TCF7 and infection: Based on the above results demonstrating the positive role of TCF1 in regulating CD8 T cell effector function, we further investigated the role of TCF1 in regulating CD8 T cell function during the effective stage via an inducible knock-out of Tcf7. We crossed mice expressing a tamoxifen-sensitive estrogen receptor variant fused to transgenic Cre recombinase (ERT2Cre) with Tcf7fl/fl mice to generate Tcf7fl/fl-ERT2Cre mice for an inducible deletion of Tcf7 at different phases of infection.