On the other hand, NK cell inhibitory receptors (37–39), potentially druggable targets in tumor immunotherapy, are referred to as “checkpoint” receptors, which involve killer inhibitory receptors (KIRs), CD94/NKG2A, T cell immunoreceptor with Ig, and immunoreceptor tyrosine-based inhibition motif (ITIM) domains (TIGIT), CD96, T cell immunoglobulin- and mucin-domain-containing molecule 3 (TIM-3), PD-1, CTLA-4, lymphocyte activation gene 3 (LAG-3), and V domain immunoglobulin suppressor of T cell activation (VISTA). The gene discussed is PDCD1; the disease is neoplasm.