such an accident, the Company could be held liable for any
damages that result and any such liability could exceed the resources of the
Company.

EMPLOYEES

As of February 28, 1998, the Company had 76 employees, 59 of whom were
engaged in research and development and 17 in finance and other administration.
The Company also had consulting arrangements with nine individuals. No employee
of the Company is covered by collective bargaining agreements, and the Company
believes that its relationship with its employees is good.

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ADDITIONAL BUSINESS RISKS

The Company's business is subject to the following risks in addition to
those discussed above and elsewhere in this report.

Early Stage of Product Development. The Company's pathogen inactivation
systems for blood transfusion components are in the research and development
stage and will require additional preclinical and clinical testing prior to
submission of any regulatory application for commercial use. The Company has not
commenced the large-scale clinical trials that would, if successful, lead to
filing product approval applications with the FDA. The Company's products are
subject to the risks of failure inherent in the development of medical device,
pharmaceutical and biological products and products based on new technologies.
These risks include the possibility that the Company's approach to pathogen
inactivation will not be safe or effective, that the Company's products will not
be easy to use or cost-effective, that third parties will develop and market
superior or equivalent products, that any or all of the Company's products will
fail to receive any necessary regulatory approvals, that such products will be
difficult or uneconomical to manufacture on a commercial scale, that proprietary
rights of third parties will preclude the Company from marketing such products
and that the Company's products will not achieve market acceptance. As a result
of these risks, there can be no assurance that the Company's research and
development activities will result in any commercially viable products.

Uncertainty Associated with Preclinical and Clinical Testing. The
regulatory process includes preclinical and clinical testing of each product to
establish its safety and efficacy, and may include post-marketing studies
requiring expenditure of substantial resources. The results from preclinical
studies and early clinical trials conducted by the Company may not be predictive
of results obtained in later clinical trials, and there can be no assurance that
clinical trials conducted by the Company will demonstrate sufficient safety and
efficacy to obtain the requisite approvals or that marketable products will
result. For example, at the request of the FDA, the Company designed and
commenced a pilot Phase 2c clinical trial in 15 thrombocytopenic patients to
assess the effect of treated platelets on post-transfusion bleeding time
correction and platelet count increment. The results of this pilot Phase 2c
clinical trial, given its small size, cannot satisfactorily be evaluated
statistically. Thus, non-statistically significant variations in bleeding times,
or other measures of the trial, may result in the FDA requiring additional
patients to be enrolled in the Phase 2c trial. Due to the nature of the trial,
its implementation and its assessment of bleeding times, enrollment of a
significant number of additional patients could be impracticable to accomplish
on a timely basis and could significantly delay completion of this trial and, as
a result, commencement of the proposed Phase 3 clinical trial. This Phase 2c
trial currently is not expected to be completed until at least the third quarter
of 1998. The rate of completion of the Company's clinical trials may be delayed
by many other factors, including slower than anticipated patient enrollment or
any other adverse event occurring during the clinical trials. Completion of
testing, studies and trials may take several years, and the length of time
generally varies substantially with the type, complexity, novelty and intended
use of the product. Data obtained from preclinical and clinical activities are
susceptible to varying interpretations, which could delay, limit or prevent
regulatory approval. In addition, delays or rejections may be encountered based
upon many factors, including changes in regulatory policy during the period of
product development. The Company's products under development require
significant additional research and development efforts. No assurance can be
given that any of the Company's development programs will be successfully
completed, that any further INDs or IDEs will become effective or that
additional clinical trials will be allowed by the FDA or other regulatory
authorities, that clinical trials will commence as planned, that required United
States or foreign regulatory approvals will be obtained on a timely basis, if at
all, or that any products for which approval is obtained will be commercially
successful. Due to the uncertain nature of clinical trial programs, there can be
no assurance that the proposed schedules for IND or IDE and clinical protocol
submissions to the FDA, initiations of studies and completions of clinical
trials can be maintained. Any delays in the Company's clinical trials or
failures to obtain required regulatory approvals would have a material adverse
effect on the Company's business, financial condition and results of operations.

Reliance on Baxter. Under the terms of the Agreements, the Company
relies on Baxter for significant funding, product development support, the
manufacture and supply of certain system components and the marketing of its
planned products. The Company anticipates that, prior to commencement of product
sales, if any, the Company's principal source of revenue will continue to be
payments under the Agreements.

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The development programs under the Agreements may be terminated by
Baxter on 90 days' notice. If the Agreements were terminated, if Baxter failed
to provide the committed funding or if Baxter's product development efforts were
unsuccessful, the Company may need to obtain additional funding from other
sources and would be required to devote additional resources to the development
of its products, delaying the development of its products. Any such delay would
have a material adverse effect on the Company's business, financial condition
and results of operations. There can be no assurance that disputes will not
arise in the future with respect to the Agreements. Possible disagreements
between Baxter and the Company could lead to delays in the research, development
or commercialization of certain planned products or could require or result in
time-consuming and expensive litigation or arbitration and would have a material
adverse effect on the Company's business, financial condition and results of
operations.

Under the terms of the Agreements, Baxter is responsible for
manufacturing the disposable units, such as blood storage containers and related
tubing, as well as any devices associated with the inactivation processes. If
the Agreements were terminated or if Baxter otherwise failed to deliver an
adequate supply of components, the Company would be required to identify other
third-party component manufacturers. There can be no assurance that the Company
would be able to identify such manufacturers on a timely basis or enter into
contracts with such manufacturers on reasonable terms, if at all. Any delay or
change in the availability of devices or disposables from Baxter or its
suppliers could adversely affect the timely submission of products for
regulatory approval or the market introduction and subsequent sales of such
products and would have a material adverse effect on the Company's business,
financial condition and results of operations. Moreover, the inclusion of
components manufactured by others could require the Company to seek new
approvals from government regulatory authorities, which could result in delays
in product delivery. There can be no assurance that the Company would receive
any such required regulatory approvals. Any such delay would have a material
adverse effect on the Company's business, financial condition and results of
operations.

The Agreements provide for key decision-making regarding development and
commercialization by a management board comprised of equal representation from
Baxter and the Company and, in the case of FFP and red blood cells, one
independent member. There can be no assurance that such board's decisions will
be consistent with the Company's interests, that Baxter will not elect to pursue
alternative technologies or product strategies or that its corporate interests
and plans will remain consistent with those of the Company. In the Agreements,
Baxter agreed to certain limited restrictions on its ability to independently
develop and market products that compete with the products under the Agreements.
There can be no assurance that these provisions will prevent Baxter from
developing or marketing competing products. The Company is aware that Baxter is
developing an alternative pathogen inactivation system for FFP based on
methylene blue. The development and commercialization of the Company's pathogen
inactivation systems could be materially adversely affected by competition with
Baxter or by Baxter's election to pursue alternative strategies or technologies
in lieu of those of the Company.

Government Regulation. All of the Company's products under development
and anticipated future products are or will be subject to extensive and rigorous
regulation by the federal government (principally the FDA) and state, local, and
foreign governments. Such regulations govern, among other things, the
development, testing, manufacturing, labeling, storage, pre-market clearance or
approval, advertising, promotion, sale and distribution of such products. The
process of obtaining regulatory approvals or clearances is generally lengthy,
expensive and uncertain. To date, none of the Company's products under
development has been approved for sale in the United States or any foreign
market. Satisfaction of pre-market approval or clearance or other regulatory
requirements of the FDA, or similar requirements of foreign regulatory agencies,
typically takes several years, and may take longer,

15
<PAGE> 18

depending upon the type, complexity, novelty and intended use of the product.
There can be no assurance that the FDA or any other regulatory agency will grant
approval or clearance for any product being developed by the Company on a timely
basis, if at all. If regulatory approval of a product is granted, such approval
may impose limitations on the indicated uses for which a product may be
marketed. Further, even if regulatory approval is obtained, later discovery of
previously unknown problems with a product may result in restrictions on the
product, including withdrawal of the product from the market. The policies of
the FDA and foreign regulatory bodies may change, and additional regulations may
be promulgated, which could prevent or delay regulatory approval of the
Company's planned products. Delay in obtaining or failure to obtain regulatory
approvals could have a material adverse effect on the Company's business,
financial condition and results of operations. Among the conditions for FDA
approval of a pharmaceutical, biologic or device is the requirement that the
manufacturer's quality control and manufacturing procedures conform to cGMP
requirements, which must be followed at all times. The FDA enforces cGMP
requirements through periodic inspections. There can be no assurance that the
FDA will determine that the facilities and manufacturing procedures of Baxter or
any other third-party manufacturer of the Company's planned products will
conform to cGMP requirements.

Blood centers and others that ship blood and blood products interstate
will likely be required to obtain approved license supplements from the FDA
before shipping products processed with the Company's pathogen inactivation
systems. This requirement and/or FDA delays in approving such supplements may
deter some blood centers from using the Company's products, and blood centers
that do submit supplements may face disapproval or delays in approval that could
provide further disincentives to use the systems. The regulatory impact on
potential customers could have a material adverse effect on the Company's
business, financial condition and results of operations.

No Assurance of Market Acceptance; Concentrated Market. The Company
believes that market acceptance of the Company's pathogen inactivation systems
will depend, in part, on the Company's ability to provide acceptable evidence of
the safety, efficacy and cost-effectiveness of its products, as well as the
ability of blood centers to obtain FDA approval and adequate reimbursement for
such products. The Company believes that market acceptance of its pathogen
inactivation systems also will depend upon the extent to which physicians,
patients and health care payors perceive that the benefits of using blood
components treated with the Company's systems justify the systems' additional
costs and processing requirements in a blood supply that has become safer in
recent years. While the Company believes that its pathogen inactivation systems
are able to inactivate pathogens in excess of concentrations that the Company
believes typically are present in contaminated blood components when the blood
is donated, there can be no assurance that contamination levels will never
exceed the capacity of the Company's pathogen inactivation systems. The Company
does not expect that its planned products will be able to inactivate all known
and unknown infectious pathogens, and there can be no assurance that the
inability to inactivate certain pathogens will not affect the market acceptance
of its products. There can be no assurance that the Company's pathogen
inactivation systems will gain any significant degree of market acceptance among
blood centers, physicians, patients and health care payors, even if clinical
trials demonstrate safety and efficacy and necessary regulatory approvals and
health care reimbursement approvals are obtained.

In the United States, approximately 55% of platelets are collected by
apheresis. The Company's Phase 3 United States clinical trial protocol for its
platelet pathogen inactivation system has been designed to assess the
therapeutic efficacy of such system in treating apheresis platelets only. There
can be no assurance that the market share for apheresis platelets will increase.
If such market share does not increase, the Company may decide to conduct
additional clinical studies in order to obtain FDA approval of the system for
use in treating random donor platelets. In addition, there currently are three
principal manufacturers of automated apheresis collection equipment used in the
United States, including Baxter. The equipment of each manufacturer collect
platelets into plastic disposables designed for that equipment; thus, a pathogen
inactivation system designed for disposables used by one manufacturer will not
necessarily be compatible with the other manufacturers' collection equipment.
The Company intends initially to seek FDA approval of a platelet pathogen
inactivation system configured for Baxter's apheresis collection equipment. If
the Company determines that compatibility with other equipment is desirable, it
will need to develop additional processing procedures. Although the Company
believes that the FDA would accept the clinical data from the original system
for platelets collected using other equipment and procedures and would require
only limited additional studies to show comparability, there can be no assurance
that it would do so.

16
<PAGE> 19

The Company's target customers are the limited number of national and
regional blood centers, which collect, store and distribute blood and blood
components. The failure to penetrate even a small number of these customers
could have a material adverse effect on the Company's business, financial
condition and results of operations.

Rapid Technological Change; Significant Competition. The
biopharmaceutical field is characterized by rapid and significant technological
change. Accordingly, the Company's success will depend in part on its ability to
respond quickly to medical and technological changes through the development and
introduction of new products. Product development involves a high degree of
risk, and there can be no assurance that the Company's product development
efforts will result in any commercially successful products. Technological
developments may result in the Company's products becoming obsolete or
non-competitive before the Company is able to generate any significant revenue.
Any such occurrence would have a material adverse effect on the Company's
business, financial condition and results of operations.

The Company expects to encounter competition in the sale of products it
may develop, and its success will be dependent upon its ability to compete. Many
companies and organizations that may be competitors or potential competitors
have substantially greater financial and other resources than the Company and
may have greater experience in preclinical testing, human clinical trials and
other regulatory approval procedures. The Company's ability to compete
successfully will depend, in part, on its ability to develop proprietary
products, develop and maintain products that reach the market first, are
technologically superior to and/or are of lower cost than other products on the
market, attract and retain scientific personnel, obtain patent or other
proprietary protection for its products and technologies, obtain required
regulatory approvals, and manufacture, market and sell any product that it
develops. In addition, other technologies or products may be developed that have
an entirely different approach or means of accomplishing the intended purposes
of the Company's products, or that might render the Company's technology and
products uncompetitive or obsolete. Furthermore, there can be no assurance that
the Company's competitors will not obtain patent protection or other
intellectual property rights that would limit the Company's ability to use the
Company's technology or commercialize products that may be developed.

Dependence on Key Employees. The Company is highly dependent on the
principal members of its management and scientific staff. The loss of the
services of one or more of these employees could have a material adverse effect
on the Company's business, financial condition and results of operations. The
Company believes that its future success will depend in large part upon its
ability to attract and retain highly skilled scientific and managerial
personnel. Competition for such personnel is intense. There can be no assurance
that the Company will be successful in attracting and retaining such personnel
and the failure to do so could have a material adverse effect on the Company's
business, financial condition and results of operations. In addition, a
substantial portion of the stock options currently held by many of the Company's
key employees are vested and may be fully vested over the next several years
before the Company achieves significant revenues or profitability. The Company
intends to grant additional options and provide other forms of incentive
compensation to attract and retain such key personnel, although there can be no
assurance such objective will be achieved.

Patent and License Uncertainties. The Company's success depends in part
on its ability to obtain patents, to protect trade secrets, to operate without
infringing upon the proprietary rights of others and to prevent others from
infringing on the proprietary rights of the Company. There can be no assurance
that any patents owned by, or licensed to, the Company will afford protection
against competitors or that any pending patent applications now or hereafter
filed by, or licensed to, the Company will result in patents being issued. In
addition, the laws of certain foreign countries do not protect the Company's
intellectual property rights to the same extent as do the laws of the United
States. There can be no assurance that the Company's planned or potential
products will not be covered by third-party patents or other intellectual
property rights, in which case continued development and marketing of such
products would require a license under such patents or other intellectual
property rights. There can be no assurance that such required licenses will be
available to the Company on acceptable terms, if at all. If the Company does not
obtain such licenses, it could encounter delays in product introductions while
it attempts to design around such patents, or could find that the development,
manufacture or sale of products requiring such licenses is foreclosed.
Litigation may be necessary to defend against or assert claims of infringement,
to enforce patents issued to the Company, to protect trade secrets or know-how
owned by the Company or to determine the scope and validity of the proprietary
rights of others. In addition, interference proceedings declared by the United
States Patent and Trademark Office may be necessary to determine the priority of
inventions with respect to patent applications of the

17
<PAGE> 20

Company. Litigation or interference proceedings could result in substantial
costs to and diversion of effort by the Company, and could have a material
adverse effect on the Company's business, financial condition and results of
operations. The Company may rely, in certain circumstances, on trade secrets to
protect its technology. However, trade secrets are difficult to protect. The
Company seeks to protect its proprietary technology and processes, in part, by
confidentiality agreements with its employees and certain contractors. There can
be no assurance that these agreements will not be breached, that the Company
will have adequate remedies for any breach, or that the Company's trade secrets
will not otherwise become known or be independently discovered by competitors.

Limited Operating History; History of Losses and Expectation of Future
Losses. The Company's net losses in fiscal years 1997, 1996 and 1995 were
$14.7 million, $10.2 million and $2.4 million, respectively. As of December 31,
1997, the Company had an accumulated deficit of approximately $34.9 million. The
Company has not received any revenues from product sales, and all revenues
recognized by the Company to date have resulted from the Agreements and federal
research grants. All of the Company's planned pathogen inactivation systems are
in the research and development stage. The Company will be required to conduct
significant research, development, testing and regulatory compliance activities
on these products that, together with anticipated general and administrative
expenses, are expected to result in substantial losses in future periods. The
Company expects that the amount of such losses will fluctuate from quarter to
quarter as a result of differences in the timing of expenses incurred and
potential revenues from Baxter under the Agreements, and such fluctuations may
be significant. The Company's ability to achieve a profitable level of
operations will depend on successfully completing development, obtaining
regulatory approvals and achieving market acceptance of its pathogen
inactivation systems. There can be no assurance that the Company will ever
achieve a profitable level of operations.

Reliance on Third-Party Manufacturing; Dependence on Key Suppliers. The
Company has no experience in manufacturing products for commercial purposes and
does not have any manufacturing facilities. Consequently, the Company is
dependent on contract manufacturers for the production of compounds and on
Baxter for other system components for development and commercial purposes.
There can be no assurance that existing manufacturers or any new manufacturer
will be able to provide sufficient quantities of the compounds needed for the
Company's pathogen inactivation systems in the future or that the Company will
be able to enter into arrangements for the commercial-scale manufacture of such
compounds on reasonable terms, if at all.

In the event that the Company is unable to obtain or retain third-party
manufacturing, it will not be able to commercialize its products as planned.
Failure of any third-party manufacturer to deliver the required quantities of
products on a timely basis and at commercially reasonable prices would
materially adversely affect the Company's business, financial condition and
results of operations. In addition, inclusion of components manufactured by
other third parties could require the Company to seek new approvals from
government regulatory authorities, which could result in delays in product
delivery. There can be no assurance that such approval would be obtained. In the
event the Company undertakes to establish its own commercial manufacturing
capabilities, it will require substantial additional funds, manufacturing
facilities, equipment and personnel.

The Company purchases certain key components of its compounds from a
limited number of suppliers. While the Company believes that there are
alternative sources of supply for these components, establishing additional or
replacement suppliers for any of the components in the Company's compounds, if
required, may not be accomplished on a timely basis and could involve
significant additional costs. Any failure by the Company to obtain any of the
components used to manufacture the Company's compounds from alternative
suppliers, if required, could limit the Company's ability to manufacture its
compounds and would have a material adverse effect on the Company's business,
financial condition and results of operations.

Risk of Product Liability. The testing, marketing and sale of the
Company's products will entail an inherent risk of product liability, and there
can be no assurance that product liability claims will not be asserted against
the Company. The Company intends to secure limited product liability insurance
coverage prior to the commercial introduction of any product, but there can be
no assurance that the Company will be able to obtain product liability insurance
on acceptable terms or that insurance subsequently obtained will provide
adequate coverage against any or all potential claims. Any product liability
claim against the Company, regardless of its merit or eventual outcome, could
have a material adverse effect upon the Company's business, financial condition
and results of operations.

18
<PAGE> 21

Environmental Regulation; Use of Hazardous Substances. The Company is
subject to federal, state and local laws, rules, regulations and policies
governing the use, generation, manufacture, storage, air emission, effluent
discharge, handling and disposal of certain materials, biological specimens and
wastes. There can be no assurance that the Company will not be required to incur
significant costs to comply with additional environmental and health and safety
regulations in the future. The Company's research and development involves the
controlled use of hazardous materials, including certain hazardous chemicals and
radioactive materials and pathogens. Although the Company believes that its
safety procedures for handling and disposing of such materials comply with the
standards prescribed by state and federal regulations, the risk of accidental
contamination or injury from these materials cannot be eliminated. In the event
of such an accident, the Company could be held liable for any damages that
result and any such liability could exceed the resources of the Company.

Uncertainty Regarding Health Care Reimbursement and Reform. The future
revenues and profitability of biopharmaceutical and related companies as well as
the availability of capital to such companies may be affected by the continuing
efforts of the United States and foreign governments and third-party payors to
contain or reduce costs of health care through various means. In the United
States, given recent federal and state government initiatives directed at
lowering the total cost of health care, it is likely that the Congress and state
legislatures will continue to focus on health care reform and the cost of
pharmaceuticals and on the reform of the Medicare and Medicaid systems. While
the Company cannot predict whether any such legislative or regulatory proposals
will be adopted, the announcement or adoption of such proposals could have a
material adverse effect on the Company's business, financial condition and
results of operations.

The Company's ability to commercialize its products successfully will
depend in part on the extent to which appropriate reimbursement levels for the
cost of the products and related treatment of blood components are obtained from
governmental authorities, private health insurers and other organizations, such
as health maintenance organizations ("HMOs"). Third-party payors are
increasingly challenging the prices charged for medical products and services.
The trend toward managed health care in the United States and other countries
and the concurrent growth of organizations such as HMOs, which could control or
significantly influence the purchase of health care services and products, as
well as legislative proposals to reform health care or reduce government
insurance programs, may all result in lower prices for the Company's products.
The cost containment measures that health care payors and providers are
instituting and the effect of any health care reform could materially adversely
affect the Company's ability to operate profitably.

Volatility of Stock Price. The trading price of the Company's Common
Stock is subject to significant fluctuations. Factors such as the announcements
of scientific achievements or new products by the Company or its competitors;
governmental regulation; health care legislation; developments in patent or
other proprietary rights of the Company or its competitors, including
litigation; fluctuations in the Company's operating results; comments made by
analysts, including changes in analysts' estimates of the Company's financial
performance; and market conditions for health care stocks in general could have
significant impact on the future price of the Common Stock. In addition, the
stock market has from time to time experienced extreme price and volume
fluctuations, which may be unrelated to the operating performance of particular
companies. In the past, securities class action litigation has often been
instituted following periods of volatility in the market price for a company's
securities. Such litigation could result in substantial costs and a diversion of
management attention and resources, which could have a material adverse effect
on the Company's business, financial condition and results of operations.

19
<PAGE> 22

EXECUTIVE OFFICERS OF THE REGISTRANT

The executive officers of the Company and their ages as of February 27,
1998 are as follows:

<TABLE>
<CAPTION>
NAME AGE POSITION
---- --- --------
<S> <C> <C>
Stephen T. Isaacs ............... 49 President, Chief Executive Officer and Director
David S. Clayton ................ 54 Vice President, Finance and Chief Financial Officer
Laurence M. Corash .............. 53 Vice President, Medical Affairs
John E. Hearst .................. 62 Vice President, New Science Opportunities
</TABLE>

STEPHEN T. ISAACS founded the Company in September 1991 and has served
as President, Chief Executive Officer and a member of the Board of Directors
since that time. Mr. Isaacs was previously President and Chief Executive Officer
of HRI, a research and development company, from September 1984 to December
1996. From 1975 to 1986, Mr. Isaacs held a faculty research position at the
University of California at Berkeley.

DAVID S. CLAYTON has been Chief Financial Officer of the Company since
May 1996 and Vice President, Finance of the Company since July 1996. From 1992
to May 1996, Mr. Clayton was a financial consultant to various companies,
including the Company. From 1989 through May 1992, Mr. Clayton was the Executive
Vice President of Trans Ocean Ltd., a company engaged in leasing of
international maritime shipping containers.

LAURENCE M. CORASH, M.D., a co-founder of the Company, has been Vice
President, Medical Affairs of the Company since July 1996. From July 1994 until
he assumed his current position, Dr. Corash was Director of Medical Affairs. Dr.
Corash was a consultant to the Company from 1991 to July 1994. Dr. Corash has
been a Professor of Laboratory Medicine at the University of California, San
Francisco since July 1985 and Chief of the Hematology Laboratory for the Medical
Center at the University of California, San Francisco since January 1982. Dr.
Corash has served as a consultant to the FDA Advisory Panel for Hematology
Devices since 1990.

JOHN E. HEARST, PH.D., D.SC., a co-founder of the Company, was elected
Vice President, New Science Opportunities in July 1996. From January 1996 until
July 1996, Dr. Hearst served as Director, New Science Opportunities. He has
served as a member of the Board of Directors of the Company since January 1992.
Dr. Hearst has been a Professor of Chemistry at the University of California at
Berkeley since 1972. In 1984, Dr. Hearst co-founded HRI.

ITEM 2. PROPERTIES

The Company leases approximately 17,400 square feet for its main
facility and approximately 9,900 square feet for an additional facility, both of
which contain laboratory and office space, in Concord, California. The lease of
the main facility extends through June 1999 with two five-year renewal options.
The lease of the additional facility extends through January 1999, with renewal
options for up to six years. The Company also has a short-term lease for
approximately 4,500 square feet at a facility located near its main facility in
Concord. The Company believes that its facilities will be adequate to meet its
needs for the foreseeable future.

ITEM 3. LEGAL PROCEEDINGS

Not applicable.

ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

Not applicable.

20
<PAGE> 23

PART II

ITEM 5. MARKET FOR THE REGISTRANT'S COMMON EQUITY AND RELATED STOCKHOLDER
MATTERS

(a) The Company's Common Stock is traded on the Nasdaq National Market
under the symbol "CERS." The Company completed the initial public offering of
its Common Stock on January 30, 1997. The following table sets forth, for the
periods indicated, the high and low sales prices for the Common Stock as
reported by the Nasdaq National Market:

<TABLE>
<CAPTION>
HIGH LOW
---- ---
<S> <C> <C>
Fiscal 1997:
First Quarter (from January 30) . $ 12 3/8 $ 7 3/4
Second Quarter .................. 12 3/4 8 1/2
Third Quarter ................... 18 8
Fourth Quarter .................. 25 1/2 16 7/8
</TABLE>

On February 27, 1998, the last reported sale price of the Company's
Common Stock on the Nasdaq National Market was $16 1/8 per share. At February
27, 1998, the Company had approximately 282 holders of record of its Common
Stock.

(b) On January 30, 1997, the Company sold 2,000,000 shares of Common
Stock in an initial public offering for which the Company received net proceeds
of $21,070,000. Of such proceeds, the Company has applied $10,650,000 to
contracts and consultants, $5,450,000 to employee salaries and related expenses,
$1,440,000 to supplies and office expenses, $1,390,000 to professional fees,
$1,360,000 to facilities and the purchase and installation of equipment,
$460,000 to travel and entertainment, $250,000 to insurance, $70,000 to
repayment of indebtedness.

21
<PAGE> 24

ITEM 6. SELECTED FINANCIAL DATA

The following table summarizes certain selected financial data for the
fiscal year ended December 31, 1997. The information presented should be read in
conjunction with the financial statements and notes included elsewhere herein.
The selected financial data for the periods prior to the financial statements
included herein are derived from audited financial statements.

<TABLE>
<CAPTION>
YEARS ENDED DECEMBER 31,
-----------------------------------------------------------------------
1997 1996 1995 1994 1993
----------- ----------- ----------- ----------- -----------
(IN THOUSANDS, EXCEPT PER SHARE DATA)
<S> <C> <C> <C> <C> <C>
STATEMENT OF OPERATIONS DATA:
Revenue ......................... $ 6,851 $ 3,609 $ 6,799 $ 4,796 $ 230
Operating expenses:
Research and development ...... 19,569 12,080 8,125 5,680 2,485
General and administrative .... 3,163 2,200 1,517 1,194 1,210
----------- ----------- ----------- ----------- -----------
Total operating expenses .. 22,732 14,280 9,642 6,874 3,695
----------- ----------- ----------- ----------- -----------
Loss from operations ............ (15,881) (10,671) (2,843) (2,078) (3,465)
Other income (expense), net ..... 1,217 464 483 278 (50)
----------- ----------- ----------- ----------- -----------
Net loss ........................ $ (14,664) $ (10,207) $ (2,360) $ (1,800) $ (3,515)
=========== =========== =========== =========== ===========
Net loss per share-basic and
diluted(1) .................... $ (1.76) $ (5.98) $ (1.67) $ (1.24) $ (2.35)
Shares used in computing net loss
per share-basic and diluted(1) 8,351,872 1,705,821 1,413,969 1,456,336 1,492,785
</TABLE>

<TABLE>
<CAPTION>
DECEMBER 31,
-----------------------------------------------------------------------
1997 1996 1995 1994 1993
--------- --------- --------- --------- ----------
(IN THOUSANDS)
<S> <C> <C> <C> <C> <C>
BALANCE SHEET DATA:
Cash and cash equivalents . $ 11,604 $ 6,002 $ 9,659 $ 7,802 $ 6,076
Working capital ........... 21,374 2,653 7,263 5,865 3,884
Total assets .............. 27,315 8,812 11,349 9,684 6,807
Capital lease obligations,
less current portion .... 43 92 32 94 --
Accumulated deficit ....... (34,870) (20,206) (9,999) (7,639) (5,838)
Total stockholders' equity
(deficit) ............... 22,475 4,839 8,663 5,439 (516)
</TABLE>

(1) See Note 1 of Notes to Financial Statements for a description of the
method used in computing the net loss per share. The net loss per share
amounts prior to 1997 have been restated as required to comply with
Statement of Financial Accounting Standards No. 128, "Earnings Per Share"
(Statement No. 128) and the Securities and Exchange Commission's Staff
Accounting Bulletin No. 98, (SAB 98). For further discussion of net loss
per share and the impact of Statement No. 128 and SAB 98, see the notes
to the consolidated financial statements.

22
<PAGE> 25

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
OF OPERATIONS

The following discussion of the financial condition and results of
operations of the Company should be read in conjunction with the Financial
Statements and the Notes thereto included elsewhere in this report. This report
contains forward-looking statements that involve risks and uncertainties. The
Company's actual results could differ significantly from those discussed in
these forward-looking statements as a result of certain factors, including those
set forth under "Business" and elsewhere herein.

OVERVIEW

Cerus is developing systems designed to improve the safety of blood
transfusions by inactivating infectious pathogens in blood components used for
transfusion (platelets, plasma and red blood cells) and inhibiting the leukocyte
(white blood cell) activity that is responsible for certain adverse immune and
other transfusion-related reactions. The Company's platelet and plasma pathogen
inactivation systems are in Phase 2 clinical trials in the United States, and
its red blood cell pathogen inactivation system is in preclinical development.

Since its inception in 1991, Cerus has devoted substantially all of its
efforts and resources to the research, development and clinical testing of
techniques and systems for inactivating pathogens in blood transfusion
components. The Company has been unprofitable since inception and, as of
December 31, 1997, had an accumulated deficit of approximately $34.9 million.
All of the Company's pathogen inactivation systems are in the research and
development stage. The Company will be required to conduct significant research,
development, testing and regulatory compliance activities on these products
that, together with anticipated general and administrative expenses, are
expected to result in substantial losses at least until commercialization of its
products under development. The Company's ability to achieve a profitable level
of operations in the future will depend on its ability to successfully complete
development, obtain regulatory approvals and achieve market acceptance of its
pathogen inactivation systems. As a result, there can be no assurance that the
Company will ever achieve a profitable level of operations. Further, a
significant portion of the Company's development funding is provided by Baxter
Healthcare Corporation ("Baxter") under the agreements described below. There
can be no assurance that such agreements will not be modified or terminated as
provided therein.

In December 1993, Cerus entered into a development and commercialization
agreement with Baxter to develop a system for inactivation of pathogens in
platelets. The agreement provides for Baxter to make an equity investment and
certain up-front license and milestone payments. The agreement further provides
for Baxter and the Company to generally share system development costs equally,
subject to mutually agreed budgets established from time to time. The agreement
also provides for a sharing of revenue from sales of inactivation system
disposables, after each party is reimbursed for its cost of goods above a
specified level. In January 1997, the Company and Baxter amended the agreement
to provide that the Company would receive an additional 2.2% of the adjusted
product revenue from the sale of the platelet pathogen inactivation system
disposables in return for payment by the Company to Baxter of $5.5 million in
1997 in four equal quarterly installments for development costs.

In January and July 1995, Cerus received approximately $2.6 million from
Baxter in connection with interim funding agreements related to the development
of pathogen inactivation systems for plasma for transfusions (fresh frozen
plasma or "FFP") and red blood cells. In April 1996, Cerus entered into a second
development and commercialization agreement with Baxter, principally focused on
the FFP and red blood cell pathogen inactivation systems. The agreement provides
for Baxter to make certain equity investments, including two future
milestone-based investments of $5 million each at 120% of the market price at
the time of the investment. The agreement also provides for Baxter and the
Company to generally share development costs of the systems equally, subject to
mutually agreed budgets established from time to time. The agreement further
provides for the Company and Baxter to share gross profits from the sale of
inactivation system disposables, after deducting from such gross profits a
specified percentage allocation to be retained by the marketing party for
marketing and administration expenses.

23
<PAGE> 26

Through December 31, 1997, Baxter has paid the Company up-front license fees
and milestone and development payments totaling $14.8 million and has invested
$17.5 million in the capital stock of the Company under the agreements described
above.

In March 1998, the Company and Baxter entered into an amendment to the April
1996 agreement providing that, to the extent the approved spending for 1998 for
the red blood cell project exceeds $7.3 million, Cerus will fund all expenses
for the red blood cell project in 1998 in excess of such amount, up to the
amount of the approved budget. To compensate Cerus for such excess expenditures,
Baxter will fully fund the first expenditures under the approved budget for the
red cell project for 1999 in an amount equal to such excess expenditures, after
which the parties shall equally share the expenses of the red cell project. If
for any reason there is not an approved budget for the red cell project for
1999, Baxter will fully fund the first expenditures for 1999 under the approved
budget for such other Cerus-Baxter program or programs as Cerus shall designate
in an amount equal to the Cerus 1998 excess expenditures. If by July 1, 1999,
however, there is not an approved budget for such other Cerus-Baxter program or
programs that is at least equal to such excess expenditures, Baxter will
promptly pay to Cerus one-half of the amount by which the excess expenditures
exceed the amount of expenditures to be funded by Baxter. Cerus anticipates that
the expenditures for 1998 for the FFP program will exceed the previously
approved budget. Cerus and Baxter are discussing the level of funding each
company will support in 1998 for the FFP program. There can be no assurance that
the parties will agree on a budget that would permit the FFP program to proceed
in accordance with the Company's Plans.

To date, the Company has not received any revenue from product sales and it
will not derive revenue from product sales unless and until one or more planned
products receives regulatory approval and achieves market acceptance. The
Company anticipates that its sources of revenue until product sales occur will
be limited to payments under development and commercialization agreements with
Baxter in the area of blood component pathogen inactivation, payments from the
United States government under research grant programs, payments from future
collaboration agreements, if any, and interest income. Under the agreements, all
research, development, preclinical and clinical costs of the pathogen
inactivation projects are shared by Cerus and Baxter. Because more of such
research and development is typically performed internally at Cerus than at
Baxter and because Cerus is generally responsible for engaging third parties to
perform certain aspects of these projects, the Company's research and
development expenses have exceeded its share of expenses. As a result, the
Company has recognized revenue from Baxter, giving rise to a receivable due from
Baxter and corresponding periodic balancing payments to the Company. At December
31, 1997, the amount of the Baxter receivable was approximately $4.4 million. On
February 13, 1998, Baxter paid Cerus approximately $4.5 million in satisfaction
of such receivable and anticipated adjustments. Through December 31, 1997, the
Company had recognized approximately $19.2 million in revenue under its
agreements with Baxter, including the license fee and milestone amounts
described above, and approximately $3.1 million under United States government
grants.

RESULTS OF OPERATIONS

YEARS ENDED DECEMBER 31, 1997, 1996, AND 1995

Revenue. Revenue earned under the Agreements for the years ending
December 31, 1997, 1996 and 1995 was $6.2 million, $2.9 million and $6.0 million
and accounted for 90%, 79% and 89% of the Company's total revenue, respectively.
Revenue from Baxter increased in 1997 from 1996, as the Company recognized
milestone and license fee revenue related to the platelet program of
approximately $1.7 million and recognized increased development revenue
primarily relating to its FFP and red blood cell programs. Revenue from Baxter
decreased to approximately $2.9 million in 1996 from 1995, as no milestone or
license fee revenue relating to the platelet program was recognized, as compared
with approximately $1.7 million in milestone and related license fee revenue
recognized during 1995. In addition, FFP and red blood cell development revenue
decreased in 1996 by approximately $1.2 million, principally reflecting lower
revenue during 1996 under the interim funding agreements. Government grant
revenue, generally unchanged among the periods, was approximately $660,000,
$758,000 and $751,000 for the years 1997, 1996 and 1995, respectively.

Research and Development Expenses. Research and development expenses for
the years ending December 31, 1997, 1996 and 1995 were $19.6 million, $12.1
million and $8.1 million, respectively. The increases in 1997 and 1996 were due
principally to third party costs, particularly toxicology studies, compound
manufacturing development and initiation of clinical trials relating to the
platelet and plasma programs, as well as to increased

24
<PAGE> 27

activity at the Company in the FFP and red blood cell programs. A significant
portion of the increase was the result of increased payroll and other personnel
expenses, related laboratory supplies, equipment and facilities expansion. In
addition, as described above, under an amendment to the 1993 platelet agreement,
Cerus made payments to Baxter in 1997 of $5.5 million for development costs in
return for an additional 2.2% share of platelet pathogen inactivation system
adjusted product revenue.

General and Administrative Expenses. General and administrative expenses
were approximately $3.2 million in 1997, $2.2 million in 1996 and $1.5 million
in 1995. The increases were primarily attributable to increased personnel levels
associated with the expansion of the Company's operations.

Other Income (Expense). Interest income was approximately $1.2 million
in 1997, $482,000 in 1996 and approximately $500,000 in 1995. The increase from
1996 to 1997 was attributable primarily to increased average cash balances
related to proceeds from the Company's initial public offering and private
placement to Baxter (see Liquidity and Capital Resources below). The increase
from 1995 to 1996 was attributable primarily to increased average cash balances
related to financings and funding under the Baxter platelet agreement. Interest
expense was relatively unchanged and was approximately $15,000, $18,000 and
$17,000 for the years 1997, 1996 and 1995, respectively.

LIQUIDITY AND CAPITAL RESOURCES

From inception to December 31, 1997, Cerus has financed its operations
primarily through private placements of preferred and common equity securities,
an initial public offering of common stock totaling approximately $60.1 million
and project funding provided by Baxter totaling $19.2 million. During that
period, the Company received approximately $3.1 million under United States
government grants and approximately $2.6 million in interest income. At December
31, 1997, the Company had cash and cash equivalents of approximately $11.6
million and short-term investments of approximately $10.0 million.

Net cash used in operating activities for 1997, 1996, and 1995 was
approximately $16.6 million, $8.9 million and $3.4 million, respectively,
resulting primarily from net losses. From inception through December 31, 1997,
net cash used in investing activities of approximately $12.3 million resulted
from short-term cash investments, purchases of furniture and equipment, and
leasehold improvements.

At December 31, 1997, the Company's net operating loss carryforwards
were approximately $27.8 million and $14.1 million for federal and state income
tax purposes, respectively. The Company's federal research and development tax
credit carryforwards were approximately $1.2 million and $400,000 for federal
and state income tax purposes, respectively, at December 31, 1997. The federal
net operating loss and tax credit carryforwards expire at various dates from
2007 to 2012. The California state net operating loss expires in 2001 and 2002.
The Tax Reform Act of 1986 and state tax statutes contain provisions relating to
changes in ownership that may limit the utilization in any given year of
available net operating loss carryforwards and research and development credits.
See Note 6 of Notes to Financial Statements.

The Company's future capital requirements and the adequacy of its
available funds will depend on many factors, including progress of the platelet
and FFP programs and the related clinical trials, progress of the red blood cell
program, achievement of milestones leading to equity investments, regulatory
approval and successful commercialization of the Company's pathogen inactivation
systems, costs related to creating, maintaining and defending the Company's
intellectual property position, and competitive developments. The Company
believes that its available cash balances, together with anticipated cash flows
from existing Baxter and grant arrangements, will be sufficient to meet its
capital requirements for at least the next 12 months. In the event that
additional capital is required, the Company may seek to raise that capital
through public or private equity or debt financings or through additional
collaborative arrangements or government grants. Future capital funding
transactions may result in dilution to stockholders. There can be no assurance
that such capital will be available on favorable terms, if at all.

25
<PAGE> 28

IMPACT OF THE YEAR 2000

Computer programs using two rather than four digits to identify the year
in a date field may cause computer systems to malfunction in the year 2000. Any
computer programs that have time-related software may determine a date using
"00" as the year 1900 rather than the year 2000. This could result in a system
failure or miscalculations causing disruptions of operations, including, among
other things, a temporary inability to engage in specific business activities.

Based on a recent assessment, the Company has determined that it will be
required to upgrade or replace a portion of its software so that its computer
systems will function properly with respect to dates in the year 2000 and
thereafter. The Company believes that, with upgrades of existing software and/or
conversions to new software, the year 2000 issue will not pose significant
operational problems for its business activities.

The Company has initiated communications with its significant suppliers
to determine the extent to which the Company's operations are vulnerable to
those third parties' failure to solve their own year 2000 issues. The Company
anticipates that its costs associated with the upgrade and/or conversion of
existing computer software relating to the year 2000 issue is less than
$100,000. There can be no assurance that the systems of other companies on which
the Company relies will be converted on a timely basis and will not have an
adverse effect on the Company's operations. Estimated costs were derived
utilizing numerous assumptions of future events, including the continued
availability of certain resources and other factors. However, there can be no
assurance that these estimates will be achieved, and actual results could differ
materially from those anticipated. Specific factors that might cause such
material differences include, but are not limited to, the availability and cost
of personnel trained in this area, the ability to locate and correct all
relevant computer codes, and similar uncertainties.

ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTAL DATA

The Company's financial statements, together with related notes and
report of Ernst & Young, LLP, independent auditors, are listed in Item 14(a).

ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
FINANCIAL DISCLOSURE

Not applicable.

26
<PAGE> 29

PART III

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT

Information required by this item, insofar as it relates to directors,
will be contained under the captions "Election of Directors" and "Compliance
with Section 16(a) of the Securities Exchange Act of 1934" in the Company's
definitive proxy statement with respect to the Company's 1998 Annual Meeting of
Stockholders (the "Proxy Statement"), and is hereby incorporated by reference
thereto. The information relating to executive officers of the Company is
contained in Part I of this report.

ITEM 11. EXECUTIVE COMPENSATION

The information required by this item will be contained in the Proxy
Statement under the caption "Executive Compensation," and is hereby incorporated
by reference thereto.

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The information required by this item will be contained in the Proxy
Statement under the caption "Security Ownership of Certain Beneficial Owners and
Management," and is hereby incorporated by reference thereto.

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

The information required by this item will be contained in the Proxy
Statement under the caption "Certain Relationships and Related Transactions,"
and is hereby incorporated by reference thereto.

ITEM 14. EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K

The following documents are being filed as part of this report on Form
10-K:

<TABLE>
<S> <C> <C>
(a) Financial Statements.

Report of Independent Auditors .........................................29

Balance Sheets as of December 31, 1997 and 1996.........................30

Statements of Operations for the three
years ended December 31, 1997...........................................31

Statements of Stockholders' Equity for
the three ended December 31, 1997.......................................32

Statements of Cash Flows for the three years
ended December 31, 1997.................................................33

Notes to Financial Statements...........................................34
</TABLE>

Other information is omitted because it is either presented elsewhere,
is inapplicable or is immaterial as defined in the instructions.

(b) No reports on Form 8-K were filed during the quarter ended December 31,
1997

27
<PAGE> 30

<TABLE>
<CAPTION>
EXHIBIT
NUMBER. DESCRIPTION OF EXHIBIT
------- ----------------------
<S> <C>
3.1(1) Registrant's Amended and Restated Certificate of Incorporation.
3.2(1) Registrant's Bylaws.
10.1(1) Form of Indemnity Agreement entered into between the
Registrant and each of its directors and executive
officers.
10.2(1) 1996 Equity Incentive Plan.
10.3(1) Form of Incentive Stock Option Agreement under the 1996 Equity
Incentive Plan.
10.4(1) Form of Nonstatutory Stock Option Agreement under the 1996 Equity
Incentive Plan.
10.5(1) 1996 Employee Stock Purchase Plan Offering.
10.7(1) Warrant Agreement, dated May 11, 1992, between the
Registrant and Comdisco, Inc. to purchase Series A
Preferred Stock.
10.8(1) Warrant Agreement, dated July 12, 1993, between the
Registrant and Comdisco, Inc. to purchase Series B
Preferred Stock.
10.9(1) Warrant Agreement, dated May 25, 1994, between the
Registrant and Comdisco, Inc. to purchase Series C
Preferred Stock.
10.10(1) Warrant Agreement, dated April 25, 1995, between the
Registrant and Comdisco, Inc. to purchase Series D
Preferred Stock.
10.11(1) Form of Warrant to purchase shares of Series B Preferred
Stock of the Registrant.
10.12(1) Form of Warrant to purchase shares of Series C Preferred
Stock of the Registrant.
10.13(1) Series D Preferred Stock Purchase Agreement, dated March
1, 1995, between the Registrant and certain investors.
10.14(1) Series E Preferred Stock Purchase Agreement, dated April
1, 1996, between the Registrant and Baxter Healthcare
Corporation.
10.15(1) Common Stock Purchase Agreement, dated September 3, 1996 between the
Registrant and Baxter Healthcare Corporation.
10.16(1) Amended and Restated Investors' Rights Agreement, dated
April 1, 1996, among the Registrant and certain investors.
10.17+(1) Development, Manufacturing and Marketing Agreement, dated December 10,
1993 between the Registrant and Baxter Healthcare Corporation.
10.18+(1) Development, Manufacturing and Marketing Agreement, dated April 1,
1996, between the Registrant and Baxter Healthcare Corporation.
10.21(1) Industrial Real Estate Lease, dated October 1, 1992,
between the Registrant and Shamrock Development Company,
as amended on May 16, 1994 and December 21, 1995.
10.22(1) Real Property Lease, dated August 8, 1996, between the Registrant and
S.P. Cuff.
10.23(1) Lease, dated February 1, 1996, between the Registrant and
Holmgren Partners.
10.24(1) First Amendment to Common Stock Purchase Agreement, dated
December 9, 1996, between the Registrant and Baxter
Healthcare Corporation.
10.25+(1) Amendment, dated as of January 3, 1997, to the Agreement
filed as Exhibit 10.17.
10.26(1) Memorandum of Agreement, dated as of January 3, 1997,
between the Registrant and Baxter Healthcare Corporation.
10.27* License Agreement, dated as of November 30, 1992, by and among the
Company, Miles Inc. and Diamond Scientific Corporation.
23.1 Consent of Ernst & Young LLP, Independent Auditors.
27.1 Financial Data Schedule.
</TABLE>

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

+ Certain portions of this exhibit are subject to a confidential treatment
order.

(1) Incorporated by reference from the Company's Registration Statement on
Form S-1 (File No. 333-11341) and amendments thereto.

* Confidential treatment has been requested for certain portions of this
exhibit.

28
<PAGE> 31
Report of Ernst & Young LLP, Independent Auditors

The Board of Directors and Stockholders
Cerus Corporation

We have audited the accompanying balance sheets of Cerus Corporation as of
December 31, 1997 and 1996, and the related statements of operations,
stockholders' equity, and cash flows for each of the three years in the period
ended December 31, 1997. These financial statements are the responsibility of
the Company's management. Our responsibility is to express an opinion on these
financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of Cerus Corporation at December
31, 1997 and 1996, and the results of its operations and its cash flows for each
of the three years in the period ended December 31, 1997 in conformity with
generally accepted accounting principles.

Ernst & Young LLP

Walnut Creek, California
January 27, 1998, except for
Note 2 as to which the date is March 6, 1998

<PAGE> 32

CERUS CORPORATION

BALANCE SHEETS

<TABLE>
<CAPTION>
DECEMBER 31,
1997 1996
------------ ------------
<S> <C> <C>
ASSETS
Current assets:
Cash and cash equivalents .............................................. $ 11,603,596 $ 6,002,050
Short-term investments ................................................. 9,977,178 --
Accounts receivable from a related party ............................... 4,376,141 325,515
Other current assets ................................................... 214,687 206,015
--------------------------------
Total current assets ..................................................... 26,171,602 6,533,580
Furniture and equipment at cost:
Laboratory and office equipment ........................................ 1,309,950 900,280
Leasehold improvements ................................................. 1,440,863 1,440,863
--------------------------------
2,750,813 2,341,143
Less accumulated depreciation and amortization ......................... 1,718,984 1,156,918
--------------------------------
Net furniture and equipment .............................................. 1,031,829 1,184,225
Deferred financing costs ................................................. -- 969,142
Other assets ............................................................. 111,725 124,663
--------------------------------
Total assets ............................................................. $ 27,315,156 $ 8,811,610
================================

LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
Accounts payable ....................................................... $ 1,298,868 $ 391,267
Accrued compensation and related expenses .............................. 931,991 631,380
Accrued third-party toxicology and development expenses ................ 896,000 854,300
Accrued financing costs ................................................ -- 413,000
Other accrued expenses ................................................. 1,600,502 514,848
Deferred revenue ....................................................... -- 981,523
Current portion of capital lease obligations ........................... 69,816 94,130
--------------------------------
Total current liabilities ................................................ 4,797,177 3,880,448

Capital lease obligations, less current portion .......................... 43,002 92,127

Commitments and contingencies

Stockholders' equity:
Preferred stock, $.001 par value;
5,000,000 shares authorized: issuable in series; none issued and
outstanding at December 31, 1997, 3,001,630 at December 31, 1996;
aggregate liquidation preference of $24,485,277 at December 31, 1996 .. -- 3,002
Common stock, $.001 par value;
50,000,000 shares authorized: 9,183,629 and 1,928,807 shares issued and
outstanding at December 31, 1997 and 1996, respectively ............... 9,184 1,929
Additional paid-in capital ............................................. 57,476,775 25,425,529
Deferred compensation .................................................. (140,937) (310,387)
Notes receivable from stockholders ..................................... -- (75,206)
Accumulated deficit .................................................... (34,870,045) (20,205,832)
--------------------------------
Total stockholders' equity ............................................... 22,474,977 4,839,035
--------------------------------
Total liabilities and stockholders' equity ............................... $ 27,315,156 $ 8,811,610
================================
</TABLE>

See accompanying notes.

