Novel autoantigens for diabetogenic CD4 T cells in autoimmune diabetes

Update on the ZNT8 epitope and its role in the pathogenesis of type 1 diabetes

Type 1 diabetes (T1D) is an organ-specific chronic autoimmune disease mediated by autoreactive T cells. ZnT8 is a pancreatic islet-specific zinc transporter that is mainly located in β cells. It not only participates in the synthesis, storage and secretion of insulin but also maintains the structural integrity of insulin. ZnT8 is the main autoantigen recognized by autoreactive CD8+ T cells in children and adults with T1D. This article summarizes the latest research results on the T lymphocyte epitope and B lymphocyte epitope of ZnT8 in the current literature. The structure and expression of ZnT8, the role of ZnT8 in insulin synthesis and its role in autoimmunity are reviewed. ZnT8 is the primary autoantigen of T1D and is specifically expressed in pancreatic islets. Thus, it is one of biomarkers for the diagnosis of T1D. It has broad prospects for further research on immunomodulators for the treatment of T1D.

Hydroxychloroquine in Stage 1 Type 1 Diabetes

OBJECTIVE

Innate immune responses may be involved in the earliest phases of type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

To test whether blocking innate immaune cells modulated progression of the disease, we randomly assigned 273 individuals with stage 1 T1D to treatment with hydroxychloroquine (n = 183; 5 mg/kg per day to a maximum of 400 mg) or placebo (n = 90) and assessed whether hydroxychloroquine treatment delayed or prevented progression to stage 2 T1D (i.e., two or more islet autoantibodies with abnormal glucose tolerance).

RESULTS

After a median follow-up of 23.3 months, the trial was stopped prematurely by the data safety monitoring board because of futility. There were no safety concerns in the hydroxychloroquine arm, including in annual ophthalmologic examinations. Preplanned secondary analyses showed a transient decrease in the glucose average area under the curve to oral glucose in the hydroxychloroquine-treated arm at month 6 and reduced titers of anti-GAD and anti-insulin autoantibodies and acquisition of positive autoantibodies in the hydroxychloroquine arm (P = 0.032).

CONCLUSIONS

We conclude that hydroxychloroquine does not delay progression to stage 2 T1D in individuals with stage 1 disease. Drug treatment reduces the acquisition of additional autoantibodies and the titers of autoantibodies to GAD and insulin.

Selected Serum Markers Associated with Pathogenesis and Clinical Course of Type 1 Diabetes in Pediatric Patients-The Effect of Disease Duration

Biochemical abnormalities in the course of type 1 diabetes (T1D) may cause the production/activation of various proteins and peptides influencing treatment and causing a risk of complications. The aim of this study was to assess concentrations of selected serum substances involved in the pathogenesis and course of T1D and to correlate their concentrations with the duration of T1D. The study included patients with T1D (n = 156) at the age of 3-17, who were divided according to the duration of the disease into those newly diagnosed (n = 30), diagnosed after 3-5 (n = 77), 6-7 (n = 25), and over 7 (n = 24) years from the onset of T1D, and age-matched healthy controls (n = 30). Concentrations of amylin (IAPP), proamylin (proIAPP), catestatin (CST), chromogranin A (ChgA), nerve growth factor (NFG), platelet-activating factor (PAF), uromodulin (UMOD), and intestinal fatty acid binding protein (I-FABP) were measured in sera using immunoenzymatic tests. There were significant differences in concentrations of all the substances except UMOD and NGF between T1D patients and healthy children. The duration of the disease affected concentrations of CST, ChgA, PAF, and NGF, i.e., proteins/peptides which could have an impact on the course of T1D and the development of complications. In long-term patients, a decrease in concentrations of CST and ChgA, and an increase in PAF concentrations were found. In the case of NGF, a decrease was observed after the initial high values, followed by an increase over 7 years after T1D diagnosis. Concluding, the results show that concentrations of selected serum indicators may change in the course of T1D. Further studies are needed to establish whether these indicators could be used in the context of predicting long-term complications.

