ImmunoGen, Inc. Taxane Derivatives Show Greater Potency Than Taxol®
Against
Both Taxane-Responsive and Multi-Drug-Resistant Cancer Cell Lines

- In Vitro Data Presented at the National Medicinal Chemistry Symposium
-

CAMBRIDGE, MA, June 12, 2002 - ImmunoGen, Inc. (Nasdaq: IMGN) today
announced the presentation of data on its patented taxane derivatives
at the 28th National Medicinal Chemistry Symposium being held in San Diego, CA. Thedata show that ImmunoGen has developed taxane derivatives that can be linkedto tumor-targeting monoclonal antibodies and are more potent than Taxol®(paclitaxel) in vitro against both taxane-responsive and multi-drug-resistant cancer cell lines. These taxane derivatives further broaden the Company's Tumor-Activated Prodrug (TAP) technology platform.

ImmunoGen's TAP technology uses tumor-targeting monoclonal antibodies
to deliver a highly potent cell-killing agent - the effector molecule -
specifically to cancer cells with minimal damage to healthy tissue.
ImmunoGen has expertise in the development of humanized monoclonal
antibodies that target cancer cells and cytotoxic effector molecules
suitable for antibody delivery. ImmunoGen initiated a program to
develop a taxane effector molecule for use in its internal pipeline and in its out-licensing program because certain cancers, such as breast, ovarian and lung cancers, can be particularly sensitive to the taxane mode of action: inhibition of tubulin depolymerization.

As presented in the poster "Development of Taxoids for Tumor Specific
Delivery," ImmunoGen has developed taxane derivatives that are up to 55
times more potent in vitro than Taxol even with the molecular
modification necessary for delivery using monoclonal antibodies. Among these is a derivative that is over 200 times more potent than Taxol in cancer cell lines that are multi-drug resistant.

Walter Blättler, Ph.D., Executive Vice President, Science and
Technology, said, "We wanted to expand our effector molecule portfolio to include an agent with the mode of action of Taxol and Taxotere®, but that is more potent even with the modification we do to achieve stable attachment to an antibody. Our taxane derivatives meet these requirements and offer the added benefit of high potency against multi-drug-resistant cancer cells."

About ImmunoGen, Inc.

ImmunoGen, Inc. develops innovative biopharmaceuticals for the
treatment of cancer. The Company's TAP technology couples highly potent cytotoic agents with tumor-targeting antibodies to create effective new treatments for cancer with minimal damage to normal tissue. Two TAP products developed by ImmunoGen are in clinical trials - cantuzumab mertansine and huN901-DM1/BB-10901; the former is licensed to GlaxoSmithKline, the latter is licensed to British Biotech in certain territories. Several companies are advancing TAP products comprised of ImmunoGen's TAP technology and the partner's antibody - Genentech (Trastuzumab-DM1), Millennium (MLN591DM1) and Boehringer Ingelheim (bivatuzumab mertansine). ImmunoGen also has multi-target agreements with Genentech, Abgenix, and Millennium that can potentially yield multiple additional TAP products.

This press release includes forward-looking statements based on
management's current expectations. Factors that could cause future results to differ materially from such expectations include, but are not limited to: the success of the Company's research strategy; the applicability of the discoveries made therein; the difficulties inherent in the development of pharmaceuticals, including uncertainties as to the timing and results of preclinical studies; delayed achievements of milestones; reliance on collaborators; uncertainty as to whether the Company's potential
products will succeed in entering human clinical trials and uncertainty as to the results of such trials; uncertainty as to whether adequate reimbursement for these products will exist from the government, private healthcare insurers and third-party payors; the uncertainties as to the extent of future government regulation of the pharmaceutical business; and other factors described in ImmunoGen's periodic filings with the Securities and Exchange Commission.

Taxol® is a registered trademark of Bristol-Myers Squibb Company.
Taxotere® is a registered trademark of Aventis.
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