Posttranslational modification of HLA-DQ binding islet autoantigens in type 1 diabetes

T-Cell Epitopes and Neo-epitopes in Type 1 Diabetes: A Comprehensive Update and Reappraisal

The autoimmune disease type 1 diabetes is characterized by effector T-cell responses to pancreatic β-cell-derived peptides presented by HLA class I and class II molecules, leading ultimately to β-cell demise and insulin insufficiency. Although a given HLA molecule presents a vast array of peptides, only those recognized by T cells are designated as epitopes. Given their intimate link to etiology, the discovery and characterization of T-cell epitopes is a critical aspect of type 1 diabetes research. Understanding epitope recognition is also crucial for the pursuit of antigen-specific immunotherapies and implementation of strategies for T-cell monitoring. For these reasons, a cataloging and appraisal of the T-cell epitopes targeted in type 1 diabetes was completed over a decade ago, providing an important resource for both the research and the clinical communities. Here we present a much needed update and reappraisal of this earlier work and include online supplementary material where we cross-index each epitope with its primary references and Immune Epitope Database (IEDB) identifier. Our analysis includes a grading scale to score the degree of evidence available for each epitope, which conveys our perspective on several useful criteria for epitope evaluation. While providing an efficient summary of the arguably impressive current state of knowledge, this work also brings to light several deficiencies. These include the need for improved epitope validation, as few epitopes score highly by the criteria employed, and the dearth of investigations of the epitopes recognized in the context of several understudied type 1 diabetes-associated HLA molecules.

Hybrid Insulin Peptides Are Recognized by Human T Cells in the Context of DRB1*04:01

T cells isolated from the pancreatic infiltrates of nonobese diabetic mice have been shown to recognize epitopes formed by the covalent cross-linking of proinsulin and secretory granule peptides. Formation of such hybrid insulin peptides (HIPs) was confirmed through mass spectrometry, and responses to HIPs were observed among the islet-infiltrating T cells of pancreatic organ donors and in the peripheral blood of individuals with type 1 diabetes (T1D). However, questions remain about the prevalence of HIP-specific T cells in humans, the sequences they recognize, and their role in disease. We identified six novel HIPs that are recognized in the context of DRB1*04:01, discovered by using a library of theoretical HIP sequences derived from insulin fragments covalently linked to one another or to fragments of secretory granule proteins or other islet-derived proteins. We demonstrate that T cells that recognize these HIPs are detectable in the peripheral blood of subjects with T1D and exhibit an effector memory phenotype. HIP-reactive T-cell clones produced Th1-associated cytokines and proliferated in response to human islet preparations. These results support the relevance of HIPs in human disease, further establishing a novel posttranslational modification that may contribute to the loss of peripheral tolerance in T1D.

Post-translational modifications contribute to neoepitopes in Type-1 diabetes: Challenges for inducing antigen-specific tolerance

Type-1 Diabetes (T1D) is the major autoimmune disease affecting the juvenile population in which insulin-producing pancreatic β-cells are destroyed by self-reactive T-cells and B-cells. Emerging studies have identified the presence of autoantibodies and altered T-cell reactivity against several autoantigens in individuals who are at risk of developing T1D even before the clinical onset of diabetes. Whilst these findings could lead to the development of predictive biomarkers for early diagnosis, growing evidence on the generation of neoepitopes, epitope spreading and diverse antigen repertoire in T1D poses a major challenge for developing approaches to induce antigen-specific tolerance. Mechanisms of neoepitope generation include post-translational modifications of existing epitopes, aberrant translational products, peptide fusion, and differences in MHC binding registers. Here, we focus our discussion on how post-translational modifications can give rise to immunogenic neoepitopes in T1D and present our perspective on how it could affect the development of therapeutic approaches to induce antigen-specific tolerance.

Distinct secretion pattern of serum proinsulin in different types of diabetes

Background

Latent autoimmune diabetes in adults (LADA) is characterized by autoimmunity, late-onset and intermediate beta-cell deprivation rate between type 2 diabetes mellitus (T2DM) and type 1 diabetes mellitus (T1DM). Herein, we investigated proinsulin (PI) secretion patterns and the endoplasmic reticulum (ER) dysfunction biomarker, PI-to-C-peptide (PI:CP) ratio, to elucidate beta-cell intrinsic pathogenesis mechanisms in different types of diabetes.

Methods

Total serum fasting PI (FPI) were measured in adult-onset and newly-diagnosed diabetes patients, including 60 T1DM, 60 LADA and 60 T2DM. Thirty of each type underwent mixed meal tolerance tests (MMTTs), and hence 120 min postprandial PI (PPI) were detected. PI:CP ratio = PI (pmol/L) ÷ CP (pmol/L) × 100%. PI-related measurements among types of diabetes were compared. Correlation between PI-related measurements and beta-cell autoimmunity were analyzed. The possibility of discriminating LADA from T1DM and T2DM with PI-related measurements were tested.

Results

FPI and PPI were significantly higher in LADA than T1DM (P<0.001 for both comparisons), but lower than those in T2DM (P<0.001 and P=0.026, respectively). Fasting PI:CP ratio was significantly higher in T1DM than both LADA and T2DM (median 3.25% vs. 2.13% and 2.32%, P=0.011 and P=0.017, respectively). In LADA, positive autoantibody numbers increased by both fasting and postprandial PI:CP ratio (P=0.007 and P=0.034, respectively). Areas under receiver operation characteristic curves (AUC_ROC) of FPI and PPI for discriminating LADA from adult-onset T1DM were 0.751 (P<0.001) and 0.838 (P<0.001), respectively. Between LADA and T2DM, AUC_ROC of FPI and PPI were 0.685 (P<0.001) and 0.741 (P=0.001), respectively.

Conclusions

In the development of autoimmune diabetes, interplays between ER stress and beta-cell autoimmunity are potentially responsible for severer beta-cell destruction. PI-related measurements could help in differentiating LADA from adult-onset T1DM and T2DM.

The MHC-II peptidome of pancreatic islets identifies key features of autoimmune peptides

The nature of autoantigens that trigger autoimmune diseases has been much discussed, but direct biochemical identification is lacking for most. Addressing this question demands unbiased examination of the self-peptides displayed by a defined autoimmune major histocompatibility complex class II (MHCII) molecule. Here we examined the immunopeptidome of the pancreatic islets in non-obese diabetic (NOD) mice, which spontaneously develop autoimmune diabetes based on the I-A^g7 variant of MHCII. The relevant peptides that induced pathogenic CD4⁺ T cells at the initiation of diabetes derived from proinsulin. These peptides were also found in the MHCII peptidome of the pancreatic lymph nodes and spleen. The proinsulin-derived peptides followed a trajectory from their generation and exocytosis in β cells, to uptake and presentation in islets and peripheral sites. Such a pathway generated conventional epitopes but also resulted in the presentation of post-translationally modified peptides, including deamidated sequences. These analyses reveal the key features of a restricted component in the self-MHCII peptidome that caused autoreactivity.

Consensus guidelines for the definition, detection and interpretation of immunogenic cell death

Cells succumbing to stress via regulated cell death (RCD) can initiate an adaptive immune response associated with immunological memory, provided they display sufficient antigenicity and adjuvanticity. Moreover, multiple intracellular and microenvironmental features determine the propensity of RCD to drive adaptive immunity. Here, we provide an updated operational definition of immunogenic cell death (ICD), discuss the key factors that dictate the ability of dying cells to drive an adaptive immune response, summarize experimental assays that are currently available for the assessment of ICD in vitro and in vivo, and formulate guidelines for their interpretation.

Diabetes-induced Proteome Changes Throughout Development

BACKGROUND

Diabetes Mellitus (DM) is a multisystemic disease involving the homeostasis of insulin secretion by the pancreatic islet beta cells (β-cells). It is associated with hypertension, renal disease, and arterial and arteriolar vascular diseases.

