ULBP2 and neoplasm: As shown by Boissel et al. and several other groups, soluble NKG2D ligands (NKG2D-Ls) including MICA, MICB, ULBP1, and ULBP2, shedded by the tumor cells per se, and tumor exosomes expressing NKG2D-Ls trigger the reduction of NK cell surface NKG2D (131–135).