A Study of Belumosudil in People at Risk of Developing Graft-Versus-Host Disease After a Stem Cell Transplant

Inclusion Criteria: * Patients ≥ 18 years-old at time of consent. * Diagnosis: hematologic malignancy in morphologic remission who will be treated with RI or NMA conditioning and GVHD prophylaxis CNI-based (CNI without PTCY) plus abatacept or PTCY-based (CNI with PTCY). * Recipients of 7-8/8 related or unrelated HLA-matched or related haploidentical donor. * Peripheral blood stem cell graft * Allo-HCT day \<120 at time of consent Post-HCT inclusion criteria (within 3 weeks before start of belumosudil treatment) * Patient has received an allo-HCT transplant and is in morphologic remission (blasts \<5%, no evidence of extramedullary disease in AML or MDS). Patients with CR with incomplete count recovery (CRp or CRi) or minimal residual disease are allowed. * Patient has achieved engraftment. Engraftment is defined as ANC≥500/μL and platelets ≥ 20000/μL on 3 consecutive measurements (each occurring at least 1 day apart). The patient must not have had a platelet transfusion within 7 days before the first measurement. * Patient is ≥ 80 days and ≤ 20 days from allo-HCT infusion. * Karnofsky score ≥ 70%. * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3x upper limit of normal (ULN) * Total bilirubin ≤1.5 x ULN (unless benign congenital hyperbilirubinemia). * Glomerular filtration rate (GFR) ≥ 30 mL/min/1.73 m2 * Female subjects of childbearing potential (≤ 50 years old) have a negative serum or urine pregnancy test. Females of childbearing potential are de…