CD244 and neoplasm: In addition to some inhibitory checkpoints mentioned above, NRP‐1 (Neuiropilin‐1), 2B4 (Natural killer cell receptor 2B4), BTLA (B‐ and T‐lymphocyte attenuator), PDPN (Podoplanin), PROCR (Protein creceptor), CD160, etc also showed the same inhibitory immune checkpoint action, distributed on the surface of different types of immune cell membranes, and their corresponding ligands were distributed in various tumor tissues.