Islet-specific Glucose-6-phosphatase Catalytic Subunit-related Protein Research Articles

Extraislet expression of islet antigen boosts T cell exhaustion to partially prevent autoimmune diabetes.

Persistent antigen exposure results in the differentiation of functionally impaired, also termed exhausted, T cells which are maintained by a distinct population of precursors of exhausted T (TPEX) cells. T cell exhaustion is well studied in the context of chronic viral infections and cancer, but it is unclear whether and how antigen-driven T cell exhaustion controls progression of autoimmune diabetes and whether this process can be harnessed to prevent diabetes. Using nonobese diabetic (NOD) mice, we show that some CD8+ T cells specific for the islet antigen, islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) displayed terminal exhaustion characteristics within pancreatic islets but were maintained in the TPEX cell state in peripheral lymphoid organs (PLO). More IGRP-specific T cells resided in the PLO than in islets. To examine the impact of extraislet antigen exposure on T cell exhaustion in diabetes, we generated transgenic NOD mice with inducible IGRP expression in peripheral antigen-presenting cells. Antigen exposure in the extraislet environment induced severely exhausted IGRP-specific T cells with reduced ability to produce interferon (IFN)γ, which protected these mice from diabetes. Our data demonstrate that T cell exhaustion induced by delivery of antigen can be harnessed to prevent autoimmune diabetes.

PTPN22 R620W gene editing in T cells enhances low-avidity TCR responses.

A genetic variant in the gene PTPN22 (R620W, rs2476601) is strongly associated with increased risk for multiple autoimmune diseases and linked to altered TCR regulation and T cell activation. Here, we utilize Crispr/Cas9 gene editing with donor DNA repair templates in human cord blood-derived, naive T cells to generate PTPN22 risk edited (620W), non-risk edited (620R), or knockout T cells from the same donor. PTPN22 risk edited cells exhibited increased activation marker expression following non-specific TCR engagement, findings that mimicked PTPN22 KO cells. Next, using lentiviral delivery of T1D patient-derived TCRs against the pancreatic autoantigen, islet-specific glucose-6 phosphatase catalytic subunit-related protein (IGRP), we demonstrate that loss of PTPN22 function led to enhanced signaling in T cells expressing a lower avidity self-reactive TCR, but not a high-avidity TCR. In this setting, loss of PTPN22 mediated enhanced proliferation and Th1 skewing. Importantly, expression of the risk variant in association with a lower avidity TCR also increased proliferation relative to PTPN22 non-risk T cells. Together, these findings suggest that, in primary human T cells, PTPN22 rs2476601 contributes to autoimmunity risk by permitting increased TCR signaling and activation in mildly self-reactive T cells, thereby potentially expanding the self-reactive T cell pool and skewing this population toward an inflammatory phenotype.

Induction of tolerance to a CD4 T cell hybrid insulin peptide epitope prolongs islet graft survival and suppresses autoreactive CD8 T cells

Abstract Autoreactive T cells are thought to drive autoimmune diabetes by recognizing beta cell-derived peptide antigens. We previously discovered that hybrid insulin peptides (HIPs) are potent neoantigen peptide ligands for a subset of autoreactive CD4 T cells in both the NOD mouse model and human type 1 diabetes patients. Inducing tolerance to prominent T cell autoantigens through antigen-specific immunotherapy could prevent disease onset or recurrence after islet transplantation without the need for broad immunosuppression. Here we show that tolerogenic nanoparticle (NP) delivery of the 2.5HIP, a dominant CD4 T cell HIP epitope in the NOD mouse, can prolong islet graft survival in transplanted diabetic NOD mice. Tolerance induction to the 2.5HIP not only suppressed 2.5HIP tetramer+ CD4 T cells but also autoreactive CD4 and CD8 T cells specific for different islet antigens. 2.5HIP NP treatment induced a dysfunctional state in graft-infiltrating T cells characterized by increased expression of anergic markers on CD4 T cells and reduced inflammatory cytokine production in 2.5HIP tetramer+ CD4 T cells as well as IGRP (islet specific glucose-6-phosphatase catalytic subunit-related protein) tetramer+ CD8 T cells. In conclusion, we demonstrate that antigen-specific immunotherapy aimed at inducing tolerance to a single CD4 T cell HIP epitope can prolong islet graft survival and suppress autoreactive CD8 T cells in the NOD mouse model of autoimmune diabetes. Supported by grants from NIH (R01 DK122566, R01 DK081166, T32 DK120520) and JDRF (2-SRA-2018-566-S-B)

Tolerance induction by liposomes targeting a single CD8 epitope IGRP206-214 in a model of type 1 diabetes is impeded by co-targeting a CD4+ islet epitope.

