The researches have shown that tumor cells are more vulnerable to NK cell destruction when inhibitory receptor ligands, such MHC-I, are downregulated in combination with the abundant expression of ligands recognized by activating receptors, like the killer cell lectin-like receptor K1 (KLRK1) and the natural cytotoxicity receptors (NCRs) [56–58]. The gene discussed is KLRK1; the disease is neoplasm.