Posttransplant Cyclophosphamide Versus Anti-Thymocyte Globulin Versus Combination for Graft-Versus-host Disease Prevention in Haploidentical Transplantation for Adult Acute Myeloid Leukemia: A Report from the European Society for Blood and Marrow Transplantation Acute Leukemia Working Party

BackgroundThe optimal choice for graft-versus-host disease (GVHD) prophylaxis in haploidentical stem cell transplantation (haplo-SCT) remains debatable. Posttransplant cyclophosphamide (PTCy) and anti-thymocyte globulin (ATG) are two common strategies, but little is known about their combination.MethodsUsing the European Society for Blood and Marrow Transplantation (EBMT) registry, the authors identified 3649 adult patients with acute myeloid leukemia (AML) who underwent haplo-SCT in complete remission between 2007 and 2021 at 260 EBMT-participating centers who received either PTCy (n = 2999), ATG (n = 358), or combination prophylaxis (n = 292). Cord blood transplants, combined bone marrow and peripheral grafts, and transplants with ex vivo graft manipulation were excluded. Median follow-up was 31.8 months.ResultsOn multivariate analysis, adjusting for patient age and performance status, disease status at transplant, cytogenetic risk, conditioning intensity, stem cell source, female-to-male graft, and donor and patient CMV status, we present the following. Compared to PTCy, ATG had a higher risk of nonrelapse mortality (hazard ratio [HR], 1.6; p = .003), worse leukemia-free survival (HR, 1.4; p = .002), overall survival (HR, 1.49; p = .0009), and GVHD-free and relapse-free survival (HR, 1.29; p = .012). The combination of PTCy and ATG, however, led to significantly reduced rates of grade 2-4 (HR, 0.51; p = .0003) and grade 3-4 (HR, 0.5; p = .018) acute GVHD and did not affect any transplant outcomes compared to PTCy without ATG.ConclusionThe authors conclude that ATG alone is a less effective prophylaxis strategy compared to PTCy, however, the combination of PTCy and ATG is superior to either monotherapy. They propose that this combination could be considered a potential new standard of care for GVHD prophylaxis in haplo-SCT for AML. This study analyzed 3649 adult acute myeloid leukemia (AML) patients undergoing haploidentical stem cell transplantation (haplo-SCT) with either posttransplant cyclophosphamide (PTCy), anti-thymocyte globulin (ATG), or their combination, and showed that ATG alone had worse outcomes compared to PTCy, but combining PTCy and ATG significantly reduced acute graft-vs-host disease (GVHD) rates without affecting transplant outcomes. This suggests the PTCy and ATG combination could be a superior GVHD prophylaxis strategy in haplo-SCT for AML.