Low immunosuppressive burden after HLA-matched related or unrelated BMT using posttransplantation cyclophosphamide

The intensive and prolonged immunosuppressive therapy required to prevent or treat graft-versus-host disease (GVHD) after allogeneic blood or marrow transplantation (alloBMT) puts patients at substantial risk for life-threatening infections, organ toxicity, and disease relapse. Posttransplantation cyclophosphamide (PTCy) can function as single-agentGVHDprophylaxis after myeloablative, HLA-matched related (MRD), or HLAmatched unrelated (MUD) donor T-cell-replete bone marrow allografting, obviating the need for additional prophylactic immunosuppression. However, patients who develop GVHD require supplemental treatment. We assessed the longitudinal requirement for immunosuppressive therapy in 339 patients treated with this transplantation platform: 247 receiving busulfan/cyclophosphamide (BuCy) conditioning (data collected retrospectively) and 92 receiving busulfan/fludarabine (BuFlu) conditioning (data collected prospectively). Approximately 50% of MRD patients and 30% of MUD patients never required immunosuppression beyond PTCy. In patients requiring further immunosuppression, typically only 1 to 2 agents were required, and the median durations of systemic pharmacologic immunosuppression for the BuCy MRD, BuFluMRD, BuCyMUD, andBuFluMUDgroups allwere 4.5 to 5months. For these 4 groups, 1-year probabilities of being alive and off all systemic immunosuppression were 61%, 53%, 53%, and 51% and 3-year probabilitieswere 53%, 48%, 49%, and 56%, respectively. These data suggest that PTCy minimizes the global immunosuppressive burden experienced by patients undergoing HLAmatched alloBMT.