Proinsulin C-peptide is an autoantigen in people with type 1 diabetes

Proinsulin C-peptide is a major source of HLA-DQ8 restricted hybrid insulin peptides recognized by human islet-infiltrating CD4+ T cells

Type 1 diabetes (T1D) is an autoimmune disease that develops when T cells destroy the insulin-producing beta cells that reside in the pancreatic islets. Immune cells, including T cells, infiltrate the islets and gradually destroy the beta cells. Human islet-infiltrating CD4+ T cells recognize peptide epitopes derived from proinsulin, particularly C-peptide. Hybrid insulin peptides (HIPs) are neoepitopes formed by the fusion of two peptides derived from beta cell granule proteins and are known to be the targets of pathogenic CD4+ T cells in the non-obese diabetic (NOD) mouse and human islet-infiltrating CD4+ T cells. Proinsulin is widely recognized as a central antigen in T1D, but its role in forming HIPs is unclear. We developed a method to functionally screen TCRs derived from human islet-infiltrating CD4+ T cells and applied this to the identification of new proinsulin-derived HIPs. We generated a library of 4,488 candidate HIPs formed by fusion of proinsulin fragments and predicted to bind to HLA-DQ8. This library was screened against 109 islet-infiltrating CD4+ T cell receptors (TCRs) isolated from four organ donors who had T1D. We identified 13 unique HIPs recognized by nine different TCRs from two organ donors. HIP-specific T cell avatars responded specifically to a peptide extract from human islets. These new HIPs predominantly stimulated CD4+ T cell proliferation in peripheral blood mononuclear cells from individuals with T1D in contrast to HLA-matched controls. This is the first unbiased functional, islet-infiltrating T cell based, screen to identify proinsulin-derived HIPs. It has revealed many new HIPs and a central role of proinsulin C-peptide in their formation.

A minority of proliferating human CD4+ T cells in antigen-driven proliferation assays are antigen specific

Antigen-driven T-cell proliferation is often measured using fluorescent dye dilution assays, such as the CFSE-based proliferation assay. Dye dilution assays have been powerful tools to detect human CD4+ T-cell responses, particularly against autoantigens. However, it is not known how many cells within the proliferating population are specific for the stimulating antigen. Here we determined the frequency of CD4+ T cells specific for the stimulating antigen within the antigen-responsive population of CFSE-based proliferation assays. We compared CD4+ T-cell responses to a type 1 diabetes autoantigen (proinsulin C-peptide) and to a vaccine antigen (tetanus toxoid). The TCRs expressed by antigen-responsive CD4+ T cells were sequenced, and their antigen specificity was tested functionally by expressing them in a reporter T-cell line. Responses to C-peptide were weak, but detectable, in PBMC from individuals with T1D, whereas responses to tetanus toxoid were much stronger. The frequency of antigen-specific CD4+ T cells correlated with the strength of the response to antigen in the proliferation assay. However, antigen-specific CD4+ T cells were rare among antigen-responsive CD4+ T cells. For C-peptide, an average frequency of 7.5% (1%-11%, n = 4) of antigen-responsive CD4+ T cells were confirmed to be antigen specific. In the tetanus-toxoid-stimulated cultures, on average, 45% (16%-78%, n = 5) of the antigen-responsive CD4+ T cells were tetanus toxoid specific. These data show that antigen-specific CD4+ T cells are a minority of the cells that proliferate in response to antigen and have important implications for in vitro CD4+ T-cell proliferation assays.

Regulatory T cell-based therapy in type 1 diabetes: Latest breakthroughs and evidence

Autoimmune diseases (ADs) are among the most significant health complications, with their incidence rising in recent years. Type 1 diabetes (T1D), an AD, targets the insulin-producing β cells in the pancreas, leading to chronic insulin deficiency in genetically susceptible individuals. Regulatory immune cells, particularly T-cells (Tregs), have been shown to play a crucial role in the pathogenesis of diabetes by modulating immune responses. In diabetic patients, Tregs often exhibit diminished effectiveness due to various factors, such as instability in forkhead box P3 (Foxp3) expression or abnormal production of the proinflammatory cytokine interferon-gamma (IFN-γ) by autoreactive T-cells. Consequently, Tregs represent a potential therapeutic target for diabetes treatment. Building on the successful clinical outcomes of chimeric antigen receptor (CAR) T-cell therapy in cancer treatment, particularly in leukemias, the concept of designing and utilizing CAR Tregs for ADs has emerged. This review summarizes the findings on Treg targeting in T1D and discusses the benefits and limitations of this treatment approach for patients suffering from T1D.

Immunotherapy in type 1 diabetes: Novel pathway to the future ahead

Since the discovery of insulin over 100 years ago, the focus of research in the management of type 1 diabetes (T1D) has centered around glycemic control and management of complications rather than the prevention of autoimmune destruction of pancreatic β cells. Fortunately, in recent years, there has been significant advancement in immune-targeted pharmacotherapy to halt the natural progression of T1D. The immune-targeted intervention aims to alter the underlying pathogenesis of T1D by targeting different aspects of the immune system. The immunotherapy can either antagonize the immune mediators like T cells, B cells or cytokines (antibody-based therapy), or reinduce self-tolerance to pancreatic β cells (antigen-based therapy) or stem-cell treatment. Recently, the US Food and Drug Administration approved the first immunotherapy teplizumab to be used only in stage 2 of T1D. However, the window of opportunity to practically implement this approved molecule in the selected target population is limited. In this Editorial, we briefly discuss the various promising recent developments in the field of immunotherapy research in T1D. However, further studies of these newer therapeutic agents are needed to explore their true potential for prevention or cure of T1D.

Crinophagic granules in pancreatic β cells contribute to mouse autoimmune diabetes by diversifying pathogenic epitope repertoire

Autoimmune attack toward pancreatic β cells causes permanent loss of glucose homeostasis in type 1 diabetes (T1D). Insulin secretory granules store and secrete insulin but are also thought to be tissue messengers for T1D. Here, we show that the crinophagic granules (crinosome), a minor set of vesicles formed by fusing lysosomes with the conventional insulin dense-core granules (DCG), are pathogenic in T1D development in mouse models. Pharmacological inhibition of crinosome formation in β cells delays T1D progression without affecting the dominant DCGs. Mechanistically, crinophagy inhibition diminishes the epitope repertoire in pancreatic islets, including cryptic, modified and disease-relevant epitopes derived from insulin. These unconventional insulin epitopes are largely undetectable in the MHC-II epitope repertoire of the thymus, where only canonical insulin epitopes are presented. CD4+ T cells targeting unconventional insulin epitopes display autoreactive phenotypes, unlike tolerized T cells recognizing epitopes presented in the thymus. Thus, the crinophagic pathway emerges as a tissue-intrinsic mechanism that transforms insulin from a signature thymic self-protein to a critical autoantigen by creating a peripheral-thymic mismatch in the epitope repertoire.

Recent progress of microneedles in transdermal immunotherapy: A review

Since human skin is an immune organ, a large number of immune cells are distributed in the epidermis and the dermis of the skin. Transdermal immunotherapy shows great therapeutic advantages in innate immunotherapy and adaptive immunotherapy. To solve the problem that macromolecules are difficult to penetrate into the skin, the microneedle technology can directly break through the skin barrier using micron-sized needles in a non-invasive and painless way for transdermal drug delivery. Therefore, it is considered to be an effective technology to increase drug transdermal absorption. In this review, the types of preparation, the combinations with different techniques and the mechanisms of microneedles in transdermal immunotherapy were summarized. Compared with traditional immunotherapy like intramuscular injection and subcutaneous injection, the microneedle has many advantages in transdermal immunotherapy, such as reducing patient pain, enhancing vaccine stability, and inducing stronger immune responses. Although there are still some limitations to be solved, the application of microneedle technology in transdermal immunotherapy is undoubtedly a promising means of drug delivery.

