Clinical impact of anti-thymocyte globulin on survival and graft-versus-host disease in patients undergoing human leukocyte antigen mismatched allogeneic stem cell transplantation

Background/Aims: Rabbit anti-thymocyte globulin (ATG) is usually incorporated in hematopoietic stem cell transplantation (HSCT) to reduce the incidence of graft-versus-host disease (GVHD). This study aimed to find optimal ATG doses in patients undergoing human leukocyte antigen (HLA)-mismatched allogeneic HSCT. Methods: We retrospectively collected medical records from 352 consecutive patients with acute myeloid leukemia (n = 214), acute lymphoblastic leukemia (n = 62), or myelodysplastic syndrome (n = 76) in eight centers of Korea between 2005 and 2015. All patients received busulfan-based conditioning without total body irradiation (TBI) and received stem cells from HLA-mismatched donors. Results: In the current study, 5-year overall survival rates of patients receiving low to medium doses of ATG (2.5 to 7.5 mg/kg) were higher than those receiving other doses of ATG (hazard ratio [HR], 0.528; 95% confidence interval [CI], 0.311 to 0.897; p = 0.018). The incidence rates of extensive chronic GVHD (ecGVHD) after administration of low to medium doses of ATG were lower than those after other doses of ATG (HR, 0.447; 95% CI, 0.224 ton 0.889; p = 0.022). Conclusions: The low to medium doses of ATG may be associated with improving survival outcomes and reducing incidence of ecGVHD without enhancing the chances of relapse in patients with acute leukemia or myelodysplastic syndrome undergoing non-TBI-based HLA-mismatched allogeneic HSCT.