MGTA-145 + Plerixafor in the Mobilization of HSCs for Allogeneic Transplant in Hematologic Malignancies

Inclusion Criteria: Donor Inclusion Criteria: * Donor medical suitability and eligibility will be determined following Institution or NMDP/Be The Match standards * Age 18-65 years old at the time of signing informed consent * 8/8 (HLA- A, B, C, and DRB1) HLA-matched sibling or volunteer unrelated donor * Fulfill Institution or NMDP/Be The Match criteria to serve as a mobilized blood cell donor * Serum creatinine \< 1.5 x institution upper limit of normal (ULN) or estimated creatinine clearance (CRCL) \> 50 mL/min using the Modification of Diet in Renal Disease Study (MDRD) equation or similar method Recipient Inclusion Criteria: * At least 18 years old at the time of signing informed consent * Has an available 8/8 (HLA- A, B, C, and DRB1) HLA-matched sibling or volunteer unrelated donor willing to donate peripheral blood stem cells (PBSC) for transplant * Fulfill additional individual Transplant Center Criteria for transplant beyond NMDP/Be The Match criteria * One of the following diagnoses: * Acute myelogenous leukemia (AML) in 1st remission or beyond with ≤ 5% marrow blasts and no circulating blasts. Documentation of bone marrow assessment will be accepted within 45 days prior to the date of consent. * Acute lymphoblastic leukemia (ALL) in 1st remission or beyond with ≤ 5% marrow blasts and no circulating blasts. Documentation of bone marrow assessment will be accepted within 45 days prior to the date of consent. * Patients with myelodysplasia (MDS) with no circulating blasts and with less than 10% blasts in the bone marrow (higher blast percentage allowed in MDS due to lack of differences in outcomes with \< 5% or 5-10% blasts in MDS). Documentation of bone marrow assessment will be accepted within 45 days prior to the date of consent. * Cardiac function: Left ventricular ejection fraction at least 45% based on most recent echocardiogram or MUGA results obtained via standard of care * Estimated creatinine clearance acceptable per local institutional guidelines * Pulmonary function: diffusing capacity of the lungs for carbon monoxide (DLCO) corrected for hemoglobin at least 50% and forced expiratory volume in first second (FEV1) predicted at least 50% based on most recent DLCO results obtained via standard of care * Liver function acceptable per local institutional guidelines * Karnofsky performance status (KPS) of 70% or greater * Hematopoietic Cell Transplantation-Comorbidity Index (HCT-CI) score of 4 or less Exclusion Criteria: Donor Exclusion Criteria: * Donor unwilling or unable to give informed consent, or unable to comply with the protocol including required follow-up and testing * Donor already enrolled on another investigational agent study * Pregnant or breastfeeding females, sexually active female and male donors not willing or able to use adequate contraception, or males who do not agree to refrain from donating sperm, from the time of consent through 3 months after treatment with MGTA-145 + plerixafor Recipient Exclusion Criteria: * Subject unwilling or unable to give informed consent, or unable to comply with the protocol including required follow-up and testing * Subject whose donor does not meet the eligibility criteria and is a screen fail * Subjects with a prior allogeneic transplant * Subjects with active, uncontrolled infection at the time of the transplant preparative regimen * Pregnant or breastfeeding females, sexually active female or male subjects not willing or able to use adequate contraception, or males who do not agree to refrain from donating sperm, from the time of consent through 3 months after PBSC infusion * Subjects with clinical evidence of active Central Nervous System (CNS) tumor involvement as evidenced by documented disease on examination of spinal fluid or MRI within 45 days of start of conditioning * A condition, which, in the opinion of the clinical investigator, would interfere with the evaluation of primary and secondary endpoints * Planned treatment with a new investigational agent from the time of transplant through 30 days post-transplant