CD4⁺CD25⁺ T cells protect CD8⁺ T cells from AICD. (A) Apoptosis of anti-CD3–stimulated CD8⁺ T cells was diminished in the presence of CD4⁺CD25⁺ T cells, compared with the presence of CD4⁺CD25^– T cells. Anti-CD3 stimulation resulted in a 57% increase of apoptosis over baseline, stimulation with PMA/ionomycin yielded similar results (not shown). (B-C) Apoptosis of HCV peptide-stimulated T-cell lines of an HCV-recovered (Ch1605) and a persistently HCV-infected chimpanzee (Ch6412) was diminished in the presence of CD4⁺CD25⁺ T_Regs, compared with the presence of CD4⁺CD25^– T cells. The results are representative for 6 experiments, using HCVcore_41^-, HCV-NS3_1444^-, and HCV-NS3_1357^-stimulated T-cell lines of recovered and persistently infected chimpanzees.