ImmunoGen's SAR3419 Phase I trial data on B-cell non-Hodgkin's lymphoma presented at ASCO 2011

ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops targeted antibody-based anticancer products using its antibody expertise and Targeted Antibody Payload (TAP) technology, today announced the presentation of favorable clinical data for SAR3419 in the treatment of B-cell non-Hodgkin's lymphoma (NHL). These data were presented at the ASCO 2011 Annual Meeting taking place in Chicago, IL. SAR3419, which uses the Company's TAP technology, was initially developed by ImmunoGen and licensed to Sanofi preclinically as part of a broader collaboration.

"We believe the promising SAR3419 clinical data presented today further validate our TAP technology and the potential of our deep pipeline," said Daniel Junius, President and CEO. "SAR3419 has shown impressive efficacy and tolerability in the heavily pretreated patients enrolled in this study, half of whom were refractory to rituximab. Sanofi plans to aggressively develop SAR3419, starting with advancing it into Phase II testing later this year."

In the trial reported today, patients received SAR3419 dosed weekly for eight weeks, with longer treatment possible. New cohorts of patients received increasingly greater doses of SAR3419 until its maximum tolerated dose (MTD) was defined. Additional patients were treated with SAR3419 at this MTD in the expansion phase of the trial.

The encouraging clinical data presented today included:

• 33% (7/21) of patients treated with SAR3419 at its MTD (55 mg/m²/week) had an objective response (CR/PR).
• The duration of responses has ranged from five weeks to at least 55 weeks, with three patients still responding at the time of data cut-off for presentation.
• Among patients who received any dose level of SAR3419 for whom histological data was available, tumor shrinkage of more than 20% was reported in:
  • 50% (8/16) of patients with diffuse large B-cell lymphoma;
  • 46% (7/15) of patients with follicular lymphoma; and
  • 50% (2/4) of patients with mantle cell lymphoma.
• Benefit was seen with both indolent and aggressive NHL.
• SAR3419 is well tolerated. Of particular note is the lack of significant myelosuppression associated with SAR3419 treatment, which is appealing for use in combination with standard chemotherapy agents.

It was identified that further improvement in the tolerability of SAR3419 might be achieved by switching to a bi-weekly dosing regimen after steady state pharmacokinetics were achieved, as some toxicities occurred only after 6-8 treatment cycles (e.g., the one case of Grade 3 ocular toxicity reported, which was reversible). Following protocol amendment, SAR3419 is now being evaluated dosed weekly for 4 weeks followed by dosing every other week for another 4 doses.