Jennifer Johnson

In vitro, when the B7 molecule on the surface of antigen-presenting cells binds to the T cell surface molecules CD28 and CTLA-4, a costimulatory signal for T cell activation is generated. CTLA4Ig is a soluble form of the extracellular domain of CTLA-4 and binds B7 with high avidity. CTLA4Ig treatment in vivo suppressed T cell-dependent antibody responses to sheep erythrocytes or keyhole limpet hemocyanin. Large doses of CTLA4Ig suppressed responses to a second immunization. Thus, costimulation by B7 is important for humoral immune responses in vivo, and interference with costimulation may be useful for treatment of antibody-mediated autoimmune disease.

The MUC18 antigen is an integral membrane glycoprotein of 113 kDa whose expression on primary human melanomas correlates with poor prognosis and the development of metastatic disease. MUC18 is expressed only sporadically in benign melanocytic nevi and thin primary melanomas that have a low probability of metastasizing. However, with increasing tumor thickness, MUC18 expression becomes more frequent and it is found on 80% of advanced primary tumors and metastases. MUC18-encoding cDNA clones were obtained by screening a human melanoma phage lambda expression library with monoclonal antibodies produced against the denatured antigen. The deduced sequence of 603 amino acids consists of a signal peptide, five immunoglobulin-like domains, a transmembrane region, and a short cytoplasmic tail. The highest sequence similarity is with a group of nervous system cell adhesion molecules, which includes neural cell adhesion molecule (N-CAM). The close structural relationship with these molecules suggests that MUC18 may also be a developmentally regulated cell adhesion molecule.

Melanoma Research is a well established international forum for the dissemination of new findings relating to melanoma. The aim of the Journal is to promote the level of informational exchange between those engaged in the field. Melanoma Research aims to encourage an informed and balanced view of experimental and clinical research and extend and stimulate communication and exchange of knowledge between investigators with differing areas of expertise. This will foster the development of translational research. The reporting of new clinical results and the effect and toxicity of new therapeutic agents and immunotherapy will be given emphasis by rapid publication of Short Communications. ​Thus, Melanoma Research seeks to present a coherent and up-to-date account of all aspects of investigations pertinent to melanoma. Consequently the scope of the Journal is broad, embracing the entire range of studies from fundamental and applied research in such subject areas as genetics, molecular biology, biochemistry, cell biology, photobiology, pathology, immunology, and advances in clinical oncology influencing the prevention, diagnosis and treatment of melanoma.

The MUC18 protein, a member of the immunoglobulin superfamily and related to several adhesion molecules, shows an expression pattern in human malignant melanoma which is closely associated with tumor progression and the onset of metastasis. To determine the expression pattern of MUC18 in normal human tissues, immunohistochemical analysis was performed on frozen sections of a variety of normal human tissues using monoclonal antibodies against three different epitopes. This analysis showed that expression of MUC18 is limited to smooth muscle cells and to vascular endothelium. No reactivity could be observed with epithelial cells or with quiescent or activated hemopoetic cells. Smooth muscle cells in lung, skin, and in the gastrointestinal tract express MUC18 as does vascular smooth muscle, whereas myocardium or skeletal muscle appeared negative. Comparison of MUC18 staining with that of the panendothelial marker CD31 showed that MUC18 is expressed on the endothelia of a subset of blood capillaries and in tumor vessels but is absent on the endothelium of arterial vessels and large veins. The regulation of MUC18 expression was investigated in vascular smooth muscle cells and endothelial cells cultured in vitro. These studies revealed induction of the gene in endothelial cells upon proliferation. The observation that the MUC18 protein is not only present on melanoma cells but also on the endothelia of blood vessels penetrating primary and metastatic melanomas suggests a complex involvement of this potential cell adhesion molecule in tumor angiogenesis and metastasis.

An HLA-E-specific oligonucleotide probe was used to study the expression of HLA-E. This probe detects two HLA-E transcripts, 1.8 and 2.7 kb in size, which are present in varying ratios in all tissues and cell lines investigated. We demonstrate that alternative poly(A) site usage accounts for the differential regulation of the two HLA-E mRNA species. Sequence analysis of three cDNA clones, representing the two transcripts of HLA-E, and of an HLA-E gene encoded by cosmid cd3.14, revealed identity of gene and cDNA in the 3' untranslated region. S1 nuclease protection assays confirmed that the two HLA-E transcripts are not alternative splicing products. Introduction of cd3.14, together with human beta 2 m into the murine myeloma cell line P3X63-Ag8.653, resulted in a cell surface expression of an HLA-class I heavy chain detectable by indirect immunofluorescence whereas transfection into the human beta 2m expressing mouse L cell line, J27 was negative with regard to cell surface expression. Cell surface labeling of transfectants and immunoprecipitation with a monomorphic HLA class I-specific antibody or an antibody against human beta 2m confirmed the presence of an HLA-E H chain on the cell surface. These results indicate that the HLA-E gene codes for a class I H chain that can be expressed on the cell surface.