Press Release Details

Preclinical Results Demonstrate Potential Therapeutic and Safety Benefits of Cerus' Cancer Immunotherapy Technology

September, 22 2004

CONCORD, Calif. -- Cerus Corporation (Nasdaq:CERS) today announced the publication of preclinical efficacy and safety data for its cancer immunotherapy technology in the September 21, 2004, issue of the Proceedings of the National Academy of Sciences (PNAS). Together with two papers validating cancer antigens published by independent groups in August, Cerus now has mounting evidence supporting the intensified development of its cancer immunotherapy technology. The most recent paper describes studies in which experimental vaccines based on a proprietary attenuated Listeria strain were engineered to express tumor antigens. These vaccines were shown to elicit therapeutic anti-tumor responses, including prolonged survival and tumor regression, following vaccination of tumor-bearing mice. In addition, the Cerus strain demonstrated an over one thousand-fold increase in safety when compared to unmodified Listeria.

"These recent publications demonstrate the potential value of our Listeria-based platform and the development programs on which we are focused," said Claes Glassell, president and CEO of Cerus Corporation. "We continue to make progress toward the goal of filing our first cancer vaccine IND by the end of 2005."

In the experiments described in the PNAS paper, a strain was systematically selected from Cerus' library of genetically defined attenuated Listeria. In comparison to other strains, the optimized strain was cleared more rapidly in vivo and also showed significantly higher safety margins. The increased safety margins allowed the selected strain to be administered at higher doses, resulting in more potent T-cell responses than those produced using unmodified Listeria. Finally, therapeutic administration of an experimental vaccine using the optimized strain resulted in a significant reduction in metastases and a significant increase in survival in mice with established tumors.

Cerus' preclinical development programs are focused on two novel cancer antigens. Cerus is collaborating with Johns Hopkins University to develop a Listeria-based vaccine targeting Mesothelin, and has partnered with MedImmune, Inc. to develop a Listeria-based vaccine targeting EphA2. Both antigen targets have recently been featured in new research reports suggesting their significance as potential targets for cancer treatment.

Immune responses to Mesothelin were elicited in pancreatic cancer patients after vaccination in a trial performed at the Johns Hopkins Kimmel Cancer Center, as reported in the August 2, 2004, issue of Journal of Experimental Medicine. Three patients developed anti-Mesothelin T cell responses, and all three are alive and tumor free six years after vaccination. Cerus announced an agreement to license Mesothelin intellectual property from Johns Hopkins earlier this year.

In ovarian cancer patients, elevated levels of EphA2 were linked to cancer progression and decreased patient survival in a paper published on August 1, 2004, in Clinical Cancer Research by researchers from the University of Texas M.D. Anderson Cancer Center. EphA2 is also known to be overexpressed by other types of cancers, including breast, prostate, and melanoma (skin).

"The work described in the PNAS paper demonstrates that we've been able to greatly improve the safety of Listeria without compromising this organism's unique immunostimulatory characteristics," said David N. Cook, PhD, vice president of research and development, Cerus Corporation. "We believe that Listeria's potential ability to stimulate both innate and adaptive immunity offers significant advantages over other approaches to cancer immunotherapy, and that our results are very impressive compared to other approaches evaluated in the same preclinical model."


Cerus Corporation is developing novel technologies to provide safer and more effective therapeutic options to patients in areas with substantial unmet medical needs, particularly within the fields of cancer, infectious disease and blood safety. The Concord, California-based company is combining its proprietary vector technologies with public domain and proprietary antigens to develop new therapies for cancer and infectious disease. Cerus has two therapeutic cancer vaccine products in development using its Listeria vector technology, one in collaboration with MedImmune, Inc. and the other with Johns Hopkins University. Cerus is also collaborating with subsidiaries of Baxter International Inc. on the INTERCEPT Blood System, which is designed to enhance the safety of donated blood components by inactivating viruses, bacteria and other pathogens. The INTERCEPT Blood System is based on the company's Helinx technology for controlling biological replication. The INTERCEPT Blood System for platelets is currently being marketed in Europe.

Helinx is a trademark of Cerus Corporation

INTERCEPT Blood is a trademark of Baxter International Inc.

Statements in this news release regarding potential efficacy of products based on our Listeria platform, product development and commercial potential 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 inherent in developing biotechnology products based on new technologies, risks related to the early stage of development of our vaccine program, risks related to the initiation and completion of clinical trials, risks related to actions by collaborators and other risks discussed in Cerus' Quarterly Report on Form 10-Q for the quarter ended June 30, 2004, filed with the Securities and Exchange Commission.


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