PDCD1 and infection: However, when we assessed the two subsets of PD-1+ cells, we observed a significant decrease in the frequencies of SP-PD-1 HIV-specific CD8 T cells (P = 0.016) over the course of infection whereas the frequencies of DP CD8 T cells significantly increased (P = 0.016) from AHI to CHI (Figure 2B; right panels) confirming results obtained in the cross-sectional analysis.