Comparison of interferon-γ secretion and cytotoxic activity of HIV-1-specific CD8⁺T cells at the single epitope level. HIV-1-specific CD8⁺ T-cell responses to 5 optimal CD8⁺ T-cell epitopes are shown in study individuals AC-04 (A) and FW-003 (B), respectively. Percentages reflect the proportion of caspase-3-expressing target cells (top rows) and the corresponding proportion of interferon-γ-secreting CD8⁺ T cells (bottom rows) following co-incubation of peptide-pulsed BCL and freshly harvested PBMCs. (C) Correlation between epitope-specific interferon-γ secretion and cytotoxic activity in 53 different immune responses from 9 different study persons. Dashed lines indicate the 95% confidence intervals of the regression line.