KLRK1 and central nervous system cancer: TGF-β expressed by glioma cells enables immune evasion from the NKG2D system in several ways: (1) downregulation of NKG2DLs on the surface of glioma cells by inhibiting MICA, ULBP2 and ULBP4 transcription [144,145], (2) increased expression of inhibitory receptor CD94/NKG2A to prevent NK cell activation [144], and (3) downregulation of NKG2D receptors on CD8+ T cells and NK cells [146].