CD8A and infection: When deleting Tcf7 at an advanced stage of Cl13 chronic infection via intraperitoneally injecting mice with tamoxifen at 10~13 days after infection, we observed that the frequency and absolute number of the GP33-tetramer-positive CD8 T cell population were significantly decreased, and the expression levels of inhibitory receptors (PD1 and Tim3) on viral-specific CD8 T cells were significantly increased in Tcf7fl/fl-ERT2Cre mice at 25 days after infection (Figure 4C).