<PAGE> 33

CERUS CORPORATION

STATEMENTS OF OPERATIONS

<TABLE>
<CAPTION>
YEARS ENDED DECEMBER 31,
1997 1996 1995
------------------------------------------
<S> <C> <C> <C>
Revenue:
Licenses, milestones and development funding from a
related party ............................................ $ 6,190,781 $ 2,851,236 $ 6,047,579
Government grants ........................................... 660,066 758,305 751,356
------------------------------------------
Total revenue ................................................. 6,850,847 3,609,541 6,798,935
Operating expenses:
Research and development .................................... 19,569,469 12,080,445 8,125,311
General and administrative .................................. 3,163,012 2,200,018 1,517,152
------------------------------------------
Total operating expenses ...................................... 22,732,481 14,280,463 9,642,463
------------------------------------------
Loss from operations .......................................... (15,881,634) (10,670,922) (2,843,528)
Other income (expense):
Interest income ............................................. 1,232,322 482,384 500,028
Interest expense ............................................ (14,901) (18,347) (16,821)
------------------------------------------
Total other income (expense) .................................. 1,217,421 464,037 483,207
------------------------------------------
Net loss ...................................................... $(14,664,213) $(10,206,885) $ (2,360,321)
==========================================
Net loss per share - basic and diluted ........................ $ (1.76) $ (5.98) $ (1.67)
==========================================
Shares used in computing net loss per share - basic and diluted 8,351,872 1,705,821 1,415,969
==========================================
</TABLE>

See accompanying notes.

<PAGE> 34
CERUS CORPORATION

STATEMENTS OF STOCKHOLDERS' EQUITY

PREFERRED STOCK COMMON STOCK ADDITIONAL
------------------------------------------------------ PAID-IN
SHARES AMOUNT SHARES AMOUNT CAPITAL
---------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
Balances at December 31, 1994 ....... 2,091,593 $ 2,092 1,413,272 $ 1,413 $ 13,154,907
Exercise of stock options ......... -- -- 4,623 5 1,681
Issuance of Series D convertible
preferred stock, net of
issuance costs of $60,806 ..... 529,084 529 -- -- 5,494,047
Issuance of warrants to purchase
Series D preferred stock ...... -- -- -- -- 87,500
Net loss .......................... -- -- -- -- --
---------------------------------------------------------------------
Balances at December 31, 1995 ....... 2,620,677 2,621 1,417,895 1,418 18,738,135
Exercise of stock options ......... -- -- 510,912 511 258,411
Issuance of Series E convertible
preferred stock, net of issuance
costs of $100,777 .............. 380,953 381 -- -- 5,898,768

Payment on notes receivable ....... -- -- -- -- --

Deferred compensation ............. -- -- -- -- 530,215
Amortization of deferred
compensation ................... -- -- -- -- --
Net loss .......................... -- -- -- -- --
---------------------------------------------------------------------
Balances at December 31, 1996 ....... 3,001,630 3,002 1,928,807 1,929 25,425,529
Public offering of common stock, net
of expenses of $2,945,259 ......... -- -- 2,000,000 2,000 21,052,741
Issuance of common stock ............ -- -- 714,080 714 10,542,502
Conversion of preferred stock ....... (3,001,630) (3,002) 4,412,243 4,412 (3,118)
Issuance of common stock under stock
option and employee stock purchase
plans and warrant exercises........ -- -- 129,664 130 459,754
Common shares reacquired ............ -- -- (1,165) (1) (633)
Payment on notes receivable ......... -- -- -- -- --
Amortization of deferred
compensation ................... -- -- -- -- --
Net loss ............................ -- -- -- -- --
---------------------------------------------------------------------
Balances at December 31, 1997 ....... -- $ -- 9,183,629 $ 9,184 $ 57,476,775
=====================================================================

NOTES
RECEIVABLE TOTAL
DEFERRED FROM ACCUMULATED STOCKHOLDERS'
COMPENSATION STOCKHOLDERS DEFICIT EQUITY
----------------------------------------------------------
<C> <C> <C> <C>
Balances at December 31, 1994 ....... $ -- $ (80,588) $ (7,638,626) $ 5,439,198
Exercise of stock options ......... -- -- -- 1,686
Issuance of Series D convertible
preferred stock, net of
issuance costs of $60,806 ..... -- -- -- 5,494,576
Issuance of warrants to purchase
Series D preferred stock ...... -- -- -- 87,500
Net loss .......................... -- -- (2,360,321) (2,360,321)
----------------------------------------------------------
Balances at December 31, 1995 ....... -- (80,588) (9,998,947) 8,662,639
Exercise of stock options ......... -- -- -- 258,922
Issuance of Series E convertible
preferred stock, net of issuance
costs of $100,777 .............. -- -- -- 5,899,149

Payment on notes receivable ....... -- 5,382 -- 5,382

Deferred compensation ............. (530,215) -- -- --
Amortization of deferred
compensation ................... 219,828 -- -- 219,828
Net loss .......................... -- -- (10,206,885) (10,206,885)
----------------------------------------------------------
Balances at December 31, 1996 ....... (310,387) (75,206) (20,205,832) 4,839,035
Public offering of common stock, net
of expenses of $2,945,259 ......... -- -- -- 21,054,741
Issuance of common stock ............ -- -- -- 10,543,216
Conversion of preferred stock ....... -- -- -- (1,708)
Issuance of common stock under stock
option and employee stock purchase
plans and warrant exercises -- -- -- 459,884
Common shares reacquired ............ -- -- -- (634)
Payment on notes receivable ......... -- 75,206 -- 75,206
Amortization of deferred
compensation ................... 169,450 -- -- 169,450
Net loss ............................ -- -- (14,664,213) (14,664,213)
----------------------------------------------------------
Balances at December 31, 1997 ....... $ (140,937) $ -- $(34,870,045) $ 22,474,977
==========================================================
</TABLE>

See accompanying notes.

32
<PAGE> 35

CERUS CORPORATION

STATEMENTS OF CASH FLOWS

<TABLE>
<CAPTION>
YEARS ENDED DECEMBER 31,
1997 1996 1995
------------------------------------------
<S> <C> <C> <C>
OPERATING ACTIVITIES
Net loss ........................................................... $(14,664,213) $(10,206,885) $ (2,360,321)
Adjustments to reconcile net loss to net cash used in operating
activities:
Depreciation and amortization .................................... 562,066 477,551 369,267
Amortization of deferred compensation ............................ 169,450 219,828 --
Changes in operating assets and liabilities:
Accounts receivable from a related party ....................... (4,050,626) (325,515) --
Other current assets .......................................... (8,672) 52,568 72,220
Other assets .................................................. 12,938 36,706 42,184
Accounts payable .............................................. 907,601 133,657 (246,115)
Accrued compensation and related expenses ..................... 300,611 275,869 191,911
Accrued third-party toxicology and development expenses ....... 41,700 854,300 (586,383)
Other accrued expenses ........................................ 1,085,654 472,500 31,582
Deferred revenue .............................................. (981,523) (918,981) (933,241)
------------------------------------------
Net cash used in operating activities .............................. (16,625,014) (8,928,402) (3,418,896)

INVESTING ACTIVITIES
Purchases of furniture and equipment ............................... (378,645) (164,960) (124,359)
Purchases of short-term investments ................................ (31,977,178) -- --
Sale of short-term investments ..................................... 1,000,000 -- --
Maturities of short-term investments ............................... 21,000,000 -- --
------------------------------------------
Net cash used in investing activities .............................. (10,355,823) (164,960) (124,359)

FINANCING ACTIVITIES
Net proceeds from sale of preferred stock .......................... -- 5,899,149 5,494,576
Proceeds from issuance of common stock ............................. 32,613,983 258,922 1,686
Payment of fractional shares on preferred stock conversion ......... (1,708) -- --
Repurchase of common stock ......................................... (634) -- --
Deferred financing costs ........................................... -- (556,142) --
Payments on notes receivable from shareholders ..................... 75,206 5,382 --
Payments on capital lease obligations .............................. (104,464) (170,916) (96,265)
------------------------------------------
Net cash provided by financing activities .......................... 32,582,383 5,436,395 5,399,997
------------------------------------------
Net increase (decrease) in cash and cash equivalents ............... 5,601,546 (3,656,967) 1,856,742
Cash and cash equivalents, beginning of period ..................... 6,002,050 9,659,017 7,802,275
------------------------------------------
Cash and cash equivalents, end of period ........................... $ 11,603,596 $ 6,002,050 $ 9,659,017
==========================================
Supplemental disclosures:
Interest paid .................................................... $ 14,901 $ 18,347 $ 16,821
==========================================
Supplemental schedule of noncash investing and financing activities:
Issuance of preferred stock warrants in connection with an
operating lease line ........................................... $ -- $ -- $ 87,500
==========================================
Capital lease obligations incurred ............................... $ 31,025 $ 226,936 $ 79,624
==========================================
Deferred compensation related to stock option grants ............. $ -- $ 530,215 $ --
==========================================
Conversion of preferred stock to common stock .................... $ 24,534,998 $ -- $ --
==========================================
</TABLE>

See accompanying notes.

<PAGE> 36
CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS

DECEMBER 31, 1997

1. THE COMPANY AND ITS SIGNIFICANT ACCOUNTING POLICIES

BASIS OF PRESENTATION

Cerus Corporation (the "Company") (formerly Steritech, Inc.), incorporated
in California on September 19, 1991, is developing systems designed to improve
the safety of blood transfusions by inactivating infectious pathogens in blood
components used for transfusion (platelets, fresh frozen plasma ("FFP") and red
blood cells) and inhibiting the leukocyte (white blood cell) activity that is
responsible for certain adverse immune and other transfusion-related reactions.
The Company has entered into two development and commercialization agreements
with Baxter Healthcare Corporation ("Baxter") to develop, manufacture and market
these pathogen inactivation systems (see Note 2). The Company has not received
any revenues from product sales, and all revenues recognized by the Company to
date have resulted from the Company's agreements with Baxter and federal
research grants. The Company will be required to conduct significant research,
development, testing and regulatory compliance activities on its pathogen
inactivation systems that, together with anticipated general and administrative
expenses, are expected to result in substantial additional losses in future
periods. The Company's ability to achieve a profitable level of operations will
depend on successfully completing development, obtaining regulatory approvals
and achieving market acceptance of its pathogen inactivation systems. There can
be no assurance that the Company will ever achieve a profitable level of
operations.

USE OF ESTIMATES

The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts of assets and liabilities at the
date of the financial statements and the reported amounts of revenues and
expenses during the reporting period. Actual results could differ from those
estimates.

REVENUES AND RESEARCH AND DEVELOPMENT EXPENSES

Revenues related to the cost reimbursement provisions under development
contracts are recognized as the costs on the project are incurred. Revenues
related to milestones specified under development contracts are recognized as
the milestones are achieved. Prepaid license fees, included in deferred revenue,
are recognized as revenues upon achievement of milestones. Research and
development costs are expensed as incurred.

The Company receives certain United States government grants which support
the Company's research effort in defined research projects. These grants
generally provide for reimbursement of approved costs incurred as defined in the
various grants. Revenues associated with these grants are recognized as costs
under each grant are incurred.

CASH, CASH EQUIVALENTS, AND SHORT-TERM INVESTMENTS

The Company considers all highly liquid investments with original
maturities less than three months to be cash and cash equivalents. Cash
equivalents consist principally of short-term money market instruments and
commercial paper.

34
<PAGE> 37

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

1. THE COMPANY AND ITS SIGNIFICANT ACCOUNTING POLICIES (CONTINUED)

CASH, CASH EQUIVALENTS, AND SHORT-TERM INVESTMENTS (CONTINUED)

In accordance with Statement of Financial Accounting Standards No. 115,
"Accounting for Certain Investments in Debt and Equity Securities," the Company
has classified all debt securities as available-for-sale at the time of purchase
and re-evaluates such designation as of each balance sheet date. The
available-for-sale securities recorded at December 31, 1997 totaled $21,580,375.

Unrealized gains and losses at December 31, 1997 and 1996 and realized
gains and losses for the years then ended were not material. Accordingly, the
Company has not made a provision for such amounts in its balance sheets. The
cost of securities sold is based on the specific identification method.
Substantially, all of the Company's cash, cash equivalents, and short-term
investments are maintained by three major financial institutions.

FURNITURE AND EQUIPMENT

Furniture and equipment are stated at cost less accumulated depreciation
and amortization. Depreciation on furniture and equipment is calculated on a
straight-line basis over the estimated useful lives of the assets (principally
five years for laboratory equipment and furniture and three years for office
equipment). Leasehold improvements are amortized on a straight-line basis over
the shorter of the lease term or the estimated useful lives of the improvements.

STOCK-BASED COMPENSATION

In October 1995, the Financial Accounting Standards Board issued Statement
of Financial Accounting Standards No. 123, "Accounting for Stock-Based
Compensation" ("FAS 123"). The Company adopted FAS 123 in 1996. The Company
accounts for employee stock options in accordance with Accounting Principles
Board Opinion No. 25 and has adopted the "disclosure only" alternative described
in FAS 123.

INCOME TAXES

The Company accounts for income taxes based upon Financial Accounting
Standards Board Statement No. 109, "Accounting for Income Taxes." Under this
method, deferred tax assets and liabilities are determined based on differences
between the financial reporting and tax bases of assets and liabilities and are
measured using the enacted tax rates and laws that will be in effect when the
differences are expected to reverse.

NET LOSS PER SHARE - BASIC AND DILUTED

In February 1997, the Financial Accounting Standards Board issued Statement
No. 128, "Earnings Per Share" ("FAS 128"), which is required to be adopted for
the period ended December 31, 1997. FAS 128 replaced the calculation of primary
and fully diluted net income (loss) per share with basic and diluted net income
(loss) per share. Unlike primary net income (loss) per share, basic net income
(loss) per share excludes any dilutive effects of options, warrants and
convertible securities.

<PAGE> 38

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

1. THE COMPANY AND ITS SIGNIFICANT ACCOUNTING POLICIES (CONTINUED)

NET LOSS PER SHARE - BASIC AND DILUTED (CONTINUED)

In February 1998, Staff Accounting Bulletin No. 98 ("SAB 98") was issued
and amends the existing Securities and Exchange Commission staff guidance
primarily to give effect to FAS 128. Topic 4.D of SAB 98 revises the
instructions regarding the dilutive effects of stock issued for consideration
below the initial public offering ("IPO") price or options and warrants to
purchase common stock with exercise prices below the IPO price, previously
referred to as cheap stock. The new guidance highlights the treatment that
should be given to the dilutive effect of common stock or options and warrants
to purchase common stock issued for nominal consideration.

All net loss per share amounts for all periods have been presented, and
where appropriate, restated to conform to the FAS 128 and SAB 98 requirements.
Common stock equivalent shares from convertible preferred stock and from stock
options and warrants are not included as the effect is anti-dilutive.

PRO FORMA NET LOSS PER SHARE

Pro forma net loss per share is computed as described above and also gives
effect, even if anti-dilutive, to common equivalent shares from convertible
preferred shares that automatically converted to common shares upon the closing
of the Company's initial public offering (using the as-if-converted method):

<TABLE>
<CAPTION>
YEARS ENDED DECEMBER 31,
1997 1996 1995
------------------------------------------
<S> <C> <C> <C>
Net loss ...................................................... $(14,664,213) $(10,206,885) $ (2,360,321)
==========================================

Weighted average common shares outstanding .................... 8,351,872 1,705,821 1,415,969
Adjustment to reflect the effect of the assumed conversion of
convertible preferred stock ................................ -- 4,202,396 3,722,770
------------------------------------------
Shares used in computing pro forma basic and diluted net loss
per share .................................................. 8,351,872 5,908,217 5,138,739
==========================================

Pro forma basic and diluted net loss per share ................ $ (1.76) $ (1.73) $ (0.46)
==========================================
</TABLE>

Common stock equivalents are excluded from the diluted net loss per share
calculation, as the effect is anti-dilutive.

RECLASSIFICATION OF PRIOR YEAR BALANCES

Certain balances in the 1996 financial statements have been reclassified to
conform to the current year financial statement presentation.

<PAGE> 39
CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

1. THE COMPANY AND ITS SIGNIFICANT ACCOUNTING POLICIES (CONTINUED)

IMPACT OF RECENTLY ISSUED ACCOUNTING STANDARDS

In June 1997, the Financial Accounting Standards Board issued Statement No.
130, "Reporting Comprehensive Income" ("FAS 130"), and Statement No. 131,
"Disclosure about Segments of an Enterprise and Related Information" ("FAS
131"). The Company is required to adopt these statements in fiscal year 1999.
FAS 130 establishes new standards for reporting and displaying comprehensive
income and its components. FAS 131 requires disclosure of certain information
regarding operating segments, products and services, geographic areas of
operation and major customers. Adoption of these statements is not expected to
have a significant impact on the Company's consolidated financial position,
results of operations or cash flows.

2. LICENSING AGREEMENTS WITH BAXTER HEALTHCARE CORPORATION, A RELATED PARTY OF
THE COMPANY

In December 1993, Cerus entered into a development and commercialization
agreement with Baxter Healthcare Corporation ("Baxter") to develop a system for
inactivation of pathogens in platelets. The agreement provides for Baxter to
make an equity investment and certain up-front license and milestone payments.
The agreement further provides for Baxter and the Company to generally share
system development costs equally, subject to mutually agreed budgets established
from time to time. The agreement also provides for a sharing of revenue from
sales of inactivation system disposables, after each party is reimbursed for its
cost of goods above a specified level. In January 1997, the Company and Baxter
amended the agreement to provide that the Company would receive an additional
2.2% of the adjusted product revenue from the sale of the platelet pathogen
inactivation system disposables in return for payment by the Company to Baxter
of $5.5 million in 1997 in four equal quarterly installments for development
costs.

In January and July 1995, Cerus received approximately $2.6 million from
Baxter in connection with interim funding agreements related to the development
of pathogen inactivation systems for plasma for transfusions (fresh frozen
plasma or "FFP") and red blood cells. In April 1996, Cerus entered into a second
development and commercialization agreement with Baxter, principally focused on
the FFP and red blood cell pathogen inactivation systems. The agreement provides
for Baxter to make certain equity investments, including two future
milestone-based investments of $5 million each at 120% of the market price at
the time of the investment. The agreement further provides for Baxter and the
Company to generally share development costs of the systems equally, subject to
mutually agreed budgets established from time to time. The agreement also
provides for the Company and Baxter to share gross profits from the sale of
inactivation system disposables, after deducting from such gross profits a
specified percentage allocation to be retained by the marketing party for
marketing and administration expenses.

37
<PAGE> 40

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

2. LICENSING AGREEMENTS WITH BAXTER HEALTHCARE CORPORATION, A RELATED PARTY OF
THE COMPANY (CONTINUED)

Under the agreements, all research, development, preclinical and clinical
costs of the pathogen inactivation projects are shared by Cerus and Baxter.
Because more of such research and development is typically performed internally
at Cerus than at Baxter and because Cerus is generally responsible for engaging
third parties to perform certain aspects of these projects, the Company's
research and development expenses have exceeded its share of expenses. As a
result, the Company has recognized revenue from Baxter, giving rise to a
receivable due from Baxter and corresponding periodic balancing payments to the
Company. At December 31, 1997, the amount of the Baxter receivable was
approximately $4.4 million. On February 13, 1998, Baxter paid Cerus
approximately $4.5 million in satisfaction of such receivable and anticipated
adjustments. Through December 31, 1997, the Company had recognized approximately
$19.2 million in revenue under its agreements with Baxter, including the license
fee and milestone and development funding amounts described above.

In March 1998, the Company and Baxter entered into an amendment to the April
1996 agreement providing that, to the extent the approved spending for 1998 for
the red blood cell project exceeds $7.3 million, Cerus will fund all expenses
for the red blood cell project in 1998 in excess of such amount, up to the
amount of the approved budget. To compensate Cerus for such excess expenditures,
Baxter will fully fund the first expenditures under the approved budget for the
red blood cell project for 1999 in an amount equal to such excess expenditures,
after which the parties shall equally share the expenses of the red blood cell
project. If for any reason there is not an approved budget for the red blood
cell project for 1999, Baxter will fully fund the first expenditures for 1999
under the approved budget for such other Cerus-Baxter program or programs as
Cerus shall designate in an amount equal to the Cerus 1998 excess expenditures.
If by July 1, 1999, however, there is not an approved budget for such other
Cerus-Baxter program or programs that is at least equal to such excess
expenditures, Baxter will promptly pay to Cerus one-half of the amount by which
the excess expenditures exceed the amount of expenditures to be funded by
Baxter. Cerus anticipates that the expenditures for 1998 for the FFP program
will exceed the previously approved budget. Cerus and Baxter are in discussion
regarding the level of funding each company will support in 1998 for the FFP
program.

As of December 31, 1997, Baxter owned 1,457,830 shares of the common stock
of the Company, representing approximately 15.9% of the outstanding common stock
of the Company. Baxter has agreed that it will not at any time, nor will it
permit any of its affiliates, to own capital stock of the Company having 20.1%
or more of the outstanding voting power of the Company. Such restrictions on
stock purchases will not apply in the event a third party makes a tender offer
for a majority of the outstanding voting securities of the Company or if the
Board of Directors of the Company determines to liquidate or sell to a third
party substantially all of the assets or a majority of the voting securities of
the Company or to approve a merger or consolidation in which the Company's
stockholders will not own a majority of the voting securities of the surviving
entity.

Revenue relating to licenses, milestones and development funding for all
periods presented are as a result of agreements with Baxter.

<PAGE> 41

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

3. INVESTMENTS

Investments classified as available-for-sale as of December 31, 1997, were
as follows:

<TABLE>
<S> <C>
Money market mutual funds ...................... $ 4,584,900
U.S. government obligations .................... 5,092,388
Commercial paper ............................... 11,903,086
------------
Total investments .............................. 21,580,374
Less: amounts classified as cash equivalents ... (11,603,196)
============
Short-term investments ......................... $ 9,977,178
============
</TABLE>

4. COMMITMENTS AND CONTINGENCIES

The Company leases its office facilities and certain equipment under
non-cancelable operating leases with initial terms in excess of one year which
require the Company to pay operating costs, property taxes, insurance and
maintenance. These facility leases generally contain renewal options and
provisions adjusting the lease payments.

Capital lease obligations represent the present value of future rental
payments under capital lease agreements for laboratory and office equipment. The
original cost and accumulated amortization on the equipment under capital leases
is $444,994 and $269,941, respectively, at December 31, 1997 and $413,969 and
$161,472, respectively, at December 31, 1996.

Future minimum payments under capital and operating leases are as follows:

<TABLE>
<CAPTION>
CAPITAL OPERATING
YEAR ENDING DECEMBER 31, LEASES LEASES
------------------
<S> <C> <C>
1998 ...................................... $ 78,648 $529,009
1999 ...................................... 32,541 172,205
2000 ...................................... 8,389 --
2001 ...................................... 4,893 --
------------------
Total minimum lease payments .............. 124,471 $701,214
========
Amount representing interest ............... 11,653
--------
Present value of net minimum lease payments 112,818
Current portion ............................ 69,816
--------
Long-term portion .......................... $ 43,002
========
</TABLE>

Rent expense for office facilities and certain equipment was $677,501,
$732,302 and $801,632 for the years ended December 31, 1997, 1996 and 1995,
respectively.

39
<PAGE> 42

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

4. COMMITMENTS AND CONTINGENCIES (CONTINUED)

TRADE SECRET MATTER

In August 1996, an Australian entity, alleged that its unspecified trade
secrets and know-how were used in the development by the Company of unspecified
compounds for the Company's red blood cell program without its consent. This
entity has indicated that it is seeking compensation in the form of royalties or
a lump-sum payment. Based on its investigation of the matter to date, the
Company believes that the claims are without merit. However, any future
litigation involving these allegations would be subject to inherent
uncertainties, especially in cases where complex technical issues are decided by
a lay jury. There can be no assurance that, if a lawsuit were commenced, it
would not be decided against the Company, in which case, settlement of this
claim could have a material adverse effect upon the Company's business,
financial condition and results of operations.

5. STOCKHOLDERS' EQUITY

COMMON STOCK

On January 30, 1997, the Company completed an initial public offering of
2,000,000 shares of common stock at $12.00 per share. The Company received net
proceeds of $21.1 million. In conjunction with the initial public offering, the
Company sold an additional 496,878 shares of its common stock to Baxter for an
aggregate purchase price of approximately $5.5 million. Additionally, at the
time of the initial public offering, 33,315 warrants to purchase 47,605 shares
of common stock were exercised for an aggregate price paid to the Company of
$183,000 and Series A, B, C, D and E preferred stock converted into 4,412,243
shares of common stock.

1992 STOCK OPTION PLAN

In January 1992, the Company's Board of Directors approved the 1992 Stock
Option Plan (the "Plan"), which provides for the grant of stock options to
purchase up to 588,000 of the Company's common stock. On May 18, 1996, the
Company's Board of Directors approved an increase in the number of shares of
common stock reserved for issue under the Plan from 588,000 to 1,029,000. Under
the Plan, two types of options may be granted: Incentive Stock Options ("ISOs")
and Non-Qualified Stock Options ("NQSOs"). The ISOs may be granted at a price
per share not less than the fair market value at the date of grant. The NQSOs
may be granted at a price per share not less than 85% of the fair market value
at the date of grant. The option term is 10 years. Vesting, as determined by the
Board of Directors, generally occurs ratably over four years. In the event
option holders cease to be employed by the Company, except in the event of death
or disability or as otherwise provided in the option grant, all unvested options
are forfeited and all vested options must be exercised within a three-month
period, otherwise the options are forfeited. Options granted are immediately
exercisable and unvested (but issued) shares are subject to repurchase by the
Company if the holder is no longer employed by the Company. As of December 31,
1997, 84,173 shares were subject to this repurchase provision.

On July 24, 1996, the Company adopted the 1996 Equity Incentive plan (the
"Incentive Plan") (approved by the stockholders in January 1997) as an amendment
and restatement of the Company's 1992 Stock Option Plan, and reserved an
additional 441,000 shares of common stock for issuance thereunder. The Incentive
Plan provides for grants of incentive stock options to employees and non
statutory stock options, restricted stock purchase awards, stock appreciation
rights and stock bonuses to employees, directors and consultants of the Company.

<PAGE> 43
CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

5. STOCKHOLDERS' EQUITY (CONTINUED)

1992 STOCK OPTION PLAN (CONTINUED)

The Company has elected to follow Accounting Principles Board Opinion No.
25, "Accounting for Stock Issued to Employees" ("APB 25") and related
interpretations in accounting for its employee stock options because, as
discussed below, the alternative fair value accounting provided for under FAS
123 requires the use of option valuation models that were not developed for use
in valuing employee stock options.

"As adjusted" information regarding net loss and net loss per share is
required by FAS 123, and has been determined as if the Company had accounted for
its employee stock options and grants under its employee stock purchase plan
described below under the fair value method of that Statement. The fair value
for these options and shares was estimated at the date of grant using a
Black-Scholes option pricing model with the following weighted-average
assumptions:

<TABLE>
<CAPTION>
YEARS ENDED DECEMBER 31,
1997 1996 1995
---------------------------------
<S> <C> <C> <C>
Expected dividend yield .......... 0% 0% 0%
Expected volatility .............. .7424 .5925 .5925
Risk-free interest rate .......... 6.13% 5.09% 5.35%
Expected life of the option ...... 2.6 years 5 years 5 years
</TABLE>

The Black-Scholes option valuation model was developed for use in
estimating the fair value of traded options which have no vesting restrictions
and are fully transferable. In addition, option valuation models require the
input of highly subjective assumptions including the expected stock price
volatility. Because the Company's employee stock options and purchased shares
have characteristics significantly different from those of traded options, and
because changes in the subjective input assumptions can materially affect the
fair value estimate, in management's opinion, the existing models do not
necessarily provide a reliable single measure of the fair value of its employee
stock options.

For purposes of "as adjusted" disclosures, the estimated fair value of the
options is amortized to expense over the options' vesting period. The effects of
applying FAS 123 on "as adjusted" net loss are not likely to be representative
of the effects on reported net loss/income for future years. The Company's
reported and "as adjusted" information at December 31 follows:

<TABLE>
<CAPTION>
1997 1996 1995
----------------------------------------------------
<S> <C> <C> <C>
Net loss, as reported ............................... $(14,664,213) $(10,206,885) $(2,360,321)
Net loss, "as adjusted" ............................. (14,966,213) (10,509,885) (2,365,321)
Net loss per share - basic and diluted, as reported . (1.76) (5.98) (1.67)
Net loss per share - basic and diluted, "as adjusted" (1.79) (6.16) (1.67)
</TABLE>

<PAGE> 44

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

5. STOCKHOLDERS' EQUITY (CONTINUED)

1992 STOCK OPTION PLAN (CONTINUED)

Activity under the Plan is set forth below:

<TABLE>
<CAPTION>
OUTSTANDING OPTIONS
---------------------------------- WEIGHTED AVERAGE
NUMBER OF PRICE EXERCISE PRICE OF
SHARES PER SHARE SHARES UNDER PLAN
---------------------------------------------------------
<S> <C> <C> <C>
Balances at December 31, 1994................................... 498,256 $ .262- .544
Granted....................................................... 75,705 .714 $ .714
Cancelled..................................................... (63,290) .262- .544 .376
Exercised..................................................... (4,623) .262- .544 .365
---------------------------------------------------------
Balances at December 31, 1995................................... 506,048 .262- .714 .670
Granted....................................................... 418,126 .714- 10.200 2.533
Cancelled..................................................... (5,879) .714 .714
Exercised..................................................... (510,912) .262- 2.721 .344
---------------------------------------------------------
Balances at December 31, 1996................................... 407,383 .262- 10.200 2.523
Granted....................................................... 51,300 10.625- 23.875 14.925
Cancelled..................................................... (10,184) .544- 4.082 3.240
Exercised..................................................... (61,229) .262- 2.721 1.045
---------------------------------------------------------
Balances at December 31, 1997................................... 387,270 $ .262- 23.875 $ 4.380
=========================================================
</TABLE>

The weighted average fair value of options granted during 1997, 1996 and
1995 is $8.107, $6.005 and $1.024 per share, respectively. Options to purchase
507,116 shares of common stock were available for future grant.

The following table summarizes information concerning outstanding and
vested options as of December 31, 1997:

<TABLE>
<CAPTION>
OPTIONS OUTSTANDING OPTIONS VESTED
---------------------------------------------------- ---------------------------------------
WEIGHTED
AVERAGE WEIGHTED
NUMBER OF REMAINING WEIGHTED AVERAGE NUMBER OF AVERAGE
RANGE OF EXERCISE PRICES SHARES CONTRACTUAL LIFE EXERCISE PRICE SHARES EXERCISE PRICE
- ------------------------------ --------------- ----------------- ------------------ ---------------------------------------
<S> <C> <C> <C> <C> <C>
$0.262-0.7143............. 47,033 6.82 $ 0.611 38,247 $ 0.598
$2.721-4.082.............. 274,605 8.38 $ 2.814 106,879 $ 2.801
$8.163-14.000............. 53,932 9.28 $ 11.952 9,962 $ 10.877
$19.000-23.875............ 11,700 9.87 $ 21.375 - -
=============== ================= ================== =======================================
387,270 8.36 $ 4.380 155,088 $ 2.776
=============== ================= ================== =======================================
</TABLE>

<PAGE> 45
CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

5. STOCKHOLDERS' EQUITY (CONTINUED)

The Company recognized deferred compensation of $530,215 for the difference
between the exercise price and deemed fair value of certain stock options
granted during the year ended December 31, 1996. This amount is being amortized
by periodic charges to operations over the four year vesting periods of the
individual options. Amortization expense related to deferred compensation
totaled $169,450 and $219,828 for the years ended December 31, 1997 and 1996,
respectively.

EMPLOYEE STOCK PURCHASE PLAN

On July 24, 1996, the Company's Board of Directors approved the Employee
Stock Purchase Plan (the "Purchase Plan") (approved by the stockholders in
January 1997) covering an aggregate 220,500 shares of common stock. The Purchase
Plan is intended to qualify as an employee stock purchase plan within the
meaning of Section 423(b) of the Code. Under the Purchase Plan, the Board of
Directors may authorize participation by eligible employees, including officers,
in periodic offerings following the adoption of the Purchase Plan. The offering
period for any offering will be no more than 27 months. During 1997, employees
purchased 20,830 shares under the Purchase Plan. At December 31, 1997, 199,670
shares were available for issuance.

WARRANTS

The Company had the following warrants issued in connection with an
operating lease line, outstanding at December 31, 1997 to purchase shares of
common stock, all of which expire in February 2002:

<TABLE>
<CAPTION>
NUMBER EXERCISE DATE
OF SHARES PRICE PER SHARE ISSUED
--------- --------------- ------
<S> <C> <C>
30,545 $2.62 May 1992

5,805 $3.45 July 1993

9,187 $5.44 May 1994

6,615 $7.14 April 1995
==============
52,152
==============
</TABLE>

43
<PAGE> 46
CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

5. STOCKHOLDERS' EQUITY (CONTINUED)

REINCORPORATION AND STOCK SPLIT

On January 14, 1997, the Company effected a stock split of all outstanding
shares of common stock such that each share of common stock will be split into
1.47 shares of common stock. All common shares in the accompanying financial
statements have been retroactively adjusted to reflect the stock split. In
connection with the stock split, the conversion and exercise provisions of the
outstanding shares of preferred stock, stock options and warrants have been
adjusted accordingly. At the same time, the Board authorized the Company to
proceed with the reincorporation of the Company into Delaware. Upon the
reincorporation, the authorized stock of the Company became 5,000,000 shares of
preferred stock, par value $.001 per share, and 50,000,000 shares of common
stock, par value $.001 per share. Also upon reincorporation, the Board of
Directors received the authority, without further action by the stockholders, to
issue up to 5,000,000 shares of preferred stock in one or more series and to fix
the designations, powers, preferences, privileges, and relative participating,
optional or special rights and the qualifications, limitations, or restrictions
thereof, including dividend rights, conversion rights, voting rights, and terms
of redemption and liquidation preferences, any or all of which may be greater
than the rights of the common stock.

6. INCOME TAXES

Deferred income taxes reflect the net tax effects of temporary differences
between the carrying amounts of assets and liabilities for financial reporting
purposes and the amounts used for income tax purposes. Significant components of
the Company's deferred tax assets are as follows:

<TABLE>
<CAPTION>
DECEMBER 31,
1997 1996
-----------------------------
<S> <C> <C>
Net operating loss carryforward .......................... $ 10,200,000 $ 6,400,000
Research and development credit carryforward ............. 1,600,000 800,000
Certain expenses not currently deductible for tax purposes 2,200,000 --
Deferred revenue ......................................... -- 400,000
Capitalized research and development ..................... 900,000 400,000
Other .................................................... 300,000 200,000
-----------------------------
Gross deferred tax assets ................................ 15,200,000 8,200,000
Valuation allowance ...................................... (15,200,000) (8,200,000)
-----------------------------
Net deferred tax assets .................................. $ -- $ --
=============================
</TABLE>

<PAGE> 47

CERUS CORPORATION

NOTES TO FINANCIAL STATEMENTS (CONTINUED)

6. INCOME TAXES (CONTINUED)

The valuation allowance increased by $7,000,000 and $4,000,000 for the
fiscal years ended in 1997 and 1996, respectively. The increase is primarily
attributable to the increase in the net operating loss and tax credit
carryforwards. The Company believes that, based on a number of factors, the
available objective evidence creates sufficient uncertainty regarding the
realizability of the deferred tax assets such that a full valuation allowance
has been recorded. These factors include the Company's history of net losses
since its inception, the need for FDA approval of the Company's products prior
to commercialization, expected near-term future losses, the nature of the
Company's deferred tax assets, the lack of firm sales backlog, no significant
excess of appreciated asset value over the tax basis of the Company's net assets
and the absence of taxable income in prior carryback years. The valuation
allowance at December 31, 1997 includes $400,000 related to deferred tax assets
arising from tax benefits associated with stock option plans. This benefit, when
realized, will be recorded as an increase in stockholders' equity rather than as
a reduction in the income tax provision.

Although management's operating plans assume, beyond the near-term, taxable
and operating income in future periods, management's evaluation of all available
information in assessing the realizability of the deferred tax assets in
accordance with Financial Accounting Standards Board Statement No. 109,
"Accounting for Income Taxes," indicates that such plans are subject to
considerable uncertainty. Therefore, the valuation allowance has been increased
to fully reserve the Company's deferred tax assets. The Company will continue to
assess the realizability of the deferred tax assets based on actual and
forecasted operating results.

At December 31, 1997, the Company had net operating loss carryforwards of
approximately $27,800,000 for federal and $14,100,000 for state income tax
purposes. The Company also had research and development tax credit carryforwards
of approximately $1,200,000 for federal income tax purposes and approximately
$400,000 for state income tax purposes at December 31, 1997. The federal net
operating loss and tax credit carryforwards expire between the years 2007 and
2012. The state net operating loss carryforward expires in 2001 and 2002.

Utilization of the Company's net operating losses and credits are subject
to a substantial annual limitation due to the ownership change limitations
provided by the Internal Revenue Code. The annual limitation may result in the
expiration of net operating losses and credits before utilization.

7. RETIREMENT PLAN

The Company maintains a defined contribution savings plan (the "401(k)
Plan") that qualifies under the provisions of Section 401(k) of the Internal
Revenue Code and covers all employees of the Company. Under the terms of the
401(k) Plan, employees may contribute varying amounts of their annual
compensation. The Company may contribute a discretionary percentage of qualified
individual employee's salaries, as defined, to the 401(k) Plan. Company
contributions of $3,500 and $2,700 were charged to operations in 1996 and 1995,
respectively, in order to cover certain costs of the 401(k) Plan. The Company
did not contribute to the 401(k) Plan in 1997.

<PAGE> 48

SIGNATURES

Pursuant to the requirement of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the Registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized, in the City of
Concord, State of California, on the 6th day of March, 1998.

CERUS CORPORATION

By: /s/ Stephen T. Isaacs
--------------------------------------
Stephen T. Isaacs
President and Chief Executive Officer

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

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

/s/ Stephen T. Isaacs President, Chief Executive Officer and March 6, 1998
- ---------------------------------
Stephen T. Isaacs Director
(Principal Executive Officer) March 6, 1998

/s/ David S. Clayton Vice President, Finance and Chief Financial March 6, 1998
- ---------------------------------
David S. Clayton Officer
(Principal Financial and Accounting Officer) March 6, 1998

/s/ B. J. Cassin Chairman of the Board
- ---------------------------------
B. J. Cassin

/s/ John E. Hearst Director March 6, 1998
- ---------------------------------
John E. Hearst

/s/ Peter H. McNerney Director March 6, 1998
- ---------------------------------
Peter H. McNerney

/s/ Dale A. Smith Director March 6, 1998
- ---------------------------------
Dale A. Smith

/s/ Henry E. Stickney Director March 6, 1998
- ---------------------------------
Henry E. Stickney
</TABLE>

<PAGE> 49

EXHIBIT INDEX

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

+ Certain portions of this exhibit are subject to a confidential treatment
order.

(1) Incorporated by reference from the Company's Registration Statement on
Form S-1 (File No. 333-11341) and amendments thereto.

* Confidential treatment has been requested for certain portions of this
exhibit.

<PAGE> 1
EXHIBIT 10.27

***TEXT OMITTED AND FILED SEPARATELY
CONFIDENTIAL TREATMENT REQUESTED
UNDER 17.C.F.R. Sections 200.80(B)(4),
200.83 AND 240.24B-2

LICENSE AGREEMENT

THIS Agreement, effective November 30, 1992 by and between STERITECH,
INC., a California corporation, having a principal office at 2341 Stanwell
Drive, Concord, California 94520 ("STERITECH") and MILES INC., an Indiana
corporation, Mobay Road, Pittsburgh, Pennsylvania 15205 ("MILES"), and DIAMOND
SCIENTIFIC CORPORATION, a ________ corporation, ("DIAMOND").

WITNESSETH THAT:

WHEREAS, United States Patent No. 4,545,987, entitled: "PSORALEN
INACTIVATED DOUBLE-STRANDED RNA VIRAL VACCINES", was issued on October 8, 1985,
a copy of which is attached hereto as Exhibit A;

WHEREAS, United States Patent No. 4,693,981, entitled: "PREPARATION OF
INACTIVATED VIRAL VACCINES", was issued on September 15, 1987, a copy of which
is attached hereto as Exhibit B;

WHEREAS, United States Patent No. 4,727,027, entitled: "PHOTOCHEMICAL
DECONTAMINATION TREATMENT OF WHOLE BLOOD OR BLOOD COMPONENTS", was issued on
February 23, 1988, a copy of which is attached hereto as Exhibit C;

WHEREAS, United States Patent No. 4,748,120, entitled: "PHOTOCHEMICAL
DECONTAMINATION TREATMENT OF WHOLE BLOOD OR BLOOD COMPONENTS", was issued on May
31, 1988, a copy of which is attached hereto as Exhibit D;

WHEREAS, United States Patent No 4,791,062, entitled: "FVR VACCINE", was
issued on December 13, 1988, a copy of which is attached hereto as Exhibit E;

WHEREAS, United States Patent No. 5,106,619, entitled: "PREPARATION OF
INACTIVATED VIRAL VACCINES", was issued on April 21, 1992, a copy of which is
attached hereto as Exhibit F;

WHEREAS, DIAMOND, which is a wholly owned subsidiary of MILES, is the
owner by assignment of U.S. Patent Nos.: 4,545,987; 4,693,981; 4,727,027;
4,748,120; 4,791,062; and 5,106,619 and has the right to grant licenses under
these patents;

1
<PAGE> 2

WHEREAS, DIAMOND, which is a wholly owned subsidiary of MILES, is the
owner of the foreign patents and patent applications that correspond to the
above patents and are identified in Exhibit G and has the right to grant
licenses under the foreign patents and patent applications.

WHEREAS, STERITECH desires to obtain [...***...] license to the
inventions and discoveries embodied in U.S. Patent Nos.: 4,545,987; 4,693,981;
4,727,027; 4,748,120; 4,791,062; and 5,106,619 Related Patents and Patent
Applications, and the Foreign Patents and Patent Applications (identified in
Exhibit G) in the field of [...***...];

WHEREAS, MILES is willing to grant STERITECH such [...***...] in the
field of [...***...], subject to rights reserved by the U.S. government, to U.S.
Patent Nos.: 4,545,987; 4,693,981; 4,727,027; 4,748,120; 4,791,062; and
5,106,619; Related Patents and Patent Applications, and the Foreign Patents and
Patent Applications (identified in Exhibit G);

WHEREAS, MILES is willing to grant STERITECH a license, subject to
rights reserved by the U.S. government, to U.S. Serial No. 07/350,335, and its
related foreign applications (identified in Exhibit H) which applications are
jointly owned by DIAMOND and the Regents of the University of California at San
Francisco.

NOW THEREFORE, the parties agree as follows:

1. DEFINITIONS

The following definitions will apply throughout this Agreement:

LICENSED PATENTS shall mean U.S. Patent Nos.: 4,545,987; 4,693,981;
4,727,027; 4,748,120; 4,791,062; and 5,106,619 as well as the Foreign Patents
identified in Exhibits G and H;

RELATED PATENTS AND PATENT APPLICATIONS shall mean any continuation,
reissue, reexamination, continuation-in-part, extension or divisional
application of a Licensed Patent and/or any letters patent that issue thereon;

FOREIGN PATENT APPLICATIONS shall mean the foreign patent applications
identified in Exhibits G and H or that may be filed in the future as foreign
counterparts of the Licensed Patents and/or any letters patent that issue
thereon;

LICENSED PRODUCT shall mean any product for use in the field of
[...***...] that is covered by a claim of a Licensed Patent in the country in
which it is sold and/or any product utilizing a process covered by a claim of a
Licensed Patent in the country in which it is used; and

AFFILIATES OF STERITECH shall mean all organizations that are at least
50% owned or controlled by STERITECH or any organization owning at least 50% of
or controlling STERITECH or subsidiaries of such organizations owning at least
50% of or controlling STERITECH.

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

2
<PAGE> 3

NET SALES shall mean the gross revenues received by STERITECH and its
Affiliates from the sale of Licensed Products less sales, use and/or value added
taxes actually paid, import and/or export duties, tariffs and other excise taxes
actually paid, transportation prepaid or allowed, and amounts allowed or
credited due to returns, rebates, discounts and the like (not to exceed the
original billing or invoice amount). For cases in which the Licensed Product is
a product covered by a claim of a Licensed Patent, Net Sales shall be computed
on the revenues received by STERITECH and its Affiliates from sales of such
product. For cases in which the process covered by the claim of a Licensed
Patent is used (e.g., [...***...]), Net Sales shall be computed on the revenues
received by STERITECH and its Affiliates from the sales of the materials that
perform such process. Where such materials are sold as components of a system
(e.g., [...***...]) the royalty base on which Net Sales will be computed shall
be the [...***...] that permit performance of the licensed process, rather than
[...***...].

2. GRANT

MILES and DIAMOND hereby grant to STERITECH, and its Affiliates, a
[...***...] license in the field of [...***...], including [...***...], subject
to rights reserved by the U.S. government, under the Licensed Patents, Related
Patents and Patent Applications, and Foreign Patent Applications, for
[...***...], with the right to make, have made, use, and sell products covered
by a claim thereunder and practice any process covered by a claim thereunder,
including the right to sub-license others to make, have made, use, or sell any
such product or practice any such process.

This license is [...***...] with respect to U.S. Serial No. 07/350,335
only with respect to MILES' rights under this application, which application is
jointly owned by DIAMOND and The Regents of the University of California at San
Francisco.

3. CONSIDERATION AND ROYALTIES

3.1 PAYMENTS MADE IN CONSIDERATION OF THE EXECUTION OF THE LICENSE
AGREEMENT. As consideration for the licenses granted herein, STERITECH will pay
a non-refundable license fee, upon execution of this Agreement, of $[...***...].

3.2 ADVANCED ROYALTIES TO BE PAID DURING LICENSE. In addition to
the fee specified in Paragraph 3.1, STERITECH will pay a non-refundable
milestone payment of $[...***...] upon [...***...] for the [...***...] Licensed
Product and a non-refundable milestone payment of $[...***...] upon [...***...]
for the [...***...] Licensed Product. These milestone payments will be credited
against royalties.

3.3 ROYALTY. STERITECH will pay MILES a royalty equal to
[...***...] of Licensed Products. Only [...***...] shall be paid under this
Agreement for each Licensed Product sold regardless of [...***...] of Licensed
Patents that are applicable thereto. No royalty shall be payable on [...***...]
is purchasing the Licensed Product for use in its own commercial activities,

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

3
<PAGE> 4

excluding use solely for [...***...]. Royalties shall otherwise be payable on
the [...***...] of STERITECH.

3.4 CESSATION OF OBLIGATION TO PAY ROYALTY. STERITECH's obligation
to pay a royalty for a Licensed Product which is made, used or sold in any given
country shall cease:

(a) if every one of the claims directed to Licensed Product
which would be infringed but for the license granted herein and all of the
claims directed to the process(es) of making and using that Licensed Product
which would be infringed but for the license granted herein are held invalid and
unenforceable by a court of competent jurisdiction in a final, unappealable
decision; or

(b) upon expiration of the last to expire of the Licensed
Patents; or

(c) if no claim of any Licensed Patent covers Licensed Product
in the country where the product is sold and no claim of any Licensed Patent
covers Licensed Product in the country in which Licensed Product is produced or
used.

3.5 MINIMUM ROYALTIES. STERITECH shall pay the following minimum
royalties, inclusive of royalties payable under Section 3.3:

<TABLE>
<CAPTION>
AMOUNT YEAR
<S> <C> <C>
$[...***...] [...***...]

$[...***...] [...***...]

$[...***...] [...***...]
</TABLE>

The first year to which minimum royalty requirement shall apply shall be the
earlier of [...***...] or the [...***...] for the first Licensed Product. Each
twelve months period thereafter shall constitute a year for the purpose of
calculating minimum royalties. In the event minimum royalties are not paid as
provided above for any year, MILES may, by notice to STERITECH given within
[...***...] of the end of the respective year:

(a) terminate this License Agreement, if STERITECH is not then
exercising reasonable good faith efforts to develop and/or market Licensed
Products, or

(b) [...***...].

4. PAYMENT

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

4
<PAGE> 5
4.1 ACCOUNTS. STERITECH shall keep a complete and correct account
of the number of Licensed Products sold in sufficient detail to determine the
amounts due to MILES. STERITECH shall keep such account for at least three years
after making the royalty payment.

STERITECH's records shall be available upon written request for
inspection at reasonable times during regular business hours by an independent
certified public accountant selected by MILES to whom STERITECH has no
reasonable objection for the purpose of verifying royalty statements and
payments made by STERITECH under this Agreement. This accountant shall not
disclose to MILES any information other than the quantities and payments
required to be reported hereunder. MILES shall hold all such information in
confidence.

