CD8A and cancer: Previous studies have shown that the upregulation of PD-L1 and its connection to antigen-specific CD8+ T cells can explain the confined host immunity in cancers (known as adaptive immune resistance), yet the high expression of PD-1, PD-L1 and other immunosuppressive molecules could be attributed to not only the mutations of tumor cells, but also the induction of tumor-infiltrating cells (12, 77).