A structural basis of T cell cross-reactivity to native and spliced self-antigens presented by HLA-DQ8

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that has a strong HLA association, where a number of self-epitopes have been implicated in disease pathogenesis. Human pancreatic islet-infiltrating CD4+ T cell clones not only respond to proinsulin C-peptide (PI40-54; GQVELGGGPGAGSLQ) but also cross-react with a hybrid insulin peptide (HIP; PI40-47-IAPP74-80; GQVELGGG-NAVEVLK) presented by HLA-DQ8. How T cell receptors recognize self-peptide and cross-react to HIPs is unclear. We investigated the cross-reactivity of the CD4+ T cell clones reactive to native PI40-54 epitope and multiple HIPs fused at the same N-terminus (PI40-54) to the degradation products of two highly expressed pancreatic islet proteins, neuropeptide Y (NPY68-74) and amyloid polypeptide (IAPP23-29 and IAPP74-80). We observed that five out of the seven selected SKW3 T cell lines expressing TCRs isolated from CD4+ T cells of people with T1D responded to multiple HIPs. Despite shared TRAV26-1-TRBV5-1 gene usage in some T cells, these clones cross-reacted to varying degrees with the PI40-54 and HIP epitopes. Crystal structures of two TRAV26-1+-TRBV5-1+ T cell receptors (TCRs) in complex with PI40-54 and HIPs bound to HLA-DQ8 revealed that the two TCRs had distinct mechanisms responsible for their differential recognition of the PI40-54 and HIP epitopes. Alanine scanning mutagenesis of the PI40-54 and HIPs determined that the P2, P7, and P8 residues in these epitopes were key determinants of TCR specificity. Accordingly, we provide a molecular basis for cross-reactivity towards native insulin and HIP epitopes presented by HLA-DQ8.

Ultrasensitive Hierarchical AuNRs@SiO2@Ag SERS Probes for Enrichment and Detection of Insulin and C-Peptide in Serum

Introduction

Insulin and C-peptide played crucial roles as clinical indicators for diabetes and certain liver diseases. However, there has been limited research on the simultaneous detection of insulin and C-peptide in trace serum. It is necessary to develop a novel method with high sensitivity and specificity for detecting insulin and C-peptide simultaneously.

Methods

A core-shell-satellites hierarchical structured nanocomposite was fabricated as SERS biosensor using a simple wet-chemical method, employing 4-MBA and DTNB for recognition and antibodies for specific capture. Gold nanorods (Au NRs) were modified with Raman reporter molecules and silver nanoparticles (Ag NPs), creating SERS tags with high sensitivity for detecting insulin and C-peptide. Antibody-modified commercial carboxylated magnetic bead@antibody served as the capture probes. Target materials were captured by probes and combined with SERS tags, forming a "sandwich" composite structure for subsequent detection.

Results

Under optimized conditions, the nanocomposite fabricated could be used to detect simultaneously for insulin and C-peptide with the detection limit of 4.29 × 10-5 pM and 1.76 × 10-10 nM in serum. The insulin concentration (4.29 × 10-5-4.29 pM) showed a strong linear correlation with the SERS intensity at 1075 cm-1, with high recoveries (96.4-105.3%) and low RSD (0.8%-10.0%) in detecting human serum samples. Meanwhile, the C-peptide concentration (1.76 × 10-10-1.76 × 10-3 nM) also showed a specific linear correlation with the SERS intensity at 1333 cm-1, with recoveries 85.4%-105.0% and RSD 1.7%-10.8%.

Conclusion

This breakthrough provided a novel, sensitive, convenient and stable approach for clinical diagnosis of diabetes and certain liver diseases. Overall, our findings presented a significant contribution to the field of biomedical research, opening up new possibilities for improved diagnosis and monitoring of diabetes and liver diseases.

Dendritic cells and antigen-specific immunotherapy in autoimmune rheumatic diseases

Dendritic cells (DCs) are professional antigen-presenting cells and trigger downstream immune responses to antigen while integrating cellular pathogen and damage-associated molecular pattern (PAMP and DAMP) or immunomodulatory signals. In healthy individuals, resting and tolerogenic DCs draining skin and intestine facilitate expansion of regulatory T cells (Treg) to maintain peripheral antigen-specific immune tolerance. In patients with rheumatic diseases, however, DCs activated by PAMPs and DAMPs expand self-reactive effector T cells, including follicular helper T cells that promote the expansion of activated autoreactive B cells, chronic inflammation and end-organ damage. With the development of cellular and nanoparticle (NP)-based self-antigen-specific immunotherapies we here consider the new opportunities and the challenges for restoring immunoregulation in the treatment and prevention of autoimmune inflammatory rheumatic conditions through DCs.

Tracking DNA-based antigen-specific T cell receptors during progression to type 1 diabetes

T cells targeting self-proteins are important mediators in autoimmune diseases. T cells express unique cell-surface receptors (TCRs) that recognize peptides presented by major histocompatibility molecules. TCRs have been identified from blood and pancreatic islets of individuals with type 1 diabetes (T1D). Here, we tracked ~1700 known antigen-specific TCR sequences, islet antigen or viral reactive, in bulk TCRβ sequencing from longitudinal blood DNA samples in at-risk cases who progressed to T1D, age/sex/human leukocyte antigen-matched controls, and a new-onset T1D cohort. Shared and frequent antigen-specific TCRβ sequences were identified in all three cohorts, and viral sequences were present across all ages. Islet sequences had different patterns of accumulation based upon antigen specificity in the at-risk cases. Furthermore, 73 islet-antigen TCRβ sequences were present in higher frequencies and numbers in T1D samples relative to controls. The total number of these disease-associated TCRβ sequences inversely correlated with age at clinical diagnosis, indicating the potential to use disease-relevant TCR sequences as biomarkers in autoimmune disorders.

Monitoring immunomodulation strategies in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease. Short-term treatment with agents targeting T cells, B cells and inflammatory cytokines to modify the disease course resulted in a short-term pause in disease activity. Lessons learnt from these trials will be discussed in this review. It is expected that effective disease-modifying agents will become available for use in earlier stages of T1D. Progress has been made to analyze antigen-specific T cells with standardization of T cell assay and discovery of antigen epitopes but there are many challenges. High-dimensional profiling of gene, protein and TCR expression at single cell level with innovative computational tools should lead to novel biomarker discovery. With this, assays to detect, quantify and characterize the phenotype and function of antigen-specific T cells will continuously evolve. An improved understanding of T cell responses will help researchers and clinicians to better predict disease onset, and progression, and the therapeutic efficacy of interventions to prevent or arrest T1D.

Monitoring islet specific immune responses in type 1 diabetes clinical immunotherapy trials

The number of immunotherapeutic clinical trials in type 1 diabetes currently being conducted is expanding, and thus there is a need for robust immune-monitoring assays which are capable of detecting and characterizing islet specific immune responses in peripheral blood. Islet- specific T cells can serve as biomarkers and as such can guide drug selection, dosing regimens and immunological efficacy. Furthermore, these biomarkers can be utilized in patient stratification which can then benchmark suitability for participation in future clinical trials. This review focusses on the commonly used immune-monitoring techniques including multimer and antigen induced marker assays and the potential to combine these with single cell transcriptional profiling which may provide a greater understanding of the mechanisms underlying immuno-intervention. Although challenges remain around some key areas such as the need for harmonizing assays, technological advances mean that multiparametric information derived from a single sample can be used in coordinated efforts to harmonize biomarker discovery and validation. Moreover, the technologies discussed here have the potential to provide a unique insight on the effect of therapies on key players in the pathogenesis of T1D that cannot be obtained using antigen agnostic approaches.

Peripheral blood mononuclear cells reactivity in recent-onset type I diabetes patients is directed against the leader peptide of preproinsulin, GAD65271-285 and GAD65431-450

Introduction

T cell reactivity against pancreatic autoantigens is considered one of the main contributors to the destruction of insulin-producing cells in type 1 diabetes (T1D). Over the years, peptide epitopes derived from these autoantigens have been described in NOD mice and in both HLA class II transgenic mice and humans. However, which ones are involved in the early onset or in the progressive phases of the disease is still unclear.