4.2 PAYMENT. Within [...***...] after the end of each of
STERITECH's operating quarters, STERITECH shall send MILES a written statement,
setting forth all sales of Licensed Product and a computation of royalties on
these sales to MILES in accordance with this Agreement. Such statements shall be
accompanied by payment of the total amount of royalty due. To the extent no
royalty is due because of credits for previous milestone payments, this shall be
reported by STERITECH.

5. LITIGATION

5.1 NOTIFICATION. MILES agrees to notify STERITECH in writing if
the validity, infringement, or priority of invention of any of the Licensed
Patents is put in issue by any person not a party hereto.

5.2 INFRINGEMENT. MILES agrees to use all reasonable measures to
enforce the Licensed Patents against infringers. Upon learning of infringement
of a Licensed Patent, STERITECH shall promptly notify MILES of the infringement
and provide MILES with such notice concerning such infringement. MILES shall
have [...***...] from the date of STERITECH's notice to abate the infringement
or to file suit against the infringer.

5.3 LAWSUITS. If MILES brings suit against an infringer of a
Licensed Patent, it shall give notice of such suit to STERITECH and STERITECH
shall have [...***...] in which to elect to join MILES in the prosecution of the
suit. If STERITECH so elects, MILES and STERITECH shall share equally in the
expenses, costs, attorneys fees, and proceeds of such suit for past
infringement. If STERITECH elects not to join MILES, MILES shall be responsible
for all expenses and shall take all proceeds for past infringement. If STERITECH
elects not to join with MILES, MILES shall keep STERITECH reasonably informed of
the status of any such litigation.

5.4 FAILURE TO SUE. If MILES fails to bring suit [...***...] after
notice by STERITECH as specified by Section 5.2 above, STERITECH may elect to
file suit on its own. STERITECH's obligation to continue paying royalties
hereunder shall not be affected by the bringing of such suit. Proceeds from the
litigation, if any, shall be divided between MILES and Steritech in proportion
to their contribution to the cost of litigation.

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

5
<PAGE> 6

5.5 SETTLEMENT. For as long as this [...***...], MILES shall not
have the power to accept any settlement that includes a license for future
activities in that country without STERITECH's written consent, which consent
shall not be unreasonably withheld.

5.6 INFRINGEMENT OF THIRD PARTY RIGHTS. In the event of any
infringement or likely infringement by any of the licensed subject matter of any
third party's intellectual property (collectively, "Infringing Rights"), MILES
and STERITECH shall cooperate in good faith and on a mutual and reasonable
basis, with each party responsible for its respective expenses:

(a) To negotiate and settle any dispute with any such third
party concerning the Infringing Rights, and otherwise resolve any such
infringement and secure STERITECH's continued rights to the Infringing Rights;
and

(b) To make a reasonable and equitable adjustment, if any, to
the royalties paid or otherwise due under this Agreement in respect of licenses
or other rights obtained by STERITECH from third parties under such Infringing
Rights in order for STERITECH to continue to exercise rights granted under this
Agreement.

6. MISCELLANEOUS

6.1 NOTICE. Until such time as either party shall give notice to
the other party of a change of address, reports, notices, and other
communications to MILES shall be addressed to:

Divisional Controller
MILES INC.
Animal Health Products
12707 West 63rd
Shawnee Mission, KS 66216

and notices and other communications to STERITECH shall be addressed as follows:

STERITECH, INC.
2341 Stanwell Drive
Concord, California 94520
Attention: President

6.2 GOVERNING LAW. This Agreement shall be interpreted under the
laws of California.

6.3 TERMINATION.

(a) MILES may terminate this License Agreement for
noncompliance by STERITECH of any material provision by giving notice of its
intention to do so [...***...]

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

6
<PAGE> 7

before termination. If STERITECH shall, within the [...***...] notice period
correct the noncompliance, the notice shall have no further effect and the
Agreement shall continue.

(b) STERITECH may terminate this License Agreement by giving
notice of its intention to do so [...***...] before termination.

6.4 SOLE AGREEMENT. This Agreement constitutes the entire
understanding between the parties and neither party shall be obligated by any
condition or representation other than those expressly stated herein or as may
be subsequently agreed to by the parties hereto in writing.

6.4 HEADINGS. The headings and subheading of the various Articles
and Sections of this Agreement are inserted merely for the purpose of
convenience and do not express or imply any limitation, definition, or extension
of the specific terms of the Articles and Sections so designated.

6.6 WARRANTIES.

(a) MILES represents and warrants that it is the owner of
DIAMOND which is the owner of the entire right, title and interest in and to the
Licensed Patents, Related Patents and Patent Applications, and Foreign Patent
Applications with the exception of U.S. Serial No. 07/350,335 and its
corresponding Foreign Patent Applications which are jointly owned by DIAMOND and
The Regents of the University of California at San Francisco and has the right
to grant the licenses given hereunder.

(b) MILES warrants and represents that there are no known
outstanding claims or licenses or other encumbrances upon Licensed Patents,
Related Patents and Patent Applications, and Foreign Patent Applications with
the exception of the limited rights reserved by the U.S. government and the
joint ownership of U.S. Serial No. 07/350,335 and that MILES is not now in the
possession of any information which would, in MILES' opinion, render any of the
claims of any of the Licensed Patents invalid and/or unenforceable.

6.7 PATENT RELATED EXPENSES. MILES will pay all annuities, taxes,
and other expenses due and owing to maintain any Licensed Patent, Related Patent
and Patent Application, and Foreign Patent Application in full force and in
effect for any year (i.e., calendar year or twelve-month period, as the case may
be) in which royalties, license fees and milestone payments owed or paid by
STERITECH equal or exceed such annuities, taxes and expenses. In the event
STERITECH pays royalties, license fees and milestone payments less than the
total annuities, taxes and expenses due in a given year, MILES shall advise
STERITECH and provide STERITECH with the option to pay the excess expense so as
to maintain the Licensed Patent, Related Patent or Patent Application, or
Foreign Patent Application.

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

7
<PAGE> 8

6.8 FOREIGN PATENT PROSECUTION. In the event that STERITECH and
MILES shall agree, each acting reasonably and in good faith, that it is
desirable to obtain foreign patent protection of the licensed subject matter
beyond the Foreign Patents and Foreign Patent Applications identified herein,
MILES shall prepare, file and prosecute foreign applications with respect
thereto. Expenses of obtaining and maintaining such patent protection shall be
allocated as provided in Section 6.7. In the event MILES does not agree with
STERITECH concerning the desirability of obtaining such protection, MILES shall
execute such documents as shall permit STERITECH to undertake such preparation,
filing and prosecution, in which case STERITECH shall bear the expenses thereof,
but shall be entitled to credit such expenses against royalties payable
hereunder.

6.9 LICENSE GRANTED BACK TO MILES. At any time during the term of
this Agreement, MILES has the right to obtain a non-exclusive license under any
Licensed Patent under reasonable conditions. It is expressly agreed that any
license granted by STERITECH to MILES under this paragraph shall be limited to
only those rights reasonable necessary for [...***...] thereof including but not
limited to [...***...].

- ----------
*CONFIDENTIAL TREATMENT REQUESTED

8
<PAGE> 9

IN WITNESS WHEREOF, the parties heretofore have affixed their authorized
signatures as of the date given.

ATTEST: MILES, INC.

By: /s/ Thomas W. Roy By: /s/ Mark Yogman
--------------------------------- -------------------------------------
Title: Vice President,
Strategic Planning
Date: November 19, 1992

ATTEST: DIAMOND SCIENTIFIC CORPORATION

By: /s/ Kathryn L. Johns By: /s/ Spencer J. Nunley
--------------------------------- -------------------------------------
Title: Secretary
Date: November 20, 1992

ATTEST: STERITECH, INC.

By: /s/ D. Hall By: /s/ Stephen T. Isaacs
--------------------------------- -------------------------------------
Title: Chief Executive Officer
Date: November 30, 1992

9
<PAGE> 10
EXHIBIT A

United States Patent [19] [11] Patent Number: 4,545,987
Giles et al. [45] Date on Patent: Oct. 8, 1985
- --------------------------------------------------------------------------------

[54] PSORALEN INACTIVATED DOUBLE-STRANDED RNA VIRAL VACCINES

[75] Inventors: Richard E. Giles, Alameda; David R. Stevens, Fremont; Gary P.
Wiesehahn, Alameda, all of Calif.

[73] Assignee: Advanced Genetics Research Institute, Oakland, Calif.

[21] Appl. No.: 563,939

[22] Filed: Dec. 20, 1983

[51] Int. CL4. . . . . . . . . . . . . . . . . A61K 39/12

[52] U.S. CL . . . . . . . . . . . . . . . . . 424/89; 435/235; 435/238

[58] Field of Search . . . . . . . . . . . . . 435/235, 238; 424/89

[56] References Cited

PUBLICATIONS

Theiler, Vet. J., (1980), 64:600-607.
Kemeny and Drehle, Am. J. Vet. Res. (1961), 22:921-925.
Alexander and Haig, Onderstepoort J. Vet. Res., (1951), 25:3-15.
Parker et al., Vet. Rec., (1975), 96:284-287.
Isaacs et al., Biochemistry, (1977), 16:1058-1064.
Hearst and Thiry, Nucleic Acids Res., (1977), 4:1339-1347.
Hanson et al., J. Gen. Virol., (1978), 40:345-358.
Talib and Banerjee, Virology, (1982), 118:430-438.
Hanson, Medical Virology II, Proceedings of the 1982 International Symposium on
Medical Virology, de la Maza and Peterson, eds., New York: Elsevier Biomedical,
1983, pp. 45-75.
J. Parker et al., (1975), Vet. Rec. 96:284-287.
J. L. Stott, et al., (1979), Proc. Annu. Meet US Anim Health Assoc., 177:55-62.
B. I. Osburn et al., and J. L. Stott et al., (1979), Fed. Proc. 38 (3 part 1)
1091 Coden: FEPRA.

Primary Examiner -- Shep K. Rose
Attorney, Agent or Firm -- Townsend & Townsend

[57] ABSTRACT

Novel vaccines of double-stranded RNA viruses are prepared by psoralen
inactivation under mild conditions in an inert atmosphere, optionally in the
presence of a mild singlet oxygen scavenger. The resulting inactivated virus can
be used as a vaccine for inoculation of hosts to provide for the stimulation of
the immune system to the virus.

11 Claims, No Drawings

<PAGE> 11
4,545,987

PSORALEN INACTIVATED DOUBLE-STRANDED RNA VIRAL VACCINES

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disease Bluetongue is a systemic viral infection of ruminants, such
as sheep and cattle. The Bluetongue virus (BTV) is transmitted by small biting
flies and is known to occur in twenty serotypic variants that do not provide
cross-protection immunologically.

The Bluetongue virus is the prototype orbivirus and is composed of ten
double-stranded RNA genomic segments. Bluetongue virions have an inner capsid
of five polypeptides and a diffuse non-enveloped outer layer containing two
polypeptides. It is found that variable amino acid sequences in P2, the major
surface polypeptide, are responsible for immunologic serotype specificity. A
core protein, P7, is detected by the complement fixation assay and determines
cross-reacting group specificity.

In the United States, the primary serotypes observed are 11 and 17,
with serotypes 2, 10 and 13 being observed less frequently.

The first vaccine for BTV was an attenuated live virus vaccine, which
has been utilized over forty years in South Africa. Other modified live virus
Bluetongue vaccines have also been reported. These attenuated live virus
vaccines induce teratogenic lesions in fetuses and may also result in the
emergence of recombinant virus strains. There is, therefore, need for an
effective vaccine against Bluetongue, which provides protection to an
inoculated mammalian host, without the hazards observed with attenuated live
Bluetongue virus.

2. Description of the Prior Art

Theiler, Vet. J. (1908) 64:600-607 describes an attenuated live
Bluetongue virus vaccine. Kemeny and Drehle, Am. J. Vet. Res. (1961) 22:921-925
describe a tissue culture-propagated BTV for vaccine preparation. Alexander and
Haig, Onderstepoort J. Vet. Res. (1951) 25:3-15 describe the use of attenuated
BTV in the production of a polyvalent vaccine for sheep. Parker et al, Vet.
Rec. (1975) 96:284-287 describe an inactivated vaccine against Bluetongue.

Isaacs et al, Biochemistry (1977) 16:1058-1064, describe the synthesis
of several psoralen derivatives and their photoreactivity with double-stranded
RNA. Hearst and Thiry, Nucleic Acids Research (1977) 4:1339-1347; Hanson et al,
J. Gen. Virol. (1978) 40:345-358; and Talib and Banerjee, Virology (1982)
118:430-438, describe the photoreactivity of various psoralen derivatives with
animal viruses. Hanson, in Medical Virology II, Proceedings of the 1982
International Symposium on Medical Virology, de la Maza and Peterson, eds., New
York: Elsevier Biomedical, 1983, pp. 45-75, has cited unpublished data on the
inactivation of Bluetongue virus utilizing psoralen photochemistry.

SUMMARY OF THE INVENTION

Vaccines are provided for inoculation against Bluetongue virus, which
inactivated vaccines are prepared by irradiating the virus suspension with light
in the presence of psoralen in an inert atmosphere for a time sufficient to
completely inactivate the virus. The resulting inactivated virus suspension
may then be stored for subsequent use.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Vaccines are provided for inoculation of ruminants against Bluetongue.
The vaccines are prepared by inactivation of one or more serotypes of
Bluetongue virus (BTV), a multisegmented double-stranded RNA orbivirus. The BTV
is inactivated by combining a suspension of the BTV in an appropriate medium
with a sufficient amount of a psoralen to provide for complete inactivation of
BTV upon irradiation with long wavelength ultraviolet light (UVA), while
maintaining an inert atmosphere. The resulting inactivated virus preparation
may be stored until used for inoculation. Inoculated ruminants react to
vaccination with the subject vaccine by producing neutralizing antibodies.

Any of the serotypes of BTV may be inactivated by the subject method.
Serotypes of particular interest include 2,10,11,13 and 17, which are the
serotypes observed most frequently in the United States, but the other
serotypes prevalent in other geographic areas can also be employed.

In preparing the vaccine, the BTV is grown in cultured mammelian cells.
Illustrative cells include Vero cells, monkey kidney cells, CCL 10 hamster
cells, LMTK-cells, or other cells permissive for BTV which can be grown in vitro
as monolayer cultures or in suspension culture. The host cells are grown to
nominally 80% saturation density, and infected with BTV at a lower multiplicity
of infection (MOI) generally less than about 0.05, and more than about 0.005,
preferably about 0.01. After absorbing the viral inoculum to the cells by
incubation for a limited period of time at a temperature in the range of about
35 degrees to 40 degrees C., an appropriate mammalian cell growth or maintenance
medium is added and the cells incubated at a temperature in the range of about
35 degrees to 40 degrees C., in the presence of about 5% carbon dioxide in air
for sufficient time to observe that at least 50% of the cell culture exhibits
cytopathic effect (CPE). The CPE is characterized by cell rounding (in
monolayers), cell detachment (from monolayers) and cell degeneration.

The crude cell lysate is allowed to incubate overnight at a temperature
in the range from about 0 degrees to 5 degrees C. The material is harvested and
collected by low speed centrifugation. The resulting pellet is extracted several
times in an appropriate buffer, at a pH in the range from about 8 to 9.5,
preferably about 8.5 to 9. The extracted pellet suspension is centrifuged at low
speed and the supernatant containing the virus is collected. The pellet may be
extracted repeatedly with buffer to enhance the total yield of virus. The
virus-containing liquid is then clarified by low speed centrifugation, retaining
the virus suspended in the liquid, which may then be stored at 4 degrees C.

Tris buffer (2 mM pH 8.8) may be used as the extraction and storage
buffer, although other appropriate buffers which will not interfere with the
subsequent processing may be used.

The particular medium which is used for the growth of the cells will
be a conventional mammalian cell culture medium, such as Eagle's Minimum
Essential Medium or Medium 199, usually supplemented with additives such as
broth prepared from dehydrated standard microbial culture media, fetal bovine
serum, calf serum, or the like.

The compounds which are used for viral inactivation are furocoumarins.
These compounds are primarily
<PAGE> 12

4,545,987

illustrated by the class of compounds referred to as psoralens, which includes
psoralen and derivatives thereof, where the substituents will be: alkyl,
particularly of from 1 to 3 carbon atoms, e.g., methyl; alkoxy, particularly of
from 1 to 3 carbon atoms, e.g., methoxy; and substituted alkyl, of 1 to 6, more
usually 1 to 3 carbon atoms having from 1 to 2 heteroatoms, which will be oxy,
particularly hydroxy or alkoxy of from 1 to 3 carbon atoms, e.g., hydroxymethyl
and methoxymethyl; or amino, including mono- and diakyl amino or aminoalkyl
having a total of from 0 to 6 carbon atoms, e.g., aminomethyl. There will be
from 1 to 5, usually 2 to 4 substituents, which will normally be at the 4,5,8,4'
and 5' positions, particularly at the 4'-position. Illustrative compounds
include 5-methoxypsoralen; 8-methoxypsoralen (8-MOP); 4, 5', 8-trimethylpsoralen
(TMP); 4'-hydroxymethyl-4,5'8-trimethylpsoralen (HMT); 4'-aminomethyl-4,5',
8-trimethylpsoralen (AMT); 4-methylpsoralen; 4,4'-dimethylpsoralen;
4,5'-dimethylpsoralen; 4' 8-dimethylpsoralen; and 4'-methoxymethyl-4,5',
8-trimethylpsoralen. Of particular interest is AMT.

The furocoumarins may be used individually or in combination. Each of the
furocoumarins may be present in amounts ranging from about 0.01 (greek mu)g/ml
to 1 mg/ml, preferably from about 0.5 (greek mu)g/ml to 100 (greek mu)g/ml,
there not being less than about 1 (greek mu)g/ml nor more than about 1 (greek
mu)mg/ml of furocoumarins.

In carrying out the invention the furocoumarin(s), in an appropriate
solvent which is substantially inert and sufficiently polar to allow for
dissolution of the furocounarin(s), is (are) combined with the viral suspension,
conveniently a viral suspension in an aqueous buffered medium, such as used for
storage. The amount of virus will generally be about 1x10(6) to 10(10), more
usually about 1x10(7) to 10(9) and preferably about 1x10(8) to 5x10(8) pfu/ml.
The furocoumarin will be at a concentration of about 0.001 mg/ml to 0.5 mg/ml,
more usually about 0.05 mg/ml to 0.2 mg/ml. The amount of solvent which is used
to dissolve the furocoumarin will be sufficiently small so as to readily
dissolve in the aqueous viral suspension and have little, if any, effect on the
results.

The psoralen may be added to the viral suspension in a signal addition or
in multiple additions, where the virus is irradiated between additions. Usually,
the number of additions will be from about 1 to 5, more usually from about 1 to
4, and preferably from about 2 to 4. The total amount of psoralen which will be
added will be sufficient to provide a concentration of at least about 0.01 mg/ml
to about 1 mg/ml, usually not more than about 0.75 mg/ml and preferably not more
than about 0.5 mg/ml. Since a substantial proportion of the psoralen will have
reacted with the RNA between additions, the total concentration of psoralen in
solution will generally not exceed about 0.1 mg/ml.

The total time for the irradiation will vary depending upon the light
intensity, the concentration of the psoralen, the concentration of the virus,
and the manner of irradiation of the virus, where the intensity of the
irradiation may vary in the medium. The total time will usually be at least
about 2 hrs. and not more than about 60 hrs., generally ranging from about 10
hrs. to 50 hrs. The times between additions of psoralen, where the psoralen is
added incrementally, will generally vary from about 1 hr. to 24 hrs., more
usually from about 2 hrs. to 20 hrs.

The temperature for the irradiation is preferably under 25 degrees C.,
more preferably under 20 degrees C. and will generally range from about - 10
degrees to 15 degrees C., more usually from about 0 degrees to 10 degrees C.

The irradiation is normally carried out in an inert atmosphere, where all
or substantially all of the air has been removed. Inert atmospheres include
nitrogen, helium, argon, etc.

The light which is employed will generally have a wavelength in the range
from about 300 nm to 400 nm. The intensity will generally range from about 0.1
mW/cm(2) to about 5 W/cm(2).

Optionally, a small amount of a singlet oxygen scavenger may be included
during the virus inactivation. Singlet oxygen scavengers include ascorbic acid,
dithioerythritol, sodium thionite, glutathione, etc. The amount of scavenger
will generally be at a concentration of about 0.001 M to 0.5 M, more usually at
about 0.05 M to 0.2 M, where the addition may be made in a single or multiple
additions.

During irradiation, the medium may be maintained still, stirred or
circulated and may be either continuously irradiated or be subject to
alternating periods of irradiation and non-irradiation. The circulation may be
in a closed loop system or in a single pass system ensuring that all of the
sample has been exposed to irradiation.

It may be desirable to remove the unexpended furocoumarin and/or its
photobreakdown products from the irradiation mixture. This can be readily
accomplished by one of several standard laboratory procedures such as dialysis
across an appropriately sized membrane or through an appropriately sized hollow
fiber system after completion of the irradiation. Alternatively, one could use
affinity columns for one or more of the low molecular weight materials to be
removed.

The inactivated vaccine may then be formulated in a variety of ways for
use for inoculation. The concentration of the virus will generally be from about
10(6) to 10(9) pfu/ml, as determined prior to inactivation. The vaccine may
include cells or may be cell-free. It may be in an inert physiologically
acceptable medium, such as ionized water, phosphate-buffered saline, saline, or
the like, or may be administered in combination with a physiologically
acceptable immunologic adjuvant, including but not limited to mineral oils,
vegetable oils, mineral salts and immunopotentiators, such as muramyl dipeptide.
The vaccine may be administered subcutaneously, intramuscularly, or
intraperitoneally. Usually, a specific dosage at a specific site will range from
about 0.1 ml to 4 ml, where the total dosage will range from about 0.5 ml to 8
ml. The number of injections and their temporal spacing may be highly variable,
but usually 1 to 3 injections at 1, 2 or 3 week intervals are effective.

The following examples are offered by way of illustration and not by way
of limitation.

EXPERIMENTAL

Virus Growth and Tissue Culture

Hamster cells [BHK-21 (C-13), American Type Culture Collection, (CCL 10)]
are grown as monolayers in plastic cell culture vessels in Eagle's Minimum
Essential Medium with Earle's Salts (MEM) and non-essential amino acids (MEN)
supplemented with 10% heat inactivated calf serum (C) and 10% tryptose phosphate
broth (Tp, Difco 0060). Cell cultures are used to produce live BTV from master
seed virus obtained from

<PAGE> 13
4,545,987

Dr. T.L. Barber, USDA, Denver, Colorado. Cells are grown in culture vessels to
80% to 100% confluency (approximately 1 times 10(5) to 2 times 10(5) cells/
cm(2) of growth surface area) using standard mammalian cell culture techniques.
Generally, Corning plastic roller bottles (Corning No. 25140-850) with a growth
surface area of 850 cm(2), containing 100 ml of MEN supplemented with 10% C(1)
and 10% Tp and 1 times 10(8) to 2 times 10(8) CCL 10 cells per bottle are used
for virus production . The cell cultures are initiated by seeding approximately
1 times 10(6) to 5 times 10(7) cells into 100 ml growth medium in a roller
bottle containing about 5% CO(2) in air and incubating the roller bottle on a
roller bottle rotator at 1 to 5 rpm at 35 degrees C. to 38 degrees C. The
cultures are grown to 80% to 100% confluency over a 7 to 14 day period with a
100% medium change every 2 to 4 days.

When the monolayers are 80% to 100% confluent the culture medium is
removed and the monolayer is infected with approximately 1 times 10(6) to 2
times 10(6) plaqueforming units (pfu) of STV in 20 ml of MEN with 2%
heat-inactivated fetal bovine serum (F(i)). The multiplicity of infection (MOI)
is approximately 0.01. The virus inoculum is adsorbed to the cells by
incubation at 35 degrees C. to 38 degrees C. for 1 hr. at 1 to 5 rpm. One
hundred milliliters of MEN containing 10% C(i) and 10% TP is added per roller
bottle. The post-infection incubation is at 35 degree C. to 38 degrees C. in 5%
CO(2) in air with rotation. Two to four days post-infection, BTV cytopathic
effect (CPE) is evident. The CPE is characterized by cell rounding, cell
detachment, and cell degeneration. When at least 50% of the cell monolayer
exhibits CPE the contents of the roller bottle are swirled or scraped with a
rubber policeman to remove loosely attached materials from the roller bottle
walls. The roller bottles and contents are incubated at 4 degrees C. overnight.
The harvest material is decanted into sterile contrifuge bottles. The virus,
cells, and cell debris are pelleted by centrifugation at 2,000 times g for 60
min., at 4 degrees C.

The pellet is resuspended aseptically in 8 ml of 2 mM Tris-HCl, pH
8.8, for each original roller bottle. The suspension is mixed vigorously on a
vortex mixer, and/or sonicated at 4 degrees C. for 1 min., and centrifuged at
1,400 times g for 30 min. at 4 degrees C. The virus-containing supernatant is
collected and the pellet is extracted twice more with 8 ml/roller bottle
aliquots of 2 mM Tris-HCl, pH 8.8 The virus-containing supernatants are pooled
and clarified by centrifugation at 4,000 times g for 30 min. at 4 degrees C.
The clarified supernatant is stored at 4 degrees C.

Virus Assay

Confluent monolayers of LMTK - or Vero (ATCC CCL 81) cells are prepared
in 6 cm diameter mammalian cell culture plastic petri dishes (Corning #25010)
or other convenient cell culture vessel. The growth medium used for LMTK - cell
is alpha-modified Eagle's Minimum Essential Medium, Earle's Salts ((greek
alpha)ME) + 10% F(i) and the growth medium used for Vero cells is MEN + 5% F(i).
Ten-fold serial dilutions of virus samples are made by adding 0.5 ml of the
virus sample to 4.5 ml of phosphate buffered saline (PBS), pH 7.2 to 7.4 + 2%
F(i) in a screw cap tube. The growth medium is removed from a 6 cm culture dish
cell monolayer, 0.1 ml virus sample (undiluted or diluted) is added, and the
virus is absorbed to the monolayer for 1 to 2 hrs. at 35 degrees C. to 38
degrees C. Two or more dishes are used for each sample. Five ml of overlay
medium is added per 6 cm culture dish. The overlay medium is prepared by mixing
equal parts of solution A (100 ml 2 times MEM with L-

glutamine. GIBCO #320-1935, + 10 ml F(i) and 1.8% to 2% Noble Agar (Difco 0142)
in deionized H(2)O at 44 degrees C. to 45 degrees C. The cultures are incubated
at 35 degrees C. to 38 degrees C. in 5% CO(2) in air for 5 days. A second
overlay containing Neutral Red at a final concentration of 0.005% is added on
day 5. Plaques are counted on a day 6 or day 7 post-infection. The virus liter
in pfu/ml is calculated by multiplying the average number of plaques per dish by
the reciprocal of the dilution. The pfu/ml is the value used to determine the
amount of virus needed to infect cells at a MOI of approximately 0.01. The
pfu/ml in a virus preparation prior to inactivation is used to determine the
vaccine dose.

Inactivation Protocol

Twenty-five ml of BTV serotype 11 (1.5 times 10(8) pfu/ml) is mixed
with 0.25 ml of 4'-aminomethyl 4,5', 8-trimethylpsoralen (AMT; 1 mg/ml in
DMSO). The mixture is placed in a 150 cm(2) tissue culture flask (T-150;
Corning #25120). The viral suspension in the flask is placed in an argon
atmosphere for 10 min. and then a stream of argon gas is blown over the viral
suspension for an additional 2 min. The flask is tightly capped and the
suspension is irradiated for 3.25 hours at 4 degrees C. using GE BLB
fluorescent bulbs at an intensity of 1.5 mW/cm(2). An additional 0.25 ml of AMT
is then added to the viral suspension, the suspension is transferred by pipet
to a new T-150 flask, and the solution is again flushed with argon. The flask is
irradiated for an additional 14.75 hrs. at 4 degrees C. under the same long
wavelength UV light source. After this irradiation an additional 0.25 ml of
AMT solution is added to the suspension and it is again transferred to a new
T-150 flask. The solution is flushed with argon as before and irradiated for an
additional 5.5 hrs. at 4 degrees C. The inactivated BTV is stored at 4
degrees C.

Assessment of Inactivation by Blind Passage

CCL 10 cells are grown to confluency in 850 cm(2) roller bottles using
standard cell culture procedures as described above. The culture medium is
removed from the roller bottle and 2.0 ml of the inactivated virus preparation,
mixed with 18 ml of medium containing 2% F(i), is adsorbed to the roller bottle
cell monolayer for 60 min at 35 degrees C. to 38 degrees C. with rotation at 1
to 5 rpm. After adsorption the unabsorbed inoculum is removed and 100 ml of
growth medium (MFN with 10% C(i) and 10% Tp) is added and the roller bottle
culture incubated at 35 degrees C. to 38 degrees C. for 7 days with daily
observation for viral CPE (see plaque assay above for description of CPE). The
roller bottle culture should receive a 100% medium change every 2 to 3 days. If
no CPE is observed during the first roller bottle passage, the cell monolayer
is chilled at 4 degrees C. for 12 to 24 hrs. The cells are scraped into the
medium which is then decanted into a centrifuge bottle. The cells are pelleted
by centrifugation at 4 degrees C. at 2,000 times g for 30 min. and resuspended
in 2.0 ml of 2 mM Tris-HCl (pH 8.8) by vigorous mixing using a vortex mixer.
The resuspended material is centrifuged at 2,000 times g for 20 min. at 4
degrees C. The supernatant is added to 18 ml of growth medium containing 2% F(i)
and used to infect a new confluent roller bottle culture of CCL 10 cells as
described immediately above. The second roller bottle blind passage is observed
for 7 days and fed every 2 to 3 days. If no CPE is observed during the second
roller bottle blind passage, a third roller bottle blind passage is performed.
If no CPE has been

<PAGE> 14
4,545,987

observed by the end of the third roller bottle blind passage the virus
preparation is considered inactivated.

EXAMPLE I

Four New Zealand white rabbits were randomly assigned to 2 groups,
designated A and B. Both groups were given 4 immunizations at two week
intervals. The first immunization consisted of 1 ml of vaccine (10(8) pfu BTV
serotype 11) and 1 ml of Freund's Complete Adjuvant. The second through fourth
immunizations utilized 1 ml of vaccine (10(8) pfu BTV serotype 11) and 1 ml of
Freund's Incomplete Adjuvant. All immunizations were given intramuscularly
(TM). The vaccine given to Group A (Vaccine #1) was inactived with AMT-UVA in
the presence of 0.01 M ascorbic acid. Vaccine #1 was dialyzed for 12 hours
against 2 mM Tris,ph 8.6. The vaccine given to Group B (Vaccine #2) was
inactivated with AMT-UVA without ascorbic acid and sonicated three times (2
minutes each time) using a cup horn probe (Heat Systems Model 431A) at a power
setting of 3 (Heat Systems Model W220). Both Vaccine #1 and Vaccine #2 were
deemed inactivated since no live virus was detected during blind passage.
Inactivated vaccine was also tested for safety by chicken embryo inoculation.
Egg deaths attributable to live virus were not encountered. Both rabbit groups
were bled via auricular venipuncture one week following the second, third, and
fourth immunizations. Serum from each rabbit was pooled with that of its
groupmate, and the pooled sera were tested for anti-BTV antibodies by two
standard serologic assays, serum neutralization (Jochim and Jones, Am, J. Vet.
Res. (1976) 37:1345-1347) and agar gel precipitation (Jochim et al., Am. Assoc.
Vet. Lab, Diag., 22nd Proceed: 463-471, 1979). Pre-immunization rabbit serum
was used as the negative control; BTV immune sheep serum was used as the
positive control of both immunologic procedures.
Pooled sera from Groups A and B reduced the number of viral plaques
(serum neutralization) greater than eighty percent when the sera were diluted
1:40, which was the highest dilution examined. Negative and positive control
sera behaved as expected.
<TABLE>
<CAPTION>
TABLE 1
- ------------------------------------------------------------------------------
Serum Neutralization Data From Rabbits
Vaccinated with AMT-UVA-inactivated
Bluetongue Virus Vaccines.
--------------------------------------

TITER*:
----------------------------------------------
GROUP 1 5 40
- ------------------------------------------------------------------------------
<S> <C> <C> <C>
A + + +
B + + +
Normal Rabbit Serum + - -
BTV-Immune Sheep Serum + + +
- ------------------------------------------------------------------------------
</TABLE>
* Reciprocal of serum dilution neutralizing 80 percent of BTV plaque activity
on BHK cells. The data are from post-second immunization serum samples.

Pooled post-immunization sera from Groups A and B precipitated BTV
antigen in immunodiffusion plates when tested at dilutions up to 1:16. Normal
rabbit serum did not precipitate the standard BTV antigen. BTV-immune sheep
serum did precipitate the BTV antigen, but not at dilutions greater than 1:2.
Of the two immunologic procedures utilized, serum neutralization is
predictive for immunity to live BTV challenge in the target species.

EXAMPLE II

Each of two adult sheep, known to be susceptible to BTV, were
inoculated subcutaneously (SQ) with 2 ml of AMT-UVA inactivated BTV plus
adjuvant (1:1;

vaccine to aluminum hydroxide adjuvant). The vaccine contained approximately
10(8) pfu/ml of BTV prior to inactivation. A third sheep was inoculated SQ with
6 ml of the identical vaccine without adjuvant. Seven weeks later the three
sheep were given identical inoculations SQ that consisted of 5 ml of vaccine and
aluminum hydroxide adjuvant (2:1 vaccine to adjuvant; 10(8) pfu BTV/ml of
vaccine).
The three sheep were monitored for clinical evidence of BTV, including
daily body temperature recording and bi-daily virus isolation attempts. No
evidence of BTV was observed, indicating that the vaccine was inactivated.
Serum was collected weekly for serum neutralization and agar gel
precipitation testing. Normal sheep sera and BTV-immune sheep sera were used
for negative and positive control samples in the serologic tests. The first
vaccine inoculations induced precipitating anti-BTV antibody in all three sheep.
Their pre-exposure sera were uniformly negative for anti-BTV precipitating
antibody. Modest neutralizing anti-BTV anti-body titers (1:5) were elicited in
two of three sheep following one immunization. The second immunization elicited
a distinct immunologic anamnestic response, inducing neutralizing titers of
1:40, 1:80, or 1,1600 in the three sheep.

<TABLE>
<CAPTION>
TABLE 2
- ------------------------------------------------------------------------------
Serum Neutralization Data From Sheep Immunized with an AMT-UVA Inactivated BTV
Vaccine. -------------------------------------

TITERS*
Sheep No.:
----------------------------------------------
1 2 3
- ------------------------------------------------------------------------------
<S> <C> <C> <C>
Pre-First Immunization
------------------------
Day 0 <5 <5 <5
Post-First Immunization
------------------------
Day 21 5 5 <5
Post-Second Immunization
------------------------
Day 7 80 160 40
Day 14 80 40 40
Day 21 80 80 40
Day 42 80 80 80
Post-Challenge
--------------
Day 7 160 160 80
Day 14 320 160 80

- ------------------------------------------------------------------------------
</TABLE>
* Reciprocal of highest 2-fold dilution reducing BTV plaque activity on BHK
cells by 80 percent.

The sheep were challenged by SQ syringe inoculation 10(5) egg lethal
doses for BTV serotype 11. The three sheep remained clinically normal during
the BTV challenge period, indicating that the vaccine was efficaceous.
It is evident from the above results that the BTV which is
psoralen-inactivated retains its immunogenicity, particularly as to those sites
which elicit an immune response which is effective in protecting a host against
subsequent BTV-infection. Thus, the psoralen inactivation can be carried out
under conditions which do not modify the immunogenic sites of the virus, so as
to elicit an immunogenic response which will be effective against the live BTV.
Furthermore, the BTV RNA virus is efficiently inactivated under mild conditions
to the point of complete inactivation, whence it may be safely administered to a
host.
Although the foregoing invention has been described in some detail by
way of illustration and example for purposes of clarity of understanding, it
will be obvious
<PAGE> 15
4,545,987
9

that certain changes and modifications may be practiced within the scope of the
appended claims.

What is claimed is:

1. A vaccine useful for inoculation of a mammalian host susceptible to
infection by Bluetongue virus (BTV), which comprises at least one
furocoumarin-inactivated BTV serotype in from about 10(6) to 10(9)
pfu/ml, wherein said inactivation is as a result of irradiation of BTV in the
presence of an inactivating furocoumarin with long wavelength ultraviolet light
at a temperature below about 40 degrees C. for a time sufficient to inactivate
said BTV to a non-infectious degree, and an immunologic adjuvant.

2. A vaccine according to claim 1, wherein said furocoumarin is
4'-aminomethyl-4,5',8-trimethylpsoralen.

3. A vaccine according to claim 2, wherein said BTV is of serotype 11.

4. A vaccine according to claim 1, wherein said BTV is inactivated in the
presence of a singlet oxygen scavenger.

5. A vaccine according to claim 1, wherein said inactivation is performed
in the substantial absence of oxygen.

6. A vaccine according to claim 1, wherein said BTV is grown in
substantially confluent monolayers of cells immediately prior to inactivation.

7. A vaccine useful for inoculation of a mammalian host susceptible to
infection by Bluetongue virus (BTV), which comprises BTV serotype 11
inactivated with 4'-aminomethyl-4,5',8-trimethylpsoralen by irradiation with
long wavelength ultraviolet light at a temperature in the range of about -- 10
degrees to 25 degrees C. for a time sufficient to inactivate said BTV to become
non-infectious, said BTV being present in an amount of about 10(6) to 10(9)
pfu/ml, and an immunologic adjuvant.

8. A vaccine useful for inoculation of a mammalian host susceptible to
infection by Bluetongue virus (BTV), which comprises at least one
furocoumarin-inactivated BTV serotype in from about 10(6) to 10(9) pfu/ml,
wherein said inactivation is as a result of irradiation of BTV in the presence
of an inactivating furocoumarin with long wavelength ultraviolet light at a
temperature below about 40 degrees C. for a time sufficient to inactivate said
BTV to a non-infectious degree.

9. A vaccine useful for inoculation of a mammalian host susceptible to
infection by Bluetongue virus (BTV), which comprises BTV serotype 11
inactivated with 4'-aminomethyl-4,5',8-trimethylpsoralen by temperature in the
range of about -- 10 degrees to 25 degrees C. for a time sufficient to
inactivate said BTV to become non-infectious, said BTV being present in an
amount of 10(6) to 10(9) pfu/ml.

10. A method for producing a vaccine for inoculation of a mammalian host
susceptible to infection by bluetongue virus (BTV), which method comprises
inactivating at least one BTV serotype by exposure to long wavelength
ultraviolet light in the presence of a furocoumarin at a temperature below
about 40 degrees C. for a time sufficient to inactivate said BTV to a
non-infectious degree, and combining said inactivated BTV with an appropriate
adjuvent.

11. A method for producing a vaccine for inoculation of a mammalian host
susceptible to infection by bluetongue virus (BTV), which method comprises
exposure of at least one BTV serotype to long wavelength ultraviolet light in
the presence of 4'-aminomethyl-4,5',8-trimethylpsoralen at a temperature in the
range from about -- 10 degrees C to 25 degrees C. for a time sufficient to
inactivate the BTV to a non-infectious degree, and combining said inactivated
BTV with a suitable adjuvant.

* * * * *
<PAGE> 16
EXHIBIT B

UNITED STATES PATENT [19] [11] PATENT NUMBER: 4,693,981
WIESEHAHN ET AL. [45] DATE OF PATENT: Sep. 15, 1987
- --------------------------------------------------------------------------------

[54] PREPARATION OF INACTIVATED VIRAL VACCINES

[75] Inventors: Gary P. Wiesehahn, Alameda; Richard P. Creagan, Alta Loma;
David R. Stevens, Fremont; Richard Giles, Alameda all of Calif.

[73] Assignee: Advanced Genetics Research Institute, Oakland, Calif.

[*] Notice: The portion of the term of this patent subsequent to Oct. 8,
2002 has been disclaimed.

[21] Appl. No.: 785,354

[22] Filed Oct. 7, 1985

RELATED U.S. APPLICATION DATA

[63] Continuation-in-part of Ser. No. 563,939. Dec. 20, 1983, Pat. No.
4,545,987, and a continuation-in-part of Ser. No. 592,661, Mar. 23, 1984,
abandoned.

[51] Int. Cl(4).......................................................A61K 39/12
[52] U.S. Cl....................................................435/238; 424/89;
424/90
[58] Field of Search........................................424/89, 90; 435/235,
435/238

[56] REFERENCES CITED
U.S. PATENT DOCUMENTS
4,124,598 11/1978 Hearst.......................................260/343.21
4,169,204 9/1979 Hearst..........................................546/270
4,196,281 4/1980 Hearst...........................................536/28
4,545,987 10/1985 Giles et al......................................424/89
4,568,542 2/1986 Kronenberg.......................................424/90

FOREIGN PATENT DOCUMENTS

0066886 12/1982 European Pat. Off.

OTHER PUBLICATIONS

Hearst & Thiry, Nucleic Acids Research, 1977, 4:1339-1347.
Talib and Banerjee, Virology 118, 1982, 430-438.
Carl V. Hanson, Medical Virology II, de la Maza & Peterson, eds., Elsevier
Biomedical, New York, pp. 45-79.
deMol and van Henegouwen (1981) Photochem. Photobiol. 33:815-819.
deMol et al. (1981) Photochem. Photobiol. 34:661-666.
Joshi and Pathak (1983) Biochem. Biophys. Res. Comm. 112:638-646.
Grossweiner (1982) NCI Monograph No. 66, 47-54.
Rodighiero and Dall'Acqua (1982) NCI Monograph No. 66, 31-40.
deMol et al. (1981) 95:74462k p. 74467 Chem. Interactions.

Primary Examiner -- Shep K. Rose
Attorney, Agent, or Firm -- Bertram I. Rowland

[57] ABSTRACT

Vaccines employing inactivated viruses having improved retention of antigenic
characteristics are prepared by psoralen-inactivation of the live virus in a
non-oxidizing atmosphere. By excluding oxygen and other oxidizing species from
the inactivation medium, degradation of the antigen characteristics resulting
from irradiation with ultraviolet light is largely prevented. The resulting
inactivated viruses are employed in vaccine preparations for the inoculation of
susceptible hosts to inhibit viral infection.

9 CLAIMS, NO DRAWINGS

<PAGE> 17
4,693,981

PREPARATION OF INACTIVATED VIRAL VACCINES

This application is a continuation-in-part of application Ser. No.
563,939, filed on Dec. 20, 1983, now U.S. Pat. No. 4,545,987, and application
Ser. No. 592,661, filed on Mar. 23, 1984, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to the preparation of inactivated viral
vaccines. More particularly, the invention relates to psoralen inactivation of
viral particles under conditions which limit antigenic degradation of the viral
particles caused by the inactivation.

Vaccination against both bacterial and viral diseases has been one of the
major accomplishments of medicine over the past century. While effective
vaccines have been developed for a large number of diseases, development of
safe and effective vaccines for a number of other diseases remains problematic.
The use of inactivated or killed microbial agents as a vaccine, although
generally safe, will not always be effective if the immunogenic characteristics
of the agent are altered. Indeed, the preferential degradation of certain
antigens on the inactivated microorganisms might produce an immune response
which allows for an immunopathological response when the host is later
challenged with the live microorganism. In contrast, the preparation of live,
attenuated microbial agents as a vaccine will often provide improved
immunologic reactivity, but increases the risk that the vaccine itself will be
infectious, e.g., as a result of reversion, and that the organism will be able
to propagate and provide a reservoir for future infection.

Thus, one must generally choose between improved effectiveness and greater
degree of safety when selecting between the viral inactivation and viral
attenuation techniques for vaccine preparation. The choice is particularly
difficult when the virus is resistant to inactivation and requires highly
rigorous inactivation conditions which are likely to degrade the antigenic
characteristics.

It is therfore desirable to provide improved methods for inactivating
viruses, which methods are capable of inactivating even the most resistant
viruses under conditions which do not substantially degrade the antigenic
structure of the viral particles. In particular, the inactivated viruses should
be useful as vaccines and free from adverse side effects at the time of
administration as well as upon subsequent challenge with the live virus.

2. Description of the Prior Art

The reactivity of psoralen derivatives with viruses has been studied. See,
Hearst and Thiry (1977) Nuc. Acids Res. 4:1339-1347; and Talib and Banerjee
(1982) Virology 118:430-438. U.S. Pat. No. 4,124,598 and 4,196,281 to Hearst el
al. suggest the use of psoralen derivatives to inactivate RNA viruses, but
include no discussion of the suitability of such inactivated viruses as
vaccines. U.S. Pat. No.4,169,204 to Hearst el al. suggests that psoralens may
provide a means for inactivating viruses for the purpose of vaccine production
but presents no experimental support for this proposition. European patent
application 0 066 886 by Kronenberg teaches the use of psoralen inactivated
cells, such as virus-infected mammalian cells, for use as immunological reagents
and vaccines. Hanson (1983) in: Medical

Virology II, de la Maza and Peterson, eds., Elsevier Biomedical, New York, pp.
45-79, reports studies which have suggested that oxidative photoreactions
between psoralens and proteins may occur.

SUMMARY OF THE INVENTION

The present invention provides for the production of furocoumarin-
inactivated viral vaccines under conditions which substantially preserve the
antigenic characteristics of the inactivated viral particles. It has been
recognized by the inventors herein that the inactivation of viruses by exposure
to ultraviolet radiation in the presence of furocoumarin compounds can degrade
the anitgenic structure of the viral particle. While such degradation can be
limited by employing less rigorous inactivation conditions, certain recalcitant
viruses require relatively harsh inactivation conditions in order to assure
that all residual infectivity is eliminated. The inactivation conditions
required to eliminate substantially all infectivity in such recalcitrant viruses
can so degrade the viral particle that it is unsuitable for use as the
immunogenic substance in a vaccine. Even if the degradation is not so complete,
partial degradation of the antigenic characteristics may render the vaccine
less effective than would be desirable. That is, the vaccine may require higher
concentrations of the inactivated viral particles in each inoculation, and/or
the vaccination program may require additional inoculations in order to achieve
immunity.

According to the present invention, vaccines are prepared by treatment with
furocoumarins and long wavelength ultraviolet (UVA) light under conditions which
limit the availability of oxygen and other reactive, particularly oxidizing,
species. It has been found that such conditions allow for the inactivation of
even recalcitrant viral particles without substantial degradation of the
antigenic characteristics of those particles. Thus, viruses which have
heretofore been resistant to furocoumarin-inactivation may now be inactivated
without loss of the desired immunogenicity, and viruses which have previously
been successfully inactivated may now be inactivated under conditions which
better preserve their antigenic characteristics, making them more efficient
immunogenic substances for use in vaccines.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

According to the present invention, vaccines useful for the inoculation of
mammalian hosts, including both animals and humans, against viral infection are
provided. The vaccines are prepared by inactivation of live virus in an
inactivation medium containing an amount of an inactivating furocoumarin
sufficient to inactivate the virus upon subsequent irradiation with long
wave-length ultraviolet radiation. Degradation of the antigenic characteristics
of the live virus is reduced or eliminated by limiting the availability of
oxygen and other oxidizing species in the inactivation medium. Suitable
vaccines may be prepared by combining the inactivated viruses with a
physiologically-acceptable carrier, typically an adjuvant, in an appropriate
amount to elicit an immune response, e.g., the production of serum neutralizing
antibodies, upon subsequent inoculation of the host.

The present invention is suitable for producing vaccines to a wide variety
of viruses, including human viruses and animal viruses, such as canine, feline,
bo-

<PAGE> 18
4,693,981

vine, porcine, equine, and ovine viruses. The method is suitable for
inactivating double stranded DNA viruses, single-stranded DNA viruses,
double-stranded RNA viruses, and single-stranded RNA viruses, including both
enveloped and nonenveloped viruses. The following list is representative of
those viruses which may be inactivated by the method of the present invention.

dsDNA
------
Adenoviruses Adenovirus canine adenovirus 2
Herpesviruses Herpes simplex viruses,
Feline Herpes 1

Papovaviruses Polyoma, Papilloma
Poxviruses Vaccinia
ssDNA
------
Parvovirus Canine parvovirus, Feline
panleukopenia

dsRNA
------
Orbiviruses Bluetongue virus
Reoviruses Reovirus

ssRNA
------
Calicivirus Feline calicivirus
Coronavirus Feline infectious peritonitis
Myxovirus Influenza virus
Paramyxovirus Measles virus, Mumps virus,
Newcastle disease virus,
Canine distemper virus,
Canine parainfluenza 2 virus

Picornavirus Polio virus, Foot and mouth
disease virus

Retrovirus Feline leukemia virus, Human
T-cell lymphoma virus, types
I, II and III.

Rhabdovirus Vesicular stomatitis virus
rabies
Togavirus Yellow fever virus, Sindbis
virus, Encephalitis virus

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

Of particular interest are those viruses for which conventional vaccine
approaches have been unsuccessful or marginally successful. For such viruses,
inactivation procedures which are sufficiently rigorous to assure the total loss
of infectivity often result in partial or complete destruction of the antigenic
characteristics of the virus. With such loss of antigenic characteristics, the
viruses are incapable of eliciting a protective immunity when administered to a
susceptible host. While it would be possible to utilize less rigorous
inactivation conditions in order to preserve the antigenic integrity of the
virus, this approach is not desirable since it can result in incomplete
inactivation of the virus.

