CD40-L Blockade for Prevention of Acute Graft-Versus-Host Disease

Inclusion Criteria: * Hematologic malignancy or blood disorder requiring allogeneic HCT * Adequate vital organ function as defined per protocol * Karnofsky Performance Status Score (KPS) ≥ 80% * Participants must have an available 8/8 HLA-A, -B, -C, and -DRB1 matched-related or unrelated donor Exclusion Criteria: * Active infection not controlled with appropriate antimicrobial therapy * HIV, hepatitis B or C infection or known history of HIV, hepatitis B or C(all patients will be tested for HIV, hepatitis B and C as part of standard pre-transplant testing, and will be excluded from this trial if positive) * Anti-thymocyte globulin, or cyclophosphamide administered within 14 days before or planned to receive with HCT conditioning or as part of GVHD prophylaxis in the 14 days after HCT * Known allergic reactions to components of the study drug * Concurrent treatment with another investigational drug * History of thromboembolism, transient ischemic attack, stroke, myocardial infarction within 3 months preceding the transplant, or uncontrolled congestive heart failure or cardiac arrhythmias. * Post-transplant maintenance therapies such as FLT3 inhibitor, tyrosine kinase inhibitor, JAK inhibitors etc. are not allowed if plan is to initiate such therapies \<90 days post-transplant. Patient will be eligible if plan to initiate maintenance therapy is after day 90 post-transplant.