Virus-specific CD8 T cells during chronic HIV infection (Chr-tet⁺ cells). PBMCs were studied as described in Figure 1. HIV-specific cells, identified by labeling with MHC class I tetramers loaded with HIV peptides, were subdivided according to their CD27/CD28 phenotype. (A) For each donor, 60 cells individual cells from each of the CD27/CD28 subpopulations were studied. In some of these patients, particular subpopulations were very rare so we could not recover 60 individual cells. Data from these subpopulations were not included. Thus, although we studied a total of 14 patients, results are the mean ± SD of 9 Chr-tet⁺ donors for DP, 14 Chr-tet⁺ donors for CD27SP, and 12 Chr-tet⁺ donors for DN. Data from HIV-seronegative donors from Figure 1 are included in gray to facilitate comparison. Increased frequencies of Ifng expression in all subsets: P < .005; decreased frequencies in CD27SP and DN: Prf1, P < .002; Gzma, P < .005; Gzmb, P < .002; and Fasl, P < .001. (B) Perforin and granzyme protein expression in Chr-tet⁺ cells from one subject and T_EM cells from a HIV-seronegative donor studied in the same experiment. Similar results were obtained in 5 other experiments.