Suppressive function of CD8+ Tregs in vitro. (A) CD8+ Tregs were isolated from TILs of NPC patients by sorting the CD8+CD25+ T cells by flow cytometry. Representative dot plots for CD8, CD25, and Foxp3 before and after sorting are shown. (B) The suppressive activity of CD8+ Tregs on naïve CD4+ T cells in vitro was detected by proliferation of CSFE-labeled naïve CD4+ T cells. CSFE-labeled naïve CD4+ T cells were cultured alone or with CD8+ Tregs at different ratios, in the outer and inner chamber of a transwell system, or in the presence of anti-IL-10 or anti-IFNγ antibodies in low IL-2 medium in 96-well or 24-well plates coated with OKT3 for 5 days. Representative results from one of five experiments are shown.