Methods

In this work we have investigated, in early-onset T1D pediatric patients and HLA-matched controls from Sardinia, the potential of preproinsulin (PPI) and glutamate decarboxylase 65 (GAD65)-derived peptides to induce spontaneous T cell proliferation responses of peripheral blood mononuclear cells (PBMCs).

Results

Significant T cell responses against PPI1-18, PPI7-19 and PPI31-49, the first two belonging to the leader sequence of PPI, and GAD65271-285 and GAD65431-450, were found in HLA-DR4, -DQ8 and -DR3, -DQ2 T1D children.

Conclusions

These data show that cryptic epitopes from the leader sequence of the PPI and GAD65271-285 and GAD65431-450 peptides might be among the critical antigenic epitopes eliciting the primary autoreactive responses in the early phases of the disease. These results may have implications in the design of immunogenic PPI and GAD65 peptides for peptide-based immunotherapy.

Using mass spectrometry to identify neoantigens in autoimmune diseases: The type 1 diabetes example

In autoimmune diseases, recognition of self-antigens presented by major histocompatibility complex (MHC) molecules elicits unexpected attack of tissue by autoantibodies and/or autoreactive T cells. Post-translational modification (PTM) may alter the MHC-binding motif or TCR contact residues in a peptide antigen, transforming the tolerance to self to autoreactivity. Mass spectrometry-based immunopeptidomics provides a valuable mechanism for identifying MHC ligands that contain PTMs and can thus provide valuable insights into pathogenesis and therapeutics of autoimmune diseases. A plethora of PTMs have been implicated in this process, and this review highlights their formation and identification.

Islet-specific CD8+ T cells gain effector function in the gut lymphoid tissues via bystander activation not molecular mimicry

Type 1 diabetes (T1D) is caused by aberrant activation of autoreactive T cells specific for the islet beta cells. How islet-specific T cells evade tolerance to become effector T cells is unknown, but it is believed that an altered gut microbiota plays a role. Possible mechanisms include bystander activation of autoreactive T cells in the gut or "molecular mimicry" from cross-reactivity between gut microbiota-derived peptides and islet-derived epitopes. To investigate these mechanisms, we use two islet-specific CD8⁺ T cell clones and the non-obese diabetic mouse model of type 1 diabetes. Both insulin-specific G9C8 cells and IGRP-specific 8.3 cells underwent early activation and proliferation in the pancreatic draining lymph nodes but not in the Peyer's patches or mesenteric lymph nodes. Mutation of the endogenous epitope for G9C8 cells abolished their CD69 upregulation and proliferation, ruling out G9C8 cell activation by a gut microbiota derived peptide and molecular mimicry. However, previously activated islet-specific effector memory cells but not naïve cells migrated into the Peyer's patches where they increased their cytotoxic function. Oral delivery of butyrate, a microbiota derived anti-inflammatory metabolite, reduced IGRP-specific cytotoxic function. Thus, while initial activation of islet-specific CD8⁺ T cells occurred in the pancreatic lymph nodes, activated cells trafficked through the gut lymphoid tissues where they gained additional effector function via non-specific bystander activation influenced by the gut microbiota.

Glutamine deamidation does not increase the immunogenicity of C-peptide in people with type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease in which the insulin-producing beta cells are destroyed. While it is clear that full-length C-peptide, derived from proinsulin, is a major antigen in human T1D it is not clear how and why C-peptide becomes a target of the autoimmune CD4⁺ T-cell responses in T1D. Neoepitopes formed by the conversion of glutamine (Q) residues to glutamic acid (E) by deamidation are central to the immune pathogenesis of coeliac disease and have been implicated in autoimmune responses in T1D. Here, we asked if the immunogenicity of full-length C-peptide, which comprises four glutamine residues, was enhanced by deamidation, which we mimicked by substituting glutamic acid for glutamine residue. First, we used a panel of 18 well characterized CD4⁺ T-cell lines specific for epitopes derived from human C-peptide. In all cases, when the substitution fell within the cognate epitope the response was diminished, or in a few cases unchanged. In contrast, when the substitution fell outside the epitope recognized by the TCR responses were unchanged or slightly augmented. Second, we compared CD4⁺ T-cell proliferation responses, against deamidated and unmodified C-peptide, in the peripheral blood of people with or without T1D using the CFSE-based proliferation assay. While, as reported previously, responses were detected to unmodified C-peptide, no deamidated C-peptide was consistently more stimulatory than native C-peptide. Overall responses were weaker to deamidated C-peptide compared to unmodified C-peptide. Hence, we conclude that deamidated C-peptide does not play a role in beta-cell autoimmunity in people with T1D.

Insulin B-chain hybrid peptides are agonists for T cells reactive to insulin B:9-23 in autoimmune diabetes

Insulin is considered to be a key antigenic target of T cells in Type 1 Diabetes (T1D) and autoimmune diabetes in the NOD mouse with particular focus on the B-chain amino acid sequence B:9-23 as the primary epitope. Our lab previously discovered that hybrid insulin peptides (HIPs), comprised of insulin C-peptide fragments fused to other β-cell granule peptides, are ligands for several pathogenic CD4 T cell clones derived from NOD mice and for autoreactive CD4 T cells from T1D patients. A subset of CD4 T cell clones from our panel react to insulin and B:9-23 but only at high concentrations of antigen. We hypothesized that HIPs might also be formed from insulin B-chain sequences covalently bound to other endogenously cleaved ß-cell proteins. We report here on the identification of a B-chain HIP, termed the 6.3HIP, containing a fragment of B:9-23 joined to an endogenously processed peptide of ProSAAS, as a strong neo-epitope for the insulin-reactive CD4 T cell clone BDC-6.3. Using an I-Ag7 tetramer loaded with the 6.3HIP, we demonstrate that T cells reactive to this B-chain HIP can be readily detected in NOD mouse islet infiltrates. This work suggests that some portion of autoreactive T cells stimulated by insulin B:9-23 may be responding to B-chain HIPs as peptide ligands.

The Contribution of Neutrophils and NETs to the Development of Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing beta cells in pancreatic islets. T lymphocytes are the claimed pathogenic effectors but abnormalities of other immune cell types, including neutrophils, also characterize T1D development. During human T1D natural history, neutrophils are reduced in the circulation, while accumulate in the pancreas where release of neutrophil extracellular traps (NETs), or NETosis, is manifest. Recent-onset T1D patients also demonstrate activated circulating neutrophils, associated with a unique neutrophil gene signature. Neutrophils can bind to platelets, leading to the formation of platelet-neutrophil aggregates (PNAs). PNAs increase in the circulation during the development of human T1D and provide a mechanism for neutrophil activation and mobilization/recruitment to the pancreas. In non-obese diabetic or NOD mice, T1D autoimmunity is accompanied by dynamic changes in neutrophil numbers, activation state, PNAs and/or NETosis/NET proteins in the circulation, pancreas and/or islets. Such properties differ between stages of T1D disease and underpin potentially indirect and direct impacts of the innate immune system in T1D pathogenesis. Supporting the potential for a pathogenic role in T1D, NETs and extracellular histones can directly damage isolated islets in vitro, a toxicity that can be prevented by small polyanions. In human T1D, NET-related damage can target the whole pancreas, including both the endocrine and exocrine components, and contribute to beta cell destruction, providing evidence for a neutrophil-associated T1D endotype. Future intervention in T1D could therefore benefit from combined strategies targeting T cells and accessory destructive elements of activated neutrophils.

Mechanisms of COVID-19 Pathogenesis in Diabetes

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, is a global pandemic impacting 254 million people in 190 countries. Comorbidities, particularly cardiovascular disease, diabetes, and hypertension, increase the risk of infection and poor outcomes. SARS-CoV-2 enters host cells through the angiotensin-converting enzyme-2 receptor, generating inflammation and cytokine storm, often resulting in multiorgan failure. The mechanisms and effects of COVID-19 on patients with high-risk diabetes are not yet completely understood. In this review, we discuss the variety of coronaviruses, structure of SARS-CoV-2, mutations in SARS-CoV-2 spike proteins, receptors associated with viral host entry, and disease progression. Furthermore, we focus on possible mechanisms of SARS-CoV-2 in diabetes, leading to inflammation and heart failure. Finally, we discuss existing therapeutic approaches, unanswered questions, and future directions.

