Impact of graft-versus-host disease after reduced-intensity conditioning allogeneic stem cell transplantation for acute myeloid leukemia: a report from the Acute Leukemia Working Party of the European group for blood and marrow transplantation. 
This report investigated the impact of graft-versus-host disease (GVHD) on transplantation outcomes in 1859 acute myeloid leukemia patients given allogeneic peripheral blood stem cells after reduced-intensity conditioning (RIC allo-SCT).  Grade I acute GVHD was associated with a lower risk of relapse (hazards ratio (HR)=0.7, P=0.02) translating into a trend for better overall survival (OS; HR=1.3; P=0.07).  Grade II acute GVHD had no net impact on OS, while grade III-IV acute GVHD was associated with a worse OS (HR=0.4, P<0.0.001) owing to high risk of nonrelapse mortality (NRM; HR=5.2, P<0.0001).  In time-dependent multivariate Cox analyses, limited chronic GVHD tended to be associated with a lower risk of relapse (HR=0.72; P=0.07) translating into a better OS (HR=1.8; P<0.001), while extensive chronic GVHD was associated with a lower risk of relapse (HR=0.65; P=0.02) but also with higher NRM (HR=3.5; P<0.001) and thus had no net impact on OS.  In-vivo T-cell depletion with antithymocyte globulin (ATG) or alemtuzumab was successful at preventing extensive chronic GVHD (P<0.001), but without improving OS for ATG and even with worsening OS for alemtuzumab (HR=0.65; P=0.001).  These results highlight the role of the immune-mediated graft-versus-leukemia effect in the RIC allo-SCT setting, but also the need for improving the prevention and treatment of severe GVHD.