Foxp3+ T cells exist in both non-proliferating (CFSE+hi) and dividing (CFSE+low) TCR-stimulated CD4+CD25- T cells. CD4+CD25- T cells were labeled with CFSE (2.5 μM) and cultured with anti-CD3 and anti-CD28 for 3 and 5 days. Cells were then counter-stained intracellularly with PE-conjugated anti-Foxp3 antibody. The cells were analyzed with FACS and a representative profile of CFSE vs. Foxp3 or its control antibody (mIgG2a) is displayed. The experiments were repeated three times with similar results. Data not shown here are the cultures with cells in medium alone. No CFSE dilution (CFSE+low) or Foxp3+ cells were observed.