Advances in oral peptide drug nanoparticles for diabetes mellitus treatment

Peptide drugs play an important role in diabetes mellitus treatment. Oral administration of peptide drugs is a promising strategy for diabetes mellitus because of its convenience and high patient compliance compared to parenteral administration routes. However, there are a series of formidable unfavorable conditions present in the gastrointestinal (GI) tract after oral administration, which result in the low oral bioavailability of these peptide drugs. To overcome these challenges, various nanoparticles (NPs) have been developed to improve the oral absorption of peptide drugs due to their unique in vivo properties and high design flexibility. This review discusses the unfavorable conditions present in the GI tract and provides the corresponding strategies to overcome these challenges. The review provides a comprehensive overview on the NPs that have been constructed for oral peptide drug delivery in diabetes mellitus treatment. Finally, we will discuss the rational application and give some suggestions that can be utilized for the development of oral peptide drug NPs. Our aim is to provide a systemic and comprehensive review of oral peptide drug NPs that can overcome the challenges in GI tract for efficient treatment of diabetes mellitus.

•Oral administration of peptide drugs is a promising strategy for diabetes mellitus treatment

•A series of formidable unfavorable conditions in gastrointestinal tract result in the low oral bioavailability of peptide drugs

•Nanoparticles can improve the oral bioavailability of peptide drugs

Metabolite-based dietary supplementation in human type 1 diabetes is associated with microbiota and immune modulation

BACKGROUND

Short-chain fatty acids (SCFAs) produced by the gut microbiota have beneficial anti-inflammatory and gut homeostasis effects and prevent type 1 diabetes (T1D) in mice. Reduced SCFA production indicates a loss of beneficial bacteria, commonly associated with chronic autoimmune and inflammatory diseases, including T1D and type 2 diabetes. Here, we addressed whether a metabolite-based dietary supplement has an impact on humans with T1D. We conducted a single-arm pilot-and-feasibility trial with high-amylose maize-resistant starch modified with acetate and butyrate (HAMSAB) to assess safety, while monitoring changes in the gut microbiota in alignment with modulation of the immune system status.

RESULTS

HAMSAB supplement was administered for 6 weeks with follow-up at 12 weeks in adults with long-standing T1D. Increased concentrations of SCFA acetate, propionate, and butyrate in stools and plasma were in concert with a shift in the composition and function of the gut microbiota. While glucose control and insulin requirements did not change, subjects with the highest SCFA concentrations exhibited the best glycemic control. Bifidobacterium longum, Bifidobacterium adolescentis, and vitamin B7 production correlated with lower HbA1c and basal insulin requirements. Circulating B and T cells developed a more regulatory phenotype post-intervention.

CONCLUSION

Changes in gut microbiota composition, function, and immune profile following 6 weeks of HAMSAB supplementation were associated with increased SCFAs in stools and plasma. The persistence of these effects suggests that targeting dietary SCFAs may be a mechanism to alter immune profiles, promote immune tolerance, and improve glycemic control for the treatment of T1D.

TRIAL REGISTRATION

ACTRN12618001391268. Registered 20 August 2018, https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=375792 Video Abstract.

Using the T Cell Receptor as a Biomarker in Type 1 Diabetes

T cell receptors (TCRs) are unique markers that define antigen specificity for a given T cell. With the evolution of sequencing and computational analysis technologies, TCRs are now prime candidates for the development of next-generation non-cell based T cell biomarkers, which provide a surrogate measure to assess the presence of antigen-specific T cells. Type 1 diabetes (T1D), the immune-mediated form of diabetes, is a prototypical organ specific autoimmune disease in which T cells play a pivotal role in targeting pancreatic insulin-producing beta cells. While the disease is now predictable by measuring autoantibodies in the peripheral blood directed to beta cell proteins, there is an urgent need to develop T cell markers that recapitulate T cell activity in the pancreas and can be a measure of disease activity. This review focuses on the potential and challenges of developing TCR biomarkers for T1D. We summarize current knowledge about TCR repertoires and clonotypes specific for T1D and discuss challenges that are unique for autoimmune diabetes. Ultimately, the integration of large TCR datasets produced from individuals with and without T1D along with computational 'big data' analysis will facilitate the development of TCRs as potentially powerful biomarkers in the development of T1D.

T cell receptor recognition of hybrid insulin peptides bound to HLA-DQ8

HLA-DQ8, a genetic risk factor in type I diabetes (T1D), presents hybrid insulin peptides (HIPs) to autoreactive CD4+ T cells. The abundance of spliced peptides binding to HLA-DQ8 and how they are subsequently recognised by the autoreactive T cell repertoire is unknown. Here we report, the HIP (GQVELGGGNAVEVLK), derived from splicing of insulin and islet amyloid polypeptides, generates a preferred peptide-binding motif for HLA-DQ8. HLA-DQ8-HIP tetramer⁺ T cells from the peripheral blood of a T1D patient are characterised by repeated TRBV5 usage, which matches the TCR bias of CD4+ T cells reactive to the HIP peptide isolated from the pancreatic islets of a patient with T1D. The crystal structure of three TRBV5+ TCR-HLA-DQ8-HIP complexes shows that the TRBV5-encoded TCR β-chain forms a common landing pad on the HLA-DQ8 molecule. The N- and C-termini of the HIP is recognised predominantly by the TCR α-chain and TCR β-chain, respectively, in all three TCR ternary complexes. Accordingly, TRBV5 + TCR recognition of HIP peptides might occur via a 'polarised' mechanism, whereby each chain within the αβTCR heterodimer recognises distinct origins of the spliced peptide presented by HLA-DQ8.

Proinsulin-specific T-cell responses correlate with estimated c-peptide and predict partial remission duration in type 1 diabetes

Objective

Type 1 diabetes (T1D) is an autoimmune disorder in which autoreactive T cells destroy insulin-producing β-cells. Interventions that preserve β-cell function represent a fundamental therapeutic goal in T1D and biomarkers that predict and monitor β-cell function, and changes in islet autoantigenic signatures are needed. As proinsulin and neoantigens derived from proinsulin peptides (hybrid insulin peptides, HIPs) are important T1D autoantigens, we analysed peripheral blood CD4⁺ T-cell autoantigen-specific proliferative responses and their relationship to estimated β-cell function.

Methods

We recruited 72 people with and 42 without T1D, including 17 pre-diabetic islet antibody-positive and 9 antibody-negative first-degree relatives and 16 unrelated healthy controls with T1D-risk HLA types. We estimated C-peptide level at 3-month intervals for 2 years post-diagnosis and measured CD4⁺ T-cell proliferation to proinsulin epitopes and HIPs using an optimised bioassay.

Results

We show that CD4⁺ T-cell proliferation to any islet peptide and to multiple epitopes were significantly more frequent in pre-diabetic islet antibody-positive siblings and participants with T1D ≤ 3 months of duration, than in participants with T1D > 3 months or healthy controls. Among participants with T1D and first-degree relatives, CD4⁺ T-cell proliferation occurred most frequently in response to proinsulin_33-63 (full-length C-peptide). Proinsulin_33-63-specific responses were associated with HLA-DR3-DQ2 and/or HLA-DR4/DQ8. In children with T1D, proinsulin_33-63-specific T-cell proliferation positively associated with concurrent estimated C-peptide and predicted survival in honeymoon.

Conclusion

CD4⁺ T-cell proliferative responses to proinsulin-containing autoantigens are common before and immediately after diagnosis of T1D but decline thereafter. Proinsulin_33-63-specific CD4⁺ T-cell response is a novel marker of estimated residual endogenous β-cell function and predicts a better 2-year disease outcome.

