NKG2D operates as an activating receptor on natural killer (NK) cells and costimulates the effector function of ab CD81 T cells. Ligands of NKG2D, the MHC class I chain-related (MIC) and UL16 binding protein (ULBP) molecules, are expressed on a variety of human tumors, including melanoma. Recent studies in mice demonstrated that NKG2D mediates tumor immune surveillance, suggesting that antitumor immunity in humans could be enhanced by therapeutic manipulation of NKG2D ligand (NKG2DL) expression. However, signals and mechanisms regulating NKG2DL expression still need to be elucidated. Here, we asked whether the proinflammatory cytokine Interferon-c (IFN-c) affects NKG2DL expression in melanoma. Cell lines, established from MHC class I-negative and -positive melanoma metastases, predominantly expressed MICA and ULBP2 molecules on their surface. Upon IFN-c treatment, expression of MICA, in some cases, also of ULBP2 decreased. Besides melanoma, this observation was made also for glioma cells. Down-regulation of NKG2DL surface expression was dependent on the cytokine dose and the duration of treatment, but was neither due to an intracellular retention of the molecules nor to an increased shedding of ligands from the tumor cell surface. Instead, quantitative RT-PCR revealed a decrease of MICA-specific mRNA levels upon IFN-c treatment and siRNA experiments pointed to an involvement of STAT-1 in this process. Importantly, IFN-c-treated MHC class I-negative melanoma cells were less susceptible to NKG2D-mediated NK cell cytotoxicity. Our study suggests that IFN-c, by down-regulating ligand expression, might facilitate escape of MHC class I-negative melanoma cells from NKG2D-mediated killing by NK cells. ' 2008 Wiley-Liss, Inc.Key words: melanoma; MHC class I loss; natural killer cell; NKG2D; interferon-c Malignant melanoma is well characterized for its recognition by cytotoxic ab CD8 1 T lymphocytes (CTLs) that respond to tumorassociated peptide antigens presented in the complex with classical MHC class I surface molecules.1 Indeed, CTLs can eliminate metastatic tumors in melanoma patients, as demonstrated in different clinical trials of adoptive T cell transfer.2 The efficiency of tumor cell killing is determined by the strength of the antigen signal and co-stimulatory signals sensed by different activating receptors. Very recently, it was demonstrated that triggering of the co-stimulatory receptor NKG2D on CTLs strongly enhanced the T cells capacity to kill melanoma cells. 3Besides the importance of antigen-specific CTLs in immune surveillance of melanoma, one can assume that early detection and elimination of premalignant and malignant cutaneous melanocytes might be a major task of skin-resident innate NK cells and innate-like Vd1 gd T lymphocytes. 4 Both effectors are capable of preventing and inhibiting the growth of autologous human melanoma grafted into the skin of severe combined immunodeficient (SCID) mice.5 Interestingly, the receptor NKG2D is constitutively expressed on Vd1 gd T cells present in normal human sk...

Purpose:Total loss of surface presentation of human leukocyte antigen (HLA) class I molecules, protecting tumor cells from the recognition by cytotoxic host CD8 + Tcells, is known to be caused by mutations in the h2-microglobulin (b2m) gene. We asked whether abnormalities of chromosome 15, harboring the b2m gene on 15q21, in addition to b2m gene mutations, are causative for the HLA class I^negative phenotype of melanoma cells. Experimental Design: To answer this, we established primary cell lines from the h2m-negative metastatic melanoma tissues of four different patients and analyzed them for b2m gene mutations and chromosome 15 aberrations, the latter by loss of heterozygosity analysis, fluorescence in situ hybridization (FISH), and multicolor FISH. Results: Mutations at the b2m gene level were detected in all cell lines. The loss of heterozygosity analysis of microsatellite markers located on chromosome 15 in three of the four cell lines pointed to an extensive loss of chromosome 15 material. Subsequent molecular cytogenetic analysis revealed the coexistence of apparently normal and rearranged versions of chromosome 15 in three cell lines whereas the fourth cell line solely showed rearranged versions.Two of the four cell lines exhibited a special type of intrachromosomal rearrangement characterized by FISH signals specific for the subtelomeric region of 15q at both ends of the chromosome and one centromeric signal in between. Conclusions: Our data indicate that the complete loss of HLA class I expression in melanoma cells is due to the coincidence of the following mutational events: (a) chromosome 15 instability associated with an extensive loss of genetic material and (b) b2m gene mutations.Melanoma cells can be effectively eradicated in vivo by the cytotoxic activity of HLA class I-restricted tumor antigenspecific CD8 + T cells as recently shown in clinical trials of adoptive T-cell transfer (1, 2). However, these studies also showed that adoptively transferred T cells infiltrating the metastasis not only act as cytotoxic immune effectors but also as immune editors (3, 4) selecting for tumor cell variants that escape immune surveillance by down-regulation of antigen expression (1). Besides antigen down-regulation, other properties of melanoma cells that interfere with T-cell effector function have been described, such as release of immunosuppressive cytokines (5, 6), release of Fas ligand-bearing microvesicles (7), and alterations in the surface presentation of HLA class I molecules (8-10).HLA class I molecules are heterodimeric noncovalently associated complexes consisting of the constant h2-microglobulin (h2m) light chain and the variable HLA heavy a chain. Irreversible alterations in the HLA class I phenotype of melanoma cells, such as loss of a single HLA allele, an HLA locus, or an HLA haplotype, are generally caused by