The autoimmune disease type 1 diabetes is predominantly mediated by CD8+ cytotoxic T-cell destruction of islet beta cells, of which islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206-214 is a dominant target antigen specificity. Previously, we found that a liposome-based antigen-specific immunotherapy encapsulating the CD4+ T-cell islet epitope 2.5mim together with the nuclear factor-κB inhibitor calcitriol induced regulatory T cells and protected from diabetes in NOD mice. Here we investigated whether the same system delivering IGRP206-214 could induce antigen-specific CD8+ T-cell-targeted immune regulation and delay diabetes. Subcutaneous administration of IGRP206-214 /calcitriol liposomes transiently activated and expanded IGRP-specific T-cell receptor transgenic 8.3 CD8+ T cells. Liposomal co-delivery of calcitriol was required to optimally suppress endogenous IGRP-specific CD8+ T-cell interferon-γ production and cytotoxicity. Concordantly, a short course of IGRP206-214 /calcitriol liposomes delayed diabetes progression and reduced insulitis. However, when IGRP206-214 /calcitriol liposomes were delivered together with 2.5mim /calcitriol liposomes, disease protection was not observed and the regulatory effect of 2.5mim /calcitriol liposomes was abrogated. Thus, tolerogenic liposomes that target either a dominant CD8+ or a CD4+ T-cell islet epitope can delay diabetes progression but combining multiple epitopes does not enhance protection.

Tolerance to Proinsulin-1 Reduces Autoimmune Diabetes in NOD Mice.

T-cell responses to insulin and its precursor proinsulin are central to islet autoimmunity in humans and non-obese diabetic (NOD) mice that spontaneously develop autoimmune diabetes. Mice have two proinsulin genes proinsulin -1 and 2 that are differentially expressed, with predominant proinsulin-2 expression in the thymus and proinsulin-1 in islet beta-cells. In contrast to proinsulin-2, proinsulin-1 knockout NOD mice are protected from autoimmune diabetes. This indicates that proinsulin-1 epitopes in beta-cells maybe preferentially targeted by autoreactive T cells. To study the contribution of proinsulin-1 reactive T cells in autoimmune diabetes, we generated transgenic NOD mice with tetracycline-regulated expression of proinsulin-1 in antigen presenting cells (TIP-1 mice) with an aim to induce immune tolerance. TIP-1 mice displayed a significantly reduced incidence of spontaneous diabetes, which was associated with reduced severity of insulitis and insulin autoantibody development. Antigen experienced proinsulin specific T cells were significantly reduced in in TIP-1 mice indicating immune tolerance. Moreover, T cells from TIP-1 mice expressing proinsulin-1 transferred diabetes at a significantly reduced frequency. However, proinsulin-1 expression in APCs had minimal impact on the immune responses to the downstream antigen islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) and did not prevent diabetes in NOD 8.3 mice with a pre-existing repertoire of IGRP reactive T cells. Thus, boosting immune tolerance to proinsulin-1 partially prevents islet-autoimmunity. This study further extends the previously established role of proinsulin-1 epitopes in autoimmune diabetes in NOD mice.

Deficiency of the innate immune adaptor STING promotes autoreactive T cell expansion in NOD mice.

