Magenta Therapeutics announced positive preliminary results from its Phase 2 clinical trial of MGTA-145 plus plerixafor in patients with multiple myeloma, which were accepted for presentation at the European Hematology Association (EHA) Congress, to be held virtually June 9-17, 2021. Magenta also provided initial direction regarding the acute myeloid leukemia(AML) and myelodysplastic syndromes(MDS) patients it expects to evaluate in its planned clinical trial with MGTA-117. Multiple Myeloma Phase 2 Clinical Trial: The investigator-initiated, 25-patient Phase 2 open-label clinical trial, ongoing at Stanford University School of Medicine, is designed to evaluate the ability of MGTA-145, in combination with plerixafor, to mobilize and collect stem cells for autologous stem cell transplant in patients with multiple myeloma. Preliminary results: All patients (10/10) met the primary endpoint of mobilization and collection of 2 million CD34+ stem cells per kg in up to two days of same-day mobilization and apheresis. Nine of 10 patients achieved the primary endpoint in a single day. The median number of stem cells collected in one day was 5.4 million CD34+ stem cells per kg. Patients could also be successfully mobilized and apheresed on a second day, if needed, based upon protocol requirements. The median number of stem cells collected on day 1 and 2 (if needed) was 7.1 million CD34+ stem cells per kg in all patients. Current standard of care with G-CSF regimens require a minimum of five days of dosing to initiate stem cell collection. All transplanted patients (6/6) successfully engrafted, with median recovery of neutrophils after 12 days and platelets after 17 days, which are within transplant expectations in multiple myeloma. The CD34+ stem cells collected were enriched for CD90 expression (31% of CD34 cells were CD34+CD90+), a stem cell population associated with durable engraftment, which is three-fold greater than observed with G-CSF historically. The regimen of MGTA-145 and plerixafor was well tolerated. Acute, transient, MGTA-145-related grade 1 bone or musculoskeletal pain was observed in 40% of patients following MGTA-145 infusion. This study has broad and clinically representative inclusion criteria and is enrolling patients that represent the general transplant eligible population of patients with multiple myeloma, some of whom may have additional risk factors that may impact stem cell collection. Risk factors can include myeloma-directed therapies that are known to impact stem cell collection, previous malignancy treated with chemotherapy and/or radiation and other co-morbid conditions. Mobilization agents may be less effective in patients with multiple risk factors.