News

• Novel antibody-drug conjugate is designed to selectively target and kill CD33-expressing acute myeloid leukemia cells, including leukemic stem cells, while sparing normal cells.
• IMGN779 utilizes one of the Company's new DNA-acting payload agents, DGN462.
• ImmunoGen is on track to submit an IND for IMGN779 in 2015.

IMMUNOGEN, INC. ANNOUNCES PRECLINICAL FINDINGS FOR IMGN779, A POTENTIAL TREATMENT FOR ACUTE MYELOID LEUKEMIA

• Novel antibody-drug conjugate is designed to selectively target and kill CD33-expressing acute myeloid leukemia cells, including leukemic stem cells, while sparing normal cells.
• IMGN779 utilizes one of the Company's new DNA-acting payload agents, DGN462.
• ImmunoGen is on track to submit an IND for IMGN779 in 2015.

ImmunoGen, Inc. (NASDAQ: IMGN), a biotechnology company that develops novel anticancer therapeutics using its antibody-drug conjugate (ADC) technology, disclosed for the first time preclinical data for IMGN779. The data were presented at the 19^th Congress of the European Hematology Association (EHA) meeting in Milan, Italy (abstract# P802). IMGN779 is a novel, CD33-targeting, DNA-alkylating ADC that is a potential treatment for acute myeloid leukemia (AML).

"Despite good initial responses to existing therapies, many AML patients relapse, driving the need for new treatment options," commented Dr. Charles Morris, Executive Vice President and Chief Development Officer. "We believe the unique profile of IMGN779 will enable the achievement of desired activity with a better tolerability profile than other agents currently used to treat this disease."

IMGN779 is an ADC designed to selectively target and kill AML cells, including leukemic stem cells, while sparing normal cells. IMGN779 utilizes DGN462, one of the Company's new DNA-acting payload agents.

In preclinical findings reported at EHA, IMGN779 demonstrated potent, targeted activity against primary AML patient cells in vitro. IMGN779 can selectively kill leukemic cells (blasts) while sparing normal hematopoietic (blood) stem cells. IMGN779 was found to be highly active against human AML xenografts in vivo, demonstrating potent and targeted activity. IMGN779 was well tolerated without delayed toxicity in animal models.

IMGN779 is on track to become the Company's next wholly owned clinical-stage compound. ImmunoGen is preparing to submit the IMGN779 IND in mid-2015.

About IMGN779

IMGN779 is a novel, DNA-alkylating ADC. Its payload, linker and antibody were developed by ImmunoGen and are wholly owned by the Company. IMGN779 comprises the highly potent, DNA-alkylating payload DGN462 conjugated via cleavable disulfide linker to the CD33-targeting antibody, Z4681A.

About ImmunoGen's DNA-acting Payload Agents

Created by ImmunoGen scientists, the IGN family of DNA-acting payload agents, including DGN462, are designed to effectively alkylate DNA, while avoiding the delayed toxicity that can develop with agents that cross-link DNA in addition to alkylating it.¹ ImmunoGen developed its IGN family of DNA-acting payload agents to complement its successful family of tubulin-acting agents (e.g., DM1, DM4), as some cancers respond more to DNA-acting agents than to tubulin-acting agents.^1,2

The Company began by developing DNA-acting agents with both DNA-crosslinking and -alkylating properties. However, ImmunoGen scientists identified that such agents were associated with significant delayed toxicity. To achieve the dual objective of efficacy and tolerability with this platform, ImmunoGen developed more advanced IGN agents which are DNA-alkylators only. These IGN payload agents retain high potency, but avoid delayed toxicity.

About AML

Acute myeloid leukemia (AML) is a hematologic malignancy that starts in the bone marrow where different types of new blood cells are made. In the US in 2014, more than 18,000 adults will be newly diagnosed with AML and more than 10,000 will die from the disease.³

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer therapeutics. The Company's ADC technology uses tumor-targeting antibodies to deliver an ImmunoGen cell-killing agent specifically to cancer cells; the Company has also developed antibodies with anticancer activity of their own. The first product with ImmunoGen's ADC technology is Roche's Kadcyla^®. ImmunoGen has three wholly owned product candidates in clinical testing with additional compounds in clinical testing through the Company's partnerships with Amgen, Bayer HealthCare, Biotest and Sanofi. More information about ImmunoGen can be found at www.immunogen.com.

¹ Miller et al., AACR-NCI-EORTC 2013, abstract #C160.

² Whiteman et al., AACR-NCI-EORTC 2013, abstract #C162.

³ American Cancer Society (2014), Leukemia: Acute Myeloid Detailed Guide.

Kadcyla^® is a registered trademark of Genentech, a member of the Roche Group.

This press release includes forward-looking statements. 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. It should be noted that there are risks and uncertainties related to the development of novel anticancer products, including IMGN779, including risks related to preclinical and clinical studies, their timings and results. A review of these risks can be found in ImmunoGen's Annual Report on Form 10-K for the fiscal year ended June 30, 2013 and other reports filed with the Securities and Exchange Commission.

For Investors:

ImmunoGen, Inc.
Carol Hausner, 781-895-0600
info@immunogen.com
or
For Media:
Pure Communications, Inc.
Dan Budwick, 973-271-6085

Source: ImmunoGen, Inc.

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