In preparing the subject vaccines, sufficient amounts of the virus to be
inactivated may be obtained by growing seed virus in a suitable mammalian cell
culture. Seed virus, in turn, may be obtained by isolation from an infected
host. Suitable mammalian cell cultures include primary or secondary cultures
derived from mammalian tissues or established cell lines such as Vero cells,
monkey kidney cells, BHK21 hamster cells, LMTK(31) cells, and other cells
permissive for the desired virus and which may be grown in vitro as monolayer or
suspension cultures. The cell cultures are grown to approximately 80% saturation
density, and infected with the virus at a low multiplicity of infection (MOI),
usually between about 0.05 and 0.005, preferably at about 0.01. After absorbing
the viral inoculum to the cells by incubation for a limited period of time at a
temperature in the range from 35 degrees C. to 40 degrees C., an appropriate
growth or maintenance medium is added. The cells are further incubated at about
the same temperature, in the pres-

ence of about 5% carbon dioxide in air, until a sufficient amount of virus has
been produced.

The growth and maintenance medium will usually be a conventional mammalian
cell culture medium, such as Eagle's Minimum Essential Medium or Medium 199,
usually supplemented with additives such as broth prepared from dehydrated
standard microbial culture media, fetal bovine serum, fetal calf serum, or the
like.

The furocoumarins useful for inactivation are primarily illustrated by the
class of compounds referred to as psoralens, including psoralen and substituted
psoralens where the substituents may be alkyl, particularly having from one to
three carbon atoms, e.g., methyl; alkoxy, particularly having from one to three
carbon atoms, e.g., methodoxy: and substituted alkyl having from one to six,
more usually from one to three carbon atoms and from one to two heteroatoms,
which may be oxy, particularly hydroxy or alkoxy having from one to three carbon
atoms, e.g., hydroxy methyl and methoxy methyl, or amino, including mono- and
dialkyl amino or aminoalkyl, having a total of from zero to six carbon atoms,
e.g., aminomethyl. There will be from 1 to 5, usually from 2 to 4 substituents,
which will normally be at the 4, 5, 8, 4' and 5' positions, particularly at the
4' position. Illustrative compounds include 5-methoxypsoralen; 8-methoxypsoralen
(8-MOP); 4.5', 8-trimethylpsoralen (TMP); 4'-hydroxymethyl-4.5',
8-trimethylpsoralen (HMT); 4'-aminomethyl-4.5', 8-trimethylpsoralen (AMT);
4-methylpsoralen; 4.4'-dimethylpsoralen; 4.5'-dimethylpsoralen;
4', 8-dimethylpsoralen; and 4'-methoxymethyl-4.5', 8-trimethylpsoralen. Of
particular interest are AMT and 8-MOP.

In carrying out the invention the furocoumarin(s), in an appropriate
solvent which is substantially inert and sufficiently non-polar to allow for
dissolution of the furocoumarin(s), are combined with the viral suspension,
conveniently a viral suspension in an aqueous buffered medium, such as used for
storage. The amount of virus will generally be about 1x10(6) to 10(11), more
usually about 1x10(7) to 10(9) and preferably about 1x10(8) to 5x10(8) pfu/ml.
The furocoumarin(s) will be at a concentration of about 0.001 mg/ml to 0.5
mg/ml, more usually about 0.05 mg/ml to 0.2 mg/ml. The amount of solvent which
is used to dissolve the furocoumarin will be sufficiently small so as to
readily dissolve in the aqueous viral suspension.

Although viral inactivation according to the present invention will
normally be carried out in an inactivation medium as just described, in some
cases it may be desirable to introduce furocoumarins to the virus by addition
to a cell culture medium in which the virus is grown. The inactivation is then
carried out by separating the live viral particles from the culture medium, and
exposure of the particles to ultraviolet light in an inactivation medium which
may or may not contain additional furocoumarins. This method of inactivation is
useful where the virus is resistant to inactivation when the furocoumarin is
added to the inactivation medium only.

When employing furocoumarins with limited aqueous solubility, typically
below about 50 g/ml, it has been found useful to add an organic solvent, such as
<PAGE> 19
4,693,981

dimethyl sulfoxide (DMSO), ethanol, glycerol, polyethylene glycol (PEG) or
polypropylene glycol, to the aqueous treatment solution. Such furocoumarins
having limited solubility include 8-MOP, TMP, and psoralen. By adding small
amounts of such organic solvents to the aqueous composition, typically in the
range from about 1 to 25% by weight, more typically from about 2 to 10% by
weight, the solubility of the furocoumarin can be increased to about 200
greek mu g/ml. or higher. Such increased furocoumarin concentration may permit
the use of shorter irradiation times. Also, inactivation of particularly
recalcitrant microorganisms may be facilitated without having to increase the
length or intensity of ultraviolet exposure, and the addition of an organic
solvent may be necessary for inactivation of some viruses with particular
furocoumarins. The ability to employ less rigorous inactivation conditions is of
great benefit in preserving the antigenicity of the virus during inactivation.

At times, it may be desirable to employ organic solvents, particularly
DMSO, with all furocoumarins regardless of solubility. For some microorganisms,
particularly viruses having tight capsids, the addition of the organic solvent
may increase the permeability of the outer coat or membrane of the
microorganism. Such increase in permeability would facilitate penetration by the
furocoumarins and enhances the inactivation of the microorganism.

The furocoumarin may be added to the viral suspension in a single addition
or in multiple additions, where the virus is irradiated between additions, or
may be added continuously during the entire treatment period, or a portion
thereof. Usually, the number of additions will be from about 1 to 50, more
usually from about 10 to 40, and preferably from about 2 to 4. The total amount
of furocoumarin which will be added will be sufficient to provide a
concentration of at least about 0.01 mg/ml to about 1 mg/ml. usually not more
than about 0.75 mg/ml. and preferably not more than about 0.5 mg/ml. Since a
substantial proportion of the furocoumarin will have reacted with the nucleic
acid between additions, the total concentration of furocoumarin in solution will
generally not exceed about 0.1 mg/ml. In cases where the furocoumarin(s)
employed are particularly unstable, it may be beneficial to add the furocoumarin
solution continuously during the irradiation procedure.

In order to preserve the antigenic characteristics of the virus,
irradiation is carried out in the substantial absence of oxygen and other
oxidizing species. This is particularly important when employing psoralens that
generate more singlet oxygen on a molar basis. For example, AMT generates more
singlet oxygen than 8-MOP. Conveniently, oxygen and other gases may be removed
from the inactivation medium by maintaining the medium in a non-oxidizing gas
atmosphere, e.g., hydrogen, nitrogen, argon, helium, neon, carbon dioxide, and
the like. The inactivation medium may be held in an enclosed vessel, and the
space above the liquid medium surface filled with the non-oxidizing gas.
Oxidizing species initially in the medium will be exchanged for the
non-oxidizing gases according to gas-liquid equilibrium principles. Preferably,
the space above the inactivation medium will be flushed with non-oxidizing gas
to remove the oxidizing species and further lower their equilibrium
concentration in the liquid medium. Depending on the volume of the inactivation
medium, the flushing should be continued for at least 1 minute, pref-

erably at least 2 minutes, usually being in the range from about 3 to 30
minutes. Flushing may be continued during the irradiation period, but need not
be so long as the oxidizing species have been substantially removed and the
vessel remains sealed to prevent the intrusion of air. Optionally, a single
oxygen scavenger may be added to the inactivation medium prior to irradiation to
further prevent interaction of oxygen with the furocoumarin and the virus.
Suitable oxygen scavengers include ascorbic acid, dithioerythritol, sodium
thionate, glutathione, and the like. The scavenger will be present at a
concentration sufficient to block active oxygen species, usually being between
0.001M and 0.5M. more usually being between about 0.005M and 0.02M, where the
addition may be in single, multiple, or continuous additions.

The concentration of dissolved oxygen may be reduced through the use of
enzyme systems, either in solution or immobilized on a solid substrate. Suitable
enzyme systems include glucose oxidase or catalase in the presence of glucose
and ascorbic acid oxidose in the presence of ascorbate. Such enzyme systems may
be employed alone or together with the other methods for oxygen reduction
discussed above.

The total time for the irradiation will vary depending upon the light
intensity, the concentration of the furocoumarin, the concentration of the
virus, and the manner of irradiation of the virus, where the intensity of the
irradiation may vary in the medium. The time of irradiation necessary for
inactivation will be inversely proportional to the light intensity. The total
time will usually be at least about 2 hrs. and not more than about 60 hrs.,
generally ranging from about 10 hrs. to 50 hrs. The times between additions of
furocoumarin, where the furocoumarin is added incrementally, will generally vary
from about 1 hour to 24 hrs., more usually from about 2 hrs. to 20 hrs.

The light which is employed will generally have a wavelength in the range
from about 300 nm to 400 nm. Usually, an ultraviolet light source will be
employed together with a filter for removing UVB light. The intensity will
generally range from about 0. 1mW/cm(2) to about 5W/cm(2), although in some
cases, it may be much higher.

The temperature for the irradiation is preferably under 25 degrees C., more
preferably under 20 degrees C. and will generally range from about -10 degrees
C. to 15 degrees C., more usually from about 0 degrees to 10 degrees C.

During irradiation, the medium may be maintained still, stirred or
circulated and may be either continuously irradiated or be subject to
alternating periods of irradiation and non-irradiation. the circulation may be
in a closed loop system or in a single pass system ensuring that all of the
sample has been exposed to irradiation.

It may be desirable to remove the unexpended furocoumarin and/or its
photobreakdown products from the irradiation mixture. This can be readily
accomplished by one of several standard laboratory procedures such as dialysis
across an appropriately sized membrane or through an appropriately sized hollow
fiber system after completion of the irradiation. Alternatively, one could use
affinity methods for one or more of the low molecular weight materials to be
removed.

dosage of at least 10(5) pfu/dose, usually at least 10(6) pfu/dose,
preferably at least 10(7) pfu/dose. The total dosage will usually be at or near
about 10(9) pfu/dose, more usually being about 10([ILLEGIBLE]) pfu/dose. The
vaccine may include cells or may be cell-free. it may be an inert
physiologically acceptable medium, such as ionized water, phosphate-buffered
saline, saline, or the like, or may be administered in combination with a
physiologically acceptable immunologic adjuvant, including but not limited to
mineral oils, vegetable oils, mineral salts and immunopotentiators, such a
muramyl dipeptide. The vaccine may be administered subcutaneously,
intramuscularly, intraperitoneally, orally, or nasally. Usually, a specific
dosage at a specific site will range from about 0.1 ml to 4 ml. where the total
dosage will range from about 0.5 ml to 8 ml. The number of injections and their
temporal spacing may be highly variable, but usually 1 to 3 injections at 1, 2,
or 3 week intervals are effective.

The following examples are offered by way of illustration, not by way of
limitation.

EXPERIMENTAL

Materials and Methods

A. Virus Growth and Tissue Culture

Hamster cells [BHK-21(C-13), American Type Culture Collection (ATCC), CCL
10] were grown as monolayers in plastic cell culture vessels in
Eagle's Minimum Essential Medium (MEM) with Earle's salts and nonessential
amino acids (MEN) supplemented with 10% heat inactivated calf serum (C(i)) and
10% tryptose phosphate broth (Tp. e.g., Difco 0060). Cell cultures were used to
produce live vesicular stomatitis virus. New Jersey serotype (VSV-NJ) from
master seed virus originally obtained from the ATCC (VR-159), and live
blue-tongue virus (BTV) from master seed virus originally obtained from Dr. T.
L. Barber, USDA, Denver, Colorado. Cells were grown in culture vessels to 80%
to 100% confluency (approximately 2 x 10(5) cells per cm(2) of growth surface
area) using standard mammalian cell culture techniques. Corning plastic roller
bottles (Corning No. 25140-850) with a growth surface area of 850
cm(2)-containing 100 ml of MEN supplemented with 10% C(i) and 10% Tp and 1 x
10(8) to 2 x 10(8) CCL 10 cells/bottle were used for virus production. The cell
cultures were initiated by seeding approximately 1 x 10(6) to 5 x 10(7) cells
into 100 mls of growth medium in a roller bottle containing 5% CO(2) in air on a
roller bottle rotator at 1 to 5 rpm at 35 degrees C. to 38 degrees C. The
cultures were grown to 80% to 100% confluency over a six to fourteen day period
with a medium change every two to four days.

When the monolayers reached 80% to 100% confluency, the culture medium was
removed and the monolayer was infected with approximately 1 x 10(6) to 2 x 10(6)
plaque forming units (pfu) of VSV or BTV in 20 mls of MEN, with 2%
heat-inactivated fetal bovine serum (F(i)) added for BTV. The multiplicity of
infection (MOI) was approximately 0.01. the MOI may range from 0.001 pfu/cell
to 0.033 pfu/cell. The virus inoculum was adsorbed to the cells by incubation
at 35 degrees C. to 38 degrees C. for one hour at 1 to 5 rpm. One hundred mls
of MEN containing 10% YELP supplement (v/v) for VSV, or 10% C(1) and 10% Tp for
BTV, was added per roller bottle. YELP supplement contains: yeast extract BBL
11929, 5 g/liter; lactalbumin hydrolysate GIBCO 670-1800, 25 g/liter; and
Bacto-Peptone (Difco 0118), 50 g/liter. The post-infection incubation was
carried out

at 35 degrees C. to 38 degrees C. in 5% CO(2)/95% air with
rotation. Sixteen to forty-eight hours post-infection, VSV cytopathic effect
(CPE) was evident, while BTV CPE became apparent from 2 to 4 days post
infection.

The CPE was characterized by cell rounding, cell detachment, and cell
degeneration. When visual or microscopic examination indicated that at least 50%
of the cell monolayer exhibited CPE, the contents of the roller bottle were
swirled to remove loosely attached materials from the roller bottle walls. The
harvest material was decanted from the roller bottles into centrifuge bottles.
The crude VSV harvest was clarified by centrifugation at 500 to 1000 x g for 20
minutes, at 4 degrees C. The BTV harvest was centrifuged at 2,000 x g for 60
minutes at 4 degrees C.

The clarified VSV preparations were concentrated by ultrafiltration
using a Pellicon cassette system (Millipore XX42ASY60) with a cassette having a
nominal exclusion limit of 10(5) daltons (Millipore PTHK 000C5). The Pellicon
cassette system was sterilized by filling the assembled unit with IN NaOH and
incubating the unit 12 to 24 hours at room temperature. The NaOH solution was
pumped out of the cassette system and the system was flushed with two to four
liters of sterile H(2)O. The assembly and operation of the Pellicon system were
in accordance with the instructions furnished by the manufacturer. All steps in
the concentration were performed aseptically. The clarified VSV was concentrated
15 to 40 fold, dimethylsulfoxide (Sigma D-5879) added to a final concentration
of 7.5% v/v, and suitable aliquots of the virus stored frozen at -80 degrees C.
to -100 degrees C.

For BTV, the pellet resulting from centrifugation was resuspended
aseptically in 8 ml of 2mM Tris-HCl, pH 8.8, for each original roller bottle.
The suspension was mixed vigorously on a vortex mixer, and/or sonicated at 4
degrees C for 1 min., and centrifuged at 1,400 times g for 30 min. at 4 degrees
C. The virus-containing supernatant was collected and the pellet was extracted
twice more with 8 ml/roller bottle aliquots of 2mM Tris-HCl, pH 8.8. The
virus-containing supernatants were pooled and clarified by centrifugation at
4,000 x g for 30 min. at 4 degrees C. The clarified supernatant was stored at 4
degrees C.

Feline herpes I virus (FVR, the infective agent of feline viral
rhinotracheitis) was grown as follows.

Cat cell lines AKD (ATCC CCL150) or Fc3Tg (ATCC CCL176) were grown as
monolayers in plastic cell culture vessels in a standard defined culture medium
consisting of MEN; F12K; MEM; or alpha MEM. Medium was supplemented with 2% to
15% inactivated fetal calf serum (F(i)) or 2% to 20% YELP. Cell cultures
were used to produce live Feline Herpes I virus from master seed virus derived
from Feline Herpes I virus (ATCC VR636). Cells were grown in culture vessels to
80% to 100% confluency (approximately 1 x 10(5) to 2 x 10(5) cells per cm(2) of
growth surface area) using standard mammalian cell culture techniques as
follows.

Corning plastic roller bottles containing 50 to 100 ml of MEN
supplemented with 10% F(i) and 1 x 10(8) to 2 x 10(8) AKD or Fc3Tg cells/bottle
were used for Feline Herpes I virus production. The cell cultures were initiated
by seeding approximately 1 x 10(6) to 5 x 10(6) cells into 50 to 100 mls of
growth medium in a roller bottle containing about 5% CO(2) in air and incubating
the roller bottle on a roller bottle rotator at 1 to 5 rpm at 35 degrees C. to
38 degrees C. The cultures were grown to 80% to
<PAGE> 21
4,693,981

100% confluency over a 7 to 14 day period with a 100% medium change every 3 to 5
days.

When the monolayers were 80% to 100% confluent, the culture medium was
removed and the monolayer was washed with 20 to 50 mls of phosphate buffered
saline (PBS) pH 7.2 to 7.4 (NaCl 8 g+KCl 0.2 g+Na(2)NPO(4) 1.14 g+KH(2)PO(4)0.2
g). The PBS wash was discarded, and the roller bottle was infected by the
addition of approximately 1 x 10(7) to 2 x 10(7) plaque forming units (pfu) of
Feline Herpes 1 virus in 10 mls of PBS containing 2% F(i). The multiplicity of
infection (MOI) was approximately 0.1. The virus inoculum was adsorbed to the
cells by incubation at 35 degrees C. to 38 degrees C. for one hour at 1 to 5
rpm. The inoculation fluid was removed and 50 mls of MEN containing 10% F(i) was
added per roller bottle. The post-infection incubation was at 35 degrees C. to
38 degrees C. in 5% CO(2) in air with rotation. Herpesvirus cytopathic effect
(CPE) was evident forty to forty-eight hours post-infection. The CPE was
characterized by cell rounding, cell detachment, and cell degeneration.

The contents of the roller bottle were swirled 48 hours post-infection to
remove loosely attached materials from the roller bottle walls, and the contents
of the roller bottles were decanted into centrifuge bottles. The virus, cells,
and cell debris were pelleted by centrifugation at 10,000 x g for 30 minutes.

Cell associated (CA) Feline Herpes I virus was prepared by:

1. resuspending the 10,000 x g pellet in approximately 5 ml of a
resuspension medium containing 80 parts F12K, 10 parts F(i) and 10 parts
dimethylsulfoxide (DMSO) for each original roller bottle;

2. freezing the resuspended CA virus at -20 degrees C. for 1.5 to 2 hours,
and

3. transferring the CA virus frozen at -20 degrees C. to temperatures
ranging from -80 degrees C. to -100 degrees C.

Cell free (CF) Feline Herpes I virus was prepared by:

1. resuspending the 10,000 x g pellet in F12K;

2. freezing and thawing the resuspended material 3 times;

3. clarifying the freeze-thawed material by centrifugation at 10,000 x g
for 30 minutes; and

4. freezing the clarified supernatant (CF virus) at temperatures ranging
from -80 C. to -100 C.

CF or CA virus was thawed by gentle agitation at 37 degrees C. in a water
bath.

B. Virus Assay

Confluent monolayers of LMTK-, Vero (ATCC CCL 81), Fc3Tg, or AKD cells were
prepared in 6 cm diameter mammalian cell culture plastic petri dishes (Corning
#25010) or other convenient cell culture vessels. The growth medium used for
LMTK- cells was alpha ME (alpha modified Eagles Minimum Essential Medium,
Earle's Salts)+10% F(i). The growth medium used for Vero cells was MEN+5% F(i).
The growth medium used for Fc3Tg cells was MEN+10% F(i) and the growth medium
used for AKD cells was F12K+15% F(i) (VSV and BTV were titered on LMTK- or Vero
cells. Feline Herpes I was titered on Fc3Tg or AKD cells). Ten fold serial
dilutions of virus samples were made by adding 0.5 ml of the virus sample to 4.5
mls of diluent (phosphate buffered saline, pH 7.2 to 7.4, plus 2% F(i) in a
screw cap tube. The growth medium was removed from a 6 cm culture dish cell
monolayer, 0.1 ml of virus sample (undiluted or diluted) was added, and the
virus was adsorbed to the mono-

layer for 1 to 2 hours at 35 degrees C. to 38 degrees C. Two or more monolayers
were used for each sample.

Five ml of overlay medium was added per 6 cm culture dish, except for
Feline Herpes I, where the unadsorbed inoculum was removed, and 4 mls of overlay
medium was added per 6 cm culture dish. The overlay medium for BTV or VSV was
prepared by mixing equal parts of solution A (100 ml 2X MEM with L-glutamine.
GIBCO #320-1935, +10 ml F(i) and 1.8% to 2% Noble Agar (Difco 0142)in deionized
H(2)0 at 44 degrees C. to 45 degrees C. The overlay medium for Feline Herpes I
was prepared by mixing equal parts solution A and 1% methyl cellulose (4,000
centriposes) in deionized H(2)0 (Fisher M-281 sterilized by autoclaving).

The virus infected cultures were incubated at 35 degrees C. to 38 degrees
C. in 5% CO(2) in air. Twenty-four hours before plaques were counted, a second
overlay containing Neutral Red at a final concentration of 0.005% was added.
Plaques were counted on day 2 or day 3 post-infection for VSV, on day 2 to 4 for
FVR and on day 6 or 7 for BTV. The virus titer in pfu/ml was calculated by
multiplying the average number of plaques per dish by the reciprocal of the
dilution. The pfu/ml was the value used to determine the amount of virus needed
to infect cells at a MOI of approximately 0.01. The pfu/ml in a virus
preparation prior to inactivation was used to determine the immunizing dose.

C. Virus Inactivation

1. VSV Inactivation

The thawed stock of VSV was pipetted into sterile T-150 tissue culture
flasks (nominally 25 ml into each of four flasks). To each flask was added 0.25
ml of 4'-aminomethyl-4.5', 8-trimethylpsoralen (AMT) stock solution (stock
solution is 1 mg/ml AMT dissolved in sterile, deionized water). Each flask was
allowed to equilibrate in an argon atmosphere for at least 10 minutes. After
equilibration, a stream of argon gas was directed into each flask for a least
two minutes. The flasks were then tightly capped and placed under a long
wavelength ultraviolet (320 nm to 400 nm) light source (GE BLB fluorescent
bulbs) at a temperature between 0 degree C. and 20 degrees C. for approximately
11 hours. The incident light intensity was approximately lmW/cm(2) (measured by
a J-221 long wavelength UV meter).

After the irradiation was completed, the flasks were removed from the light
source and an additional 0.25 ml of AMT stock solution was mixed into each
flask. The contents of each flask were pipetted into new, sterile T-150 flasks,
and the flasks were again flushed with argon and irradiated for an additional 11
hours. This procedure was repeated three more times until five additions (a
total of approx. 50 (greek mu)g/ml) of AMT had been performed, the virus sample
had been irradiated for at least 55 hours, and at least four flask changes had
been performed.

After all of the irradiations had been completed, the contents of the
flasks were aseptically transferred to a common sterile container and stored
at -85 degrees C.

2. BTV Inactivation

Twenty-five ml of BTV serotype 11 (1.5 x 10(8) pfu/ml) was mixed with 0.25
ml of 4'-aminomethyl 4,5', 8-trimethylpsoralen (AMT; 1 mg/ml in DMSO). The
mixture was placed in a 150cm(2) tissue culture flask (T-150; Corning #25120).
The viral suspension in the flask was placed in an argon atmosphere for 10 min.,

<PAGE> 22
4,693,981

and a stream of argon gas as then blown over the viral suspension for an
additional 2 min. The flask was tightly capped and the suspension irradiated
for 3.25 hrs. at 4 degrees C. using GE BLB fluorescent bulbs at an intensity of
1.5mW/cm(2). An additional 0.25 ml of AMT was then added to the viral
suspension, the suspension transferred by pipette to a new T-150 flask, and the
solution again flushed with argon. The flask was irradiated for an additional
14.75 hours at 4 degrees C. under the same long wavelength UV light source.
After this irradiation an additional 0.25 ml of AMT solution was added to the
suspension, and it was again transferred to a new T-150 flask. The solution was
flushed with argon as before and irradiated for an additional 5.5 hours at 4
degrees C. The inactivated BTV was stored at 4 degrees C.

3. Feline Herpes I Inactivation

a. Cell Free Virus

Nineteen mls of CF-FVR (1.9 x 10(7) pfu/ml) were mixed with 0.4 ml of
hydroxymethyltrioxsalen (HMT: 1 mg/ml in DMSO) and 1.9 ml of sodium ascorbate
(0.1 M in H(2)O). The mixture was prepared in 150 cm(2) tissue culture flasks
(T-150, Corning No. 25120) that were subsequently deaerated for 2 minutes with
pure argon gas. The virus-containing flasks were irradiated for 55 minutes at 4
degrees C. using G.E. BLB fluorescent bulbs at an intensity of 1.5 mW/cm(2).
The FVR/HMT/ascorbate mixture was then transferred by pipet into a second T-150
flask, which was deaerated for 2 minutes using pure argon gas. The second T-150
flask was irradiated for an additional 28 minutes at 4 degrees C. under the
same long wavelength UV light source.

The CFV-FVR preparation was stored at -100 degrees C. in a REVCO freezer.
Subsequently the CF-FVR preparation was thawed and placed into a T-150 flask.
The flask was deaerated with pure argon gas for 2 minutes and irradiation was
continued as described above for an additional 15 hours and 40 minutes.

b. Cell Associated Virus

Cells from 10 roller bottles (about 1x10(8) to 2x10(8) cells/roller
bottle) were resuspended in 28 mls of cell culture media. Twenty mls of the
suspension were placed into a T-150 flask. To this flask was added 2 ml of
freshly prepared sterile 0.1 M sodium ascorbate and 0.4 ml HMT (1 mg/ml in
DMSO). The flask was deaerated with pure argon gas for 2 minutes, and the flask
was irradiated at 4 degrees C. using G.E. BLB fluorescent bulbs at an intensity
of 1.5 mW/cm(2) for 75 minutes. The viral suspension was then transferred by
pipet from the T-150 flask into a second T-150 flask and again deaerated with
pure argon gas for 2 minutes. Irradiation was continued for an additional 95
minutes. The CA-FVR preparation was adjusted to 10% DMSO and the suspension was
frozen at -20 degrees C. for 1 hour and then stored at -100 degrees C. in a
REVCO freezer.

The stored frozen CA-FVR preparation was subsequently thawed, and the
cells were pelleted in a clinical centrifuge. The cells were resuspended in 21
mls of serum-free medium to which 2.1 mls of freshly prepared 0.1 M sodium
ascorbate and 0.4 ml of HMT (1 mg/ml in DMSO) were added. The sample was
transferred by pipet to a T-150 flask, and irradiation was continued for an
additional 15 hours and 40 minutes.

Results

A. Bluetongue Virus

1. Assessment of Inactivation by Blind Passage

CCL 10 cells were grown to confluency in 850 cm(2) roller bottles using
standard cell culture procedures, as described above. The culture medium was
removed from the roller bottle, and 2.0 ml of the inactivated virus preparation
mixed with 18 ml of medium containing 2% F(i) was adsorbed to the roller bottle
monolayer for 60 min at 35 degrees C. to 38 degrees C. with rotation at 1 to
5rpm. After adsorption, the residual unabsorbed inoculum was removed, and 100
ml of growth medium (MEN with 10% C(i) and 10% Tp) was added and the roller
bottle culture incubated at 35 degrees C. to 38 degrees C. for 7 days with
daily observation for viral CPE. The roller bottle culture received a 100%
medium change every 2 to 3 days. If no CPE was observed during the first roller
bottle passage, the cell monolayer was chilled at 4 degrees C. for 12 to 24
hrs. The cells were scraped into the medium which was then decanted into a
centrifuge bottle. The cells were pelleted by centrifugation at 4 degrees C. at
2,000 x g for 30 min. and resuspended in 2.0 ml of 2mM Tris-HCl (pH 8.8) by
vigorous mixing using a vortex mixer. The resuspended material was centrifuged
at 2,000 x g for 20 min. at 4 degrees C. The supernatant was added to 18 ml of
growth medium containing 2% F(i) and used to infect a new confluent roller
bottle culture of CCL 10 cells, as described immediately above. The second
roller bottle blind passage was observed for 7 days and fed ever 2 to 3 days. If
no CPE was observed during the second roller bottle blind passage, a third
roller bottle blind passage was performed. If no CPE had been observed by the
end of the third roller bottle blind passage the virus preparation was
considered inactivated and suitable for in vivo testing.

2. Immunization of Rabbits with Psoralen-inactivated
BTV Vaccine

a. Example 1

4,693,981

serologic assays, serum neutralization (Jochim and Jones, Am. J. Vet. Res.
(1976) 37:1345-1347) and agar gel precipitation (Jochim et al., Am. Assoc. Vet.
Lab. Diag., 22nd Proceed.: 463-471, 1979) Pre-immunization rabbit serum was used
as the negative control; BTV immune sheep serum was used as the positive control
for both immunologic procedures.

Pooled sera from Groups A and B reduced the number of viral plaques (serum
neutralization) greater than eighty percent (arbitrarily selected end point)
when the sera were diluted 1:40, which was the highest dilution examined.
Negative and positive control sera behaved as expected.

<TABLE>
<CAPTION>
TABLE 1
- --------------------------------------------------------------------------------

Serum Neutralization Data From Rabbits
Vaccinated with AMT-UVA-inactivated
Bluetongue Virus Vaccines
---------------------------------------
Titer*
-----------------------------------
Group 1 5 40
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
A + + +
B + - +
Normal Rabbit Serum - - -
BTV-Immune Sheep Serum + + plus or
minus
- --------------------------------------------------------------------------------
* Reciprocal of serum dilution neutralizing [ILLEGIBLE] percent of BTV plaque
activity on BHA cells. The data are from the post-second immunization serum
samples.
</TABLE>

Of the two immunologic procedures utilized, serum neutralization is
considered predictive for immunity to live BTV challenge in the target species.

b. Example 2

Twelve New Zealand white rabbits were randomly assigned to six groups,
A-F, two rabbits per group. An additional four rabbits were assigned to group
G. These sixteen rabbits were vaccinated twice subcutaneously with the AMT-UVA
inactivated Bluetongue virus vaccines described in Table 2. Preinactivation
titer was approximately 10(8) pfu for each serotype. The vaccines were
formulated with 20% (v/v) aluminum hydroxide adjuvant, and were given with a
three week interval between the first and second inoculations.

The sixteen rabbits were bled by auricular venipuncture on days 0, 14 and
35. Each serum was heat-inactivated and tested against BTV serotypes 10, 11, 13
and 17 for serum neutralizing antibody. All vaccinated rabbits developed SN
titers against the homologous vaccine serotypes (Table 3). These data
demonstrated the immunopotency of a multivalent AMT-UVA inactivated Bluetongue
virus vaccine.

<TABLE>
<CAPTION>
TABLE 2
- --------------------------------------------------------------------------------

Serotype Composition of Inactivated Bluetongue
Virus Vaccines Tested in Rabbits
----------------------------------------------
BTV Serotype
Group Rabbit # Composition
- --------------------------------------------------------------------------------
<S> <C> <C>
A 1, 2 10
B 3, 4 11
C 5, 6 13
D 7, 8 17
E 9, 10 11, 17
F 11, 12 10, 11, 17
G 13, 14, 15, 16 10, 11, 13, 17
- --------------------------------------------------------------------------------
</TABLE>

<TABLE>
<CAPTION>
14

TABLE 3
- --------------------------------------------------------------------------------

Serum Neutralizing Data from Rabbits Vaccinated
with AMT-UVA Single and Multi-Serotypes Bluetongue
Virus Vaccines
---------------------------------------------------
SN Titer* Against
------------------------------------------------------
Group Rabbit BTV-10 BTV-11 BTV-13 BTV-17
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
A 1 1:160 1:10 1:10 1:10
2 1:320 1:10 1:10 1:10
B 3 1:10 1:320 1:10 1:10
4 1:10 1:80 1:10 1:10
C 5 1:20 1:20 1:160 1:10
6 1:20 1:10 1:40 1:10
D 7 1:10 1:10 1:10 1:320
8 1:10 1:10 1:10 1:320
E 9 1:20 1:160 1:20 1:160
10 1:20 1:160 1:20 1:160
F 11 1:160 1:160 1:20 1:160
12 1:40 1:40 1:20 1:80
G 13 1:160 1:160 1:80 1:160
14 1:160 1:160 1:80 1:160
15 1:160 1:160 1:40 1:160
16 1:80 1:160 1:160 1:160
- --------------------------------------------------------------------------------
* Reciprocal of serum dilution neutralizing [ILLEGIBLE] of BTV plaque activity
on [ILLEGIBLE] cells. The data are from the post-second immunization sera (Day
35). Negative and positive control sera behaved as expected in the SN assay.

</TABLE>
3. Immunization of Sheep with Psoralen-inactivated
BTV Vaccine

a. Example 1

Each of two adult sheep, known to be susceptible to BTV, was inoculated
subcutaneously (SQ) with 2 ml of AMT-UVA inactivated BTU plus adjuvant (1:1;
vaccine to aluminum hydroxide adjuvant). The vaccine contained approximately
10(8) pfu/ml of BTV prior to inactivation. A third sheep was inoculated SQ with
6 ml of the identical vaccine without adjuvant. Seven weeks later the three
sheep were given identical inoculations SQ that consisted of 5 ml of vaccine and
aluminum hydroxide adjuvant (2:1 vaccine to adjuvant; 10(8) pfu BTV/ml of
vaccine).

The three sheep were monitored for clinical evidence of BTV, including
daily body temperature recording and bi-daily virus isolation attempts. No
evidence of BTV was observed, indicating that the vaccine was inactivated.

Serum was collected weekly for serum neutralization and agar gel
precipitation testing. Normal sheep sera and BTV-immune sheep sera were used for
negative and positive control samples in the serologic tests.

The first vaccine inoculations induced precipitating anti-BTV antibody in
all three sheep. Their pre-exposure sera were uniformly negative for anti-BTV
precipitating antibody. Modest neutralizing anti-BTV antibody titers (1:5) were
elicited in two of three sheep following one immunization. The second
immunization elicited a distinct immunologic anamnestic response, inducing
neutralizing titers of 1:40, 1:80, or 1:160 in the three sheep.

<TABLE>
<CAPTION>
TABLE 4
- --------------------------------------------------------------------------------

Serum Neutralization Data From Sheep Immunized
with an AMT-UVA Inactivated BTV Vaccine
----------------------------------------------
TITERS*
Sheep No.:
-----------------------------------
1 2 3
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
Pre-First Immunization
Day 0 <5 <5 <5

Post-First Immunization
Day 21 5 5 <5

Post-Second Immunization
- --------------------------------------------------------------------------------
</TABLE>
<PAGE> 24
4,693,981

15
<TABLE>
<CAPTION>

TABLE 4-continued
- -------------------------------------------------------------------------------
Serum Neutralization Data From Sheep Immunized
with an AMT-UVA Inactivated BTV Vaccine.
- ------------------------------------------------------------------------------
TITTERS*
Sheep No.:
---------------------------------------

<S> <C> <C> <C>
1 2 3
- -------------------------------------------------------------------------------
Day 7 80 160 40
Day 14 80 40 40
Day 21 80 80 40
Day 42 80 80 80
Post-Challenge
-----------
Day 7 160 160 80
Day 14 320 160 80
- -------------------------------------------------------------------------------

*reciprocal of highest 2-fold dilution reducing BTV plaque activity on BHA cell
by 80 percent

</TABLE>

The sheep were challenged by SQ syringe inoculation of 10(5) egg lethal
doses of BTV serotype 11. The three sheep remained clinically normal during the
BTV challenge period, indicating that the vaccine was efficaceous.

It is evident from the above results that the BTV which is
psoralen-inactivated retains its immunogenicity, particularly as to those sites
which elicit an immune response which is effective in protecting a host against
subsequent BTV-infection. Thus, the psoralen inactivation can be carried out
under conditions which do not modify the immunogenic sites of the virus, so as
to elicit an immunogenic response which will be effective against the live BTV.
Furthermore, the BTV RNA virus is efficiently inactivated under mild conditions
to the point of complete inactivation, whence it may be safely administered to a
host.

b. Example 2

Eight experimental and four control sheep, known to be Bluetongue Virus
susceptible, were housed together in an insect-proof facility. The experimental
sheep were inoculated twice subcutaneously with AMT-UVA inactivated BTV Serotype
11 vaccine. Each vaccinate received approximately 3 x 10(8) pfu BTV-11
formulated with twenty-five percent (v/v) aluminum hydroxide adjuvant. Three
weeks elapsed between immunizations. Control sheep were inoculated with tissue
culture fluid in 25% percent (v/v) aluminum hydroxide. Serum samples were
collected prior to vaccination, following vaccinations, and following challenge,
and tested for SN antibodies. All sheep were challenged by subcutaneous
inoculation of 2 x 10(5) ELD(50) BTV-11 four weeks post-second vaccination.
Virus isolation was performed twice weekly post-challenge for six weeks. Virus
isolation from sheep blood was done by intravenous chicken embryo inoculation,
followed by specific BTV serotype identification by neutralization in vitro.
Five of the eight vaccinated sheep developed SN titers of 1:20 post-second
vaccination. All eight vaccinates resisted subcutaneous challenge with 2 x 10(5)
ELD(50) BTV-11, whereas the four control sheep developed uniform viremia as
assessed by egg inoculation. Sheep data are given in Table 5.

TABLE 5
- -------------------------------------------------------------------------------
Serum Neutralization and Virus Isolation Data from Sheep
Vaccinated with AMT-UVA Inactivated BTV-11 Vaccine and
Subsequently Challenged with 2 x 10(5) ELD(50) of Live BTV-11
- -------------------------------------------------------------------------------
SN Titer Virus Isolation
Sheep Base- Post-Second Post- Post-Challenge Day
------------------
No. line Vaccination Challenge 4 11 15 18
- -------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C> <C>

</TABLE>

16
<TABLE>
<CAPTION>

TABLE 5-continued
- -------------------------------------------------------------------------------
Serum Neutralization and Virus Isolation Data from Sheep
Vaccinated with AMT-UVA Inactivated BTV-11 Vaccine and
Subsequently Challenged with 2 x 10(5) ELD(50) of Live BTV-11
- -------------------------------------------------------------------------------

SN Titer Virus Isolation
Sheep Base- Post-Second Post- Post-Challenge Day
------------------
No. line Vaccination Challenge 4 11 15 18
- -------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C> <C>
Experimental
- -----------
650 neg 1:20 1:160 - - - -
651 neg 1:20 1:40 - - - -
652 neg 1:20 1:160 - - - -
653 neg 1:20 1:40 - - - -
656 neg 1:10 1:160 - - - -
658 neg 1:10 1:40 - - - -
659 neg 1:20 1:160 - - - -
660 neg 1:10 1:160 - - - -
Controls
- --------
654 neg neg 1:10 - + + +
655 neg neg neg + + + +
661 neg neg 1:40 + + + +
662 neg neg 1:160 - - - -
- -------------------------------------------------------------------------------
</TABLE>

B. Feline Herpes Virus I

1. Assessment of Inactivation by Blind Passage

Fc3Tg or AKD cells were grown to confluency in 850 cm(2) roller bottles
using standard cell culture procedures as described above. The culture medium
was removed from the roller bottle, and 2.0 mls of the inactivated virus
preparation, mixed with 18 mls of medium containing 2% F(i), were absorbed to
the roller bottle cell monolayer for 60 minutes at 35 degrees C. to 38 degrees
C. with rotation at 1 to 5 rpm. After adsorption, the inoculum was removed and
150 ml of maintenance medium (MEN or F12K with 2% F(i)) added. The roller bottle
culture was then incubated at 35 degrees C. to 38 degrees C. for 7 days with
daily observation for viral CPE. The roller bottle culture received a 100%
medium change after 3 to 5 days. If no CPE was observed during the first roller
bottle passage, the cell monolayer was scraped into the maintenance medium which
was then decanted into a centrifuge bottle. The cells were pelleted by
centrifugation at room temperature at 1,000 x g for 15 minues, resuspended in 20
ml of fresh maintenance medium, and passed to a new confluent roller bottle
culture of Fc3Tg or AKD cells as described above. The second roller bottle blind
passage was observed for 7 days and fed once on day 3 to 5. If no CPE was
observed during the second roller bottle behind passage, a third roller bottle
blind passage was performed. If no CPE was observed by the end of the third
roller bottle passage, the virus preparation was considered inactive.

2. Administration Procedure for Psoralen-inactivated
FVR Vaccines

Photochemically inactivated FVR was inoculated via syringe into cats by
various routes, including but not limited to intravenously (IV), subcutaneously
(SQ), intramuscularly (IM), or intraperitoneally (IP). The vaccine was
administered in various volumes (0.5 to 3.0 ml) and in various concentrations
(10(6) to 10(8) pfu; either CF, CA or in combination). In the following
examples, the vaccine was administered in combination with aluminum hydroxide as
an immunologic adjuvant. The number of injections and their temporal spacing was
as set forth in each example.
<PAGE> 25
4,693,981

17
3. Immunization with Psoralen-inactivated CF-FVR Vaccine

The experimental group consisted of four specific pathogen free kittens (2
males, 2 females) four months old (Liberty Laboratories, Liberty Corner, N.J.).
The control group consisted of two similar female kittens. The experimental
group was inoculated IM with 3x10(7) pfu (3 mls) of HMT inactivated CF-FVR on
days 0 and 21, and again inoculated with 3x10(7) pfu HMT inactivated with an
equal amount of 2% aluminum hydroxide [AI(OH)(3)] adjuvant on day 61. Controls
were vaccinated at eight weeks and at thirteen weeks of age with a commercial
FVR vaccine using the manufacturer's recommended procedure. Sireum samples were
collected weekly and tested for anti-FVR neutralizing antibodies.

Following live virus challenge (10(6) pfu intranasally and
intraconjunctivally), a numerical scoring system (Table 6) was used to assess
the clinical response of both experimental and control cats.

TABLE 6

<TABLE>
<CAPTION>
- -------------------------------------------------------------------------------
Scoring System for Clinical
Effects of Herpesvirus Challenge in Cats

Factor Degree Score
- -------------------------------------------------------------------------------
<S> <C> <C>

Fever 101 to 102 degrees F. 0
102 to 103 1
103 to 104 3
greater than 104 5

Depression slight 1
moderate 3
severe 5

Sneezing occasional 1
moderate 3
paroxysmal 5

Lacrimation serous 1
mucoid 3
purulent 5

Nasal Discharge serous 1
mucoid 3
purulent 5

Appetite normal, eats all food 0
fair, eats more than 1
1/2 of food
poor; eats less than 3
1/2 of food
none; eats nothing 5
- -------------------------------------------------------------------------------
</TABLE>

Three of four experimental cats developed serum neutralizing anti-FVR
antibody (SN) titers of 1:2 that were detected between day 42 and day 58.
Following the third immunization (day 61), four of four experimental cats had
SN titers of 1:4 (day 80). Baseline SN antibody titers on the experimental cats
were negative. The control cats die not develop detectable SN antibody titers
during the pre-challenge period.

All cats were exposed to 10(6) pfu of live FVR by intraconjunctival and
intranasal exposure on day 91. Each cat was monitored twice daily for the
absence, presence and degree of severity of factors given in Table 6. A
composite clinical score was derived for each cat after a 15 day observation
period.

Three of four experimental cats demonstrated mild temperature elevation
and serous ocular or nasal discharge along with mild intermittent depression
and appetite suppression. Their composite scores were 39, 42, and 35
respectively for the 15 day observation period. The fourth experimental cat was
more severely affected (composite score = 84) by moderate, but transient,
sneezing and mucoid nasal discharge. Both control cats were severely affected
by live virus challenge. Severe purulent nasal and ocular discharge and lack of

appetite were apparent. The control cats had composite scores of 133 and 253.

Three weeks following live FVR challenge, all cats were tested for SN
antibody titers against FVR. Three of four experimental cats had SN antibody
titers of 1:16 while the fourth cat had a 1:8 titer. One of the control cats
had an SN antibody titer of 1:4 while the second control lacked an SN antibody
titer against FVR.

4. Immunization with Psoralen-inactivated CA-FVR Vaccine

Nine age-matched specific pathogen free kittens, 4 months old (Liberty
Laboratories, Liberty Corner, N.J.), were randomly assigned to three
experimental groups designated A, B, and C.

Group A (controls) was inoculated twice with 1 ml tissue culture fluid and
1 ml aluminum hydroxide adjuvant. Group B was inoculated twice with a
commercial FVR vaccine according to the manufacturer's recommendation. Group C
was inoculated three times with 10(7) HMT-inactivated CA-FVR in aluminum
hydroxide (total volume = 2 ml; 1:1 vaccine to adjuvant). All injections were
given IM at three week intervals.

Live FVR virus (10(6) pfu intransally and intraconjunctivally) was given
on day 63 and a numerical scoring system (Table 6) was used to assess the
kittens' clinical response for a 15 day post-challenge period. Serum samples
were collected from all kittens prior to vaccination, prior to the second and
third immunizations, prior to live FVR challenge, and at 15 days
post-challenge. The sera were utilized to assess neutralizing antibody titers
by standard procedures.

The control kittens (Group A) maintained SN antibody titers less than 1:2
(negative) throughout the pre-challenge period. Fifteen days following live FVR
challenge Group A kittens uniformly had SN antibody titers of 1:2. Kittens in
Groups B and C lacked detectable anti-FVR antibody titers pre-immunization, but
all kittens in Groups B and C had SN antibody titers of 1:2 or 1:4 after two
immunizations. The third immunization in Group C kittens did not significantly
alter their SN antibody titers. Following a 15 day post-challenge period,
kittens in Groups B and C demonstrated an anamnestic immunologic response, with
SN antibody titers ranging from 1:16 to 1:64.

Clinically, Group A kittens were severely affected by live FVR challenge,
whereas kittens in Groups B and C were significantly protected by their
respective vaccines.

The composite clinical scores for Group A were 125, 141, and 128 for the
15 day post-challenge period. The composite clinical scores for Group B were 25,
20, and 64, while Group C had composite clinical scores of 21, 15, and 34. The
clinical signs evident were characteristic of FVR.

From the SN data and clinical scoring, it is evident that kittens
immunized with the experimental HMT-inactivated FVR vaccines (cell-free or cell
associated) in the above examples were significantly immune to the clinical
effects of severe FVR challenge.

C. Vesicular Stomatitis Virus

1. Assessment of Inactivation by Intracerebral Inoculation of Mice

Suckling mice (0 to 10 days old) were inoculated intracerebrally with 0.02
ml of the psoralen-inactivated

<PAGE> 26
4,693,901

VSV-NJ using a tuberculin syringe and a 28 or 30 gauge needle. Each vaccine lot
was tested in four to nine suckling mice. The mice were observed three times
daily for a minimum of seven days. Residual low-level live VSV kills suckling
mice in two to five days. The sensitivity of this assay is approximately 1 to 5
pfu of live VSV per intracerebral dose. Inactivated VSV-NJ vaccine was
considered safe (inactivated) if all inoculated suckling mice survived the seven
day observation period. The VSV-NJ vaccine batches used hereinafter each passed
the suckling mouse safety test prior to use.

2. Virus Neutralization in Mice Immunized with Psoralen-inactivated VSV-NJ
Vaccine

Groups of ten adult white mice each were injected using three immunological
adjuvants (aluminum hydroxide gel, incomplete Freund's, or oil emulsion) with
one of three psoralen-inactivated VSV-NJ vaccine doses (10(9), 10(8), or 10(7)
pfu/dose). The oil emulsion was prepared as described by Stone et al. (1978)
Avian Dis. 22:666-674. All mice were injected IP once each, on day 0 and day 21.
Serum samples were collected from the orbital sinus on day 20 and on day 33 and
pooled serum samples were assessed for serum neutralization (SN) activity by
standard procedures. See, Castaneda et al. (1964) Proc. US Livestock San. Assoc.
68:455-468. Serum samples were negative for neutralizing antibodies to VSV-NJ
prior to vaccination.

The vaccine with oil emulsion adjuvant induced the highest SN titers after one
injection. All three vaccine doses, regardless of adjuvant, induced SN titers of
at least 1:2000 after two injections. Serum dilutions were tested for SN
activity only to 1:2560. The results are set forth in Table 7.

<TABLE>
<CAPTION>
TABLE 7
- --------------------------------------------------------------------------------
Virus Neutralization Indices* of Mouse Sera
After One and Two Injections of Psoralen-
Inactivated VSV-NJ Vaccine
- --------------------------------------------------------------------------------
Log(10) of Vaccine
Concentration (pfu/dose)
No. of --------------------------------------
Adjuvant Injections 7 8 9
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
Aluminum hydroxide gel 1 67* 905 905
Aluminum hydroxide gel 2 >2560 2560 >2560
Freund's Incomplete 1 226 57 905
Freund's Incomplete 2 2033 >2560 >2560
Oil Emulsion 1 >2560 >2560 >2560
Oil Emulsion 2 >2560 >2560 >2560
- --------------------------------------------------------------------------------
*Virus neutralization index is the reciprocal of the serum dilution that
neutralized 32 TCID(30) of VSV-NJ
</TABLE>

3. Virus Neutralization in Hamsters Vaccinated with Psoralen-inactivated
VSV-NJ Vaccine

Groups of five MHA hamsters each were injected with either 10(9), 10(8), or
10(7) pfu psoralen-inactivated VSV-NJ per dose, with or without aluminum
hyroxide adjuvant (1:1). All hamsters were injected intramuscularly (IM) once
each, on day 0 and again on day 21. Pooled serum samples were collected on day
21 and on day 34 for serum neutralization testing by standard procedures. Serum
neutralizing antibodies were elicited by all three vaccine doses tested, with or
without aluminum hydroxide adjuvant. SN titers are given in Table 8.

