Parameters that influence CD4+ T cell diabetogenic potential

St. Jude Children'S Research Hospital, Memphis TN

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Abstract

DESCRIPTION (provided by applicant): Type 1 diabetes (T1D) is a complex disease that is mediated by T cell entry into pancreatic islets and the subsequent destruction of insulin-producing b cells. The mechanisms that control these events are poorly understood, a greater understanding of which could lead to the development of novel therapeutic strategies. A significant limitation in addressing these complex issues has been the availability of appropriate genetic tools. We have developed a new approach for the rapid generation of TCR Tg mice, which we refer to as retrogenic (Rg) mice. We will use a panel of TCRs specific for two primary autoantigens of considerable interest, insulin (Ins) and chromogranin A (ChgA), that possess a very broad range of insulitogenic and diabetogenic potentials, novel mouse models and innovative, cutting-edge techniques to determine the biophysical and temporal parameters that regulate CD4+ T cell insulitogenicity and diabetogenicity. This is the primary focus and long-term objective of this project. The simplest hypothesis is that 'highly diabetogenic CD4+ T cells are optimally generated and activated in the pancreatic lymph node (PLN), and have a unique biophysical, kinetic and migratory signature which dictates their pathogenicity'. This hypothesis will be tested and parameters defined in two highly integrated Aims: Aim 1: Biophysical parameters that influence CD4+ T cell diabetogenicity. (A) Do the biophysical properties of the TCR dictate the insulitogenic and diabetogenic potential of CD4+ T cells? In collaboration with Brian Evavold (Emory Univ.), we will determine the 2D affinity, association (on) rate, and dissociation (off) rate of the Ins- and ChgA-specific TCRs for their cognate peptide-MHC complex (pMHC). Together with the sensitivity of TCR Rg T cells in functional assays, we will determine if these biophysical parameters dictate their diabetogenic potential. (B) Does antigen availability affect CD4+ T cell islet entry and diabetogenicity? We will generate NOD mice in which the b cell-restricted expression of a model autoantigen, GAD65, can be externally controlled. We will assess how antigen expression levels and TCR functional avidity cooperate to influence T cell pathogenicity. Aim 2: Temporal parameters that influence CD4+ T cell diabetogenicity. (A) Does the kinetics of CD4+ T cell islet entry determine diabetogenic potential? We will compare the kinetics of T cell islet infiltration, assessed by flow cytometric and histological analysis, and the rate of b cell destruction, determined using non- invasive, bioluminescent imaging of live mice. (B) Do the intra-islet migratory characteristics of CD4+ T cells dictate diabetogenic potential? In collaboration with Alexander Chervonsky (Univ. Chicago), multiphoton intravital microscopy will be used to track CD4+ T cell migration within the islets to determine whether there is a correlation between their migratory characteristics and their insulitogenic and diabetogenic potential.