Sanofi-aventis plans to increase its stake in Regeneron to approximately 19%

TARRYTOWN, NY, USA | November 29, 2007 | Regeneron Pharmaceuticals, Inc. (Nasdaq: REGN) and sanofi-aventis (Euronext: SAN and NYSE: SNY) announced today that they have entered into a global, strategic collaboration agreement to discover, develop, and commercialize fully-human therapeutic antibodies utilizing Regeneron’s proprietary VelociSuite of technologies (including VelocImmune(R)).

Sanofi-aventis will also increase its ownership of Regeneron’s outstanding common stock from approximately 4 percent to approximately 19 percent by purchasing 12 million newly issued shares of Regeneron common stock at a price of $26.00 per share, subject to customary closing conditions including antitrust clearance.

As part of the research agreement, sanofi-aventis will make an $85 million upfront payment to Regeneron and will fund up to $475 million of research over the next five years. Sanofi-aventis will have an option to extend the research agreement for up to an additional three years.

Sanofi-aventis will have the exclusive option to co-develop with Regeneron each drug candidate in the collaboration portfolio. Development costs will be shared between the two companies, with sanofi-aventis funding drug candidate development costs up front and Regeneron reimbursing half of the development costs from its share of future profits to the extent they are sufficient for this purpose.

The first therapeutic antibody to enter clinical development under the collaboration is an antibody to the Interleukin-6 receptor (IL-6R), which has started clinical trials in rheumatoid arthritis. The second is expected to be an antibody to Delta-like ligand-4 (Dll4), which is currently slated to start its clinical development in 2008.

For any new product successfully developed as part of the collaboration, sanofi-aventis will take the lead in commercialization activities and will consolidate the sales. Regeneron will have the right to co-promote any and all collaboration products worldwide. In the United States, profits will be shared equally. Outside the United States, profits will be split on a pre-determined sliding scale with sanofi-aventis’ share ranging from 65 percent to 55 percent. In addition, Regeneron will be entitled to receive up to a total of $250 million of sales milestone payments when the collaboration achieves certain aggregate annual ex-U.S. sales levels, starting at $1 billion.

About the Regeneron VelociSuite of Technologies

Regeneron has developed and validated a group of novel technology platforms, known as the VelociSuite of technologies, to improve its ability to develop new product candidates. VelociGene(R) and VelociMouse(TM) are designed to aid in the identification of specific genes of therapeutic interest for a particular disease or cell type and validate targets through high-throughput production of mammalian models. VelocImmune(R) increases the speed and efficiency of fully-human therapeutic monoclonal antibody development and is currently being used to generate antibodies to address clinically relevant targets of therapeutic interest.

About sanofi-aventis

Sanofi-aventis, a leading global pharmaceutical company, discovers, develops and distributes therapeutic solutions to improve the lives of everyone. Sanofi-aventis is listed in Paris (EURONEXT : SAN) and in New York (NYSE : SNY).

About Regeneron Pharmaceuticals

Regeneron is a biopharmaceutical company that discovers, develops, and intends to commercialize therapeutic medicines for the treatment of serious medical conditions. Regeneron has therapeutic candidates in clinical trials for the potential treatment of cancer, eye diseases, and inflammatory diseases and has preclinical programs in other diseases and disorders. Additional information about Regeneron and recent news releases are available on Regeneron’s worldwide web site at www.regeneron.com

SOURCE: Regeneron Pharmaceuticals, Inc.