Similar to the in vitro activation data using PD-1–/– T cells, concurrent anti–PD-1 treatment also resulted in an increased apoptosis in the PD-1+ T cells by AICD, and this was not observed in the PD-1– OT-1 T cells following infection, also demonstrating the specificity of the blockade on the PD-1+ cells with both activation and AICD increases (Figure 4G). This evidence concerns the gene PDCD1 and infection.