Framingham, MA -- May 20, 2005 -- GTC Biotherapeutics, Inc. ("GTC") (Nasdaq: GTCB) will webcast its 2005 Annual Meeting of Stockholders on May 25, 2005 starting at approximately 2:00 p.m. Eastern Time. The annual meeting is to be held at the Forefront Center for Meetings & Conferences in Waltham, Massachusetts. GTC expects to conduct the formal business portion of the meeting followed by a presentation to its stockholders. To access the 2005 Annual Meeting live via the Internet, please log onto www.gtc-bio.com approximately 15 minutes before the start of the meeting to allow for any software downloads that may be necessary. Following the webcast of the meeting, an archive will be available at the same address. The webcast is also being distributed through the Thomson StreetEvents Network. Individual investors can listen to the call at www.earnings.com, Thomson's individual investor portal, powered by StreetEvents. Institutional investors can access the call via Thomson StreetEvents (www.streetevents.com), a password-protected event management site. GTC Biotherapeutics is a leader in the development, production, and commercialization of therapeutic proteins through transgenic animal technology. GTC currently has five products in its internal pipeline and a portfolio of external program production opportunities. GTC's lead program is ATrynŽ, its recombinant form of human antithrombin. A Market Authorization Application is under review by the European Medicines Evaluation Agency for the use of ATrynŽ in patients with a hereditary antithrombin deficiency. In addition to the ATrynŽ program, GTC is developing a recombinant human albumin, a recombinant human alpha-1 antitrypsin, a malaria vaccine, and a CD137 antibody to stimulate the immune system as a potential treatment for solid tumors. In its external programs, GTC's technology is used to develop transgenic production of its partners' proprietary products, including both large-volume protein therapeutics as well as products that are difficult to produce in significant quantities from conventional recombinant production systems. One of the external programs is in clinical trials with a transgenically produced product. Additional information is available on the GTC web site, http://www.gtc-bio.com. GTC Biotherapeutics
Thomas E. Newberry
Vice President, Corporate Communications
(508) 370-5374 Feinstein Kean Healthcare
Francesca DeVellis (investors)
Barbara Askjaer (media)
(617) 577-8110
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