DISCUSSION

The classification of diabetes is identified as type 1 (gene linked β-cell destruction in childhood) and type 2 (late onset associated with β-cell overload and insulin resistance in peripheral tissues. Type 1 diabetes is characterized by insulin deficiency, type 2 diabetes by both insulin deficiency and insulin resistance. The former is a genetically programmed loss of insulin secretion whereas the latter constitutes a disruption of the homeostatic relationship between the opposing activity of β- cell insulin and alpha cell (α-cell) glucagon of the Islets of Langerhans. The condition could also occur in pregnancy, as a prenatal occurring event, possibly triggered by the hormonal changes of pregnancy combined with β-cell overload. This review discusses the molecular basis of the biomolecular changes that occur with respect to glucose homeostasis and related diseases in DM. The underlying link between pancreatic, renal, and microvascular diseases in DM is based on oxidative stress and the Unfolded Protein Response (UPR).

CONCLUSION

Studying proteome changes in diabetes can deepen our understanding of the biomolecular basis of disease and help us acquire more efficient therapies.

A pilot study of preproinsulin peptides reactivity in Chinese patients with type 1 diabetes

BACKGROUND

The aim of our study is to investigate whether preproinsulin (PPI) could trigger a proinflammatory CD4⁺ T cell response in Chinese patients with type 1 diabetes (T1D).

METHODS

Peripheral blood mononuclear cells were stimulated by a pool of 13 PPI peptides. Additional five PPI peptides previously proved to be antigenic in other cohorts of patients with T1D were also used. PPI reactive T cell responses were measured by interferon (IFN)-γ ELISPOT assay.

RESULTS

Fifty-one Chinese patients with T1D were enrolled in this study and 72.34% of them were positive for at least one islet autoantibody. The stimulation index (SI) value of IFN-γ response to PPI peptide pool or peptides with dominant epitopes was below 3 in patients when SI≥3 was used as the positive cut-off value. Two peptides (B9-23 and C19-A3) restricted to DQ8 or DR4 molecule failed to induce positive IFN-γ response in patients with high-risk HLA-DQ8 or HLA-DR4/DR9 alleles. RNA-seq analysis of PPI specific CD4⁺ T cell lines further showed that most of the IFN-γ associated genes remained unchanged.

CONCLUSIONS

This is the first report of CD4⁺ T cell epitope mapping of PPI in Chinese T1D. The lack of positive IFN-γ response to PPI peptides indicates that PPI might not be the principal antigenic candidate for autoreactive CD4⁺ T cells in Chinese T1D. Therefore, the efficacy of PPI-based immunotherapies in attenuating proinflammatory CD4⁺ T cell response requires further investigation.

MHCII-restricted T helper cells: an emerging trigger for chronic tactile allodynia after nerve injuries

Nerve injury-induced chronic pain has been an urgent problem for both public health and clinical practice. While transition to chronic pain is not an inevitable consequence of nerve injuries, the susceptibility/resilience factors and mechanisms for chronic neuropathic pain after nerve injuries still remain unknown. Current preclinical and clinical studies, with certain notable limitations, have shown that major histocompatibility complex class II–restricted T helper (Th) cells is an important trigger for nerve injury-induced chronic tactile allodynia, one of the most prevalent and intractable clinical symptoms of neuropathic pain. Moreover, the precise pathogenic neuroimmune interfaces for Th cells remain controversial, not to mention the detailed pathogenic mechanisms. In this review, depending on the biology of Th cells in a neuroimmunological perspective, we summarize what is currently known about Th cells as a trigger for chronic tactile allodynia after nerve injuries, with a focus on identifying what inconsistencies are evident. Then, we discuss how an interdisciplinary perspective would improve the understanding of Th cells as a trigger for chronic tactile allodynia after nerve injuries. Finally, we hope that the expected new findings in the near future would translate into new therapeutic strategies via targeting Th cells in the context of precision medicine to either prevent or reverse chronic neuropathic tactile allodynia.

Prediction and Prevention of Type 1 Diabetes

Type 1 Diabetes (T1D) is one of the most common chronic autoimmune diseases in children. The disease is characterized by the destruction of beta cells, leading to hyperglycemia, and to a lifelong insulin-dependent state. Although several studies in the last decades have added relevant insights, the complex pathogenesis of the disease is not yet completely understood. Recent studies have been focused on several factors, including family history and genetic predisposition (HLA and non-HLA genes) as well as environmental and metabolic biomarkers, with the aim of predicting the development and progression of T1D. Once a child becomes symptomatic, beta cell mass has already reached a critical threshold (usually a residual of 20-30% of normal amounts), thus representing only the very late phase of the disease. In particular, this final stage follows two preceding asymptomatic stages, which have been precisely identified. In view of the long natural history and complex pathogenesis of the disease, many strategies may be proposed for primary, secondary, and tertiary prevention. Strategies of primary prevention aim to prevent the onset of autoimmunity against beta cells in asymptomatic individuals at high risk for T1D. In addition, the availability of novel humoral and metabolic biomarkers that are able to characterize subjects at high risk of progression, have stimulated several studies on secondary and tertiary prevention, aimed to preserve residual beta cell destruction and/or to prolong the remission phase after the onset of T1D. This review focuses on the major current knowledge on prediction and prevention of T1D in children.

Phenotypic Analysis of Human Lymph Nodes in Subjects With New-Onset Type 1 Diabetes and Healthy Individuals by Flow Cytometry

Background: Ultrasound guided sampling of human lymph node (LN) combined with advanced flow cytometry allows phenotypic analysis of multiple immune cell subsets. These may provide insights into immune processes and responses to immunotherapies not apparent from analysis of the blood.

Methods: Ultrasound guided inguinal LN samples were obtained by both fine needle aspiration (FNA) and core needle biopsy in 10 adults within 8 weeks of diagnosis of type 1 diabetes (T1D) and 12 age-matched healthy controls at two study centers. Peripheral blood mononuclear cells (PBMC) were obtained on the same occasion. Samples were transported same day to the central laboratory and analyzed by multicolour flow cytometry.

Results: LN sampling was well-tolerated and yielded sufficient cells for analysis in 95% of cases. We confirmed the segregation of CD69⁺ cells into LN and the predominance of CD8⁺ Temra cells in blood previously reported. In addition, we demonstrated clear enrichment of CD8⁺ naïve, FOXP3⁺ Treg, class-switched B cells, CD56^bright NK cells and plasmacytoid dendritic cells (DC) in LNs as well as CD4⁺ T cells of the Th2 phenotype and those expressing Helios and Ki67. Conventional NK cells were virtually absent from LNs as were Th22 and Th1Th17 cells. Paired correlation analysis of blood and LN in the same individuals indicated that for many cell subsets, especially those associated with activation: such as CD25⁺ and proliferating (Ki67⁺) T cells, activated follicular helper T cells and class-switched B cells, levels in the LN compartment could not be predicted by analysis of blood. We also observed an increase in Th1-like Treg and less proliferating (Ki67⁺) CD4⁺ T cells in LN from T1D compared to control LNs, changes which were not reflected in the blood.

Conclusions: LN sampling in humans is well-tolerated. We provide the first detailed “roadmap” comparing immune subsets in LN vs. blood emphasizing a role for differentiated effector T cells in the blood and T cell regulation, B cell activation and memory in the LN. For many subsets, frequencies in blood, did not correlate with LN, suggesting that LN sampling would be valuable for monitoring immuno-therapies where these subsets may be impacted.

