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NK cells play a significant role in tumor cell recognition and cytotoxicity (Trinchieri et al, Adv Immunol, 1990). Few NK-cell activating ligands have been identified with the exception of those found to interact with the C-type lectin-like receptor NKG2D. Among these ligands are surface glycoproteins, MICA and MICB, which are expressed on many epithelial cell tumors (Bauer et al, Science, 1999). Recently, the UL16-binding proteins (ULBPs) have been identified as NKG2D ligands and have been found on numerous tumor cell lines (Pende et al, Cancer Res, 2002). Enhanced cytotoxicity of allogeneic NK cells against solid tumor cells has been demonstrated in the MHC-C mismatched setting (Igarashi et al, Blood, 2004). In this study, we compared the expression of NKG2D ligands MICA, MICB and ULBPs-1, 2 and 3 in neuroblastoma (NB: NBL, NGP, SH-SY5Y), Burkitt’s lymphoma (Daudi), DLBCL (Pfeiffer), CML (K562), and ALL (REH, RS4:11, SUPB-15). Genomic expression was determined by mRNA isolation, reverse transcription generated cDNA and polymerase chain reaction (PCR) amplified all ligand sequences. Primers included the following: MICA: 5’-GTGCCCCAGTCCTCCAGAGCTCAG3’ and 5’GTGGCATCCCTGTGGTCACTCGTC3’; MICB: 5’GGCGTCAGGATGGGGTATCTTTGA3’ and 5’GGCAGGAGCAGTCGTGAGTTTGCC3’; ULBP1: 5’CTGCAGGCCAG-GATGTCTTGTGAG3’ and 5’TGAGGGTGGTGGCCATGGCCTTGG3’; ULBP2: 5’CTGCAGGCAAGGATGTCTTGTGAG3’ and 5’TGAGGGTGGTGGCTGTGGCCCTGA3’; ULBP3: 5’CTGCAGGTCAGGATGTCTTGTGAG3’ and 5’TGAGGGTGGTGGCTATGGCTTTGG3’; GADPH was used as control. Cell surface expression of the NKG2D ligands was determined by flow cytometry. Increased expression of MIC+/ULBP+ by PCR was seen in all ALL, CML, and B-NHL cell lines, however, MIC-/ULBP+ was expressed in neuroblastoma cell lines (Table). Surface expression of MIC and ULBP ligand receptors was significantly increased in Daudi and K562 vs Pfeiffer and all ALL and NB cell lines (p<0.001, respectively) (Table). These data suggest that specific pediatric malignancies express NKG2D ligands that might potentially enhance NK cell cytolytic activity and form the basis of adoptive immunotherapy.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]