T-cell clonality in immune responses

Hypoxia/reoxygenation induction of monocyte chemoattractant protein-1 in melanoma cells: involvement of nuclear factor-kappaB, stimulatory protein-1 transcription factors and mitogen-activated protein kinase pathways

Monocyte chemoattractant protein-1 (MCP-1) expression is found in malignant melanoma and melanoma metastases. Since areas of hypoxia/reoxygenation (H/R) are a common feature of malignant tumours and metastases, we addressed the question whether melanoma cells produce MCP-1 upon exposure to H/R. In the present study, we show that melanoma cells up-regulate MCP-1 mRNA and protein under H/R. By means of reporter gene analysis, we further demonstrate that H/R induces transcriptional activation of the MCP-1 promoter carrying a stimulatory protein-1 (SP1) and two nuclear factor-kappaB (NF-kappaB) binding motifs. Accordingly, H/R-stimulated melanoma cells showed enhanced binding activity of both transcription factors NF-kappaB and SP1 in electrophoretic mobility-shift assay. A common upstream activator of NF-kappaB, inhibitory kappaBalpha kinase, was not significantly activated under H/R conditions. Further analysis of upstream signalling events revealed that members of the mitogen-activated protein kinases family, namely extracellular signal-regulated protein kinase, c-Jun N-terminal kinase/ stress-activated protein kinase and p38 stress kinase, may be involved in MCP-1 transcriptional regulation under H/R. In summary, we conclude that H/R induces MCP-1 production in melanoma cells via the co-operative action of both transcription factors NF-kappaB and SP1, and involves mitogen-activated protein kinase signalling pathways. Functionally, H/R-induced MCP-1 production may contribute to tumour progression by committing selective pressure on tumour cells via chemoattraction and activation of tumour-infiltrating monocytes/macrophages.

Expression of stress-induced MHC class I related chain molecules on human melanoma

Cellular immune responses to melanoma are tightly regulated and include specific T cell responses to self antigens such as Mart-1 and gp100. Thus, additional signals apart from those mediated by the T cell receptor are needed to ensure T cell activation. Recently, the stress inducible major histocompatibility complex molecules, MHC class I related chain, were identified as an activator of both natural killer and T cells via interaction with their receptor NKG2D. Herein, we report the expression of MIC in 31 of 40 primary cutaneous melanomas and in 13 of 20 metastatic lesions. Moreover, lymphocytes infiltrating the tumor were found to express NKG2D. Detailed analysis identified both CD3+ T cells as well as CD56+ natural killer cells contributing to this NKG2D+ tumor infiltrating lymphocyte population present.

Differential expression of CD28 and CD94/NKG2 on T cells with identical TCR beta variable regions in primary melanoma and sentinel lymph node

NK cell tolerance is maintained by the interaction of killer inhibitory receptors with self MHC class I gene products. A subset of T cells also express killer inhibitory receptors, but the functional significance of this is unclear. Here we demonstrate that the expression of the C-lectin-like killer inhibitory receptor CD94 / NKG2 on T cells depends on the state of differentiation during the immune response to solid tumors. To this end we identified clonally expanded T cells which were present both in the sentinel lymph node of primary melanoma, as well as in the tumor itself. In situ characterization of such T cell clonotypes revealed that within the early stages of T cell activation, i. e. priming in the lymph node, T cells did not express CD94 / NKG2 whereas the same T cell clones expressed high levels of CD94 / NKG2 having reached the effector state at the tumor site. Moreover, while the phenotype of these T cell clones was CD28high in the lymph node only CD28low or CD28- T cells were found within the tumor. Double staining for CD94 and CD28 conformed that CD94 / NKG2-expressing cells were preferentially CD28-. Thus, T cells may down-regulate CD28 and up-regulate NK receptors as consequence of prolonged activation for cytolytic effector function. It is likely that NK receptors are involved in peripheral regulatory mechanisms avoiding overwhelming immune responses and immunopathology, particularly in situations of long-lasting immune activation.