Thymically-derived Foxp3+ regulatory T cells are the primary regulators of type 1 diabetes in the non-obese diabetic mouse model

Regulatory T cells (Tregs) are an immunosuppressive population that are identified based on the stable expression of the fate-determining transcription factor forkhead box P3 (Foxp3). Tregs can be divided into distinct subsets based on whether they developed in the thymus (tTregs) or in the periphery (pTregs). Whether there are unique functional roles that distinguish pTregs and tTregs remains largely unclear. To elucidate these functions, efforts have been made to specifically identify and modify individual Treg subsets. Deletion of the conserved non-coding sequence (CNS)1 in the Foxp3 locus leads to selective impairment of pTreg generation without disrupting tTreg generation in the C57BL/6J background. Using CRISPR-Cas9 genome editing technology, we removed the Foxp3 CNS1 region in the non-obese diabetic (NOD) mouse model of spontaneous type 1 diabetes mellitus (T1D) to determine if pTregs contribute to autoimmune regulation. Deletion of CNS1 impaired in vitro induction of Foxp3 in naïve NOD CD4+ T cells, but it did not alter Tregs in most lymphoid and non-lymphoid tissues analyzed except for the large intestine lamina propria, where a small but significant decrease in RORγt+ Tregs and corresponding increase in Helios+ Tregs was observed in NOD CNS1-/- mice. CNS1 deletion also did not alter the development of T1D or glucose tolerance despite increased pancreatic insulitis in pre-diabetic female NOD CNS1-/- mice. Furthermore, the proportions of autoreactive Tregs and conventional T cells (Tconvs) within pancreatic islets were unchanged. These results suggest that pTregs dependent on the Foxp3 CNS1 region are not the dominant regulatory population controlling T1D in the NOD mouse model.

HLA-DQA1 and HLA-DQB1 Alleles, Conferring Susceptibility to Celiac Disease and Type 1 Diabetes, are More Expressed Than Non-Predisposing Alleles and are Coordinately Regulated

HLA DQA1*05 and DQB1*02 alleles encoding the DQ2.5 molecule and HLA DQA1*03 and DQB1*03 alleles encoding DQ8 molecules are strongly associated with celiac disease (CD) and type 1 diabetes (T1D), two common autoimmune diseases (AD). We previously demonstrated that DQ2.5 genes showed a higher expression with respect to non-CD associated alleles in heterozygous DQ2.5 positive (HLA DR1/DR3) antigen presenting cells (APC) of CD patients. This differential expression affected the level of the encoded DQ2.5 molecules on the APC surface and established the strength of gluten-specific CD4⁺ T cells response. Here, we expanded the expression analysis of risk alleles in patients affected by T1D or by T1D and CD comorbidity. In agreement with previous findings, we found that DQ2.5 and DQ8 risk alleles are more expressed than non-associated alleles also in T1D patients and favor the self-antigen presentation. To investigate the mechanism causing the high expression of risk alleles, we focused on HLA DQA1*05 and DQB1*02 alleles and, by ectopic expression of a single mRNA, we modified the quantitative equilibrium among the two transcripts. After transfection of DR7/DR14 B-LCL with HLA-DQA1*05 cDNA, we observed an overexpression of the endogenous DQB1*02 allele. The DQ2.5 heterodimer synthesized was functional and able to present gluten antigens to cognate CD4⁺ T cells. Our results indicated that the high expression of alpha and beta transcripts, encoding for the DQ2.5 heterodimeric molecules, was strictly coordinated by a mechanism acting at a transcriptional level. These findings suggested that, in addition to the predisposing HLA-DQ genotype, also the expression of risk alleles contributed to the establishment of autoimmunity.

The role of proteomics in assessing beta-cell dysfunction and death in type 1 diabetes

Introduction: Type 1 diabetes (T1D) is characterized by autoimmune-induced dysfunction and destruction of the pancreatic beta cells. Unfortunately, this process is poorly understood, and the current best treatment for type 1 diabetes is the administration of exogenous insulin. To better understand these mechanisms and to develop new therapies, there is an urgent need for biomarkers that can reliably predict disease stage. Areas covered: Mass spectrometry (MS)-based proteomics and complementary techniques play an important role in understanding the autoimmune response, inflammation and beta-cell death. MS is also a leading technology for the identification of biomarkers. This, and the technical difficulties and new technologies that provide opportunities to characterize small amounts of sample in great depth and to analyze large sample cohorts will be discussed in this review. Expert opinion: Understanding disease mechanisms and the discovery of disease-associated biomarkers are highly interconnected goals. Ideal biomarkers would be molecules specific to the different stages of the disease process that are released from beta cells to the bloodstream. However, such molecules are likely to be present in trace amounts in the blood due to the small number of pancreatic beta cells in the human body and the heterogeneity of the target organ and disease process.

Engineering immunomodulatory biomaterials for type 1 diabetes

A cure for type 1 diabetes (T1D) would help millions of people worldwide, but remains elusive thus far. Tolerogenic vaccines and beta cell replacement therapy are complementary therapies that seek to address aberrant T1D autoimmune attack and subsequent beta cell loss. However, both approaches require some form of systematic immunosuppression, imparting risks to the patient. Biomaterials-based tools enable localized and targeted immunomodulation, and biomaterial properties can be designed and combined with immunomodulatory agents to locally instruct specific immune responses. In this Review, we discuss immunomodulatory biomaterial platforms for the development of T1D tolerogenic vaccines and beta cell replacement devices. We investigate nano- and microparticles for the delivery of tolerogenic agents and autoantigens, and as artificial antigen presenting cells, and highlight how bulk biomaterials can be used to provide immune tolerance. We examine biomaterials for drug delivery and as immunoisolation devices for cell therapy and islet transplantation, and explore synergies with other fields for the development of new T1D treatment strategies.

The Evolving Landscape of Autoantigen Discovery and Characterization in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease that is caused, in part, by T cell-mediated destruction of insulin-producing β-cells. High risk for disease, in those with genetic susceptibility, is predicted by the presence of two or more autoantibodies against insulin, the 65-kDa form of glutamic acid decarboxylase (GAD65), insulinoma-associated protein 2 (IA-2), and zinc transporter 8 (ZnT8). Despite this knowledge, we still do not know what leads to the breakdown of tolerance to these autoantigens, and we have an incomplete understanding of T1D etiology and pathophysiology. Several new autoantibodies have recently been discovered using innovative technologies, but neither their potential utility in monitoring disease development and treatment nor their role in the pathophysiology and etiology of T1D has been explored. Moreover, neoantigen generation (through posttranslational modification, the formation of hybrid peptides containing two distinct regions of an antigen or antigens, alternative open reading frame usage, and translation of RNA splicing variants) has been reported, and autoreactive T cells that target these neoantigens have been identified. Collectively, these new studies provide a conceptual framework to understand the breakdown of self-tolerance, if such modifications occur in a tissue- or disease-specific context. A recent workshop sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases brought together investigators who are using new methods and technologies to identify autoantigens and characterize immune responses toward these proteins. Researchers with diverse expertise shared ideas and identified resources to accelerate antigen discovery and the detection of autoimmune responses in T1D. The application of this knowledge will direct strategies for the identification of improved biomarkers for disease progression and treatment response monitoring and, ultimately, will form the foundation for novel antigen-specific therapeutics. This Perspective highlights the key issues that were addressed at the workshop and identifies areas for future investigation.

Antibodies to oxidized insulin improve prediction of type 1 diabetes in children with positive standard islet autoantibodies

BACKGROUND

Antibodies to posttranslationally modified insulin (oxPTM-INS-Ab) are a novel biomarker of type 1 diabetes (T1D). Here, we evaluated whether oxPTM-INS-Ab can improve T1D prediction in children with positive standard islet autoantibodies (AAB).

METHODS

We evaluated sensitivity, specificity, accuracy, and risk for progression to T1D associated with oxPTM-INS-Ab and the standard islet AAB that include insulin (IAA), GAD (GADA), and tyrosine phosphatase 2 (IA-2A) in a cohort of islet AAB-positive (AAB⁺ ) children from the general population (median follow-up 8.8 years).

