PDCD1 and neoplasm: Immune checkpoints (ICs), such as programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1, CD274), lymphocyte activating 3 (LAG3), cytotoxic T-lymphocyte associated protein 4 (CTLA4), hepatitis A virus cellular receptor 2 (HAVCR2, TIM3), and T cell immunoreceptor with Ig and ITIM domains (TIGIT), serve a vital role in tumor immunoevasion [4–6].