iTc17 depletion protects mice from lethal aGVHD. Lethally irradiated (A-E) B6D2F1, (F) Balb/c, or (G) Bm1 mice received CD8⁺ T cell–depleted, G-CSF–mobilized WT.B6 allografts supplemented with purified CD8⁺ T cells derived from WT.B6 (Tc17 intact), IL-17^CreRosa26^iDTR, IL-17^CreRosa26^iDTR (Tc17 depleted), or IL-17A–deficient (Tc17 ko) mice as indicated. WT.B6 G-CSF–mobilized WT allografts depleted of both CD4⁺ and CD8⁺ T cells were used as no-GVHD controls (TCD). All groups received continued DT treatment during weeks 1 to 3 as described in Materials and methods. (B-C) CD8⁺YFP⁺ T-cell depletion was assessed d7 posttransplant in B6D2F1 recipients of grafts containing IL-17^CreRosa26^eYFP/iDTR heterozygous CD8⁺ T cells. (B-C) CD8⁺YFP⁺ T-cell frequencies after Tc17 depletion were enumerated by flow cytometry (mean ± SEM, n = 5 mice/group; *P < .05, **P < .01). (D) Quantitative GVHD histopathology analysis was performed on colon tissue isolated d7 posttransplant from B6D2F1 recipients of allografts as described in (A) (Tc17 intact, 6 mice/group; Tc17 depleted, 8 mice/group; TCD, 4 mice/group; *P < .05). Representative d7 colon histology images are shown (scale bar = 0.1 mm). (E-G) Survival indices by Kaplan-Meier analyses are shown for (E) B6D2F1, (F) Balb/c, and (G) Bm1 recipients of allo-SCT as described before. (E) Data are pooled from 4 independent experiments (Tc17 intact; Tc17 depleted, 36 mice/group; Tc17 ko, 20 mice/group; TCD, 16 mice/group; **P < .01). (F) Data are pooled from 2 independent experiments (Tc17 intact; Tc17 depleted, 10 mice/group; TCD, 6 mice/group; *P < .05). (G) Data are derived from 1 experiment (Tc17 intact; Tc17 depleted, 9 mice/group; TCD, 3 mice/group; *P < .05).