– MGTA-117 conditioning for precise depletion of cells in the bone marrow could potentially increase patients’ benefit from Beam’s base editing therapies for sickle cell disease and beta thalassemia –

CAMBRIDGE, MA, USA I June 15, 2020 IMagenta Therapeutics (Nasdaq: MGTA) and Beam Therapeutics (Nasdaq: BEAM) today announced a non-exclusive research and clinical collaboration agreement to evaluate the potential utility of MGTA-117, Magenta’s novel targeted ADC for conditioning of patients with sickle cell disease and beta-thalassemia receiving Beam’s base editing therapies. Beam is pursuing two differentiated base editing approaches to treat hemoglobinopathies: its hereditary persistence of fetal hemoglobin (HPFH) program to precisely and robustly elevate fetal hemoglobin, which could be used in treatments for both sickle cell disease and beta-thalassemia, as well as a novel approach to directly correct the sickle causing point mutation (Makassar).

Conditioning is a critical component necessary to prepare a patient’s body to receive the edited cells, which carry the corrected gene and must engraft in the patient’s bone marrow in order to be effective. Today’s conditioning regimens rely on nonspecific chemotherapy or radiation, which are associated with significant toxicities. MGTA-117 precisely targets only hematopoietic stem and progenitor cells, sparing immune cells, and has shown high selectivity, potent efficacy, wide safety margins and broad tolerability in non-human primate models. MGTA-117 may be capable of clearing space in bone marrow to support long-term engraftment and rapid recovery in patients.

Beam has demonstrated the ability to edit individual DNA bases in hematopoietic stem cells at high efficiency and with little impact on the viability of edited cells relative to unedited cells using its novel base editing technology. Combining MGTA-117 with Beam’s HPFH and Makassar base editors could meaningfully advance the treatment of patients with sickle cell disease or beta-thalassemia.

“We believe patients will benefit from a more precise process to remove hematopoietic stem cells and prepare them to receive genetic medicines. Magenta has developed targeted ADCs as the preferred modality for our conditioning programs, and we have designed MGTA-117 specifically to optimize it for use with a genetically-modified cell product delivered in a transplant setting,” said Jason Gardner, D.Phil., president and chief executive officer, Magenta Therapeutics. “Beam’s next-generation base editing technology complements our next-generation conditioning approach very well, and we are excited to combine these strengths to address the still-significant unmet medical needs of the sickle cell and beta-thalassemia patient communities.”

“Base editing has the potential to offer lifelong treatment for patients with many diseases, including sickle cell disease and beta-thalassemia. Our novel base editors create precise single base changes in genes without cutting the DNA, enabling durable correction of hematopoietic stem cells with minimal effects on cell viability or genomic integrity,” said John Evans, chief executive officer of Beam. “Combining the precision of our base editing technology with the more targeted conditioning regimen enabled by MGTA-117 could further improve therapeutic outcomes for patients suffering from these severe diseases. We look forward to partnering with the Magenta team to explore these novel technologies together.”

Beam will be responsible for clinical trial costs related to development of Beam’s base editors when combined with MGTA-117, while Magenta will continue to be responsible for all other development costs of MGTA-117. Magenta will also continue to develop MGTA-117 in other diseases, including blood cancers and genetic diseases. Each company will retain all commercial rights to their respective technologies.

About MGTA-117

MGTA-117, Magenta’s most advanced conditioning program, is a CD117-targeted antibody engineered for the transplant setting and conjugated to amanitin, a toxin in-licensed from Heidelberg Pharma. It is designed to precisely deplete only hematopoietic stem and progenitor cells and has shown high selectivity, potent efficacy, wide safety margins and broad tolerability in non-human primate models, suggesting that it may be capable of clearing space in bone marrow to support long-term engraftment and rapid recovery in patients. Magenta plans to complete IND-enabling studies this year and initiate clinical studies in 2021. Magenta will continue to develop MGTA-117 in other diseases, including blood cancers and genetic diseases.

About Magenta Therapeutics

Magenta Therapeutics is a clinical-stage biotechnology company developing medicines to bring the curative power of immune system reset through stem cell transplant to more patients with autoimmune diseases, genetic diseases and blood cancers. 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 world to revolutionize immune reset for more patients. Magenta is based in Cambridge, Mass. For more information, please visit www.magentatx.com. Follow Magenta on Twitter: @magentatx.

About Base Editing and Beam Therapeutics
Beam Therapeutics (Nasdaq: BEAM) is a biotechnology company developing precision genetic medicines through the use of base editing. Beam’s proprietary base editors create precise, predictable and efficient single base changes, at targeted genomic sequences, without making double-stranded breaks in the DNA. This enables a wide range of potential therapeutic editing strategies that Beam is using to advance a diversified portfolio of base editing programs. Beam is a values-driven organization focused on its people, cutting-edge science, and a vision of providing life-long cures to patients suffering from serious diseases. For more information, visit www.Beamtx.com.

SOURCE: Magenta Therapeutics