Extended posttransplantation administration of PS-1145 protects animals from lethal GVHD and does not induce fatal gut toxicity. Lethally irradiated (1000 cGy) B6 mice underwent transplantation with TCD B10.BR BM alone (□, n = 6) or together with spleen cells adjusted to yield a dose of 2 × 10⁶ B10.BR T cells. (A) Animals that received transplanted B10.BR T cells were administered DMSO (▪, n = 11) or PS-1145 (•, n = 11) (50 mg/kg for 10 days beginning the day of transplantation). Survival is shown in panel A, and weight loss, in panel B. Overall cellularity (C), absolute number of B cells (D), and donor T-cell chimerism (E) in the spleens of mice that survived 60 days after transplantation are shown (□, TCD BM; ▨, DMSO; ▪, PS-1145). Data in bar graphs are presented as the mean ± SEM. Spleen cellularity: DMSO versus PS-1145, P = .006; TCD versus PS-1145, P < .001. Total splenic B cells: DMSO versus PS-1145, P = .04; TCD versus PS-1145, P < .001. Percentage donor T cells: DMSO versus PS-1145, P = .66; TCD versus PS-1145, P < .001