Human NK cells express several activation receptors important in tumour cell recognition including NKG2D, DNAM-1 and the natural cytotoxicity receptors NKp30, NKp44 and NKp46 and several studies have identified the reduced expression of these molecules and weakened NK cell activity in human cancer [5], [6], [9], [10], [11], [12], [13]. This evidence concerns the gene KLRK1 and cancer.