Th17/Tc17 are a significant source of GM-CSF in the GI tract after allo-SCT. Cytokine and transcription factor expression by CD4⁺YFP⁺ and CD8⁺YFP⁺ T cells was assessed in the colon and mLN 1, 2, and 4 weeks after allogeneic (B6.IL-17^CreRosa26^eYFP→Balb/c) transplant. (A) Representative flow cytometry plots gated on isotype controls demonstrating GM-CSF expression in YFP⁺ vs YFP⁻ T cells 4 weeks after allo-SCT. (B) Frequency of GM-CSF expression in CD4⁺ and CD8⁺ T cells within YFP⁺ and YFP⁻ compartments from colon and mLN at 1, 2, and 4 weeks after allo-SCT. (C) Frequency of YFP expression within CD4⁺GM-CSF⁺ and CD8⁺GM-CSF⁺ T cells from colon and mLN at 1, 2, and 4 weeks after allo-SCT. (D) Total number of CD4⁺ GM-CSF⁺YFP⁺, GM-CSF⁺YFP⁻, and total CD4⁺ T cells in colon and mLN at 1, 2, and 4 weeks after allo-SCT. (E) Total number of CD8⁺ GM-CSF⁺YFP⁺, GM-CSF⁺YFP⁻, and total CD8⁺ T cells in colon and mLN at 1, 2, and 4 weeks after allo-SCT. (A-E) The data are combined from 3 replicate experiments (n = 14-16 mice per group). (F) Representative histograms showing BATF expression in RORγt⁺ and RORγt⁻ CD4⁺ and CD8⁺ T cell fractions in colon 2 and 4 weeks after allo-SCT. (G) Representative histograms showing BATF expression in GM-CSF⁺ and GM-CSF⁻ colonic CD4⁺ T cells fractions 2 and 4 weeks after allo-SCT. (H) Batf relative gene expression in YFP⁺ and YFP⁻ colonic CD4⁺ T cells 4 weeks after allo-SCT (n = 6 per group). Statistical analyses were performed by unpaired Student t test when comparing between 2 groups and 1-way analysis of variance when comparing over time (mean ± standard error of the mean [SEM]). *P < .05; **P < .01; ***P < .001; ****P < .0001.