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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 10-K

Commission file number 0-21937

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

        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 ý    No o

        Indicate by check mark whether the registrant is an accelerated filer (as defined in Exchange Act Rule 12b-2). Yes ý    No o

        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. o

        The approximate aggregate market value of the common stock held by non-affiliates of the registrant as of the last business day of the registrant's most recently completed second fiscal quarter, based upon the closing sale price of the registrant's common stock listed on the Nasdaq National Market, was $156,794,700.(1)

        As of February 29, 2004, there were 22,104,766 shares of the registrant's common stock outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

        Portions of the registrant's definitive Proxy Statement in connection with the registrant's 2004 Annual Meeting of Stockholders, to be filed with the Securities and Exchange Commission pursuant to Regulation 14A not later than April 30, 2004, are incorporated by reference into Part III of this annual report on Form 10-K.

(1)

Based on a closing sale price of $7.52 per share on June 30, 2003. Excludes 1,151,684 shares of the registrant's common stock held by executive officers, directors and affiliates at June 30, 2003.

TABLE OF CONTENTS

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PART I

        This report contains forward-looking statements. These forward-looking statements are based on our current expectations about our business and industry, and include, but are not limited to, statements concerning our plans or expectations concerning development and commercialization of our current products and product candidates; conduct of clinical trials of our product candidates; regulatory approvals; our ability to address certain markets; manufacturing and supply for our clinical trial and commercial requirements; reliance on a third party for a marketing, sales and distribution capability; evaluation of additional product candidates for subsequent clinical and commercial development; and potential outcomes of litigation. In some cases, these statements may be identified by terminology such as "may," "will," "should," "expect," "plan," "anticipate," "believe," "estimate," "predict," "potential" or "continue" or the negative of such terms and other comparable terminology. In addition, statements that refer to expectations or other characterizations of future events or circumstances are forward-looking statements. These statements involve known and unknown risks and uncertainties that may cause our or our industry's results, levels of activity, performance or achievements to be materially different from those expressed or implied by the forward-looking statements. Factors that may cause or contribute to such differences include, among others, those discussed under the captions "Business," "Risk Factors" 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. We undertake no obligation to update any forward-looking statements to reflect events or circumstances after the date of this report.

        Cerus and Helinx are U.S. registered trademarks of Cerus Corporation. INTERCEPT, INTERCEPT Blood, INTERSOL and Amicus are trademarks of Baxter International Inc.

Item 1.    Business

Overview

        We are developing medical systems, therapeutics and vaccines. Our most advanced programs are focused on systems to enhance the safety of blood products used for transfusion. The INTERCEPT Blood System, which is being developed in collaboration with subsidiaries of Baxter International Inc., is based on our proprietary Helinx® technology for controlling biological replication. The INTERCEPT Blood System is designed to inactivate viruses, bacteria, other pathogens and white blood cells. We also are pursuing therapeutic and vaccine technologies, including our Helinx technology, to treat and prevent serious diseases.

        The INTERCEPT Blood System is designed to target and inactivate blood-borne pathogens, such as HIV and hepatitis B and C, as well as harmful white blood cells, while leaving intact the therapeutic properties of the blood components. The INTERCEPT Blood System inactivates a broad array of pathogens and has the potential to reduce the risk of transmission of pathogens for which testing is not completely effective or is not currently performed. We believe that the INTERCEPT Blood System also has the potential to inactivate new pathogens before they are identified and before tests are developed to detect their presence in donated blood.

        We are conducting product development and commercialization activities with Baxter pursuant to agreements for the development, manufacturing and marketing of the INTERCEPT Blood System. These agreements provide for Baxter and us to generally share development expenses, except for the INTERCEPT Blood System for plasma, for which we are solely responsible for development expenses. These agreements also provide for Baxter's exclusive right and responsibility to market the systems worldwide and for us to receive a share of the gross profits from the sale of the systems.

        The INTERCEPT Blood System for platelets has received CE Mark approval and is being marketed by Baxter in several countries in Europe. Baxter will need to complete validation studies and obtain reimbursement approvals in some individual European countries to market the product in those

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countries. The level of additional product testing varies by country. In certain countries, including the United Kingdom, France and Germany, the system must be approved for purchase or use by a specific governmental or non-governmental (such as the Paul Ehrlich Institute in Germany) entity or entities in order for it to be adopted by a specific customer. Baxter has informed us that it has been notified by the regulatory body in France that the review of the INTERCEPT platelet marketing application is complete and the agency has granted authorization for the preparation, distribution and therapeutic use of the product. Commercial availability of the product in France is subject to successful completion of certain laboratory studies, publication of a decree in the Official Journal to register INTERCEPT platelets and define their specifications and reimbursement approval.

        We completed our Phase III clinical trial of the INTERCEPT Blood System for platelets in the United States in March 2001 and have submitted data from this trial, along with several other modules of our pre-market approval application, to the United States Food and Drug Administration, or FDA. Based on discussions with the FDA, we are performing additional analyses of the clinical trial data and, if the outcome of such additional analyses is acceptable to the FDA, plan to conduct a supplemental clinical trial. Data from the additional analyses and supplemental clinical trial will need to be submitted to the FDA before we can complete our regulatory submission.

        We are in various stages of the regulatory application process for the INTERCEPT Blood System for platelets in certain other countries in which we are not expecting to receive significant revenue from product sales.

        We are in late stage development of the INTERCEPT Blood System for plasma and have recently completed enrollment in the last of three planned Phase III clinical trials.

        In September 2003, we terminated Phase III clinical trials of our INTERCEPT Blood System for red blood cells due to the detection of antibodies in two patients. As a result, we restructured our operations to focus on our pathogen inactivation products for platelets and plasma and our pipeline of therapeutics and vaccines. The restructuring was intended to reduce operating expenses and included a reduction in our workforce of approximately 25%. The observations from this trial do not affect the development or commercialization of the pathogen inactivation programs for platelets and plasma, which use a different technology and mechanism of action. We have begun an evaluation of the antibody detected in the red blood cell trial and are investigating whether process changes could prevent antibody formation and allow the modified red blood cell system to undergo clinical trials. These activities may take a long time to complete and may not be successful.

        We are also developing a proprietary, versatile technology to stimulate the immune system to target and attack cancer cells and infectious diseases. This platform technology is based on specially designed strains of the bacterium Listeria monocytogenes. Our scientists have demonstrated that proprietary strains of Listeria are capable of inducing potent immune responses in laboratory tests. We believe that the combination of proprietary strains of Listeria with specific cancer antigens, such as Mesothelin, has the potential to harness the power of the immune system to selectively attack malignant cells. Additionally, we are further evaluating our Listeria platform technology with our Helinx technology for the development of potentially safe and potent therapies and vaccines for certain indications.

        Two investigator-sponsored clinical trials are evaluating our Helinx technology in specific applications: our allogeneic cellular immune therapy (ACIT) technology, designed to improve the outcome of bone marrow transplantation procedures through use of T-cells treated with the Helinx technology and an Epstein-Barr virus (EBV) cellular vaccine are in Phase I clinical trials.

        Cerus was incorporated in California in 1991 and reincorporated in Delaware in 1996. Information regarding Cerus' revenue, losses and total assets for the last three fiscal years can be found in the financial statements and related notes included elsewhere in this report.

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Industry Background

        Blood Supply Market.    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 80 million whole blood donations occur each year. Approximately 40 million of those donations occur in North America, Western Europe and Japan, the primary geographical markets for the INTERCEPT Blood System.

        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, or blood clotting, while red blood cells carry oxygen to tissues and carbon dioxide to the lungs. White blood cells play a critical role in immune and other defense systems, but can cause harmful transfusion-related immune reactions in, or transmit disease to, transfusion recipients.

        Blood collection centers periodically experience shortages of critical blood components due to temporary increases in demand, reduced donor availability during holiday periods and the limited shelf life of cellular blood components. To efficiently allocate the limited available blood supply and to optimize transfusion therapy, essentially all donated blood is separated into platelets, plasma and red blood cells. These blood components are obtained either by manually processing donor units of whole blood or by apheresis, an automated process by which a specific blood component is separated and collected from the donor's blood while the other components are simultaneously returned to the donor.

