Treatment of primary T cells with a SIRT inhibitor results in increased Foxp3⁺ cell numbers. Isolated primary T cells were cultured in the presence of IL-2, anti-CD3, and anti-CD28 (mouse splenocytes were also cultured in the presence of transforming growth factor-β). Cells were treated with the SIRT activator resveratrol, the SIRT inhibitor NAM, or carrier as control. The percentage of Foxp3⁺ cells was determined using FACS technology. T cells originated from human PBMCs (A), human skin (B), mouse spleen (C), and a human T-cell clone (D). Results are the means of at least 4 independent experiments. **P < .01.