KLRK1 and glioblastoma: Interestingly, rare malignancies such as GBM generate significant quantities of major histocompatibility complex (MHC) class I molecules, which serve as ligands for inhibitory receptors, despite the presence of NK cell-stimulating ligands such as UL-16 binding protein (ULBP) and MICB (ligand for NKG2D), thus evading the NK-mediated regulation of tumor growth and neutralizing the immunoprotective activities of NK cells (Fig. 3B) [48].