        Patients requiring transfusions typically are treated with one or more specific blood components required for their particular deficiency, except, very rarely, 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 products that are administered to expand blood volume, fight infections or treat diseases such as hemophilia.

        Blood Supply Contaminants. A primary goal of every blood collection center is to provide blood components for transfusion that are free of viruses, bacteria and other pathogens. Despite improvements in donor screening and in the testing and processing of blood, patients receiving blood transfusions still face a number of significant risks from blood contaminants, as well as adverse immune and other transfusion-related reactions induced by white blood cells. Viruses, such as hepatitis B (HBV), hepatitis C (HCV), human immunodeficiency virus (HIV), cytomegalovirus (CMV), West Nile virus 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. Many other agents can transmit disease during transfusion, including the protozoa that cause malaria, babesiosis and Chagas' disease.

        Infectious pathogens are not the only cause of adverse events arising from the transfusion of blood components. White blood cells present in a blood unit can multiply after transfusion, mounting a potentially fatal graft-versus-host immune response against the recipient. Similarly, alloimmunization, an immune response that can develop from repeated exposure to transfused white blood cells, can significantly reduce the efficacy of subsequent transfusions. Moreover, white blood cells themselves may harbor and transmit bacteria and infectious viruses, such as HIV, CMV and HTLV.

        Emerging and unidentified pathogens also present a threat to the blood supply, a problem illustrated by HIV. It is estimated that HIV was present in the blood supply for at least seven years before it was identified as the causative agent of AIDS and at least eight years before a test was

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commercially implemented to detect the presence of HIV antibodies in donated blood. During those years, many transfusion recipients were infected with the virus, including approximately 70% of patients with severe hemophilia. More recently, West Nile virus has been transmitted through blood transfusions. In addition, new variants of HIV and other viruses, such as hepatitis G, have been identified. Transfused blood is not routinely tested for these emerging viruses, despite the potential risk to transfusion recipients.

        The risk of transmission of pathogens from an infected donor is compounded by a number of factors. If a unit of blood contains an infectious pathogen, dividing the blood into its components may expose three or more patients to the pathogen in that unit. Blood products are commonly pooled from several donors to form a single therapeutic dose, which increases the recipient's risk of infection. Similarly, patient populations that require frequent transfusions, such as patients with cancer, suppressed immune systems, congenital anemias and kidney and liver disorders, experience a heightened risk of infection due to multiple donor exposures.

        Current Approaches to Address Blood Supply Contamination.    Public awareness of the significant rates of hepatitis, HIV and other viral transmission from blood transfusions has led to expanded efforts to improve the safety of the blood supply. For many years, the only approach available to reduce the risk of transmission of diseases was donor screening through interviews. In addition to required donor screening, diagnostic tests have been developed over time to detect the presence of certain infectious pathogens that are transmitted in blood. However, there remain a number of other blood-borne pathogens for which tests are not routinely administered, and for many of these, no tests have been developed.

        Although donor screening and diagnostic testing of donated blood have been successful in reducing the incidence of transmission of some known pathogens, these methods have significant limitations. Tests are currently performed for only a limited number of blood-borne pathogens. Moreover, current methods of testing are not completely effective, which can lead to the release of contaminated blood into transfusion inventory. Most tests used in blood centers in the United States are intended to detect antibodies directed against a pathogen or surface antigens. All tests currently in use by blood centers can fail if performed during the "infectivity window," that is, early in the course of an infection before agents appear in detectable quantities. Nucleic acid testing for HIV and HCV is mandatory in most blood centers in Europe, and is used by most blood centers in the United States. Although nucleic acid testing is more effective at detecting HIV and HCV in earlier stages of infection in a donor, it does not close the infectivity window completely. For example, transfusion recipients in the United States, Europe and Japan have been infected from blood transfusions for which nucleic acid testing failed to detect the virus. Furthermore, nucleic acid testing, like other testing currently performed on donated blood, is of limited benefit as it is effective only for specific viruses for which the testing is performed. In addition, tests for viral infection may be ineffective in detecting a genetic variant of the virus that the test was not developed to detect. For instance, certain strains of HIV, such as Subtype O, are not always detected in standard HIV tests. Finally, there are no current tests available to screen effectively for many emerging pathogens, and testing cannot be performed for pathogens that have yet to be identified. As a result of these limitations, many infected blood products continue to pass into the blood supply.

        In light of these continuing concerns, many patients have attempted to mitigate the risks of transfusion through "autologous donation," which is the donation of the patient's own blood for anticipated future use, or, where autologous donation is impracticable, through the designation of donors such as family members. Although autologous donations eliminate many risks, the blood collected is still subject to the risk of bacterial growth during storage and is rarely available in emergency situations or when a patient is chronically ill. In addition, the statistical incidence of infected units from designated donor blood has been found to be as high as in general volunteer donor blood.

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        Blood centers and health care providers have initiated additional procedures in an effort to address pathogen transmission issues. For example, platelet apheresis is sometimes used to limit donor exposure from pooled, manually collected platelets. In addition, blood centers may quarantine single donor plasma apheresis units until after the infectivity window has elapsed, followed by confirmatory retesting of the donor, if the donor is available, to help verify the safety of the donated plasma. However, quarantining plasma is expensive, and inventory is difficult to manage. Moreover, quarantining cannot be used with platelets and red blood cells because these components have shelf lives that are shorter than the infectivity window related to antibody production. No commercial processes are currently available to eliminate pathogens in platelets and red blood cells. Two pathogen inactivation methods are used commercially for FFP: treatment with solvent-detergent and methylene blue, which is used in Europe. Because the solvent-detergent process pools hundreds of units of plasma, the potential risk of transmitting pathogens not inactivated by the process is increased. Methylene blue has not been shown to be effective in the inactivation of intracellular viruses and bacteria.

        Some blood centers are currently using gamma irradiation to inactivate white blood cells. This nonspecific method has a narrow range of efficacy: insufficient treatment can leave viable white blood cells in the blood, while excessive treatment can impair the therapeutic function of the desirable blood components being transfused. White blood cell depletion by filtration decreases the concentration of these cells in transfusion units, but does not inactivate or completely eliminate white blood cells or inactivate the immunological functions of the cells not removed by the filtration process.

        Economic Costs of Blood Supply Contamination.    In economically developed countries, many of the tests and inactivation measures described above are mandated by regulatory agencies, resulting in a safer and more uniform blood supply, but also significantly increasing costs of processing and delivering blood products.

        Moreover, the development and widespread implementation of testing for many unusual or low-incidence pathogens is not cost-effective or practical. For example, the development of tests to specifically detect the presence of all forms of harmful bacteria would be extremely expensive. As a result, the only test specific to a bacterium that is conducted in all blood products is the test for the bacterium that causes syphilis.

        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, have created the need for a new approach to pathogen inactivation that is safe, easy to implement and cost-effective. We believe that such an approach should be effective in inactivating a broad spectrum of clinically significant pathogens, preserve the therapeutic properties of the blood components and be safe for use.

The INTERCEPT Blood System and Helinx Technology

        We are developing the INTERCEPT Blood System with Baxter to address the problem of transmission of infectious diseases through blood transfusions. The INTERCEPT Blood System employs our proprietary nucleic-acid targeting Helinx technology. We have conducted studies that have demonstrated the ability of the Helinx technology to inactivate a broad array of viral and bacterial pathogens that may be transmitted in blood transfusions. We believe that the mechanism of action of our Helinx technology provides the potential to inactivate many new pathogens before they are identified and before tests are developed to detect their presence in the blood supply. Because the INTERCEPT Blood System is designed to inactivate rather than merely test for pathogens, the system also has the potential to reduce the risk of transmission of pathogens that would otherwise remain undetected by testing.