<TABLE>
<CAPTION>
TABLE 8
- --------------------------------------------------------------------------------
Virus Neutralization Indices* of Hamster
Sera After One and Two Injections of
Psoralen-Inactivated VSV-NJ Vaccine
- --------------------------------------------------------------------------------
Log(10) of Vaccine
Concentration (pfu/dose)
No. of --------------------------------------
Adjuvant Injections 7 8 9
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
None 1 134* 134 1076
None 2 >1280 1810 >2560
Aluminum hydroxide gel 1 538 538 >2560
Aluminum hydroxide gel 2 >1810 1920 2560
- --------------------------------------------------------------------------------
*Virus neutralization index is the reciprocal of the serum dilution that
neutralized 32 TCID(30) of VSV-NJ
</TABLE>

4. Live VSV-NJ Challenge of Mice Vaccinated with Psoralen-inactivated
VSV-NJ Vaccine

Three groups of fourteen, sixteen and seventeen adult white mice each were
injected with either 10(7), 10(6), or 10(5) pfu psoralen-inactivated VSV-NJ per
dose, respectively, using oil emulsion adjuvant with all injections. Each mouse
was injected once IP (day 0). Pooled serum samples were collected on day 0 and
again on day 21, and these samples were tested for SN antibody titers by
standard procedures. The results are set forth in Table 9.

<TABLE>
<CAPTION>
TABLE 9
- --------------------------------------------------------------------------------
Virus Neutralization Indices* of Mouse
Sera After One Injection with Psoralen-
Inactivated VSV-NJ Vaccine, Using Oil
Emulsion Adjuvant
- --------------------------------------------------------------------------------
Log(10) of Vaccine
Concentration (pfu/dose)
- --------------------------------------------------------------------------------
Day 5 6 7
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
0 --* -- --
21 -- -- 40
- --------------------------------------------------------------------------------
* Virus neutralization index is the reciprocal of the serum dilution that
neutralized 56 TCID(30) of VSV-NJ
</TABLE>

Each group of white mice was subdivided into three groups of about five
mice each. Each mouse group was challenged with either 1, 10 or 100 minimum
lethal doses (MLD) of live VSV by intracerebral inoculation on day 33.

Two of five mice that were immunized with 10(6) pfu psoralen-inactivated
VSV-NJ survived a one MLD VSV challenge but five of five mice that were
immunized with 10(7) pfu psoralen-inactivated VSV-NJ vaccine survived both a 1
or 10 MLD VSV challenge. One of four mice that were vaccinated at 10(7) pfu/dose
psoralen-inactivated VSV-NJ survived a 100 MLD VSV challenge. The results (no.
dead/no. challenged) are set forth in Table 10.

<TABLE>
<CAPTION>
TABLE 10
- --------------------------------------------------------------------------------
Live VSV-NJ Challenge of Mice Injected with
Psoralen-Inactivated VSV-NJ
- --------------------------------------------------------------------------------
Challenge Dilution
Dose Psoralen- -------------------------------------------------------------
Inactivated 10-(5) 10-(4) 10-(3)
VSV-NJ Vaccine (1 MLD) 10 (MLD) (100 MLD)
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
10(7) pfu 0/5* 0/5 3/4
10(6) pfu 3/5 4/5 3/6
10(5) pfu 5/5 4/5 7/7
- --------------------------------------------------------------------------------
*Number dead/number challenged
</TABLE>

<PAGE> 27
4,693,981

5. Virus Neutralization in Cattle Immunized with Psoralen-inactivated
VSV-NJ Vaccine

Four groups of six mature beef cattle each were injected with either
10(6) or 10(7) pfu/dose psoralen-inactivated VSV-NJ vaccine, with or without
aluminum hydroxide adjuvant (1:1). Each cow was vaccinated subcutaneously (SQ)
on day 0 and again on day 21. A control group consisted of an additional six
cattle that were inoculated only with adjuvant on day 0 and again on day 21.
All cattle were bled on days 0, 14, 21, and 35. Serum from each animal was
tested for SN antibodies to VSV-NJ by standard procedures.

The aluminum hydroxide adjuvant was required to elicit significant SN
titers in cattle, and 10(8) pfu/dose induced the highest responses. The results
are set forth in Table 11. A VSV-NJ virus neutralization index greater than
1000 has been reported to represent protection against 10(6) ID(50) of live VSV
by intralingual challenge in cattle. See, Castaneda et al. (1964) Proc. US
Livestock San Assoc. 68:455-468.

<TABLE>
<CAPTION>
TABLE 11
- ------------------------------------------------------------------------------
Virus Neutralization Indices* From Cattle
Injected With Psoralen-Inactivated VSV-NJ
Vaccine
------------------------------------------
Day Serum Collected
------------------------------
Group Treatment Animal 0** 14 21** 15
- ------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C>
A 10(8) pfu/dose 310 -- 16 16 256
+ Al(OH) (3) 731 -- -- -- >16
911 -- 128 64 2048
921 -- 8 8 1024
943 -- 16 32 1024
944 -- 32 32 512
B 10(7) pfu/dose 303 -- -- -- 256
+ Al(OH) (3) 304 -- -- -- 64
308 4 4 8 512
542 -- -- -- 8
914 -- 16 4 512
1670 -- -- -- >128
C Controls 305 -- -- -- --
309 -- -- -- --
314 -- -- -- --
315 -- -- -- --
316 -- -- -- --
318 -- -- -- --
D 10(8) pfa/dose 302 -- -- -- 4
without adjuvant 611 -- -- -- 4
714 -- -- -- 8
732 -- -- -- 4
747 -- -- -- --
996 -- -- -- 32
E 10(7) pfa/dose 101 -- -- -- --
without adjuvant 312 -- -- -- 4
616 -- -- -- --
721 -- -- -- --
722 -- -- -- --
1944 -- -- -- --
- ------------------------------------------------------------------------------
* Virus neutralization nodes in the required of the serum dilutions that
neutralized 32 TCID (50) of VSV-NJ
** Immunization Days
</TABLE>
6. Live VSV-NJ Challenge of Cattle Vaccinated with
Psoralen-inactivated VSV-NJ Vaccine

Ten mature cattle were divided into two groups of five animals each.
Group I was designated experimental and Group II was designated control. All
ten cattle were clinically normal and lacked evidence of previous VSV exposure;
that is, they were negative for serum neutralizing (SN) antibody. Group I
cattle were vaccinated subcutaneously with 10(8) pfu (prior to inactivation)
psoralen-inactivated VSV twice with a three week interval. Vaccine volume was
2 ml. containing aluminum

hydroxide adjuvant. Group II cattle were not exposed to the
psoralen-inactivated VSV.

Approximately two weeks post-second vaccination, the cattle of both
Groups I and II were challenged intradermalingually with 0.1 ml live VSV in log
dilutions of 5.6 pfu to 5.6 x 10(5) pfu/injection site. Thus each animal's
tongue received six separate 0.1 ml injections, representing a quantitative
challenge system. Serum neutralizing titers for cattle in each group measured
before and after challenge are presented in Table 12.

<TABLE>
<CAPTION>
TABLE 12
- -------------------------------------------------------------------------------
Serum Neutralization Titers From Cattle
Vaccinated With Psoralen-Inactivated VSV-NJ
Vaccine
-------------------------------------------
After After Day of Post
Arrival 1st vacc 2nd vacc[ILLE- Challenge[ILLE- Challenge[ILLE-
GIBLE] GIBLE] GIBLE]
Animal Day
No. 0 18 35 42 60
- -------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
Group I
- -------
4009-V neg* 1:160 1:1280 1:1280 1:1280
4383-V neg 1:80 1:1280 1:1280 1:2560
4389-V neg 1:80 1:640 1:2560 ND
6153-V neg 1:80 1:1280 1:1280 (equal 1:20480
6244-V neg 1:320 1:1280 1:1280 to or ND
GROUP II greater
- -------- than)
3780-C neg neg neg neg 1:10240
3781-C neg neg neg neg 1:10240
3784-C neg neg neg neg 1:10240
4007-C neg neg neg neg 1:10240
7912-C neg neg neg neg 1:10240
- -------------------------------------------------------------------------------
* 100 TCID (50) of VSV-NJ
8 = 1000 TCDI (50) OF VSV-NJ
[ILLEGIBLE] 37 TCID (50) of VSV-NJ
* negative at 1:20, the lowest dilution tested
ND = not done
</TABLE>

Vaccinated animals had a fifty percent reduction in lesion number, and
lesions on vaccinates were fifty percent smaller and healed faster than on
controls. Control animals developed lesions at both earlier and later time
points. On post-challenge day eighteen, all five controls had lesions, whereas
four of five vaccinates were normal. The fifth vaccinate's lesions were milder
than those of any control animal on post-challenge day eighteen.

Using the Mann-Whitney modification of Wilcoxon's two sample test, the
vaccinates were significantly protected against live VSV challenge (P=.075). On
the average, vaccinated cattle were protected against 25 times the minimum
infectious dose required to produce lesions in control animals.

According to the present invention, viruses inactivated with
furocoumarins and ultraviolet radiation in the substantial absence of oxygen
and other oxidizing species retain their immunogenicity and are suitable as the
immunogenic substance in vaccines against a number of virally-induced diseases.
The inactivated viruses of the present invention are non-infectious and safe
when administered to a host for vaccination, yet display enhanced antigenic
integrity when compared to vaccines inactivated in the presence of oxygen.

Although the foregoing invention has been described in some detail by
way of illustration and example for purposes of clarity of understanding, it
will be obvious that certain changes and modifications may be practiced within
the scope of the appended claims.

What is claimed is:

<PAGE> 28
4,693,981

1. A method for inactivating a live virus without substantially degrading
their antigenic characteristics, said method comprising:

exposing the virus to a preselected intensity of long wavelength
ultraviolet radiation and a preselected concentration of an inactivating
furocoumarin for a time period sufficiently long to render the virus
non-infectious but less than that which would result in degradation of its
antigenic characteristics, wherein said exposure is performed in the
substantial absence of oxygen and other oxidizing species.

2. A method as in claim 1, wherein the furocoumarin is added to an
inactivation medium containing the live virus.

3. A method as in claim 1, wherein the furocoumarin is introduced to the
live virus by addition to a cell culture medium in which the virus is grown.

4. A method as in claim 1, wherein the inactivation medium is maintained
under a non-oxidizing gas atmosphere.

5. A method as in claim 4, wherein the inactivation medium is flushed
with the non-oxidizing gas.

6. A method as in claim 4, wherein the non-oxidizing gas is selected from
the group consisting of hydrogen, nitrogen, argon, helium, neon, carbon
dioxide, and mixtures thereof.

7. A method as in claim 1, wherein an oxygen scavenger is added to the
inactivation medium.

8. A method as in claim 7, wherein the oxygen scavenger is sodium
ascorbate.

9. An improved method for inactivating viruses, said method being of the
type wherein the virus is inactivated by exposure to long wavelength
ultraviolet radiation in the presence of an inactivating furocoumarin, said
improvement comprising performing said exposure to ultraviolet radiation in the
substantial absence of oxygen and other oxidizing species.

* * * * *

<PAGE> 29

EXHIBIT C

United States Patent [19] [11] Patent Number 4,727,027
Wiesehahn et al. [45] Date of Patent: Feb. 23, 1988

[54] PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD OR
BLOOD COMPONENTS

[75] Inventors: Gary P. Wiesehahn, Alameda;
Richard P. Creagan, Alta Loma, both
of Calif.

[73] Assignee: Diamond Scientific Co.,
Des Moines, Iowa

[21] Appl. No.: 785,356

[22] Filed: Oct. 7, 1985

Related U.S. Application Data

[63] Continuation-in-part of Ser. No. 928,841, Oct. 20, 1986, which is a
continuation of Ser. No. 490,681, May 2, 1983, abandoned.

[51] Int. Cl.(4) ................C12N 13/00; C07K 13/00;
A61K 39/00; C07G 7/00
[52] U.S. Cl. ......................435/173; 530/380;
530/381; 530/382; 530/385; 530/386; 530/387;
530/388; 530/392; 530/393; 530/347; 514/2;
514/6; 424/88; 424/89; 424/92; 424/101;
422/24; 422/28; 422/29; 426/234; 426/318;
[58] Field of Search.........435/173, 183, 188, 236,
435/238, 269, 800, 814, 172.1; 260/112 R, 112
B, 121; 424/89, 90, 101, 88, 92; 514/2, 6, 8;
530/350, 363, 380-394, 412-414, 427

[56] References Cited

U.S. PATENT DOCUMENTS

4,124,598 11/1978 Hearst et al. ........................260/343.21
4,169,204 9/1979 Hearst et al. ...........................546/270
4,321,919 3/1982 Edelson................................128/214 R
4,327,086 4/1982 Fukushima et al. ....................... 424/177
4,568,542 2/1986 Kronenberg............................... 424/90
4,595,653 6/1986 Kronenberg................................ 435/5

OTHER PUBLICATIONS

deMol and van Henegouwen (1981) Photochem.
Photobiol. 33:815-819.
deMol et al. (1981) Photochem. Photobiol, 34:661-666.
Joshi and Pathak (1983) Biochem. Biophys. Res. Comm., 112:638-646.
Grossweiner (1982) NCI Monograph No. 66, 47-54.
Rodighiero and Dall'Acqua (1982), NCI Monograph No. 66, 31-40.
deMol et al. (1981) 95:74462k,p. 74467 Chem. Interactions.
Hyde and Hearst (1978) Biochemistry 17:1251-1257.
Hanson et al. (1978), J. Gen. Virol. 40-345-358.
Swanstrom et al. (1981), Virol. 113:613-622.
Redfield et al.(1981), Infec. and Immun. 32:1216-1226.
Hanson "Inactivation of Viruses for Use as Vaccines ...
Med. Virol, II, de La Maza & Peterson, eds.
Cremer et al., (1982) J. Clin, Microbiol., 15:815-823.
Veronese, F. M., et al., (1981), Photochem. Photobiol.
34:351.
Veronese et al. (1982), Photochem. Photobiol. 36:25.
Singh and Vadasz (1978) Photochem. Photobiol. 28:539-545.
Musajo et al., Experentia, vol. XXI, pp. 22-24, "Photosensitizing
Furocovmanhs-Interaction with DNA and Photoinactivation of DNA Containing
Viruses".

Primary Examiner--Thomas G. Wiseman
Assistant Examiner--Robin Lyn Tieskin
Attorney, Agent, or Firm--Zarley McKee, Thomte, Voorhees & Sease

[57] ABSTRACT

Biological compositions are decontaminated by treatment with furocoumarin
derivatives and irradiation under particular conditions in which the proteins
retain their original physiological activities and any pathogenic
microorganisms and polynucleotide fragments thereof are rendered inactive. It
has been found that reduction of the amount of dissolved oxygen in the
treatment solution substantially inhibits denaturation of the proteins.

22 Claims, No Drawings

<PAGE> 30

4,727,027

PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD
OR BLOOD COMPONENTS

This application is a continuation-in-part of application Ser. No.
928,841, filed Oct. 20, 1986, which is a continuation of application Ser. No.
490,681, filed on May 2, 1983 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Recipients of blood and blood components risk acquiring infections from
pathogenic microorganisms, either pre-existing in the blood at the time of
collection or transmitted to the blood product during manipulation. Medical
personnel who are in contact with collected human blood or clinical samples also
have a significant chance of being exposed to potentially lethal blood-borne or
sample-borne organisms. Blood components today are obtained from blood donors
and frequently involve pooled lots, where one or more of the donors may be
harboring a viral, bacterial or other infection. Since the blood or blood
components are required to provide physiological functions in a mammalian host,
normally a human host, these functions must not be impaired by the
decontamination treatment of the biological composition. In addition, the blood
or blood components may not be modified in such a way as to make them
immunogenic which could result in an adverse immune response. Finally, any
treatment should not leave residues or products detrimental to the health of the
host or such residues or products should be readily removable.

2. Description of the Prior Art

U.S. Pat. No. 4,327,086 describes a method for heat treating an aqueous
solution containing human blood coagulation factor XIII. U.S. Pat. No.
4,321,919 proposes extracorporeal treatment of human blood with
8-methoxypsoralen (8-MOP) and ultraviolet light. Hyde and Hearst, Biochemistry
(1978) 17: 1251-1257, describe the binding of two psoralen derivatives to DNA
and chromatin. Musajo et al., Experientia (1965) XXI, 22-24, describe
photo-inactivation of DNA-containing viruses with photosensitizing
furocoumarins. See also, Hanson et al. (1978) J. Gen. Virol. 40: 345-358;
Swanstrom et al. (1981) Virol. 113: 613-622; Redfield et al. (1981) Infec. and
Immun. 32: 1216-1226; Hanson (1983) "Inactivation of viruses for Use as
Vaccines and Immunodiagnostic Reagents" in Medical Virology II, de al Maza and
Peterson, eds, and Cremer et al. (1982) J. Clin. Microbiol. 15: 815-823, each
of which describe viral inactivation by exposure to ultraviolet radiation in the
presence of furocoumarins.

Some data showing substantial impairment of the biological function of
certain enzyme proteins using furocoumarins are published in the scientific
literature (see for example, Veronese, F. M. et al., Photochem. Photobiol. 34:
351 (1981); Veronese, F. M. et al., Photochem. Photobiol. 36: 25 (1982)). Singh
and Vadasz (1978) Photochem. Photobiol. 28: 539-545 attribute the
photoinactivation of E. coli ribosomes by ultraviolet radiation in the presence
of furocoumarins to the presence of singlet oxygen.

SUMMARY OF THE INVENTION

Methods and compositions are provided for the decontamination of biological
compositions, such as blood

<PAGE> 31
and blood products, by inactivating microorganisms and polynucleotide fragments
thereof capable of causing a pathological effect in mammalian hosts. The
biological compositions are decontaminated by treatment with furocoumarins and
long wavelength ultraviolet (UVA) light under conditions which limit the
availability of oxygen and other reactive species. It has been found that such
conditions allow for inactivation of even recalcitrant viral pathogens without
degrading biologically active proteins, such as Factor VIII, which are present
in the composition.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In accordance with the subject invention, biological compositions which may
harbor microorganisms capable of causing harmful physiological effects in a host
are combined with furocoumarin compositions and treated with UVA light under
predetermined conditions, whereby the microorganisms and polynucleotide
fragments thereof are inactivated while the physiological activities of
non-nucleic acid components of the compositions are retained. The treatment
conditions are selected to minimize the likelihood that biologically active
non-nucleic acid components of the compositions, such as proteins, are
degraded. In particular, precautions are taken to reduce the level of dissolved
oxygen and other reactive species in the composition during exposure to the
ultraviolet light. As used hereinafter and in the claims, the term
"microorganisms" should be understood to mean

(1) prokoryotic, eukaryotic and viral microorganisms containing nucleic
acids (either DNA or RNA), and

(2) nucleic acid genomes or sub-genomic fragments from microorganisms.

Various biological compositions may be decontaminated by the methods of the
present invention, particularly aqueous compositions containing biologically
active proteins derived from blood or blood components. Whole blood, packed red
cells, platelets, and plasma (fresh or fresh frozen plasma) are exemplary of
such compositions. Blood components of particular interest include plasma,
protein portion, antihemophilic factor (AHF, Factor VIII); Factor IX and Factor
IX complex (Factors II, VII, IX and X); fibrinogens, Factor XIII, prothrombin
and thrombin (Factor II and IIa); immunoglobulins (e.g. IgA, IgD, IgE, IgG and
IgM and fragments thereof e.g., Fab, F(ab')(2), and Fc); hyper-immune globulins
as used against tetanus and hepatitis B; cryoprecipitate; albumin; interferons;
lymphokines; transfer factors; etc. Other biological compositions include
vaccines, recombinant DNA produced proteins, oligopeptide ligands, etc. The
protein concentration in the acqueous biological compositions will generally
range from about 1 (greek mu)g/ml to 500 mg/ml, more usually from about 1 mg/ml
to 100 mg/ml. The pH will normally be close to physiologic pH (-7.4), generally
in the range of about 6 to 9, more usually about 7. Other components may be
present in the compositions, such as salts, additives, buffers, stabilizers, or
the like. These components will be conventional components, which will be added
for specific functions.

Furocoumarins useful for inactivation include psoralen and derivatives,
where the substituents will be: alkyl, particularly of from 1 to 3 carbon atoms,
e.g. methyl; alkoxy, particularly of from 1 to 3 carbon atoms, e.g., methoxy;
and substituted alkyl, of 1 to 6, more usually 1 to 3 carbon atoms having from 1
to 2

<PAGE> 32
4,727,027

heteroatoms, which will be oxy, particularly hydroxy or alkoxy of from 1 to 3
carbon atoms, e.g. hydroxymethyl and methoxymethyl, or amino, including mono-
and dialkyl amino having a total of from 1 to 6 carbon atoms, e.g., aminomethyl.
There will be from 1 to 5, usually 2 to 4 substituents, which will normally be
at the 4, 5, 8, 4' and 5'-positions, particularly at the 4'-position.
Illustrative compounds include 5-methoxypsoralen, 8-methoxypsoralen (8-MOP),
4,5',8-trimethylpsoralen (TMP), 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT),
4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), 4-methylpsoralen,
4,4'-dimethylpsoralen, 4,5'-dimethylpsoralen, 4',8-dimethylpsoralen, and
4'-methoxymethyl-4,5',8-trimethylpsoralen.

When employing furocoumarins with limited aqueous solubility, typically
below about 50 (greek mu)g/ml, it has been found useful to add an organic
solvent, such as dimethyl sulfoxide (DMSO), ethanol, glycerol, polyethylene
glycol (PEG), or polypropylene glycol to the aqueous treatment solution. Such
furocoumarins having limited solubility include 8-MOP, TMP, and psoralen. By
adding small amounts of such organic solvents to the aqueous composition,
typically in the range from about 1 to 25% by weight, more typically from about
2 to 10% by weight, the solubility of the furocoumarin can be increased to about
200 (greek mu)g/ml, or higher. Such increased furocoumarin concentration may
permit the use of shorter irradiation times. Also, inactivation of particularly
recalcitrant microorganisms may be facilitated without having to increase the
length or intensity of ultraviolet exposure, and the addition of an organic
solvent may be necessary for inactivation of some viruses with particular
furocoumarins. The ability to employ less rigorous inactivation conditions is of
great benefit in preserving the biologic activity of blood proteins during
decontamination.

The subject furocoumarins are active with a wide variety of pathogenic
microorganisms, viruses, and polynucleotide fragments thereof, DNA or RNA,
whether single stranded or double stranded. Illustrative viruses include:
adenovirus, arenavirus, bacteriophage, bunyavirus, hepatitis viruses, including
types A, B and non-A, non-B (also designated type C), herpesvirus, retroviruses
such as human T-lymphtropic viruses (HTLV), including HTLV types I, II and III,
orthomyxovirus, papovavirus, paramyxovirus, picornavirus, poxvirus, reovirus,
rhabdovirus, and togavirus. Additional pathogenic microorganisms include
bacteria, chlamydia, mycoplasma, protozoa, rickettsia and other unicellular
microorganisms. This inactivation method will also be effective against
uncharacterized infectious agents which contain nucleic acids, either DNA or
RNA.

The furocoumarins may be added to the biological composition by any
convenient means in a manner substantially assuring the uniform distribution of
the furocoumarins in the composition. Such addition may be made in a single
dose, in a series of doses over time, or continuously during the entire
treatment period or a portion thereof. The composition may be irradiated under
conditions ensuring that the entire composition is exposed to sufficient
irradiation, so that the furocoumarins may react with any polynucleotide
present to inactivate the polynucleotide. Depending upon the nature of the
composition, particularly its opacity, as in the case of blood, the depth of
the solution subject to irradiation will vary widely. Usually, the depth will be
not less than about 0.025 millimeter, but may be a centimeter or more. With
whole blood, the depth will generally range from about 0.025 millimeter to 2.5
millimeters. The light which is employed will generally have a wavelength in
the range of about 300 nm to 400 nm. Usually, an ultraviolet light source will
be employed together with a filter for removing UVB light. The intensity will
generally range from about 0.1 mW/cm(2) to about 5 W/cm(2), although in some
cases it may be much higher. The medium being irradiated may be irradiated
while still, stirred or circulated, and may either be continuously irradiated
or be subject to alternating periods of irradiation and non-irradiation. The
circulation may be in a closed loop system or it may be in a single pass system
ensuring that all of the sample has been exposed to irradiation. The total time
for irradiation will vary depending upon the nature of the sample, the
furocoumarin derivative used, the intensity and spectral output of the light
source and the nature of the polynucleotides which may be present. The time of
irradiation necessary for inactivation will be inversely proportional to the
light intensity. Usually, the time will be at least 1 min. and not more than
about 20 hrs., more usually from about 15 mins. to about 2 hrs. When circulating
the solution, the rate of flow will generally be in the range of about 0.1
ml/min to 50 liters/min.

In order to inhibit denaturation of biologically active proteins, it is
desirable to reduce the availability of dissolved oxygen and other reactive
species in the biological composition before or during the exposure to
ultraviolet radiation. A variety of steps to reduce the oxygen availability may
be taken, either individually or in combination. Oxygen scavengers, such as
ascorbate, glutathione, sodium thionate, and the like, may be added which
combine with singlet oxygen and other reactive oxygen species to prevent
reaction with the proteins. Physiologically acceptable proteins, such as human
or bovine serum albumin (BSA), and the like, may also be added. Such large
proteins act both to bind metals which catalyze reactions involving oxygen as
well as by preferentially binding the oxygen and other reactive radicals. The
biological composition may also be flushed with inert or less reactive gases,
such as hydrogen, helium, neon, carbon dioxide, nitrogen, argon, and the like,
to reduce the concentration of oxygen and other dissolved gases in the
biological composition by equilibrium exchange (mass transfer) with the
flushing gas. Flushing may be accomplished by passing the inert gas over or
through the biological composition, for a predetermined minimum amount of time,
usually at least 30 minutes, more usually at least one hour, prior to exposure
to the ultraviolet radiation.

The concentration of dissolved oxygen may also be reduced through the use
of enzyme systems either in
<PAGE> 33
4,727,027

solution or immobilized on a solid substrate. Suitable enzyme systems include
glucose oxidase or catalase in the presence of glucose and ascorbic acid
oxidase in the presence of ascorbate. Such enzyme systems may be employed alone
or together with the other methods for oxygen reduction discussed above.

To further inhibit denaturation of the biologically active proteins, the
temperature of the biological composition should be maintained below about 60
degrees C., preferably below 40 degrees C., more preferably in the range from
- -10 degrees C. to 30 degrees C., during exposure to the ultraviolet radiation.

It may be desirable to remove the unexpended furocoumarin and/or its
photobreakdown products from the irradiation mixture. This can be readily
accomplished by a variety of conventional separation techniques, such as
dialysis across an appropriately sized membrane or through an appropriately
sized hollow fiber system after completion of the irradiation. It may be
desirable in certain applications to remove bound or unbound furocoumarins
using affinity methods (e.g., magnetic beads) or using antibodies, including
monoclonal antibodies, either in solution or attached to a substrate. Enzymes,
either in solution or attached to a substrate, could be used to convert the
furocoumarins to nontoxic unreactive products. Alternatively, desirable
components such as factor VIII could be removed by precipitation or affinity
methods by leaving the furocoumarins in solution.

The following examples are offered by way of illustration and not by way of
limitation.

EXPERIMENTAL

The following experiments were performed in order to demonstrate the
ability of psoralen photoreaction to destroy microbial contaminants contained
in whole blood and blood products without destroying the biological activity of
blood proteins.

Since whole blood exhibits very high optical density for longwave UV light
(320 nm to 380 nm), the blood was irradiated through a suitably short optical
path length. In Example 1, blood was pumped through polyethylene capillary
tubing of 0.875 millimeter inside diameter. The tubing was coiled around a 1.27
centimeter diameter tube and immersed in water which was maintained at 18
degrees C. The blood was continuously circulated through the tubing by means of
a peristaltic pump. The blood required approximately 2.5 minutes for a complete
cycle through the capillary tubing and was in the light beam for approximately
20% of the stated irradiation time. The light source was a low pressure mercury
lamp filtered through a cobalt glass filter. The filter transmits light of
approximately 320 nm - 380 nm. with peak transmittance at 360 nm. The incident
intensity at the sample was approximately 40 mW/cm(2). The apparatus employed
for Examples II through XI consisted of an upper and lower bank of lamps
emitting longwave ultraviolet light (e.g. GE F20T 12 BLB bulbs, 320 - 400 nm).
Samples were placed on plate glass between the light sources. Irradiation times
and intensities were as described for each Example.

EXAMPLE I

Inactivation of feline rhinotracheitis

Feline rhinotracheitis virus, a member of herpes-virus family, was added
to heparinized whole rabbit blood in an amount that would give a final
concentration of approximately 2 x 10(7) PFU/ml. 4'-hydroxymeth-

yl-4,5',8-trimethylpsoralen (HMT) was added to a portion of the rabbit blood
and aliquots were irradiated for various periods of time. To test for remaining
live virus, duplicate plaque assays were performed using cultured feline cells
(Fc3Tg) (ATCC CCL 176), with a methyl-cellulose overlay. Virus titers were
obtained as the arithmetical mean of viral plaques observed in duplicate assays
cultures 72 hours after exposure to test samples.

The blood aliquot that received HMT only and no irradiation gave a titer
of 5.3 x 10(6)PFU/ml. The aliquot that received HMT and five minutes of
irradiation exhibited a titer of 4.5 x 10(6)PFU/ml. In the aliquot that
received psoralen plus one hour of irradiation there was not detectable live
virus remaining. The sensitivity of this assay should have permitted detection
of residual virus at titers (greater than or equal to) 1.0 x 10(1) PFU/ml. A
blood sample which had received HMT and one hour of irradiation also showed no
apparent damage to the red blood cells as judged by phase contrast microscope
analysis and by absence of visible hemolysis. These data therefore demonstrate
that high virus titers present in whole blood can be inactivated by psoralen
plus light treatment which leaves the red cell component of the blood intact.

EXAMPLE II

Protective effect of inert gas flushing on Factor VIII activity

Eight samples of pooled normal plasma were prepared and treated as
follows. Samples 5-8 were continuously flushed with argon. AMT (20 (greek
mu)g/ml) and TMP (5 (greek mu)g/ml) were added to samples 2, 4, 6, and 8.
Samples 3, 4, 7, and 8 were exposed to UVA radiation (4.2 mW/cm(2), 320-400nm).
Factor VIII activity was determined for each sample after six hours of such
treatment. The results are set forth in Table 1.

<TABLE>
<CAPTION>
TABLE 1
- -------------------------------------------------------------------------------
FVIII Activity
Sample Argon UVA Drugs units/ml % Retained
- -------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>

1 0 0 0 0.86 Control
2 0 0 + 0.84 98
3 0 + 0 0.58 67
4 0 + + 0.10 12
5 + 0 0 0.75 87
6 + 0 + 0.64 74
7 + + 0 0.58 67
8 + + + 0.45 52
- -------------------------------------------------------------------------------
</TABLE>

These results demonstrate that argon flushing to reduce the level of
dissolved oxygen in the treatment solution substantially enhances the retention
of Factor VIII activity.

EXAMPLE III

Protective effect of ascorbate on Factor VIII activity

Three samples of Factor VIII concentrate were prepared with 3% BSA added.
Test samples 2 and 3 were flushed with argon prior to UVA exposure. Nothing
further was added to the first sample. AMT (180 (greek mu)g/ml) was added to the
second and third samples, while 5 mM ascorbate was added to the third sample
only. The second and third samples were exposed to UVA (4.2 mW/cm(2), 320-400
nm) radiation for the four hour period, while the first sample was kept in the
dark (control). Factor VIII activity of all samples was measured after the four
hour test period and the retained activity was determined. The results are
summarized in Table 2.
<PAGE> 34
4,727027

<TABLE>
<CAPTION>
TABLE 2
- -------------------------------------------------------------------------------------
FVIII ACTIVITY
SAMPLE UVA AMT ASCORATE UNITS/ML
- --------------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
1 0 0 0 0.81
2 + + 0 0.38
3 + + + 0.59
- --------------------------------------------------------------------------------------
</TABLE>

These results demonstrate that the addition of ascorbate to the
treatment solution substantially enhances the retention of Factor VIII activity
in samples treated with psoralens and exposed to ultraviolet radiation.

EXAMPLE IV

Protective effect of BSA on Factor VIII activity

Six samples of Factor VIII concentrate were flushed with argon and then
exposed for three hours to UVA radiation (4.2 mW/cm2, 320-400 nm). Selected
amounts of AMT and/or BSA were added to certain samples prior to irradiation.
Factor VIII activity was measured before and after irradiation, and the
percentage of retained activity determined. The results are set forth in Table
3.

<TABLE>
<CAPTION>
TABLE 3
- -------------------------------------------------------------------
RETAINED
SAMPLE AMT ((greek mu)g/ml) BSA(%) FVIII ACTIVITY(%)
- -------------------------------------------------------------------
<S> <C> <C> <C>
1 0 0 88
2 0 10 110
3 30 1 77
4 30 5 98
5 30 10 86
6 60 10 84
- -------------------------------------------------------------------
</TABLE>
These results demonstrate that BSA enhances the retention of Factor
VIII activity when exposed to UVA radiation, both in the presence and absence
of AMT.

EXAMPLE V

Inactivation of Mycoplasma species Acholeplasma
laidlawii with 8-MOP

Culture: Six days old and approximately 10(7) cells/ml.

Irradiation: Irradiated samples were exposed to UVA (approximately 4.2
mW/cm(2)) for three exposure periods of two hours each. Samples were
transferred to a new vessel for each period of UVA treatment.

Furocoumarin: 8 metoxypsoralen (8-MOP) in DMSO was used at the
concentrations given in Table 4. After each two hour period of irradiation, a
fresh aliquot of furocourmarin was added to restore the minimal drug
concentration to the level indicated in Table 4.

Additives: Additional DMSO and/or sodium ascorbate (ASC) were added to
samples as indicated in Table 4.

Assay: Residual live mycoplasma were assayed using the standard
microbiological culture tests prescribed by U.S. Department of Agriculture in
9CFR part 113.28.

<TABLE>
<CAPTION>
TABLE 4
- ---------------------------------------------------------------
MYCOPLASMA GROWTH TEST
--------------------------------------
%
DMSO
DIRECT BULK FINAL
TREATMENT OF SAMPLES PLATING BROTH (V/V)
- ---------------------------------------------------------------
<S> <C> <C> <C>
UVA only + + 0
DMSO (6% v/v) + + 6
ASC (10 mM) + + 0
UVA + ASC + + 0
UVA + DMSO + ASC + + 6
</TABLE>

<TABLE>
<CAPTION>
TABLE 4 - continued
- ---------------------------------------------------------------
MYCOPLASMA GROWTH TEST
--------------------------------------
%
DMSO
DIRECT BULK FINAL
TREATMENT OF SAMPLES PLATING BROTH (V/V)
- ---------------------------------------------------------------
<S> <C> <C> <C>
ASC + DMSO + + 6
UVA + ASC + 8-MOP
(100 (greek mu)g/ml) - + 2.3
UVA + DMSO + ASC +
8-MOP - + 8.2
(100 (greek mu)g/ml)
UVA + ASC + 8-MOP
(200 (greek mu)g/ml) - - 4.6
UVA + DMSO + ASC
8-MOP - - 10.6
(200 (greek mu)g/ml)
- ---------------------------------------------------------------
</TABLE>
+ = growth
- - = no growth
These results demonstrate that the decontamination method of the
present invention is useful for the inactivation of bacterial species.

EXAMPLE IV

Inactivation of Mycoplasma species Mycoplasma orale
with AMT and TMP without additives

Culture: Seven days old and approximately 2.9 X 10(6) cells/ml.

Irradiation: Same as for Example V except irradiated samples were only
exposed for one treatment period of the duration indicated in Table 5.

Furocoumarins: 4' aminomethyl-4,5', 8-trimethlylpsoralen (AMT)
4,5',8-trimethylpsoralen(TMP)

Additives: None

Assay: Same as for Example V.

<TABLE>
<CAPTION>
TABLE 5

- ---------------------------------------------------------------
MYCOPLASMA GROWTH TEST
----------------------------
DIRECT BULK
TREATMENT OF SAMPLES PLATING BROTH
- ---------------------------------------------------------------
<S> <C> <C>
No treatment + +
UVA (1 hour) + ND
UVA (3 hours) - ND
AMT (30 (greek mu)g/ml) + ND
AMT (30 (greek mu)g/ml) = UVA (1 hour) - +
AMT (30 (greek mu)g/ml) = UVA (3 hours) - -
TMP (7.5 (greek mu)g/ml) = UVA (1 hour) - -
- ---------------------------------------------------------------
</TABLE>

ND = not done, + = growth, - = no growth

These results further confirm the efficacy of the present invention
in inactivating bacterial species.

EXAMPLE VII

Inactivation of vesicular stomatitis virus and retention
of Factor VIII activity

Treatment samples comprising vesicular stomatitis virus (3.3 X 10(8)
pfu/ml) were prepared in PBS-diluted AHF concentrate. The VSV was inactivated
in two samples by the addition of AMT (180 (greek mu)g/ml), 1% BSA, 10mM
ascorbate, and exposure to UVA (6.4 mW/cm(2), 320-400 nm) for approximately nine
hours. The samples were continuously flushed with argon. Inactivation was
confirmed by plaque assay on LM(TK-) mouse cells any by injection of 20 (greek
mu)l into suckling mouse brains. The mouse brain assay will detect 10 pfu/ml.
Both samples were shown to be non-infective. Factor VIII activity was monitored
in the treated samples as well as a control sample which was not irradiated
using a modified APTT assay. The effect on the Factor VIII activity is shown in
Table 6.
<PAGE> 35

4,727,027

<TABLE>
<CAPTION>
TABLE 6
- --------------------------------------------------------------------------------
Elapsed VSV FVIII
Sample Time (pfu/ml) Activity (U/ml)
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
1 0 10(8) 7.2
9 0 6.6
2 0 10(8) 6.25
2 0 ND
9 0 5.6
CONTROL 0 10(8) *
9 10(8) *
- --------------------------------------------------------------------------------
</TABLE>

ND: Not done
*No significant loss of activity

These results demonstrate that a virally infected biological composition
may be decontaminated by the method of the present invention without
substantial loss of biological activity of a biologically-active protein.

EXPERIMENT VIII

Inactivation of non-A, non-B hepatitis virus

A study was undertaken to evaluate the effects of furocoumarin and UVA on
the virus which causes non-A, non-B hepatitis. This virus is believed to be the
major cause of post-transfusion hepatitis in the United States. The only
suitable animal model for this virus is the chimpanzee model. Samples of Non-A,
non-B hepatitis virus were inactivated, as described below, and injected into
chimpanzees. The samples were injected intravenously into chimpanzees
anesthetized with ketamine. These animals were naive with respect to non-A,
non-B hepatitis, had been followed for an extended period with normal liver
enzymes (SGPT, SGOT), and had at least two normal liver biopsies examined by
light and electron microscopy in the two month period prior to inoculation.
During the trial, liver enzymes were checked weekly and periodic liver biopsies
were done. Results through 26 weeks post-inoculation indicate that there were no
significant liver enzyme elevations, and liver biopsies were negative.

Inactivation was as follows. Four coded samples were obtained which
contained from 100 to 100,000 chimpanzee infectious doses (CID(50)) of the
Hutchinson strain of non-A, non-B hepatitis virus in 1.0 ml of fetal calf serum.
These samples were treated under code as follows. Each sample was diluted with
phosphate buffered saline to a total of 10.0 ml containing a final
concentration of the following:

1% Bovine serum albumin
5 mM Sodium ascorbate
20 (greek mu)g/ml AMT
0.5 (greek mu)g/ml TMP

Each 10.0 ml sample was added to a T-75 flask (Corning) prerinsed with 5%
BSA, flushed with argon and incubated in the dark overnight at room temperature
(21 degrees C.). The flasks were then irradiated at an average of 5.0 mW/cm(2)
under black light bulbs emitting UVA light (G.E. BLB F20T12). At 1 hour
intervals an additional 20 (greek mu)g/ml AMT and 0.5 (greek mu)g/ml TMP were
added and the flasks reflushed with argon. At three hour intervals the samples
were transferred to fresh BSA-rinsed flasks.

Parallel flasks with 10(8) pfu/ml vesicular stomatitis virus (VSV) in place
of the non-A, non-B virus (inactivation control) were prepared and irradiated as
above. Samples were taken for testing at 0, 1, 3 and 6 hours. Parallel flasks
with 10% factor VIII concentrate (Koate, Cutter Biological) were prepared and
irradiated as above. Samples were taken at time 0 and at 3 hour intervals and
frozen at -80 degrees C. After 9 hours the experiment

was stopped temporarily and resumed the next morning. Samples were kept at
room temperature (21 degrees C.) during this time. Conditions for the second 9
hours were the same as for the first 9 hours except that a second parallel VSV
sample was prepared with 10(8) VSV/ml. Aliquots from this second VSV sample were
removed at 2, 4, and 5 hours for subsequent assays. The VSV aliquots were
assayed for residual viral activity by plaque assay on LM(TK-) cells and by
injection into suckling mouse brains. Factor VIII activity in the concentrate
samples was determined by a one stage clotting test.

At the conclusion of the second 9 hours, the samples containing non-A,
non-B hepatitis were sent under code to Southwest Foundation for Research and
Education (SFRE), now known as Southwest Foundation for Biomedical Research
(SFBR), for inoculation of chimpanzees. Chimpanzees received the following
doses of inactivated non-A, non-B hepatitis virus:

<TABLE>
<CAPTION>
- --------------------------------------------------------------------------------
Chimp No. Inactivated Virus (CID(50))
- --------------------------------------------------------------------------------
<S> <C>
72 100
83 1,000
80 10,000
97 100,000
- --------------------------------------------------------------------------------
</TABLE>

All four chimps remained negative for non-A, non-B hepatitis infection
during six months of clinical observation. Following the six month observation
period, chimp no. 97 who had received the highest dose (approx. 100,000
CID(50)) of inactivated non-A, non-B hepatitis virus, was inoculated with
approximately 33 CID(50) live virus. This challenge dose was prepared from a
reserved aliquot of the original sera from which the inactivated viruses had
been obtained. Chimp no. 97 developed symptoms of infection 10 weeks after
inoculation, thus demonstrating the chimp's susceptibility to the virus. This
experiment demonstrated that the inactivation procedures used were capable of
killing at least 10(3.5) CID(50) virus.

In the parallel experiments, VSV at 3.4 X 10(8) pfu/ml (average of 2
experiments) was reduced to non-detectable levels in plaque assays after two
hours of the inactivation procedure. No residual infectivity was detected by
the more sensitive suckling mouse brain assay in inocula subjected to four
hours of inactivation (Table 7).

<TABLE>
<CAPTION>
TABLE 7
- --------------------------------------------------------------------------------
Fucoumarins/UVA VSV Plaques Suckling Mice
(hours) (pfu/ml) (days to death)
- --------------------------------------------------------------------------------
<S> <C> <C>
0 3.4 x 10(8) 2, 2, 2, 2, 2
1 7.2 x 10(2) NT
2 0 NT
3 0 NT
4 0 no deaths
5 0 no deaths
6 0 no deaths
- --------------------------------------------------------------------------------
</TABLE>

NT = not tested

In the second set of parallel experiments, handling and sample
manipulation in the T-75 tissue culture flasks produced greater loss of factor
VIII activity than was caused by the inactivation procedure (Table 8). After 18
hours of treatment, activity in the sample containing fucoumarins and exposed
to UVA was 98% of that remaining in the shielded handling control which
contained no fucoumarins. These results (Table 8)demon-
<PAGE> 36
4,727,027

strated that the activity of a highly labile protein can be preserved under
conditions capable of inactivating high titers of non-A, non-B hepatitis virus.

<TABLE>
<CAPTION>
TABLE 8
- -------------------------------------------------------------------------------
Factor VIII Activity
(units/ml)
------------------------
Fucoumarins/UVA Handling % Activity Retained
(hours) Test Control (Test/Control) x 100
- -------------------------------------------------------------------------------
<S> <C> <C> <C>
3 0.91 1.02 89
6 0.79 0.82 96
9 0.69 0.89 79
12 0.74 0.79 94
13 0.66 0.73 90
18 0.59 0.60 98
- -------------------------------------------------------------------------------
</TABLE>

EXPERIMENT IX

Inactivation of non-A, non-B hepatitis and hepatitis B
viruses in combination

Two samples, each of which contained about 10(4.5) CID(50) of MS-2 (ayw)
strain of hepatitis B virus (HBV) and 10(4) CID(50) of the Hutchinson stain of
non-A, non-B hepatitis virus (NANB), were prepared for inactivation. The
diluent for one sample was reconstituted AHF concentrate (Factor VIII). The
diluent for the other sample was phosphate-buffered saline (PES). Each sample
contained an aliquot of bacteriophaze R17 as an internal control. The HBV and
NANB viruses were portions of National Institutes of Health stock materials
diluted in fetal calf serum (FCS) or 1% bovine serum albumin (BSA). Heparin (1
unit/ml) was included in sample preparation to control any activated clotting
factors present in the calf serum. 8-Methoxypsoralen was dissolved in dimethyl
sulfoxide (DMSO) and added to each sample at final concentration of 300
micrograms per ml. The DMSO was present as 6% of the total sample volume of
5 ml.

Samples containing vesicular stomatitis virus (VSV), feline leukemia virus
(FeLV), and bacteriophages fd and R17 were prepared in factor VIII diluent and
inactivated in parallel with the hepatitis virus samples to serve as external
controls.

Experimental and control samples were mixed in 50 ml polypropylene conical
vials, then pipetted gently into silanized glass medicine bottles (250 cc)
prior to inactivation. Sample bottles were capped with cuffed rubber stoppers
fitted with blunt cannulas. Prior to inactivation, samples were flushed with a
mixture of 4% hydrogen in pre-purified nitrogen for 1 hour. The oxygen level
throughout the flushing cycle was below 1 ppm of oxygen as measured by a
Couloximeter (Chemical Sensor Development, Torrance, CA). Samples were
irradiated at approximately 5 mW/cm(2). After five hours irradiation, the
hepatitis samples (Nos. 5 and 6) were transferred to fresh bottles, a second
aliquot of R17 was added to the hepatitis samples, and the bottles were flushed
for 30 minutes with the hydrogen/nitrogen mixture. These samples were then
irradiated for an additional five hours. Results of the assays for infectivity
of control viruses are presented in Table 9.

<TABLE>
<CAPTION>
TABLE 9
- ---------------------------------------------------------------------------------------------------
Hours UVA (pfu/ml or ffu/ml)
Sample -----------------------------------------------------------------------------
(virus) 0 1 2 2.5 3 4 5 7.5 10
- ---------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C> <C> <C> <C>

No. 5 [-10(6)] -- -- -- -- -- 0 -- 0
(R17)(*)
No. 6 [-10(6)] -- -- -- -- -- 0 -- 0
(R17)(*)
</TABLE>

<TABLE>
<CAPTION>
TABLE 9 - continued
- ---------------------------------------------------------------------------------------------------
Hours UVA (pfu/ml or ffu/ml)
Sample -----------------------------------------------------------------------------
(virus) 0 1 2 2.5 3 4 5 7.5 10
- ---------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C> <C> <C> <C>

VSV-2(**) 1.83 x 10(2) -- -- 0 -- -- 0 0 0
FeLV-2 2 x 10(4) -- -- 0 -- -- 0 0 0
R17-2 6.1 x 10(8) 2.5 x 10(4) 0 -- 0 0 0 -- --
fd-2 6.6 x 10(10) <10 0 -- 0 0 0 -- --

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

Safety tests for endotoxins were performed by injecting 0.2 ml crude R17
filtrate into the ear vein of one rabbit and 0.2 ml of 10([ILLEGIBLE])
dedication into the ear vein of another rabbit. No reactions were seen during
the two-week observation period following the injection.

"An aliquot of this sample inactivated for 10 hours was tested by suckling
mouse brain assay for residual infectivity. 10 suckling mice <14 days old were
injected intracerebrally with 20 (greek mu)l of the VSV sample. Two died of
trauma, while the remaining 8 were alive and well at 14 days.

As seen in Table 9, the internal control virus (R17), a single stranded RNA
bacteriophage, was completely inactivated in both samples No. 5 and No. 6 at the
5 hour time point. Initial titer was 10(8) pfu/ml. A second aliquot containing
10(8) fu/ml was added at five hours. After 10 hours this second aliquot was also
completely inactivated.

Parallel samples containing factor VIII concentrate were prepared and
irradiated as described above. Results are shown in Table 10. No loss of factor
VIII activity was observed after 10 hours of treatment.