Enhancing Antigen Presentation and Inducing Antigen-Specific Immune Tolerance with Amphiphilic Peptides

Ag-specific immunotherapy to restore immune tolerance to self-antigens, without global immune suppression, is a long-standing goal in the treatment of autoimmune disorders such as type 1 diabetes (T1D). However, vaccination with autoantigens such as insulin or glutamic acid decarboxylase have largely failed in human T1D trials. Induction and maintenance of peripheral tolerance by vaccination requires efficient autoantigen presentation by APCs. In this study, we show that a lipophilic modification at the N-terminal end of CD4⁺ epitopes (lipo-peptides) dramatically improves peptide Ag presentation. We designed amphiphilic lipo-peptides to efficiently target APCs in the lymph nodes by binding and trafficking with endogenous albumin. Additionally, we show that lipophilic modification anchors the peptide into the membranes of APCs, enabling a bivalent cell-surface Ag presentation. The s.c. injected lipo-peptide accumulates in the APCs in the lymph node, enhances the potency and duration of peptide Ag presentation by APCs, and induces Ag-specific immune tolerance that controls both T cell- and B cell-mediated immunity. Immunization with an amphiphilic insulin B chain 9-23 peptide, an immunodominant CD4⁺ T cell epitope in NOD mice, significantly suppresses the activation of T cells, increases inhibitory cytokine production, induces regulatory T cells, and delays the onset and lowers the incidence of T1D. Importantly, treatment with a lipophilic β-cell peptide mixture delays progression to end-stage diabetes in acutely diabetic NOD mice, whereas the same doses of standard soluble peptides were not effective. Amphiphilic modification effectively enhances Ag presentation for peptide-based immune regulation of autoimmune diseases.

Hidden in Plain View: Discovery of Chimeric Diabetogenic CD4 T Cell Neo-Epitopes

The T cell antigens driving autoimmune Type 1 Diabetes (T1D) have been pursued for more than three decades. When diabetogenic CD4 T cell clones and their relevant MHCII antigen presenting alleles were first identified in rodents and humans, the path to discovering the peptide epitopes within pancreatic beta cell proteins seemed straightforward. However, as experimental results accumulated, definitive data were often absent or controversial. Work within the last decade has helped to clear up some of the controversy by demonstrating that a number of the important MHCII presented epitopes are not encoded in the natural beta cell proteins, but in fact are fusions between peptide fragments derived from the same or different proteins. Recently, the mechanism for generating these MHCII diabetogenic chimeric epitopes has been attributed to a form of reverse proteolysis, called transpeptidation, a process that has been well-documented in the production of MHCI presented epitopes. In this mini-review we summarize these data and their implications for T1D and other autoimmune responses.

A TCR-like antibody against a proinsulin-containing fusion peptide ameliorates type 1 diabetes in NOD mice

Type 1 diabetes (T1D) is an autoimmune disease caused by destruction of insulin-producing β cells. The response of autoreactive T cells to β cell antigens plays a central role in the development of T1D. Recently, fusion peptides composed by insulin C-peptide fragments and other proteins were reported as β cell target antigens for diabetogenic CD4⁺ T cells in non-obese diabetic (NOD) mice. In this study, we generated a T cell-receptor (TCR)-like monoclonal antibody (mAb) against a fusion peptide bound to major histocompatibility complex (MHC) class II component to elucidate the function of the fusion peptides in T1D. In addition, we developed a novel NFAT-GFP TCR reporter system to evaluate the TCR-like mAb. The NFAT-GFP reporter T cells expressing the diabetogenic TCR were specifically activated by the fusion peptide presented on the MHC class II molecules. By using the NFAT-GFP reporter T cells, we showed that the TCR-like mAb blocks the diabetogenic T cell response against the fusion peptide presented on the MHC class II molecules. Furthermore, the development of T1D was ameliorated when pre-diabetic NOD mice were treated with this mAb. These findings suggest that NFAT-GFP reporter T cells are useful to assess the function of specific TCR and the recognition of fusion peptides by T cells is crucial for the pathogenesis of T1D.

T Cells from NOD-PerIg Mice Target Both Pancreatic and Neuronal Tissue

It has become increasingly appreciated that autoimmune responses against neuronal components play an important role in type 1 diabetes (T1D) pathogenesis. In fact, a large proportion of islet-infiltrating B lymphocytes in the NOD mouse model of T1D produce Abs directed against the neuronal type III intermediate filament protein peripherin. NOD-PerIg mice are a previously developed BCR-transgenic model in which virtually all B lymphocytes express the H and L chain Ig molecules from the intra-islet-derived anti-peripherin-reactive hybridoma H280. NOD-PerIg mice have accelerated T1D development, and PerIg B lymphocytes actively proliferate within islets and expand cognitively interactive pathogenic T cells from a pool of naive precursors. We now report adoptively transferred T cells or whole splenocytes from NOD-PerIg mice expectedly induce T1D in NOD.scid recipients but, depending on the kinetics of disease development, can also elicit a peripheral neuritis (with secondary myositis). This neuritis was predominantly composed of CD4⁺ and CD8⁺ T cells. Ab depletion studies showed neuritis still developed in the absence of NOD-PerIg CD8⁺ T cells but required CD4⁺ T cells. Surprisingly, sciatic nerve-infiltrating CD4⁺ cells had an expansion of IFN-γ^- and TNF-α^- double-negative cells compared with those within both islets and spleen. Nerve and islet-infiltrating CD4⁺ T cells also differed by expression patterns of CD95, PD-1, and Tim-3. Further studies found transitory early B lymphocyte depletion delayed T1D onset in a portion of NOD-PerIg mice, allowing them to survive long enough to develop neuritis outside of the transfer setting. Together, this study presents a new model of peripherin-reactive B lymphocyte-dependent autoimmune neuritis.

