287-OR: TCR/HLA Humanized Mice Reveal Reduced Tolerance and Increased Immunogenicity of Posttranslationally Modified GAD65 Epitope

T cells specific for post-translationally modified (PTM) islet antigens have been implicated as critical players in the development of type 1 diabetes. T cells reactive to the deamidated version of glutamic acid decarboxylase 65 (GAD65) 115-127 epitope accumulate in peripheral blood of patients as they progress to disease. However, knowledge regarding the development, activation, differentiation and islet recruitment of PTM reactive T cells is limited. Using retroviral gene delivery, we have developed a humanized TCR/HLA mouse model to assess the in vivo function of human TCRs reactive to either the wild type (GADWT) or the deamidated (GAD120E) GAD65_115-127 epitope. Both TCRs supported efficient thymic selection; however, fewer regulatory T cells developed in mice expressing the PTM reactive TCR, which was partially rescued by the thymic delivery of GAD120E peptide. Immunization of immune sufficient polyclonal DR4.NOD mice with GAD120E/CFA elicited a stronger response compared to GADWT/CFA, confirming that tolerance to the wild type autoantigen is more robust. Interestingly, while islet infiltration in GAD120E single TCR mice was dependent on priming with the cognate PTM peptide, GADWT-TCR T cells could be induced to infiltrate islets after priming with either GADWT or GAD120E peptide, despite the vastly different functional affinity (EC50, GADWT: 0.047μM vs. GAD120E: ≥1.4μM). These findings suggest that the development and expansion of GAD65 PTM reactive CD4+ T cells are less restricted in peripheral lymphoid organs, but their recruitment to the tissue site is dependent on the availability of PTM antigen.