RecruitingDrug trialPost-Transplant Cyclophosphamide, Bortezomib and Abatacept for the Prevention of Graft-versus-Host-Disease (GvHD)This is a phase I-II clinical trial. Adult subjects with hematological malignancies undergoing allogeneic HSCT from an HLA matched sibling or ≥7 out of 8 allele level HLA matched unrelated donor are eligible for the study if they meet the criteria defined in our standard operation procedures (SOPs), meet all inclusion criteria, and do not satisfy any exclusion criteria. Subjects will receive a standard of care conditioning regimen. Subjects will receive investigational PTCy, investigational bortezomib and investigational abatacept as GvHD prophylaxis.