RESULTS

oxPTM-INS-Ab was the most sensitive and specific autoantibody biomarker (74% sensitivity, 91% specificity), followed by IA-2A (71% sensitivity, 91% specificity). GADA and IAA showed lower sensitivity (65% and 50%, respectively) and specificity (66% and 68%, respectively). Accuracy (AUC of ROC) of oxPTM-INS-Ab was higher than GADA and IAA (P = 0.003 and P = 0.017, respectively), and similar to IA-2A (P = 0.896). oxPTM-INS-Ab and IA-2A were more effective than IAA for detecting progr-T1D when used as second-line biomarker in GADA⁺ children. Risk for diabetes was higher (P = 0.03) among multiple AAB⁺ who were also oxPTM-INS-Ab⁺ compared with those who were oxPTM-INS-Ab^- . Importantly, when replacing IAA with oxPTM-INS-Ab, diabetes risk increased to 100% in children with oxPTM-INS-Ab⁺ in combination with GADA⁺ and IA-2A⁺ , compared with 84.37% in those with IAA⁺ , GADA⁺ , and IA-2A⁺ (P = 0.04).

CONCLUSIONS

Antibodies to oxidized insulin (oxPTM-INS-Ab), compared with IAA which measure autoantibodies to native insulin, improve T1D risk assessment and prediction accuracy in AAB⁺ children.

Neoepitopes: a new take on beta cell autoimmunity in type 1 diabetes

Type 1 diabetes is an autoimmune disease caused by T cell-mediated destruction of pancreatic insulin-producing beta cells. The epitopes recognised by pathogenic T cells in human type 1 diabetes are poorly defined; however, a growing body of evidence suggests that T cell responses against neoepitopes contribute to beta cell destruction in type 1 diabetes. Neoepitopes are formed when self-proteins undergo post-translational modification to create a new epitope that is recognised by T- or B cells. Here we review the role of human T cell responses against neoepitopes in the immune pathogenesis of type 1 diabetes. Specifically, we review the different approaches to identifying neoepitopes relevant to human type 1 diabetes and outline several advances in this field that have occurred over the past few years. We also discuss the application of neoepitopes to the development of antigen-specific therapies for type 1 diabetes and the unresolved challenges that need to be overcome before the full repertoire of neoepitopes recognised by pathogenic human T cells in type 1 diabetes can be determined. This information may then be used to develop antigen-specific therapies for type 1 diabetes and assays to monitor changes in pathogenic, beta cell-specific T cell responses.

Antigen-based immune modulation therapy for type 1 diabetes: the era of precision medicine

Precision medicine has emerged as a mantra for therapeutic approaches to complex diseases. The defining concept relies on a detailed insight into disease pathogenesis and therapeutic mechanism. Although the type 1 diabetes field has gained new insights into disease endotypes and indications of efficacy for several therapies, none of these is yet licensed, partly because of immune suppressive side-effects beyond control of islet autoimmunity. New strategies designed to regulate the immune system continue to emerge as basic science discoveries are made, including the use of antigen-based immunotherapies. A single agent or approach seems unlikely to halt disease progression in all people with or at risk of type 1 diabetes; as such, tailored methods relying on patient subgroups and knowledge of disease endotypes are gaining attention. Recent insights into disease mechanisms and emerging trial data are being translated into opportunities for tissue-specific prevention of progressive loss of β-cell function and survival. Results so far point to feasibility, safety, and tolerability of administration of islet autoantigens and peptides thereof into recipients with or at risk of type 1 diabetes. Findings from mechanistic studies suggest favourable changes in islet autoimmunity, with signs of immune regulation. Major challenges remain, including those related to dose and dosing frequency, route of administration, and use of adjuvants. However, the first steps towards tissue-specific and personalised medicine in type 1 diabetes have been made, which will guide future studies into induction of immune tolerance to intervene in the initiation and progression of islet autoimmunity and disease.

Bioluminescent reporter assay for monitoring ER stress in human beta cells

During type 1 diabetes development, cells in the islets of Langerhans engage adaptive mechanisms in response to inflammatory signals to cope with stress, to restore cellular homeostasis, and to preserve cell function. Disruption of these mechanisms may induce the formation of a repertoire of stress-induced neoantigens, which are critical in the loss of tolerance to beta cells and the development of autoimmunity. While multiple lines of evidence argue for a critical role of the endoplasmic reticulum in these processes, the lack of tools to specifically monitor beta cell stress hampers the development of therapeutic interventions focusing on maintaining endoplasmic reticulum homeostasis. Here we designed and evaluated a stress-induced reporter in which induction of stress correlates with increased light emission. This Gaussia luciferase-based reporter system employs the unconventional cytoplasmic splicing of XBP1 to report ER stress in cells exposed to known ER-stress inducers. Linking this reporter to a human beta cell-specific promotor allows tracing ER-stress in isolated human beta cells as well as in the EndoC-βH1 cell line. This reporter system represents a valuable tool to assess ER stress in human beta cells and may aid the identification of novel therapeutics that can prevent beta cell stress in human pancreatic islets.

Possible Prevention of Diabetes with a Gluten-Free Diet

Gluten seems a potentially important determinant in type 1 diabetes (T1D) and type 2 diabetes (T2D). Intake of gluten, a major component of wheat, rye, and barley, affects the microbiota and increases the intestinal permeability. Moreover, studies have demonstrated that gluten peptides, after crossing the intestinal barrier, lead to a more inflammatory milieu. Gluten peptides enter the pancreas where they affect the morphology and might induce beta-cell stress by enhancing glucose- and palmitate-stimulated insulin secretion. Interestingly, animal studies and a human study have demonstrated that a gluten-free (GF) diet during pregnancy reduces the risk of T1D. Evidence regarding the role of a GF diet in T2D is less clear. Some studies have linked intake of a GF diet to reduced obesity and T2D and suggested a role in reducing leptin- and insulin-resistance and increasing beta-cell volume. The current knowledge indicates that gluten, among many environmental factors, may be an aetiopathogenic factors for development of T1D and T2D. However, human intervention trials are needed to confirm this and the proposed mechanisms.

Oxidative Modifications in Tissue Pathology and Autoimmune Disease

SIGNIFICANCE

Various autoimmune syndromes are characterized by abnormalities found at the level of tissues and cells, as well as by microenvironmental influences, such as reactive oxygen species (ROS), that alter intracellular metabolism and protein expression. Moreover, the convergence of genetic, epigenetic, and even environmental influences can result in B and T lymphocyte autoimmunity and tissue pathology. Recent Advances: This review describes how oxidative stress to cells and tissues may alter post-translational protein modifications, both directly and indirectly, as well as potentially lead to aberrant gene expression. For example, it has been clearly observed in many systems how oxidative stress directly amplifies carbonyl protein modifications. However, ROS also lead to a number of nonenzymatic spontaneous modifications including deamidation and isoaspartate modification as well as to enzyme-mediated citrullination of self-proteins. ROS have direct effects on DNA methylation, leading to influences in gene expression, chromosome inactivation, and the silencing of genetic elements. Finally, ROS can alter many other cellular pathways, including the initiation of apoptosis and NETosis, triggering the release of modified intracellular autoantigens.

CRITICAL ISSUES

This review will detail specific post-translational protein modifications, the pathways that control autoimmunity to modified self-proteins, and how products of ROS may be important biomarkers of tissue pathogenesis.

FUTURE DIRECTIONS

A clear understanding of the many pathways affected by ROS will lead to potential therapeutic manipulations to alter the onset and/or progression of autoimmune disease.