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        Helinx technology prevents the replication of DNA or RNA, which is present in viruses, bacteria and other pathogens. Therapeutic blood components (platelets, FFP and red blood cells) do not contain nuclear DNA or RNA—the targets for the Helinx technology. When our proprietary inactivation compounds are combined with the blood components for treatment, they cross bacterial cell walls or viral membranes and 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. This process prevents infection because a virus, bacteria or other pathogen must replicate its DNA or RNA to proliferate and cause infection. The Helinx compounds react in a similar manner with the nucleic acid in white blood cells, inhibiting the 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 INTERCEPT Blood System is being designed to integrate into current blood collection, processing and storage procedures. Furthermore, we believe that the use of the INTERCEPT Blood System, in addition to eliminating the need to implement costly new testing procedures, could potentially lead to a reduction in the use of certain costly procedures that are currently employed in blood component transfusions, such as gamma irradiation, CMV testing and white blood cell filtration.

Our Strategy

        Our objective is to develop medical systems, therapeutics and vaccines that provide safer and more effective treatment options to patients. The INTERCEPT Blood System, based on our Helinx technology, is designed to inactivate viruses, bacteria, other pathogens and harmful white blood cells in blood components for transfusion. We also are pursuing therapeutic and vaccine technologies, including our Helinx technology, to treat and prevent serious diseases. Our strategy incorporates the following key elements:

        Establish the INTERCEPT Blood System as the Standard of Care.    Domestically, the target customers for the INTERCEPT Blood System are the approximately 105 community blood center organizations that collect approximately 85% of blood in the United States. There is an even greater concentration among blood centers in foreign countries. Baxter has a significant marketing presence in these blood centers in the United States and abroad. In addition, we have developed strong relationships with prominent transfusion medicine experts in a number of these centers as well as in the broader medical communities worldwide. We intend to work with these experts to encourage support for the adoption of the INTERCEPT Blood System as the standard of care.

        Use Strategic Alliances.    We have received significant development funding from Baxter, and intend to leverage Baxter's manufacturing, marketing and distribution expertise and resources. We believe that Baxter's established position as a manufacturer and leading supplier of devices, disposables and other products related to the transfusion of human blood products can provide us with access to an established marketing, sales and distribution network. The INTERCEPT Blood System is being designed to integrate into Baxter's current product line and into current blood collection, processing and storage processes. We are also collaborating with the U.S. Armed Forces on several initiatives intended to improve the safety and availability of the military's blood supply. We intend to continue to develop our products, including our pre-clinical vaccines program, together with partners that can provide direct funding and manufacturing, marketing and distribution resources and expertise.

        Protect and Enhance Proprietary Position.    We believe that the protection of our proprietary technologies is important to our business prospects and that our intellectual property position may create competitive barriers to entry into the blood component treatment market. We currently hold issued and allowed patents covering a number of fundamental aspects of our Helinx technology and our

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blood component treatment system technology. We intend to continue to pursue our patent filing strategy and to vigorously defend our intellectual property position against infringement.

Product Development

        We are developing systems to inactivate infectious pathogens and harmful white blood cells in platelets, FFP and red blood cells and vaccine platforms for cancer and infectious diseases. We have incurred total research and development expenses of $52.5 million, $56.4 million and $48.2 million for the years ended December 31, 2003, 2002 and 2001, respectively. The following table identifies our product development programs:

        Clinical Trial Design.    We conduct clinical trials using several designs. In a controlled study, treated and untreated blood components are administered to subjects who are randomly assigned to either a test group or a control group, and the results are compared. In a cross-over study, each subject receives both treated and untreated blood components in random order. To avoid bias in reporting side effects, studies are usually blinded. In a single-blind study, subjects are not told whether they are receiving treated or untreated blood components. In a double-blind study, neither the subject (patient) nor the investigator (physician) knows whether the subject is receiving treated or untreated blood components.

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Platelet Program

        Platelet Usage and Market.    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 patients, such as those undergoing chemotherapy or organ transplantation. 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). A principal motivation for platelet apheresis is to limit patient exposure to pooled, manually collected platelets from different donors.

        We estimate the production of platelets in 2003 to have been 2.2 million transfusion units in North America, 1.4 million transfusion units in Western Europe and 0.7 million transfusion units in Japan. Based on the Report on Blood Collection and Transfusion in the United States in 2001 prepared by the National Blood Data Resource Center, the estimated base cost for a transfusion unit of apheresis platelets ranged from approximately $461 to $489, and the estimated base cost for a transfusion unit of random donor platelets ranged from approximately $209 to $345. These estimates include donor screening and diagnostic tests, such as those for HIV, HTLV, HBV and HCV. Blood centers may also charge for additional procedures, such as gamma irradiation and CMV screening. The frequency of use and additional charge for each procedure vary widely.

        INTERCEPT Blood System for Platelets.    The INTERCEPT Blood System for platelets uses our Helinx compound, amotosalen, which is a synthetic small molecule from a class of compounds known as psoralens. The selection of amotosalen was based on an extensive analysis of the compound's safety, its ability to inactivate pathogens and harmful white blood cells and the preservation of platelet and plasma coagulation factor function following treatment with amotosalen.

        When illuminated, amotosalen undergoes a specific and irreversible chemical reaction with DNA and RNA. This chemical reaction renders a broad array of pathogens and cells incapable of replication. Viruses, bacteria or other pathogenic cells cannot cause an infection if they cannot replicate. A similar reaction with the nucleic acid in white blood cells inhibits the activity that is responsible for certain adverse transfusion-related reactions. Studies with pre-clinical models have indicated that, following illumination and transfusion, the amotosalen and its breakdown products are rapidly metabolized and excreted. As a further safety measure, the INTERCEPT Blood System for platelets employs a removal process designed to reduce the amount of residual amotosalen and breakdown products following illumination.

        Cerus and Baxter have designed the INTERCEPT Blood System for platelets to be used in the blood center. The system consists of a disposable processing set, containing the amotosalen compound and a compound adsorption device (CAD), and an illumination device to deliver light to trigger the inactivation reaction. The collection of the platelets is performed, as normal except that two-thirds of the donor's plasma that would normally be collected with the platelets is replaced by a platelet additive solution, called INTERSOL. The platelets are then transferred through a pouch containing the amotosalen compound into an illumination container. The mixture of platelets, amotosalen and INTERSOL is illuminated for approximately three to six minutes. Following the CAD treatment, a passive process that takes approximately four to sixteen hours, the platelets are transferred to the final storage container, to be stored until ready to be transfused.

        Development Status.    In Europe, the INTERCEPT Blood System for platelets has received CE Mark approval for use with pooled whole blood platelets collected using the buffy coat process and for apheresis platelets collected on Baxter's Amicus apheresis platform. A CE Mark also has been received for preparation sets for platelets collected using the Haemonetics and Cobe apheresis systems. We completed our Phase III clinical trial of the INTERCEPT Blood System for platelets in the United

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States in March 2001 and have submitted data from this trial, along with several other modules of our pre-market approval application, to the FDA. Based on discussions with the FDA, we are performing additional analyses of the clinical trial data and, if the outcome of such additional analyses is acceptable to the FDA, plan to conduct a supplemental clinical trial. Data from the additional analyses and supplemental clinical trial will need to be submitted to the FDA before we can complete our regulatory submission.

        Pathogen Inactivation Studies.    Published results of laboratory and animal model studies have demonstrated the efficacy of the INTERCEPT Blood System for the inactivation of a broad array of viral, bacterial and parasitic pathogens transmitted through platelet transfusions, including HIV, CMV, HTLV, model hepatitis viruses, West Nile Virus and the virus that causes Severe Acute Respiratory Syndrome (SARS), 19 strains of bacteria, including syphilis, and the parasites that cause malaria, leishmaniasis and Chagas' disease. A pre-clinical study conducted in collaboration with the National Institutes of Health demonstrated that platelet concentrates contaminated with high levels of hepatitis B virus or hepatitis C virus, and treated with the INTERCEPT Blood System, did not transmit the viruses to susceptible animals. We have tested these pathogens at and above concentrations that we believe may be present in contaminated platelet concentrates. Similar laboratory studies have indicated inhibition of white blood cell activity, including the inhibition of synthesis of certain proteins associated with adverse immune reactions. In addition, three studies have indicated that use of the platelet pathogen inactivation system prevented graft-versus-host disease in two pre-clinical mouse models.

