Grade 3-4 acute GVHD by conditioning regimen intensity. The 6-month incidence of grade 3-4 acute GVHD was 21% (95% CI, 17-24) for Bu4/Cy, 19% (95% CI, 16-23) for Flu/Bu4, 15% (95% CI, 11-19) for Flu/Bu4 + ATG, 16% (95% CI, 13-20) for Flu/Bu2, 14% (95% CI, 10-18) for Flu/Bu2 + ATG, 19% (95% CI, 14-25) for Flu/Mel, and 26% (95% CI, 16-37) for Flu/Mel + ATG.