KLRK1 and neoplasm: While it was demonstrated that TGF-β impairs effector functions of NK cells against target cells, the underlying mechanisms remained elusive until it was reported by Moretta and colleagues that TGF-β downregulates the surface expression of the activating NK receptors NKG2D and NKp30, thereby impairing NK cytolysis of tumor cell lines in vitro (103) (Figure 1).