Press Release Details

Cerus Acquires Additional Rights to Mesothelin Cancer Antigen from Chugai Pharmaceutical

December, 22 2004

CONCORD, CA, December 22, 2004 - Cerus Corporation (NASDAQ: CERS) today announced it has acquired from Chugai Pharmaceutical Co., Ltd., an exclusive license in the field of cancer vaccines covering Chugai's patent on the DNA sequence of Mesothelin. Mesothelin is an antigen expressed in pancreatic and ovarian malignancies. Cerus is using Mesothelin in combination with its proprietary attenuated Listeria platform to develop active immunotherapies for treating pancreatic and ovarian cancers. Cerus has previously acquired rights from Johns Hopkins University covering vaccine compositions and methods of using Mesothelin.

"This agreement with Chugai solidifies our leadership in the development of Mesothelin-based active immunotherapies," said Claes Glassell, president and CEO of Cerus Corporation. "Mesothelin has recently emerged as a highly promising target for the immune system based on published human studies in pancreatic cancer patients, as well as on a growing body of preclinical data with our product candidate." He noted that the Listeria-Mesothelin vaccine is part of an emerging cancer immunotherapy portfolio that also includes Listeria-EphA2, being developed in collaboration with MedImmune.

The terms of the Chugai license agreement include an up-front payment, development milestone payments to Chugai, and royalties on product sales.

Immune responses to Mesothelin have been documented in pancreatic cancer patients receiving an experimental whole-cell cancer vaccine, as reported in the August 2, 2004, issue of Journal of Experimental Medicine. In this study, three patients developed anti-Mesothelin T cell responses, and all three were alive and tumor free six years after vaccination. The goal of the Cerus cancer therapy, which is in preclinical development, is to use the Listeria platform to stimulate the patient's immune system to selectively recognize and kill pancreatic and ovarian tumor cells that express the Mesothelin cancer antigen.

ABOUT CERUS
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 also is collaborating with subsidiaries of Baxter International Inc. on the INTERCEPT Blood System, which is being developed 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 approved for use in the European Union, and is being developed for commercialization in Japan and certain other Asian countries by BioOne Corporation.

Helinx is a trademark of Cerus Corporation
Baxter and INTERCEPT are trademarks of Baxter International Inc.

Statements in this news release regarding potential future payments under the agreement and the fulfillment of contractual commitments, as well as statements regarding potential efficacy and safety of products based on our vaccine platform, potential regulatory approvals and 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 and uncertainties inherent in developing biotechnology products based on new technologies, the timing and results of clinical trials and other development activities, the acceptability of any data by regulatory authorities, actions by regulatory authorities at any stage of the development process, actions by collaborators, competitive conditions and other factors discussed in the company's Form 10-Q for the third quarter of fiscal 2004, as well as in other reports filed from time to time with the Securities and Exchange Commission. The company assumes no obligation to update any forward-looking statements.

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