<TABLE>
<CAPTION>
TABLE 10
- -------------------------------------------------------------------------------
Sample
--------------------------
No. 1 No. 2
- -------------------------------------------------------------------------------
<S> <C> <C>
8-MOP 0 0.06 ml (300 (greek mu)g)
UVA (hours) 0 10
Barbital Buffer 0.06 ml 0
Koate 0.84 ml 0.84
R.17/fd* 0.10 0.10
Viral activity (pfu/ml) 1.2 x 10(10) 0
Factor VIII activity units/ml 19.4 19.4
- -------------------------------------------------------------------------------
*Virus prepared as 1:10 dilution in 5% BSA
</TABLE>

At Southwest Foundation for Biomedical Research, chimp No. 64 was
inoculated with sample No. 5 and chimp No. 216 was inoculated with sample No.
6. These chimps had been on baseline evaluation for several months and had no
elevations in liver enzymes on weekly testing. The animals were bled weekly,
and the samples were tested for SGPT, SGOT, and HBsAg, anti-Hbs and anti-HBc.
Liver biopsies were obtained at weeks 5, 7, 9, 11, 13, 15, 20, and 26. Biopsy
material was examined by light microscopy immunofluorescence and electron
microscopy for changes characteristic of hepatitis infection. During the
26-week observation period following inoculation, enzyme levels remained low,
histology examinations were normal, and no HBV markers were detected.

EXPERIMENT X

Inactivation of Simian AIDS (SAIDS) Virus (an RNA virus) with AMT.

Vacutainer tubes (10cc) were prepared with 0.5 ml of the fresh sterile
solutions indicated in Table 11 and stored overnight at 4 degrees C. 0.5 ml of
SAIDS virus suspension was added sterilely to each tube. Samples were irradiated
with approximately 5 mW/cm(2) UVA for the times indicated in Table 11.
Non-irradiated samples were stored in the dark at 4 degrees C. All samples were
added to Raji cells and observed fior syncytia induction over a 10 day period.
Cultures were then expanded and observed for an additional 10 days. Samples
that had been positive (1, 3, 5, 8, 9) were expanded into flasks and

<PAGE> 37
4,727,027

supernatants from the flasks were filtered through a 0.45 (greek mu)g filter.
The filtrates were added to fresh Raji cells and observed for syncytia
induction.

Results are show in Table 11. The initial syncytial induction in samples 1,
8 and 9 may have been due to the presence of inactivated virus. The samples
which remained positive after expansion were the ones which received no UVA
treatment (samples 3, 5, 9 and the untreated control).

<TABLE>
<CAPTION>
TABLE 11
- --------------------------------------------------------------------------------

AMT Ascorbate PBS-A Syncytia Formation
Sample 1* 1** 1 UVA Initial Subculture
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C>
1 - 50 450 2 hr + -
2 20 - 480 2 hr - -
3 - - 500 - + +
4 - - 500 2 hr - -
5 20 50 430 - + +
6 20 50 430 15 min - -
7 20 50 430 30 min - -
8 20 50 430 1 hr + -
9 20 50 430 2 hr + -
untreated - - - - + +
- --------------------------------------------------------------------------------
* AMT, 5 mg/ml in dH(2)O (filter sterilized)
** Sodium ascorbate, 200 mM in dH(2)O (filter sterilized)
</TABLE>

EXPERIMENT XI
Inactivation of Feline Leukemia Virus (FeLV-A) (an
RNA virus) with 8-MOP in DMSO.

Two-ml aliquots of FeLV-A at 2x10(7) FFU/ml in F-12K medium were placed in
vacutainer tubes. 8-MOP was dissolved in DMSO and added to the virus-containing
samples to a final concentration of 50 (greek mu)g/ml as shown in Table 14. All
samples were flushed with argon for 30 min. Irradiated samples were exposed to
UVA at approximately 4 mW/cm(2) for the times shown in Table 14. The
unirradiated controls were stored in the dark at 4 degrees C. The two 25-hour
samples received additions of 8-MOP at 0, 5, 10, 15 and 20 hours. After each
addition the tubes were flushed with argon for 30 min. Assessment of
inactivation was by Clone 81 focus assay for all samples and blind passage on
AK-D cells for 6 weeks for sample H.

Results of the focus assays are given in Table 12. No live virus was
detected in any of the experimental samples following 2 hr UVA irradiation.

<TABLE>
<CAPTION>
TABLE 12
- --------------------------------------------------------------------------------

8-MOP UVA Tube Cl-81 Focus Assay
Sample (greek mu)g/ml (hrs) Changes Titer (FFU/ml)
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
A 0 0 3 1.71 x 10(7)
B 0 25 3 6.45 x 10(6)
C 250* 0 3 1.8 x 10(7)
D 50 1 0 9.71 x 10(2)
E 50 2 0 0
F 50 4 0 0
G 50 6 0 0
H 250* 25 3 0
- --------------------------------------------------------------------------------
* (50 (greek mu)g/ml) x 5 additions
</TABLE>
EXPERIMENT XII

Effect of Oxygen Levels on Factor VIII Exposed to
Furocoumarins and UVA

The following experiment was conducted to determine the effect of
different levels of molecular oxygen on factor VIII exposed to furocoumarins
and UVA light.

Furocoumarins used for this experiment were 8-methyoxypsoralen (8-MOP) and
4'-aminomethyl-4,5',8-

trimethylpsoralen (AMT). Samples of factor VIII concentrate (Koate, Cutter
Biological) were flushed with gas containing various levels of molecular oxygen
for a time sufficient to reach equilibrium (equal to or greater than 1 hour).
The samples were contained in 10 ml red-top vacutainer tubes (Becton-Dickinson).
8-MOP or AMT was added to give a final concentration of 0.2 mM furocoumarin
(8-MOP: 43.2 (greek mu)g/ml; AMT: 58.6 (greek mu)g/ml). Total sample volume was
1.0 ml. The sample tubes were irradiated at approximately 2.5 mW/cm(2) for 10
hours. Results of factor VIII assays are given in Table 13.

<TABLE>
<CAPTION>
TABLE 13
- --------------------------------------------------------------------------------
Factor VIII Activity
Oxygen level (units/ml)
---------------------------------------------------------
(parts per) 8-MOP AMT Control
million and UVA and UVA no UVA
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
1 20.4 20.0 -
54 15.2 8.8 -
988 10.0 5.3 18.8*
210,000 3.4 0.3 20.0**
(Room air)
- --------------------------------------------------------------------------------
* 8-MOP added, flushed
** no drug, no flushing
</TABLE>

Decreasing the oxygen level has a protective effect on factor VIII exposed
to furocoumarin and UVA light. There was no discernible loss of factor VIII
activity at the lowest level of oxygen used (approx. 1 ppm). This oxygen effect
was seen for both 8-MOP and for AMT, although the loss of factor VIII activity
at the higher levels of oxygen was more marked for AMT. This is much more
active on a molar basis than 8-MOP as a singlet oxygen generator.

It is evident from the above results, and in accordance with the subject
invention, that polynucleotides in biochemical compositions can be inactivated
to provide a safe composition of administration to a mammalian host. The
proteins present in the composition retain their physiological activity, so
that they can fulfill their physiological function in a mammalian host. The
method is simple, rapid, and can be expanded to treat large samples. The small
amount of chemical reagent required will not generally be harmful to the host.

Although the foregoing invention has been described in some detail by way
of illustration and example for purposes of clarity of understanding, it will
be obvious that certain changes and modifications may be practiced within the
scope of the appended claims.

What is claimed is:

1. A method for decontaminating a blood clotting factor containing
composition of viral contaminants, in a manner which substantially maintains the
biological activity of the blood clotting factors, said method comprising adding
to the blood clotting factor containing composition at least one furocoumarin,
and irradiating the furocoumarin containing composition under U-V light, wherein
the amount of furocoumarin and irradiation conditions are sufficient to
inactivate substantially all the viral contaminants, and wherein the
concentration of dissolved oxygen is reduced to a level sufficient to
substantially inhibit the denaturation of the blood clotting factors.

2. A method as in claim 1, wherein the level of dissolved oxygen is
reduced by addition of an oxygen scavenger to the composition.

3. A method as in claim 1, wherein the level of dissolved oxygen is
reduced by equilibrium exchange with an inert or less reactive gas.
<PAGE> 38
4,727,027

4. A method as in claim 1, wherein the level of dissolved oxygen and
other reactive species is reduced by addition of a physiologically-acceptable
protein.

5. A method as in claim 4, wherein the physiologically acceptable
protein is human or bovine serum albumin.

6. A method as in claim 1, wherein the solubility of the furocoumarin
in the aqueous composition is increased by the addition of from about 1% to 25%
by weight of an organic solvent.

7. A method as in claim 6, wherein the organic solvent is selected
from the group consisting of dimethyl sulfoxide, ethanol, glycerol,
polyethylene glycol, and propylene glycol.

8. A method according to claim 1, wherein at least two furocoumarins
are present.

9. A method according to claim 1 wherein any unreacted furocoumarin(s)
or photobreakdown products thereof are selectively removed.

10. A method according to claim 1 wherein furocoumarins or biological
components which have reacted with the furocoumarin(s) are selectively removed
by antibodies to those modified components.

11. A method for decontaminating a blood clotting factor containing
composition of viral contaminants in a manner which substantially maintains the
biological activity of the blood clotting factors, said method comprising
adding to the blood clotting factor containing composition at least one
furocoumarin such that the total furocoumarin concentration is at least 1
(greek mu)g/ml and not more than 300 (greek mu)g/ml, and irradiating the
furocoumarin containing composition under U-V light which wavelengths are in
the range of about 300 nm to 400 nm and at an intensity of about 0.1 mw/cm(2)
to 5 w/cm(2) and at a depth of at least 0.025 millimeters for a total
irradiation time of about 5 minutes to about 12 hours, and wherein the level of
dissolved oxygen in the blood clotting factor containing composition is
substan-

tially reduced to substantially inhibit the denaturation of the blood clotting
factors.

12. A method as in claim 11, wherein the level of dissolved oxygen is
reduced by addition of an oxygen scavenger to the composition.

13. A method as in claim 11, wherein the level of dissolved oxygen is
reduced by equilibrium exchange with a less reactive gas.

14. A method as in claim 11, wherein the level of dissolved oxygen and
other reactive species is reduced by addition of a physiologically-acceptable
protein.

15. A method as in claim 14, wherein the physiologically acceptable
protein is human or bovine serum albumin.

16. A method as in claim 11, wherein the solubility of the
furocoumarin in the aqueous composition is increased by the addition of from
about 1% to 25% by weight of an organic solvent.

17. A method as in claim 16, wherein the organic solvent is selected
from the group consisting of dimenthyl sulfoxide, ethanol, glycerol,
polyethylene glycol, and propylene glycol.

18. A method according to claim 11, wherein two furocoumarins are
added to said composition.

19. A method according to claim 18, wherein said two furocoumarins are
4'-hydroxymethyl-4,5',8-trimethylpsoralen and
4'-aminomethyl-4,5',8-trimethylpsoralen.

20. A method according to claim 11, wherein the viral contaminants
comprise at least one of Hepatitis A, Hepatitis B, and Non-A Non-B Hepatitis
viruses.

21. A method according to claim 11 wherein the viral contaminants
comprise a virus which causes Acquired Immune Deficiency Syndrome (AIDS).

22. A method according to claim 11 wherein the furocoumarin added is
8-methoxypsoralen.

* * * * *

<PAGE> 39
EXHIBIT D

UNITED STATES PATENT [19] [11] PATENT NUMBER: 4,748,120
Wiesehahn [45] DATE OF PATENT: *May 31, 1988
- --------------------------------------------------------------------------------

[54] PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD OR BLOOD COMPONENTS

[75] Inventor: Gary P. Wiesehahn, Alameda, Calif.

[73] Assignee: Diamond Scientific Co., Des Moines, Iowa

[* ] Notice: The portion of the term of this patent subsequent to Feb. 23,
2005 has been disclaimed.

[21] Appl. No.: 928,841

[22] Filed: Oct. 20, 1986

RELATED U.S. APPLICATION DATA

[63] Continuation of Ser. No. 490,681, May 2, 1983, abandoned.

[51] Int. Cl.(4) .................................. C12N 13/00; A61K 39/00;
A61K 35/14; A61K 35/48

[52] U.S. Cl. ..................................... 435/173; 424/85; 424/89;
424/90; 424/101; 514/2;
514/6; 530/380; 530/381;
530/383; 530/387; 530/389;
530/829

[58] Field of Search .............................. 435/172.1, 173, 183,
435/188, 236. 238, 269,
800, 814; 424/89, 90, 101,
85; 514/2; 530/350, 363,
380-388, 412-414, 427

[56] REFERENCES CITED

U.S. PATENT DOCUMENTS

4,124,598 11/1978 Hearst et al. ............ 260/343.21
4,169,204 9/1979 Hearst et al. ............ 546/270
4,321,919 3/1982 Edelson .................. 128/214 R

OTHER PUBLICATIONS

Musajo et al, Experentia, vol. XXI, pp. 22-24, "Photo-sensitizing Furocoumanns:
Interaction with DNA and Photo-Inactivation of DNA Containing Viruses".

Veronese et al, Photochem Photobiol, vol. 36, pp. 25-30, "Photoinactivation of
Enzymes by Linear and Angular Furocoumanns".

De Mol et al., Chem. Abst., vol. 95, No. 74462k, p. 197, 1981, "On the
Involvement of Singlet Oxygen in Mutation Induction by 8-Methoxypsoraten and UVA
Radiation in Escherichia coli K-12".

De Mol et al, Photochem Photobiol, vol. 33, pp. 815-819, 1981, "Relation
Between Some Photobiological Properties of Furocoumanns and their Extent of
Singlet Oxygen Formation".

deMol et al. (1981) Photochem. Photobiol. 34:661-666.

Joshi and Pathak (1983) Biochem. Biophys. Res. Comm., 112:638-646.

Grossweiner (1982) NCI Monograph, No. 66, 47-54.

Rodighiero and Dall'Acqua (1982) NCI Monograph, No. 66, 31-40.

Primary Examiner - Thomas G. Wiseman
Assistant Examiner - Robin Lyn Teskin
Attorney, Agent, or Firm - Zarley, McKee, Thomte, Voorhees & Sease

[57] ABSTRACT

Biological compositions are freed of functional polynucleotides by treatment of
the biological composition with psoralen derivatives under irradiation
conditions in which the proteins retain their original physiological activities
and any polynucleotide present is rendered inactive.

32 CLAIMS, NO DRAWINGS

<PAGE> 40
4,748,120

PHOTOCHEMICAL DECONTAMINATION TREATMENT OF
WHOLE BLOOD OR BLOOD COMPONENTS

This is a continuation of application Ser. No. 490,681, filed May 2, 1983,
now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Recipients of blood and blood components risk acquiring infections from
foreign biological organisms, either pre-existing in the blood at the time of
collection or transmitted to the blood product during manipulation. Medical
personnel who are in contact with collected human blood or clinical samples also
have a significant chance of being exposed to potentially lethal blood-borne or
sample-borne biological organisms. Blood components today are obtained from
blood donors and frequently involve pooled lots, where one or more of the donors
may be harboring a viral, bacterial or other infection. Since the blood or blood
components are required to provide physiological functions in a mammalian host,
normally a human host, these functions must not be impaired by the
decontamination treatment of the biological composition. In addition, the blood
or blood components may not be modified in such a way as to make them
immunogenic which could result in an adverse immune response. Finally, any
treatment should not leave residues or products detrimental to the health of the
host or such residues or products should be readily removable.

2. Description of the Prior Art

U.S. Pat. No. 4,327,086 describes the method for heat treating an aqueous
solution containing human blood coagulation factor XIII. U.S. Pat. No. 4,321,919
proposes extracorporeal treatment of human blood with 8-methoxypsoralen (8-MOP).
Hyde and Hearst, Bio-chemistry (1978) 17:1251-1257, describe the binding of two
psoralen derivatives to DNA and chromatin. Musajo et al., Experientia (1965)
XXI, 22-24, describe proto-inactivation of DNA-containing viruses with
photosensitizing furocoumarins. U.S. Pat. Nos. 4,350,594, 4,348,283 and
4,350,156 describe filtration methods for selective removal of blood components
based on molecular weight. U.S. Pat. No. 4,329,986 describes extracorporal
treatment of blood with a chemotherapeutic agent which is subsequently removed
by dialysis. The July/August 1982 issue of Genetic Engineering News proposed the
use of psoralens to sterilize "clinical or commercial reagents or instruments."

SUMMARY OF THE INVENTION

Methods and compositions are provided for decontamination of biological
compositions, permanently inactivating polynucleotides capable of having
pathological effect in a mammalian host. Particularly, furocoumarin comparisons
are employed for inactivating polynucleotides, such as viral genomes, capable
of infectious replication in a mammalian host. Compositions for use in a
mammalian host may be decontami-

nated by treatment with furocoumarins and long wave-length ultraviolet (UVA)
light.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In accordance with the subject invention, compositions to be employed with
mammalian hosts, which may harbor polynucleotides capable of detrimental
physiological effects in a host, are combined with furocoumarin compositions
and treated with UVA light under predetermined conditions, whereby the
physiological activities of the non-nucleic acid components are retained.
(Wherever the term "polynucleotide" is used in this application it should be
understood to mean: (1) microorganisms containing nucleic acids (either DNA or
RNA), (2) nucleic acid genomes or sub-genomic fragments from microorganisms,
from procaryotes (lower life forms) or from eucaryotes (higher life forms), or
(3) any other nucleic acid fragments.)

In decontaminating the biological composition, an aqueous medium containing
the biological preparation is combined with an appropriate amount of the
furocoumarin composition and irradiated with ultraviolet light under conditions
where all of the polynucleotide is inactivated, while the components other than
nucleic acid retain their normal physiological activities.

Various biological compositions may be employed, particularly protein
compositions involving blood or blood components. Whole blood, packed red cells,
platelets, and plasma (fresh or fresh frozen plasma) are of interest. Other
blood components of interest include plasma protein portion, antihemophilic
factor (AHF, Factor VIII); Factor IX and Factor IX complex (Factors II, VII, IX
and X); fibrinogens, Factor XIII, prothrombin and thrombin (Factor II and IIa);
immunoglobulins (e.g. IgA, IgD, IgE, IgG and IgM and fragments thereof e.g. Fab,
F(ab')(2), Fc); hyper-immune globulins as used against tenanus and hepatitis B;
cryoprecitate; albumin; interferons; lymphokines; transfer factors; etc. Other
biological compositions include vaccines, recombinant DNA produced proteins,
oligopeptide ligands, etc. the protein concentration in the aqueous medium will
generally range from about 1 (greek mu)g/ml to 500 mg/ml, more usually from
about 1 mg/ml to 100 mg/ml. The pH will normally be close to physiologic
pH(~7.4), generally in the range of about 6 to 9, more usually about 7. Other
components may be present in the medium, such as salts, additives, buffers,
stabilizers, or the like. These components will be conventional components,
which will be added for specific functions.

The furocoumarins will include psoralen and derivatives, where the
substitutents will be: alkyl, particularly of from 1 to 3 carbon atoms, e.g.
methyl; alkoxy, particularly of from 1 to 3 carbon atoms, e.g. methoxy; and
substituted alkyl, of 1 to 6, more usually 1 to 3 carbon atoms having from 1 to
2 heteroatoms, which will be oxy, particularly hydroxy or alkoxy of from 1 to 3
carbon atoms, e.g. hydroxymethyl and methoxymethyl, or amino, including mono-
and dialkyl amino having a total of from 1 to 6 carbon atoms, e.g. aminomethyl.
There will be from 1 to 5, usually 2 to 4 substituents, which will normally be
at the 4, 5, 8, 4' and 5' positions, particularly at the 4'-position.
Illustrative compounds include 5-methoxypsoralen, 8-methoxypsoralen (8-MOP),
4, 5',8-trimethylpsoralen (TMP), 4'-hydroxymethyl-4,5',8-trimethylpsoralen
(HMT), 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), 4-methylpsoralen,
4,4'-dimethylpsoralen, 4,5'-dimethylp-
<PAGE> 41
4,748,120

sorslen, 4'8-dimethylpsoralen, and 4'-methoxymethyl-4,5',8-trimethylpsoralen.

The subject furocoumarins are active with a wide variety of viruses and
other polynucleotides, DNA or RNA, whether single stranded or double stranded.
Illustrative viruses include: adenovirus, arenavirus, bacteriophage, bunyavirus,
herpesvirus, orthomyxovirus, papovavirus, paramyxovirus, picornavirus, poxvirus,
reovirus, retrovirus, rhabdovirus, and togavirus. Additional pathogenic
microorganisms include bacteria, chlamydia, mycoplasma, protozoa, rickettsia and
other unicellular microorganisms. Furocoumarins may also be effective in
inactivating Hepatitis B and Non-A Non-B Hepatitis viruses. This inactivation
method may also be used against uncharacterized infectious agents which may
contain nucleic acid (such as the agent which causes Acquired Immune Deficiency
Syndrome).

In addition to the furocoumarins, additives may be included which scavenge
for singlet oxygen or other highly reactive oxygen containing species. Such
additives include ascorbate, glutathione, sodium thionine, etc. In some
instances these additives may have adverse effects, so that in each instance,
their use will be determined empirically. Where such additives are present, they
will be present in amounts ranging from about 20 (greek mu)g to 20 mg per ml.

The furocoumarins may be used individually or in combination, preferably in
combination. Each of the furocoumarins may be present in amounts ranging from
about 0.01 (greek mu)g/ml to 1 mg/ml, preferably from about 0.5 (greek mu)g/ml
to 100 (greek mu)g/ml, there not being less than about 1 (greek mu)g/ml nor more
than about 1 mg/ml of furocoumarins. For RNA, the preferred furocoumarins are
AMT and HMT. For DNA, the preferred furocoumarin is TMP. For mixtures of DNA-
and RNA-containing polynucleotides, or for inactivation of infectious agents or
possibly infectious agents of unknown or uncertain nucleic acid classification,
or for protection against infections of unknown etiology, preferably TMP and AMT
are used in combination.

In carrying out the invention, the furocoumarins may be added to the
biological composition by any convenient means in a manner substantially
assuring the uniform distribution of the furocoumarins in the composition. The
composition may then be irradiated under conditions ensuring that the entire
composition is exposed to sufficient irradiation, so that the furocoumarins may
react with any polynucleotide present to inactivate the polynucleotide.
Depending upon the nature of the medium, particularly its opacity, as in the
case of blood, the depth of the solution subject to irradiation will vary
widely. Usually, the depth will be not less than about 0.025 millimeter, but may
be a centimeter or more. With whole blood, the depth will generally range from
about 0.025 millimeter to 2.5 millimeters. The light which is employed will
generally have a wavelength in the range of about 300 nm to 400 nm. The
intensity will generally range from about 0.1 mW/cm(2) to about 5 W/cm(2). In
order to prevent denaturation, the temperature should be maintained below about
60 degrees C., preferably below about 40 degrees C., usually from about -10
degrees C. to 30 degrees C. The medium being irradiated may be irradiated while
still, stirred or circulated, and may either be continuously irradiated or be
subject to alternating periods of irradiation and non-irradiation. The
circulation may be in a closed loop system or it may be in a single pass system
ensuring that all of the sample has been exposed to

irradiation. The total time for irradiation will vary depending upon the nature
of the sample, the furocoumarin derivative used, the intensity and spectral
output of the light source and the nature of the polynucleotides which may be
present. Usually, the time will be at least 1 min. and not more than about 6
hrs., more usually from about 15 mins. to about 2 hrs. When circulating the
solution, the rate of flow will generally be in the range of about 0.1 ml/min
to 50 liters/min. It may be desirable to remove the unexpended psoralen and/or
its photobreakdown products from the irradiation mixture. This can be readily
accomplished by dialysis across an appropriately sized membrane or through an
appropriately sized hollow fiber system after completion of the irradiation. It
may be desirable in certain applications to remove bound or unbound
furocoumarins using antibodies, including monoclonal antibodies, either in
solution or attached to a substrate.

The following examples are offered by way of illustration and not by way
of limitation.

EXPERIMENTAL

The following experiments were performed in order to demonstrate the
ability of the psoralen photoreaction to destroy microbial contaminants
contained in whole blood and blood products.

(1) Feline rhinotracheitis virus, a member of the herpesvirus family, was
added to heparinized whole rabbit blood in an amount that would give a final
concentration of approximately 2 x 10(7)PFU/ml.4'-hydroxymethyl-4,5',8-
trimethylpsoralen (HMT) was added to a portion of the rabbit blood and aliquots
were irradiated for various periods of time. To test for remaining live virus,
duplicate plaque assays were performed using cultured feline cells (Fc3Tg)(ATCC
CCL 176), with a methylcellulose overlay. Virus titers were obtained as the
arithmetical mean of viral plaques observed in duplication assay cultures 72
hours after exposure to test samples. The results are as follows:

The blood aliquot that received HMT only and no irradiation gave a titer of
5.3 X 10(6)PFU/ml. The aliquot that received HMT and five minutes of irradiation
exhibited a titer of 4.5 X 10(6)PFU/ml. In the aliquot that received psoralen
plus one hour of irradiation there was no detectable live virus remaining. The
sensitivity of this assay should have permitted detection of residual virus at
titers greater than or equal to 1.0 x 10(1)PFU/ml. A blood sample which had
received HMT and one hour of irradiation also showed no apparent damage to the
red blood cells as judged by phase contrast microscope analysis and by absence
of visible hemolysis. These data therefore demonstrate that high virus titers
present in whole blood can be inactivated by psoralen plus light treatment which
leaves the red cell component of the blood intact.

(2) In the second experiment Blue Tongue Virus (Serotype 11), a member of
the reovirus family, and Feline Rhinotracheitis Virus, and Simian Virus 40 were
added to a solution of Profilate (a commercial preparation of human clotting
factor VIII produced by Alpha Therapeutics). The lyophilized preparation of
Profilate (180 units) was dissolved in 10 ml of sterile water included with the
commercial preparation. This solution was further diluted with barbital buffer
(11.75 g sodium barbital and 14.67 g NaCl dissolved in 2 liters of de-ionized
water and filtered through a 0.22 micron filter) to a final concentration of 5
units per milliliter. One portion (2 ml) was set aside at room temperature in
the dark. This was sample 190 1. A second 2 ml portion was
<PAGE> 42
4,748,120

pumped through the apparatus described below for 1 hour with irradiation. This
was sample #2. Through addition of appropriate amounts of reagents a third 2 ml
portion was adjusted to contain 10 (greek mu)g/ml AMT and 10 (greek mu)g/ml HMT
and was also irradiated for 1 hour. This was sample #3. The fourth 2 ml portion
was adjusted to 10 (greek mu)g/ml AMT, 10 (greek mu)g/ml AMT, and 10 mM sodium
ascorbate and was also irradiated for 1 hour. This was sample #4. All the
samples were kept at 20 degrees C. throughout the manipulations. The total
elapsed time from dissolving of the lyophilized preparation to the completion of
the clotting factor VIII assays was 6 and one-half hours.

The clotting factor VIII assays were performed at a variety of dilutions
(ranging from 1:5 to 1:100) for each sample and were compared with the activity
in normal human serum and with pooled normal human serum. The results are
summarized in Table 1.
<TABLE>
<CAPTION>

TABLE 1
- --------------------------------------------------------------------------------
Effect of Photochemical Inactivation
Procedure and Its Components* on in vitro
Activity of Factor VIII(+)
-----------------------------------------
Sample
--------------------------------------
#1 #2 #3
dilution normal pool F(-),UVA(-) F(-),UVA(+) F(+),UVA(+)
- --------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
1:5 97 108 225 150 186
1:10 102 102 245 155 186
1:20 93 92 280 176 196
1:50 101 95 265 190 232
1:100 -- 100 255 196 263
--- --- --- --- ---
Average 98 99 254 173 213
- --------------------------------------------------------------------------------
*F -- Furocoumarins;
UVA -- long wavelength ultraviolet light;
(+) Factor VIII activity expressed in % of normal activity.
100% -- IU/ml of Factor VIII activity.
</TABLE>

The sample that was subjected to the psoralen inactivation protocol (sample
#3) retained 84% of the factor VIII activity that was present in the control
sample (#1). This was higher than the product activity retained by the sample
that was only irradiated (68% retained for sample #2) and indicates that the
psoralen photochemistry has little or no effect on the activity of factor VIII.

Samples otherwise identical to sample 1, 2, and 3 above were seeded with
2X10(6)PFU/ml of Feline Rhinotracheitis Virus (FeRT), 1X10(7)PFU/ml of Blue
Tongue Virus (BTV), and 4X10(8)PFU/ml of Simian Virus 40 (SV-40). Table 2 shows
the results of the plaque assays on those samples.

TABLE 2
- --------------------------------------------------------------------------------
Effect of Photochemical Inactivation
Procedure and Its Components* on Infectivity of
Virus in Factor VIII preparation.(+)
-----------------------------------------------
Sample 1 Sample 2 Sample 3
F(-),UVA(-) F(-),UVA(+) F(+),UVA(+)
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
FeRT Titer 8.6 X 10(5) 3.5 X 10(5) 0.0
BTV Titer 3.8 X 10(7) 1.4 X 10(7) 1.1 X 10(2)
SV-40 Titer 2.5 X 10(8) 1.6 X 10(8) 1.2 X 10(3)
- --------------------------------------------------------------------------------

*F -- Furocoumarins;
UVA -- long wavelength ultraviolet light;
(+) Infectivity determined by plaque assays in tissue culture.
</TABLE>

In the case of FeRT the number of detectable virus particles was reduced by
more than five orders of magnitude to beneath the limit of detection in the
plaque assay. The BTV infectivity was reduced by about five orders of magnitude
to 110 PFU/ml. The SV40 infectivity was reduced to a titer of 1.2X10(3). Thus,
it is shown that multiple, widely distinct types of virus can be simultaneously
inactivated by at least five orders of

magnitude in the presence of factor VIII, using the simple, convenient,
brief process described above, with retention of at least 84% of factor VIII
activity. Based on the above observations, it is predictable that by extending,
repeating or modifying the treatment, the probability of an infectious virus
particle remaining can be reduced to an arbitrarily low value. In this manner
suitable safety margins can be achieved for any of the cited applications.

APPARATUS AND SYSTEM

Since whole blood exhibits very high optical density for longwave UV light
(absorption is high for visible light in the 400 nm to 500 nm range), blood was
irradiated through a suitably short optical path length. In this experiment
blood was pumped through polyethylene capillary tubing of 0.875 millimeter
inside diameter. The tubing was coiled around a 1.27 centimeter diameter tube
and immersed in water which was maintained at 18 degrees C. The blood was
continuously circulated through the tubing by means of a peristaltic pump. The
blood required approximately 2.5 minutes for a complete cycle through the
capillary tubing and was in the light beam for approximately 20% of the stated
irradiation time. The light source was a low pressure mercury lamp filtered
through a cobalt glass filter. The filter transmit light of approximately 320
nm-380 nm, with peak transmittance at 360 nm. The incident intensity at the
sample was approximately 40 mW/cm(2).

It is evident from the above results, and in accordance with the subject
invention, that polynucleotides in biochemical compositions can be inactivated
to provide a safe composition for administration to a mammalian host. The
proteins present in the composition retain their physiological activity, so that
they can fulfill their physiological function in a mammalian host. The method
is simple, rapid, and can be expanded to treat large samples. The small amount
of chemical reagent required will not generally be harmful to the host.

Although the foregoing invention has been described in some detail by way
of illustration and example for purposes of clarity of understanding, it will
be obvious that certain changes and modifications may be practiced within the
scope of the appended claims.

What is claimed is:

1. A method for decontaminating blood components suspected of containing
viruses, said blood components being selected from the group consisting of red
blood cells, platelets, blood clotting factors, plasma and immunoglobulins,
without substantial impairment of the physiological activities of the treated
blood components, said method comprising:

(a) adding to a blood component selected from the group consisting of red
blood cells, platelets, blood clotting factors, plasma and
immunoglobulins at least one psoralen compound in an amount
sufficient to inactivate substantially all contaminating viruses
prevent; and thereafter

(b) irradiating said psoralen treated blood component with long wavelength
ultraviolet light under operating conditions which maintain the
concentrations of reactive oxygen species at levels which do not
substantially impair the physiological activity of the treated blood
component, and wherein said irradiation is conducted for a time
sufficient to inactivate substantially all contaminating viruses
present.
<PAGE> 43
4,748,120

2. A method according to claim 1 wherein the conditions which maintain the
concentration of reactive oxygen species at levels which do not substantially
impair the physiological activity of the treated blood component comprise the
addition of an oxygen scavenger.

3. A method according to claim 2 further comprising selectively removing
any unreacted psoralen(s) or photobreakdown products thereof by ultrafiltration
of dialysis.

4. A method according to claim 1, wherein at least two psoralens are
present.

5. A method according to claim 1, wherein said component is immunoglobin.

6. A method according to claim 1, wherein said blood component is red
cells.

7. A method according to claim 1, wherein said blood component is a
clotting factor.

8. A method according to claim 1, wherein said blood component is
platelets.

9. A method according to claim 1, wherein said blood component is plasma.

10. A method according to claim 1, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 3 carbon atoms, alkoxy of from 1 to 3
carbon atoms, or substituted aklyl of from 1 to 6 carbon atoms having 1 to 2
heteroatoms which are oxy or amino.

11. A method according to claim 1, wherein said psoralen has at least one
substitutent which is alkoxy of from 1 to 3 carbon atoms.

12. A method according to claim 11, wherein said psoralen is
5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) or 4'-methoxymethyl-4,5',
8-trimethylpsoralen.

13. A method according to claim 1, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 3 carbon atoms.

14. A method according to claim 13, wherein said psoralen is
4,5',8-trimethylpsoralen (TMP), 4-methylpsoralen, 4,4'-dimethylpsoralen,
4,5'-dimethylpsoralen or 4',8-dimethylpsoralen.

15. A method according to claim 1, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 6 carbon atoms having from 1 to 2
heteroatoms which are oxy or amino.

16. A method according to claim 15, wherein said psoralen is
4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) or
4'-aminomethyl-4,5',8-trimethylpsoralen (AMT).

17. A method for decontaminating blood components suspected of containing
viruses, said blood components being selected from the group consisting of red
blood cells, platelets, blood clotting factors, plasma and immunoglobulins,
without substantial impairment of the physiological activity of the treated
blood components, said method comprising:

(a) adding to a blood component selected from the group consisting of red
blood cells, platelets, blood clotting factors, plasma and
immunoglobulins at least one psoralen compound in a total psoralen

concentration of at least 1 ug/ml and not more than 300 ug/ml; and
thereafter

(b) passing said psoralen treated blood component through a light beam
with a wavelength in the range of 300 nm to 400 nm at an intensity of
about 0.1 mw/cm(2) to 5 W/m(2) at a depth of at least 0.025 mm for a
total radiation time of about 5 minutes to about 12 hours, wherein
said irradiation is conducted under operating conditions which
maintain the concentrations of reactive oxygen species at levels which
do not substantially impair the physiological activity of the treated
blood component.

18. A method according to claim 17 wherein the conditions which maintain
the concentrations of reactive oxygen species at levels which do not
substantially impair the physiological activity of the treated blood component
comprise the addition of an oxygen scavenger.

19. A method according to claim 18 further comprising selectively removing
any unreacted psoralen(s) or photobreakdown products thereof by ultrafiltration
or dialysis.

20. A method according to claim 17, wherein at least two psoralen are
present.

21. A method according to claim 17, wherein said blood component is red
cells.

22. A method according to claim 17, wherein said blood component is
platelets.

23. A method according to claim 17, wherein said blood component is plasma.

24. A method according to claim 17, wherein said blood component is a
clotting factor.

25. A method according to claim 17, wherein said blood component is an
immunoglobin.

26. A method according to claim 17, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 3 carbon atoms, alkoxy of from 1 to 3
carbon atoms, or substituted alkyl of from 1 to 6 carbon atoms having 1 to 2
heteroatoms which are oxy or amino.

27. A method according to claim 17, wherein said psoralen has at least one
substituent which is alkoxy of from 1 to 3 carbon atoms.

28. A method according to claim 27, wherein said psoralen is
5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) or
4'-methoxymethyl-4,5',8-trimethylpsoralen.

29. A method according to claim 17, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 3 carbon atoms.

30. A method according to claim 29, wherein said psoralen is
4,5',8-trimethylpsoralen (TMP), 4-methylpsoralen, 4,4'-dimethylpsoralen,
4,5'-dimethylpsoralen or 4',8-dimethylpsoralen.

31. A method according to claim 17, wherein said psoralen has at least one
substituent which is alkyl of from 1 to 6 carbon atoms having from 1 to 2
heteroatoms which are oxy or amino.

32. A method according to claim 31, wherein said psoralen is
4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) or
4'-aminomethyl-4,5',8-trimethylpsoralen (AMT).

* * * * *

<PAGE> 44
EXHIBIT E

UNITED STATES PATENT [19] [11] Patent Number: 4,791,062
Wiesehahn et al. [45] Date of Patent: Dec. 13, 1988
- --------------------------------------------------------------------------------
[54] FVR VACCINE

[75] Investors: Gary P. Wiesehahn, Alameda;
Richard E. Giles, Union City;
David R. Stevens, Fremont, all of Calif.

[73] Assignee: Diamond Scientific Co., Des Moines, Iowa

[21] Appl. No.: 20,201

[22] Filed: Jul. 6, 1987

Related U.S. Application Data

[63] Continuation of Ser. No. 707,102, Feb. 28, 1985, abandoned.

[51] Int. Cl.(4).................A61K 39/12; A61K 39/245
[52] U.S. Cl. ..........................435/238; 424/89;
435/236
[58] Field of Search.........................424/89, 90;
435/235-239

[56] References Cited

U.S. PATENT DOCUMENTS

4,522,810 6/1985 Pedersen.........................435/235
4,545,987 10/1985 Giles et al. ....................435/235
4,556,556 12/1985 Wiesehahn et al. ................ 424/90
4,693,981 9/1987 Wiesehahn et al. ................435/238
4,727,027 2/1988 Wiesehahn et al. ................ 424/89
4,748,120 5/1988 Wiesehahn et al. ................ 424/89

Primary Examiner--Shep K. Rose
Attorney, Agent, or Firm--Zarley, McKee, Thomte,
Voorhees & Sease

[57] ABSTRACT

Novel vaccines for feline viral rhinotracheitis are prepared by psoralen
inactivation of live Feline Herpesvirus I by exposure to ultraviolet radiation
in the presence of an inactivating furocoumarin. The resulting inactivated
viruses are suitable as the immunogenic substances in vaccines, which vaccines
are useful for inoculation of hosts susceptible to feline virus rhinotracheitis.

10 CLAIMS, NO DRAWINGS

<PAGE> 45
4,791,062

FVR VACCINE

This is a continuation of copending application Ser. No. 707,102 filed on
Feb. 28, 1985 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Vaccination against both bacterial and viral diseases has been one of the
major accomplishments of modern medicine. While effective vaccines have been
developed for a large number of animal and human diseases, development of safe
and effective vaccines for a number of other diseases remains problematic. In
preparing suitable vaccines, the primary objectives are eliciting an
immunogenic response which provides immunity against the disease of interest
while assuring that the vaccine itself is non-pathogenic.

In preparing vaccines, a number of general approaches have been developed.
The use of killed microbial agents as a vaccine, although generally save, will
not always be effective if the immunogenic characteristics of the agent are
altered. In contrast, the preparation of live attenuated microbial agents as a
vaccine will often provide improved immunologic reactivity, but will increase
the risk that the vaccine itself will become pathogenic, e.g., as a result of
reversion. Thus, although much experience has been gained over the years
relating to the preparation of vaccines, the successful preparation of an
effective vaccine against a particular infectious agent can never be assured,
even when employing techniques which were previously successful for other
microorganisms.

Feline viral rhinotracheitis (FVR) is species specific and enzootic in cat
populations worldwide. The causative agent is a Herpesvirus (Feline Herpes I),
and transmission is by direct contact or by infectious aerosols. Infection
affects the nasal and ocular mucous membranes initially. Clinical signs, which
commence within 2 to 10 days post infection, may include sneezing, coughing,
lacrimation (excessive tearing), serous to mucopurulent nasal discharge,
conjunctivitis, rhinitis, anorexia, dehydration, dyspnea, and severe depression.
Cutaneous, ocular, nasal or oral ulcers and abortions may also be encountered.
Pyrexia, up to 105 degrees F. (40.5 degrees C.), and a mild to moderate
neutraphilic leukocytosis or mild anemia may be present. However, pyrexia and
neutraphilia are mainly associated with secondary bacterial infection.

The course is often 1 to 3 weeks, but more prolonged systemic disease such
as pneumonia or hepatitis may occur, especially in kittens. In fatal cases the
course may extend to 4 or 5 weeks. Individual cats may die from the more severe
manifestations or from secondary complications. At necropsy, respiratory tract
lesions are most consistently encountered. These include hyperemic nasal and
respiratory passages often covered with fibrinous or mucopurulent exudate.
Secondary bacterial pneumonia may result in widely disseminated bacterial
emboli. Microscopically, intranuclear inclusions, if present, occur most often
in respiratory epithelium. Prior to the introduction of vaccines, 15% to 20% of
isolated cat populations were reported to be asymptomatic carriers of FVR,
providing a continuous reservoir for infection. Urban cat populations have
carrier rates of 50% to 80%.

2. Description of the Prior Art

Feline viral rhinotracheitis was first recognized as a disease entity by
Crandell and Mauer (1958) Proc. Soc. Expt. Bio. Med. 97:487-490. Experimental
FVR infection results in low serum neutralizing antibody titers (e.g., 1:4 to
1:10). See Crandall et al. (1961) J.A.V.- M.A., 138:191-196; and Hoover et al.
(1970) Am. J. Path. 58:269-282. Individual cats may be resistant to reinfection
with FVR, although they have little or no detectable serum antibody against FVR
(Bartholomew et al. (1968) Cornell Vet. 58:248-265). Infection immunity is
short-lived, and cats may be reinfected six months following a primary
infection. Reinfection elicits mild clinical signs and reduced viral shedding
(Walton and Gillespie (1970) Cornell Vet. 60:232-239).

Previous attempts at vaccine development for FVR have included formalin
inactivation (Fisher, et al. (1966) VM/SAC 61:1182-1189; Tan et al. (1971)
N.Z. Vet. J. 19:12-15; and Povey et al. (1978) Feline Pract. 8:36-42);
temperature sensitive mutants (Slater et al. (1976) Develop. Biol. Stand.
33:410-416); and tissue culture attenuated live virus isolates (Bittle et al.
(1974) VM/SAC 69:1503-1505; Bittle et al. (1975) Am. J. Vet. Res. 36:89-91; F.
Scott (1975) Feline Practice Jan.-Feb.:-17-22; and Edwards et al. (1977) VM/SAC
Feb:2-05-209). Chemically inactivated FVR vaccines failed to induce immunity
(Fisher et al. (1966) VM/SAC 61:1182-1189), although later trials with formalin
inactivated FVR vaccines were somewhat successful (Tan et al. (1971) N.Z. Vet.
J. 19:12-15 and Povey et al. (1978) Feline Pract. 8:36-42). Formalin inactivated
FVR vaccines are critically dependent on the incorporation of a suitable
immunologic adjuvant such as mineral oil.

One FVR vaccine production method utilized DNA inhibitors to select
biochemically uncharacterized FVR mutants that were subsequently inactivated by
UV irradiation (Davis et al. (1976) VM/SAC Oct: 1405-1410). Inactivation was
less than 100%, and the remaining live virus was cloned at 30 degrees C.
((plus or minus)2 degrees C.) and subjected to repeated cycles of the same
process, resulting in an attenuated virus strain. See, U.S. Pat. No. 4,031,204.
U.S. Pat. No. 4,287, 178 discloses that temperature sensitive FVR mutants can be
utilized as an attenuated live virus vaccine for FVR. Attenuated live FVR
vaccines are efficacious, but may induce clinical disease or abortions.
Combination vaccines have been described in which FVR and other feline pathogens
are incorporated (Bittle et al. (1975) Feline Practice Nov. - Dec:- 13-15 and
Edwards et al. (1977) Feline Practice July:4-5-50). These vaccines are also
produced by standard procedures known to the art.

The preparation of psoralens and their use in inactivating viruses are
described in U.S. Pat. Nos. 4,196,281 and 4,124,598.

SUMMARY OF THE INVENTION

Vaccines for inoculation against feline viral rhinotracheitis are prepared
by irradiating live Feline Herpes I virus, the etiologic agent which causes FVR,
with light in the presence of an inactivating furocoumarin compound for a time
sufficient to render the virus completely non-infectious. It has been found that
inactivated Feline Herpes I virus retains immunogenicity, and that inoculation
of a susceptible host with such inactivated viruses elicits the production of
serum neutralizing antibody and protects the host against subsequent challenge
with live, infectious Feline Herpes I virus. The inactivated Feline Herpesvirus
I may be combined with a physiologically-acceptable carrier or
<PAGE> 46
4,791,062

adjuvant, usually at from about 10(6) to 10(9) pfu/ml, to form the vaccine.

DESCRIPTION OF THE SPECIFIC
EMBODIMENTS

Vaccines useful for the inoculation of feline hosts against feline
viral rhinotracheitis are provided. The vaccines are prepared by inactivation
of live Feline Herpes I virus in an appropriate medium with a sufficient amount
of an inactivating furocoumarin to provide for inactivation of the virus upon
subsequent irradiation with long wavelength ultraviolet (UV) radiation. The
resulting inactivated virus may be stored until used for inoculation. Prior to
inoculation, the inactivated virus will usually be combined with a
physiologically-acceptable carrier or immunologic adjuvant.

Any of the isolates of Feline Herpes I virus, or combinations thereof,
may be inactivated and utilized to prepare a vaccine according to the present
invention. Such live, virulent viruses can be obtained from cats suffering
from feline viral rhinotracheitis according to conventional techniques. See,
e.g., Crandell and Mauer, supra.; Bittle et al. (1960) Amer. J. Vet. Res.
21:547; and Ditchfield and Grinyer (1965) Virology 26:504. Generally, virus
obtained from the nasal and conjunctival membranes of infected cats are used to
infect suitable feline cells grown in tissue culture. The viruses are
replicated and isolated by serial passage following well known techniques.
Alternatively, the virus may be derived from generally available sources, such
as Feline Herpes 1 virus available from the American Type Culture Collection
under designation VR636. A specific method for growing virus from seed virus
is set forth in the Experimental section hereinafter.

In preparing the subject vaccines, the desired virus is grown in
mammalian cell culture. Suitable cell lines include the AKD cell line (ATCC CCL
150) and Fc3Tg (ATCC CCL 176), and other cell lines permissive for Feline Herpes
I virus and which can be grown in vitro as monolayer cultures or as suspension
cultures. The cell cultures are grown to approximately 80% saturation density
and infected with the feline herpesvirus at a multiplicity of infection (MOI),
usually between about 0.03 and 0.3, preferably about 0.1. After adsorbing the
viral inoculum to the cells by incubation for a limited period of time at a
temperature in the range from about 35 degrees c. to 40 degrees C., an
appropriate growth or maintenance medium is added. The cells are incubated at
temperatures in the range from about 35 degrees C. to 40 degrees C., in the
presence in the range from about 35 degrees C. to 40 degrees C., in the presence
of about 5% carbon dioxide in air until at least about 50% of the cell culture
exhibits cytopathic effect (CPE). CPE is characterized by cell rounding (in
monolayers) and cell degeneration.

The culture vessel is shaken to detach loosely adhering cells and
cellular debris, and the contents of each vessel are aseptically decanted into
centrifuge bottles. The crude virus preparation is centrifuged at 10,000 X g for
30 minutes and the supernatant is discarded. The pellet is resuspended in
one-twentieth the original volume of maintenance medium containing 7 to 10%
(v/v) dimethly sulfoxide (Sigma Chemical Co., St. Louis, MO 63178, cat. no. D
5879). For cell-associated virus preparations, the foregoing suspension is
stored frozen at or below -80 degrees c. Cell-free virus preparations are
produced from the foregoing suspension by freezing and thawing the suspension
three times, centrifuging the resulting lysate at 10,000Xg or 30 minutes, and
collect-

ing and storing the virus-containing supernatant at or below -80 degrees
C. Cell-free virus may also be prepared from a suspension which lacks dimethyl
sulfoxide.

The particular growth and maintenance medium may be a conventional
mammalian cell culture medium, such as Eagle's Minimum Essential Medium or
Medium 199, usually supplemented with additives such as fetal bovine serum,
fetal calf serum, broth prepared from dehydrated standard microbial culture
media, or the like.

The furocoumarins useful for inactivation are primarily illustrated by
the class of compounds referred to as psoralens, which includes psoralens and
substituted psoralens where the substitutents will be: alkyl, particularly
having from 1 to 3 carbon atoms, e.g., methyl; alkoxy, particularly having from
1 to 3 carbon atoms, e.g., methoxy; and substituted alkyl having from 1 to 6,
more usually from 1 to 3, carbon atoms and from 1 to 2 heteroatoms, which will
be oxy, particularly hydroxy or alkoxy having from 1 to 3 carbon atoms, e.g.,
hydroxy methyl and methoxy methyl, or amino, including mono- and dialkyl amino
or aminoalkyl, having a total of from 0 to 6 carbon atoms, e.g., aminomethyl.
There will be from 1 to 5, usually from 2 to 4 substituents, which will normally
be at the 4, 5, 8, 4' and 5' positions, particularly at the 4' position.
Illustrative compounds include 5-methoxypsoralen; 8-methoxypsoralen (8-MOP);
4,5',8-trimethylpsorlen (TMP); 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT);
4'-aminomethyl-4,5',8-trimethylpsoralen (AMT); 4-methylpsoralen;
4,4'-dimethylpsoralen; 4,5'-methyoxymethyl-4,5'8-trimethylpsorlen. Of
particular interest are HMT, AMT and 8-MOP.

