KLRK1 and neoplasm: The fusion molecules containing one or two NK activating receptors binding scFv or IgG (CD16-binding scFv and NKG2D binding IgG VHH or NKp46 binding Fc) and one or more tumor-specific antigens binding regions have been engineered as the trifunctional or tetrafunctional NK cell engager that targets tumor-specific antigens and activates NK cells for eliminating the tumors significantly with minimized side effects [38,277,278,279].