Comparison of two doses of antithymocyte globulin in patients undergoing matched unrelated donor allogeneic stem cell transplantation.

Antithymocyte globulin (ATG) as part of conditioning regimens is known to reduce the incidence and severity of acute and chronic graft-versus-host disease (aGVHD, cGVHD). The influence of ATG on transplant-related mortality (TRM) and disease-free survival (DFS) is controversial, and may depend on the dose and timing of ATG. We retrospectively compared 2 doses of ATG-Fresenius (ATG-F) in patients undergoing matched unrelated donor allogeneic hematopoetic stem cell transplantation (HSCT) for hematologic malignancies. A dose of 60 mg/kg body weight has previously been recommended for ATG-F. All patients received cyclosporine A and short course methotrexate. ATG-F was administered at a dose of 30 mg/kg on day -1 (ATG-30 group, n = 34) or 20 mg/kg/day on days -3 to -1 (ATG-60 group, n = 49). There was no difference in time to leukocyte and platelet engraftment in the 2 groups. The incidence of aGVHD grade II-IV (50% versus 53%, P = .83) and grade III-IV (27 versus 20%, P = .60) was similar in the ATG-30 versus ATG-60 groups, respectively. There was a trend to a higher incidence of cGVHD in the ATG-30 group (59% versus 40%, P = .14). The estimated 3-year incidence of relapse was similar in the ATG-30 and ATG-60 groups (15% versus 16%, P = .84) whereas the 2-year TRM was lower for the ATG-30 group (12% versus 33%, P = 0.02), mainly because of a higher incidence of fatal infections in the ATG-60 group. This resulted in a better DFS (73% versus 51%, P = .07) for the ATG-30 group. ATG-F (30 mg/kg) administered as a single dose on day -1 may lead to better outcome in patients undergoing unrelated donor allogeneic HSCT compared to 60 mg/kg given in 3 equivalent doses. A prospective randomized study comparing these 2 doses of ATG-F is warranted.