Tacrolimus plus sirolimus with or without ATG as GVHD prophylaxis in HLA-mismatched unrelated donor allogeneic stem cell transplantation.

HLA-matched related or unrelated donors are not universally available. Consequently, patients can be offered hematopoietic stem cell transplantation (HSCT) from alternative donors, including mismatched unrelated donors (MMURD), known to cause a higher incidence of acute GVHD (aGVHD) and chronic GVHD. In vivo T-cell-depletion strategies, such as antithymocyte globulin (ATG) therapy, significantly decrease the risk of GVHD. We performed a multicenter, retrospective study comparing tacrolimus (TAC) and sirolimus (SIR) with or without ATG in 104 patients (TAC-SIR=45, TAC-SIR-ATG=59) who underwent MMURD HSCT. Use of ATG was associated with a lower incidence, albeit not statistically significant, of grades 2-4 aGVHD (46% vs 64%, P=0.09), no difference in grades 3-4 aGVHD (10% vs 15%, P=0.43), a trend for a lower incidence of moderate/severe chronic GVHD (16% vs 37%, P=0.09) and more frequent Epstein-Barr virus reactivation (54% vs 18%, P=0.0002). There were no statistically significant differences in 3-year overall survival (OS) (TAC-SIR-ATG=40% (95% confidence interval (CI)=24-56%) vs TAC-SIR=54% (95% CI=37-70%), P=0.43) or 3-year cumulative incidence of relapse/progression (TAC-SIR-ATG=40% (95% CI=28-58%) vs TAC-SIR=22% (95% CI=13-39%), P=0.92). An intermediate Center for International Blood & Marrow Transplant Research disease risk resulted in a significantly lower non-relapse mortality and better OS at 3 years. Our study suggests that addition of ATG to TAC-SIR in MMURD HSCT does not affect OS when compared with TAC-SIR alone.