PD-1 up-regulation occurs on effector memory CD8⁺ T-cell subsets from TP patients. (A) Distribution of memory CD8⁺ T-cell subsets in representative individuals from each group. The percentage of each memory subset within the total memory CD8⁺ T-cell pool is shown in each quadrant. (B) Pooled data show the frequencies of memory PD-1⁺CD8⁺ T-cell subsets in each group. P values are shown. Error bars indicate standard deviation. (C) Distribution of HIV-specific memory CD8⁺ T-cell subsets from LTNPs (n = 5) and TP patients (n = 7). The percentage of memory subsets of HIV-specific CD8⁺ T cells is shown in the upper right quadrant. (D) Distribution of HIV-specific memory CD8⁺ T-cell subsets that express PD-1 in representative individuals from the LTNP (n = 5) and TP group (n = 7). The percentage of PD-1⁺ cells within the pentamer⁺CD8⁺ memory T-cell subset is shown in the upper right quadrant.