A Study of Vadastuximab Talirine Given Prior to or After Allogeneic Hematopoietic Stem Cell Transplant in AML Patients

Inclusion Criteria: * Relapsed/refractory acute myeloid leukemia (AML) except for acute promyelocytic leukemia * Eastern Cooperative Oncology Group status of 0 or 1 * Adequate baseline renal and hepatic function * For Pre-allo Part A (before stem cell transplant): Relapsed or refractory AML (greater than 5% blasts) * For Pre-allo Part A (before stem cell transplant): Availability of an HLA matched related or unrelated donor * For Pre-allo Part A (before stem cell transplant): Eligible for an allogeneic hematopoietic stem cell transplant * For Post-allo Part B: Transplant must have been performed with active AML (greater than 5% blasts) using a conventional conditioning regimen and have achieved CR or CRi post-alloSCT (with ANC greater than or equal to 1,000 and platelet greater than or equal to 50,000) * For Post-allo Part B: Treatment must begin at least 42 days, but no more than 100 days post-transplant. Exclusion Criteria: * Inadequate heart function * Inadequate lung function * Previous central nervous system leukemia * Any history of another metastatic malignancy * Anti-leukemia treatment within14 days of study drug (other than hydroxyurea or 6-mercaptopurine), immunosuppressive therapy (except for GVHD treatment/prophylaxis in Part B), or investigational agents * For Pre-allo Part A (before stem cell transplant): Partially matched donors (related or unrelated) and umbilical cord blood cells are excluded as the source of hematopoietic stem cells * For Pre-allo Part A (before stem cell transplant): Prior alloSCT * For Post-allo Part B: Active GVHD Grade 2 or higher * For Post-allo Part B:History of veno-occlusive disease requiring defibrotide * For Post-allo Part B: History of Grade 2 or higher hepatic GVHD * For Post-allo Part B: Concurrent use of corticosteroids equivalent of prednisone at a dose of greater than 0.5 mg/kg