PDCD1 and cancer: While cancer cells evade the immune system by expressing “normal cell” checkpoints such as PD-L1 which bind to T-cell PD-1 and inhibit T-cell killing of tumor cells, commensal Bifidobacterium facilitates PD-L1 and CTLA-4 blockade which unmask the tumor cell and promotes T-cell killing of tumor cell and can increase effectiveness of cancer therapies.