Antigen presenting cell-targeted proinsulin expression converts insulin-specific CD8+ T-cell priming to tolerance in autoimmune-prone NOD mice.

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing pancreatic ß cells. Therapies need to incorporate strategies to overcome the genetic defects that impair induction or maintenance of peripheral T-cell tolerance and contribute to disease development. We tested whether the enforced expression of an islet autoantigen in antigen-presenting cells (APC) counteracted peripheral T-cell tolerance defects in autoimmune-prone NOD mice. We observed that insulin-specific CD8+ T cells transferred to mice in which proinsulin was transgenically expressed in APCs underwent several rounds of division and the majority were deleted. Residual insulin-specific CD8+ T cells were rendered unresponsive and this was associated with TCR downregulation, loss of tetramer binding and expression of a range of co-inhibitory molecules. Notably, accumulation and effector differentiation of insulin-specific CD8+ T cells in pancreatic lymph nodes was prominent in non-transgenic recipients but blocked by transgenic proinsulin expression. This shift from T-cell priming to T-cell tolerance exemplifies the tolerogenic capacity of autoantigen expression by APC and the capacity to overcome genetic tolerance defects.

APC-targeted proinsulin expression inactivates insulin-specific memory CD8+ T cells in NOD mice.

Type 1 diabetes (T1D) results from T-cell-mediated autoimmune destruction of pancreatic ß cells. Effector T-cell responses emerge early in disease development and expand as disease progresses. Following ß-cell destruction, a long-lived T-cell memory is generated that represents a barrier to islet transplantation and other cellular insulin-replacement therapies. Development of effective immunotherapies that control or ablate ß-cell destructive effector and memory T-cell responses has the potential to prevent disease progression and recurrence. Targeting antigen expression to antigen-presenting cells inactivates cognate CD8+ effector and memory T-cell responses and has therapeutic potential. Here we investigated this in the context of insulin-specific responses in the non-obese diabetic mouse where genetic immune tolerance defects could impact on therapeutic tolerance induction. Insulin-specific CD8+ memory T cells transferred to mice expressing proinsulin in antigen-presenting cells proliferated in response to transgenically expressed proinsulin and the majority were rapidly deleted. A small proportion of transferred insulin-specific Tmem remained undeleted and these were antigen-unresponsive, exhibited reduced T cell receptor (TCR) expression and H-2Kd/insB15-23 tetramer binding and expressed co-inhibitory molecules. Expression of proinsulin in antigen-presenting cells also abolished the diabetogenic capacity of CD8+ effector T cells. Therefore, destructive insulin-specific CD8+ T cells are effectively inactivated by enforced proinsulin expression despite tolerance defects that exist in diabetes-prone NOD mice. These findings have important implications in developing immunotherapeutic approaches to T1D and other T-cell-mediated autoimmune diseases.

Maintenance of peripheral tolerance to islet antigens.

Reestablishment of immune tolerance to the insulin-producing beta cells is the desired goal for type 1 diabetes (T1D) treatment and prevention. Immune tolerance to multiple islet antigens is defective in individuals with T1D, but the mechanisms involved are multifaceted and may involve loss of thymic and peripheral tolerance. In this review we discuss our current understanding of the varied mechanisms by which peripheral tolerance to islet antigens is maintained in healthy individuals where genetic protection from T1D is present and how this fails in those with genetic susceptibility to disease. Novel findings in regards to expression of neo-islet antigens, non-classical regulatory cell subsets and the impact of specific genetic variants on tolerance induction are discussed.

Short Duration Alagebrium Chloride Therapy Prediabetes Does Not Inhibit Progression to Autoimmune Diabetes in an Experimental Model.

Mechanisms by which advanced glycation end products (AGEs) contribute to type 1 diabetes (T1D) pathogenesis are poorly understood. Since life-long pharmacotherapy with alagebrium chloride (ALT) slows progression to experimental T1D, we hypothesized that acute ALT therapy delivered prediabetes, may be effective. However, in female, non-obese diabetic (NODShiLt) mice, ALT administered prediabetes (day 50-100) did not protect against experimental T1D. ALT did not decrease circulating AGEs or their precursors. Despite this, pancreatic ß-cell function was improved, and insulitis and pancreatic CD45.1+ cell infiltration was reduced. Lymphoid tissues were unaffected. ALT pre-treatment, prior to transfer of primed GC98 CD8+ T cell receptor transgenic T cells, reduced blood glucose concentrations and delayed diabetes, suggesting islet effects rather than immune modulation by ALT. Indeed, ALT did not reduce interferon-γ production by leukocytes from ovalbumin-pre-immunised NODShiLt mice and NODscid recipients given diabetogenic ALT treated NOD splenocytes were not protected against T1D. To elucidate ß-cell effects, NOD-derived MIN6N8 ß-cell major histocompatibility complex (MHC) Class Ia surface antigens were examined using immunopeptidomics. Overall, no major changes in the immunopeptidome were observed during the various treatments with all peptides exhibiting allele specific consensus binding motifs. As expected, longer MHC Class Ia peptides were captured bound to H-2Db than H-2Kb under all conditions. Moreover, more 10-12 mer peptides were isolated from H-2Db after AGE modified bovine serum albumin (AGE-BSA) treatment, compared with bovine serum albumin (BSA) or AGE-BSA+ALT treatment. Proteomics of MIN6N8 cells showed enrichment of processes associated with catabolism, the immune system, cell cycling and presynaptic endocytosis with AGE-BSA compared with BSA treatments. These data show that short-term ALT intervention, given prediabetes, does not arrest experimental T1D but transiently impacts ß-cell function.