        Pre-Clinical Safety Studies.    We have successfully completed and published the results of a comprehensive series of pre-clinical safety studies for the INTERCEPT Blood System for platelets. Completed safety studies of amotosalen and the INTERCEPT Blood System for platelets include acute toxicology, three-month tolerability, general pharmacology, reproductive toxicology, genotoxicity, carcinogenicity, phototoxicity and absorbance, distribution, metabolism and excretion (ADME) studies. Results from each of these studies have consistently demonstrated a strong safety profile for the INTERCEPT Platelet System.

        Clinical Trials.    In March 1996, we completed a Phase Ia single-blind, randomized clinical trial in 24 healthy human subjects at two sites. This study used a cross-over design in which all subjects received both treated and untreated platelets. The study compared the proportion of transfused platelets circulating in the first hours after transfusion (post-transfusion recovery) and the length of time the transfused platelets circulate in the recipient's bloodstream (lifespan) of a small volume of five-day-old treated and untreated platelets. Under current FDA regulations, platelets may not be stored for more than five days after collection from the donor. This pilot study was conducted without the use of the CAD, which was evaluated in Phase Ib.

        In September 1996, we completed a Phase Ib single-blind, randomized, cross-over clinical trial in ten healthy human subjects. This study compared the tolerability and safety of photochemically treated platelets processed with the CAD with untreated platelets. This second study involved the transfusion of full therapeutic doses of platelets given at the maximum tolerable transfusion rate. No adverse events attributable to transfusion with the treated platelets were reported. Post-transfusion levels of amotosalen in plasma and clearance of amotosalen were measured. These clinical data, together with our pre-clinical data, reflected acceptable safety margins and cleared the INTERCEPT Platelet System for a Phase IIa clinical trial.

        In November 1996, we completed a Phase IIa clinical trial designed to measure the post-transfusion platelet recovery and lifespan of photochemically treated platelets processed with the CAD and stored for five days. This study was conducted in 16 healthy subjects from the Phase Ia study to permit comparisons with prior results. The average post-transfusion recovery of five-day-old platelets treated with our platelet pathogen inactivation system was lower than that of the untreated five-day-old platelets. Although this difference was statistically significant, the average post-transfusion recovery was

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within the range of average recoveries reported in most published studies funded by NIH and Baxter, as well as in a number of other studies reported in the scientific literature. These published studies used currently approved processing and storage systems. In addition, the average lifespan of treated platelets was shorter than that of untreated platelets. Although this difference was statistically significant and the average lifespan was lower than the range of average untreated platelet lifespans reported in the published studies referred to above, the average lifespan was within the distribution of ranges of untreated platelet lifespans reported in such studies. Post-transfusion recovery and lifespan of five-day-old standard platelets varies widely, even in healthy individuals. As a result, there is no established regulatory or clinical standard for post-transfusion recovery and lifespan of platelets. The clinical investigators reported no adverse events attributable to transfusion with the treated platelets.

        In July 1997, we completed a Phase IIb clinical trial in 15 healthy subjects available from the Phase IIa clinical trial to assess the combined effect of treatment with the INTERCEPT Blood System and gamma irradiation on post-transfusion platelet recovery and lifespan. The mean platelet recovery and life span data collected in Phase IIb were consistent with those of the Phase IIa study, and fell within the range of published studies of currently approved platelet concentrates. The clinical investigators reported no adverse events attributable to transfusion with the treated platelets. We believe, based on discussions with the FDA, that the post-transfusion recovery and lifespan of platelets following treatment with the INTERCEPT Blood System are clinically acceptable.

        In November 1998, we completed a Phase IIc clinical trial in 42 platelet-deficient patients. The Phase IIc trial was initially designed as a double-blind, randomized, cross-over study in which double dose platelet transfusions were given to platelet-deficient patients and post-transfusion platelet count increment and bleeding time correction were measured. To increase our experience in patients prior to a Phase III trial, we amended the Phase IIc protocol to include patients for whom platelet count increment, but not bleeding time correction, would be measured and to add a second site to evaluate the system with platelets collected using alternate automated collection equipment. Based on the results from this study, the FDA cleared us to proceed into a Phase III clinical trial. The Phase IIc clinical trial, given its small size, was of limited statistical power.

        In August 2000, we completed our European Phase III euroSPRITE clinical trial which compared conventional platelets with treated pooled random donor platelets in 103 thrombocytopenic patients (patients with low platelet counts and at high risk for bleeding) requiring repeated platelet transfusions for up to 56 days. The study was conducted in four European countries and served as the pivotal trial for the CE Mark approval in Europe, which was received in 2002. The whole blood platelets were collected using the buffy coat process, which is the predominant method used in Europe to prepare platelet concentrates. The trial was a double-blind, randomized, controlled study designed to assess the therapeutic efficacy of platelets treated with the INTERCEPT Blood System.

        The trial had co-primary endpoints: corrected count increment and platelet count increment, each measured one hour after transfusion. The corrected count increment measures the increase in the patient's platelet count after a platelet transfusion, corrected for transfusion platelet dose and the patient's blood volume. For this measure, one hour after transfusion, the performance of treated platelets was similar to that of the untreated platelets. The platelet count increment, which measures the platelet count increase without correcting for dosage or blood volume, is influenced by the platelet dose the patient receives. In this study the platelet dose per transfusion of treated platelets was approximately ten percent lower than that of untreated platelets. A preliminary analysis of the EuroSPRITE data showed the resulting platelet count increment one hour after transfusion of treated platelets was statistically lower than that after transfusion of untreated platelets. However, both the platelet dose per transfusion and the platelet count increment one hour after transfusion were within the typical therapeutic range reported in medical literature for untreated platelets and considered clinically acceptable. Additional statistical analysis presented at the meeting of the American Society of Hematology in December 2000 showed comparable efficacy of INTERCEPT platelets to that of control

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platelets and the preservation of platelet performance and function following pathogen inactivation with the INTERCEPT Blood System.

        Secondary endpoints for the study included multiple factors relevant to clinical efficacy and safety. The results for two important indicators of clinical efficacy, the number of patients with a major bleeding episode and the number of red blood cell transfusions, were comparable for the treated and untreated patients. Similarly, the time between platelet transfusions, the total platelet dose per patient and the number of adverse events were similar between the two groups. Both the platelet count increment and the corrected count increment measured 24 hours after transfusion, while statistically lower than those following the transfusion of untreated platelets, were within the typical therapeutic range reported in the medical literature for untreated platelets. No serious adverse events were directly attributed to the use of the INTERCEPT Blood System for platelets.

        We also completed a 21-patient clinical trial in Europe to qualify the system for its commercial configuration and completed a 43-patient clinical trial in Europe to extend qualification of the system to platelets collected by the Amicus apheresis platform.

        In March 2001, we completed our United States Phase III SPRINT clinical trial. The randomized, controlled, double-blind 671-patient clinical trial was designed to evaluate the therapeutic efficacy and safety of INTERCEPT platelets. In the trial, platelet transfusions were administered to reduce the risk of bleeding during severe thrombocytopenia and to treat active bleeding. The primary endpoint of the study was comparison of the proportion of patients with moderate bleeding following platelet transfusion with either INTERCEPT platelets or platelets that had not been treated with a pathogen inactivation process. The data showed that the proportion of patients with moderate bleeding between the patients who received INTERCEPT platelets and patients who received control platelets was statistically equivalent and within 1% of each other, achieving the trial's primary endpoint of a less than 12.5% difference between the two groups.

        The study also evaluated a number of secondary endpoints comparing INTERCEPT platelets to untreated platelets. Severe bleeding and duration of platelet support were not statistically different between the groups. The trial data also demonstrated that INTERCEPT platelets were associated with a statistically lower number of transfusion reactions than untreated platelets. Evaluation of other secondary measures of platelet count increment (measurements of post-transfusion platelet count increase) and number of platelet transfusions per patient showed a significant difference between the group of patients who received INTERCEPT platelets and the group of patients who received untreated platelets, but these differences did not affect the primary trial endpoint of demonstrating equivalence in the proportion of patients with moderate bleeding between the two groups. Although differences were observed for specific adverse event terms, adverse events and serious adverse events in the aggregate were not statistically different between the groups and were consistent with expectations in the seriously ill patient population undergoing intensive chemotherapy. Pursuant to discussions with the FDA, we are conducting additional analyses. The additional analyses include blinded reviews of certain adverse event data by independent experts.

