Various mechanisms of NK cell anti-tumor activity inhibition have been described, including: downregulation of NK-activating receptors, that is, natural cytotoxic receptors (NCRs) and NKG2D; upregulation of inhibitory receptors, that is, killer-cell immunoglobulin-like receptors (KIRs) and NKG2A; and modifications of expression of receptor-specific ligands. The gene discussed is KLRK1; the disease is neoplasm.