A randomized trial of GVHD prophylaxis in haploidentical PBSC transplantation: ATG, PTCy, and low-dose combination therapy.

The optimal graft-versus-host disease (GVHD) prophylaxis strategy in haploidentical peripheral blood stem cell transplantation remains controversial. In this open-label, phase 3 study, patients aged 14 to 70 years with acute myeloid leukemia or myelodysplastic syndromes with excess blasts Ⅰ or Ⅱ were randomized (2:1:1) to receive low-dose antithymocyte globulin (ATG; 5 mg/kg) plus posttransplant cyclophosphamide (PTCy; 50 mg/kg; referred to as ATG/PTCy), standard-dose ATG (total dose, 10 mg/kg), or a PTCy-based (total dose, 100 mg/kg) regimen for GVHD prophylaxis. The coprimary end points were the cumulative incidence (CI) of grade 2 to 4 acute GVHD (aGVHD) by day 100 and GVHD-free, relapse-free survival at 1 year after transplant. A total of 407 patients were randomized to receive an ATG/PTCy (185 patients), ATG (113 patients), or PTCy (109 patients) regimen for GVHD prophylaxis. By day +100, the CI of grade 2 to 4 aGVHD did not differ significantly among the 3 groups (P = .210). Although the overall incidence of chronic GVHD (cGVHD) was comparable across all groups (P = .110), the 2-year CI of moderate-to-severe cGVHD was numerically lower in the ATG/PTCy (17.4%) and ATG (17.3%) groups than the PTCy group (28.3%), without reaching statistical significance (P = .095). No significant differences were observed in survival outcomes among the 3 groups. Notably, the CI of neutrophil and platelet recovery was significantly higher in the ATG/PTCy group than in the other groups (P< .001). This trial suggested that the 3 GVHD prophylaxis strategies presented similar efficacy in preventing grade 2 to 4 aGVHD and yielded comparable survival. This trial was registered at www.clinicaltrials.gov as NCT03608059.