        The Phase III United States SPRINT trial was designed to assess the therapeutic efficacy of platelets treated with the INTERCEPT Blood System for platelets collected by Baxter's apheresis collection system. In order to obtain FDA approval of the INTERCEPT Blood System for use in treating pooled random donor platelets, we will need to complete development of an additional configuration of our platelet system and conduct additional clinical studies. Additionally, because of the risk of bacterial growth, current FDA rules require that pooled platelets be transfused within four hours of pooling, and, as a result, most pooling occurs at hospitals. The INTERCEPT Blood System is intended to permit storage of platelets for five days after treatment and pooling by the blood center, which would reduce hospital costs associated with the pooling process. In order for the INTERCEPT Blood System to be effectively implemented at blood centers for use with pooled random donor platelets, the FDA-imposed limit on the time between pooling and transfusion will need to be lengthened or eliminated for INTERCEPT platelets.

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Plasma Program

        Plasma Usage and Market.    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. The frozen plasma is then designated for use as FFP for transfusion or made available for fractionation into plasma derivatives. Plasma is the primary source of blood clotting factors and is used to control bleeding in patients who have clotting factor deficiencies, such as patients undergoing transplants or other extensive surgical procedures and patients with chronic liver disease or certain genetic clotting factor deficiencies, and to treat certain diseases that require plasma exchange therapy.

        We estimate the production of FFP in 2003 to have been 3.7 million units for transfusion in North America, 2.2 million transfusion units in Western Europe and 2.3 million transfusion units in Japan. Based on the Report on Blood Collection and Transfusion in the United States in 2001 prepared by the National Blood Data Resource Center, the estimated base price of a 250 ml transfusion unit of FFP in the United States ranged from approximately $51 to $55. A typical therapeutic transfusion consists of four transfusion units of FFP.

        INTERCEPT Blood System for Plasma.    The INTERCEPT Blood System for plasma uses the same psoralen compound and illumination device and a CAD similar to that being used with the INTERCEPT Blood System for platelets. In the INTERCEPT Blood System for plasma, untreated plasma is transferred to a disposable container with amotosalen. The mixture of amotosalen and plasma is then illuminated for approximately three to five minutes. The treated plasma then undergoes a removal step, which uses the CAD to reduce the amount of residual amotosalen and amotosalen breakdown products, and is transferred into the final storage container and frozen in accordance with standard protocols.

        Development Status.    The INTERCEPT Blood System for plasma has completed patient enrollment in the last of three planned Phase III clinical trials in the United States.

        Pathogen Inactivation Studies.    Published results of laboratory studies to date have demonstrated the efficacy of the INTERCEPT Blood System for plasma for the inactivation of a broad array of pathogens transmitted through blood transfusion, including HIV, model hepatitis viruses and syphilis. A pre-clinical study conducted in collaboration with the NIH demonstrated that FFP contaminated with high levels of hepatitis B virus or hepatitis C virus, and treated with the INTERCEPT Blood System, did not transmit the viruses to susceptible animals. We have conducted laboratory studies indicating the efficacy of the INTERCEPT Blood System for the inactivation of the parasite that causes Chagas' disease in FFP. Because of the mechanism of action of the INTERCEPT Blood System for plasma, we believe that the system also inhibits white blood cell activity. To date, we have conducted no studies to detect inhibition of white blood cell activity in FFP.

        Coagulation Function Studies.    We have assessed the impact of amotosalen photochemical treatment on the function of plasma proteins. Plasma derived from whole blood or apheresis must be frozen within eight hours of collection to meet the standard as "fresh frozen plasma." After freezing, FFP may be stored for up to one year, thawed once and must be transfused within four hours of thawing. We have performed laboratory studies measuring the coagulation function activity of various clotting factors in FFP after photochemical treatment, CAD treatment, freezing and thawing. We believe that data from these laboratory studies indicate that treated FFP maintained adequate levels of coagulation function for FFP. There can be no assurance that the FDA or foreign regulatory authorities would view such levels of coagulation function as adequate.

        Pre-Clinical Safety Studies.    We have successfully completed and published results of a series of pre-clinical safety studies for the INTERCEPT Blood System for plasma. Completed safety studies

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include acute toxicology, three-month tolerability, general pharmacology, reproductive toxicology, genotoxicity, carcinogenicity, phototoxicity and ADME studies. Results from each of these studies have consistently demonstrated a strong safety profile for the INTERCEPT Blood System for plasma. While we believe that all pre-clinical safety studies required for regulatory approval have been completed, regulatory authorities may require additional pre-clinical safety studies to be performed.

        Clinical Trials.    In July 1997, we completed a Phase I clinical study in healthy subjects that demonstrated the safety and tolerability of FFP treated with the INTERCEPT Blood System as well as the comparability of post-transfusion coagulation factors between subjects transfused with treated and untreated FFP.

        In November 1998, we completed a Phase IIa clinical trial. In this study, 27 healthy subjects donated plasma. The Phase IIa study showed that post-transfusion coagulation factor levels of subjects receiving FFP treated with the INTERCEPT Blood System were comparable to those of subjects receiving untreated FFP. There were no safety issues attributable to transfusion of the treated FFP.

        In 1999, we completed a Phase IIb clinical trial of the INTERCEPT Blood System for plasma. The study was a controlled, double-blind trial in 13 patients diagnosed with chronic liver diseases. Each patient, prior to an invasive surgical or diagnostic procedure, received a therapeutic dose of up to two liters of either treated or untreated FFP. Correction of patients' blood clotting time and certain coagulation factor levels after transfusion of treated FFP were recorded and compared, and found to be comparable to those of patients receiving untreated FFP. The Phase IIb clinical trial, given its small size, was of limited statistical power.

        In January 2001, we completed a Phase IIIa clinical trial of the INTERCEPT Blood System for plasma. The open-label trial, which was conducted in collaboration with the National Hemophilia Foundation's Hemophilia Research Society, included 34 patients with a variety of hereditary blood clotting factor deficiencies. Patients with these deficiencies are susceptible to bleeding or increased blood clotting and may require plasma transfusions to prevent or stop bleeding. The Phase IIIa results, although not statistically powered, showed that infusions of plasma treated with the INTERCEPT Blood System were well tolerated and resulted in an increase in blood clotting factor levels consistent with historical controls using non-pathogen inactivated plasma.

        In May 2001, we completed a Phase IIIb clinical trial of the INTERCEPT Blood System for plasma. The multi-center, randomized, controlled, double-blind trial included 121 patients with acquired defects in coagulation, primarily due to end-stage liver disease. These patients generally require plasma support during surgery or other invasive procedures, including liver transplantation. The trial evaluated the blood clotting function of INTERCEPT plasma compared to untreated plasma to determine whether the pathogen inactivation treatment process affected therapeutic performance. Blood clotting function was measured using prothrombin (PT) and partial thromboplastin (PTT) times, widely used measures of blood clotting function. The primary endpoint of the trial was a comparison of PT and PTT responses between INTERCEPT plasma and untreated plasma during a seven-day treatment period. The results, which achieved the trial's statistical threshold, showed that the ability of INTERCEPT plasma to treat bleeding was statistically comparable to untreated plasma. In addition, the safety and adverse events of INTERCEPT plasma compared to untreated plasma showed comparability between the two groups.

        Patient enrollment has recently been completed in a Phase IIIc trial. The trial is a prospective, double-blind, randomized, controlled study of treated versus untreated FFP used in therapeutic plasma exchange of 30 patients with a disease called thrombotic thrombocytopenic purpura (TTP).

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Red Blood Cell Program

        Red Blood Cell Usage and Market.    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.

        INTERCEPT Blood System for Red Blood Cells.    The INTERCEPT Blood System for red blood cells uses a Helinx compound, S-303, which undergoes irreversible chemical reactions with DNA and RNA, as does amotosalen, but does not require light. S-303, a small molecule synthesized by us, is one of a proprietary class of compounds called frangible anchor-linker-effectors (FRALEs). The selection of S-303 was based on an extensive analysis of the compound's safety and its ability to inactivate pathogens and harmful white blood cells, and red blood cell survival and function after treatment with S-303. The active S-303 compound has been designed to rapidly decompose into non-reactive byproducts following the pathogen inactivation process.