Gene silencing of ZnT8 attenuates inflammation and protects pancreatic tissue injury in T1D

T lymphocyte mediated inflammation contributes to the development of T1D. Zinc Transporter 8 (ZnT8) has emerged as a target of autoreactive T cells in human T1D in recent years. However, the regulating of ZnT8 in T1D has not been identified. We make a hypothesis that whether alternation of ZnT8 level could attenuate inflammation and protect pancreatic tissue injury in T1D. In this study, we utilized ZnT8 shRNA to inhibit ZnT8 expression, and detected inflammation, glucose tolerance and pancreatic tissue of NOD mice. We found that ZnT8 shRNA attenuated specific CD8+ T cell activation and cytotoxicity. In addition, ZnT8 shRNA protected glucose tolerance and pancreatic tissue injury via down-regulation of ZnT8 in NOD mice. Therefore, the results suggest that RNAi represents a promising target reducing ZnT8 mediated inflammation, and provides a novel therapeutical clue in T1D.

Role of TGF-β in Self-Peptide Regulation of Autoimmunity

Transforming growth factor (TGF)-β has been implicated in regulation of the immune system, including autoimmunity. We have found that TGF-β is readily produced by T cells following immunization with self-peptide epitopes that downregulate autoimmune responses in type 1 diabetes (T1D) prone nonobese diabetic (NOD) mice. These include multiple peptide epitopes derived from the islet β-cell antigens GAD65 (GAD65 p202-221, GAD65 p217-236), GAD67 (GAD67 p210-229, GAD67 p225-244), IGRP (IGRP p123-145, IGRP p195-214) and insulin B-chain (Ins. B:9-23) that protected NOD mice from T1D. Immunization of NOD mice with the self-MHC class II I-A^g7 β-chain-derived peptide, I-Aβ^g7 p54-76 also induced large amounts of TGF-β and also protected these mice from diabetes development. These results indicate that peptides derived from disease related self-antigens and MHC class II molecules primarily induce TGF-β producing regulatory Th3 and Tr1-like cells. TGF-β produced by these cells could enhance the differentiation of induced regulatory iTreg and iTreg17 cells to prevent induction and progression of autoimmune diseases. We therefore suggest that peripheral immune tolerance could be induced and maintained by immunization with self-peptides that induce TGF-β producing T cells.

Loss of NOX-Derived Superoxide Exacerbates Diabetogenic CD4 T-Cell Effector Responses in Type 1 Diabetes

Reactive oxygen species (ROS) play prominent roles in numerous biological systems. While classically expressed by neutrophils and macrophages, CD4 T cells also express NADPH oxidase (NOX), the superoxide-generating multisubunit enzyme. Our laboratory recently demonstrated that superoxide-deficient nonobese diabetic (NOD.Ncf1(m1J)) mice exhibited a delay in type 1 diabetes (T1D) partially due to blunted IFN-γ synthesis by CD4 T cells. For further investigation of the roles of superoxide on CD4 T-cell diabetogenicity, the NOD.BDC-2.5.Ncf1(m1J) (BDC-2.5.Ncf1(m1J)) mouse strain was generated, possessing autoreactive CD4 T cells deficient in NOX-derived superoxide. Unlike NOD.Ncf1(m1J), stimulated BDC-2.5.Ncf1(m1J) CD4 T cells and splenocytes displayed elevated synthesis of Th1 cytokines and chemokines. Superoxide-deficient BDC-2.5 mice developed spontaneous T1D, and CD4 T cells were more diabetogenic upon adoptive transfer into NOD.Rag recipients due to a skewing toward impaired Treg suppression. Exogenous superoxide blunted exacerbated Th1 cytokines and proinflammatory chemokines to approximately wild-type levels, concomitant with reduced IL-12Rβ2 signaling and P-STAT4 (Y693) activation. These results highlight the importance of NOX-derived superoxide in curbing autoreactivity due, in part, to control of Treg function and as a redox-dependent checkpoint of effector T-cell responses. Ultimately, our studies reveal the complexities of free radicals in CD4 T-cell responses.

