Transgenic expression of proinsulin to inactivate insulin-specific CD8+ T-cell responses in autoimmune diabetes

Abstract

Type 1 diabetes (T1D) results from autoimmune destruction of pancreatic β cells. The current treatment for the fatal insulin-deficiency in T1D is injection of exogenous insulin. Despite the dramatic increase in survival from the use of exogenous insulin, complications develop from imperfect glycemic control and exogenous insulin does not rectify the underlying cause of disease, the diabetogenic autoimmune response. Hence, there is a need for an effective therapy that impedes the progress of the pathogenic autoimmune response. β cell-reactive CD8 + In the NOD mouse model of T1D, insulin is the primary β-cell antigen that elicits disease. As such, I have investigated T-cell tolerance to insulin in an adoptive transfer setting in which TCR transgenic (G9) CD8 + T cells specific for insulin B15-23 (InsB15-23) were transferred to transgenic mice over-expressing proinsulin in APC. Subsequently, I examined the effect of introducing transgenic proinsulin expression on diabetes development in wild type NOD mice.When transferred to mice transgenically expressing proinsulin, naïve G9 T cells proliferated extensively prior to undergoing rapid deletion. In proinsulin transgenic recipients, the remaining population of G9 T cells displayed reduced T-cell receptor (TCR) expression and bound less InsB15-23-loaded, H2-K d -tetramer compared to G9 T cells that had been transferred to non-transgenic NOD recipients. Interestingly, TCR down-regulation represented that which occurred for OVA-specific CD8 + T cells transferred to mice expressing OVA in APC in a non-autoimmune prone strain.Importantly, naïve G9 T cells did not expand or produce the important effector cytokine, interferon (IFN)-γ, in response to InsB15-23 immunisation after transfer to proinsulin transgenic mice. These data confirm naïve G9 T cells undergo rapid deletion and inactivation after transfer to mice transgenically-expressing proinsulin, despite genetic tolerance defects in NOD mice. Memory CD8 + T cells (Tmem) perpetuate β-cell autoimmunity and pose a distinct barrier to immunotherapy. It was pertinent to determine whether inactivation of insulin-specific CD8 + Tmem also occurs after transfer to mice expressing proinsulin in APC. To test inactivation of insulin-specific CD8 + Tmem, G9 Tmem were generated using an in vitro culture method. Cultured G9 Tmem were validated by assessing phenotypic markers and cytokine production. Similarly to naïve G9 T cells, G9 Tmem proliferated extensively and most G9 Tmem were rapidly deleted after transfer to mice overexpressing proinsulin in APC. The remaining, non-deleted population of G9 Tmem was infrequent ii and exhibited reduced TCR expression. Furthermore, G9 Tmem did not expand or produce IFN-γ in response to InsB15-23 immunisation, consistent with functional inactivation. These results demonstrate transgenic proinsulin expression in APC overcomes genetic defects in NOD mice to induce tolerance in insulin-specific CD8 + Tmem.From the data described above, transgenic proinsulin expression is tolerogenic for in...