Press Release Details

Cerus Completes Successful Phase 1B Clinical Trial of its Red Blood Cell Pathogen Inactivation System Study Demonstrates Viability of Treated Red Blood Cells; No Immune Response Detected

October, 26 1999

CONCORD Calif., Oct. 26 /PRNewswire/ -- Cerus Corporation (Nasdaq: CERS) today announced positive results of a Phase 1b clinical trial of its proprietary system to inactivate viruses, bacteria and other pathogens in red blood cells intended for transfusion. The Phase 1b study was designed to determine if red blood cells treated with Cerus' proprietary S-303 pathogen inactivation system would cause an immune response to occur in individuals receiving the treated cells through transfusion.

The study, which included 30 healthy subjects that received four transfusions of S-303-treated red blood cells, demonstrated there was no detectable immune response directed against the treated red blood cells. The study also showed that the viability of S-303 treated red blood cells after 35 days of storage exceeded the American Association of Blood Banks standard.

"Our findings that the S-303 treated red blood cells were circulating well and that they did not provoke an immune response represent a critical step forward for this program," stated Laurence Corash, M.D., Vice President for Medical Affairs at Cerus. "We will be presenting these data at the American Society of Hematology meeting in early December, along with data from clinical trials of each of our other development programs."

"Our Phase 1b data will be solid support for moving into the next planned trial for this program," said Cerus President and Chief Executive Officer Stephen Isaacs. "We are now working to complete the design and testing of the disposable set for full unit transfusions."

The Cerus red blood cell pathogen inactivation system has been developed to target and inactivate blood-borne pathogens while leaving the therapeutic properties of red blood cells intact. An estimated 31 million units of red blood cells are transfused worldwide each year to treat various indications ranging from severe trauma to genetic disorders.

Cerus Corporation is developing systems designed to enhance the safety of blood transfusions by inactivating pathogens in blood components (platelets, fresh frozen plasma (FFP) and red blood cells) used for transfusion and for source plasma used for fractionation into various plasma products. The Cerus systems are also designed to inactivate white blood cells, which are associated with a variety of adverse transfusion reactions. The company's pathogen inactivation systems for platelets, FFP and source plasma are based on Cerus' proprietary light-activated compound, S-59. The platelet system is currently in a Phase 3 clinical trials in Europe and the United States. The FFP system is currently in a United States Phase 3 trial. The system for source plasma is in preclinical development.

The company's platform technologies, which prevent viral, bacterial and cellular replication, have potential applications in the health care field beyond pathogen inactivation in blood components. Cerus has ongoing clinical trials of its S-59 technology in the field of stem cell transplantation to treat leukemia and other hematologic malignancies.

Cerus Corporation is collaborating with the Fenwal Division of Baxter Healthcare Corporation to develop, manufacture and market pathogen inactivation systems for blood components used for transfusion. Baxter, a global medical products and services company, focuses on critical therapies for life-threatening conditions. Baxter is a leader in technologies related to blood and the circulatory system. Cerus is also collaborating with the Consortium for Plasma Science to develop pathogen inactivation systems for plasma for fractionation.

Statements in this news release regarding product development and clinical development are forward-looking statements that involve risks and uncertainties. Actual results could differ materially from the above forward-looking statements as a result of certain factors, including the uncertainty of the timing and results of any trials, regulation by the FDA, the uncertainty of replication of animal data in humans, the uncertainty of market acceptance of any products, competitive conditions, the uncertainty of future financing and other factors discussed in the company's 1998 Annual Report on Form 10-K.

For more information, contact:

 Cerus Corporation Noonan/Russo Communications, Inc. 925-603-9071415-677-4455 Stephen Isaacs, President and CEO Amy Giller, Investors Greg W. Schafer, CFOAmy Flood, Media

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