PTCy- vs ATG-based GvHD prophylaxis in MMUD allo-HSCT: A CIBMTR analysis

Results from a secondary analysis of a Center for International Blood and Marrow Transplant Research (CIBMTR) dataset (P-5891), comparing post-transplant cyclophosphamide (PTCy)- vs antithymocyte globulin (ATG)-based graft-versus-host disease (GvHD) prophylaxis in adults undergoing first 7/8 human leukocyte antigen (HLA)-mismatched unrelated donor (MMUD) allogeneic hematopoietic stem cell transplantation (allo-HSCT) during 2017–2021, were published in Transplantation and Cellular Therapy by Rodriguez-Rodriguez et al. The analysis included 834 adults who received PTCy + calcineurin inhibitor (CNI) + mycophenolate mofetil (MMF; n = 613) or ATG + CNI + methotrexate (MTX; n = 221). Endpoints of interest included GvHD-free, relapse-free survival (GRFS), overall survival (OS), relapse, non-relapse mortality (NRM), and incidence of acute and chronic GvHD.

Key data: At 24 months, PTCy vs ATG was associated with improved GRFS (44.9% vs 26.7%; adjusted hazard ratio [aHR], 0.58; p < 0.001) and OS (63.9% vs 46.6%; aHR, 0.60; p < 0.001). NRM was lower with PTCy vs ATG (17.2% vs 35.1%; aHR, 0.44; p < 0.001), while cumulative incidence of relapse (CIR) at 24 months was comparable between groups (25.9% vs 24.6%; aHR, 1.07; p = 0.68). The cumulative incidences of Grade 2–4 and Grade 3–4 acute GvHD (aGvHD) at 3 months were lower with PTCy vs ATG (30.7% vs 50.3%; aHR, 0.51 and 7.7% vs 23.8%; aHR, 0.29, respectively; both p < 0.001), while moderate-to-severe chronic GvHD (cGvHD) did not significantly differ at 24 months (15.8% vs 19.3%; aHR, 0.72; p = 0.081).

Key learning: These registry-based data support the use of PTCy-based GvHD prophylaxis in adults undergoing 7/8 MMUD allo-HSCT. Prospective studies comparing this approach to ATG-based prophylaxis in MMUD recipients are needed to confirm these findings.