GVHD and GVL responses are enhanced by type I-IFN signaling in donor grafts. (A) Survival and clinical scores in lethally irradiated B6D2F1 mice transplanted with 5 × 10⁶ BM and 2 × 10⁶ T cells from either B6.WT or B6.IFNAR1^−/− donors (^#P < .005, **P < .01, *P < .05; combined data from 3 experiments, n = 26-30 in BM + T groups, n = 13 in TCD controls). (B) Leukemic death after administration of host derived P815^luc+ tumor (5 × 10³) with the donor graft (*P < .05, B6.WT vs B6.IFNAR1^−/− donors; combined data from 2 experiments, n = 18 in BM + T groups, n = 8 in TCD control groups). (C) Bioluminescence at day 12 after transplantation with P815^luc+ tumor (**P < .01, B6.WT vs B6.IFNAR1^−/− donors; combined data from 2 experiments, n = 18 per gp) with representative images shown. (D) In vivo cytotoxicity index at day 12 after BM transplantation (data combined from 2 experiments and expressed as mean ± SEM; *P < .05, B6.WT vs B6.IFNAR1^−/− donors, n = 7-11 per group). (E) Leukemic death after transplantation of lethally irradiated B6D2F1 mice with a combination of either B6.WT or B6.IFNAR1^−/− BM with B6.WT or B6.IFNAR1^−/− T cells and P815^luc+ tumor (**P < .01, *P < .05, combined data from 2 experiments, n = 16 in BM + T groups, n = 8 in TCD). (F) B6.WT recipients were lethally irradiated and 24 hours later 10⁷ BM and 10⁶ CD8⁺ T cells from C3H.SW donors transplanted with 2.5 × 10⁴ EL-4^luc+ tumor. After the establishment of low-level tumor as determined by bioluminescence, recombinant IFNα or saline was administered every other day and tumor burden assessed 1 week later (data combined from 2 experiments and expressed as mean ± SEM; **P < .01 saline day 0 vs day 7).