Insulin: a critical autoantigen and potential therapeutic agent in Type 1 diabetes

Promoting Immune Regulation in Type 1 Diabetes Using Low-Dose Interleukin-2

Dysregulation of the immune system contributes to the breakdown of immune regulation, leading to autoimmune diseases, such as type 1 diabetes (T1D). Current therapies for T1D include daily insulin, due to pancreatic β-cell destruction to maintain blood glucose levels, suppressive immunotherapy to decrease the symptoms associated with autoimmunity, and islet transplantation. Genetic risks for T1D have been linked to IL-2 and IL-2R signaling pathways that lead to the breakdown of self-tolerance mechanisms, primarily through altered regulatory T cell (Treg) function and homeostasis. In attempt to correct such deficits, therapeutic administration of IL-2 at low doses has gained attention due to the capacity to boost Tregs without the unwanted stimulation of effector T cells. Preclinical and clinical studies utilizing low-dose IL-2 have shown promising results to expand Tregs due to their high selective sensitivity to respond to IL-2. These results suggest that low-dose IL-2 therapy represents a new class of immunotherapy for T1D by promoting immune regulation rather than broadly suppressing unwanted and beneficial immune responses.

New insight on human type 1 diabetes biology: nPOD and nPOD-transplantation

The Juvenile Diabetes Research Foundation (JDRF) Network for Pancreatic Organ Donors with Diabetes (JDRF nPOD) was established to obtain human pancreata and other tissues from organ donors with type 1 diabetes (T1D) in support of research focused on disease pathogenesis. Since 2007, nPOD has recovered tissues from over 100 T1D donors and distributed specimens to approximately 130 projects led by investigators worldwide. More recently, nPOD established a programmatic expansion that further links the transplantation world to nPOD, nPOD-Transplantation; this effort is pioneering novel approaches to extend the study of islet autoimmunity to the transplanted pancreas and to consent patients for postmortem organ donation directed towards diabetes research. Finally, nPOD actively fosters and coordinates collaborative research among nPOD investigators, with the formation of working groups and the application of team science approaches. Exciting findings are emerging from the collective work of nPOD investigators, which covers multiple aspects of islet autoimmunity and beta cell biology.

The IL-2/IL-2R system: from basic science to therapeutic applications to enhance immune regulation

IL-2 plays a critical role in the normal function of the immune system. A trophic factor for lymphocytes, IL-2 is required for mounting and sustaining adaptive T cell responses; however, IL-2 is also critical for immune regulation via its effects on regulatory T cells (Treg cells). Over the years, we have contributed to the understanding of the biology of IL-2 and its signaling through the IL-2 receptor and helped define the key role played by IL-2 in Treg development and function. Our data show that Treg cells have a heightened sensitivity to IL-2, which may create a therapeutic window to promote immune regulation by selective stimulation of Treg cells. We are now developing new efforts to translate this knowledge to the clinical arena, through our focused interest in Type 1 diabetes as a prototypic autoimmune disease. Specifically, we aim at developing IL-2-based therapeutic regimens and incorporate means to enhance antigen-specific Treg responses, for improved and more selective regulation of islet autoimmunity. In parallel, we are pursuing studies in preclinical models of autoimmunity and transplantation to define critical factors for successful adoptive Treg therapy and develop clinically applicable therapeutic protocols.

Insulin2 gene (Ins2) transcription by NOD bone marrow-derived cells does not influence autoimmune diabetes development in NOD-Ins2 knockout mice

Insulin is a critical autoantigen for the development of autoimmune diabetes in non-obese diabetic (NOD) mice. About 80% of NOD females and 30-40% of NOD males develop diabetes. However, Insulin2 (Ins2) knockout NOD mice develop autoimmune diabetes with complete penetrance in both sexes, at an earlier age, and have stronger autoimmune responses to insulin. The severe diabetes phenotype observed in NOD-Ins2-/- mice suggests that lack of Ins2 expression in the thymus may compromise immunological tolerance to insulin. Insulin is a prototypical tissue specific antigen (TSA) for which tolerance is dependent on expression in thymus and peripheral lymphoid tissues. TSA are naturally expressed by medullary thymic epithelial cells (mTEC), stromal cells in peripheral lymphoid tissues and bone marrow (BM)-derived cells, mainly CD11c(+) dendritic cells. The natural expression of TSA by mTEC and stromal cells has been shown to contribute to self-tolerance. However, it is unclear whether this also applies to BM-derived cells naturally expressing TSA. To address this question, we created BM chimeras and investigated whether reintroducing Ins2 expression solely by NOD BM-derived cells delays diabetes development in NOD-Ins2-/- mice. On follow-up, NOD-Ins2-/- mice receiving Ins2-expressing NOD BM cells developed diabetes at similar rates of those receiving NOD-Ins2-/- BM cells. Diabetes developed in 64% of NOD recipients transplanted with NOD BM and in 47% of NOD mice transplanted with NOD-Ins2-/- BM (P = ns). Thus, NOD-Ins2-/- BM did not worsen diabetes in NOD recipients and Ins2 expression by NOD BM-derived cells did not delay diabetes development in NOD-Ins2-/- mice.