Stimulator of IFN genes (STING) is a central hub for cytosolic nucleic acid sensing and its activation results in upregulation of type I IFN production in innate immune cells. A type I IFN gene signature seen before the onset of type 1 diabetes has been suggested as a driver of disease initiation both in humans and in the NOD mouse model. A possible source of type I IFN is through activation of the STING pathway. Recent studies suggest that STING also has antiproliferative and proapoptotic functions in T cells that are independent of IFN. To investigate whether STING is involved in autoimmune diabetes, we examined the impact of genetic deletion of STING in NOD mice. CRISPR/Cas9 gene editing was used to generate STING-deficient NOD mice. Quantitative real-time PCR was used to assess the level of type I IFN-regulated genes in islets from wild-type and STING-deficient NOD mice. The number of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206-214-specific CD8+ T cells was determined by magnetic bead-based MHC tetramer enrichment and flow cytometry. The incidence of spontaneous diabetes and diabetes after adoptive transfer of T cells was determined. STING deficiency partially attenuated the type I IFN gene signature in islets but did not suppress insulitis. STING-deficient NOD mice accumulated an increased number of IGRP206-214-specific CD8+ T cells (2878 ± 642 cells in NOD.STING-/- mice and 728.8 ± 196 cells in wild-type NOD mice) in peripheral lymphoid tissue, associated with a higher incidence of spontaneous diabetes (95.5% in NOD.STING-/- mice and 86.2% in wild-type NOD mice). Splenocytes from STING-deficient mice rapidly induced diabetes after adoptive transfer into irradiated NOD recipients (median survival 75days for NOD recipients of NOD.STING-/- mouse splenocytes and 121days for NOD recipients of NOD mouse splenocytes). Data suggest that sensing of endogenous nucleic acids through the STING pathway may be partially responsible for the type I IFN gene signature but not autoimmunity in NOD mice. Our results show that the STING pathway may play an unexpected intrinsic role in suppressing the number of diabetogenic T cells.

CD226 Deletion Reduces Type 1 Diabetes in the NOD Mouse by Impairing Thymocyte Development and Peripheral T Cell Activation.

The costimulatory molecule CD226 is highly expressed on effector/memory T cells and natural killer cells. Costimulatory signals received by T cells can impact both central and peripheral tolerance mechanisms. Genetic polymorphisms in CD226 have been associated with susceptibility to type 1 diabetes and other autoimmune diseases. We hypothesized that genetic deletion of Cd226 in the non-obese diabetic (NOD) mouse would impact type 1 diabetes incidence by altering T cell activation. CD226 knockout (KO) NOD mice displayed decreased disease incidence and insulitis in comparison to wild-type (WT) controls. Although female CD226 KO mice had similar levels of sialoadenitis as WT controls, male CD226 KO mice showed protection from dacryoadenitis. Moreover, CD226 KO T cells were less capable of adoptively transferring disease compared to WT NOD T cells. Of note, CD226 KO mice demonstrated increased CD8+ single positive (SP) thymocytes, leading to increased numbers of CD8+ T cells in the spleen. Decreased percentages of memory CD8+CD44+CD62L– T cells were observed in the pancreatic lymph nodes of CD226 KO mice. Intriguingly, CD8+ T cells in CD226 KO mice showed decreased islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-tetramer and CD5 staining, suggesting reduced T cell receptor affinity for this immunodominant antigen. These data support an important role for CD226 in type 1 diabetes development by modulating thymic T cell selection as well as impacting peripheral memory/effector CD8+ T cell activation and function.

Increased islet antigen-specific regulatory and effector CD4+ T cells in healthy individuals with the type 1 diabetes-protective haplotype.

The DRB1*15:01-DQB1*06:02 (DR1501-DQ6) haplotype is linked to dominant protection from type 1 diabetes, but the cellular mechanism for this association is unclear. To address this question, we identified multiple DR1501- and DQ6-restricted glutamate decarboxylase 65 (GAD65) and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific T cell epitopes. Three of the DR1501/DQ6-restricted epitopes identified were previously reported to be restricted by DRB1*04:01/DRB1*03:01/DQB1*03:02. We also used specific class II tetramer reagents to assess T cell frequencies. Our results indicated that GAD65- and IGRP-specific effector and CD25+CD127-FOXP3+ regulatory CD4+ T cells were present at higher frequencies in individuals with the protective haplotype than those with susceptible or neutral haplotypes. We further confirmed higher frequencies of islet antigen-specific effector and regulatory CD4+ T cells in DR1501-DQ6 individuals through a CD154/CD137 up-regulation assay. DR1501-restricted effector T cells were capable of producing interferon-γ (IFN-γ) and interleukin-4 (IL-4) but were more likely to produce IL-10 compared with effectors from individuals with susceptible haplotypes. To evaluate their capacity for antigen-specific regulatory activity, we cloned GAD65 and IGRP epitope-specific regulatory T cells. We showed that these regulatory T cells suppressed DR1501-restricted GAD65- and IGRP-specific effectors and DQB1*03:02-restricted GAD65-specific effectors in an antigen-specific fashion. In total, these results suggest that the protective DR1501-DQ6 haplotype confers protection through increased frequencies of islet-specific IL-10-producing T effectors and CD25+CD127-FOXP3+ regulatory T cells.