The furocoumarins may be used individually or in combination. Each of
the furocoumarins may be present in amounts ranging from about 0.01 (greek
mu)g/ml to 1 mg/ml, preferably from about 5 (greek mu)g/ml to 300 (greek
mu)g/ml, there not being less than about 1 g/ml nor more than about 1 mg/ml of
furocoumarins.

In carrying out the invention the furocoumarin(s), in an appropriate
solvent which is substantially inert and sufficiently polar to allow for
dissolution of the furocoumarin(s), are combined with the viral suspensions,
conveniently a viral suspension in an aqueous buffered medium, such as used for
storage. The amount of virus will generally be about 1 X 10(6) to 10(11), more
usually about 1 X 10(7) to 10(9) and preferably about 1 X 10(8) to 5 X 10(8)
pfu/ml. The furocoumarin will be at a concentration of about 0.001 mg/ml to 0.5
mg/ml, more usually about 0.02 mg/ml to 0.3 mg/ml. The amount of solvent which
is used to dissolve the furocoumarin will be sufficently small so as to readily
dissolve in the aqueous viral suspension and have little, if any, effect on the
results.

The furocoumarin may be added to the viral suspension in a single
addition or in multiple additions, where the virus is irradiated between
additions. Usually, the numer of additions will be from aboutr 1 to 50, more
usually from about 10 to 40, and preferably from about 20 to 40. The total
amount of furocoumarin which will be added will be sufficient to provide a
concentration of at least about 0.01 mg/ml to about 1 mg/ml, usually not more
than about 0.75 mg/ml. Since a substantial proportion of the furocoumarin will
have reacted with the nucleic acide between additions, the total concentration
of furocoumarin in solution will generally not exceed about 0.3 mg/ml.
<PAGE> 47
4,791,062

The total time for the irradiation will vary depending upon the light
intensity, the concentration of the furocoumarin, the concentration of the
virus, and the manner of irradiation of the virus, where the intensity of the
irradiation may vary in the medium. The total time will usually be at least
about 2 hrs. and not more than about 80 hrs., generally ranging from about 10
hrs. to 50 hrs. The times between additions of furocoumarin, where the
furocoumarin is added incrementally, will generally vary from about 30 min. to
24 hrs., more usually from about 1 hr. to 3 hrs.

The temperature for the irradiation is preferably under 25 degrees C., more
preferably under 20 degrees C. and will generally range from about -10
degrees C. to 15 degrees C., more usually from about 0 degrees to 10 degrees C.

The irradiation is normally carried out in an inert atmosphere, where all
or substantially all of the oxygen has been removed. Inert atmospheres include
nitrogen, helium, argon, etc.

The light which is employed will generally have a wavelength in the range
from about 300 nm to 400 nm. The intensity will generally range from about 0.1
mW/cm(2) to about 5W/cm(2).

Optionally, a small amount of a singlet oxygen scavenger may be included
during the virus inactivation. Singlet oxygen scavengers include ascorbic acid,
dithioerythritol, sodium thionite, glutathione, etc. The amount of scavenger
will generally be at a concentration of about 0.001M to 0.5M, more usually at
about 0.01M to 0.1M, where the addition may be made in a single or multiple
additions.

It may be desirable to remove the unexpended furocoumarin and/or its
photobreakdown products from the irradiation mixture. This can be readily
accomplished by one of several standard laboratory procedures such as dialysis
across an appropriately sized membrane or through an appropriately sized
hollow fiber system after completion of the irradiation. Alternatively, one
could use affinity columns for one or more of the low molecular weight
materials to be removed.

The inactivated virus may then be formulated in a variety of ways for
use for inoculation. The concentration of the virus will generally be from
about 10(6) to 10(9) pfu/ml, as determined prior to inactivation, with a total
dosage of at least 10(5) pfu/dose, usually at least 10(6) pfu/dose, preferably
at least 10(7) pfu/dose. The total dosage will usually be at or near about
10(8) pfu/dose, more usually being about 10(6) to 10(7) pfu/dose. The vaccine
may include cells or may be cell-free. It may be an inert physiologically
acceptable medium, such as ionized water, phosphate-buffered saline, saline, or
the like, or may be administered in combination with a physiologically
acceptable immunologic adjuvant, including but not limited to mineral oils,
vegetable oils, mineral salts and immunopotentiators, such as muramyl
dipeptide. The vaccine may be administered subcutaneously, intramuscularly, or
intraperitoneally. Usually, a specific dosage at a specific site will range
from about 0.1 ml to 4 ml, where the total dosage will range from about 0.5 ml.
to 8 ml. The number of injections and their temporal

spacing may be highly variable but usually 1 to 3 injections at 1, 2 or 3 week
intervals are effective.

The following examples are offered by way of illustration, not by way of
limitation.

EXPERIMENTAL

Materials and Methods

A. Virus Growth

Cat cell lines AKD (ATCC CCL150) or Fc3Tg (ATCC CCL176) were grown as
monolayers in plastic cell culture vessels in a standard defined culture media
consisting of Minimum Essential Medium (MEM) and Earles salts with non-essential
amino acids (MEN); F12K; MEM; or alpha MEM. Medium was supplemented with 2% to
15% inactivated fetal calf serum (F(i)) or 2% to 20% YELP (YELP consists of:
yeast extract 5 g; lactalbumin hydrolysate 25 g; Bacto-peptone 50 g; deionized
H(2)0 1000 mls sterilized by autoclaving or filtration). Cell cultures were used
to produce live Feline Herpes I virus from master seed virus derived from Feline
Herpes I virus (ATCC VR636). Cells were grown in culture vessels to 80% to 100%
confluency (approximately 1 x 10(5) to 2 x 10(5) cells per cm(2) of growth
surface area) using standard mammalian cell culture techniques as follows:

Corning plastic roller bottles (Corning No. 25140-850) with a growth
surface area of 850 cm(2) containing 50 to 100 ml of MEN supplemented with 10%
F(i) and 1 x 10(8) to 2 x 10(8) AKD or Fc3Tg cells/bottle were used for virus
production. The cell cultures were initiated by seeding approximately 1 x 10(6)
to 5 x 10(6) cells into 50 to 100 mls of growth medium in a roller bottle
containing about 5% CO(2) in air and incubating the roller bottle on a roller
bottle rotator at 1 to 5 rpm at 35 degrees C. to 38 degrees C. The cultures were
grown to 80% to 100% confluency over a 7 to 14 day period with a 100% medium
change every 3 to 5 days.

When the monolayers were 80% to 100% confluent, the culture medium was
removed and the monolayer was washed with 20 to 50 mls of phosphate buffered
saline (PBS) pH 7.2 to 7.4 (NaCl 8 g + KCl 0.2 g + Na(2)HPO(4) 1.14 g +
KH(2)PO(4) 0.2 g). The PBS wash was discarded, and the roller bottle was
infected by the addition of approximately 1 x 10(7) to 2 x 10(7) plaque forming
units (pfu) of Feline Herpes I virus in 10 mls of PBS containing 2% F(i). The
multiplicity of infection (MOI) was approximately 0.1. The virus inoculum was
adsorbed to the cells by incubation at 35 degrees C. to 38 degrees C. for one
hour at 1 to 5 rpm. The inoculation fluid was removed and 50 mls of MEN
containing 10% F(i) was added per roller bottle. The post-infection incubation
was at 35 degrees C. to 38 degrees C. in 5% CO(2) in air with rotation.
Herpesvirus cytopathic effect (CPE) was evident forty to forty-eight hours
post-infection. The CPE was characterized by cell rounding, cell detachment, and
cell degeneration.

Cell associated (CA) virus was prepared by:

1. resuspending the 10,000 x g pellet in approximately 5 ml of a
resuspension medium containing 80 parts F12K, 10 parts Fi, and 10 parts
dimethylsulfoxide (DMSO) for each original roller bottle;

<PAGE> 48
4,791,062

2. freezing the resuspended CA virus at -20 degrees C. for 1.5 to 2 hours;
and

3. transferring the CA virus frozen at -20 degrees to temperatures ranging
from -80 degrees C. to -100 degrees C.

Cell free (CF) virus is prepared by:

1. resuspending the 10,000 x g pellet in F12K;

2. freezing and thawing the resuspended material 3 times;

3. clarifying the freeze-thawed material by centrifugation at 10,000 x g
for 30 minutes; and

4. freezing the clarified supernatant (CF virus) at temperatures ranging
from -80 degrees C. to -100 degrees C.

CF or CA virus was thawed by gentle agitation at 37 degrees C. in a water
bath.

B. Virus Assay

Confluent monolayers of FC3Tg or AKD cells were prepared in 6 cm diameter
mammalian cell culture plastic petri dishes (Corning No. 25010). The growth
medium used for Fc3Tg cells was MEN + 10% F(i) and the growth medium used for
AKD cells was F12K + 15% F(i). Ten fold serial dilutions of virus samples were
made by adding 0.5 ml of the virus sample to 4.5 mls of PBS + 2% F(i) in a screw
cap tube. The growth medium was removed from a 6 cm culture dish cell monolayer,
1.00 ml of virus sample (undiluted or diluted) was added, and the virus was
adsorbed to the monolayer for 2 hours at 35 degrees C. to 38 degrees C. Two or
more dishes were used for each sample. The unadsorbed inoculum was removed, and
4 mls of overlay medium was added per 6 cm culture dish. The overlay medium was
prepared by mixing equal parts solution A (100 ml 2 x MEM with L-glutamine,
GIBCO #320-1935, +4 ml F(i)) and 1% methyl cellulose (4,000 centipoises) in
deionized H2O (Fisher M-281 sterilized by autoclaving). After the overlay was
added the cultures were incubated at 35 degrees C. to 38 degrees C. in 5% CO(2)
in air for at least 48 hours and examined for virus plaques which appeared as
either open circular areas in the monolayer with rounded cells at the edge of
the open area or as foci of multinucleated syncytial cells. The virus titer in
pfu/ml was calculated by multiplying the average number of plaques per dish by
the reciprocal of the dilution. The pfu/ml was the value used to determine the
amount of virus needed to infect cells at a MOI of approximately 0.1. The pfu/ml
in a virus preparation prior to inactivation was used to determine the
immunizing dose.

C. Inactivation of Cell Free Virus (CF-FVR)

Nineteen mls of CF-FVR (1.9 x 10(7) pfu/ml) were mixed with 0.4 ml of
hydroxymethyltrioxsalen (HMT; 1 mg/ml in DMSO) and 1.9 ml of sodium ascorbate
(0.1 M in H(2)O). The mixture was prepared in 150 cm(2) tissue culture flasks
(T-150, Corning No. 25120) that were subsequently deaerated for 2 minutes with
pure argon gas. The virus-containing flasks were irradiated for 55 minutes at 4
degrees C. using G.E. BLB fluorescent bulbs at an intensity of 1.5 mW/cm(2). The
FVR/HMT/ascorbate mixture was then transferred by pipet into a second T-150
flask, which was deaerated for 2 minutes using pure argon gas. The second T-150
flask was irradiated for an additional 28 minutes at 4 degrees C. under the same
long wavelength UV light source.

The CF-FVR preparation was stored at -100 degrees C in a REVCO freezer.
Subsequently the CF-FVR preparation was thawed and placed into a T-150 flask.
The flask was deaerated with pure argon gas for 2 minutes and

irradiation was continued as described above for an additional 15 hours and 40
minutes.

D. Inactivation of Cell Associated Virus (CA-FVR)

Cells from 10 roller bottles (about 1 x 10(8) to 2 x 10(8) cells/roller
bottle) were resuspended in 28 mls of cell culture media. Twenty mls of the
suspension were placed into a T-150 flask. To this flask was added 2 ml of
freshly prepared sterile 0.1 M sodium ascorbate and 0.4 ml HMT (1 mg/ml in
DMSO). The flask was deaerated with pure argon gas for 2 minutes, and the flask
was irradiated at 4 degrees C. using G.E. BLB fluorescent bulbs at an intensity
of 1.5 mW/cm(2) for 75 minutes. The viral suspension was then transferred by
pipet from the T-150 flask into a second T-150 flask and again deaerated with
pure argon gas for 2 minutes. Irradiation was continued for an additional 95
minutes. The CA-FVR preparation was adjusted to 10% DMSO and the suspension was
frozen at -20 degrees C. for 1 hour and then stored at -100 degrees C. in a
REVCO freezer.

The stored frozen CA-FVR preparation was subsequently thawed, and the cells
were pelleted in a clinical centrifuge. The cells were resuspended in 21 mls of
serum-free medium to which 2.1 mls of freshly prepared 0.1 M sodium ascorbate
and 0.4 ml of HMT (1 mg/ml in DMSO) were added. The sample was transferred by
pipet to a T-150 flask, and irradiation was continued for an additional 15 hours
and 40 minutes.

E. Assessment of Inactivation by Blind Passage

Fc3Tg or AKD cells were grown to confluency in 850 cm(2) roller bottles
using standard cell culture procedures as described above. The culture medium
was removed from the roller bottle, and 2.0 mls of the inactivated virus
preparation, mixed with 18 mls of medium containing 2% F(i), were adsorbed to
the roller bottle cell monolayer for 60 minutes at 35 degrees C. to 38 degrees
C. with rotation at 1 to 5 rpm. After adsorption, the inoculum was removed and
150 ml of maintenance medium (MEN or F12K with 2% F(i)) added. The roller bottle
culture was then incubated at 35 degrees C. to 38 degrees C. for 7 days with
daily observation for viral CPE (see plaque assay above for description of CPE).
The roller bottle culture received a 100% medium change after 3 to 5 days. If no
CPE was observed during the first roller bottle passage, the cell monolayer was
scraped into the maintenance medium which was then decanted into a centrifuge
bottle. The cells were pelleted by centrifugation at room temperature at 1,000 x
g for 15 minutes, resuspended in 20 ml of fresh maintenance medium, and passed
to a new confluent roller bottle culture of Fc3Tg or AKD cells as described
above. The second roller bottle blind passage was observed for 7 days and fed
once on day 3 to 5. If no CPE was observed during the second roller bottle
blind passage, a third roller bottle blind passage was performed. If no CPE was
observed by the end of the third roller bottle passage, the virus preparation
was considered inactive.

F. Administration Procedure

Photochemically inactivated FVR is inoculated via syringe into cats by
either single or multiple routes, including but not limited intravenously (IV),
subcutaneously (SQ), intramuscularly (IM), or intraperitoneally (IP). The
vaccine is administered in various volumes (0.5 to 3.0 ml) and in various
concentrations (10(6) to 10(8) pfu; either CF, CA or in combination). In the
following examples the vaccine was administered in combination
<PAGE> 49
4,791,062

with aluminum hydroxide as an immunologic adjuvant. The number of injections
and their temporal spacing was as set forth in each example.

RESULTS

A. Inoculation with CF-FVR

The experimental group consisted of four specific pathogen free kittens
(2 males, 2 females) four months old (Liberty Laboratories, Liberty Corner,
N.J.). The control group consisted of two similar female kittens. The
experimental group was inoculated IM with 3x10(7) pfu (3 mls) of HMT inactivated
CF-FVR on days 0 and 21, and again inoculated with 3x10(7) pfu HMT inactivated
with an equal amount of 2% aluminum hydroxide [A1(OH)(3)] adjuvant on day 61.
Controls were vaccinated at eight weeks and at thirteen weeks of age with a
commercial FVR vaccine using the manufacturer's recommended procedure. Serum
samples were collected weekly and tested for anti-FVR neutralizing antibodies.

Following live virus challenge (106 pfu intranasally and
intraconjunctivally), a numerical scoring system (Table 1) was used to assess
the clinical response to both experimental and control cats.

<TABLE>
<CAPTION>
TABLE 1
- -------------------------------------------------------------------------------
Scoring System for Clinical
Effects of Herpesvirus Challenge in Cats
-----------------------------------------

FACTOR DEGREE SCORE
- -------------------------------------------------------------------------------
<S> <C> <C>
Fever 101 to 102 degrees F. 0
102 to 103 1
103 to 104 3
greater than 104 5
Depression slight 1
moderate 3
severe 5
Sneezing occasional 1
moderate 3
paroxysmal 5
Lacrimation serous 1
mucoid 3
purulent 5
Nasal Discharge serous 1
mucoid 3
purulent 5
Appetite normal; eats all food 0
fair; eats more than 1/2 of food 1
poor; eats less than 1/2 of food 3
none; eats nothing 5
- -------------------------------------------------------------------------------
</TABLE>

Three of four experimental cats developed serum neutralizing anti-FVR
antibody (SN) titers of 1:2 that were detected between day 42 and day 58.
Following the third immunization (day 61), four of four experimental cats had
SN titers of 1:4 (day 80). Baseline SN antibody titers on the experimental cats
were negative. The control cats did not develop detectable SN antibody titers
during the pre-challenge period.

All cats were exposed to 10(6) pfu of live FVR by intraconjunctival and
intranasal injection on day 91. Each cat was monitored twice daily for the
absence, presence and degree of severity of factors given in Table 1. A
composite clinical score was derived for each cat after a 15 day observation
period.

affected (composite score = 84) by moderate, but transient, sneezing and mucoid
nasal discharge. Both control cats were severely affected by live virus
challenge. Severe purulent nasal and ocular discharge and lack of appetite were
apparent. The control cats had composite scores of 133 and 253.

B. Inoculation with CA-FVR

Nine age-matched specific pathogen free kittens, 4 months old (Liberty
Laboratories, Liberty Corner, N.J.), were randomly assigned to three
experimental groups designated A, B, and C.

Group A (controls) was inoculated twice with 1 ml tissue culture fluid
and 1 ml aluminum hydroxide adjuvant. Group B was inoculated twice with a
commercial FVR vaccine according to the manufacturer's recommendation. Group C
was inoculated three times with 10(7) HMT-inactivated CA-FVR in aluminum
hydroxide (total volume = 2 ml; 1:1 vaccine to adjuvant). All injections were
given IM at three week intervals.

Live FVR virus (10(6) pfu intranasally and intraconjunctivally) was
given on day 63 and a numerical scoring system (Table 1) was used to assess the
kittens' clinical response for a 15 day post-challenge period. Serum samples
were collected from all kittens prior to vaccination, prior to the second and
third immunizations, prior to live FVR challenge, and at 15 days
post-challenge. The sera were utilized to assess neutralizing antibody titers
by standard procedures.

The control kittens (Group A) maintained SN antibody titers less than
1:2 (negative) throughout the pre-challenge period. Fifteen days following live
FVR challenge Group A kittens, uniformly had SN antibody titers of 1:2. Kittens
in Group B and C lacked detectable anti-FVR antibody titers pre-immunization,
but all kittens in Groups B and C had SN antibody titers of 1:2 or 1:4 after
two immunizations. The third immunization in Group C kittens did not
significantly alter their SN antibody titers. Following a 15 day post-challenge
period, kittens in Groups B and C demonstrated an anamnestic immunologic
response, with SN antibody titers ranging from 1:16 to 1:64.

Clinically, Group A kittens were severely affected by live FVR
challenge, whereas kittens in Groups B and C were significantly protected by
their respective vaccines.

The composite clinical scores for Group A were 125, 141, and 128 for
the 15 day post-challenge period. The composite clinical scores for Group B
were 25, 20, and 64, while Group C had composite clinical scores of 21, 15, and
34. The clinical signs evident were characteristic of FVR.

According to the present invention, furocoumarin-inactivated feline
herpesvirus I retains its immunogenicity and is suitable as the immunogenic
substance in a vaccine against feline viral rhinotracheitis. The inacti-

<PAGE> 50
4,791,062

vated virus of the present invention is non-infectious and is safe when
administered to a host for vaccination.

Although the foregoing invention has been described in some detail by way of
illustration and example for purposes of clarity of understanding, it will be
obvious that certain changes and modifications may be practiced within the
scope of the appended claims.

What is claimed is:

1. A method of making a vaccine useful for inoculation of a feline host
susceptible to feline virus rhinotracheitis, said method comprising:

(1) inactivating at least one feline Herpesvirus I isolate by

(a) adding to said feline Herpesvirus I isolate a small but inactivating
effective amount of a furocoumarin; and thereafter

(b) exposing said feline Herpesvirus I to ultraviolet light having a
wavelength within the range of from about 300 nm to 400 nm and an
intensity of from about 0.1 mW/cm(2) to 5 W/cm(2) at a temperature below
about 40 degrees C. for a time sufficient to render said virus
noninfectious without destroying the characteristic immunologenic
response of said feline Herpesvirus I isolate.

2. The method according to claim 1 wherein said furocoumarin is
4'-hydroxymethyl-4,5', 8-trimethylpsoralen.

3. The method of claim 1 wherein said inactivating occurs in the substantial
absence of oxygen.

4. The method according to claim 1 wherein said virus is inactivated in the
presence of a singlet oxygen scavenger.

5. The method according to claim 1 wherein said virus is grown in
substantially confluent monolayers of host cells immediately prior to said
inactivating procedure.

6. A method of preparing a vaccine useful for inoculation of a feline host
susceptible to feline virus rhinotracheitis, said method comprising:

subjecting at least one inactivated feline Herpesvirus I isolate to
ultraviolet light having a wavelength within the range of from about 300
nm to 400 nm and an intensity of from about 0.1 mW/cm(2) to 5W/cm(2) at
a temperature below about 40 degrees C. in the presence of an
inactivating furocoumarin for a time sufficient to render said virus
noninfectious without destroying its characteristic immunogenic
response.

7. The method according to claim 6 wherein said furocoumarin is
4'-hydroxymethyl-4,5', 8-trimethylpsoralen.

8. The method of claim 6 wherein said inactivating occurs in the substantial
absence of oxygen.

9. The method according to claim 6 wherein said virus is inactivated in the
presence of a singlet oxygen scavenger.

10. The method according to claim 6 wherein said virus is grown in
substantially confluent monolayers of host cells immediately prior to said
inactivating procedure.

* * * * *

<PAGE> 51

EXHIBIT F

UNITED STATES PATENT [19] [11] PATENT NUMBER: 5,106,619

WIESEHAHN ET AL. [45] DATE OF PATENT: APR. 21, 1992

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

[54] PREPARATION OF INACTIVATED VIRAL VACCINES

[75] Inventors: GARY P. WIESEHAHN, Alameda; RICHARD P. CREAGAN, Alta Loma;
DAVID R. STEVENS, Fremont; RICHARD GILES, Alameda, all of
Calif.

[73] Assignee: DIAMOND SCIENTIFIC CO., Des Moines, Iowa

[21] Appl. No.: 463,081

[22] Filed: JAN. 10, 1990

RELATED U.S. APPLICATION DATE

[60] Continuation of Ser. No. 69,117, Jul. 2, 1987, abandoned, which is a
division of Ser. No. 785,354, Oct. 7, 1985, Pat. No. 4,693,981, which is a
continuation-in-part of Ser. No. 592,661, Mar. 23, 1984, Pat. No.
4,556,556, which is a continuation-in-part of Ser. No. 563,939, Dec. 20,
1983, Pat No. 4,545,987.

[51] Int. Cl.(5) .................................... A61K 39/12; C12N 7/04

[52] U.S. Cl. ............................................. 424/89; 424/90;
435/236; 435/238; 546/270

[58] Field of Search ..................................424/89, 90; 435/236,
435/238; 546/270

[56] REFERENCES CITED

U.S. PATENT DOCUMENTS

4,036,952 7/1977 Bauer et al. ......................424/89

Primary Examiner -- Johnnie R. Brown
Assistant Examiner -- Abdel A. Mohamed
Attorney, Agent, or Firm -- Joseph C. Gil; Lyndanne M. Whalen

[57] ABSTRACT

12 CLAIMS, NO DRAWINGS

<PAGE> 52
5,106,619

PREPARATION OF INACTIVATED VIRAL VACCINES

This application is a continuation of application Ser. No. 07/069,117,
filed Jul. 2, 1987, now abandoned, which is a divisional of Ser. No.
06/785,354, filed Oct. 7, 1985 (U.S. Pat. No. 4,693,981), which is a
continuation-in-part of Ser. No. 06/592,661, filed Mar. 23, 1984 (U.S. Pat. No.
4,556,556), which is a continuation-in-part of Ser. No. 06/563,939, filed Dec.
20, 1983 (U.S. Pat. No. 4,545,987).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The Present invention relates to the preparation of inactivated viral
vaccines. More particularly, the invention relates to psoralen inactivation of
viral particles under conditions which limit antigenic degradation of the viral
particles caused by the inactivation.

It is therefore desirable to provide improved methods for inactivating
viruses, which methods are capable of inactivating even the most resistant
viruses under conditions which do not substantially degrade the antigenic
structure of the viral particles. In particular, the inactivated viruses should
be useful as vaccines and free from adverse side effects at the time of
administration as well as upon subsequent challenge with the live virus.

2. Description of the Prior Art

The reactivity of psoralen derivatives with viruses has been studied. See,
Hearst and Thiry (1977) Nuc. Acids Res. 4:1339-1347; and Talib and Banerjee
(1982) Virology 118:430-438. U.S. Pat. Nos. 4,124,598 and 4,196,281 to Hearst
et al. suggest the use of psoralen derivatives to inactivate RNA viruses, but
include no discussion of the suitability of such inactivated viruses as
vaccines. U.S. Pat. No. 4,169,204 to Hearst et al. suggests that psoralens may
provide a means for inactivating viruses for the purpose of vaccine production
but presents no experimental support for this proposition.

European patent application 0 066 886 by Kronenberg teaches the use of psoralen
inactivated cells, such as virus-infected mammalian cells, for use as
immunological reagents and vaccines. Hanson (1983) in: Medical Virology II, de
la Maza and Peterson, eds., Elsevier Biomedical, New York, pp. 45-79, reports
studies which have suggested that oxidative photoreactions between psoralens and
proteins may occur.

SUMMARY OF THE INVENTION

The present invention provides for the production of
furocoumarin-inactivated viral vaccines under conditions which substantially
preserve the antigenic characteristics of the inactivated viral particles. It
has been recognized by the inventors herein that the inactivation of viruses by
exposure to ultraviolet radiation in the presence of furocoumarin compounds can
degrade the antigenic structure of the viral particle. While such degradation
can be limited by employing less rigorous inactivation conditions, certain
recalcitrant viruses require relatively harsh inactivation conditions in order
to assure that all residual infectivity is eliminated. The inactivation
condition required to eliminate substantially all infectivity in such
recalcitrant viruses can so degrade the viral particle that it is unsuitable
for use as the immunogenic substance in a vaccine. Even if the degradation is
not so complete, partial degradation of the antigenic characteristics may
render the vaccine less effective than would be desirable. That is, the vaccine
may require higher concentrations of the inactivated viral particles in each
inoculation, and/or the vaccination program may require additional inoculations
in order to achieve immunity.

According to the present invention, vaccines are prepared by treatment
with furocoumarins and long wavelength ultraviolet (UVA) light under conditions
which limit the availability of oxygen and other reactive, particularly
oxidizing, species. It has been found that such conditions allow for the
inactivation of even recalcitrant viral particles without substantial
degradation of the antigenic characteristics of those particles. Thus, viruses
which have heretofore been resistant to furocoumarin-inactivation may now be
inactivated without loss of the desired immunogenicity, and viruses which have
previously been successfully inactivated may now be inactivated under
conditions which better preserve their antigenic characteristics, making them
more efficient immunogenic substances for use in vaccines.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

According to the present invention, vaccines useful for the inoculation of
mammalian hosts, including both animals and humans, against viral infection are
provided. The vaccines are prepared by inactivation of live virus in an
inactivation medium containing an amount of an inactivating furocoumarin
sufficient to inactivate the virus upon subsequent irradiation with long
wavelength ultraviolet radiation. Degradation of the antigenic characteristics
of the live virus is reduced or eliminated by limiting the availability of
oxygen and other oxidizing species in the inactivation medium. Suitable
vaccines may be prepared by combining the inactivated viruses with a
physiologically-acceptable carrier, typically an adjuvant, in an appropriate
amount to elicit an immune response, e.g., the production of serum neutral-
<PAGE> 53
5,106,619

izing antibodies, upon subsequent inoculation of the host.

The present invention is suitable for producing vaccines to a wide variety
of viruses, including human viruses and animal viruses, such as canine, feline,
bovine, porcine, equine, and ovine viruses. The method is suitable for
inactivating double stranded DNA viruses, single-stranded DNA viruses,
double-stranded RNA viruses, and single-stranded RNA viruses, including both
enveloped and non-enveloped viruses. The following list is representative of
those viruses which may be inactivated by the method of the present invention.

- --------------------------------------------------------------------------------
Viruses which may be inactivated
---------------------------------------------
Representative Viruses
- --------------------------------------------------------------------------------
dsDNA
-----
Adenoviruses Adenovirus, canine adenovirus 2
Herpesviruses Herpes simplex viruses,
Feline Herpes I
Papovaviruses Polyoma, Papilloma
Poxviruses Vaccinia

ssDNA
-----
Parvovirus Canine parvovirus, Feline
panleukopenia

dsRNA
-----
Orbiviruses Bluetongue virus
Reoviruses Reovirus

ssRNA
-----
Calicivirus Feline calicivirus
Coronavirus Feline infectious peritonitis
Myxovirus Influenza virus
Paramyxovirus Measles virus, Mumps virus,
Newcastle disease virus,
Canine distemper virus,
Canine parainfluenza 2 virus
Picornavirus Polio virus, Foot and mouth
disease virus
Retrovirus Feline leukemia virus, Human
T-cell lymphoma virus, types
I, II and III
Rhabdovirus Vesicular stomatitis virus,
rabies
Togavirus Yellow fever virus, Sindbis
virus, Encephalitis virus
- --------------------------------------------------------------------------------

In preparing the subject vaccines, sufficient amounts of the virus to be
inactivated may be obtained by growing seed virus in a suitable mammalian cell
culture. Seed virus, in turn, may be obtained by isolation from an infected
host. Suitable mammalian cell cultures include primary or secondary cultures
derived from mammalian tissues or established cell lines such as Vero cells,
monkey kidney cells, BHK21 hamster cells, LMTK- cells, and other cells
permissive for the desired virus and which may be grown in vitro as monolayer or
suspension cultures. The cell cultures are grown to approximately 80% saturation
density, and infected with the virus at a low multiplicity of infection (MOI),
usually between about 0.05 and 0.005, preferably at about 0.01.

After adsorbing the viral inoculum to the cells by incubation for a limited
period of time at a temperature in the range from 35 degrees C. to 40 degrees
C., an appropriate growth or maintenance medium is added. The cells are further
incubated at about the same temperature, in the presence of about 5% carbon
dioxide in air, until a sufficient amount of virus has been produced.

The furocoumarins useful for inactivation are primarily illustrated by the
class of compounds referred to as psoralens, including psoralen and substituted
psoralens where the substituents may be alkyl, particularly having from one to
three carbon atoms, e.g., methyl; alkoxy, particularly having from one to three
carbon atoms, e.g., methoxy; and substituted alkyl having from one to six, more
usually from one to three carbon atoms and from one to two heteroatoms, which
may be oxy, particularly hydroxy or alkoxy having from one to three carbon
atoms, e.g., hydroxy methyl and methoxy methyl, or amino, including mono- and
dialkyl amino or aminoalkyl, having a total of from zero to six carbon atoms,
e.g., aminomethyl. There will be from 1 to 5, usually from 2 to 4 substituents,
which will normally be at the 4, 5, 8, 4' and 5' positions, particularly at the
4' position. Illustrative compounds include 5-methoxypsoralen; 8-methoxypsoralen
(8-MOP); 4,5',8-trimethylpsoralen (TMP); 4'-hydroxymethyl-4,5',8-trimethyl-
psoralen (HMT); 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT); 4-methylpsoralen;
4,4'-dimethylpsoralen; 4,5'-dimethylpsoralen; 4',8-dimethylpsoralen; and
4'-methoxymethyl-4,5',8-trimethylpsoralen. Of particular interest are AMT and
8-MOP.

The furocoumarins may be used individually or in combination. Each of the
furocoumarins may be present in amounts ranging from about 0.01 (greek mu)/ml to
1 mg/ml, preferably from about 0.5 (greek mu)/ml to 100 (greek mu)/ml, there not
being less than about 1 (greek mu)/ml nor more than about 1 mg/ml or
furocoumarins.

In carrying out the invention the furocoumarin(s), in an appropriate
solvent which is substantially inert and sufficiently non-polar to allow for
dissolution of the furocoumarin(s), are combined with the viral suspension,
conveniently a viral suspension in an aqueous buffered medium, such as used for
storage. The amount of virus will generally be about 1 x 10(6) to 10(11), more
usually about 1 x 10(7) to 10(9) and preferably about 1 x 10(8) to 5 x 10(8)
pfu/ml. The furocoumarin(s) will be at a concentration of about 0.001 mg/ml to
0.5 mg/ml, more usually about 0.05 mg/ml to 0.2 mg/ml. The amount of solvent
which is usually to dissolve the furocoumarin will be sufficiently small so as
to readily dissolve in the aqueous viral suspension.

Although viral inactivation according to the present invention will
normally be carried out in an inactivation medium as just described, in some
cases it may be desirable to introduce furocoumarins to the virus by addition to
a cell culture medium in which the virus is grown. The inactivation is then
carried out by separating the live viral particles from the culture medium, and
exposure of the particles to ultraviolet light in an inactivation medium which
may or may not contain additional furocoumarins. This method of inactivation is
useful
<PAGE> 54

5,106,619

where the virus is resistant to inactivation when the furocoumarin is added to
the inactivation medium only.

When employing furocoumarins with limited aqueous solubility, typically
below about 50 (greek mu)g/ml, it has been found useful to add an organic
solvent, such as dimethyl sulfoxide (DMSO) ethanol, glycerol, polyethylene
glycol (PEG) or polypropylene glycol, to the aqueous treatment solution. Such
furocoumarins having limited solubility include 8-MOP, TMP, and psoralen. By
adding small amounts of such organic solvents to the aqueous composition,
typically in the range of about 1 to 25% by weight, more typically from about 2
to 10% by weight, the solubility of the furocoumarin can be increased to about
200 (greek mu)g/ml, or higher. Such increased furocoumarin concentration may
permit the use of shorter irradiation times. Also, inactivation of particularly
recalcitrant microorganisms may be facilitated without having to increase the
length or intensity of ultraviolet exposure, and the addition of an organic
solvent may be necessary for inactivation of some viruses with particular
furocoumarins. The ability to employ less rigorous inactivation conditions is of
great benefit in preserving the antigenicity of the virus during inactivation.

The furocoumarin may be added to the viral suspension in a single addition
or in multiple additions, where the virus is irradiated between additions, or
may be added continuously during the entire treatment period, or a portion
thereof. Usually, the number of additions will be from about 1 to 50, more
usually from about 10 to 40, and preferably from about 2 to 4. The total amount
of furocoumarin which will be added will be sufficient to provide a
concentration of at least about 0.01 mg/ml to about 1 mg/ml, usually not more
than about 0.75 mg/ml and preferably not more than about 0.5 mg/ml. Since a
substantial proportion of the furocoumarin will have reacted with the nucleic
acid between additions, the total concentration of furocoumarin in solution will
generally not exceed about 0.1 mg/ml. In cases where the furocoumarin(s)
employed are particularly unstable, it may be beneficial to add the furocoumarin
solution continuously during the irradiation procedure.

In order to preserve the antigenic characteristics of the virus,
irradiation is carried out in the substantial absence of oxygen and other
oxidizing species. This is particularly important when employing psoralens that
generate more singlet oxygen on a molar basis. For example, AMT generates more
singlet oxygen than 8-MOP. Conveniently, oxygen and other gases may be removed
from the inactivation medium by maintaining the medium in a non-oxidizing gas
atmosphere, e.g., hydrogen, nigrogen, argon, helium, neon, carbon dioxide, and
the like. The inactivation medium may be held in an enclosed vessel, and the
space above the liquid medium surface filled with the non-oxidizing gas.
Oxidizing species initially in the medium will be exchanged for the
non-oxidizing gases according to gas-liquid equilibrium principles. Preferably,
the space above the inac-

tivation medium will be flushed with non-oxidizing gas to remove the oxidizing
species and further lower their equilibrium concentration in the liquid medium.
Depending on the volume of the inactivation medium, the flushing should be
continued for at least 1 minute, preferably at least 2 minutes, usually being in
the range from about 3 to 30 minutes. Flushing may be continued during the
irradiation period, but need not be so long as the oxidizing species have been
substantially removed and the vessel remains sealed to prevent the intrusion of
air. Optionally, a singlet oxygen scavenger may be added to the inactivation
medium prior to irradiation to further prevent interaction of oxygen with the
furocoumarin and the virus. Suitable oxygen scavengers include ascorbic acid,
dithioerythritol, sodium thionate, glutathione, and the like. The scavenger will
be present at a concentration sufficient to block active oxygen species, usually
being between 0.001M and 0.5M, more usually being between about 0.005M and
0.02M, where the addition may be single, multiple, or continuous additions.

The concentration of dissolved oxygen may be reduced through the use of
enzyme systems, either in solution or immobilized on a solid substrate.
Suitable enzyme systems include glucose oxidase or catalase in the presence of
glucose and ascorbic acid catalase in the presence of ascorbate. Such enzyme
system may be employed alone or together with the other methods for oxygen
reduction discussed above.

The total time for the irradiation will vary depending upon the light
intensity, the concentration of the furocoumarin, the concentration of the
virus, and the manner of irradiation of the virus, where the intensity of the
irradiation may vary in the medium. The time of irradiation necessary for
inactivation will be inversely proportional to the light intensity. The total
time will usually be at least about 2 hrs. and not more than about 60 hrs.,
generally ranging from about 10 hrs. to 50 hrs. The times between additions of
furocoumarin, where the furocoumarin is added incrementally, will generally
vary from about 1 hour to 24 hrs., more usually from about 2 hrs. to 20 hrs.

The light which is employed will generally have a wavelength in the range
from about 300 nm to 400 nm. Usually, an ultraviolet light source will be
employed together with a filter for removing UVB light. The intensity will
generally range from about 0.1 mW/cm(2) to about 5 W/cm(2), although in some
cases, it may be much higher.

natively, one could use affinity methods for one or more of the low molecular
weight materials to be removed.

The inactivated virus may then be formulated in a variety of ways for use
as a vaccine. The concentration of the virus will generally be from about 10(6)
to 10(9) pfu/ml, as determined prior to inactivation, with a total dosage of at
least 10(5) pfu/dose, usually at least 10(6) pfu/dose, preferably at least
10(7) pfu/dose. The total dosage will usually be at or near about 10(9)
pfu/dose, more usually being about 10(8) pfu/dose. The vaccine may include
cells or may be cell-free. It may be an inert physiologically acceptable
medium, such as ionized water, phosphate-buffered saline, saline, or the like,
or may be administered in combination with a physiologically acceptable
immunologic adjuvant, including but not limited to mineral oils, vegetable
oils, mineral salts and immunopotentiators, such as muramyl dipeptide. The
vaccine may be administered subcutaneously, intramuscularly, intraperitoneally,
orally, or nasally. Usually, a specific dosage at a specific site will range
from about 0.1 ml to 4 ml, where the total dosage will range from about 0.5 ml
to 8 ml. The number of injections and their temporal spacing may be highly
variable, but usually 1 to 3 injections at 1, 2 or 3 week intervals are
effective.

The following examples are offered by way of illustration, not by way of
limitation.

EXPERIMENTAL

Materials and Methods

A. Virus Growth and Tissue Culture

Hamster cells [BHK-21(C-13), American Type Culture Collection (ATCC), CCL
10] were grown as monolayers in plastic cell culture vessels in Eagle's Minimum
Essential Medium (MEM) with Earle's salts and non-essential amino acids (MEN)
supplemented with 10% heat inactivated calf serum (C(i)) and 10% tryptose
phosphate broth (Tp, e.g., Difco 0060). Cell cultures were used to produce live
vesicular stomatitis virus, New Jersey serotype (VSV-NJ) from master seed virus
originally obtained from the ATCC (VR-159), and live bluetongue virus (BTV) from
master seed virus originally obtained from Dr. T. L. Barber, USDA, Denver, Colo.
Cells were grown in culture vessels to 80% to 100% confluency (approximately 2 x
10(5) cells per cm(2) of growth surface area) using standard mammalian cell
culture techniques. Corning plastic roller bottles (Corning No. 25140-850) with
a growth surface area of 850 cm(2) containing 100 ml of MEN supplemented with
10% C(i) and 10% Tp and 1x10(8) to 2x10(8) CCL 10 cells/bottle were used for
virus production. The cell cultures were initiated by seeding approximately
1x10(6) to 5x10(7) cells into 100 mls of growth medium in a roller bottle
containing 5% CO(2) in air on a roller bottle rotator at 1 to 5 rpm at 35
degrees C. to 38 degrees C. The cultures were grown to 80% to 100% confluency
over a six to fourteen day period with a medium change every two to four days.

containing 10% YELP supplement (v/v) for VSV, or 10% C(i) and 10% Tp for
BTV, was added per roller bottle. YELP supplement contains: yeast extract BBL
11929, 5 g/liter; lactalbumin hydrolysate GIBCO 670-1800, 25 g/liter; and
Bacto-Peptone (Difco 0118), 50 g/liter. The post-infection incubation was
carried out at 35 degrees C. to 38 degrees C. in 5% CO(2)/95% air with rotation.
Sixteen to forty-eight hours post-infection, VSV cytopathic effect (CPE) was
evident, while BTV CPE became apparent from 2 to 4 days post infection.

The CPE was characterized by cell rounding, cell detachment, and cell
degeneration. When visual or microscopic examination indicated that at least
50% of the cell monolayer exhibited CPE, the contents of the roller bottle were
swirled to remove loosely attached materials from the roller bottle walls. The
harvest material was decanted from the roller bottles into centrifuge bottles.
The crude VSV harvest was clarified by centrifugation at 500 to 1000 x g for 20
minutes, at 4 degrees C. The BTV harvest was centrifuged at 2,000xg for 60
minutes at 4 degrees C.

The clarified VSV preparations were concentrated by ultrafiltration using
a Pellicon cassette system (Millipore XX42ASY60) with a cassette having a
nominal exclusion limit of 10(5) daltons (Millipore PTHK 000C5). The Pellicon
cassette system was sterilized by filling the assembled unit with 1N NaOH and
incubating the unit 12 to 24 hours at room temperature. The NaOH solution was
pumped out of the cassette system and the system was flushed with two to four
liters of sterile H(2)O. The assembly and operation of the Pellicon system were
in accordance with the instructions furnished by the manufacturer. All steps in
the concentration were performed aseptically. The clarified VSV was
concentrated 15 to 40 fold, dimethylsulfoxide (Sigma D-5879) added to a final
concentration of 7.5% v/v, and suitable aliquots of the virus stored frozen at
- -80 degrees C. to -100 degrees C.

For BTV, the pellet resulting from centrifugation was resuspended
aseptically in 8 ml of 2 mM Tris-HCl, pH 8.8, for each original roller bottle.
The suspension was mixed vigorously on a vortex mixer, and/or sonicated at 4
degrees C. for 1 min., and centrifuged at 1,400 x g for 30 min. at 4 degrees C.
The virus-containing supernatant was collected and the pellet was extracted
twice more with 8 ml/roller bottle aliquots of 2 mM Tris-HCl, 8.8. The
virus-containing supernatants were pooled and clarified by centrifugation at
4,000 x g for 30 min. at 4 degrees C. The clarified supernatant was stored at 4
degrees C.

Feline herpes I virus (FVR, the infective agent of feline viral
rhinotracheitis) was grown as follows.

Cat cell lines AKD (ATCC CCL150) or Fc3Tg (ATCC CCL176) were grown as
monolayers in plastic cell culture vessels in a standard defined culture medium
consisting of MEN; F12K; MEM; or alpha MEM. Medium was supplemented with 2% to
15% inactivated fetal calf serum (F(i)) or 2% to 20% YELP. Cell cultures were
used to produce live Feline Herpes I virus from master seed virus derived from
Feline Herpes I virus (ATCC VR636). Cells were grown in culture vessels to 80%
to 100% confluency (approximately 1x10(5) to 2x10(5) cells per cm2 of growth
surface area) using standard mammalian cell culture techniques as follows.

Corning plastic roller bottles containing 50 to 100 ml of MEN supplemented
with 10% F(i) and 1x10(8) to 2x10(8) AKD or Fc3Tg cells/bottles were used for
Feline Herpes I virus production. The cell cultures were
<PAGE> 56
5,106,619

initiated by seeding approximately 1 x 10(6) to 5 x 10(6) cells into 50 to 100
mls of growth medium in a roller bottle containing about 5% CO(2) in air and
incubating the roller bottle on a roller bottle rotator at 1 to 5 rpm at 35
degrees C. to 38 degrees C. The cultures were grown to 80% to 100% confluency
over a 7 to 14 day period with a 100% medium change every 3 to 5 days.

When the monolayers were 80% to 100% confluent, the culture medium was
removed and the monolayer was washed with 20 to 50 mls of phosphate buffered
saline (PBS) pH 7.2 to 7.4 (NaCl 8 g + KCl 0.2 g + Na(2)HPO(4) 1.14 g +
KH(2)PO(4)0.2 g). The PBS wash was discarded, and the roller bottle was infected
by the addition of approximately 1 x 10(7) to 2 x 10(7) plaque forming units
(pfu) of Feline Herpes I virus in 10 mls of PBS containing 2% F(i). The
multiplicity of infection (MOI) was approximately 0.1. The virus inoculum wase
adsorbed to the cells by incubation at 35 degrees C. to 38 degrees C. for one
hour at 1 to 5 rpm. The inoculation fluid was removed and 50 mls of MEN
containing 10% F(i) was added per roller bottle. The post-infection incubation
was at 35 degrees C. to 38 degrees C. in 5% CO(2) in air with rotation. Herpes
virus cytopathic effect (CPE) was evident forty to forty-eight hours
post-infection. The CPE was characterized by cell rounding, cell detachment,
and cell degeneration.

The contents of the roller bottle were swirled 48 hours post-infection to
remove loosely attached materials from the roller bottle walls, and the
contents of the roller bottles were decanted into centrifuge bottles. The
virus, cells, and cell debris were pelleted by centrifugation at 10,000 x g for
30 minutes.

Cell associated (CA) Feline Herpes I virus was prepared by:

1. resuspending the 10,000 x g pellet in approximately 5 ml of a
resuspension medium containing 80 parts F12K, 10 parts F(i), and 10 parts
dimethylsulfoxide (DMSO) for each original roller bottle;

2. freezing the resuspended CA virus at -20 degrees C. for 1.5 to 2 hours;
and

3. transferring the CA virus frozen at -20 degrees C. to temperatures
ranging from -80 degrees C. to -100 degrees C.

Cell free (CF) Feline Herpes I virus was prepared by:

1. resuspending the 10,000 x g pellet in F12K;

2. freezing and thawing the resuspended material 3 times;

3. clarifying the freeze-thawed material by centrifugation at 10,000 x g
for 30 minutes; and

4. freezing the clarified supernatant (CF virus) at temperatures ranging
from -80 degrees C. to -100 degrees C.

CF or CA virus was thawed by gentle agitation at 37 degrees C. in a water
bath.

B. Virus Assay

Confluent monolayers of LMTK-, Vero (ATCC CCL 81), Fc3Tg, or AKD cells were
prepared in 6 cm diameter mammalian cell culture plastic petri dishes (Corning
#25010) or other convenient cell culture vessels. The growth medium used for
LMTK- cells was alpha ME (alpha modified Eagles Minimum Essential Medium,
Earle's Salts) + 10% F(i). The growth medium used for Vero cells was MEN + 5%
F(i). The growth medium used for Fc3Tg cells was MEN + 10% F(i), and the growth
medium used for AKD cells was F12K + 15% F(i) (VSV and BTV were titered on LMTK-
or Vero cells. Feline Herpes I was titered on Fc3Tg or AKD cells). Ten fold
serial dilutions of virus samples were made by adding 0.5 ml of the virus sample

to 4.5 mls of diluent (phosphate buffered saline, pH 7.2 to 7.4, plus 2% F(i))
in a screw cap tube. The growth medium was removed from a 6 cm culture dish cell
monolayer, 0.1 ml of virus sample (undiluted or diluted) was added, and the
virus was adsorbed to the monolayer for 1 to 2 hours at 35 degrees C. to 38
degrees C. Two or more monolayers were used for each sample.

Five ml of overlay medium was added per 6 cm culture dish, except for
Feline Herpes I, where the unadsorbed inoculum was removed, and 4 mls of
overlay medium was added per 6 cm culture dish. The overlay medium for BTV or
VSV was prepared by mixing equal parts of solution A (100 ml 2X MEM with
L-glutamine, GIBCO #320-1935, + 10 ml F(i)) and 1.8% to 2% Noble Agar (Difco
0142) in deionized H(2)O at 44 degrees C. to 45 degrees C. The overlay medium
for Feline Herpes I was prepared by mixing equal parts solution A and 1% methyl
cellulose (4,000 centriposes) in deionized H(2)O (Fisher M-281 sterilized by
autoclaving).