Inflammation-Induced Citrullinated Glucose-Regulated Protein 78 Elicits Immune Responses in Human Type 1 Diabetes

The β-cell has become recognized as a central player in the pathogenesis of type 1 diabetes with the generation of neoantigens as potential triggers for breaking immune tolerance. We report that posttranslationally modified glucose-regulated protein 78 (GRP78) is a novel autoantigen in human type 1 diabetes. When human islets were exposed to inflammatory stress induced by interleukin-1β, tumor necrosis factor-α, and interferon-γ, arginine residue R510 within GRP78 was converted into citrulline, as evidenced by liquid chromatography-tandem mass spectrometry. This conversion, known as citrullination, led to the generation of neoepitopes, which effectively could be presented by HLA-DRB1*04:01 molecules. With the use of HLA-DRB1*04:01 tetramers and ELISA techniques, we demonstrate enhanced antigenicity of citrullinated GRP78 with significantly increased CD4+ T-cell responses and autoantibody titers in patients with type 1 diabetes compared with healthy control subjects. Of note, patients with type 1 diabetes had a predominantly higher percentage of central memory cells and a lower percentage of effector memory cells directed against citrullinated GRP78 compared with the native epitope. These results strongly suggest that citrullination of β-cell proteins, exemplified here by the citrullination of GRP78, contributes to loss of self-tolerance toward β-cells in human type 1 diabetes, indicating that β-cells actively participate in their own demise.

Serum biomarkers for diagnosis and prediction of type 1 diabetes

Type 1 diabetes (T1D) culminates in the autoimmune destruction of the pancreatic βcells, leading to insufficient production of insulin and development of hyperglycemia. Serum biomarkers including a combination of glucose, glycated molecules, C-peptide, and autoantibodies have been well established for the diagnosis of T1D. However, these molecules often mark a late stage of the disease when ∼90% of the pancreatic insulin-producing β-cells have already been lost. With the prevalence of T1D increasing worldwide and because of the physical and psychological burden induced by this disease, there is a great need for prognostic biomarkers to predict T1D development or progression. This would allow us to identify individuals at high risk for early prevention and intervention. Therefore, considerable efforts have been dedicated to the understanding of disease etiology and the discovery of novel biomarkers in the last few decades. The advent of high-throughput and sensitive "-omics" technologies for the study of proteins, nucleic acids, and metabolites have allowed large scale profiling of protein expression and gene changes in T1D patients relative to disease-free controls. In this review, we briefly discuss the classical diagnostic biomarkers of T1D but mainly focus on the novel biomarkers that are identified as markers of β-cell destruction and screened with the use of state-of-the-art "-omics" technologies.

Islet stress, degradation and autoimmunity

β-cell destruction in type 1 diabetes (T1D) results from the effect of inflammation and autoimmunity. In response to inflammatory signals, islet cells engage adaptive mechanisms to restore and maintain cellular homeostasis. Among these mechanisms, the unfolded protein response (UPR) leads to a reduction of the general protein translation rate, increased production of endoplasmic reticulum chaperones and the initiation of degradation by activation of the ER associated degradation pathway (ERAD) in which newly synthetized proteins are ubiquitinylated and processed through the proteasome. This adaptive phase is also believed to play a critical role in the development of autoimmunity by the generation of neoantigens. While we have previously investigated the effect of stress on transcription, translation and post-translational events as possible source for neoantigens, the participation of the degradation machinery, yet crucial in the generation of antigenic peptides, remains to be investigated in the context of T1D pathology. In this review, we will describe the relation between the unfolded protein response and the Ubiquitin Proteasome System (UPS) and address the role of the cellular degradation machinery in the generation of antigens. Learning from tumour immunology, we propose how these processes may unmask β-cells by triggering the generation of aberrant peptides recognized by the immune cells.

From autoinflammation to autoimmunity: old and recent findings

Autoimmune diseases and autoinflammatory diseases have a number of similar etiopathogenetic and clinical characteristics, including genetic predisposition and recurrent systemic inflammatory flares. The first phase of ADs involves innate immunity: by means of TLRs, autoantigen presentation, B and T cell recruitment and autoantibody synthesis. The second phase involves adaptive immunity, a self-sustaining process in which immune complexes containing nucleic acids and autoantibodies activate self-directed inflammation. The link between autoimmunity and autoinflammation is IL-1ß, which is crucial in connecting the innate immune response due to NLR activation and the adaptive immune responses of T and B cells. In conclusion, although ADs are still considered adaptive immunity-mediated disorders, there is increasing evidence that innate immunity and inflammasomes are also involved. The aim of this review is to highlight the link between the innate and adaptive immune mechanisms involved in autoimmune diseases.

Peptide presentation by HLA-DQ molecules is associated with the development of immune tolerance

HLA class II proteins are important elements of human adaptive immune recognition and are associated with numerous infectious and immune-mediated diseases. These highly variable molecules can be classified into DP, DQ and DR groups. It has been proposed that in contrast with DP and DR, epitope binding by DQ variants rather results in immune tolerance. However, the pieces of evidence are limited and controversial. We found that DQ molecules bind more human epitopes than DR. Pathogen-associated epitopes bound by DQ molecules are more similar to human proteins than the ones bound by DR. Accordingly, DQ molecules bind epitopes of significantly different pathogen species. Moreover, the binding of autoimmunity-associated epitopes by DQ confers protection from autoimmune diseases. Our results suggest a special role of HLA-DQ in immune homeostasis and help to better understand the association of HLA molecules with infectious and autoimmune diseases.

Modifying Enzymes Are Elicited by ER Stress, Generating Epitopes That Are Selectively Recognized by CD4+ T Cells in Patients With Type 1 Diabetes

In spite of tolerance mechanisms, some individuals develop T-cell-mediated autoimmunity. Posttranslational modifications that increase the affinity of epitope presentation and/or recognition represent one means through which self-tolerance mechanisms can be circumvented. We investigated T-cell recognition of peptides that correspond to modified β-cell antigens in subjects with type 1 diabetes. Modified peptides elicited enhanced proliferation by autoreactive T-cell clones. Endoplasmic reticulum (ER) stress in insulinoma cells increased cytosolic calcium and the activity of tissue transglutaminase 2 (tTG2). Furthermore, stressed human islets and insulinomas elicited effector responses from T cells specific for modified peptides, suggesting that ER stress-derived tTG2 activity generated deamidated neoepitopes that autoreactive T cells recognized. Patients with type 1 diabetes had large numbers of T cells specific for these epitopes in their peripheral blood. T cells with these specificities were also isolated from the pancreatic draining lymph nodes of cadaveric donors with established diabetes. Together, these results suggest that self-antigens are enzymatically modified in β-cells during ER stress, giving rise to modified epitopes that could serve to initiate autoimmunity or to further broaden the antigenic repertoire, activating potentially pathogenic CD4⁺ T cells that may not be effectively eliminated by negative selection.

The receptor for advanced glycation endproducts is a mediator of toxicity by IAPP and other proteotoxic aggregates: Establishing and exploiting common ground for novel amyloidosis therapies

Proteotoxicity plays a key role in many devastating human disorders, including Alzheimer's, Huntington's and Parkinson's diseases; type 2 diabetes; systemic amyloidosis; and cardiac dysfunction, to name a few. The cellular mechanisms of proteotoxicity in these disorders have been the focus of considerable research, but their role in prevalent and morbid disorders, such as diabetes, is less appreciated. There is a large body of literature on the impact of glucotoxicity and lipotoxicity on insulin-producing pancreatic β-cells, and there is increasing recognition that proteotoxicty plays a key role. Pancreatic islet amyloidosis by the hormone IAPP, the production of advanced glycation endproducts (AGE), and insulin misprocessing into cytotoxic aggregates are all sources of β-cell proteotoxicity in diabetes. AGE, produced by the reaction of reducing sugars with proteins and lipids are ligands for the receptor for AGE (RAGE), as are the toxic pre-fibrillar aggregates of IAPP produced during amyloid formation. The mechanisms of amyloid formation by IAPP in vivo or in vitro are not well understood, and the cellular mechanisms of IAPP-induced β-cell death are not fully defined. Here, we review recent findings that illuminate the factors and mechanisms involved in β-cell proteotoxicity in diabetes. Together, these new insights have far-reaching implications for the establishment of unifying mechanisms by which pathological amyloidoses imbue their injurious effects in vivo.

