Reduction of GVHD mortality and morbidity in BMT across both isolated MHC class I (bm1 → B6; A) and minor histocompatible antigen barriers ( B10.BR → CBA; B) after reduced conditioning TBI. Solid symbols represent allogeneic groups 1,300 cGy TBI (•; n = 10) and 900 cGy TBI (▪; n = 10) and open symbols represent the syngeneic group 1,300 cGy TBI (○; n = 4 to 5). Relative bone marrow and T-cell inoculums were identical in all groups. (A) The percentage of survival: • v ▪ and ○, P < .001 by Wilcoxon signed rank-test, weight after BMT as a percentage of pretransplant weight; • v ▪, P < .01 from day 28 onward and • v ○, P < .02 from day 21 onward, clinical score; • v ▪, P < .01 from day 7 onward; ▪ v ○, P < .02 from day 28 onward. (B) The percentage of survival: • v ▪ and ○, P < .001 by Wilcoxon signed rank test, weight after BMT as a percentage of pretransplant weight; • v ▪, P < .01 from day 21 onward and • v ○, P < .02 from day 28 onward, clinical score; • v ▪, P < .01 from day 7 onward; ▪ v ○, P < .01 from day 14 onward.