The successful application of cancer immunotherapy will require a deeper understanding of CD8+ cytotoxic T lymphocyte (CTL) regulation in order to effectively control tumor growth while limiting autoimmune damage. Recent insights into the pathways of CTL activation and tolerance suggests that endogenous or transfected CTL populations can be controlled in vivo at the level of antigen-presenting cell (APC) function through manipulation of CD40-CD40L interactions. Towards this, there is clearly a need for physiologically relevant animal models of spontaneous cancer that will allow the study of these tumor-immune system interactions and permit a useful evaluation of APC-focused immunotherapeutic strategies. The goal of this research is to develop such a powerful new model system in which the capacity of APC to regulate tumor-specific CD8+ cytotoxic and CD4+ helper T cell responses can be assessed during the development of a primary endogenous tumor expressing a model self-antigen. Part of this tumor model involves transgenic mice expressing the potent SV40 T antigen oncogene under the control of the rat insulin promoter (RIP-Tag2). RIP-Tag2 mice develop pancreatic beta-cell tumors leading to autonomous insulin secretion and lethal hypoglycemia within 3-4 months. RIP-Tag2 mice will be crossed with RIP-mOVA mice that express ovalbumin (OVA) as a self-antigen in beta cells of the pancreas and proximal tubular cells of the kidney. In RIP-mOVA mice, OVA is efficiently cross-presented on host APC, leading to the deletion of OVA-specific CTL which can be blocked by CD4+ OVA-specific helper T cells. Transgenic OVA-specific CTL (OT-I cells) will be adoptively transferred to the RIP(Tag2 x mOVA) mice at various times during the development of OVA-expressing beta cell tumors. The ability of the CTL to control tumor growth versus causing autoimmune damage will be examined by i) monitoring of blood glucose levels (reflecting tumor burden and autoimmune destruction of normal beta cells), ii) histological examination of pancreas and kidneys, iii) the persistence, and activation/tolerization of transferred CTL (measured in vitro), and iv) effect on survival. APC-focused regulation of the OT-I cells will be attempted using OVA-specific CD4+ T cells or stimulatory anti-CD40 antibodies to induce and maintain OT-I cells and inhibitory anti-CD40L antibodies to tune down the responses of OT-I cells. It is hoped that this project will result in a superior animal model in which to explore factors that influence the balance between tumor control and autoimmunity in CTL-based immunotherapy.
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