Reduced dose of post-transplantation cyclophosphamide compared to ATG for graft-versus-host disease prophylaxis in recipients of mismatched unrelated donor hematopoietic cell transplantation: a single-center study.

Post-transplantation cyclophosphamide (PTCy) demonstrated effectiveness to prevent GVHD after haploidentical hematopoietic cell transplantation (HCT). Reducing toxicities with a maximized efficacy is still challenging in HCT. In this retrospective study, we analyzed the safety and efficacy of transplantation from a 1-antigen HLA-mismatched unrelated donor (9/10 MMUD) in 80 patients with hematological disorders between 2010 and 2018; 22 patients received PTCy with a reduced dose of 40 mg/kg, cyclosporine A, and mycophenolate mofetil (MMF); 58 patients received anti-thymocyte globulin (ATG), cyclosporine A, and either methotrexate or MMF for GVHD prophylaxis. Cumulative incidence (CI) of acute GVHD grades II-IV in the PTCy group was significantly lower (15% vs. 50%, p = 0.006); however, CI of chronic GVHD was (not significantly) lower in the PTCy group (26% vs. 35%, p = 0.137). One-year OS was significantly longer (p = 0.008) in the PTCy group with a similar 1-year PFS (p = 0.114) in both groups. Rates of 1-year relapse and non-relapse mortality were similar. Median time to neutrophil engraftment was comparable in both GVHD prophylaxis groups (14 days vs. 16 days, respectively, p = 0.107). Our results show that a lower dose of PTCy-based prophylaxis is an effective and safe strategy to prevent acute GVHD in HCT with 9/10 MMUD compared to ATG.