Magenta Therapeutics highlighted progress across its stem cell mobilization and collection and targeted conditioning programs and set expectations for 2021. MGTA-145: Three Phase 2 Clinical Trials Ongoing or Planned. Autologous Stem Cell Transplant of Multiple Myeloma Patients. Previously announced ongoing enrollment continues for the Phase 2 investigator-initiated clinical trial of MGTA-145, used in combination with plerixafor, to mobilize and collect stem cells for autologous stem cell transplantation in multiple myeloma patients at Stanford University. Magenta expects that this trial will provide data on stem cell mobilization and collection, durability of engraftment in transplanted patients and disease outcomes, including progression-free survival. Initial data from the study are expected in mid-2021. Allogeneic Donor Stem Cell Mobilization and Collection for Stem Cell Transplant in AML, ALL and MDS Patients. Through a collaboration with the National Marrow Donor Program®/Be The Match®, Magenta plans to initiate, within the next several weeks, a Phase 2 clinical trial using MGTA-145 to mobilize and collect stem cells from allogeneic donors for transplant in patients with AML, ALL and MDS. This clinical trial will evaluate stem cell mobilization, collection, cell quality, engraftment and disease outcomes, including Graft-versus-Host Disease (GvHD), which is of particular importance in the allogeneic transplant setting. Initial data from this clinical trial are expected in the second half of 2021. Sickle Cell Disease – Stem Cell Mobilization and Collection; Cell Characterization; Pre-Clinical Gene Modification Model. In collaboration with bluebird bio, Magenta plans to initiate a Phase 2 clinical trial in the second half of 2021 to evaluate MGTA-145, in combination with plerixafor, for the mobilization and collection of stem cells in adults and adolescents with sickle cell disease (SCD). Each party will characterize the cells and Magenta plans to gene-correct the cells and transplant them into established pre-clinical disease models to evaluate engraftment. Data from this clinical trial could provide proof-of-concept for MGTA-145, in combination with plerixafor, as the preferred mobilization regimen for patients with SCD and, more broadly, across all gene therapy applications where safe, reliable and rapid mobilization of quality stem cells for gene-modification and transplant are necessary components. About MGTA-145 Magenta is developing MGTA-145 in combination with plerixafor to harness complementary mechanisms to mobilize hematopoietic stem cells (HSCs) for collection and transplantation. This combination has the potential to be the preferred mobilization regimen for safe, rapid and reliable mobilization and collection of HSCs and could improve outcomes in autologous and allogeneic stem cell transplantation. Targeted Conditioning MGTA-117: Plans to Initiate Phase 1 Clinical Trial in mid-2021; Initial Safety and Pharmacokinetics (PK) data to be assessed in the fourth quarter of 2021 AML and MDS. Magenta is completing its IND-enabling GLP toxicology studies and GMP manufacturing process for MGTA-117, the first antibody-drug conjugate (ADC) candidate from the company’s research platform for targeted conditioning of patients prior to receiving a stem cell transplant for blood cancers or gene therapy drug products. Later this month, Magenta expects to complete its initial discussions with the U.S. Food and Drug Administration regarding the design of the first-in-human clinical trial. Magenta expects to file an Investigational New Drug (IND) application and, upon approval, plans to initiate a Phase 1 clinical trial in mid-2021 to assess the safety and PK in the first cohort of patients in the fourth quarter of 2021. 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 payload in-licensed from Heidelberg Pharma. MGTA-117 is designed to precisely deplete only hematopoietic stem and progenitor cells to clear space in the bone marrow prior to transplant, which supports long-term engraftment and disease outcomes in patients. MGTA-117 has shown high selectivity, potent efficacy, wide safety margins and broad tolerability in non-human primate models.