IC-Tagging methodology applied to the expression of viral glycoproteins and the difficult-to-express membrane-bound IGRP autoantigen

We have previously developed a methodology to produce protein microspheres (MS) that can be loaded with proteins of interest in living cells through their C or N-terminal tagging with the so-called IC-Tag. The IC-Tagging method has many applications ranging from the production of immobilized enzymes for industrial use to the production of subunit vaccines due to its intrinsic adjuvancy. Here we show the adaptation of the IC-Tagging to work inside the endoplasmic reticulum and bacteria, allowing us to produce properly modified viral glycoproteins. Additionally, we were able to express the Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), whose expression remained elusive to date possibly due to its toxicity when over-expressed. IGRP is an antigen of enormous pharmaceutical interest as it is specifically targeted during the autoimmune response taking place in both the Non-Obese Diabetic (NOD) mice and type 1 diabetes (T1D) patients leading to the destruction of insulin-producing beta cells.

Cepharanthine improves glycemic status and slows the progression of renal and vascular injury in streptozotocin‐induced diabetic rats

We have previously demonstrated that Cepharanthine improves glycemic status and reduces renal injury in streptozotocin‐induced diabetic rats via antioxidant and anti‐inflammatory mechanisms. However, the hypoglycemic mechanism of Cepharanthine remains unclear. We hypothesize that Cepharanthine reduces blood glucose in steptozotocin‐induced diabetic rats via restoring pancreatic β‐cells mass and insulin secretion. Diabetes was induced by a single i.p. injection of streptozotocin (50 mg/kg) in male Sprague Dawley rats. Control and diabetic rats were treated with Cepharanthine (10 mg/kg/day, i.p.) for six weeks (n=6–8). Cepharanthine treatment significantly reduced blood glucose levels and increased plasma insulin levels in diabetic rats (blood glucose was 290± 67 in Cepharanthine treated diabetic rats vs. 550±17 mg/dl in non‐treated diabetic rats, P<0.05). The percentage of TUNEL positive cells was significantly elevated in the pancreas of diabetic rats and these changes was reduced by Cepharanthine treatment (P<0.05). Immunohistochemcial analysis revealed a decrease in pancreatic islet‐specific glucose‐6‐phosphatase catalytic subunit related protein (IGRP) and an increase in pancreatic and duodenal homeobox 1 (PDX‐1) expression levels in Cepharanthine treated vs. non treated diabetic rats (P<0.05). Cepharanthine also improved vascular endothelial function as it significantly attenuated the impairment in aortic ring relaxation to acetylcholine in diabetic rats. Moreover, Cepharanthine reduced markers of renal injury and inflammation and slowed the progression of renal fibrosis as evidenced by the reduction in levels of albuminuria, podocalyxin excretion, renal ICAM‐1 and TGF‐β in diabetic rats. The reduction in renal inflammation and injury was associated with decreased in renal caspase 3 expression in Cepharanthine treated diabetic rats. These data suggest that Cepharanthine halts the progression of streptozotocin‐induced diabetic complications in rats via reduced pancreatic β‐cells apoptosis and increased β‐cells maturation and subsequently insulin release probably via the regulation of the PDX‐1 and IGRP transcription factors of pancreatic β‐cells.Support or Funding InformationThe work was supported by bridge funding grant from Augusta University, Augusta, Georgia to Dr. Ahmed A. ElmarakbyThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Tolerogenic Ag-PLG nanoparticles induce tregs to suppress activated diabetogenic CD4 and CD8 T cells

Type 1 diabetes (T1D) is mediated by destruction of pancreatic β cells by autoantigen-specific CD4+ and CD8+ T cells, thus the ideal solution for T1D is the restoration of immune tolerance to β cell antigens. We demonstrate the ability of carboxylated 500 nm biodegradable poly(lactide-co-glycolide) (PLG) nanoparticles PLG nanoparticles (either surface coupled with or encapsulating the cognate diabetogenic peptides) to rapidly and efficiently restore tolerance in NOD.SCID recipients of both activated diabetogenic CD4+ BDC2.5 chromagranin A-specific and CD8+ NY8.3 islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific TCR transgenic T cells in an antigen-specific manner. Further, initiation and maintenance of Ag-PLG tolerance operates via several overlapping, but independent, pathways including regulation via negative-co-stimulatory molecules (CTLA-4 and PD-1) and the systemic induction of peptide-specific Tregs which were critical for long-term maintenance of tolerance by controlling both trafficking of effector T cells to, and their release of pro-inflammatory cytokines within the pancreas, concomitant with selective retention of effector cells in the spleens of recipient mice.