        Development Status.    Phase III clinical trials of the INTERCEPT Blood System for red blood cells were terminated in September 2003 due to the detection of antibodies in two patients. The observations from this trial do not affect the development or commercialization of the pathogen inactivation programs for platelets and plasma, which use a different technology and mechanism of action. We have begun an evaluation of the antibody and are investigating process changes that could prevent antibody formation and allow the modified red blood cell system to undergo clinical trials. These activities may take a long time to complete and may not be successful.

        Pathogen Inactivation Studies.    Published results of laboratory studies have demonstrated the efficacy of the INTERCEPT Blood System for the inactivation of a broad array of viral, bacterial and parasitic pathogens, including West Nile Virus and the virus that causes SARS, with preservation of red blood cell function. We have also conducted laboratory studies that have indicated inhibition of white blood cell activity.

        Pre-Clinical Safety Studies.    We have successfully completed and published results of a number of pre-clinical safety studies for the INTERCEPT Blood System for red blood cells. Completed safety studies include acute and chronic toxicology, reproductive toxicology, general pharmacology, ADME, genotoxicity and carcinogenicity studies.

        Clinical Trials.    In May 1999, we completed a Phase Ia clinical trial of the INTERCEPT Blood System for red blood cells. The study was a randomized, controlled trial in 42 healthy subjects. The study was designed to evaluate the post-transfusion viability of treated red blood cells that were stored for 35 days prior to transfusion. The study showed that the circulation of treated red blood cells exceeded the American Association of Blood Banks' standard for red blood cell recovery 24 hours after transfusion.

        In October 1999, we completed a Phase Ib clinical trial of the INTERCEPT Blood System for red blood cells. The study included 28 healthy subjects, each of whom received four transfusions of treated red blood cells. The study demonstrated that there was no detectable immune response directed against treated red blood cells that were stored for 35 days prior to transfusion. The study also showed that circulation of treated red blood cells exceeded the American Association of Blood Banks standard for red blood cell recovery in response to multiple small doses of treated red blood cells 24 hours after transfusion.

        In July 2001, we completed a Phase Ic clinical trial of the INTERCEPT Blood System for red blood cells. The two-part trial enrolled 29 individuals in a crossover protocol under which individuals were transfused in random sequence with INTERCEPT red blood cells and conventional red blood cells that had not undergone a pathogen inactivation process. The results of this trial showed that

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INTERCEPT red blood cells demonstrated comparable survival to conventional red blood cells. The average post-transfusion recovery for both types of red blood cells exceeded the commonly accepted blood bank standard of 75%. In the second part of the study, 11 additional subjects received full unit transfusions of 35 day-old INTERCEPT red blood cells. The full unit transfusions were well tolerated.

        In January 2002 and March 2002, we initiated Phase III clinical trials of the INTERCEPT Blood System for red blood cells for acute transfusion support and for chronic transfusion support, respectively. The chronic trial enrolled patients requiring red blood cell transfusion support for the treatment of chronic anemia due to hereditary disorders, such as sickle cell disease or thalassemia. Both Phase III trials were terminated in September 2003 after two patients in the chronic trial developed antibodies to red blood cells treated with S-303. The two patients showed an antibody response but no clinical adverse events after transfusion with the S-303 treated red blood cells. The antibody response was discovered using a standard blood test that was employed as part of the clinical protocol.

        We plan to evaluate the available clinical data from the terminated Phase III clinical trials to determine the appropriate course of action for our investigational pathogen inactivation system for red blood cells. If we are successful in identifying process changes that could prevent antibody formation, it is not known what stages of clinical testing would be necessary to be completed for the reconfigured system.

Vaccine Platform Program

        Listeria Platform.    We are developing a proprietary, versatile technology to stimulate the immune system to target and attack cancer cells and infectious diseases. This platform technology is based on specially designed strains of the bacterium Listeria monocytogenes. Our scientists have demonstrated that proprietary strains of Listeria are capable of inducing potent immune responses in laboratory tests. We believe that the combination of proprietary strains of Listeria with specific cancer antigens, such as Mesothelin, has the potential to harness the power of the immune system to selectively attack malignant cells. Additionally, we are futher evaluating our Listeria platform technology with our Helinx technology for the development of potentially safe and potent therapies and vaccines for certain indications.

        Mesothelin.    We acquired certain exclusive rights to a novel cancer antigen, Mesothelin, from The Johns Hopkins University. We are using Mesothelin in combination with our proprietary cancer vaccine platform to develop therapeutic vaccines for the treatment of pancreatic and ovarian cancers. Mesothelin is an antigen that is frequently expressed in primary pancreatic and ovarian malignancies, but has limited expression in normal tissue. Research conducted at JHU has demonstrated that pancreatic cancer patients who responded to a Mesothelin-based prototype vaccine (not using our platform technology) generated an immune response against the antigen. We are developing a therapeutic vaccine that is designed to incorporate the Mesothelin antigen in our proprietary Listeria vaccine platform to potentially stimulate the patient's immune system to selectively recognize and kill pancreatic and ovarian tumor cells that express the Mesothelin cancer antigen.

        Development Status.    Our Listeria-based vaccine program is in pre-clinical research and development.

Investigator-Sponsored Clinical Trials of Helinx Technology

        We are collaborating with the National Marrow Donor Program, which is conducting a Phase Ib clinical study of our ACIT program in bone marrow transplants from unrelated donors.

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        A Phase I clinical trial of an experimental EBV cellular vaccine utilizing our Helinx technology is being conducted at Johns Hopkins University, and is supported in part by a grant from the National Institutes of Health.

        We do not plan to provide funding for these investigator-sponsored clinical trials or for further development of these programs and plan to conduct research and development supporting these applications of our Helinx technology to the extent that such activities are funded by outside sources.

Future Product Development

        In addition to our plans to pursue the therapeutic potential of our Helinx and vaccine platform technologies, we may also explore other development areas where we can address large, unmet medical needs.

Alliance with Baxter

        We have established an alliance with Baxter for the development of the INTERCEPT Blood System. Under two primary development, manufacturing and marketing agreements, Baxter and we generally share development activities with the primary development activity for the compounds and the pre-clinical and clinical studies performed by us and the primary development activity for the system disposables and devices performed by Baxter. Upon commercialization, we provide the inactivation compounds and Baxter is responsible for manufacturing and assembling the system disposables and illumination devices. Baxter is also responsible for marketing, selling and distributing the system. The programs under these agreements can be terminated by either party under certain circumstances. See "Risk Factors—We rely heavily on Baxter for development funding, manufacturing, marketing and sales."

        Agreement with Baxter for the Development of the INTERCEPT Blood System for Platelets.    We have a development and commercialization agreement with Baxter for the joint development of the INTERCEPT Blood System to inactivate infectious pathogens in platelets used for transfusion. This agreement provides for Baxter and us generally to share system development costs equally, subject to mutually determined budgets established from time to time, and for us to receive approximately 33.5% of revenue from sales of inactivation system disposables after each party is reimbursed for its cost of goods to the extent the cost exceeds specified amounts. Baxter has an exclusive, worldwide distribution license and is responsible for manufacturing and marketing the INTERCEPT Blood System for platelets. Revenue sharing payments due to us from sales of the INTERCEPT Blood System for platelets in Europe are currently being remitted by Baxter on our behalf to Baxter Capital Corporation, a financial subsidiary of Baxter International Inc., due to a dispute over the timing of repayment of a loan from Baxter Capital to us. We do not expect to receive revenue sharing payments from Baxter until this dispute is resolved.

