PDCD1 and lung cancer: However, it is already evident from the studies of anti-PD1 response in lung cancer and melanoma that the number of tumor-infiltrating CD8+ T cells is not the only requirement of response to anti-PD1 treatment; the characteristics of exhaustion state of tumor-infiltrating CD8+ T cells is also required (Thommen et al., 2015; Li et al., 2019; Sade-Feldman et al., 2019).