Impact of HLA locus mismatch on peripheral blood allogeneic hematopoietic stem cell transplantation from unrelated donors using an ATG-based GVHD prophylaxis strategy

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important treatment option for hematologic diseases. However, limited studies have evaluated the prognosis of patients receiving single human leukocyte antigen (HLA) mismatched unrelated donor allo-HSCT (HLA 9/10 MMUD-HSCT) compared to those receiving fully matched unrelated donor allo-HSCT (10/10 MUD-HSCT). This study retrospectively analyzed 126 cases of unrelated donor allo-HSCT (URD-HSCT) at our center, in which anti-human thymocyte globulin (ATG, 7.5 mg/kg) was used as a graft-versus-host disease (GVHD) prophylaxis strategy. The MUD-HSCT group had a significantly lower incidence of grade II-IV acute GVHD (13.89% vs. 35.19% in the MMUD-HSCT group, p = 0.005). In contrast, the incidence of moderate-to-severe chronic GVHD (cGVHD) did not differ significantly between the two groups (16.67% vs. 29.63%, p = 0.083). The median follow-up time was 16.98 months (range: 7.88-38.55). There were no significant differences between the two groups in the 1-year cumulative incidence of relapse (CIR) (p = 0.707), 3-year CIR (p = 0.764), 1-year disease-free survival (DFS) (p = 0.954), 3-year DFS (p = 0.888), 1-year overall survival (OS) (p = 0.611), 3-year OS (p = 0.796), 3-year non-relapse mortality (NRM) (p = 0.711), or GVHD-free relapse-free survival (GRFS) (p = 0.546). The estimated median OS and DFS times were not reached in either group. In conclusion, under an ATG-based GVHD prophylaxis regimen, HLA 9/10 MMUD-HSCT is a viable alternative donor option, offering comparable clinical outcomes to those of fully matched unrelated donor HSCT.