Press Release Details

Cerus Reports Preclinical Study Results on Its Program In Allogeneic Bone Marrow Transplant

December, 06 1999

Data Presented at American Society of Hematology Meeting

CONCORD, Calif., Dec. 6 /PRNewswire/ -- Cerus Corporation (Nasdaq: CERS) today reported data from a pre-clinical study of the company's proprietary allogeneic cellular immune therapy (ACIT) system. The study evaluated the use of T-cells treated with the company's proprietary S-59 compound in an animal bone marrow transplant model. The study demonstrated that transfusion of S-59 treated T-cells facilitated bone marrow engraftment and long-term survival without graft-versus-host disease (GVHD). In contrast, transfusion of untreated T-cells resulted in severe GVHD and early death. In addition, the treated T-cells remained reactive against leukemia. The data were presented at the 41st annual meeting of the American Society of Hematology (ASH) meeting in New Orleans.

The company's ACIT system is being developed to improve engraftment of the bone marrow transplant and reduce serious adverse immune responses relating to bone marrow transplantation procedures. Based on these preclinical results, as well as others previously announced, Cerus is conducting a Phase 1 clinical trial on allogeneic transplantation using donors who are haploidentical (half-matched) with transfusion recipients.

"The data from preclinical studies continue to support the use of our nucleic acid targeting technology for improving outcomes of bone marrow transplantation," said Cerus President and Chief Executive Officer, Stephen Isaacs. "Our ACIT program illustrates Cerus' continuing commitment to pursuing new applications of our core technologies."

Cerus also presented in vitro data demonstrating the ability of its system to prevent human T-cell proliferation while maintaining immunological functions that are believed to be important in promoting bone marrow engraftment and an anti-leukemia effect. Abstracts from these studies can be found on the Cerus website at .

Bone marrow transplantation is a highly effective treatment for many forms of leukemia and lymphomas. Bone marrow transplantation is most effective when the donor is very closely matched to the patient for the major human leukocyte antigen (HLA) groups. As part of the bone marrow transplantation procedure, patients often receive T-cells from the donor. While these T-cells improve engraftment of the bone marrow transplant and help reconstitute the patient's immune system following chemotherapy or radiation therapy, donor T-cells expose the patient to a high risk of contracting graft-versus-host disease. GVHD, which has a high mortality rate, is caused by the proliferation of donor T-cells which attack the patient's healthy tissue. The company's ACIT system has been developed to decrease the need for stringency of matching donors to patients and to inhibit the ability of donor T-cells to cause GVHD while maintaining their therapeutic properties.

The Cerus compound S-59 is a light-activated psoralen compound that has been developed to target nucleic acid and prevent the replication of DNA and the transcription of RNA, which are required for cellular replication.

Cerus Corporation is also developing proprietary systems to improve the safety of blood products through the inactivation of viruses, bacteria and other pathogens. Programs for platelets, plasma and red blood cells intended for transfusion are currently in clinical trials. Cerus is also developing a system to treat source plasma prior to fractionation into various plasma products. Cerus has collaboration agreements with Baxter Healthcare and the Consortium for Plasma Science.

Statements in this news release regarding product development and pre-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 animal studies and clinical trials, regulation by the FDA, the uncertainty of replication of animal data in humans and other factors discussed in the company's 1998 Annual Report on Form 10-K.

Contact: Stephen Isaacs, President and CEO, or Greg W. Schafer, Chief

Financial Officer, both of Cerus Corporation, 925-603-9071; or

Amy Giller, Investors, or Amy Flood, Media, both of Noonan-Russo

Communications, 415-677-4455

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