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.

Anti-thymocyte globulin overcomes the negative impact of HLA mismatching in transplantation from unrelated donors.

OBJECTIVE: About one third of patients requiring allogeneic hematopoetic stem cell transplantation (HSCT) would not find a matched sibling or alternative donor. Allogeneic HSCT from matched unrelated and mismatched donors carries an increased risk of graft-vs-host disease (GVHD) and transplant-related mortality (TRM). MATERIALS AND METHODS: We used anti-thymocyte globulin (ATG-Fresenius) at a median dose of 90 mg/kg body weight as part of a total body irradiation or busulfan-based conditioning regimen for prevention of serious GVHD. All patients received cyclosporine A and short-course methotrexate. We compared outcomes of 65 recipients of human leukocyte antigen (HLA)-mismatched unrelated grafts and 194 recipients of HLA-matched unrelated grafts. Mismatches involved one or two loci. Both groups were comparable in age, graft source, diagnosis, stage of disease, and conditioning regimen, and differed only in dose of ATG administered. RESULTS: For matched and mismatched transplants, respectively, there was no significant difference in graft failure (0.5% vs 3%; p = 0.16), in the cumulative incidence of grade II to IV acute GVHD (45% vs 35%; p = 0.14) and no difference in overall chronic GVHD (42% vs 40%; p = 0.68). Estimated overall survival (OS) and disease-free survival (DFS) at 5 years were 55% vs 50% (p = 0.99) and 47% vs 47% (p = 1.0), respectively. The cumulative incidence of relapse and TRM at 5 years were 24% vs 25% (p = 0.63), and 29% vs 27% (p = 0.59), respectively. CONCLUSION: Inclusion of ATG-Fresenius in the conditioning regimen permits HSCT from mismatched unrelated donors without excess TRM and GVHD, resulting in identical OS and DFS of recipients of HLA-matched and HLA-mismatched grafts.