Horse versus rabbit antithymocyte globulin in immunosuppressive therapy of treatment-naïve aplastic anemia: a systematic review and meta-analysis

The first-line formulation of antithymocyte globulin (ATG) remains unknown. We aimed to systematically review evidence to compare the efficacy and safety profiles of different ATGs. We did a systematic review and meta-analysis of randomized controlled trials (RCTs) and cohort controlled studies comparing horse and rabbit ATG in immunosuppressive therapy of treatment-naive aplastic anemia. We searched The Cochrane Library, PubMed, EMBASE, ClinicalTrials.gov, and conference proceedings of American Society of Hematology and European Society for Blood and Marrow Transplantation annual meetings. The outcomes were 3-, 6-, and 12-month response; early mortality; relapse; and evolution. We pooled hazard ratios for relapse and odds ratios (ORs) for other outcomes using fixed-effect or random-effect models based on the heterogeneity. This study was registered with PROSPERO, number CRD42016036945. We included 1636 participants from three RCTs and 11 cohort controlled studies. Allocation to horse ATG increased 6-month response events by 86% compared with rabbit ATG. The benefit of horse ATG was mainly driven by increase in studies with non-Asian (OR 95% CI = 2.39 (1.54–3.69), p < 0.0001) and good partial response criterion (OR 95% CI = 2.73 (1.53–4.89), p = 0.0007). The early mortality and evolution were similar between groups. Compared with rabbit ATG, horse ATG had superior remission by 6 months and equivalent safety profiles in patients with treatment-naive AA. Evidence for further responses beyond 6 to 12 months was limited.