Type 1 diabetes mellitus (T1DM) is an autoimmune disease resulting from the T cell mediated destruction of insulin-producing beta cells located in the pancreas. Current treatment, which includes insulin replacement by injection, frequent blood glucose monitoring, and dietary/exercise discipline, can prevent death from hormonal insufficiency, but is not curative and does not completely prevent the long-term complications including nerve damage, and vascular damage to both large and small blood vessels. In previous few years, we developed a transgenic mouse to express the T cell costimulatory receptor CD80 on its pancreatic insulin producing beta cells (under the control of the rat insulin promoter abbreviated RIP) and demonstrated the mouse's extraordinary sensitivity to autoantigen induced immune mediated beta cell destruction, and thus to diabetes. We refer to the diabetes induced in these RIP-CD80 mice as experimental autoimmune diabetes (EAD). Using this EAD model, we've found that relatively weak anti-beta cell autoimmune responses can cause chronic progressive and eventually complete beta cell destruction resulting in symptomatic and irreversible disease. The slow but inexorable process is highly reminiscent of the beta cell destruction leading to clinical T1DM in man, typically months to years of anti-beta cell immune activity precedes sufficient beta cell killing for the blood sugars to rise. Most other autoimmune diabetes studies involve the non-obese diabetic (NOD) mouse, which develops spontaneous diabetes, or virus-induced diabetes models. Only the RIP-CD80 transgenic mouse diabetes model is characterized by an experimental genetic susceptibility trait (in the EAD model the trait is the CD80-transgene) rendering the mouse susceptible to autoantigen-specific T lymphocyte sensitization as is thought to be present in T1DM patients. We have reported that immunizing with either experimentally-introduced autoantigen (e.g. pancreatic beta cell-expressed viral glycoprotein) or endogenous beta cell autoantigen (e.g. insulin) could lead to diabetes in RIP-CD80 mice. Further, most studies now support that the normal individual's T cell repertoire contains potentially autoreactive but quiescent T cells. We concluded that pancreatic beta cell likely contains many autoantigens and that effective control mechanisms must exist to prevent autoimmune responses in healthy individuals. Current immunological dogma suggests that naove CD8 cytotoxic T cell (CTL) precursors respond to strong antigen stimulation in a characteristic fashion by: (i) proliferating and releasing inflammatory cytokines, (ii) differentiating into CTLs and, (iii) down modulating certain surface interaction molecules to allow the CTLs to leave secondary lymphoid organs while increasing other receptors, such as integrins, to promote entry into peripheral tissues, and (iv) changing chemokine signals necessary to facilitate the relocation of activated CTL from lymph nodes (LN) to inflamed peripheral tissues. The EAD model has allowed us to study the response of beta cell-specific CD8 T cells to cognate antigen presented by either professional antigen-presenting cells (APC) like mature dendritic cells DC), or by non-professional (np) APCs like fibroblast-like cell lines (FCL). While DC-stimulated T cells produced the expected effector CTL phenotype described above, FCL-activated T cells were quite different. Relative to DC activated CTLs, the FCL-activated CTLs proliferated less, released equivalent proinflammatory cytokines, and surprisingly displayed increased cytolytic function. Moreover, FCL-stimulated T cells largely failed to switch their homing receptors predicting poor migration from the lymph nodes to the periphery. Most strikingly, however, FCL-stimulated but not DC-activated CTL expressed many of the features associated with memory CTLs;both multiple memory cell surface marker expressioon and predominant homing into secondary lymphoid organs upon adoptive transfer into naive mice. Importantly, while every CTL response gives rise to a small population of long-lived memory CTL, the mechanism that decides the fate of an individual CTL to become a memory cell remains largely unknown. Finally, the FCL-stimulated CTL induced diabetes by a slow, chronic process, suggesting that these central memory CTL might also be involved in driving human T1DM. Research goals pursued in FY 2009: Since our techniques for evaluating potential beta cell autoantigens have run into technical problems, we've temporarily shifted our focus with the rodent model to studying the beta cell target of the autoimmune attack, and potential means to overcome that autoimmune process. Toward that end, in collaborative studies, we've tested adeno-associated viruses for their ability to transduce islets with an ultimate goal being """"""""super islets"""""""" that can resist the autoimmune destructive process. We've also studied the effect of inflammatory mediators on beta cell function.
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