Blockade of PD-1 with monoclonal antibody was shown to increase tumor-infiltrating cytotoxic T lymphocytes (CTLs) resulting in anti-tumor activity against SCC growth (Belai et al., 2014), however, the depletion of CD8+ abrogated the efficacy of the anti-PD1 mAb treatment (Dodagatta-Marri et al., 2019), suggesting an association between the efficacy of PD-1 blockade therapies and the frequency of PD-1+ CD8+ T cells in the TME (Gros et al., 2014; Kansy et al., 2017; Kumagai et al., 2020). The gene discussed is PDCD1; the disease is neoplasm.