Proinflammatory donor Th17 are induced by alloantigen, IL-12/23, and IFNγ. (A-F) Donor CD4⁺ T-cell cytokine expression was examined after (A) syngeneic SCT (WT.B6 → WT.B6) or (A-F) allo-SCT, (A-B,E-F) WT.B6 → B6D2F1 (G-CSF mobilized grafts) or (C-D) WT.B6 or IL-12p40^–/– BM, WT.B6 T-cells and B6.TEa T-cells → Balb/c. (A) Proportion of CD4⁺IL-17A⁺ T cells coexpressing IFNγ d7 after either allo-SCT or syngeneic transplant (mean ± SEM, n = ≥6 mice per group, **P < .01). (B) Proportion of CD4⁺IL-17A⁺ T cells coexpressing IFNγ d7 after allo-SCT in the presence or absence of IL-12p40 blocking antibody treatment (mean ± SEM, n = ≥9 mice per group from 2 independent experiments, **P < .01). (C) Representative FACS analysis of donor TEa transgenic T cells harvested on d3, d5, and d7 after adoptive transfer. (D) Proportion of splenic and mLN CD4⁺IL-17A⁺ TEa cells coexpressing IFNγ d5 and d7 after allo-SCT in the presence and absence of donor BM-derived IL-12p40 (mean ± SD, n = 3 mice per group per time point, *P < .05, ***P < .001). (E) Representative FACS analysis and (F) proportion of CD4⁺IL-17A⁺ T cells coexpressing IFNγ d7 after allo-SCT in the presence or absence of IFNγ blocking antibody treatment (mean ± SEM, n = 6 mice per group pooled from 2 independent experiments, **P < .01).