Release issued 2nd August 2007

FRAMINGHAM, MA and PARIS, FRANCE - August 2, 2007 -- GTC Biotherapeutics, Inc. ("GTC", Nasdaq: GTCB) and LFB Biotechnologies, a wholly owned subsidiary of LFB S.A. (Laboratoire francais du Fractionnement et des Biotechnologies S.A.), announced today that they have initiated development of a transgenically produced CD20 monoclonal antibody under the existing agreement between GTC and LFB Biotechnologies. The resulting product is expected to have target specificity similar to Rituximab (Rituxan®, Mabthera®) and to have relatively higher antibody dependent cell-mediated cytotoxicity, or ADCC. The existing relevant CD20 antibody patents will expire by 2014. The transgenically produced CD20 antibody is anticipated to be commercially developed for oncology and auto-immune indications. Rituximab is used in the treatment of B-cell non-Hodgkin's lymphoma, B-cell leukemia and rheumatoid arthritis. It is also under investigation for a range of auto-immune conditions such as systemic lupus erythematosus, immune thrombocytopenic purpura (ITP), and type-1 diabetes. Rituximab had worldwide sales of nearly $4 billion in 2006 and is projected to have a $5 billion market by 2010.

"Rituximab, an antibody targeting CD20, has proven its therapeutic value in Non Hodgkin's Lymphoma and rheumatoid arthritis," stated Yann Echelard, Ph.D., Vice President of Research and Development for GTC. "We believe our transgenic production technology enables us to develop an anti-CD20 monoclonal antibody which may have clinical benefits due to enhanced ADCC and provide an attractive price to the market to encourage broader use."

"Transgenic production has the capability to drive economically beneficial large-scale production of the CD20 antibody," stated Sami Chtourou, Ph.D., Director Biopharmaceutical Development and Transgenesis Program for LFB. "The enhanced ADCC characteristics have the potential to establish a product that may offer efficacy benefits or reduced dosing requirements for patients."

This CD20 antibody may be considered for clinical development as a follow-on biologic in the US and a biosimilar in the EU as the appropriate legislation is enacted and regulatory guidance is established.

The transgenically produced CD20 antibody is being developed under the agreement between GTC and LFB established in October 2006. Costs and profits from the program are anticipated to be shared 50/50. GTC will have exclusive marketing rights in the US and Canada. LFB will have exclusive marketing rights in the EU. GTC and LFB have co-exclusive marketing rights to the rest of the world. LFB has initially demonstrated production of this CD20 antibody with enhanced ADCC in cell culture.

Production in the milk of transgenic goats is anticipated to be established in 2008 with an investigational new drug application to the US Food and Drug Administration planned for 2010.

Non-Hodgkin Lymphoma, or NHL, is a group of cancers originating in the lymphatic system that is characterized by the malignant transformation of lymphocytes. NHL has an incidence rate of about 20 cases per 100,000 population in the United States, and a worldwide incidence of 5 -15 per 100,000. It is more prevalent in males and occurs at an average age of 50. The incidence of NHL in the US rose 84% from 1975 to 2004, an average yearly increase of 2.8%. NHL is the fifth most common cancer in the United States, where an estimated 63,000 new cases of NHL will be diagnosed in 2007, and where the National Cancer Institute estimates that 18,660 deaths due to NHL will occur (approximately 5% of all US cancer deaths).

CD20 is an antigen located on the surface of mature B-lymphocytes and B-cell derived tumor cells. The CD20 monoclonal antibody recruits the body's natural defenses to target marked B-cells. Stem cells (B-cell progenitors) in bone marrow lack the CD20 antigen, allowing healthy B-cells to regenerate after treatment.

About LFB Group
With sales of 268 million euros, LFB is the fourth largest pharmaceutical company supplying drugs to hospitals in France and a major European producer of plasma-derived medicinal products. LFB provides to healthcare professionals a wide range of 19 plasma-derived medicinal products in three therapeutic fields: Hemostasis, Anesthesia-intensive Care and Immunology. LFB's medicinal products are prescribed to address emergencies but also to manage chronic diseases that require lifelong treatment. With 1300 employees, among which 200 are in R&D, LFB is recognized as one of the major European players in the field of therapeutic proteins with expertise in protein downstream processing, characterization as well as biological safety and viral clearance. LFB focuses its discovery and development activities on monoclonal antibodies and therapeutic proteins for rare and severe diseases. Ideally placed to become a driving force in new technological and therapeutic fields, LFB can use its technology platform to develop highly cytotoxic antibodies while its R&D portfolio contains high-potential projects calling on innovative technology.

About GTC Biotherapeutics
GTC Biotherapeutics develops, produces, and commercializes therapeutic proteins through transgenic animal technology. GTC obtained the first approval anywhere in the world for a transgenically produced protein when ATryn®, a recombinant form of human antithrombin, was approved by the European Commission for use in patients with hereditary antithrombin deficiency undergoing surgical procedures. GTC's intellectual property includes a patent in the United States through 2021 for the production of any therapeutic protein in the milk of any transgenic mammal as well as a patent application for enhanced ADCC. 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 prospects for development of a transgenically produced CD20 antibody, the estimated timetable for clinical studies of the compound, and the overall market size for its lead indications. 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 uncertainties associated with conducting clinical studies, and the risks and uncertainties associated with dependence upon the actions of collaboration partners and regulatory agencies. 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. GTC specifically disclaims responsibility for information describing LFB and its business other than the joint programs governed by the agreement with GTC.

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