–  Phase 1/2 clinical trial expected to open in Q4 2021 in patients with relapsed/refractory acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) –

Magenta Therapeutics, Inc. (Nasdaq: MGTA), a clinical-stage biotechnology company developing novel medicines to bring the curative power of stem cell transplant to more patients, announced today that its Investigational New Drug (IND) application for MGTA-117 is active with the U.S. Food and Drug Administration (FDA). The company expects to open the Phase 1/2 clinical trial in Q4 2021 to evaluate its MGTA-117 antibody-drug conjugate (ADC) targeted conditioning program.

“We are very pleased that our collaboration with the FDA has resulted in the clearance of the MGTA-117 IND. We have addressed the FDA’s request for a bioassay to be incorporated into the clinical trial protocol,” said Jason Gardner, D.Phil., President and Chief Executive Officer, Magenta Therapeutics. “Improving conditioning treatments is essential for broadening patient accessibility to the curative potential of stem cell transplant and gene therapies. We have designed MGTA-117 specifically to replace toxic radiation and chemotherapy-based conditioning agents used in current medical practice. This program holds significant potential for patients across several disease areas.”

The multi-center, open label Phase 1/2 clinical trial with single-dose escalating cohorts will evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of MGTA-117 as a single agent in relapsed/refractory AML and MDS patients. Magenta will continue to engage with the FDA to transition the trial to the intended primary target population of hematopoietic stem cell transplant-eligible AML and MDS patients. In addition, Magenta has planned gene therapy clinical trial collaborations with AVROBIO and Beam Therapeutics to evaluate the potential utility of MGTA-117 for conditioning gene therapy patients without the use of non-selective busulfan or other toxic chemotherapies.

About MGTA-117

Magenta’s MGTA-117 program is the company’s lead targeted conditioning product candidate, an antibody-drug conjugate (ADC) designed to selectively deplete hematopoietic stem cells (HSCs) from patients prior to transplant or HSC-based gene therapy to reduce the need for high-dose or high-intensity chemotherapeutic agents or, in the case of gene therapy applications, to potentially eliminate the need for chemotherapeutic agents altogether. MGTA-117 targets the CD117 receptor, which is highly expressed on the cell surface of HSCs and leukemia cells, making it a promising target for conditioning across broad sets of diseases, including certain blood cancers, hemoglobinopathies (sickle cell disease and beta thalassemia) and inherited metabolic disorders.

About Magenta Therapeutics

Magenta Therapeutics is a clinical-stage biotechnology company developing medicines to bring the curative power of stem cell transplants to more patients with blood cancers, genetic diseases and autoimmune diseases. Magenta is combining leadership in stem cell biology and biotherapeutics development with clinical and regulatory expertise, a unique business model and broad networks in the stem cell transplant community to revolutionize immune reset for more patients.

Magenta is based in Cambridge, Massachusetts. For more information, please visit www.magentatx.com.

Follow Magenta on Twitter: @magentatx.

Forward-Looking Statement

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