T-cell responses to hybrid insulin peptides prior to type 1 diabetes development

T-cell responses to posttranslationally modified self-antigens are associated with many autoimmune disorders. In type 1 diabetes, hybrid insulin peptides (HIPs) are implicated in the T-cell-mediated destruction of insulin-producing β-cells within pancreatic islets. The natural history of the disease is such that it allows for the study of T-cell reactivity prior to the onset of clinical symptoms. We hypothesized that CD4 T-cell responses to posttranslationally modified islet peptides precedes diabetes onset. In a cohort of genetically at-risk individuals, we measured longitudinal T-cell responses to native insulin and hybrid insulin peptides. Both proinflammatory (interferon-γ) and antiinflammatory (interluekin-10) cytokine responses to HIPs were more robust than those to native peptides, and the ratio of such responses oscillated between pro- and antiinflammatory over time. However, individuals who developed islet autoantibodies or progressed to clinical type 1 diabetes had predominantly inflammatory T-cell responses to HIPs. Additionally, several HIP T-cell responses correlated to worsening measurements of blood glucose, highlighting the relevance of T-cell responses to posttranslationally modified peptides prior to autoimmune disease development.

Diagnostic value of combined islet antigen-reactive T cells and autoantibodies assays for type 1 diabetes mellitus

AIMS/INTRODUCTION

Type 1 diabetes mellitus is a T cell-mediated autoimmune disease. However, the determination of the autoimmune status of type 1 diabetes mellitus relies on islet autoantibodies (Abs), as T-cell assay is not routinely carried out. This study aimed to investigate the diagnostic value of combined assay of islet antigen-specific T cells and Abs in type 1 diabetes mellitus patients.

MATERIALS AND METHODS

A total of 54 patients with type 1 diabetes mellitus and 56 healthy controls were enrolled. Abs against glutamic acid decarboxylase (GAD), islet antigen-2 and zinc transporter 8 were detected by radioligand assay. Interferon-γ-secreting T cells responding to glutamic acid decarboxylase 65 and C-peptide (CP) were measured by enzyme-linked immunospot.

RESULTS

The positive rate for T-cell responses was significantly higher in patients with type 1 diabetes mellitus than that in controls (P < 0.001). The combined positive rate of Abs and T-cell assay was significantly higher than that of Abs assay alone (85.2% vs 64.8%, P = 0.015). A significant difference in fasting CP level was found between the T+ and T- groups (0.07 ± 0.05 vs 0.11 ± 0.09 nmol/L, P = 0.033). Furthermore, levels of fasting CP and postprandial CP were both lower in the Ab- T+ group than the Ab- T- group (fasting CP 0.06 ± 0.05 vs 0.16 ± 0.12 nmol/L, P = 0.041; postprandial CP 0.12 ± 0.13 vs 0.27 ± 0.12 nmol/L, P = 0.024).

CONCLUSIONS

Enzyme-linked immunospot assays in combination with Abs detection could improve the diagnostic sensitivity of autoimmune diabetes.

Persistence of Coxsackievirus B4 in Pancreatic β Cells Disturbs Insulin Maturation, Pattern of Cellular Proteins, and DNA Methylation

Coxsackievirus-B4 (CV-B4) can persist in pancreatic cell lines and impair the phenoytpe and/or gene expressions in these cells; however, the models used to study this phenomenon did not produce insulin. Therefore, we investigated CV-B4 persistence and its consequences in insulin-producing pancreatic β cells. The insulin-secreting rat β cell line, INS-1, was infected with CV-B4. After lysis of a large part of the cell layer, the culture was still maintained and no additional cytopathic effect was observed. The amount of insulin in supernatants of cell cultures persistently infected with CV-B4 was not affected by the infection; in fact, a larger quantity of proinsulin was found. The mRNA expression of pro-hormone convertase 2, an enzyme involved in the maturation of proinsulin into insulin and studied using real-time reverse transcription-polymerase chain reaction, was inhibited in infected cultures. Further, the pattern of 47 cell proteins analyzed using Shotgun mass spectrometry was significantly modified. The DNA of persistently infected cell cultures was hypermethylated unlike that of controls. The persistent infection of INS-1 cells with CV-B4 had a deep impact on these cells, especially on insulin metabolism. Cellular changes caused by persistent CV-B4 infection of β cells can play a role in type 1 diabetes pathogenesis.

Proinsulin-Reactive CD4 T Cells in the Islets of Type 1 Diabetes Organ Donors

Proinsulin is an abundant protein that is selectively expressed by pancreatic beta cells and has been a focus for development of antigen-specific immunotherapies for type 1 diabetes (T1D). In this study, we sought to comprehensively evaluate reactivity to preproinsulin by CD4 T cells originally isolated from pancreatic islets of organ donors having T1D. We analyzed 187 T cell receptor (TCR) clonotypes expressed by CD4 T cells obtained from six T1D donors and determined their response to 99 truncated preproinsulin peptide pools, in the presence of autologous B cells. We identified 14 TCR clonotypes from four out of the six donors that responded to preproinsulin peptides. Epitopes were found across all of proinsulin (insulin B-chain, C-peptide, and A-chain) including four hot spot regions containing peptides commonly targeted by TCR clonotypes derived from multiple T1D donors. Of importance, these hot spots overlap with peptide regions to which CD4 T cell responses have previously been detected in the peripheral blood of T1D patients. The 14 TCR clonotypes recognized proinsulin peptides presented by various HLA class II molecules, but there was a trend for dominant restriction with HLA-DQ, especially T1D risk alleles DQ8, DQ2, and DQ8-trans. The characteristics of the tri-molecular complex including proinsulin peptide, HLA-DQ molecule, and TCR derived from CD4 T cells in islets, provides an essential basis for developing antigen-specific biomarkers as well as immunotherapies.

Generation of self-reactive, shared T-cell receptor α chains in the human thymus

The T-cell receptor (TCR) repertoire is generated in a semistochastic process of gene recombination and pairing of TCRα to TCRβ chains with the estimated total TCR diversity of >10⁸. Despite this high diversity, similar or identical TCR chains are found to recur in immune responses. Here, we analyzed the thymic generation of TCR sequences previously associated with recognition of self- and nonself-antigens, represented by sequences associated with autoimmune diabetes and HIV, respectively. Unexpectedly, in the CD4⁺ compartment TCRα chains associated with the recognition of self-antigens were generated in significantly higher numbers than TCRα chains associated with the recognition of nonself-antigens. The analysis of the circulating repertoire further showed that these chains are not lost in negative selection nor predominantly converted to the regulatory T-cell lineage. The high abundance of self-reactive TCRα chains in multiple individuals suggests that the human thymus has a predilection to generate self-reactive TCRα chains independently of the HLA-type and that the individual risk of autoimmunity may be modulated by the TCRβ repertoire associated with these chains.

Insulin's other life: an autoantigen in type 1 diabetes

One hundred years ago, Frederick Banting, John Macleod, Charles Best and James Collip, and their collaborators, discovered insulin. This discovery paved the way to saving countless lives and ushered in the "Insulin Era." Since the discovery of insulin, we have made enormous strides in understanding its role in metabolism and diabetes. Insulin has played a dramatic role in the treatment of people with diabetes; particularly type 1 diabetes (T1D). Insulin replacement is a life-saving therapy for people with T1D and some with type 2 diabetes. T1D is an autoimmune disease caused by the T-cell-mediated destruction of the pancreatic insulin-producing beta cells that leads to a primary insulin deficiency. It has become increasingly clear that insulin, and its precursors preproinsulin (PPI) and proinsulin (PI), can play another role-not as a hormone but as an autoantigen in T1D. Here we review the role played by the products of the INS gene as autoantigens in people with T1D. From many elegant animal studies, it is clear that T-cell responses to insulin, PPI and PI are essential for T1D to develop. Here we review the evidence that autoimmune responses to insulin and PPI arise in people with T1D and discuss the recently described neoepitopes derived from the products of the insulin gene. Finally, we look forward to new approaches to deliver epitopes derived from PPI, PI and insulin that may allow immune tolerance to pancreatic beta cells to be restored in people with, or at risk of, T1D.

The relationship between different C-peptide level and insulin dose of insulin pump

Background

This study aims to explore the insulin requirement profiles, and analyze the related factors of type-2 diabetes mellitus (T2DM) with different C-peptide levels on insulin pump therapy.

