PDCD1 and cancer: Antigen-specific T cells generated by cancer vaccines often express suppressor molecules, and the PD-1/PD-L1 axis is involved in signaling mediated by the TCR recognition of antigens, providing a mechanism through which tumor cells can resist attacks by T cells.213,214 Therefore, blocking the PD-1/PD-L1 signaling pathway can release the immune system “brake”, reversing the immunosuppressive microenvironment.