Business Editors/Health/Medical Writers

CONCORD, Calif.--(BUSINESS WIRE)--Oct. 23, 2003

Cerus Corporation (Nasdaq:CERS) today announced the initiation of a Phase IB clinical trial for its allogeneic cellular immune therapy (ACIT). The company's ACIT is being developed to improve stem cell transplant outcomes in patients with hematologic malignancies including leukemia and lymphoma.

"We are pleased to collaborate with Cerus on this promising approach to improve stem cell transplants," said Dennis L. Confer, M.D., chief medical officer, National Marrow Donor Program(R). "We continuously strive to improve therapeutic outcomes for our patients."

Stephen T. Isaacs, president and chief executive officer of Cerus, said, "This clinical trial will evaluate the potential of our Helinx(R) technology to benefit cancer patients, who are being treated with life saving stem cell therapy. As we seek to develop and commercialize the INTERCEPT Blood System to improve blood safety, we continue to expand our pipeline with therapeutic applications of our platform Helinx technology, positioning Cerus for long term growth."

The trial is a multi-center, investigator-sponsored study, which will evaluate three different doses. A maximum of 42 patients with hematologic malignancies will be enrolled in the study and will receive Helinx-treated T-cells as an adjunct to unrelated donor stem cell transplants. The study is designed to demonstrate the safety of a combination treatment regimen consisting of stem cells and Helinx-treated T-cells in patients with leukemia and lymphoma. Primary endpoints are the incidence of acute graft-versus-host disease and the incidence of transplant engraftment.

Stem cell transplantation is currently used as an important, and potentially curative, cancer treatment. The procedure, however, carries a significant risk of a serious and potentially fatal complication known as graft-versus-host disease (GVHD). This condition arises when the donor's leukocytes proliferate within the transplant recipient and attack the tissues and organs. Cerus' Helinx technology addresses this problem by inhibiting proliferation of leukocytes, targeting and binding their DNA. The trial will focus on the use of Helinx-treated leukocytes to promote stem cell engraftment, while reducing the serious risk of GVHD.

ABOUT NATIONAL MARROW DONOR PROGRAM(R)

The National Marrow Donor Program(R) (NMDP) is a nonprofit organization that is committed to its mission to extend and improve life through innovative stem cell therapies. The NMDP has facilitated more than 16,000 transplants throughout the world for patients with life-threatening diseases such as leukemia and aplastic anemia, as well as certain immune system and genetic disorders. The NMDP offers searching patients who do not have suitable family donors a single point of access for all three types of stem cells used in transplantation: marrow, peripheral blood and umbilical cord blood. Through its extensive U.S. and international Network, the NMDP manages the largest and most diverse Registry of more than 5 million volunteer donors, including more than 28,000 cord blood units. Matching donors to patients is only part of NMDP's life-saving mission. The NMDP also provides support for patients and physicians and conducts research studies aimed at increasing opportunities for and improving the outcomes of stem cell transplants. For more information about the NMDP, call 1-800-MARROW-2 or visit online at www.marrow.org.

ABOUT CERUS

Cerus Corporation is developing medical systems and therapeutics to provide safer and more effective options to patients. The company is developing products based on its proprietary Helinx(R) technology for controlling biological replication. Cerus' most advanced programs are focused on systems to enhance the safety of the world's blood supply. The INTERCEPT Blood System, which is being developed in collaboration with subsidiaries of Baxter International Inc., is based on the company's Helinx technology. The Intercept Blood System is designed to inactivate viruses, bacteria, other pathogens, and white blood cells. The Concord, Calif.-based company also is pursuing therapeutic applications of Helinx technology to treat and prevent serious diseases.

Helinx is a trademark of Cerus Corporation.

INTERCEPT and INTERCEPT Blood are trademarks of Baxter International Inc.

Statements in this news release regarding product development, potential efficacy of ACIT, potential efficacy of the INTERCEPT Blood System 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 risks and uncertainty of the timing and results of clinical trials and other development activities, actions by regulatory authorities at any stage of the development and commercialization process, additional financing activities, manufacturing, market acceptance of any products, competitive conditions, long term growth opportunity of Cerus and other factors discussed in the company's most recent filings with the Securities and Exchange Commission.