Methods

A retrospective study was conducted on 271 T2DM patients treated with insulin pumps from 2016 to 2018. These patients were divided into groups according to the ratio of C-peptide at 2 h after meals to fasting C-peptide (C₂h/C₀), and the dosage of insulin and influencing factors were analyzed.

Results

In comparing group A (C_2h/C₀ < 2.5) with group B (C_2h/C₀ ≥ 2.5), the percentage of the base amount in total (%TBa, 0.50 ± 0.06) in group A was higher than that in group B (0.48 ± 0.05) (P < 0.05). Furthermore, there was a correlation between C_2h/C₀ and waist circumference, HbA1c, Fasting Plasma Glucose (FPG) and Blood glucose 2 h after meal (2hPG) (r = −0.137, −0.154, −0.471, and −0.172; all, P < 0.05). The multiple linear regression analysis revealed that BMI and FPG were independent factors of %TBa (β′ = 0.124 and 0.144; all, P < 0.05), and BMI and FPG were independent factors of C_2h/C₀ (β′ = −0.134 and −0.502; all, P < 0.05).

Conclusions

The basal premeal dose ratio of T2DM with different C-peptide levels differs during intensive insulin pump therapy. Parameters that indicate the glycemic control and β-cell function should be taken into consideration for total insulin requirements.

Microneedles for painless transdermal immunotherapeutic applications

Immunotherapy has recently garnered plenty of attention to improve the clinical outcomes in the treatment of various diseases. However, owing to the dynamic nature of the immune system, this approach has often been challenged by concerns regarding the lack of adequate long-term responses in patients. The development of microneedles (MNs) has resulted in the improvement and expansion of immuno-reprogramming strategies due to the housing of high accumulation of dendritic cells, macrophages, lymphocytes, and mast cells in the dermis layer of the skin. In addition, MNs possess many outstanding properties, such as the ability for the painless traverse of the stratum corneum, minimal invasiveness, facile fabrication, excellent biocompatibility, convenient administration, and bypassing the first pass metabolism that allows direct translocation of therapeutics into the systematic circulation. These advantages make MNs excellent candidates for the delivery of immunological biomolecules to the dermal antigen-presenting cells in the skin with the aim of vaccinating or treating different diseases, such as cancer and autoimmune disorders, with minimal invasiveness and side effects. This review discusses the recent advances in engineered MNs and tackles limitations relevant to traditional immunotherapy of various hard-to-treat diseases.

Optimization of a Method to Detect Autoantigen-Specific T-Cell Responses in Type 1 Diabetes

The development of tolerizing therapies aiming to inactivate autoreactive effector T-cells is a promising therapeutic approach to control undesired autoimmune responses in human diseases such as Type 1 Diabetes (T1D). A critical issue is a lack of sensitive and reproducible methods to analyze antigen-specific T-cell responses, despite various attempts. We refined a proliferation assay using the fluorescent dye 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) to detect responding T-cells, highlighting the fundamental issues to be taken into consideration to monitor antigen-specific responses in patients with T1D. The critical elements that maximize detection of antigen-specific responses in T1D are reduction of blood storage time, standardization of gating parameters, titration of CFSE concentration, selecting the optimal CFSE staining duration and the duration of T-cell stimulation, and freezing in medium containing human serum. Optimization of these elements enables robust, reproducible application to longitudinal cohort studies or clinical trial samples in which antigen-specific T-cell responses are relevant, and adaptation to other autoimmune diseases.

A Question of Tolerance-Antigen-Specific Immunotherapy for Type 1 Diabetes

PURPOSE OF REVIEW

Antigen-specific immunotherapy (ASI) is a long sought-after goal for type 1 diabetes (T1D), with the potential of greater long-term safety than non-specific immunotherapy. We review the most recent advances in identification of target islet epitopes, delivery platforms and the ongoing challenges.

RECENT FINDINGS

It is now recognised that human proinsulin contains a hotspot of epitopes targeted in people with T1D. Beta-cell neoantigens are also under investigation as ASI target epitopes. Consideration of the predicted HLA-specificity of the target antigen for subject selection is now being incorporated into trial design. Cell-free ASI approaches delivering antigen with or without additional immunomodulatory agents can induce antigen-specific regulatory T cell responses, including in patients and many novel nanoparticle-based platforms are under development. ASI for T1D is rapidly advancing with a number of modalities currently being trialled in patients and many more under development in preclinical models.

Specificity of the T Cell Response to Protein Biopharmaceuticals

The anti-drug antibody (ADA) response is an undesired humoral response raised against protein biopharmaceuticals (BPs) which can dramatically disturb their therapeutic properties. One particularity of the ADA response resides in the nature of the immunogens, which are usually human(ized) proteins and are therefore expected to be tolerated. CD4 T cells initiate, maintain and regulate the ADA response and are therefore key players of this immune response. Over the last decade, advances have been made in characterizing the T cell responses developed by patients treated with BPs. Epitope specificity and phenotypes of BP-specific T cells have been reported and highlight the effector and regulatory roles of T cells in the ADA response. BP-specific T cell responses are assessed in healthy subjects to anticipate the immunogenicity of BP prior to their testing in clinical trials. Immunogenicity prediction, also called preclinical immunogenicity assessment, aims at identifying immunogenic BPs and immunogenic BP sequences before any BP injection in humans. All of the approaches that have been developed to date rely on the detection of BP-specific T cells in donors who have never been exposed to BPs. The number of BP-specific T cells circulating in the blood of these donors is therefore limited. T cell assays using cells collected from healthy donors might reveal the weak tolerance induced by BPs, whose endogenous form is expressed at a low level. These BPs have a complete human sequence, but the level of their endogenous form appears insufficient to promote the negative selection of autoreactive T cell clones. Multiple T cell epitopes have also been identified in therapeutic antibodies and some other BPs. The pattern of identified T cell epitopes differs across the antibodies, notwithstanding their humanized, human or chimeric nature. However, in all antibodies, the non-germline amino acid sequences mainly found in the CDRs appear to be the main driver of immunogenicity, provided they can be presented by HLA class II molecules. Considering the fact that the BP field is expanding to include new formats and gene and cell therapies, we face new challenges in understanding and mastering the immunogenicity of new biological products.

Effect of dietary anthocyanins on biomarkers of glycemic control and glucose metabolism: A systematic review and meta-analysis of randomized clinical trials

Anthocyanins, as natural food colorants, are bioactive substances with several health advantages. In this research, the effects of dietary anthocyanins on biomarkers of glycemic control and glucose metabolism was evaluated through a meta-analysis. The results revealed a significant reduction in levels of fasting blood sugar (FBS; -2.70 mg/dl, 95% CI: -4.70 to -1.31; P < 0.001), 2-h postprandial glucose (2-h PPG; -11.1 mg/dl, 95% CI: -18.7 to -3.48; P = 0.004), glycated hemoglobin (HbA1c; -11.1 mg/dl, 95% CI: -18.7 to -3.48; P = 0.004), homeostasis model assessment of insulin resistance (HOMA-IR; -0.54, 95% CI: -0.94 to -0.14; P = 0.008), resistin (-1.23 µg/l, 95% CI: -2.40 to -0.05; P = 0.041), and plasminogen activator inhibitor-1 (PAI-1; -5.09 µg/l, 95% CI: -9.45 to -0.73; P = 0.022) following administration of anthocyanins, whilst changes in the levels of fasting insulin (0.33 mU/l, 95% CI: -0.18 to 0.85; P = 0.207) and C-peptide (-0.02 µg/l, 95 %CI: -0.20 to 0.16; P = 0.816) was not statistically significant. Consumption of anthocyanins for >8 weeks and at doses >300 mg/day significantly reduced levels of FBS, 2-h PPG, HbA1c, and HOMA-IR. Moreover, anthocyanins administration reduced the levels of FBS, 2-h PPG, HbA1c, and HOMA-IR in type 2 diabetic subjects and HOMA-IR in overweight/obese individuals. Overall, dietary anthocyanins can be used as an adjuvant therapy to improve biomarkers of glycemic control and glucose metabolism specially in diabetic subjects.