The virus infected cultures were incubated at 35 degrees C. to 38 degrees
C. in 5% CO(2) in air. Twenty-four hours before plaques were counted, a second
overlay containing Neutral Red at a final concentration of 0.005% was added.
Plaques were counted on day 2 or day 3 post-infection for VSV, on day 2 to 4
for FVR and on day 6 or 7 for BTV. The virus titer in pfu/ml was calculated by
multiplying the average number of plaques per dish by the reciprocal of the
dilution. The pfu/ml was the value used to determine the amount of virus needed
to infect cells at a MOI of approximately 0.01. The pfu/ml in a virus
preparation prior to inactivation was used to determine the immunizing dose.

C. Virus Inactivation

1. VSV Inactivation

The thawed stock of VSV was pipetted into sterile T-150 tissue culture
flasks (nominally 25 ml into each of four flasks). To each flask was added 0.25
ml of 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT) stock solution (stock
solution is 1 mg/ml AMT dissolved in sterile, deionized water). Each flask was
allowed to equilibrate in an argon atmosphere for at least 10 minutes. After
equilibration, a stream of argon gas was directed into each flask for at least
two minutes. The flasks were then tightly capped and placed under a long
wavelength ultraviolet (320 nm to 400 nm) light source (GE BLB fluorescent
bulbs) at a temperature between 0 degrees C. and 20 degrees C. for
approximately 11 hours. The incident light intensity was approximately 1
mW/cm(2) (measured by a J-221 long wavelength UV meter).

After the irradiation was completed, the flasks were removed from the light
source and an additional 0.25 ml of AMT stock solution was mixed into each
flask. The contents of each flask were pipetted into new, sterile T-150 flasks,
and the flasks were again flushed with argon and irradiated for an additional 11
hours. This procedure was repeated three more times until five additions (a
total of approx. 50 (greek mu) g/ml of AMT had been performed, the virus sample
had been irradiated for at least 55 hours, and at least four flask changed has
been performed.

After all of the irradiations had been completed, the contents of the
flasks were aseptically transferred to a common sterile container and stored at
- -85 degrees C.

2. BTV Inactivation

Twenty-five ml of BTV serotype 11 (1.5x10(8) pfu/ml) was mixed with 0.25
ml of 4'-aminomethyl 4,5',8-trimethylpsoralen (AMT; 1 mg/ml in DMSO).
<PAGE> 57
5,106,619

The mixture was placed in a 150 cm(2) tissue culture flask (T-150; Corning
#251201). The viral suspension in the flask was placed in an argon atmosphere
for 10 min., and a stream of argon gas was then blown over the viral suspension
for an additional 2 min. The flask was tightly capped and the suspension
irradiated for 3.25 hrs. at 4 degrees C. using GE BLB fluorescent bulbs at an
intensity of 1.5 mW/cm(2). An additional 0.25 ml of AMT was then added to the
viral suspension, the suspension transferred by pipette to a new T-150 flask,
and the solution again flushed with argon. The flask was irradiated for an
additional 14.75 hours at 4 degrees C. under the same long wavelength UV light
source. After this irradiation an additional 0.25 ml of AMT solution was added
to the suspension, and it was again transferred to a new T-150 flask. The
solution was flushed with argon as before and irradiated for an additional 5.5
hrs. at 4 degrees C. The inactivated BTV was stored at 4 degrees C.

3. Feline Herpes I Inactivation

a. Cell Free Virus

Nineteen mls of CF-FVR (1.9 x 10(7) pfu/ml) were mixed with 0.4 ml of
hydroxymethyltrioxsalen (HMT; 1 mg/ml in DMSO) and 1.9 ml of sodium ascorbate
(0.1M in H(2)O). The mixture was prepared in 150 cm(2) tissue culture flasks
(T-150, Corning No. 25120) that were subsequently deaerated for 2 minutes with
pure argon gas. The virus-containing flasks were irradiated for 55 minutes at 4
degrees C. using G.E. BLB fluorescent bulbs at an intensity of 1.5 mW/cm(2). The
FVR/HMT/ascorbate mixture was then transferred by pipet into a second T-150
flask, which was deaerated for 2 minutes using pure argon gas. The second T-150
flask was irradiated for an additional 28 minutes at 4 degrees C. under the same
long wavelength UV light source.

The CF-FVR preparation was stored at -100 degrees C. in a REVCO freezer.
Subsequently the CF-FVR preparation was thawed and placed into a T-150 flask.
The flask was deaerated with pure argon gas for 2 minutes and irradiation was
continued as described above for an additional 15 hours and 40 minutes.

b. Cell Associated Virus

Cells from 10 roller bottles (about 1 x 10(8) to 2 x 10(8) cells/roller
bottle) were resuspended in 28 mls of cell culture media. Twenty mls of the
suspension were placed into a T-150 flask. To this flask was added 2 ml of
freshly prepared sterile 0.1M sodium ascorbate and 0.4 ml HMT (1 mg/ml in
DMSO). The flask was deaerated with pure argon gas for 2 minutes, and the flask
was irradiated at 4 degrees C. using G.E. BLB fluorescent bulbs at an
intensity of 1.5 mW/cm(2) for 75 minutes. The viral suspension was then
transferred by pipet from the T-150 flask into a second T-150 flask and again
deaerated with pure argon gas for 2 minutes. Irradiation was continued for an
additional 95 minutes. The CA-FVR preparation was adjusted to 10% DMSO and the
suspension was frozen at -20 degrees C. for 1 hour and then stored at -100
degrees C. in a REVCO freezer.

The stored frozen CA-FVR preparation was subsequently thawed, and the
cells were pelleted in a clinical centrifuge. The cells were resuspended in 21
mls of serum-free medium to which 2.1 mls of freshly prepared 0.1M sodium
ascorbate and 0.4 ml of HMT (1 mg/ml in DMSO) were added. The sample was
transferred by pipet to a T-150 flask, and irradiation was continued for an
additional 15 hours and 40 minutes.

Results

A. Bluetongue Virus

1. Assessment of Inactivation by Blind Passage

CCL 10 cells were grown to confluency in 850 cm(2) roller bottles using
standard cell culture procedures, as described above. The culture medium was
removed from the roller bottle, and 2.0 ml of the inactivated virus preparation
mixed with 18 ml of medium containing 2% F(i) was adsorbed to the roller bottle
cell monolayer for 60 min. at 35 degrees C. to 38 degrees C. with rotation at 1
to 5 rpm. After adsorption, the residual unabsorbed inoculum was removed, and
100 ml of growth medium (MEN with 10% C(i) and 10% Tp) was added and the roller
bottle culture incubated at 35 degrees C. to 38 degrees C. for 7 days with
daily observation for viral CPE. The roller bottle culture received a 100%
medium change every 2 to 3 days. If no CPE was observed during the first roller
bottle passage, the cell monolayer was chilled at 4 degrees C. for 12 to 24
hrs. The cells were scraped into the medium which was then decanted into a
centrifuge bottle. The cells were pelleted by centrifugation at 4 degrees C. at
2,000 x g for 30 min. and resuspended in 2.0 ml or 2 mM Tris-HCl (pH 8.8) by
vigorous mixing using a vortex mixer. The resuspended material was centrifuged
at 2,000 x g for 20 min. at 4 degrees C. The supernatant was added to 18 ml of
growth medium containing 2% F(i) and used to infect a new confluent roller
bottle culture of CCL 10 cells, as described immediately above. The second
roller bottle blind passage was observed for 7 days and fed every 2 to 3 days.
If no CPE was observed during the second roller bottle blind passage, a third
roller bottle blind passage was performed. If no CPE had been observed by the
end of the third roller bottle blind passage the virus preparation was
considered inactivated and suitable for in vivo testing.

2. Immunization of Rabbits with Psoralen-inactivated BTV Vaccine

a. Example 1

gel precipitation (Jochim et al., Am. Assoc. Vet. Lab. Diag., 22nd Proceed.:
463-471, 1979). Pre-immunization rabbit serum was used as the negative control;
BTV immune sheep serum was used as the positive control for both immunologic
procedures.

<TABLE>
<CAPTION>
TABLE 1
- --------------------------------------------------------------
Serum Neutralization Data From Rabbits
Vaccinated with AMT-UVA inactivated
Bluetongue Virus Vaccines.
---------------------------------------
Titer*
-------------------------------------
Group 1 5 40
- ----- ------ ------ ------
<S> <C> <C> <C>
A + + +
B + + +
Normal Rabbit Serum - - -
BTV-Immune Sheep Serum + + + -
- --------------------------------------------------------------
*Reciprocal of serum dilution neutralizing 80 percent of BTV plaque activity on
BHK cells. The data are from the post-second immunization serum samples.

</TABLE>

Of the two immunologic procedures utilized, serum neutralization is
considered predictive for immunity to live BTV challenge in the target species.

b. Example 2

Twelve New Zealand white rabbits were randomly assigned to six groups,
A-F, two rabbits per group. An additional four rabbits were assigned to Group
G. These sixteen rabbits were vaccinated twice subcutaneously with the AMT-UVA
inactivated Bluetongue virus vaccines described in Table 2. Preinactivation
titer was approximately 10(8) for each serotype. The vaccines were formulated
with 20% (v/v) aluminum hydroxide adjuvant, and were given with a three week
interval between the first and second inoculations.

The sixteen rabbits were bled by auricular venipuncture on days 0, 14, and
35. Each serum was heat-inactivated and tested against BTV serotypes 10, 11, 13
and 17 for serum neutralizing antibody. All vaccinated rabbits developed SN
titers against the homologous vaccine serotypes (Table 3). These data
demonstrated the immunopotency of a multivalent AMT-UVA inactivated Bluetongue
virus vaccine.

<TABLE>
<CAPTION>
TABLE 2
---------------------------------------
Serotype Composition of Inactivated Bluetongue
Virus Vaccines Tested in Rabbits
---------------------------------------
BTV Serotype
Group Rabbit# Composition
- ------- --------- --------------
<S> <C> <C>
A 1,2 10
B 3,4 11
C 5,6 13
D 7,8 17
E 9,10 11,17
F 11,12 10,11,17
G 13,14,15,16 10,11,13,17
- ------------------------------------------------
</TABLE>

<TABLE>
<CAPTION>
TABLE 3
- ---------------------------------------------------
Serum Neutralizing Data
From Rabbits Vaccinated with AMT-UVA Single and
Multi-Serotype Bluetongue Virus Vaccines
- ---------------------------------------------------
SN Titer* Against:
---------------------------------------
Group Rabbit BTV-10 BTV-11 BTV-13 BTV-17
- ----- ------- ------ ------ ------ ------
<S> <C> <C> <C> <C> <C>
1 1:160 1:10 1:10 1:10
A 2 1:320 1:10 1:10 1:10
3 1:10 1:320 1:10 1:10
B 4 1:10 1:80 1:10 1:10
5 1:20 1:20 1:160 1:10
C 6 1:20 1:10 1:40 1:10
7 1:10 1:10 1:10 1:320
D 8 1:10 1:10 1:10 1:320
9 1:20 1:160 1:20 1:160
E 10 1:20 1:160 1:20 1:160
11 1:160 1:160 1:20 1:160
F 12 1:40 1:40 1:20 1:80
13 1:160 1:160 1:80 1:160
14 1:160 1:160 1:80 1:160
G 15 1:160 1:160 1:40 1:160
16 1:80 1:160 1:160 1:160
- ---------------------------------------------------
*Reciprocal of serum dilution neutralizing 80% of
BTV plaque activity on Vero cells. The data are from
the post-second immunization sera (Day 35). Negative
and positive control sera behaved as expected in
the SN assay.
</TABLE>

3. Immunization of Sheep with Psoralen-inactivated BTV vaccine.

a. Example 1

Each of two adult sheep, known to be susceptible to BTV, was inoculated
subcutaneously (SQ) with 2 ml of AMT-UVA inactivated BTV plus adjuvant (1:1,
vaccine to aluminum hydroxide adjuvant). The vaccine contained approximately
10(8) pfu/ml of BTV prior to inactivation. A third sheep was inoculated SQ with
6 ml of the identical vaccine without adjuvant. Seven weeks later the three
sheep were given identical inoculations SQ that consisted of 5 ml of vaccine and
aluminum hydroxide adjuvant (2:1 vaccine to adjuvant; 10(8) pfu BTV/ml of
vaccine).

The first vaccine inoculations induced precipitating anti-BTV antibody in
all three sheep. Their pre-exposure sera were uniformly negative for anti-BTV
precipitating antibody. Modest neutralizing anti-BTV anti-body titers (1:5) were
elicited in two of three sheep following one immunization. The second
immunization elicited a distinct immunological anamnesic response, inducing
neutralizing titers of 1:40, 1:80, or 1:160 in the three sheep.

<TABLE>
<CAPTION>
TABLE 4
- --------------------------------------------------------------
Serum Neutralization Data From Sheep
Immunized with an AMT-UVA Inactivated BTV Vaccine
- --------------------------------------------------------------
Titers*
Sheep No.:
-------------------------------------
Group 1 2 3
- ----- ------ ------ ------
<S> <C> <C> <C>
Pre-First Immunization
Day 0 <5 <5 <5

Post-First Immunization
Day 21 5 5 <5

Post-Second Immunization
</TABLE>
<PAGE> 59
5,106,619

<TABLE>
<CAPTION>
TABLE 4 - continued
- --------------------------------------------------------------------------------
Serum Neutralization Data From Sheep Immunized
with an AMT-UVA Inactivated BTV Vaccine.
----------------------------------------------
TITERS*
Sheep No.:
-----------------------------------------
1 2 3
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
Day 7 80 160 40
Day 14 80 40 40
Day 21 80 80 40
Day 42 80 80 80
Post-Challenge
Day 7 160 160 80
Day 14 320 160 80
- --------------------------------------------------------------------------------
*Reciprocal of highest 2-fold dilution reducing BTV plaque activity on BHK
cells by 80 percent.
</TABLE>

The sheep were challenged by SQ syringe inoculation of 10(5) egg lethal doses
of BTV serotype 11. The three sheep remained clinically normal during the BTV
challenge period, indicating that the vaccine was efficaceous.

b. Example 2

Eight experimental and four control sheep, known to be Bluetongue Virus
susceptible, were housed together in an insect-proof facility. The experimental
sheep were inoculated twice subcutaneously with AMT-UVA inactivated BTV
Serotype 11 vaccine. Each vaccinate received approximately 3 x 10(8) pfu BTV-11
formulated with twenty-five percent (v/v) aluminum hydroxide adjuvant. Three
weeks elapsed between immunizations. Control sheep were inoculated with tissue
culture fluid in 25% percent (v/v) aluminum hydroxide. Serum samples were
collected prior to vaccination, following vaccinations, and following
challenge, and tested for SN antibodies. All sheep were challenged by
subcutaneous inoculation of 2 x 10(5) ELD(50) BTV-11 four weeks post-second
vaccination. Virus isolation was performed twice weekly post-challenge for six
weeks. Virus isolation from sheep blood was done by intravenous chicken embryo
inoculation, followed by specific BTV serotype identification by neutralization
in vitro.

Five of the eight vaccinated sheep developed SN titers of 1:20 post-second
vaccination. All eight vaccinates resisted subcutaneous challenge with 2 x
10(5) ELD(50) BTV-11, whereas the four control sheep developed uniform viremia
as assessed by egg inoculation. Sheep data are given in Table 5.

<TABLE>
<CAPTION>
TABLE 5
- --------------------------------------------------------------------------------
Serum Neutralization and Virus Isolution Data from Sheep
Vaccinated with AMT-UVA Inactivated BTV-11 Vaccine and
Subsequently Challenged with 2 x 10(5) ELD(50) of Live BTV-11
-------------------------------------------------------------
Virus Isolation
SN Titer Post-Challenge
Sheep Post-Second Post- Day
No. Baseline Vaccination Challenge ---------------
4 11 15 18
- --------------------------------------------------------------------------------
Experi-
mental
- -------
<S> <C> <C> <C> <C> <C> <C> <C>
650 neg 1:20 1:160 -- -- -- --
</TABLE>

<TABLE>
<CAPTION>
TABLE 5 - continued
- --------------------------------------------------------------------------------
Serum Neutralization and Virus Isolution Data from Sheep
Vaccinated with AMT-UVA Inactivated BTV-11 Vaccine and
Subsequently Challenged with 2 x 10(5) ELD(50) of Live BTV-11
-------------------------------------------------------------
Virus Isolation
SN Titer Post-Challenge
Sheep Post-Second Post- Day
No. Baseline Vaccination Challenge ---------------
4 11 15 18
- --------------------------------------------------------------------------------
Experi-
mental
- -------
<S> <C> <C> <C> <C> <C> <C> <C>
651 neg 1:20 1:40 -- -- -- --
652 neg 1:20 1:160 -- -- -- --
653 neg 1:20 1:40 -- -- -- --
656 neg 1:10 1:160 -- -- -- --
658 neg 1:10 1:40 -- -- -- --
659 neg 1:20 1:160 -- -- -- --
660 neg 1:10 1:160 -- -- -- --

Controls
- --------
654 neg neg 1:10 + + + +
655 neg neg neg + + + +
661 neg neg 1:40 + + + +
662 neg neg 1:160 + + + -
- --------------------------------------------------------------------------------
</TABLE>
B. Feline Herpes Virus I

1. Assessment of Inactivation by Blind Passage

Fc3Tg or AKD cells were grown to confluency in 850 cm(2) roller bottles
using standard cell culture procedures as described above. The culture medium
was removed from the roller bottle, and 2.0 mls of the inactivated virus
preparation, mixed with 18 mls of medium containing 2% F(i), were adsorbed to
the roller bottle cell monolayer for 60 minutes at 35 degrees C. to 38 degrees
C. with rotation at 1 to 5 rpm. After adsorption, the inoculum was removed and
150 ml of maintenance medium (MEN or F12K with 2% F(i)) added. The roller bottle
culture was then incubated at 35 degrees C. to 38 degrees C. for 7 days with
daily observation for viral CPE. The roller bottle culture received a 100%
medium change after 3 to 5 days. If no CPE was observed during the first roller
bottle passage, the cell monolayer was scraped into the maintenance medium
which was then decanted into a centrifuge bottle. The cells were pelleted by
centrifugation at room temperature at 1,000 x g for 15 minutes, resuspended in
20 ml of fresh maintenance medium, and passed to a new confluent roller bottle
culture of Fc3Tg or AKD cells as described above. The second roller bottle
blind passage was observed for 7 days and fed once on day 3 to 5. If no CPE was
observed during the second roller bottle blind passage, a third roller bottle
blind passage was performed. If no CPE was observed by the end of the third
roller bottle passage, the virus preparation was considered inactive.

2. Administration Procedure for Psoralen-inactivated FVR Vaccines

Photochemically inactivated FVR was inoculated via syringe into cats by
various routes, including but not limited to intravenously (IV),
subcutaneously (SQ), intramuscularly (IM), or intraperitoneally (IP). The
vaccine was administered in various volumes (0.5 to 3.0 ml) and in various
concentrations (10(6) to 10(8) pfu; either CF, CA or in combination). In the
following examples, the vaccine was administered in combination with aluminum
hydroxide as an immunologic adjuvant. The number of injections and their
temporal spacing was as set forth in each example.

3. Immunization with Psoralen-inactivated CR-FVR Vaccine

The experimental group consisted of four specific pathogen free kittens (2
males, 2 females) four months old (Liberty Laboratories, Liberty Corner, N.J.).
The
<PAGE> 60
5,106,619

17
control group consisting of two similar female kittens. The experimental group
was inoculated IM with 3 x 10(7) pfu (3 mls) of HMT inactivated CF-FVR on days
0 and 21, and again inoculated with 3 x 10(7) pfu HMT inactivated with an equal
amount of 2% aluminum hydroxide [(Al(OH)(3)] adjuvant on day 61. Controls were
vaccinated at eight weeks and at thirteen weeks of age with a commercial FVR
vaccine using the manufacturer's recommended procedure. Serum samples were
collected weekly and tested for anti-FVR neutralizing antibodies.

Following live virus challenge (10(6) pfu intranasally and
intraconjunctivally), a numerical scoring system (Table 6) was used to assess
the clinical response of both experimental and control cats.

<TABLE>
<CAPTION>
TABLE 6

- --------------------------------------------------------------------------------
Scoring System for Clinical
Effects of Herpesvirus Challenge in Cats
----------------------------------------
Factor Degree Score
- --------------------------------------------------------------------------------
<S> <C> <C>
Fever 101 to 102 degrees F. 0
102 to 103 1
103 to 104 3
greater than 104 5
Depression slight 1
moderate 3
severe 5
Sneezing occasional 1
moderate 3
paroxysmal 5
Lacrimation serous 1
mucoid 3
purulent 5
Nasal Discharge serous 1
mucoid 3
purulent 5
Appetite normal; eats all food 0
fair; eats more than 1
1/2 of food
poor; eats less than 3
1/2 of food
none; eats nothing 5
- --------------------------------------------------------------------------------
</TABLE>

Three of four experimental cats developed serum neutralizing anti-FVR
antibody (SN) titers of 1:2 that were detected between day 42 and day 58.
Following the third immunization (day 61), four of four experimental cats had
SN titers of 1:4 (day 80). Baseline SN antibody titers on the experimental
cats were negative. The control cats did not develop detectable SN antibody
titers during the pre-challenge period.

Three of four experimental cats demonstrated mild temperature elevation
and serous ocular or nasal discharge along with mild intermittent depression
and appetite suppression. Their composite scores were 39, 42, and 35
respectively for the 15 day observation period. The fourth experimental cat was
more severely affected (composite score=84) by moderate, but transient,
sneezing and mucoid nasal discharge. Both control cats were severely affected
by live virus challenge. Severe purulent nasal and ocular discharge and lack of
appetite were apparent. The control cats had composite scores of 133 and 253.

cats has an SN antibody titer of 1:4 while the second control lacked an SN
antibody titer against FVR.

4. Immunization with Psoralen-inactivated CA-FVR Vaccine.

Nine age-matched specific pathogen free kittens, 4 months old (Liberty
Laboratories, Liberty Corner, N.J.), were randomly assigned to three
experimental groups designated A, B, and C.

Group A (controls) was inoculated twice with 1 ml tissue culture fluid and
1 ml aluminum hydroxide adjuvant. Group B was inoculated twice with a
commercial FVR vaccine according to the manufacturer's recommendation. Group C
was inoculated three times with 10(7) HMT-inactivated CA-FVR in aluminum
hydroxide (total volume=2 ml; 1:1 vaccine to adjuvant). All injections were
given 1M at three week intervals.

Live FVR virus (10(6) pfu intranasally and intraconjunctivally) was given
on day 63 and a numerical scoring system (Table 6) was used to assess the
kittens' clinical response for a 15 day post-challenge period. Serum samples
were collected from all kittens prior to vaccination, prior to the second and
third immunizations, prior to live FVR challenge, and at 15 days
post-challenge. The sera were utilized to assess neutralizing antibody titers
by standard procedures.

The control kittens (Group A) maintained SN anti-body titers less than 1:2
(negative) throughout the pre-challenged period. Fifteen days following live
FVR challenge Group A kittens uniformly had SN antibody titers of 1:2. Kittens
in Groups B and C lacked detectable anti-FVR antibody titers pre-immunization,
but all kittens in Groups B and C had SN antibody titers of 1:2 or 1:4 after
two immunizations. The third immunization in Group C kittens did not
significantly alter their SN antibody titers. Following a 15 day post-challenge
period, kittens in Groups B and C demonstrated an anamnestic immunologic
response, with SN antibody titers ranging from 1:16 to 1:64.

Clinically, Group A kittens were severely affected by live FVR challenge,
whereas kittens in Groups B and C were significantly protected by their
respective vaccines.

The composite clinical scores for Group A were 125, 141, and 128 for the
15 day post-challenge period. The composite clinical scores for Group B were
25, 20, and 64, while Group C had composite clinical scores of 21, 15, and 34.
The clinical signs evident were characteristic of FVR.

C. Vesicular Stomatitis Virus

1. Assessment of Inactivation by Intracerebral Inoculation of Mice

Sucking mice (0 to 10 days old) were inoculated intracerebrally with 0.02
ml of the psoralen-inactivated VSV-NJ using a tuberculin syringe and a 28 or 30
gauge needle. Each vaccine lot was tested in four to nine suckling mice. The
mice were observed three times daily for a minimum of seven days. Residual
low-level live VSV kills suckling mice in two to five days. The sensitivity of
this assay is approximately 1 to 5 pfu of live VSV per intracerebral dose.
Inactivated VSV-NJ vaccine was considered safe (inactivated) if all inoculated
suckling

<PAGE> 61

5,106,619

mice survived the seven day observation period. The VSV-NJ vaccine batches
used hereinafter each passed the suckling mouse safety test prior to use.

2. Virus Neutralization in Mice Immunized with Psoralen-inactivated
VSV-NJ Vaccine

Groups of ten adult white mice each were injected using three
immunological adjuvants (aluminum hydroxide gel, incomplete Freund's, or oil
emulsion) with one of three psoralen-inactivated VSV-NJ vaccine doses (10(9),
10(8), or 10(7) pfu/dose). The oil emulsion was prepared as described by Stone
et al. (1978) Avian Dis. 22:666-674. All mice were injected IP once each, on
day 0 and day 21. Serum samples were collected from the orbital sinus on day 2
and on day 33 and pooled serum samples were assessed for serum neutralization
(SN) activity by standard procedures. See, Castaneda et al. (1964) Proc. US
Livestock San. Assoc. 68:455-468. Serum samples were negative for neutralizing
antibodies to VSV-NJ prior to vaccination.

The vaccine with oil emulsion adjuvant induced the highest SN titers
after one injection. All three vaccine doses, regardless of adjuvant, induced
SN titers of at least 1:2000 after two injections. Serum dilutions were tested
for SN activity only to 1:2560. The results are set forth in Table 7.

<TABLE>
<CAPTION>
TABLE 7
- -------------------------------------------------------------------------------------------
Virus Neutralization Indices* of Mouse Sera
After One and Two Injections of Psoralen-
Inactivated VSV-NJ Vaccine
-------------------------------------------
Log(10) of Vaccine Con-
centration (pfu/dose)
No. of ---------------------------------------------------------
Adjuvant Injections 7 8 9
- -------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C>
Aluminum hydroxide gel 1 67* 905 905
Aluminum hydroxide gel 2 > 2560 2560 > 2560
Freund's Incomplete 1 226 57 905
Freund's Incomplete 2 2033 > 2560 > 2560
Oil Emulsion 1 > 2560 > 2560 > 2357
Oil Emulsion 2 > 2560 > 2560 > 2560
- -------------------------------------------------------------------------------------------

*Virus neutralization index is the reciprocal of the serum dilutions that
neutralized 32 TCID(50) of VSV-NJ.
</TABLE>

3. Virus Neutralization in Hamsters Vaccinated with Psoralen-inactivated
VSV-NH Vaccine

Groups of five MHA hamsters each were injected with either 10(9), 10(8),
or 10(7) pfu psoralen-inactivated VSV-NJ per dose, with or without aluminum
hydroxide adjuvant (1:1). All hamsters were injected intramuscularly (IM) once
each, on day 0 and again on day 21. Pooled serum samples were collected on day
21 and on day 34 for serum neutralization testing by standard procedures. Serum
neutralizing antibodies were elicited by all three vaccine doses tested, with
or without aluminum hydroxide adjuvant. SN titers are given in Table 8.

TABLE 8
- -------------------------------------------------------------------------------------------
Virus Neutralization Indices* of Hamster
Sera After One and Two Injections of
Psoralen-Inactivated VSV-NJ Vaccine
-------------------------------------------
Log(10) of Vaccine Con-
centration (pfu/dose)
No. of --------------------------------------------------------
Adjuvant Injections 7 8 9
- -------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C>

None 1 134* 134 1076
None 2 1280 1810 > 2560
Aluminum hydroxide gel 1 538 538 > 2560
Aluminum hydroxide gel 2 1810 1920 2560
- -------------------------------------------------------------------------------------------

*Virus neutralization index is the reciprocal of the serum dilution that
neutralized 32 TCID(50) of VSV-NJ.
</TABLE>

4. Live VSV-NJ Challenge of Mice Vaccinated with Psoralen-inactivated
VSV-NJ Vaccine

Three groups of fourteen, sixteen and seventeen adult white mice each were
injected with either 10(7), 10(6) or 10(5) pfu psoralen-inactivated VSV-NJ per
dose, respectively, using oil emulsion adjuvant with all injections. Each mouse
was injected once IP (day 0). Pooled serum samples were collected on day 0 and
again on day 21, and these samples were tested for SN antibody titers by
standard procedures. The results are set forth in Table 9.

TABLE 9
- --------------------------------------------------------------------------------
Virus Neutralization Indices* of Mouse
Sera After One Injection With Psoralen-
Inactivated VSV-NJ Vaccine, Using Oil
Emulsion Adjuvant
-------------------------------------------
Log(10) of Vaccine con-
centration (pfu/dose)
------------------------------------------
Day 5 6 7
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
0 --* -- --
21 -- -- --
- --------------------------------------------------------------------------------

*Virus neutralization index is the reciprocal of the serum dilution that
neutralized 56 TCID(50) of VSV-NJ
</TABLE>

Each group of mice was subdivided into three groups of about five mice
each. Each mouse was challenged with either 1, 10 or 100 minimum lethal doses
(MLD) of live VSV by intracerebral inoculation on day 33.

Two of five mice that were immunized with 10(6) pfu psoralen-inactivated
VSV-NJ survived a one MLD VSV challenge but five of five mice that were
immunized with 10(7) pfu psoralen-inactivated VSV-NJ vaccine survived both a 1
or 10 MLD VSV challenge. One of four mice that were vaccinated at 10(7)
pfu/dose psoralen-inactivated VSV-NJ survived a 100 MLD VSV challenge. The
results (no, dead/no. challenged) are set forth in Table 10.

TABLE 10
- --------------------------------------------------------------------------------
Live VSV-NJ Challenge of Mice Injected with
Psoralen-Inactivated VSV-NJ
-------------------------------------------
Challenge Dilution
Dose Psoralen- --------------------------------------------------
Inactivated 10-(5) 10-(4) (10-(3)
VSV-NJ Vaccine (1 MLD) (10 MLD) (100 MLD)
- --------------------------------------------------------------------------------
<S> <C> <C> <C>
10(7) pfu 0/5* 0/5 3/4
10(6) pfu 3/5 4/5 3/6
10(5) pfu 5/5 4/5 7/7
- --------------------------------------------------------------------------------

*Number dead/number challenged
</TABLE>

5. Virus Neutralization in Cattle Immunized with Psoralen-inactivated
VSV/NJ vaccine.

Four groups of six mature beef cattle each were injected with either 10(8)
or 10(7) pfu/dose psoralen-inactivated VSV-NJ vaccine, with or without aluminum
hydroxide adjuvant (1:1). Each cow was vaccinated subcutaneously (SQ) on day 0
and again on day 21. A control group consisted of an additional six cattle that
were inoculated only with adjuvant on day 0 and again on day 21. All cattle were
bled on days 0, 14, 21, and 35. Serum from each animal was tested for SN
antibodies to VSV-NJ by standard procedures.

The aluminum hydroxide adjuvant was required to elicit significant SN
titers in cattle, and 10(8) pfu/dose induced the highest responses. The results
are set forth in Table 11. A VSV-NJ virus neutralization index greater than
1000 has been reported to represent protection against 10(6)ID(50) of live VSV
by intralingual challenge in cattle. See, Castaneda et al. (1964) Proc. US
Livestock San Assoc. 68:455-468.

TABLE 11
- -----------------------------------------------------------------------------------------
Virus Neutralization Indices* From Cattle
Injected with Psoralen-Inactivated VSV-NJ
Vaccine
-----------------------------------------
Day Serum Collected
-----------------------------------------------------
Group Treatment Animal 0** 14 21** 35
- -----------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C> <C>
A 10(8) pfu/ 310 - 16 16 256
dose + 731 - - - > 16
A1(OH)(3) 911 - 128 64 2048
921 - 8 8 1024
943 - 16 32 1024
944 - 32 32 512
B 10(7) pfu/ 303 - - - 256
dose + 304 - - - 64
A1(OH)(3) 308 4 4 8 512
542 - - - 8
914 - 16 4 512
1670 - - - > 128
C Controls 305 - - - -
309 - - - -
314 - - - -
315 - - - -
316 - - - -
318 - - - -
D 10(8) pfu/ 302 - - - 4
dose 611 - - - 4
without 714 - - - 8
adjuvant 732 - - - 4
747 - - - -
996 - - - 32
E 10(7) pfu/ 101 - - - -
dose 312 - - - 4
without 616 - - - -
adjuvant 721 - - - -
722 - - - -
1944 - - - -
- -----------------------------------------------------------------------------------------

*Virus neutralization index is the reciprocal of the serum dilution that
neutralized 32 TCID(50) of VSV-NJ.
**Immunization Days
</TABLE>

6. Live VSV-NJ Challenge of Cattle Vaccinated with Psoralen-inactivated
VSV-NJ Vaccine

Ten mature cattle were divided into two groups of five animals each. Group
I was designated experimental and Group II was designated control. All ten
cattle were clinically normal and lacked evidence of previous VSV exposure; that
is, they were negative for serum neutralizing (SN) antibody. Group I cattle were
vaccinated subcutaneously with 10(8) pfu (prior to inactivation)
psoralen-inactivated VSV twice with a three week interval. Vaccine volume was 2
ml, containing aluminum hydroxide adjuvant. Group II cattle were not exposed to
the psoralen-inactivated VSV.

Approximately two weeks post-second vaccination, the cattle of both Groups
I and II were challenged intradermalingually with 0.1 ml live VSV in log
dilutions of 5.6 pfu to 5.6 times 10(5) pfu/injection site. Thus each animal's
tongue received six separate 0.1 ml injections, representing a quantitative
challenge system. Serum neutralizing titers for cattle in each group measured
before and after challenge are presented in Table 12.

<TABLE>
<CAPTION>
TABLE 12
- -------------------------------------------------------------------------------------------------------
Serum Neutralization Titers From Cattle
Vaccinated With Psoralen-Inactivated VSV-NJ
Vaccine
-------------------------------------------
Animal Ar- After After Day of Post
No. rival 1st Vacc(a) 2nd Vacc(b) Challenge(a) Challenge(c)
Day 0 18 35 42 60
- -------------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>
Group
I:
- ------
4009-V neg* 1:160 1:1280 1:1280 1:1280
4383-V neg 1:80 1:1280 1:1280 1:2560
4389-V neg 1:80 1:640 1:2560 ND
6153-V neg 1:80 1:1280 1:1280 (greater than or equal to) 1:20480

</TABLE>

<TABLE>
<CAPTION>
TABLE 12 - continued
- -------------------------------------------------------------------------------------------------------
Serum Neutralization Titers From Cattle
Vaccinated With Psoralen-Inactivated VSV-NJ
Vaccine
-------------------------------------------
Animal Ar- After After Day of Post
No. rival 1st Vacc(a) 2nd Vacc(b) Challenge(a) Challenge(c)
Day 0 18 35 42 60
- -------------------------------------------------------------------------------------------------------
<S> <C> <C> <C> <C> <C>

6246-V neg 1:320 1:1280 1:1280 ND
Group
II:
- ------
3780-C neg neg neg neg 1:10240
3781-C neg neg neg neg 1:10240
3784-C neg neg neg neg 1:10240
4007-C neg neg neg neg 1:10240
7912-C neg neg neg neg 1:10240
- -------------------------------------------------------------------------------------------------------

(a) 100 TCID(50) of VSV-NJ
(b) greater than 1000 TCID(50) of VSV-NJ
(c) 37 TCID(50) of VSV-NJ
* negative at 1:20, the lowest dilution tested
ND = not done
</TABLE>

Vaccinated animals had a fifty percent reduction in lesion number, and
lesions on vaccinates were fifty percent smaller and healed faster than on
controls. Control animals developed lesions at both earlier and later time
points. On post-challenge day eighteen, all five controls had lesions whereas
four of five vaccinates were normal. The fifth vaccinate's lesions were milder
than those of any control animal on post-challenge day eighteen.

Using the Mann-Whitney modification of Wilcoxon's two sample test, the
vaccinates were significantly protected against live VSV challenge (P=0.075).
On the average, vaccinated cattle were protected against 25 times the minimum
infectious dose required to produce lesions in control animals.

According to the present invention, viruses inactivated with furocoumarins
and ultraviolet radiation in the substantial absence of oxygen and other
oxidizing species retain their immunogenicity and are suitable as the
immunogenic substance in vaccines against a number of virally-induced diseases.
The inactivated viruses of the present invention are non-infectious and safe
when administered to a host for vaccination, yet display enhanced antigenic
integrity when compared to vaccines inactivated in the presence of oxygen.

Although the foregoing invention has been described in some detail by way
of illumination and example for purposes of clarity of understanding, it will
be obvious that certain changes and modifications may be practiced within the
scope of the appended claims.

What is claimed is:

1. A viral vaccine produced by exposing a live virus to a preselected
intensity of long wavelength ultraviolet radiation and a preselected
concentration of an inactivating furocoumarin for a time period sufficiently
long to render the virus non-infectious but not long enough to degrade its
antigen characteristics, wherein said exposure is performed in the substantial
absence of oxygen and other oxidizing species.

2. A viral vaccine as in claim 1, wherein the inactivation medium is
maintained under a non-oxidizing gas atmosphere.

3. A viral vaccine as in claim 1, wherein the inactivation medium is
flushed with the non-oxidizing gas.

4. A viral vaccine as in claim 2, wherein the non-oxidizing gas is selected
from the group consisting of nitrogen, argon, helium, neon, carbon dioxide, and
mixtures thereof.

<PAGE> 63
5. A viral vaccine as in claim 1, wherein an oxygen scavenger is added to
the inactivation medium.

6. A viral vaccine as in claim 5, wherein the oxygen scavenger is sodium
ascorbate.

7. A viral vaccine as in claim 1, wherein the virus is exposed to the
furocoumarin by adding said furocoumarin to an inactivation medium containing
the live virus.

8. A viral vaccine as in claim 1, wherein the furocoumarin is introduced
to the live virus by addition to a cell culture medium in which the virus is
grown.

9. A viral vaccine comprising in combination: an inactivated live virus
and a physiologically acceptable vaccine carrier; said virus being further
characterized as inactivated by exposure to long wavelength ultraviolet
radiation and an amount of a furocoumarin sufficient to inactivate the virus,
which together render the virus non-infectious without destroying its antigen
characteristics.

10. The vaccine in claim 9 wherein the furocoumarin is a psoralen.

11. The vaccine in claim 9 wherein the furocoumarin is 5-methoxypsoralen
(5-MOP).

12. The vaccine in claim 11 wherein the furocoumarin is
8-methoxypsoralen. (8MOP).

* * * * *

<PAGE> 64
EXHIBIT G
1/3/1 (Item 1 from file: 351)
009031974 WPI Acc No: 92-159335/19
XRAM Acc No: C92-073563
Inactivated viral vaccines - prepd. by psoralen inactivation of live virus
in non-oxidising atmos. used for inoculation against DNA and RNA viral
Patent Assignee: (DIAM-) DIAMOND SCIENTIFIC
Author (Inventor): CREAGAN R P; GILES R; STEVENS D R; WIESEHAHN G P
Patent Family:
CC Number Kind Date Week
US 5106619 A 920421 9219 (Basic)
Priority Data (CC No Date): US 563939 (831220); US 592661 (840323); US 785354
(851007); US 69117 (870702); US 463081 (900110)

1/3/2 (Item 2 from file: 351)
008533075 WPI Acc No: 91-037138/06
XRAM Acc No: C91-015912
Decontaminating blood components to destroy viruses - by adding psoralen
cpd(s)., irradiating with long wavelength UV, and adding glucose and/or
post-treatment gassing
Patent Assignee: (DIAM-) DIAMOND SCIENTIFIC
Author (Inventor): WIESEHAHN G P; CORASH L
Patent Family:
CC Number Kind Date Week
CA 2015315 A 901111 9106 (Basic)
Priority Data (CC No Date): US 350335 (890511)
Applications (CC, No, Date): CA 15315 (900424)

1/3/3 (Item 3 from file: 351)
007742402 WPI Acc No: 89-007514/01
XRAM Acc No: C89-003599
Vaccine for feline virus rhinotracheitis - prepd. by exposing feline
herpes virus I to ultraviolet radiation in the presence of furocoumarin
Patent Assignee: (DIAM-) DIAMOND SCIENTIFIC
Author (Inventor): WISEHAHN G P; GILES R E; STEVENS D R
Patent Family:
CC Number Kind Date Week
US 4791062 A 881213 8901 (Basic)
FI 8805120 A 900508 9032
Priority Data (CC No Date): US 707102 (850228); US 70201 (870706)

1/3/4 (Item 4 from file: 351)
007443445 WPI Acc No: 88-077379/11
Related WPI Accession(s): 84-277589
XRAM Acc No: C88-034732
Photochemical viral inactivation in blood clothing factor compsns. - by
adding furocoumarin cpd(s)., reducing dissolved oxygen concn. and UV
irradiating
Patent Assignee: (DIAM-) DIAMOND SCIENTIFIC
Author (Inventor): WIESEHAHN G P; CREAGAN R P
Patent Family:
CC Number Kind Date Week
US 4727027 A 880223 8811 (Basic)
Priority Data (CC No Date): US 785356 (851007); US 490681 (830502); US
<PAGE> 65
Page 2

928841 (861020)

1/3/5 (Item 5 from file: 351)
007280343 WPI Acc No: 87-277350/39
Related WPI Accession(s): 85-210121; 85-323311
XRAM Acc No: C87-117850

Prepn. of inactivated viral vaccines - by furo-coumarin-inactivation in
non-oxidising atmos.

Patent Assignee: (ADGE-) ADVANCED GENETICS
Author (Inventor): WIESEHAHN G P; CREAGAN R P; STEVENS D R; GILES R
Patent Family:

CC Number Kind Date Week
US 4693981 A 870915 8739 (Basic)

Priority Data (CC No Date): US 785354 (851007); US 563939 (831220); US 592661
(840323)

1/3/6 (Item 6 from file: 351)
004496433 WPI Acc No: 85-323311/51
Related WPI Accession(s): 87-277350
XRAM Acc No: C85-139975

Vaccine against vesicular stomatitis virus infection contg. virus
inactivated by irradiating with UV light in presence of furocoumarin

Patent Assignee: (ADGE-) ADV GENETICS RES
Author (Inventor): WIESEHAHN G P; GILES R E
Patent Family:

CC Number Kind Date Week
US 4556556 A 851203 8551 (Basic)

Priority Data (CC No Date): UF 592661 (840323); US 785354 (851007)

1/3/7 (Item 7 from file: 351)
004383243 WPI Acc No: 85-210121/35
Related WPI Accession(s): 87-277350
XRAM Acc No: C85-091582

Bluetongue virus vaccine contg. bluetongue virus inactivated by
irradiation in presence of furocoumarin

Patent Assignee: (ADGE-) ADV GENETICS RES; (ADGE-) ADV GENETICS RES LT
Author (Inventor): GILES R E; STEVENS D R; WIESEHAHN G P
Patent Family:

CC Number Kind Date Week
AU 8435693 A 850627 8535 (Basic)
ZA 8408857 A 850515 8535
US 4545987 A 851008 8543

Priority Data (CC No Date): US 563939 (831220); US 785354 (851007)
Applications (CC, No, Date): AU 8435693 (841120); ZA 848857 (841114)

1/3/8 (Item 8 from file: 351)
004132049 WPI Acc No: 84-277589/45
Related WPI Accession(s): 88-077379
XRAM Acc No: C84-117678
XRPX Acc No: N84-207210

Decontamination of biological protein-contg. compsns. by addn. of
furo-coumarin and irradiation to inactivate polynucleotide(s)

Patent Assignee: (ADGE-) ADV GENETICS RES; (DIAS-) DIAMOND SCIENTIFIC; (DIAM-)
DIAMOND SCI CO
Author (Inventor): WIESEHAHN G P
Patent Family:
<PAGE> 66
Page 3

CC Number Kind Date Week
EP 124363 A 841107 8445 (Basic)
AU 8427521 A 841108 8501
ZA 8403270 A 841025 8508
JP 60016930 A 850128 8510
CA 1224622 A 870728 8734
US 4748120 A 880531 8824
EP 124363 B 901219 9051
DE 3483751 G 910131 9106

Priority Data (CC No Date): US 490681 (830502); US 785356 (851007); US 928841
(861020)
Applications (CC,No,Date): EP 84302845 (840427); ZA 843270 (840502); JP 8486273
(840501)

1/3/9 (Item 1 from file: 350)
002274367 WPI Acc No: 79-73577B/40
XRAM Acc No: C79-B73577
Psoralen derivs. contg. cyclic aminomethyl gp. -- to enhance solubility
and ability to react wih nucleic acids; PSORIASIS CHEMOTHERAPEUTIC
Patent Assignee: (REGC) UNIV OF CALIFORNIA
Author (Inventor): HEARST J E; RAPOPORT H; ISAACS S
Patent Family:
CC Number Kind Date Week
US 4169204 A 790925 7940 (Basic)
Priority Data (cc No Date): US 937292 (780828); US 734031 (761020)

1/3/10 (Item 2 from file: 350)
002017192 WPI Acc No: 78-30223A/17
XRAM Acc No: C78-A30223
Substd. trimethyl psoralen(s) -- for treatment of vitiligo and psoriasis,
and for virus inactivation
Patent Assignee: (REGC) UNIV OF CALIFORNIA
Patent Family:
CC Number Kind Date Week
BE 859912 A 780419 7817 (Basic)
DE 2746942 A 780427 7818
NL 7711539 A 780424 7819
JP 53053699 A 780516 7825
FR 2376859 A 780908 7841
US 4124598 A 781107 7846
GB 1556307 A 791121 7947
US 4196281 A 800401 8015
CH 635346 A 830331 8315
IT 1087022 B 850531 8623
DE 2760392 A 861009 8642
JP 87000153 B 870106 8704
JP 6201795 A 870121 8709
DE 2746942 C 880526 8821
JP 88026119 B 880527 8825
Priority Data (CC No Date): US 734031 (761020); US 937292 (780828); US 938277
(780831)

<PAGE> 67

EXHIBIT H

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3301
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MONO[ 3301 ] #[ ] ATTY[ LW ] DIV[ ]
ASSN[ DIAMOND SCIENTIFIC ]

TITL[ PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD AND
BLOOD COMPONENTS
]
INVN[ GARY P. WIESEHAHN
]

USSN[ 06/490,681 ] USFL[ 05/02/83 ] CASN[ 453,232 ] CAFL[ 05/01/84 ]

FORN[ AU - 563,557, EPO - 84/302,845, (124,363) JP - 86273/84,
ZA - 84/3270 ep 124,363 ]

USP#[ ] USIS[ ] CAP#[ 1,224,622 ] CAIS[ 07/28/87 ]

NOTE[ DIAMOND SCIENTIFIC NO. 2-2 ABANDONED CONT. FILED ]

]

-MORE-

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3301
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MONO[ 3301 CONT. ] #[ ] ATTY[ LW ] DIV[ ]
ASSN[ DIAMOND SCIENTIFIC ]

TITL[ PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD AND
BLOOD COMPONENTS
]
INVN[ GARY P. WIESEHAHN
]

USSN[ 06/928,841 ] USFL[ 10/20/86 ] CASN[ ] CAFL[ ]

FORN[
]

USP#[ 4,748,120 ] USIS[ 5/31/88] CAP#[ ] CAIS[ ]

<PAGE> 68

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3301
==============================================================================
MONO[ 3301 CONT. II ] #[ ] ATTY[ LW ] DIV[ ]
ASSN[ DIAMOND SCIENTIFIC]

TITL[ PHOTOCHEMICAL DECONTAMINATION TREATMENT OF WHOLE BLOOD AND
BLOOD COMPONENTS ]

INVN[ GARY P. WIESEHAHN ]

USSN[ 07/164,915 ] USFL[ 03/07/88 ] CASN[ ] CAFL[ ]

FORN[
]

USP#[ ] USIS[ ] CAP#[ ] CAIS[ ]

NOTE[ DIAMOND SCIENTIFIC
]

--More-- ]

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MONO[ 3301 CONT. II/CIP ] #[ ] ATTY[ LW ] DIV[ ]
ASSN[ DIAMOND SCIENTIFIC ]

TITL[ IMPROVED METHOD OF BLOOD COMPONENT DECONTAMINATION BY GLUCOSE
ADDITION AND POST-DECONTAMINATION GASING
]

INVN[ GARY P. WIESEHAHN AND LAURENCE CORASH
]

USSN[ 07/350,335 ] USFL[ 05/11/89 ] CASN[ 2,015,315 ] CAFL[ 04/24/90 ]

FORN[
]

USP#[ ] USIS[ ] CAP#[ ] CAIS[ ]

NOTE[ DIAMOND SCIENTIFIC
]
--MORE--

<PAGE> 1

EXHIBIT 23.1

CERUS CORPORATION

CONSENT OF INDEPENDENT AUDITORS

We consent to the incorporation by reference in the Registration Statement
on Form S-8 No. 333-27097 pertaining to the 1996 Equity Incentive Plan and
Employee Stock Purchase Plan of Cerus Corporation of our report dated January
27, 1998, except for Note 2 as to which the date is March 6, 1998, with respect
to the financial statements of Cerus Corporation included in the Annual Report
(Form 10-K) for the year ended December 31, 1997.

Ernst & Young LLP

Walnut Creek, California
March 6, 1998

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<SECURITIES> 9,977,178
<RECEIVABLES> 4,376,141
<ALLOWANCES> 0
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