PDCD1 and neoplasm: Immunotherapeutic agents such as oncolytic viruses (5, 6), bispecific T cell engagers (TCEs) (7, 8), chimeric antigen receptor T-cell therapy (CAR T) (9), and immune checkpoint inhibitors targeting programmed death 1 (PD-1) or cytotoxic T-lymphocyte associated protein 4 (CTLA4) (10) function primarily by inducing/triggering T cell-mediated antitumour responses and overcoming barriers present in the hostile tumour microenvironment (TME).