Maternal Type 1 Diabetes Reduces Autoantigen-Responsive CD4+ T Cells in Offspring

Autoimmunity against pancreatic β-cell autoantigens is a characteristic of childhood type 1 diabetes (T1D). Autoimmunity usually appears in genetically susceptible children with the development of autoantibodies against (pro)insulin in early childhood. The offspring of mothers with T1D are protected from this process. The aim of this study was to determine whether the protection conferred by maternal T1D is associated with improved neonatal tolerance against (pro)insulin. Consistent with improved neonatal tolerance, the offspring of mothers with T1D had reduced cord blood CD4⁺ T-cell responses to proinsulin and insulin, a reduction in the inflammatory profile of their proinsulin-responsive CD4⁺ T cells, and improved regulation of CD4⁺ T cell responses to proinsulin at 9 months of age, as compared with offspring with a father or sibling with T1D. Maternal T1D was also associated with a modest reduction in CpG methylation of the INS gene in cord blood mononuclear cells from offspring with a susceptible INS genotype. Our findings support the concept that a maternal T1D environment improves neonatal immune tolerance against the autoantigen (pro)insulin.

Characterization of Proinsulin T Cell Epitopes Restricted by Type 1 Diabetes-Associated HLA Class II Molecules

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin-producing β cells within the pancreas are destroyed. Identification of target Ags and epitopes of the β cell-reactive T cells is important both for understanding T1D pathogenesis and for the rational development of Ag-specific immunotherapies for the disease. Several studies suggest that proinsulin is an early and integral target autoantigen in T1D. However, proinsulin epitopes recognized by human CD4⁺ T cells have not been comprehensively characterized. Using a dye dilution-based T cell cloning method, we generated and characterized 24 unique proinsulin-specific CD4⁺ T cell clones from the peripheral blood of 17 individuals who carry the high-risk DR3-DQ2 and/or DR4-DQ8 HLA class II haplotypes. Some of the clones recognized previously reported DR4-restricted epitopes within the C-peptide (C25-35) or A-chain (A1-15) of proinsulin. However, we also characterized DR3-restricted epitopes within both the B-chain (B16-27 and B22-C3) and C-peptide (C25-35). Moreover, we identified DQ2-restricted epitopes within the B-chain and several DQ2- or DQ8-restricted epitopes within the C-terminal region of C-peptide that partially overlap with previously reported DQ-restricted epitopes. Two of the DQ2-restricted epitopes, B18-26 and C22-33, were shown to be naturally processed from whole human proinsulin. Finally, we observed a higher frequency of CDR3 sequences matching the TCR sequences of the proinsulin-specific T cell clones in pancreatic lymph node samples compared with spleen samples. In conclusion, we confirmed several previously reported epitopes but also identified novel (to our knowledge) epitopes within proinsulin, which are presented by HLA class II molecules associated with T1D risk.

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.

Introducing the Endotype Concept to Address the Challenge of Disease Heterogeneity in Type 1 Diabetes

The clinical diagnosis of new-onset type 1 diabetes has, for many years, been considered relatively straightforward. Recently, however, there is increasing awareness that within this single clinical phenotype exists considerable heterogeneity: disease onset spans the complete age range; genetic susceptibility is complex; rates of progression differ markedly, as does insulin secretory capacity; and complication rates, glycemic control, and therapeutic intervention efficacy vary widely. Mechanistic and immunopathological studies typically show considerable patchiness across subjects, undermining conclusions regarding disease pathways. Without better understanding, type 1 diabetes heterogeneity represents a major barrier both to deciphering pathogenesis and to the translational effort of designing, conducting, and interpreting clinical trials of disease-modifying agents. This realization comes during a period of unprecedented change in clinical medicine, with increasing emphasis on greater individualization and precision. For complex disorders such as type 1 diabetes, the option of maintaining the "single disease" approach appears untenable, as does the notion of individualizing each single patient's care, obliging us to conceptualize type 1 diabetes less in terms of phenotypes (observable characteristics) and more in terms of disease endotypes (underlying biological mechanisms). Here, we provide our view on an approach to dissect heterogeneity in type 1 diabetes. Using lessons from other diseases and the data gathered to date, we aim to delineate a roadmap through which the field can incorporate the endotype concept into laboratory and clinical practice. We predict that such an effort will accelerate the implementation of precision medicine and has the potential for impact on our approach to translational research, trial design, and clinical management.

Replacing murine insulin 1 with human insulin protects NOD mice from diabetes

Type 1, or autoimmune, diabetes is caused by the T-cell mediated destruction of the insulin-producing pancreatic beta cells. Non-obese diabetic (NOD) mice spontaneously develop autoimmune diabetes akin to human type 1 diabetes. For this reason, the NOD mouse has been the preeminent murine model for human type 1 diabetes research for several decades. However, humanized mouse models are highly sought after because they offer both the experimental tractability of a mouse model and the clinical relevance of human-based research. Autoimmune T-cell responses against insulin, and its precursor proinsulin, play central roles in the autoimmune responses against pancreatic beta cells in both humans and NOD mice. As a first step towards developing a murine model of the human autoimmune response against pancreatic beta cells we set out to replace the murine insulin 1 gene (Ins1) with the human insulin gene (Ins) using CRISPR/Cas9. Here we describe a NOD mouse strain that expresses human insulin in place of murine insulin 1, referred to as HuPI. HuPI mice express human insulin, and C-peptide, in their serum and pancreata and have normal glucose tolerance. Compared with wild type NOD mice, the incidence of diabetes is much lower in HuPI mice. Only 15–20% of HuPI mice developed diabetes after 300 days, compared to more than 60% of unmodified NOD mice. Immune-cell infiltration into the pancreatic islets of HuPI mice was not detectable at 100 days but was clearly evident by 300 days. This work highlights the feasibility of using CRISPR/Cas9 to create mouse models of human diseases that express proteins pivotal to the human disease. Furthermore, it reveals that even subtle changes in proinsulin protect NOD mice from diabetes.

Induced pluripotent stem cell macrophages present antigen to proinsulin-specific T cell receptors from donor-matched islet-infiltrating T cells in type 1 diabetes

AIMS/HYPOTHESIS

Type 1 diabetes is an autoimmune disorder characterised by loss of insulin-producing beta cells of the pancreas. Progress in understanding the cellular and molecular mechanisms underlying the human disease has been hampered by a dearth of appropriate human experimental models. We previously reported the characterisation of islet-infiltrating CD4⁺ T cells from a deceased organ donor who had type 1 diabetes.

METHODS

Induced pluripotent stem cell (iPSC) lines derived from the above donor were differentiated into CD14⁺ macrophages and tested for their capacity to present antigen to T cell receptors (TCRs) derived from islet-infiltrating CD4⁺ T cells from the same donor.

RESULTS

The iPSC macrophages displayed typical macrophage morphology, surface markers (CD14, CD86, CD16 and CD11b) and were phagocytic. In response to IFNγ treatment, iPSC macrophages upregulated expression of HLA class II, a characteristic that correlated with their capacity to present epitopes derived from proinsulin C-peptide to a T cell line expressing TCRs derived from islet-infiltrating CD4⁺ T cells of the original donor. T cell activation was specifically blocked by anti-HLA-DQ antibodies but not by antibodies directed against HLA-DR.

CONCLUSIONS/INTERPRETATION

This study provides a proof of principle for the use of iPSC-derived immune cells for modelling key cellular interactions in human type 1 diabetes.

Proinsulin peptide promotes autoimmune diabetes in a novel HLA-DR3-DQ2-transgenic murine model of spontaneous disease

AIMS/HYPOTHESIS

The molecular basis for the pathological impact of specific HLA molecules on autoimmune diseases such as type 1 diabetes remains unclear. Recent natural history studies in children have indicated a link between specific HLA genotypes and the first antigenic target against which immune responses develop. We set out to examine this link in vivo by exploring the diabetogenicity of islet antigens on the background of a common diabetes-associated HLA haplotype.

