PDCD1 and cancer: Immune checkpoint blockades (ICBs) such as PD-1/PD-L1 or CTLA-4 blocking antibodies have revolutionized cancer therapeutics by removing such inhibitory brakes,4,5 the effectiveness of which depends on the recognition of tumor-specific antigens to generate and activate tumor-specific CD8+ T cells (also known as cytotoxic T cells, CTLs).