CD8A and infection: In the group with PD-1 deficiency, cell numbers of virus-specific CD8+ T cells were only moderately enhanced in comparison to WT mice, whereas the population of virus-specific CD8+ T cells was largely expanded in the group of mice with PD-L1 deficiency on day 10, 12, and 15 after infection in the spleen and BM (Figures 1C,D).