Programmed death 1 (PD-1), an immunosuppressive receptor predominantly expressed on T-cells (49), binds to its principal ligand, programmed death ligand 1 (PD-L1), which is frequently overexpressed in malignant tumors—particularly in advanced gastric cancer associated with Epstein-Barr virus (EBV) (50, 51). Here, PDCD1 is linked to gastric cancer.