In silico and ex vivo approaches indicate immune pressure on capsid and non-capsid regions of coxsackie B viruses in the human system

Coxsackie B Virus (CBV) infection has been linked to the aetiology of type 1 diabetes (T1D) and vaccination has been proposed as prophylaxis for disease prevention. Serum neutralising antibodies and the presence of viral protein and RNA in tissues have been common tools to examine this potential disease relationship, whilst the role of anti-CBV cytotoxic T cell responses and their targets have not been studied. To address this knowledge gap, we augmented conventional HLA-binding predictive algorithm-based epitope discovery by cross-referencing epitopes with sites of positive natural selection within the CBV3 viral genome, identified using mixed effects models of evolution. Eight epitopes for the common MHC class I allele HLA-A*0201 occur at sites that appear to be positively selected. Furthermore, such epitopes span the viral genome, indicating that effective anti-viral responses may not be restricted to the capsid region. To assess the spectrum of IFNy responses in non-diabetic subjects and recently diagnosed type 1 diabetes (T1D) patients, we stimulated PBMC ex vivo with pools of synthetic peptides based on component-restricted sequences identified in silico. We found responders were more likely to recognize multiple rather than a single CBV peptide pool, indicating that the natural course of infection results in multiple targets for effector memory responses, rather than immunodominant epitopes or viral components. The finding that anti-CBV CD8 T cell immunity is broadly targeted has implications for vaccination strategies and studies on the pathogenesis of CBV-linked diseases.

Immune Recognition of β-Cells: Neoepitopes as Key Players in the Loss of Tolerance

Prior to the onset of type 1 diabetes, there is progressive loss of immune self-tolerance, evidenced by the accumulation of islet autoantibodies and emergence of autoreactive T cells. Continued autoimmune activity leads to the destruction of pancreatic β-cells and loss of insulin secretion. Studies of samples from patients with type 1 diabetes and of murine disease models have generated important insights about genetic and environmental factors that contribute to susceptibility and immune pathways that are important for pathogenesis. However, important unanswered questions remain regarding the events that surround the initial loss of tolerance and subsequent failure of regulatory mechanisms to arrest autoimmunity and preserve functional β-cells. In this Perspective, we discuss various processes that lead to the generation of neoepitopes in pancreatic β-cells, their recognition by autoreactive T cells and antibodies, and potential roles for such responses in the pathology of disease. Emerging evidence supports the relevance of neoepitopes generated through processes that are mechanistically linked with β-cell stress. Together, these observations support a paradigm in which neoepitope generation leads to the activation of pathogenic immune cells that initiate a feed-forward loop that can amplify the antigenic repertoire toward pancreatic β-cell proteins.

Gluten-free diet during pregnancy alleviates signs of diabetes and celiac disease in NOD mouse offspring

BACKGROUND

Gluten-free (GF) diet during pregnancy ameliorates autoimmune diabetes in nonobese diabetic (NOD) mouse offspring. Due to comorbidity of celiac disease in type 1 diabetes, we hypothesized that GF diet in utero alleviates the humoral and histopathological signs of celiac disease in NOD mice. We aimed to establish the mechanisms behind the diabetes-protective effect of GF diet in utero.

METHODS

Breeding pairs of NOD mice were fed a GF or gluten-containing standard (STD) diet until parturition. The offspring were nursed by mothers on STD diet and continued on this diet until ages 4 and 13 weeks. Analyses of serum antitissue transglutaminase (anti-tTG) intestine and islet histology, islet transglutaminase (TG) activity, and cytokine expression in T cells from lymphoid organs were performed.

RESULTS

GF versus STD diet in utero led to reduced serum anti-tTG titre and increased villus-to-crypt ratio at both ages. Insulitis along with systemic and local inflammation were decreased, but islet TG activity was unchanged in 13-week-old GF mice. These mice had unchanged beta-cell volumes, but increased islet numbers throughout the prediabetic period.

CONCLUSIONS

Collectively, GF diet administered during pregnancy improves signs of celiac disease and autoimmune diabetes in the offspring. The diabetes-ameliorative effect of GF diet in utero is followed by dampening of inflammation, unchanged beta-cell volume, but increased islet numbers.

HLA-DQβ1 amino acid position 87 and DQB1*0301 are associated with Chinese Han SLE

BACKGROUND

Several susceptibility loci have been identified associated with Chinese Han systemic lupus erythematosus (SLE).

METHODS

We carried out imputation of classical HLA alleles, amino acids and Single Nucleotide Polymorphisms (SNPs) across the MHC region in Chinese Han SLE genome-wide association study (GWAS) of mainland and Hong Kong populations for the first time using newly constructed Han-MHC reference panel followed by stepwise conditional analysis.

RESULTS

We mapped the most significant independent association to HLA-DQβ1 at amino acid position (Phe87, p = 7.807 × 10-17 ) and an independent association at HLA-DQB1*0301 (Pcondiational  = 1.43 × 10-7 ).

CONCLUSION

Our study illustrates the value of population-specific HLA reference panel for fine-mapping causal variants in the MHC.

Low HLA binding of diabetes-associated CD8+ T-cell epitopes is increased by post translational modifications

Background

Type 1 diabetes (T1D) is thought to be an autoimmune disease driven by anti-islet antigen responses and mediated by T-cells. Recent published data suggests that T-cell reactivity to modified peptides, effectively neoantigens, may promote T1D. These findings have given more credence to the concept that T1D may not be solely an error of immune recognition but may be propagated by errors in protein processing or in modifications to endogenous peptides occurring as result of hyperglycemia, endoplasmic reticulum (ER) stress, or general beta cell dysfunction. In the current study, we hypothesized that diabetes-associated epitopes bound human leukocyte antigen (HLA) class I poorly and that post-translational modifications (PTM) to key sequences within the insulin-B chain enhanced peptide binding to HLA class I, conferring the CD8+ T-cell reactivity associated with T1D.

Results

We first identified, through the Immune Epitope Database (IEDB; www.iedb.org), 138 published HLA class I-restricted diabetes-associated epitopes reported to elicit positive T-cell responses in humans. The peptide binding affinity for their respective restricting allele(s) was evaluated in vitro. Overall, 75% of the epitopes bound with a half maximal inhibitory concentration (IC50) of 8250 nM or better, establishing a reference affinity threshold for HLA class I-restricted diabetes epitopes. These studies demonstrated that epitopes from diabetes-associated antigens bound HLA with a lower affinity than those of microbial origin (binding threshold of 500 nM for 85% of the epitopes). Further predictions suggested that diabetes epitopes also bind HLA class I with lower affinity than epitopes associated with other autoimmune diseases. Therefore, we measured the effect of common PTM (citrullination, chlorination, deamidation, and oxidation) on HLA-A*02:01 binding of insulin-B-derived peptides, compared to native peptides. We found that these modifications increased binding for 44% of the insulin-B epitopes, but only 15% of the control peptides.

Conclusions

These results demonstrate that insulin-derived epitopes, commonly associated with T1D, generally bind HLA class I poorly, but can be subject to PTM that improve their binding capacity and may, in part, be responsible for T-cell activation in T1D and subsequent beta cell death.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0250-3) contains supplementary material, which is available to authorized users.

Pediatric endocrine and metabolic diseases and proteomics

The principles of Predictive, Preventive and Personalized Medicine (PPPM) dictate the need to recognize individual susceptibility to disease in a timely fashion and to offer targeted preventive interventions and treatments. Proteomics is a state-of-the art technology- driven science aiming at expanding our understanding of the pathophysiologic mechanisms that underlie disease, but also at identifying accurate predictive, diagnostic and therapeutic biomarkers, that will eventually promote the implementation of PPPM. In this review, we summarize the wide spectrum of the applications of Mass Spectrometry-based proteomics in the various fields of Pediatric Endocrinology, including Inborn Errors of Metabolism, type 1 diabetes, Adrenal Disease, Metabolic Syndrome and Thyroid disease, ranging from neonatal screening to early recognition of specific at-risk populations for disease manifestations or complications in adult life and to monitoring of disease progression and response to treatment.

