New Data Further Supports Liver-Directed Therapy

FOSTER CITY, Calif., June 19 /PRNewswire/ -- Cell Genesys, today announced that in preclinical studies of hemophilia gene therapy, the delivery of the factor IX gene, a blood clotting gene, into the liver demonstrated clear treatment advantages compared to intramuscular injection. Animals that received the factor IX gene in the liver using an AAV (adeno-associated viral) gene delivery system exhibited stable production of the factor IX protein throughout the duration of the study whereas those that received intramuscular injections had no detectable levels of the protein primarily due to the formation of anti-factor IX antibodies. Based on these and other findings, the company has determined that it will not pursue intramuscular delivery in human hemophilia gene therapy studies. These data were published in a June issue of the journal, Blood, the official journal of the American Society of Hematology, by Dr. James G. McArthur and colleagues at Cell Genesys.

"These newly published data further support our long-standing strategy to emphasize liver-directed gene delivery in our hemophilia gene therapy program," stated Joseph J. Vallner, PhD., executive vice president and chief operating officer at Cell Genesys, Inc. "This study and others will provide the preclinical data needed to advance this program to human clinical trials which are targeted to begin within the next year."

In the studies described in Blood, different methods of administration of AAV-based gene therapy were evaluated in genetically deficient mice which serve as a model of human hemophilia. The mice received a single injection of the human factor IX gene either by delivery into the liver or by intramuscular injection and were then monitored for the presence of the factor IX protein in their blood. Gene delivery to the liver, where the factor IX clotting factor is naturally produced, resulted in easily measurable levels of factor IX for the duration of the study (270 days) and no detectable antibodies or other inhibitors of factor IX. In contrast, intramuscular injection produced a strong antibody response to factor IX and as a result, no measurable levels of factor IX in the blood of the test animals. Based on these findings liver directed gene delivery was concluded to be the preferred route of administration for human gene therapy of hemophilia.

Cell Genesys has previously reported successful preclinical studies of hemophilia gene therapy in canine models, where normal levels of factor IX were restored following a single injection into the liver. In a canine model of hemophilia B, a significant reduction in bleeding episodes was achieved with a single administration of factor IX gene therapy. Additionally, production of the factor IX protein has now been observed for more than three years following a single injection. These studies also utilized Cell Genesys' AAV gene delivery system which permanently inserts the therapeutic gene into the DNA of the cells, thereby allowing potential long term therapeutic benefit when applied to the treatment of human diseases. For example, a single administration of gene therapy could potentially reduce the need for repetitive treatment regimens in hemophilia patients and decrease the serious and disabling complications arising from spontaneous bleeding episodes.

Cell Genesys is pursuing gene therapies for hemophilia A and hemophilia B -- genetic deficiencies in factor VIII and factor IX clotting factor genes, respectively. Cell Genesys has four different gene delivery systems and is using this technology "toolbox" to capture multiple product opportunities. The company's proprietary vector technologies include AAV, lentiviral, adenoviral and retroviral vectors engineered to provide safe and efficient therapeutic gene expression. In Cell Genesys' preclinical program for hemophilia B, an AAV vector system is employed since the factor IX gene is small enough to fit in this vector. For hemophilia A, the company has the option of employing an AAV vector system if a truncated form of the factor VIII gene can be successfully applied or a lentiviral vector system if the full length gene is required for optimal production of the deficient clotting factor protein. Successful delivery of the clotting factor genes is expected to result in production of the clotting factor proteins, representing a potential new approach to the treatment for hemophilia patients.

Cell Genesys currently has one of the largest patent portfolios in the gene therapy field including more than 295 issued or granted patents and over 330 pending patent applications. The portfolio currently contains over 150 filings pertaining to the two types of gene delivery systems - lentiviral and AAV -- with potential applicability to the treatment of hemophilia and other genetic deficiency diseases. The patent estate includes issued or granted patents for multiple gene delivery systems, specific therapeutic genes and gene therapy applications and multiple genetically modified cell types used in gene therapy independent of the gene delivery system or therapeutic gene.

Cell Genesys is focused on the development and commercialization of cancer vaccines and gene therapies to treat major, life-threatening diseases. The company is conducting clinical trials of GVAX(R) cancer vaccines in prostate cancer, pancreatic cancer, lung cancer and myeloma and expects to initiate new studies in acute leukemia during 2001. Preclinical stage programs include gene therapies for cancer, hemophilia and cardiovascular disorders. Cell Genesys' majority-owned subsidiary, Ceregene, is focused on gene therapies for central nervous system disorders. Cell Genesys also continues to hold a 10.5 percent equity interest in its former subsidiary, Abgenix, an antibody product company. For additional information, please visit the company's web site at http://www.cellgenesys.com. 

Statements made herein about Cell Genesys and its subsidiaries, other than statements of historical fact, including statements about the progress and reports of clinical trials and progress and reports of preclinical programs including those focusing on hemophilia gene therapy, marketability and success of potential products and nature of product pipelines, 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, the success and results of clinical trials, the regulatory approval process, competitive technologies and products, patents 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 April 2, 2001 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.

CO: Cell Genesys

ST: FOSTER CITY, Calif

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