Classification tree analyses. (A) Classification tree analysis of the effect of alemtuzumab level at the time of graft infusion (±72 hours) and HLA match on acute GVHD. (B) Classification tree analysis of the effect of alemtuzumab level at the time of graft infusion (±72 hours) and underlying diagnosis (marrow failure vs non–marrow failure) on the incidence of mixed chimerism.