KLRK1 and neoplasm: Soluble MICA and soluble isoforms of ULBP2 and ULBP4 have been shown to bind to NKG2D leading to internalization of the receptor, which favors the development of NK cell-acquired dysfunction; soluble MICB has been shown to bind competitively to NKG2D and to inhibit the binding of NKG2D to transmembranal ligands expressed by tumor cells, thus blocking NK cell activation [19-21].