Microbial antigen mimics activate diabetogenic CD8 T cells in NOD mice.

Both animal model and human studies indicate that commensal bacteria may modify type 1 diabetes (T1D) development. However, the underlying mechanisms by which gut microbes could trigger or protect from diabetes are not fully understood, especially the interaction of commensal bacteria with pathogenic CD8 T cells. In this study, using islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-reactive CD8 T cell receptor NY8.3 transgenic nonobese diabetic mice, we demonstrated that MyD88 strongly modulates CD8(+) T cell-mediated T1D development via the gut microbiota. Some microbial protein peptides share significant homology with IGRP. Both the microbial peptide mimic of Fusobacteria and the bacteria directly activate IGRP-specific NY8.3 T cells and promote diabetes development. Thus, we provide evidence of molecular mimicry between microbial antigens and an islet autoantigen and a novel mechanism by which the diabetogenicity of CD8(+) T cells can be regulated by innate immunity and the gut microbiota.

Perinatal tolerance to proinsulin is sufficient to prevent autoimmune diabetes.

High-affinity self-reactive thymocytes are purged in the thymus, and residual self-reactive T cells, which are detectable in healthy subjects, are controlled by peripheral tolerance mechanisms. Breakdown in these mechanisms results in autoimmune disease, but antigen-specific therapy to augment natural mechanisms can prevent this. We aimed to determine when antigen-specific therapy is most effective. Islet autoantigens, proinsulin (PI), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) were expressed in the antigen-presenting cells (APCs) of autoimmune diabetes-prone nonobese diabetic (NOD) mice in a temporally controlled manner. PI expression from gestation until weaning was sufficient to completely protect NOD mice from diabetes, insulitis, and development of insulin autoantibodies. Insulin-specific T cells were significantly diminished, were naive, and did not express IFN-γ when challenged. This long-lasting effect from a brief period of treatment suggests that autoreactive T cells are not produced subsequently. We tracked IGRP206-214-specific CD8+ T cells in NOD mice expressing IGRP in APCs. When IGRP was expressed only until weaning, IGRP206-214-specific CD8+ T cells were not detected later in life. Thus, anti-islet autoimmunity is determined during early life, and autoreactive T cells are not generated in later life. Bolstering tolerance to islet antigens in the perinatal period is sufficient to impart lasting protection from diabetes.

NOD mice are functionally deficient in the capacity of cross-presentation.

Cross-presentation by CD8(+) conventional dendritic cells (cDCs) is involved in the maintenance of peripheral tolerance and this process is termed cross-tolerance. Previous reports showed that non-obese diabetic (NOD) mice have reduced number of splenic CD8(+) cDCs compared with non-diabetic strains, and that the administration of Flt3L to enhance DC development resulted in reduced diabetes incidence. As CD8(+) cDCs are the most efficient antigen cross-presenting cells, it was assumed that reduced cross-presentation by non-activated, tolerogenic CD8(+) cDC predisposes to autoimmune diabetogenesis. Here we show for the first time that indeed NOD mice have a defect in autoantigen cross-presentation capacity. First, we showed that NOD CD8(+) cDCs were less sensitive to iatrogenic cytochrome c, which had previously been shown to selectively deplete CD8(+) cDCs that functionally cross-present. Second, we found that proliferation of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific CD8(+) T cells was impaired in NOD compared with non-obese diabetes resistant mice after immunization with cell associated recombinant fusion protein containing the cognate IGRP peptide. This study, therefore, suggests that the reduced number of CD8(+) cDCs in NOD mice, coupled with the reduced capacity to cross-present self-antigens, reduces the overall capacity to maintain peripheral tolerance in the spontaneous autoimmune type 1 diabetes mice.

Functional cytotoxic T lymphocytes against IGRP206-214 predict diabetes in the non-obese diabetic mouse.

