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CAMBRIDGE, Mass.--(BUSINESS WIRE)--Dec. 9, 2007--ImmunoGen, Inc. (Nasdaq: IMGN), a biopharmaceutical company that develops targeted anticancer therapeutics using its Tumor-Activated Prodrug (TAP) technology, announced that encouraging clinical findings with the TAP compound, AVE9633, were reported today at the American Society of Hematology (ASH) 49th Annual Meeting and Exposition. AVE9633 demonstrated evidence of biological activity in multiple patients with relapsed/refractory acute myeloid leukemia (AML) and was found to be generally well tolerated. Highly favorable preclinical findings also were reported for SAR3419, a TAP compound now in clinical testing for the treatment of non-Hodgkin's lymphoma and other B-cell malignancies.

"This ASH meeting shows the tremendous progress ImmunoGen has made in recent years," commented Mitchel Sayare, Chairman and CEO. "In the past two days, impressive clinical findings were reported with two TAP compounds - IMGN901 and AVE9633 - in the treatment of multiple myeloma and acute myeloid leukemia, respectively, and highly favorable preclinical data were reported with a third TAP compound, SAR3419, for the treatment of lymphomas. In addition to the AVE9633 and SAR3419 findings presented, our collaborator sanofi-aventis also reported very encouraging clinical data on the naked antibody, AVE1642, that we initially developed and now is in broad development by them."

AVE9633 Clinical Findings Reported

AVE9633 is in Phase I development for the treatment of AML. This TAP compound consists of ImmunoGen's DM4 cell-killing agent and huMy9-6 CD33-binding antibody. ImmunoGen initially developed AVE9633 and licensed the compound to sanofi-aventis as part of a broader collaboration between the companies. In a previous Phase I study, AVE9633 was found to be well tolerated at doses up to and including 260 mg/m2 when administered once every three weeks, leading to the evaluation of a more frequent dosage regimen.

The Phase I study reported today was designed to assess the safety of AVE9633 when administered on Days 1 and 8 of a 28-day cycle. Increasing doses of the compound were evaluated in new cohorts of patients until dose-limiting toxicity was observed, to identify these toxicities and to establish the recommended dose of the compound.

A total of seventeen patients with relapsed/refractory AML have been treated to date with doses ranging from 30 to 150 mg/m2/week (three to six patients per dose level). Dose-limiting toxicity occurred at the 150 mg/m2 dose level and consisted of elevated liver enzymes in one patient and keratitis in another patient.

Evidence of biological activity was noted in seven of these seventeen patients:

• 1 patient had a CRp (complete remission with incomplete platelet recovery) with AVE9633 at the 105 mg/m2 dose level. This patient has not required platelet transfusions and has remained on therapy with AVE9633 for more than eight months.
• 1 patient had a PR on the 130 mg/m2 dose level. This patient's disease has since progressed.
• 4 patients had a greater than 50% reduction in their bone marrow blasts. These patients received doses ranging from 50 to 130 mg/m2.
• 1 patient receiving 75 mg/m2 had a complete clearance of blasts from his/her blood during the first cycle of treatment.

Three more patients will be enrolled in this trial at the 130 mg/m2 dose level. Additionally, another Phase I study is underway that evaluates AVE9633 administered on Days 1, 4, and 7 in a 28-day cycle in patients with relapsed/refractory AML.

SAR3419 Preclinical Findings Reported

In October 2007, SAR3419 advanced into Phase I testing for the treatment of non-Hodgkin's lymphoma and other B-cell malignancies. This TAP compound comprises ImmunoGen's DM4 cell-killing agent and its huB4 CD19-targeting antibody. ImmunoGen licensed sanofi-aventis this compound as part of a broader collaboration between the companies.

The findings reported today are from preclinical studies evaluating the activity of SAR3419 against human lymphomas in xenograft animal models. In this study, SCID mice were engrafted with one of two types of human lymphomas - WSU-DLCL2 tumors (human subcutaneous disease) or WSU-FSCCL tumors (human systemic disease) - and the tumor was allowed to become established. The activity of SAR3419 against these tumors was then evaluated at alternative dose levels. The activity of CHOP and the activity of Rituxan^® (rituximab) against these tumors also were evaluated.

SAR3419 was found to be highly active against both types of tumors, and achieved 100% cures in both models. Its activity was found to be greater than that of either CHOP or Rituxan at their optimal doses in these models.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer biopharmaceuticals. The Company's proprietary TAP technology uses tumor-targeting antibodies to deliver a potent cell-killing agent specifically to cancer cells. Two TAP compounds wholly owned by ImmunoGen are in clinical testing - IMGN901 (huN901-DM1) and IMGN242 (huC242-DM4). Three TAP compounds are in clinical testing through ImmunoGen's collaborations with other companies - AVE9633 and SAR3419, in development by sanofi-aventis, and T-DM1 (trastuzumab-DM1), in development by Genentech. Additionally, the naked antibody compound, AVE1642, is in development through the Company's collaboration with sanofi-aventis. Multiple compounds are in research/preclinical development through ImmunoGen's collaborations and internal programs.

CONTACT:
Investors
ImmunoGen, Inc.
Carol Hausner, 617-995-2500
Executive Director, Investor Relations and Corporate Communications
info@immunogen.com

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