TGFβ is required for de novo induction of FOXP3. FACS sorted human CD4⁺CD25⁻CD127⁺CD45RA⁺ cells stimulated for 5 days with plate-bound anti-CD3/CD28 and 100 IU/mL IL-2 in the presence or absence of 5 ng/mL TGFβ1. Flow cytometric analysis of FOXP3 with PCH101 and 206D. FOXP3 positivity is determined by the isotype control on the same cells. Numbers on plots are percentages of total cells.