CD8(+) T cells are prominent in autoimmune diabetes of both humans and non-obese diabetic (NOD) mice. For example, CD8(+) T cells against islet-specific glucose 6-phosphatase catalytic subunit-related protein (IGRP) can be detected readily in older NOD mice. It has been suggested that the enumeration of islet-specific CD8(+) T cells in the peripheral blood may be a predictive biomarker for autoimmune type 1 diabetes (T1D). Here, we determined the natural history of the functional endogenous IGRP(206-214)-specific cytotoxic T lymphocytes (CTLs) in NOD mice with regard to age (3- to 15-week-old pre-diabetic mice and diabetic mice) and sex. We demonstrated that in vivo IGRP(206-214)-specific CTLs significantly increased after 12 weeks of age and in vivo cytotoxicity in female NOD mice was significantly higher than in male NOD mice. To determine the in vivo IGRP(206-214)-specific CTL frequency without killing the mice, we performed splenectomies on a cohort of mice after injecting IGRP(206-214)-coated targets and then followed their diabetes progression. We found that CTL frequency correlated with future of disease onset. Thus, our data support that IGRP(206-214)-specific CTLs may be a potent biomarker for T1D.

IGRP and insulin vaccination induce CD8+ T cell-mediated autoimmune diabetes in the RIP-CD80GP mouse

Autoimmune diabetes is characterized by autoantigen-specific T cell-mediated destruction of pancreatic islet beta cells, and CD8(+) T cells are key players during this process. We assessed whether the bitransgenic RIP-CD80 x RIP-LCMV-GP (RIP-CD80GP) mice may be a versatile antigen-specific model of inducible CD8(+) T cell-mediated autoimmune diabetes. Antigen-encoding DNA, peptide-loaded dendritic cells and antigen plus incomplete Freund's adjuvant were used for vaccination. Of 14 pancreatic proteins tested by DNA vaccination, murine pre-proinsulin 2 (100% of mice; median time after vaccination, 60 days) and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) (77%, 58 days) could induce diabetes. Vaccination with DNA encoding for zinc transporter 8, Ia-2, Ia-2β, glutamic acid decarboxylase 67 (Gad67), chromogranin A, insulinoma amyloid polypeptide and homeobox protein Nkx-2.2 induced diabetes development in 25-33% of mice. Vaccination with DNA encoding for Gad65, secretogranin 5, pancreas/duodenum homeobox protein 1 (Pdx1), carboxyl ester lipase, glucagon and control hepatitis B surface antigen (HBsAg) induced diabetes in <20% of mice. Diabetes induction efficiency could be increased by DNA vaccination with a vector encoding a ubiquitin-antigen fusion construct. Diabetic mice had florid T cell islet infiltration. CD8(+) T cell targets of IGRP were identified with a peptide library-based enzyme-linked immunospot assay, and diabetes could also be induced by vaccination with major histocompatibility complex (MHC) class I-restricted IGRP peptides loaded on mature dendritic cells. Vaccination with antigen plus incomplete Freund's adjuvant, which can prevent diabetes in other models, led to rapid diabetes development in the RIP-CD80GP mouse. We conclude that RIP-CD80GP mice are a versatile model of antigen specific autoimmune diabetes and may complement existing mouse models of autoimmune diabetes for evaluating CD8(+) T cell-targeted prevention strategies.

Effector-Memory T Cells Develop in Islets and Report Islet Pathology in Type 1 Diabetes

CD8(+) T cells are critical in human type 1 diabetes and in the NOD mouse. In this study, we elucidated the natural history of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific CD8(+) T cells in NOD diabetes using MHC-tetramer technology. IGRP206-214-specific T cells in the peripheral lymphoid tissue increased with age, and their numbers correlated with insulitis progression. IGRP206-214-specific T cells in the peripheral lymphoid tissue expressed markers of chronic Ag stimulation, and their numbers were stable after diagnosis of diabetes, consistent with their memory phenotype. IGRP206-214-specific T cells in NOD mice expand, acquire the phenotype of effector-memory T cells in the islets, and emigrate to the peripheral lymphoid tissue. Our observations suggest that enumeration of effector-memory T cells of multiple autoantigen specificities in the periphery of type 1 diabetic subjects could be a reliable reporter for progression of islet pathology.

