PTCy-based graft-versus-host disease prophylaxis for matched sibling donor allogeneic hematopoietic cell transplantation.

Posttransplant cyclophosphamide (PTCy) is a promising graft-versus-host disease (GVHD) prophylaxis in haploidentical and matched unrelated donor hematopoietic stem cell transplantation (HSCT), but its role in matched sibling donor (MSD) transplants remains unclear. We conducted a retrospective study of 413 MSD-HSCT patients receiving peripheral blood stem cell (PBSC) grafts from January 2010 to January 2023. Patients were categorized into 4 groups: group I (calcineurin inhibitor [CNI] + methotrexate [MTX] or mycophenolate mofetil [MMF]), group II (CNI + MTX or MMF + antithymocyte globulin [ATG]), group III (PTCy + ATG + CNI), and group IV (PTCy + CNI + MMF). PTCy was associated with a significant reduction in grade 2- 4 and grade 3-4 acute GVHD and moderate-to-severe chronic GVHD compared with CNI + MTX (or MMF)-containing regimens. PTCy did not increase relapse risk; PTCy reduced nonrelapse mortality, leading to improved GVHD-free/relapse-free survival (GRFS; Hazard Ratio, 0.4; P < .001). PTCy was also associated with improved overall survival. Bloodstream infections were increased with PTCy. The addition of ATG to PTCy did not further improve GRFS and was associated with a higher incidence of clinically significant cytomegalovirus (csCMV) and Epstein-Barr virus (csEBV) reactivation and a numerical increase in NRM. PTCy significantly appeared to improve GRFS in the MSD setting using PBSC grafts. The addition of ATG to PTCy increases csCMV and csEBV reactivation without further improving GRFS. Prospective trials and PTCy dose optimization are warranted.