Impacts of thymoglobulin in patients with acute leukemia in remission undergoing allogeneic HSCT from different donors

Antithymocyte globulin (ATG) is widely used to reduce acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD). To clarify the different impacts of ATG for conditioning across different donor types, we retrospectively analyzed patients with acute leukemia (n 5 6617) who underwent hematopoietic stem cell transplantation between 2008 and 2015 with ATG (n 5 279) or without ATG (n 5 6338). Because thymoglobulin is the only ATG drug approved for GVHD prophylaxis in Japan since September 2008, we included thymoglobulin alone in the present analysis. The survivors’ median follow-up time was 1081 days. Patients were categorized into 5 groups: cord blood (CB; n 5 1915), matched related donor (n 5 1772), 1-antigen mismatched related donor (1-MMRD; n 5 225), matched unrelated donor (MUD; n 5 1742), and 1-allele mismatched unrelated donor (1-MMUD; n 5 963). In multivariate analysis, ATG decreased overall survival (hazard ratio [HR], 1.403; P 5 .054) and GVHD-free/relapse-free survival (GRFS) (HR, 1.458; P 5 .053) in association with increased nonrelapse mortality (NRM) (HR, 1.608; P 5 .03) with CB, whereas it improved GRFS (HR, 0.515; P, .01) and decreased grades II to IV aGVHD (HR, 0.576; P, .01), extensive cGVHD (HR, 0.460; P 5 .02), and NRM (HR, 0.545; P 5 .03) with 1-MMUD. ATG did not impact survival with 1-MMRD and MUD. The use of ATG in conditioning is beneficial due to the reduction in acute/chronic GVHD without increasing NRM or disease relapse only in 1-MMUD transplantation. On the other hand, ATG is not recommended for CB transplantation.