NKG2D, CD16, NKp46 and NKp30 are constitutively expressed on healthy circulating human NK cells, but these receptors can be downregulated when interacting with tumor ligands in cancer patients [31] and are sensitive to cleavage by enzymes in the TME and subsequent activation and by TGF-β [33], as reported in gastric cancer patients [34]. Here, KLRK1 is linked to cancer.