PDCD1 and neoplasm: The frequency of PD-1-expressing CD8+ TILs increased in AT-3, B16, and 4T1 tumors (Fig. 3c) and PD-1 expression was more prevalent in Tet+ CD8+ T cells than Tet− CD8+ T cells (Fig. 3d), suggesting a higher susceptibility to PD-L1-mediated inhibition of the ISIM-induced tumor-specific CD8+ T cell infiltrates.