PDCD1 and cancer: In this review, we discuss the mechanism of tumor cell immune escape and focus on current immunotherapy (such as cytokine immunotherapy, therapeutic monoclonal antibody immunotherapy, PD-1/PD-L1 therapy, CAR-T therapy, tumor vaccine, oncolytic virus, and other new types of immunity) and its challenges as well as the latest nanotechnology (such as bionic nanoparticles, self-assembled nanoparticles, deformable nanoparticles, photothermal effect nanoparticles, stimuli-responsive nanoparticles, and other types) applications in cancer immunotherapy.