Investigation on the molecular mechanisms of antigen presentation and recognition.

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Presentation of antigenic peptides by antigen presenting cells and consequent stimulation of CD4^+ T cells is crucial in the regulation of immune response. In this research project, we studied on the recognition of antigenic peptide by T cell receptor (TCR) and signal transduction pathway in CD4^+ T cells stimulated with altered peptide ligands (APL). In addition, we established a method for ES cell-based genetic engineering of dendritic cells (DC). The following results were obtained.1)We developed an experimental system to dentify diverse T-cell epitopes from T-cell epitope-expression library, using an epitope presenting vector based on CLIP-substituted invariant chain. Using the libraries in which randomized amino acid residues were narrowed down into three successive ones, we characterized the degeneracy in the epitopes of the GAD65-reactive Th-cell clones derived from IDDM patients, and identified several microbe-derived antigens to which the Th-cell clones cross-reacted.2)We foun … More d that a human CD4^+ T cell clone showed full proliferation in response to over-expressed partially agonistic peptide/HLA-DR4 complex. However, a protein tyrosine kinase ZAP-70, which is believed to be essential for TCR-mediated T cell activation, was not tyrosine-phosphorylated and activated. Instead, we found that other kinases B-Raf and PKCm were activated in the T cells, suggesting the presence of new signaling pathways leading to full T cell proliferation that is independent of ZAP-70 activation.3)We established a method to generate mouse ES cell-derived DC (ES-DC). Genetic modification of ES-DC can be done by transfection of ES cells and subsequent differentiation to DC. OVA antigen-specific cytotoxic T lymphocytes were efficiently primed in vivo by injecting mice with ES-DCs introduced with an OVA-expression vector. Double-transfectant ES-DC expressing a chemokine along with OVA provided potent protection from OVA-expressing tumor cells. In addition, we demonstrated prevention of experimental autoimmune encephalomyelitis by treatment with genetically modified ES-DC. Less