Rabbit antithymocyte globulin (rATG; thymoglobulin, Genzyme) in combination with cyclosporine, as first-line immunosuppressive therapy, was evaluated prospectively in a multicenter, European, phase 2 pilot study, in 35 patients with aplastic anemia. Results were compared with 105 age-and disease severitymatched patients from the European Blood and Marrow Transplant registry, treated with horse ATG (hATG; lymphoglobulin) and cyclosporine. The primary end point was response at 6 months. At 3 months, no patients had achieved a complete response to rATG. Partial response occurred in 11 (34%). At 6 months, complete response rate was 3% and partial response rate 37%. There were 10 deaths after rATG (28.5%) and 1 after subsequent HSCT. Infections were the main cause of death in 9 of 10 patients. The best response rate was 60% for rATG and 67% for hATG. For rATG, overall survival at 2 years was 68%, compared with 86% for hATG (P ؍ .009). Transplant-free survival was 52% for rATG and 76% for hATG (P ؍ .002). On multivariate analysis, rATG (hazard ratio ؍ 3.9, P ؍ .003) and age more than 37 years (hazard ratio ؍ 4.7, P ؍ .0008) were independent adverse risk factors for survival. This study was registered at www.clinicaltrials.gov as NCT00471848. (Blood. 2012;119(23): 5391-5396)
IntroductionHistorically, horse antithymocyte globulin (hATG) has been the preferred animal source of ATG as first-line treatment for acquired aplastic anemia (AA) patients who are ineligible for hematopoietic stem cell transplantation (HSCT). For severe AA (SAA), the combination of ATG and cyclosporine (CSA) results in a response rate of 60% to 75% of patients, and the response is superior to using either agent alone. [1][2][3][4][5] The addition of G-CSF to the combination of ATG and CSA has shown no significant benefit either in terms of response or survival, 6-8 although it may reduce infectious complications and duration of hospital admission. 6 For patients with nonsevere AA (NSAA) who are transfusion dependent, the combination of ATG and CSA is superior to CSA alone, with a higher response rate, higher blood counts, and improved disease-free survival. 9 Rabbit ATG (rATG) is more commonly used for a second course after relapse or lack of response to a first course of hATG. Response to a second course for nonresponse to a first course varies from 30% to 77% 10,11 and only 11% in children. 12 In contrast, in patients relapsing after a first course, the response to a second course is 65%. 11,13 Until 2007, there were 2 preparations of hATG, namely, lymphoglobulin (Genzyme) and ATGAM (Pfizer). The most commonly used preparation of rATG (thymoglobulin, Genzyme) uses the same immunogen as lymophoglobulin; horses or rabbits are immunized with human thymocytes obtained at the time of cardiac surgery from newborn infants. rATG is more immunosuppressive than hATG; it results in more prolonged lymphopenia, 14 and it is more effective at preventing and treating acute renal allograft rejection. 15 We undertook a European study conducted by th...