Impact of the Addition of Antithymocyte Globulin to Post-Transplantation Cyclophosphamide in Haploidentical Transplantation with Peripheral Blood Compared to Post-Transplantation Cyclophosphamide Alone in Acute Myelogenous Leukemia: A Retrospective Study on Behalf of the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation.

The use of haploidentical hematopoietic cell transplantation (haplo-HCT) with peripheral blood stem cells (PBSCs) to treat acute myelogenous leukemia (AML) is increasing. We explored whether the addition of antithymocyte globulin (ATG) to post-transplantation cyclophosphamide (PTCy) allows better outcomes compared with PTCy alone in haplo-HCT with PBSCs (haplo-PBSCT). We included 441 adult patients undergoing a first haplo-PBSCT for AML in first or second complete remission; graft-versus-host disease (GVHD) prophylaxis contained either PTCy alone (n = 374) or ATG plus PTCy (n = 67), in addition to cyclosporine A (CsA) and mycophenolate mofetil (MMF) as other immunosuppressive agents. All transplantations were performed between 2011 and 2019. No major imbalances were observed between the 2 groups. For both groups, the median patient age was 56 years, and the median year of haplo-PBSCT was 2017. Most patients received a reduced-intensity conditioning regimen (57% in the PTCy group and 61% in the ATG+PTCy group; P = .54). The median follow-up was 19 months in the PTCy group versus 15 months in the ATG+PTCy group (P = .59), and the rate of neutrophil engraftment in the 2 groups was 97% and 98%, respectively. In univariate analysis, there were no statistical differences in transplantation outcomes between the 2 groups. In multivariate analysis, ATG+PTCy was associated with a lower risk of chronic GVHD compared with PTCy alone (hazard ratio, .46; 95% confidence interval, .23 to .93; P = .03). No between-group differences in the other transplantation outcomes were seen. In haplo-PBSCT, the addition of ATG to PTCy (with CsA and MMF) is feasible and better at preventing chronic GVHD and is associated with survival and transplantation outcomes comparable to those with PTCy alone, without increasing transplantation toxicity, mortality, or relapse incidence.