        Agreement with Baxter for the Development of the INTERCEPT Blood System for Red Blood Cells and INTERCEPT Blood System for Plasma.    We also have a development and commercialization agreement with Baxter for the joint development of the INTERCEPT Blood System to inactivate viruses, bacteria and other infectious pathogens in red blood cells and fresh frozen plasma for transfusion. This agreement provides for Baxter and us generally to share red blood cell system development costs equally, subject to mutually determined budgets established from time to time. We are solely responsible for funding the development costs of the INTERCEPT Blood System for plasma. Baxter has an exclusive, worldwide distribution license and will be responsible for manufacturing and marketing the INTERCEPT Blood System for red blood cells and INTERCEPT Blood System for plasma following regulatory approvals. The agreement also provides for an equal sharing of revenue from sales of red blood cell system disposables, and for us to receive 75% and Baxter to receive 25% of revenue from sales of plasma system disposables, in each case after each party is reimbursed for its

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cost of goods and a specified percentage, not to exceed 14% of revenue, is retained by Baxter for marketing and administrative expenses. The termination of Phase III clinical trials of the red blood cell system does not affect the terms of the agreement, but will significantly delay the development of, and any potential revenue from, sales of the red blood cell system.

        Funding from Baxter.    As of December 31, 2003, we have received $46.7 million in equity investments from Baxter and $25.9 million in an equity investment from Baxter International Inc. and Subsidiaries Pension Trust, have received proceeds from a $50.0 million loan from Baxter Capital and have recognized approximately $30.4 million in milestone and development funding revenue from Baxter, since inception. Baxter has advised us that Baxter International Inc. and Subsidiaries Pension Trust is not an affiliate of Baxter. Baxter Capital has commenced legal proceedings against us seeking immediate repayment of amounts outstanding under the loan. Baxter Capital alleges that changes in our business constitute a default under the terms of the loan. Development funding is in the form of balancing payments made by Baxter to us, if necessary, to reimburse us for development spending in excess of the levels determined by Baxter and us.

        Baxter has the ability to terminate any of the development programs under certain circumstances.

Agreement with Kirin Brewery Co. Ltd.

        In January 2001, we entered into a collaborative agreement with the Pharmaceutical Division of Kirin to develop and market products for stem cell transplantation based on our Helinx technology. Under the terms of the agreement, we will jointly develop the products with Kirin. We received an initial license fee of $1 million. The license fee is being deferred and recognized as development funding ratably over the development period. We may not receive additional funding from Kirin. Although the agreement calls for Kirin to fund all development expenses for the Asia-Pacific region and a portion of our development activities aimed at obtaining product approval in the United States, no such development activities co-funded by Kirin are currently ongoing. Upon product approval, Kirin has exclusive rights to market the products in the Asia-Pacific region, including Japan, China, Korea and Australia, and we will receive a specified share of product revenue, including a royalty and reimbursement of our cost of goods. We retain all marketing rights for the rest of the world, including the United States and Europe.

Cooperative Agreement with the Armed Forces of the United States

        In February 2001, we were awarded a $3.5 million cooperative agreement by the Army Medical Research Acquisition Activity division of the Department of Defense. In September 2002 and May 2003, we were awarded additional $6.5 million and $6.2 million cooperative agreements, respectively, both of which were awarded to continue funding of projects to develop our pathogen inactivation technologies to improve the safety and availability of blood that may be used by the United States Armed Forces for medical transfusions. Under the conditions of the agreements, we are conducting research on the inactivation of infectious pathogens, including unusual viruses, bacteria and parasites, which are of particular concern to the Armed Forces. We are collaborating with investigators at Walter Reed Army Institute of Research to investigate ways to improve the storage and shelf life of blood and blood components, which may be used for medical transfusion support in combat zones.

Product Engineering

        The INTERCEPT Blood System comprises mechanical instruments that activate the pathogen inactivation process and disposables that include plastic containers and tubing, inactivation compounds and other fluids, and compound adsorption devices. The design and engineering of the system requires substantial effort. Although we collaborate in these efforts, the bulk of this work is undertaken by Baxter.

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Manufacturing and Supply

        We have used, and intend to continue to use, third parties to manufacture and supply the inactivation compounds for our systems for use in clinical trials and for the commercialization of our products in development. We have no experience in manufacturing products for commercial purposes and do not have any manufacturing facilities. Consequently, we are dependent on contract manufacturers for the production of compounds and on Baxter for other system components for development and commercial purposes.

        Under our agreements with Baxter, we are responsible for developing and delivering our proprietary compounds 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 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.

        To provide the inactivation compounds for the INTERCEPT Blood System for platelets and INTERCEPT Blood System for plasma, we have contracted with one manufacturing facility for synthesis of amotosalen. Under this contract, we are not subject to minimum annual purchase requirements. If specified quantities of amotosalen are not purchased in any year, however, we are required to pay a maintenance fee of up to $50,000 for such year. We currently have a stock of compound sufficient to support the anticipated remaining product development planned for the INTERCEPT Blood System for platelets and INTERCEPT Blood System for plasma, and to support near-term sales of the INTERCEPT Blood System for platelets in Europe.

        Our contract manufacturers and we purchase certain raw materials from a limited number of suppliers. While we believe that there are alternative sources of supply for such materials, establishing additional or replacement suppliers for any of the raw materials, if required, may not be accomplished quickly and could involve significant additional costs. Any failure to obtain from alternative suppliers any of the materials used to manufacture our compounds, if required, would limit our ability to manufacture our compounds.

Marketing, Sales and Distribution

        The market for our pathogen inactivation systems is dominated by a small number of blood collection organizations. In the United States, the American Red Cross collects and distributes approximately 50% of the nation's supply of blood and blood components. Other major United States blood collection organizations include the New York Blood Center and United Blood Services, each of which distributes approximately 6% of the nation's supply of blood and blood components. In many countries of Western Europe and in Japan, various national blood transfusion services or Red Cross organizations collect, store and distribute virtually all of their respective nations' blood and blood components supply. In Europe, the largest markets for our products are in Germany, the United Kingdom and France. Decisions on product adoption are centralized in the United Kingdom. In Germany, decisions on product adoption are expected to be on a blood center-by-blood center basis. We have not received in-country approvals to market our platelet system in Germany or the United Kingdom, and certain additional activities are required before we can market the system in France.

        For logistical and financial reasons, the transfusion industry has not always integrated new technologies into their processes, even those with the potential to improve the safety of the blood supply. Our products may require significant changes to our potential customers' space and staffing requirements and require significant capital investment. Even if our product candidates receive regulatory approval for commercial sale, physicians, patients and healthcare payors may not believe that the benefits of using our systems justify their additional cost. Some blood product is consumed as a result of our pathogen inactivation process. If the reduction of blood product leads to increased costs,

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or requires changes in clinical regimens, customers may not adopt our product. In addition, our products do not inactivate all known pathogens, and the inability of our systems to inactivate certain pathogens may inhibit their acceptance. Our products may be inappropriate for certain patients, which could reduce the potential market size. In addition, healthcare professionals may require further safety information or additional studies before adopting our products. Baxter's ability to successfully commercialize our products will depend in part on the availability of adequate reimbursement for product costs and related treatment of blood components from governmental authorities and private health care insurers (including health maintenance organizations), which are increasingly attempting to contain health care costs by limiting both the extent of coverage and the reimbursement rate for new tests and treatments.

        Baxter is responsible for the worldwide marketing, sales and distribution of the INTERCEPT Blood System. We currently have a small marketing group that helps support Baxter's marketing organization; however, we do not intend to develop our own independent marketing and sales organization and expect to continue to rely on Baxter to market and sell the INTERCEPT Blood System.

Competition

        We believe that the INTERCEPT Blood System has certain competitive advantages over competing pathogen inactivation methods that are either on the market, or in development. The INTERCEPT Blood System is designed for use in blood centers, to integrate with current blood collection, processing and storage procedures. Competing products in development or currently on the market, such as solvent-detergent treated plasma, use centralized processing that takes the blood product away from the blood center. The INTERCEPT Blood System is designed for use with single units of blood products. Some potential competitors utilize a pooling process prior to pathogen inactivation, which significantly increases the risk of contamination by pathogens that are not inactivated. There are currently no competitors that have pathogen inactivation methods approved or in clinical trials for platelets. In addition to competition from other pathogen inactivation methods, we expect to encounter competition from other approaches to blood safety, including methods of testing blood products for pathogens.

        We believes that the primary competitive factors in the market for pathogen inactivation of blood products 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 is an important competitive factor. We believe that the INTERCEPT Blood System 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, our success will depend in part on our 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 our product development efforts will result in any commercially successful products.

