PDCD1 and neoplasm: Four “CD8+ T cell exhaustion”-associated genes by suppression T cell activity and promotion tumor immune escape were selected, including PDCD1 gene which encodes PD-1 protein, CD274 gene which encodes PD-L1 protein, CTLA4 gene (an important exhaustion feature of lymphocyte (41)), and CD86 gene whose encoding protein as the ligand of CTLA4 (42).