Natural killer (NK) cells are key innate immune cells with anti-tumor and anti-viral activity harnessed with multiple activating receptors, such as NKG2D, CD16 (FcγRIII), 2B4, DNAM-1, and natural cytotoxicity receptors (NCRs) (e.g., NKp30, NKp44, and NKp46) (1–4). The gene discussed is KLRK1; the disease is neoplasm.