Patents, Licenses and Proprietary Rights

        Our success depends in part on our 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 us. Our policy is to seek to protect our proprietary position by, among other methods, filing United States and foreign patent applications related to our proprietary technology, inventions and improvements that are important to the development of our business. As of December 31, 2003, we owned 67 issued or allowed United States patents and 60 issued or allowed

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foreign patents. Our patents expire at various dates between 2009 and 2018. In addition, we have 27 pending United States patent applications and have filed 20 corresponding patent applications under the Patent Cooperation Treaty, which are currently pending in Europe, Japan, Australia and Canada, and of which eight are also pending in China and six of which are also pending in Hong Kong. In addition, we are a licensee under a license agreement with respect to two United States patents covering inventions pertaining to psoralen-based photochemical decontamination treatment of whole blood or blood components and 12 United States patents relating to vaccines, as well as related foreign patents. Proprietary rights relating to our 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, us will afford protection against competitors or that any pending patent applications now or hereafter filed by, or licensed to, us will result in patents being issued. In addition, the laws of certain foreign countries do not protect our intellectual property rights to the same extent as do the laws of the United States.

Government Regulation

        Our products and we 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 FDA regulates the INTERCEPT Blood System as a biological medical device. The FDA's Center for Biologics Evaluation and Research is principally responsible for regulating the INTERCEPT Blood System. In addition to regulating our product, CBER also regulates the blood collection centers and the blood products they prepare using our medical device.

        Before the FDA determines whether to approve our products, we expect our approval applications to be reviewed by the Blood Products Advisory Committee, or BPAC, an advisory committee convened by and reporting to the FDA. The BPAC will make a recommendation to the FDA for, or against, approval. Before a medical device may be marketed in the United States, the FDA must clear a premarket notification (a 510(k)) or approve a premarket approval 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. Before a combination product can be marketed in the United States, it must have an approved PMA, NDA or BLA, depending on which statutory authority the FDA elects to use.

        The steps required before a medical device, drug or biologic may be approved for marketing in the United States pursuant to a PMA, NDA or BLA, respectively, generally include (i) pre-clinical laboratory and animal tests, (ii) submission to the FDA of an investigational device exemption (for medical devices) or an investigational new drug application (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 safety and efficacy for its intended indications, (v) submission to the FDA of a PMA, NDA or BLA, as appropriate and (vi) FDA review of the PMA, NDA or BLA 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) or Quality System Regulation requirements is satisfactory. The FDA will require a PMA for each of the systems for platelets, plasma and red blood cells.

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        Our European investigational plan is based on the INTERCEPT Blood System being categorized as Class III drug/device combinations under the Medical Device Directives of the European Union. The European Union requires that medical devices affix the CE Mark, an international symbol of adherence to quality assurance standards and compliance with the MDD. The INTERCEPT Blood System for platelets received the CE Mark in October 2002. Separate CE Mark certifications must be received for Baxter to sell the INTERCEPT Blood System for plasma and INTERCEPT Blood System for red blood cells in the European Union. Many individual European countries require additional in-country studies to support an approval to market the products in such countries.

        Baxter is using a modular process for its PMA application for the INTERCEPT Blood System for platelets. The content, order and submission timing of the modules must be approved by the FDA, and a modular PMA application cannot be approved until all modules have been submitted to, reviewed by and accepted by the FDA.

        In addition to the regulatory requirements applicable to our products and us, there are regulatory requirements applicable to our prospective customers, the blood centers that process and distribute blood and blood products. Blood centers and others will be required to obtain approved license supplements from the FDA before using the INTERCEPT Blood System. There can be no assurance that any blood centers will be able to obtain the required licenses on a timely basis, or at all.

        To support Baxter's requests for regulatory approval to market the INTERCEPT Blood System, we conduct various types of studies, including toxicology studies to evaluate product safety, laboratory and animal studies to evaluate product effectiveness and human clinical trials to evaluate the safety, tolerability and effectiveness of treated blood components. We believe that, in deciding whether the INTERCEPT Blood System is safe and effective, the 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 the regulatory authorities 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. We have conducted many toxicology studies designed to demonstrate the INTERCEPT Blood System's safety. There can be no assurance that regulatory authorities will not require further toxicology or other studies of our products. Based on discussions with the FDA and European regulatory authorities, we believe that data from human clinical studies is required to demonstrate the safety of treated blood components and their therapeutic comparability to untreated blood components, but that only data from laboratory 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, our clinical trial programs for the INTERCEPT Blood System consists of studies that differ from typical Phase I, Phase II and Phase III clinical studies.

        All of our clinical trials have been and are being conducted using prototype system disposables and devices. We plan to perform laboratory studies to demonstrate equivalency between the prototype and the commercial configuration. We cannot be certain that these studies will be successful or the FDA will not require additional studies, which could delay commercialization. If we decide to seek FDA approval of the INTERCEPT Blood System for platelets for use in treating pooled random donor platelets, additional clinical studies will be required. In addition, there currently are three principal manufacturers of automated apheresis collection equipment, including Baxter. The equipment of each manufacturer collects 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. Under an agreement with Haemonetics Corporation, Baxter has agreed to provide Haemonetics with a platelet storage solution proprietary to Cerus and Baxter, with the objective that platelets collected on certain future Haemonetics apheresis collection equipment may be directly treated using the INTERCEPT Blood System. However, we intend initially to seek FDA approval of the INTERCEPT Blood System for platelets configured for

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Baxter's apheresis collection equipment. If we determine that compatibility with other equipment is desirable, additional processing procedures and system configurations will need to be developed. We believe that the FDA will also require supplemental clinical data before approving its system for use with platelets collected using other equipment.

Health Care Reimbursement and Reform

        The future revenue 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 federal and state government initiatives directed at lowering the total cost of health care, it is likely that the United States 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.

        Our ability to commercialize our products successfully will depend in part on the extent to which appropriate reimbursement levels for the cost of the products and related treatment are obtained from governmental authorities, private health insurers and other organizations, such as 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 affect the prices for our products.

Employees

        As of February 29, 2003, we had 120 employees, 81 of whom were engaged in research and development and 39 in general and administrative. None of our employees are covered by collective bargaining agreements, and we believe that our relationship with our employees is good.

Available Information

        We maintain a website at www.cerus.com; however, information found on our website is not incorporated by reference into this report. We make available free of charge on or through our website our annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC.

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RISK FACTORS

        Our business faces significant risks. If any of the events or circumstances described in the following risks actually occur, our business may suffer, the trading price of our common stock could decline and our financial condition or results of operations could be harmed. These risks should be read in conjunction with the other information set forth in this report.

If our pre-clinical and clinical trials are not successful or the data are not considered sufficient by regulatory authorities to grant marketing approval, Baxter and we will be unable to commercialize our products and generate revenue.

        Except for the INTERCEPT Blood System for platelets, which has received CE Mark approval and regulatory approval in certain countries in Europe, we have no products that have received regulatory approval for commercial sale and are being marketed. Our product candidates are in various stages of development, and we face the risks of failure inherent in developing medical devices and biotechnology products based on new technologies. Our products must satisfy rigorous standards of safety and efficacy before the United States Food and Drug Administration and international regulatory authorities can approve them for commercial use. We must provide the FDA and foreign regulatory authorities with pre-clinical, clinical and manufacturing data that demonstrate our products are safe, effective and in compliance with government regulations before the products can be approved for commercial sale.

        In 2002, the INTERCEPT Blood System for platelets received CE Mark approval in Europe. Our development and marketing partner, Baxter Healthcare Corporation, will need to complete validation studies and obtain reimbursement approvals in some individual European countries to market our products in those countries. In certain countries, including the United Kingdom, France and Germany, the system must be approved for purchase, reimbursement or use by a specific governmental or non-governmental (such as the Paul Ehrlich Institute in Germany) entity or entities in order for it to be adopted by a specific customer. The level of additional product testing varies by country, but could take a long time to complete.

        We completed our Phase III clinical trial of the INTERCEPT Blood System for platelets in the United States in March 2001 and have submitted data from this trial, along with several other modules of our pre-market approval application,