[Antithymocyte globulin for graft-versus-host disease prophylaxis, past, present and future]

Antithymocyte globulin (ATG) for graft-versus-host disease (GVHD) prophylaxis has been demonstrated for chronic GVHD inhibition by a series of randomized control trials. The optimal dose of ATG remained unestablished; however, the recommended dose of ATG by the European Group for Blood and Marrow Transplantation has recently decreased. While a lower ATG dose has been used in Japan, ATG usage is recommended in peripheral blood stem cell transplantation or human leukocyte antigens (HLA) 1-locus mismatched bone marrow transplantation with myeloablative conditioning from the nation-wide retrospective studies showing that ATG inhibited chronic GVHD and improved GVHD-free, relapse-free survival. The association of absolute lymphocyte counts (ALC) before ATG administration with transplant outcomes has been reported, which suggests a possible strategy to individualize the ATG dose according to ALC before ATG. Recent studies compared the transplant outcomes using ATG and post-transplant cyclophosphamide, which has rapidly spread in haploidentical transplantation; however, further studies are needed to establish those positioning in HLA-matched/mismatched transplantation.