CD4 and neoplasm: To investigate whether TCF1-depleted CD4+ T cells directly induced PD-L1 expression in tumor cells, we flow-sorted CD4+ T cells from tumors in Cd4;Tcf7fl/fl and Cd4;Tcf7+/+ mice and co-cultured them with tumor cells using a transwell approach, allowing exchange of secreted factors but no cell–cell contact (Fig. 5 E).