IMMUNOGEN ANNOUNCES SANOFI-AVENTIS GROUP HAS EXTENDED ITS RESEARCH COLLABORATION WITH THE COMPANY

ImmunoGen, Inc. (Nasdaq: IMGN) today announced that Aventis Pharmaceuticals Inc. of the sanofi-aventis Group has exercised its right to extend the term of its research collaboration with the Company and committed to fund ImmunoGen $18.2 million in research support over the twelve months beginning September 1, 2006. This funding is in addition to the research support already committed for the three years ending August 31, 2006. Mitchel Sayare, PhD, Chairman and CEO, commented, "We are delighted that the sanofi-aventis Group has elected to extend this research collaboration. The extension enables the two companies to work together for a fourth year to develop new compounds that can potentially generate revenue for ImmunoGen."

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