Harnessing nanoparticles for immune modulation

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NPs can be generated from numerous biocompatible compounds.

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Specific physiochemical characteristics can be manipulated to modulate the immune response.

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Severe inflammation can be treated using NP-based approaches.

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Antigen delivery via NPs can restore peripheral immune tolerance.

Recent approaches using nanoparticles engineered for immune regulation have yielded promising results in preclinical models of disease. The number of nanoparticle therapies is growing, fueled by innovations in nanotechnology and advances in understanding of the underlying pathogenesis of immune-mediated diseases. In particular, recent mechanistic insight into the ways in which nanoparticles interact with the mononuclear phagocyte system and impact its function during homeostasis and inflammation have highlighted the potential of nanoparticle-based therapies for controlling severe inflammation while concurrently restoring peripheral immune tolerance in autoimmune disease. Here we review recent advances in nanoparticle-based approaches aimed at immune-modulation, and discuss these in the context of concepts in polymeric nanoparticle development, including particle modification, delivery and the factors associated with successful clinical deployment.

Chromogranin A is a T cell antigen in human type 1 diabetes

Chromogranin A (ChgA) is a beta cell secretory granule protein and a peptide of ChgA, WE14, was recently identified as a ligand for diabetogenic CD4 T cell clones derived from the NOD mouse. In this study we compared responses of human CD4 T cells from recent onset type 1 diabetic (T1D) and control subjects to WE14 and to an enzymatically modified version of this peptide. T cell responders to antigens were detected in PBMCs from study subjects by an indirect CD4 ELISPOT assay for IFN-γ. T1D patients (n = 27) were recent onset patients within one year of diagnosis, typed for HLA-DQ8. Controls (n = 31) were either 1st degree relatives with no antibodies or from the HLA-matched general population cohort of DAISY/TEDDY. A second cohort of patients (n = 11) and control subjects (n = 11) was tested at lower peptide concentrations. We found that WE14 is recognized by T cells from diabetic subjects vs. controls in a dose dependent manner. Treatment of WE14 with transglutaminase increased reactivity to the peptide in some patients. This work suggests that ChgA is an important target antigen in human T1D subjects and that post-translational modification may play a role in its reactivity and relationship to disease.

Do post-translational beta cell protein modifications trigger type 1 diabetes?

Type 1 diabetes is considered an autoimmune disease characterised by specific T cell-mediated destruction of the insulin-producing beta cells. Yet, except for insulin, no beta cell-specific antigens have been discovered. This may imply that the autoantigens in type 1 diabetes exist in modified forms capable of specifically triggering beta cell destruction. In other immune-mediated diseases, autoantigens targeted by the immune system have undergone post-translational modification (PTM), thereby creating tissue-specific neo-epitopes. In a similar manner, PTM of beta cell proteins might create beta cell-specific neo-epitopes. We suggest that the current paradigm of type 1 diabetes as a classical autoimmune disease should be reconsidered since the immune response may not be directed against native beta cell proteins. A modified model for the pathogenetic events taking place in islets leading to the T cell attack against beta cells is presented. In this model, PTM plays a prominent role in triggering beta cell destruction. We discuss literature of relevance and perform genetic and human islet gene expression analyses. Both direct and circumstantial support for the involvement of PTM in type 1 diabetes exists in the published literature. Furthermore, we report that cytokines change the expression levels of several genes encoding proteins involved in PTM processes in human islets, and that there are type 1 diabetes-associated polymorphisms in a number of these. In conclusion, data from the literature and presented experimental data support the notion that PTM of beta cell proteins may be involved in triggering beta cell destruction in type 1 diabetes. If the beta cell antigens recognised by the immune system foremost come from modified proteins rather than native ones, the concept of type 1 diabetes as a classical autoimmune disease is open for debate.

Rodent models for investigating the dysregulation of immune responses in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease mediated by T cells that selectively destroy the insulin-producing β cells. Previous reports based on epidemiological and animal studies have demonstrated that both genetic factors and environmental parameters can either promote or attenuate the progression of autoimmunity. In recent decades, several inbred rodent strains that spontaneously develop diabetes have been applied to the investigation of the pathogenesis of T1D. Because the genetic manipulation of mice is well developed (transgenic, knockout, and conditional knockout/transgenic), most studies are performed using the nonobese diabetic (NOD) mouse model. This paper will focus on the use of genetically manipulated NOD mice to explore the pathogenesis of T1D and to develop potential therapeutic approaches.