It is well defined that human NK cells can kill tumor targets by the use of major activating surface receptors (i.e., NKp46, NKp30, NKp44, NKG2D, DNAM1), which recognize antigens overexpressed by tumor cells, and avoid attacking normal cells by means of inhibitory receptors (KIRs, NKG2A, and LILRB1) recognizing HLA class I molecules (whose expression is indeed often downregulated in tumor cells) [1,2]. The gene discussed is KLRK1; the disease is neoplasm.