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CAMBRIDGE, Mass.--(BUSINESS WIRE)--July 8, 2004--ImmunoGen, Inc. (Nasdaq: IMGN) today announced the publication in Cancer Research of preclinical data on its product candidate huN901-DM1 in multiple myeloma. The data demonstrate that huN901-DM1 has significant activity against multiple myeloma cancer cells. ImmunoGen expects to initiate a clinical study with the compound in hematologic malignancies including multiple myeloma later this year.

The publication, "In Vitro and in Vivo Activity of the Maytansinoid Immunoconjugate huN901-N2'-Deacetyl-N2'-(3-Mercapto-1-Oxopropyl)-Maytansine against CD56+ Multiple Myeloma Cells" by Pierfrancesco Tassone et al. presents findings from research conducted in the laboratory of Kenneth C. Anderson, M.D., at the Dana-Farber Cancer Institute.

The research was designed to assess the activity of huN901-DM1 in multiple myeloma in vitro and in vivo. huN901-DM1 is a novel therapeutic agent designed to target and kill cancer cells that express the CD56 antigen. It comprises the humanized antibody huN901, which targets CD56-expressing cells, and DM1, a potent cancer-killing agent. CD56-positive cancers include both solid tumor malignancies such as small-cell lung cancer and other neuroendocrine cancers, and hematologic, or "liquid," cancers such as multiple myeloma and acute myeloid leukemia. Two studies are currently underway with huN901-DM1 in solid tumor malignancies; the Company expects to start a study with the compound in CD56-positive liquid cancers later this year.

The data published in Cancer Research include the findings from assessment of the presence of CD56 on multiple myeloma patient cells, the activity of huN901-DM1 against CD56-positive multiple myeloma cells, the selectivity of huN901-DM1 for CD56-positive multiple myeloma cells, and the ability of huN901-DM1 to kill CD56-positive multiple myeloma cells in settings where the cancer cells can resist killing by standard chemotherapeutic agents.

The researchers confirmed the previously reported finding that most multiple myeloma cases express CD56, and found the antigen is typically strongly expressed when present.

In terms of the specificity and activity of huN901-DM1, the researchers report:

• huN901-DM1 selectively kills CD56-positive multiple myeloma cells and not CD56-negative cells. This selective killing is due to the attachment of DM1 to the huN901 antibody - the antibody alone lacks significant cancer-killing effects and the DM1 alone lacks selectivity.
• In tumor xenograft models, huN901-DM1 inhibited the growth of tumors and improved survival. The huN901 antibody component alone had no significant effect on either tumor growth or survival.
• huN901-DM1 had substantial activity even when the multiple myeloma cells were in the presence of bone marrow stromal cells (BMSCs). There is evidence that multiple myeloma cells adhering to BMSCs are able to resist being killed by standard chemotherapeutic agents.

The authors conclude that "(their) data therefore demonstrate that huN901-DM1 has significant in vitro and in vivo antimyeloma activity at doses that are well tolerated in a murine model."

Walter Blattler, Ph.D., Executive Vice President, Science and Technology at ImmunoGen, commented, "While there have been advances in the treatment of multiple myeloma in recent years, there continues to be a significant need for better treatments. We plan to initiate a clinical trial with huN901-DM1 in CD56-positive hematologic malignancies including multiple myeloma later this year to expand our clinical experience with the compound beyond the studies in solid tumors currently underway. We recently hired Dr. Robert Fram, Vice President, Clinical Development, to lead the clinical program for huN901-DM1 and for other products in our pipeline."

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer biopharmaceuticals. The Company's proprietary Tumor-Activated Prodrug (TAP) technology uses tumor-targeting antibodies to deliver a potent cell-killing agent specifically to cancer cells. Two ImmunoGen-developed TAP products have begun clinical evaluation: cantuzumab mertansine and huN901-DM1. ImmunoGen out-licenses its TAP technology in exchange for upfront, milestone, and manufacturing payments plus royalties. Companies developing products using ImmunoGen's TAP technology include Boehringer Ingelheim (bivatuzumab mertansine), Millennium Pharmaceuticals (MLN2704), and Genentech (Trastuzumab-DM1); ImmunoGen also has multitarget agreements with Genentech, Abgenix, and Millennium. ImmunoGen and Aventis have a collaboration to discover, develop, and commercialize antibody-based anticancer therapeutics. The agreement provides ImmunoGen with committed funding and includes milestone payments, royalties, and co-promotion rights.

This press release includes forward-looking statements based on management's current expectations. For these statements, ImmunoGen claims the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. Various factors could cause the Company's actual results to differ materially from those discussed or implied in the forward-looking statements and you are cautioned not to place undue reliance on these forward-looking statements, which are current only as of the date of this release. Factors that could cause future results to differ materially from such expectations include, but are not limited to: the outcome of the Company's research and clinical development processes, including the anticipated advancement into the next stages of clinical testing of cantuzumab mertansine and huN901-DM1; the difficulties inherent in the development of pharmaceuticals, including uncertainties as to the timing, expense and results of preclinical studies and clinical trials, such as the timing and results for the planned huN901-DM1 study in hematologic malignancies; the Company's dependence upon existing and potential collaborative partners, and the outcome of the clinical testing of TAP compounds being developed by the Company's existing partners; uncertainty as to whether the Company's potential products or those of the Company's collaborators will succeed in entering human clinical trials and uncertainty as to the results of such trials; the risk that the Company and/or its collaborators may not be able to obtain regulatory approvals necessary to commercialize their product candidates; the potential development by competitors of competing products and technologies; uncertainty whether the Company's TAP technology will produce safe, effective and commercially viable products; and other factors more fully described in ImmunoGen's Annual Report on Form 10-K for the fiscal year ended June 30, 2003 and other reports filed with the Securities and Exchange Commission.

CONTACT: ImmunoGen, Inc.
Carol Hausner (Investors)
617-995-2500
info@immunogen.com
or
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SOURCE: ImmunoGen, Inc.