KLRK1 and acute myeloid leukemia: Natural killer group 2D (NKG2D) ligands contain six members of the UL16-binding protein, or the retinoic acid early transcript (ULBP/RAET) family and two members of the MHC class I-related chain (MIC) family [44], all of which are either absent or minimally expressed on healthy tissues but widely expressed on numerous malignancies (including ovarian cancer [45] and AML [46]).