The effect of different ATG preparations on immune recovery after allogeneic hematopoietic stem cell transplantation for severe aplastic anemia

Anti-thymocyte globulin (ATG) is widely used in the conditioning regimen before allogeneic stem cell transplantation for aplastic anemia. However, there are several different preparations of ATG and little is known about the difference of their effects on transplantation outcome. Therefore, in this study, we retrospectively compared the effect of two different rabbit ATG preparations [Thymoglobulin (ATG-G) and ATG-Fresenius (ATG-F)] on immune recovery and cytomegalovirus infection after transplantation. The conditioning regimen was a combination of fludarabine, cyclophosphamide, and ATG. Low dose total body irradiation was added in alternative donor transplantation. Four patients received ATG-F at 5 mg/kg/day from day -7 to day -3, whereas ATG-G was given at 2•5 mg/kg/day from day -5 to day -2 in three patients. There was no graft rejection and no grade II-IV acute graft-versus-host disease. All three patients in the ATG-G group developed positive cytomegalovirus antigenemia including two with high-grade antigenemia, whereas two of the four patients in the ATG-F group were persistently negative. Immunological evaluation on day 60 revealed that both CD4+ and CD8+ T-cell recoveries were delayed in the ATG-G group. These findings suggested that ATG-G has a stronger immunosuppressive activity than the ATG-F with a dose ratio of 1:2•5.