This project will continue investigations of 1) the cellular and molecular changes necessary to convert an islet beta cell into a metastatic carcinoma, and 2) the mechanisms and interrelationship of self tolerance, autoimmunity, and the failure of tumor immunity. These topics are interconnected by the system under study: transgenic mice carrying insulin promoted SV40 T antigen genes (RIP-Tag) that target Tag oncoprotein expression to the pancreatic beta cells. The Tag oncoprotein induces aberrant cell proliferation and the eventual development of islet cell carcinomas in a pathway of clearly separated stages. Yet two distinctive immunological phenotypes are evident: alternative self-tolerance toward Tag, or non-tolerance and consequent autoimmunity. The tumorigenesis section will: i) identify and study a beta cell mitogen implicated in the first step to hyperproliferation; ii) assess the importance of the observed up-regulation of the growth factor IGF-II during this multistep pathway; iii) evaluate the down-regulation of the cell adhesion molecule E-cadherin in large tumors; iv) compare highly metastatic intestinal carcinoid tumors with the rarely metastatic beta cell tumors that arise simultaneously in one transgenic line to identify candidates for the metastatic phenotype; and v) seek to endow the beta cell tumors with a highly metastatic capability so as to define the necessary conditions for this progression. The immunology section will: i) identify the lymphocyte cell types rendered non-responsive to Tag; ii) use transgenic mice carrying gene knockouts which effect a lack of CD8 T cells, or CD4 T cells, or B cells to determine which of these lymphocyte cell types are necessary for establishing self tolerance to the beta cells; iii) produce transgenic mice carrying a rearranged T cell antigen receptor specific for Tag to visualize the response of developing anti-Tag T cells to an antigen expressed in a rare cell type; iv) generate transgenic mice expressing a transformation defective Tag in their beta cells to address our postulate that two conditions are necessary for autoimmunity, non-tolerance and target cell abnormalities; and v) investigate the failure of tumor immunity, and define conditions that create tumor visibility and effect their rejection. One long term goal is to understand all of the stages in tumor development as a precedent to designing specific interventions targeted at different points in the reproducible tumorigenesis pathway evident in these transgenic mice. Another goal is to clarify the nature of alternative immune tolerance or autoimmunity toward the pancreatic beta cells, which are the target of autoimmunity in human type I diabetes. Finally, the immune tolerance of the tumors is surprising, and suggests that important mechanisms of tumor invisibility are involved; their delineation may prove of relevance to the larger goals of eliciting effective cancer immunotherapy.
