IFN-γ–deficient allogeneic donor T cells induce severe GVHD without enhanced GVL effects. Survival (A-B) and mean GVHD clinical scores (C-D) of mice that received 3 × 10³ FACS-sorted HSCs + 3 × 10⁵ MACS-enriched splenic T cells from with either WT or IFN-γ knockout (IFN-γ^−/−) mice with or without 5 × 10⁴ FACS-purified pDCs in C57BL/6J→CD90.1⁺ BA.B10 transplant model. Leukemic recipients also were injected with 1 × 10⁵ viable LBRM tumor cells on day −1, 1 day after radiation and 1 day before BMT. n = 10 mice per group in panel A and n = 20 mice per group in panel B. **P < .01 comparing HSCs + WT T with HSCs + WT T + pDCs for days 13-22; #P < .05 comparing HSCs + WT T with HSCs + WT T + pDCs for days 44-58; *P < .05 comparing HSCs + WT T with HSCs + IFN-γ^−/− T for days 22-33 in panel C; and ***P = < .001 comparing HSCs + WT T with HSCs + IFN-γ^−/− T for day 19 after transplantation; *P = < .05 comparing HSCs + WT T with HSCs + IFN-γ^−/− T for days 22-41 after transplantation; $P = < .05 comparing HSCs + WT T with HSCs + WT T + pDCs for days 26-54 after transplantation; #P < .01 comparing HSCs + WT T with HSCs + IFN-γ^−/− T + pDCs for days 13-26 in panel D.