Haploidentical versus matched unrelated donor hematopoietic cell transplantation for adult patients with refractory/relapsed acute lymphoblastic leukemia: a study from the Global Committee and the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation.

The optimal alternative donor for relapsed/refractory acute lymphoblastic leukemia (R/R ALL) patients remains controversial. We retrospectively analyzed adult R/R ALL patients who underwent a first allogeneic hematopoietic cell transplantation (allo-HCT) between 2010 and 2022 from either a haploidentical donor (Haplo-HCT) or a 10/10 matched unrelated donor (MUD-HCT). The analysis comprised 249 patients (80 Haplo-HCT and 169 MUD-HCT). For graft-versus-host disease (GVHD) prophylaxis, all Haplo-HCT recipients received post-transplant cyclophosphamide (PTCy)-based regimen, whereas all MUD-HCT recipients received anti-thymocyte globulin (ATG) only. After propensity score matching, 47 Haplo-HCT and 69 MUD-HCT recipients were enrolled. No significant differences were observed in the incidence of Day 180 grade II-IV aGVHD (34.4% vs. 26.8%; P = 0.27), or 2-year cGVHD (19.2% vs. 13.8%; P = 0.543). However, the incidence of Day 180 grade III-IV aGVHD was significantly higher in the Haplo-HCT group (23.4% vs. 8%; P = 0.048). Two-year overall survival (31.8% vs. 29.2%; P = 0.742), leukemia-free survival (20.4% vs. 24.4%; P = 0.531), relapse incidence (48.1% vs. 53.1%; P = 0.113), or non-relapse mortality (31.5% vs. 22.5%; P = 0.191) were comparable between Haplo-HCT group and MUD-HCT group, respectively. In conclusion, despite a higher incidence of grade III-IV aGVHD, outcomes for R/R ALL patients receiving Haplo-HCT with PTCy were comparable to those receiving 10/10 MUD-HCT with ATG.