Shearman & Sterling advised Cell Genesys, Inc. in its definitive merger agreement with BioSante Pharmaceuticals, Inc. by which the companies will merge in an all-stock transaction, with BioSante as the surviving company.

The merger agreement has been approved unanimously by the boards of directors of both BioSante and Cell Genesys and will need to be approved by both BioSante’s and Cell Genesys’ stockholders. The merger is subject to customary closing conditions as well as a condition requiring Cell Genesys’ net cash, less certain expenses and liabilities, to be a specified minimum amount as of 10 calendar days prior to the anticipated closing date of the merger. The transaction is expected to be completed in the late third quarter or early fourth quarter of 2009.

Cell Genesys is a South San Francisco-based biotechnology company that, since its inception, has focused primarily on the development and commercialization of novel biological therapies for patients with cancer. BioSante is a specialty pharmaceutical company focused on developing products for female sexual health, menopause, contraception and male hypogonadism.

Principal attorneys working on the transaction are San Francisco-based Mergers & Acquisitions partners Michael Dorf and Michael Kennedy.