iTc17 development posttransplant is primarily driven by IL-6 and regulated by IFNγ and IL-12p40. (A-D) iTc17 development was assessed by enumeration of CD8⁺YFP⁺ T cells 7 days post–allo-SCT (B6.IL-17^CreRosa26^eYFP→B6D2F1). Mice were treated with either isotype control mAbs or blocking mAbs targeting (A) IL-6R, (B) TGFβ, (C) IL-12/IL-23p40, and (D) IFNγ. (E-F) CD8⁺YFP⁺ T-cell frequencies 7 days posttransplant in (E) a B6.IL-17^CreRosa26^eYFP→bm1 model, wherein only donor CD8⁺ T cells react to alloantigen, or (F) a B6.IL-17^CreRosa26^eYFP→CD11c.DOG-F1 model, wherein recipient mice were treated with DT to deplete DCs before transplant. Data are pooled from 2 independent experiments (3-10 mice/group total ± SEM; *P < .05, **P < .01, ***P < .001).