It has been described in solid tumors that cytotoxic TILs upregulate PD-1 expression and secrete IFN-γ when they encounter tumor antigens, which triggers an adaptive response to IFN-γ with a consequent upregulation of PD-L1 expression in tumor cells and infiltrating immune cells in the vicinity (54, 55). This evidence concerns the gene PDCD1 and neoplasm.