ATRA enhances FoxP3 expression independent of Stat5. CD8-depleted thymocytes from Stat5^fl/flCD4-Cre mice were polyclonally stimulated for 3 days with media alone, IL-6, IL-2, and TGF-β1, or IL-2 and TGFβ-1 in the presence or absence of 1 μM ATRA. IL-17 and FoxP3 expression were measured on CD4⁺ gated fixed cells by intracellular staining. Data are representative of 2 independent experiments. Numbers on plots are percentages of total cells.