HIV-specific cells during acute infection (Ac-tet⁺ cells). PBMCs were studied as described in Figure 1. HIV-specific cells were identified by labeling with MHC class I tetramers loaded with HIV peptides (tet⁺ cells) and were subdivided according to their CD27/CD28 phenotype. (A) Frequency of T_EM subpopulations with different CD27/CD28 phenotypes in individual donors. ND indicates not detected. (B) In each donor, expression frequencies were determined in 60 individual cells from each of the CD8 subpopulations. Results are the mean ± SD of 9 Ac-tet⁺ donors. The values from HIV-seronegative donor from Figure 1 are included in gray to facilitate comparison. Differences between seronegative and HIV-infected donors were: Ifng DP, P < .0001; CD27SP, P < .002; and Gzmb DP, P < .03. (C) Expression of lytic proteins in tet⁺ cells from one patient with acute infection and T_EM cells from one HIV-seronegative donor, studied in the same experiment. Similar results were obtained in 4 experiments. (D) The expression frequencies of different TF determined as described in panel B. Up-regulation of Tbx21 in DP cells: P < .05; down-regulation of Eomes in CD27SP: P < .003.