GVHD exacerbates donor BM-derived peripheral T-cell apoptosis in recipients of allogeneic T cell–replete BMT. Lethally irradiated (1100 cGy) LP mice were transplanted with 5 × 10⁶ TCD B6 Ly5.2⁺ BM and 0.5 × 10⁶ B6 Ly5.1⁺ T cells. Values represent mean (± SEM). n = 5-10 mice per group, combined from 2 or more independent experiments. (A,B) Apoptosis of donor BM-derived and infused T cell–derived populations was determined on days 14 and 21 after transplantation by annexin-V staining. Donor cells were all negative for Ly9.1; donor BM was Ly5.2⁺ and donor T cells were Ly5.1⁺. B6 mice that did not receive transplants were analyzed as the control group. (C,D) Cleaved caspase 8 and 9 levels in donor BM-derived and infused T cell–derived populations (gated as in A,B) were measured on days 14 and 21 after transplantation. LP mice that did not receive transplants were also analyzed. (E,F) Intracellular Bcl-2 and Bcl-X_L levels were determined in donor BM-derived and infused T cell–derived populations (gated as in A,B) were measured on days 14 and 21 after transplantation. LP mice that did not receive transplants were also analyzed.