KLRK1 and hematologic disorder: Natural killer group 2 member D (NKG2D), which is expressed by NK cells, CD8+ T cells, γδT cells, and NKT cells, is an activation receptor and can interact with eight NKG2D ligands (NKG2DLs), including MICA/B and UL16-binding proteins (ULBP1-6), which have been reported to be expressed on a variety of solid tumors and hematologic malignancies [33, 34].