CD4 T cells adapt their immune function to the local tissue environment by differentiating into various functional subsets. At steady state, regulatory CD4 T cells (Treg) and interleukin (IL)-17-producing CD4 T cells (Th17 cells) reside in the intestinal lamina propria whereas CD4 cytotoxic T lymphocytes (CTL) are present in the epithelial layer. The differentiation into these functional subtypes is mutually exclusive and controlled by key transcription factors. Cytokine TGFβ, an important regulator of CD4 T helper subset differentiation, induces the master transcription factor, FOXP3 in Treg or RORγt in Th17 cells.