FRAMINGHAM, MA - April 10, 2007 -- GTC Biotherapeutics, Inc. ("GTC", Nasdaq: GTCB) announced today that it has been granted a non-exclusive worldwide license from Start Licensing, Inc., a joint venture between Geron Corporation (Nasdaq: GERN) and Exeter Life Sciences, Inc., for the patents and patent applications developed by the Roslin Institute to apply nuclear transfer to the production of therapeutic proteins in the milk of transgenic animals. Nuclear transfer may be utilized, as an alternative to micro-injection, to provide schedule predictability in developing the first animal that incorporates into its genome the transgene for a therapeutic protein to be expressed in milk. Nuclear transfer may also be used to speed the development of large scale transgenic production capacity. Financial terms include an upfront payment of $200,000 to Start and a total of 278,370 shares of GTCB common stock, based on the 10-day average closing price ending April 5, divided equally between Start and Exeter. There will also be a royalty payable to Start for those products developed with the patented nuclear transfer technology. The license agreement remains in place through the last patent to expire, which is expected in 2016 for the currently issued patents.

"We are pleased to enter into this licensing agreement to ensure we have the freedom to operate for those programs where the application of nuclear transfer is appropriate for product development," stated Geoffrey F. Cox, Ph.D., GTC's Chairman of the Board and Chief Executive Officer. "Our intellectual property portfolio provides patent protection for both the practice of our technology and the commercialization of our products. Last year, we received a patent in the United States for the production of therapeutic proteins in the milk of any transgenic mammal through 2021. This broad and long-lived intellectual property, all of which is independent of traditional bioreactor-based intellectual property, supports our strategic focus on the development and commercialization of recombinant plasma proteins and monoclonal antibodies."

About Start Licensing
Start is a joint venture of the Geron Corporation (Nasdaq: GERN) and Exeter Life Sciences, Inc. Start manages and licenses a broad portfolio of intellectual property rights related to animal reproductive technologies, including foundational nuclear transfer cloning technology that was developed at the Roslin Institute for the cloning of Dolly the sheep. Start's licensees are on the cutting edge of research and product development in food production, medical applications and many other fields.

About GTC Biotherapeutics, Inc.
GTC Biotherapeutics develops, produces, and commercializes therapeutic proteins through transgenic animal technology. ATrynŽ, our recombinant form of human antithrombin, is the first transgenically produced protein to be approved anywhere in the world, having recently been approved by the European Commission for the prophylactic treatment of deep vein thrombosis in patients with hereditary antithrombin deficiencies that are undergoing surgical procedures. ATrynŽ is produced in the milk of goats developed using micro-injection technology to incorporate a human antithrombin transgene. In addition to ATrynŽ, GTC is developing additional recombinant forms of therapeutic proteins normally found in human blood plasma as well as monoclonal antibodies. These products have potential applications in hematology, oncology, and autoimmune diseases.

GTC has also recently been granted a patent in the United States through 2021 for the production of any therapeutic protein in the milk of any transgenic mammal. GTC's transgenic production platform is particularly well suited to enabling cost effective development of proteins that are difficult to express in traditional recombinant production systems as well as those that are required in large volumes. Additional information is available on the GTC web site, http://www.gtc-bio.com.

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, including without limitation statements regarding the prospects for applying nuclear transfer in the development of transgenic animals expressing therapeutic proteins in milk. Such forward-looking statements are subject to a number of risks, uncertainties and other factors that could cause actual results to differ materially from future results expressed or implied by such statements. Factors that may cause such differences include, but are not limited to, the risks and uncertainties discussed in GTC's most recent Annual Report on Form 10-K and its other periodic reports filed with the Securities and Exchange Commission, including the risks and uncertainties associated with the development of therapeutic. GTC cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this document, and GTC undertakes no obligation to update or revise the statements, except as may be required by law.