SIGNIFICANCE

Proteomics is a state-of-the art technology- driven science aiming at expanding our understanding of the pathophysiologic mechanisms that underlie disease, but also at identifying accurate predictive, diagnostic and therapeutic biomarkers that will eventually lead to successful, targeted, patient-centric, individualized approach of each patient, as dictated by the principles of Predictive, Preventive and Personalized Medicine. In this review, we summarize the wide spectrum of the applications of Mass Spectrometry-based proteomics in the various fields of Pediatric Endocrinology, including Inborn Errors of Metabolism, type 1 diabetes, Adrenal Disease, Metabolic Syndrome and Thyroid disease, ranging from neonatal screening, accurate diagnosis, early recognition of specific at-risk populations for the prevention of disease manifestation or future complications.

T cells specific for post-translational modifications escape intrathymic tolerance induction

Establishing effective central tolerance requires the promiscuous expression of tissue-restricted antigens by medullary thymic epithelial cells. However, whether central tolerance also extends to post-translationally modified proteins is not clear. Here we show a mouse model of autoimmunity in which disease development is dependent on post-translational modification (PTM) of the tissue-restricted self-antigen collagen type II. T cells specific for the non-modified antigen undergo efficient central tolerance. By contrast, PTM-reactive T cells escape thymic selection, though the PTM variant constitutes the dominant form in the periphery. This finding implies that the PTM protein is absent in the thymus, or present at concentrations insufficient to induce negative selection of developing thymocytes and explains the lower level of tolerance induction against the PTM antigen. As the majority of self-antigens are post-translationally modified, these data raise the possibility that T cells specific for other self-antigens naturally subjected to PTM may escape central tolerance induction by a similar mechanism.

Post-translational modifications are associated with autoimmune diseases but definitive evidence of their contribution to escape from central tolerance mechanisms is needed. Here, the authors show that T cells specific for post-translational modifications of type II collagen escape intrathymic tolerance induction in a mouse model of rheumatoid arthritis.

Expression level of risk genes of MHC class II is a susceptibility factor for autoimmunity: New insights

To date, the study of the impact of major hystocompatibility complex on autoimmunity has been prevalently focused on structural diversity of MHC molecules in binding and presentation of (auto)antigens to cognate T cells. Recently, a number of experimental evidences suggested new points of view to investigate the complex relationships between MHC gene expression and the individual predisposition to autoimmune diseases. Irrespective of the nature of the antigen, a threshold of MHC-peptide complexes needs to be reached, as well as a threshold of T cell receptors engaged is required, for the activation and proliferation of autoantigen-reactive T cells. Moreover, it is well known that increased expression of MHC class II molecules may alter the T cell receptor repertoire during thymic development, and affect the survival and expansion of mature T cells. Many evidences confirmed that the level of both transcriptional and post-transcriptional regulation are involved in the modulation of the expression of MHC class II genes and that both contribute to the predisposition to autoimmune diseases. Here, we aim to focus some of these regulative aspects to better clarify the role of MHC class II genes in predisposition and development of autoimmunity.

Type 1 Diabetes: A Chronic Anti-Self-Inflammatory Response

Inflammation is typically induced in response to a microbial infection. The release of proinflammatory cytokines enhances the stimulatory capacity of antigen-presenting cells, as well as recruits adaptive and innate immune effectors to the site of infection. Once the microbe is cleared, inflammation is resolved by various mechanisms to avoid unnecessary tissue damage. Autoimmunity arises when aberrant immune responses target self-tissues causing inflammation. In type 1 diabetes (T1D), T cells attack the insulin producing β cells in the pancreatic islets. Genetic and environmental factors increase T1D risk by in part altering central and peripheral tolerance inducing events. This results in the development and expansion of β cell-specific effector T cells (Teff) which mediate islet inflammation. Unlike protective immunity where inflammation is terminated, autoimmunity is sustained by chronic inflammation. In this review, we will highlight the key events which initiate and sustain T cell-driven pancreatic islet inflammation in nonobese diabetic mice and in human T1D. Specifically, we will discuss: (i) dysregulation of thymic selection events, (ii) the role of intrinsic and extrinsic factors that enhance the expansion and pathogenicity of Teff, (iii) defects which impair homeostasis and suppressor activity of FoxP3-expressing regulatory T cells, and (iv) properties of β cells which contribute to islet inflammation.

Optimizing Multiplexed Detections of Diabetes Antibodies via Quantitative Microfluidic Droplet Array

Sensitive, single volume detections of multiple diabetes antibodies can provide immunoprofiling and early screening of at-risk patients. To advance the state-of-the-art suspension assays for diabetes antibodies, porous hydrogel droplets are leveraged in microfluidic serpentine arrays to enhance reagent transport. This spatially multiplexed assay is applied to the detection of antibodies against insulin, glutamic acid decarboxylase, and insulinoma-associated protein 2. Optimization of assay protocol results in a shortened assay time of 2 h, with better than 20 pg mL Supporting Information detection limits across all three antibodies. Specificity and cross-reactivity tests show negligible background, nonspecific antibody-antigen, and nonspecific antibody-antibody bindings. Multiplexed detections are able to measure within 15% of target concentrations from low to high ranges. The technique enables quantifications of as little as 8000 molecules in each 500 µm droplet in a single volume, multiplexed assay format, a breakthrough necessary for the adoption of diabetes panels for clinical screening and monitoring in the future.

Type 1 Diabetes: Disease Stratification

Type 1 diabetes, a disorder characterized by immune-mediated loss of functional pancreatic beta cells, is a disease continuum with specific presymptomatic stages with defined risk of progression to symptomatic disease. Prognostic biomarkers have been developed for disease staging and for stratification of subjects that address the heterogeneity in rate of disease progression. Using biomarkers for stratification of subjects at different stages of type 1 diabetes will enable smaller and shorter intervention clinical trials with greater effect size. Addressing the heterogeneity of the disease will allow precision medicine-based approaches to prevention and interception of presymptomatic stages of disease and treatment and cure of symptomatic disease.

Respiratory infections are temporally associated with initiation of type 1 diabetes autoimmunity: the TEDDY study

AIMS/HYPOTHESIS

Respiratory infections and onset of islet autoimmunity are reported to correlate positively in two small prospective studies. The Environmental Determinants of Diabetes in the Young (TEDDY) study is the largest prospective international cohort study on the environmental determinants of type 1 diabetes that regularly monitors both clinical infections and islet autoantibodies. The aim was to confirm the influence of reported respiratory infections and to further characterise the temporal relationship with autoantibody seroconversion.

METHODS

During the years 2004-2009, 8676 newborn babies with HLA genotypes conferring an increased risk of type 1 diabetes were enrolled at 3 months of age to participate in a 15 year follow-up. In the present study, the association between parent-reported respiratory infections and islet autoantibodies at 3 month intervals up to 4 years of age was evaluated in 7869 children. Time-dependent proportional hazard models were used to assess how the timing of respiratory infections related to persistent confirmed islet autoimmunity, defined as autoantibody positivity against insulin, GAD and/or insulinoma antigen-2, concordant at two reference laboratories on two or more consecutive visits.

RESULTS

In total, 87,327 parent-reported respiratory infectious episodes were recorded while the children were under study surveillance for islet autoimmunity, and 454 children seroconverted. The number of respiratory infections occurring in a 9 month period was associated with the subsequent risk of autoimmunity (p < 0.001). For each 1/year rate increase in infections, the hazard of islet autoimmunity increased by 5.6% (95% CI 2.5%, 8.8%). The risk association was linked primarily to infections occurring in the winter (HR 1.42 [95% CI 1.16, 1.74]; p < 0.001). The types of respiratory infection independently associated with autoimmunity were common cold, influenza-like illness, sinusitis, and laryngitis/tracheitis, with HRs (95% CI) of 1.38 (1.11, 1.71), 2.37 (1.35, 4.15), 2.63 (1.22, 5.67) and 1.76 (1.04, 2.98), respectively.