Therapeutic Use of a Selective S1P1 Receptor Modulator Ponesimod in Autoimmune Diabetes

In the present study, we investigated the therapeutic potential of a selective S1P1 receptor modulator, ponesimod, to protect and reverse autoimmune diabetes in non-obese diabetic (NOD) mice. Ponesimod was administered orally to NOD mice starting at 6, 10, 13 and 16 weeks of age up to 35 weeks of age or to NOD mice showing recent onset diabetes. Peripheral blood and spleen B and T cell counts were significantly reduced after ponesimod administration. In pancreatic lymph nodes, B lymphocytes were increased and expressed a transitional 1-like phenotype. Chronic oral ponesimod treatment efficiently prevented autoimmune diabetes in 6, 10 and 16 week-old pre-diabetic NOD mice. Treatment withdrawal led to synchronized disease relapse. Ponesimod did not inhibit the differentiation of autoreactive T cells as assessed by adoptive transfer of lymphocytes from treated disease-free NOD mice. In addition, it did not affect the migration, proliferation and activation of transgenic BDC2.5 cells into the target tissue. However, ponesimod inhibited spreading of the T cell responses to islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP). Treatment of diabetic NOD mice with ponesimod induced disease remission. However, here again, upon treatment cessation, the disease rapidly recurred. This recurrence was effectively prevented by combination treatment with a CD3 antibody leading to the restoration of self-tolerance. In conclusion, treatment with a selective S1P1 modulator in combination with CD3 antibody represents a promising therapeutic approach for the treatment of autoimmune diabetes.

Alternative splicing and differential expression of the islet autoantigen IGRP between pancreas and thymus contributes to immunogenicity of pancreatic islets but not diabetogenicity in humans

Thymic expression of self-antigens during T-lymphocyte development is believed to be crucial for preventing autoimmunity. It has been suggested that G6PC2, the gene encoding islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), is differentially spliced between pancreatic beta cells and the thymus. This may contribute to incomplete elimination of IGRP-specific T lymphocytes in the thymus, predisposing individuals to type 1 diabetes. We tested whether specific splice variation in islets vs thymus correlates with loss of tolerance to IGRP in type 1 diabetes. Expression of G6PC2 splice variants was compared among thymus, purified medullary thymic epithelial cells and pancreatic islets by RT-PCR. Differential immunogenicity of IGRP splice variants was tested in patients and healthy individuals for autoantibodies and specific cytotoxic T lymphocytes using radiobinding assays and HLA class I multimers, respectively. Previously reported G6PC2 splice variants, including full-length G6PC2, were confirmed, albeit that they occurred in both pancreas and thymus, rather than islets alone. Yet, their expression levels were profoundly greater in islets than in thymus. Moreover, three novel G6PC2 variants were discovered that occur in islets only, leading to protein truncations, frame shifts and neo-sequences prone to immunogenicity. However, autoantibodies to novel or known IGRP splice variants did not differ between patients and healthy individuals, and similar frequencies of IGRP-specific cytotoxic T lymphocytes could be detected in both patients with type 1 diabetes and healthy individuals. We propose that post-transcriptional variation of tissue-specific self-proteins may affect negative thymic selection, although this need not necessarily lead to disease.

DEC-205-mediated antigen targeting to steady-state dendritic cells induces deletion of diabetogenic CD8+ T cells independently of PD-1 and PD-L1

CD8⁺ T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) have been implicated in type 1 diabetes in both humans and non-obese diabetic (NOD) mice, in which T cells specific for IGRP₂₀₆₋₂₁₄ are highly prevalent. We sought to manipulate these pathogenic T cells by exploiting the ability of steady-state dendritic cells (DCs) to present antigens in a tolerogenic manner. The endocytic receptor DEC-205 was utilized to deliver an IGRP₂₀₆₋₂₁₄ mimotope to DCs in NOD mice, and the impact of this delivery on a polyclonal population of endogenous islet-reactive cognate T cells was determined. Assessment of islet-infiltrating CD8⁺ T cells showed a decrease in the percentage, and the absolute number, of endogenous IGRP₂₀₆₋₂₁₄-specific T cells when the mimotope was delivered to DCs, compared with delivery of a specificity control. Employing an adoptive transfer system, deletion of CD8⁺ T cells as a result of DEC-205-mediated antigen targeting was found to occur independently of programmed death-1 (PD-1) and its ligand (PD-L1), both often implicated in the regulation of peripheral T-cell tolerance. Given its promise for the manipulation of self-reactive polyclonal T cells demonstrated here, the distinctive characteristics of this antigen delivery system will be important to appreciate as its potential as an intervention for autoimmune diseases continues to be investigated.