Company Press Release

Cell Genesys Reports Encouraging Results in Preclinical Studies of Parkinson's Disease Gene Therapy

Single Gene Therapy Treatment Eliminates the Need for Daily L-dopa Treatment

FOSTER CITY, Calif and SEATTLE, Jan. 28 /PRNewswire/ -- Cell Genesys, Inc. (Nasdaq: CEGE - news) and the University of Washington today published data demonstrating that after a single gene therapy injection, genetically modified mice exhibiting certain symptoms of Parkinson's disease could survive without daily L-dopa treatments for at least one year, the duration of the study. Without L-dopa treatment, these mice die of malnutrition by three weeks of age. An adeno-associated viral (AAV) gene delivery system was used to deliver the genes required for the production of L-dopa to specific regions of the brain where L-dopa production could be detected throughout the observation period. L-dopa is a commonly prescribed drug which is converted to dopamine, the neurotransmitter chemical missing in these mice and in patients with Parkinson's disease. This work was published in the journal, Neuron, by a team of scientists led by Mark Szczypka, Ph.D. and Richard Palmiter, Ph.D. at the University of Washington and Ronald J. Mandel, Ph.D. and Richard O. Snyder, Ph.D. of Cell Genesys.

``A single gene therapy treatment for Parkinson's disease would be a significant improvement over the currently available treatment for this disease,'' stated Mitchell H. Finer, Ph.D., vice president, research at Cell Genesys. ``These studies are among the first observation that gene therapy with AAV vectors can be used to correct a genetic defect in specific regions of the brain.''

``The most striking finding in our experiments was the elimination of the need for daily L-dopa treatment in the mice receiving the gene therapy. This represents a remarkable rescue of an otherwise lethal mutation in these genetically modified mice,'' stated Dr. Richard Palmiter, Investigator of the Howard Hughes Medical Institute and Professor of Biochemistry at the University of Washington. ``In the published work, the motivation of the mice to eat and drink was restored following the single administration of gene therapy.''

In the published experiments, mice dependent upon daily injections of L-dopa for their survival, were injected with AAV vectors carrying the tyrosine hydroxylase and GTP cyclohydrolase I genes directly to the striatum, one of the principal regions of the brain affected in Parkinson's disease. L-dopa was then produced at therapeutic levels by the genetically modified brain cells for the duration of the study making daily treatment with exogenous L-dopa unnecessary. These data further support previous findings that both of these two genes are required for L-dopa synthesis in the brain and suggest a potential treatment strategy for patients with Parkinson's disease.

The mouse model used in this study was created in Dr. Palmiter's laboratory using gene-targeting techniques. The genetically modified mice are unable to make tyrosine hydroxylase, a critical enzyme for dopamine synthesis in the brain. These mice develop severe movement dysfunction that resembles that of Parkinson's disease patients. The mice also have behavioral defects and will not eat and drink enough to survive without L-dopa therapy.

Gene delivery systems, or vectors, are the means by which therapeutic genes are introduced into target cells or tissues to induce a therapeutic effect and are a critical component of any successful gene therapy. The AAV gene delivery system is one of four vector systems under development at Cell Genesys. Cell Genesys holds a broad U.S. patent covering all gene therapy products that utilize AAV vectors to deliver genes as therapeutic agents. The patent includes composition of matter claims which cover the essential component of any AAV gene delivery system, specifically any recombinant AAV vector products, free of contaminating wild-type AAV, regardless of the method of production. Cell Genesys has one of the largest patent estates in gene therapy with over 150 issued or granted patents and over 300 pending patent applications.

Cell Genesys is focused on the development and commercialization of gene therapies to treat major, life-threatening diseases including cancer and AIDS. The company is conducting Phase I/II human clinical trials for its GVAX(TM) cancer vaccine in prostate cancer, lung cancer and melanoma. The company's AIDS gene therapy is in Phase II human clinical testing. Preclinical stage programs include gene therapy for hemophilia, Parkinson's disease and cardiovascular disorders. Cell Genesys' current business strategy is to seek a licensing partner for its Parkinson's disease gene therapy program. Cell Genesys' assets outside gene therapy include its approximately 30 percent ownership of Abgenix and the company's licensing program in gene activation technology.

Statements made herein, other than statements of historical fact, including statements about the company's progress and results of preclinical studies, clinical trials, marketability of potential products and nature of product pipelines, availability of financing and adequacy of capital resources, the amount of expected available cash resources, technology, corporate partnerships, licenses and intellectual property are forward-looking statements and are subject to a number of uncertainties that could cause actual results to differ materially from the statements made, including risks associated with the success of research and development programs, results achieved in future preclinical studies and clinical trials, the regulatory approval process, competitive technologies and products, patents, corporate partnerships and additional financings. For information about these and other risks which may affect Cell Genesys, please see the company's Annual Report on Form 10-K dated March 31, 1998 as well as Cell Genesys' reports on Form 10-Q and 8-K and other reports filed from time to time with the Securities and Exchange Commission.

SOURCE: Cell Genesys, Inc.