CONCLUSIONS/INTERPRETATION

Recent respiratory infections in young children correlate with an increased risk of islet autoimmunity in the TEDDY study. Further studies to identify the potential causative viruses with pathogen-specific assays should focus especially on the 9 month time window leading to autoantibody seroconversion.

Deciphering the Pathogenesis of Human Type 1 Diabetes (T1D) by Interrogating T Cells from the "Scene of the Crime"

PURPOSE OF REVIEW

Autoimmune-mediated destruction of insulin-producing β-cells within the pancreas results in type 1 diabetes (T1D), which is not yet preventable or curable. Previously, our understanding of the β-cell specific T cell repertoire was based on studies of autoreactive T cell responses in the peripheral blood of patients at risk for, or with, T1D; more recently, investigations have included immunohistochemical analysis of some T cell specificities in the pancreas from organ donors with T1D. Now, we are able to examine live, islet-infiltrating T cells from donors with T1D.

RECENT FINDINGS

Analysis of the T cell repertoire isolated directly from the pancreatic islets of donors with T1D revealed pro-inflammatory T cells with targets of known autoantigens, including proinsulin and glutamic acid decarboxylase, as well as modified autoantigens. We have assayed the islet-infiltrating T cell repertoire for autoreactivity and function directly from the inflamed islets of T1D organ donors. Design of durable treatments for prevention of or therapy for T1D requires understanding this repertoire.

New insights into non-conventional epitopes as T cell targets: The missing link for breaking immune tolerance in autoimmune disease?

The mechanism by which immune tolerance is breached in autoimmune disease is poorly understood. One possibility is that post-translational modification of self-antigens leads to peripheral recognition of neo-epitopes against which central and peripheral tolerance is inadequate. Accumulating evidence points to multiple mechanisms through which non-germline encoded sequences can give rise to these non-conventional epitopes which in turn engage the immune system as T cell targets. In particular, where these modifications alter the rules of epitope engagement with MHC molecules, such non-conventional epitopes offer a persuasive explanation for associations between specific HLA alleles and autoimmune diseases. In this review article, we discuss current understanding of mechanisms through which non-conventional epitopes may be generated, focusing on several recently described pathways that can transpose germline-encoded sequences. We contextualise these discoveries around type 1 diabetes, the prototypic organ-specific autoimmune disease in which specific HLA-DQ molecules confer high risk. Non-conventional epitopes have the potential to act as tolerance breakers or disease drivers in type 1 diabetes, prompting a timely re-evaluation of models of a etiopathogenesis. Future studies are required to elucidate the disease-relevance of a range of potential non-germline epitopes and their relationship to the natural peptide repertoire.

T1D Autoantibodies: room for improvement?

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is now predictable by measuring major islet autoantibodies (IAbs) against insulin and other pancreatic β cells proteins including GAD65 (GADA), islet antigen 2 (IA-2A), and zinc transporter 8 (ZnT8A). The assay technology for IAbs has made great progress; however, several important aspects still need to be addressed and improved.

RECENT FINDINGS

Currently a radio-binding assay has been well established as the 'gold' standard assay for all four IAbs. New generation of nonradioactive IAb assay with electrochemiluminescence technology has been shown to further improve sensitivity and disease specificity. Recently, multiplexed assays have opened the possibility of more efficient screening in large populations. Identification of potential new autoantibodies to neo-antigens or neo-epitopes posttranslational modification is a new important field to be explored.

SUMMARY

Individuals having a single positive autoantibody are at low risk for progression to T1D, whereas individuals expressing two or more positive autoantibodies, especially on multiple tests over time, have nearly 100% risk of developing clinical T1D when followed for over two decades. More efficient and cost effective IAb assays will hopefully lead to point-of-care screening in the general population.

Antibodies to post-translationally modified insulin as a novel biomarker for prediction of type 1 diabetes in children

AIMS/HYPOTHESIS

We have shown that autoimmunity to insulin in type 1 diabetes may result from neoepitopes induced by oxidative post-translational modifications (oxPTM). Antibodies specific to oxPTM-insulin (oxPTM-INS-Ab) are present in most newly diagnosed individuals with type 1 diabetes and are more common than autoantibodies to native insulin. In this study, we investigated whether oxPTM-INS-Ab are present before clinical onset of type 1 diabetes, and evaluated the ability of oxPTM-INS-Ab to identify children progressing to type 1 diabetes.

METHODS

We used serum samples collected longitudinally from the 'All Babies in Southeast Sweden (ABIS)' cohort tested for the gold standard islet autoantibodies to insulin (IAA), GAD (GADA), tyrosine phosphatase 2 (IA-2A) and zinc transporter 8 (ZnT8A). We studied 23 children who progressed to type 1 diabetes (progr-T1D) and 63 children who did not progress to type 1 diabetes (NP) after a median follow-up of 10.8 years (interquartile range 7.7-12.8). Of the latter group, 32 were positive for one or more islet autoantibodies (NP-AAB⁺). oxPTM-INS-Ab to insulin modified by ^•OH or HOCl were measured by our developed ELISA platform.

RESULTS

Antibodies to at least one oxPTM-INS were present in 91.3% of progr-T1D children. oxPTM-INS-Ab co-existed with GADA, IA-2A, IAA or ZnT8A in 65.2%, 56.5%, 38.9% and 33.3% progr-T1D children, respectively. In addition, oxPTM-INS-Ab were present in 17.4%, 26.1%, 38.9% and 41.6% of progr-T1D children who were negative for GADA, IA-2A, IAA and ZnT8A, respectively. ^•OH-INS-Ab were more common in progr-T1D children than in NP-AAB⁺ children (82.6% vs 19%; p < 0.001) and allowed discrimination between progr-T1D and NP-AAB⁺ children with 74% sensitivity and 91% specificity. None of the NP-AAB^- children were positive for oxPTM-INS-Ab.

CONCLUSIONS/INTERPRETATION

oxPTM-INS-Ab are present before the clinical onset of type 1 diabetes and can identify children progressing to type 1 diabetes.

Autoreactive T cells in type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease that causes severe loss of pancreatic β cells. Autoreactive T cells are key mediators of β cell destruction. Studies of organ donors with T1D that have examined T cells in pancreas, the diabetogenic insulitis lesion, and lymphoid tissues have revealed a broad repertoire of target antigens and T cell receptor (TCR) usage, with initial evidence of public TCR sequences that are shared by individuals with T1D. Neoepitopes derived from post-translational modifications of native antigens are emerging as novel targets that are more likely to evade self-tolerance. Further studies will determine whether T cell responses to neoepitopes are major disease drivers that could impact prediction, prevention, and therapy. This Review provides an overview of recent progress in our knowledge of autoreactive T cells that has emerged from experimental and clinical research as well as pathology investigations.

Cell Therapy for Type 1 Diabetes: Current and Future Strategies

PURPOSE OF THE REVIEW

Type 1 diabetes (T1D) is defined by an autoimmune destruction of insulin producing β-cells located in the endocrine part of the pancreas, the islets of Langerhans. As exogenous insulin administration fails at preventing severe complications associated with this disease, cell replacement therapies are being considered as a means to treat T1D. The purpose of this manuscript is to review the challenges associated with current strategies and discuss the potential of stem cell therapy for the treatment of T1D.

RECENT FINDINGS

The most prominent therapy offered to T1D patients is exogenous insulin administration which, despite formulations improvement, remains a suboptimal treatment, due to the frequency of injections and the issues associated with precise dosing. As immunotherapy approaches have remained unsuccessful, the only cure for T1D is transplantation of donor-derived pancreas or islets. However, donor scarcity, graft loss, and immune response to the foreign tissue are issues challenging this approach and limiting the number of patients who can benefit from such treatments. In this review, we discuss the causes of T1D and the shortcomings of the current treatments. Furthermore, we summarize the cutting edge research that aims to tackle the current challenges in reaching a quality-controlled product with long-term effects, with a focus on regenerative medicine approaches using human pluripotent stem cells.