Impact of Low-Dose rATG Prior to Matched Sibling Donor Hematopoietic Stem Cell Transplantation for Hematologic Malignancies: Reduced Risk of Chronic Graft-versus-Host Disease and Improved Survival Outcomes

PURPOSE: To explore the efficacy of low-dose rabbit antithymocyte globulin (rATG) in matched sibling donor hematopoietic stem cell transplantation (MSD-HSCT) for patients with acute leukemia or myelodysplastic syndrome. PATIENTS AND METHODS: We performed a retrospective study of 79 patients with hematologic malignancies who received MSD-HSCT. All patients received standard graft-versus-host disease (GVHD) prophylaxis comprising cyclosporine, mycophenolate mofetil and short-term methotrexate. Among them, 38 were administered 5 mg/kg rATG as part of GVHD prophylaxis. Clinical outcomes including overall survival (OS), GVHD and relapse were analyzed. RESULTS: No graft failure occurred in the antithymocyte globulin (ATG) or non-ATG group. The cumulative incidences of grade 2–4 and 3–4 acute GVHD at day +100 were 13.3% versus 19.5% (p=0.507) and 5.7% versus 15.2% (p=0.196), respectively. The 2-year cumulative incidences of chronic GVHD (cGVHD) were 35.4% and 60.4% (p=0.039), and those of extensive cGVHD were 12.9% and 40.0% (p=0.015), respectively. In a multivariate analysis, the use of low-dose rATG was an independent protective factor for extensive cGVHD (hazard ratio [HR] 0.256; 95% confidence interval [CI], 0.080 to 0.822, p=0.022). The 2-year OS was 88.1% and 68.4% (p=0.038), respectively, and the use of low-dose rATG was the only protective factor in the multivariate analysis (HR 0.216; 95% CI, 0.059 to 0.792, p=0.021). There was no significant difference between the two groups in terms of the 2-year cumulative incidence of relapse, leukemia-free survival or GVHD-free and relapse-free survival. CONCLUSION: Low-dose rATG used in MSD-HSCT as part of the conditioning regimen results in a reduced incidence of cGVHD and improves survival outcomes.