METHODS

We generated a novel HLA-transgenic mouse model that expresses high-risk genes for type 1 diabetes (DRB1*03:01-DQA1*05:01-DQB1*02:01) as well as human CD80 under the rat insulin promoter and human CD4, on a C57BL/6 background. Adjuvanted antigen priming was used to reveal the diabetogenicity of candidate antigens and peptides.

RESULTS

HLA-DR3-DQ2⁺huCD4⁺IA/IE^-/-RIP.B7.1⁺ mice spontaneously developed autoimmune diabetes (incidence 46% by 35 weeks of age), accompanied by numerous hallmarks of human type 1 diabetes (autoantibodies against GAD65 and proinsulin; pancreatic islet infiltration by CD4⁺, CD8⁺ B220⁺, CD11b⁺ and CD11c⁺ immune cells). Disease was markedly accelerated and had deeper penetrance after adjuvanted antigen priming with proinsulin (mean onset 11 weeks and incidence 100% by 20 weeks post challenge). Moreover, the diabetogenic effect of proinsulin located to the 15-residue B29-C11 region.

CONCLUSIONS/INTERPRETATION

Our study identifies a proinsulin-derived peptide region that is highly diabetogenic on the HLA-DR3-DQ2 background using an in vivo model. This approach and the peptide region identified may have wider implications for future studies of human type 1 diabetes.

Clinical manifestation and islet β-cell function of a subtype of latent autoimmune diabetes in adults (LADA): positive for T cell responses in phenotypic type 2 diabetes

AIMS

To investigate the possibility of identifying a subtype of latent autoimmune diabetes in adults (LADA), T-LADA (T cell responses-positive and autoantibody-negative) from patients with phenotypic type 2 diabetes (T2D) by enzyme-linked immunospot (ELISPOT).

METHODS

Eighty-two patients with phenotypic T2D were studied. Autoantibodies against glutamic acid decarboxylase (GAD), insulinoma-associated protein-2 and zinc transporter 8 were measured by radioligand assay. Thirty-nine Ab⁺ and 43 Ab^- patients with phenotypic T2D were enrolled for T cell assay of responses to GAD65 and C-peptide antigen by ELISPOT.

RESULTS

(1) Eleven of 43 Ab^- participants with phenotypic T2D were demonstrated interferon (IFN)-γ secreting T cells by ELISPOT, while 13 of 39 Ab⁺ patients with phenotypic T2D were positive for T cells responses to islet antigens. (2) The onset ages of T cell⁺ people with phenotypic T2D were younger than that of T cell^- individuals (42.7 ± 9.3 vs. 48.2 ± 10.2 years, P = 0.025). Moreover, T cell⁺ patients with T2D displayed a significantly lower fasting C-peptide (FCP) compared with T cell^- participants [0.28 (0.02-0.84) vs. 0.42 (0.05-1.26) nmol/L, P = 0.013]. (3) Ab^-T⁺ group had a significantly lower FCP compared with Ab^-T^- group [0.31 (0.13-0.84) vs. 0.51 (0.07-1.26) nmol/L, P = 0.023].

CONCLUSIONS

By measuring T cell responses to islet antigens in patients with phenotypic T2D, we identified a specific subtype of LADA who may be associated with worse basal β-cell function than classic T2D (Ab^-T^-).

Position β57 of I-Ag7 controls early anti-insulin responses in NOD mice, linking an MHC susceptibility allele to type 1 diabetes onset

The class II region of the major histocompatibility complex (MHC) locus is the main contributor to the genetic susceptibility to type 1 diabetes (T1D). The loss of an aspartic acid at position 57 of diabetogenic HLA-DQβ chains supports this association; this single amino acid change influences how TCRs recognize peptides in the context of HLA-DQ8 and I-Ag7 using a mechanism termed the P9 switch. Here, we built register-specific insulin peptide MHC tetramers to examine CD4+ T cell responses to Ins12-20 and Ins13-21 peptides during the early prediabetic phase of disease in nonobese diabetic (NOD) mice. A single-cell analysis of anti-insulin CD4+ T cells performed in 6- and 12-week-old NOD mice revealed tissue-specific gene expression signatures. TCR signaling and clonal expansion were found only in the islets of Langerhans and produced either classical TH1 differentiation or an unusual Treg phenotype, independent of TCR usage. The early phase of the anti-insulin response was dominated by T cells specific for Ins12-20, the register that supports a P9 switch mode of recognition. The presence of the P9 switch was demonstrated by TCR sequencing, reexpression, mutagenesis, and functional testing of TCRαβ pairs in vitro. Genetic correction of the I-Aβ57 mutation in NOD mice resulted in the disappearance of D/E residues in the CDR3β of anti-Ins12-20 T cells. These results provide a mechanistic molecular explanation that links the characteristic MHC class II polymorphism of T1D with the recognition of islet autoantigens and disease onset.

Hybrid insulin peptides are neo-epitopes for CD4 T cells in autoimmune diabetes

PURPOSE OF REVIEW

The current review covers recent advances in our knowledge of the newest autoantigen neo-epitopes in type 1 diabetes (T1D): hybrid insulin peptides or HIPs. These ligands for autoreactive T cells are formed by peptide fusion, a novel posttranslational modification process that we first reported in 2016.

RECENT FINDINGS

Two major HIPs in the nonobese diabetic mouse model, ligands for diabetogenic CD4 T-cell clones, have been incorporated into tetramers and used to track HIP-reactive T cells during progression of disease. HIPs have also been used in strategies for induction of antigen-specific tolerance and show promise for delaying or reversing disease in the nonobese diabetic mouse. Importantly, CD4 T cells reactive to various HIPs have been detected in the islets and peripheral blood mononuclear cell of T1D patients and newly developed human T-cell clones are being employed to gather more data on the phenotype and function of HIP-reactive T cells in patients.

SUMMARY

These new hybrid insulin peptide epitopes may provide the basis for establishing autoreactive T cells as biomarkers of disease and as potential tolerogens for treatment of T1D.

Standardizing T-Cell Biomarkers in Type 1 Diabetes: Challenges and Recent Advances

Type 1 diabetes (T1D) results from the progressive destruction of pancreatic β-cells in a process mediated primarily by T lymphocytes. The T1D research community has made dramatic progress in understanding the genetic basis of the disease as well as in the development of standardized autoantibody assays that inform both disease risk and progression. Despite these advances, there remains a paucity of robust and accepted biomarkers that can effectively inform on the activity of T cells during the natural history of the disease or in response to treatment. In this article, we discuss biomarker development and validation efforts for evaluation of T-cell responses in patients with and at risk for T1D as well as emerging technologies. It is expected that with systematic planning and execution of a well-conceived biomarker development pipeline, T-cell-related biomarkers would rapidly accelerate disease progression monitoring efforts and the evaluation of intervention therapies in T1D.

A Novel Liposome Formulation Carrying Both an Insulin Peptide and a Ligand for Invariant Natural Killer T Cells Induces Accumulation of Regulatory T Cells to Islets in Nonobese Diabetic Mice

Type 1 diabetes (T1D) is an autoimmune disease caused by the destruction of pancreatic β cells by autoantigen-reactive diabetogenic cells. Antigen-specific therapies using islet autoantigens for restoring immune tolerance have emerged as promising approaches for the treatment of T1D but have been unsuccessful in humans. Herein, we report that RGI-3100-iB, a novel liposomal formulation carrying both α-galactosylceramide (α-GalCer), which is a representative ligand for invariant natural killer T (iNKT) cells, and insulin B chain 9-23 peptide, which is an epitope for CD4⁺ T cells, could induce the accumulation of regulatory T cells (Tregs) in islets in a peptide-dependent manner, followed by the remarkable prevention of diabetes onset in nonobese diabetic (NOD) mice. While multiple administrations of a monotherapy using either α-GalCer or insulin B peptide in a liposomal formulation was confirmed to delay/prevent T1D in NOD mice, RGI-3100-iB synergistically enhanced the prevention effect of each monotherapy and alleviated insulitis in NOD mice. Immunopathological analysis showed that Foxp3⁺ Tregs accumulated in the islets in RGI-3100-iB-treated mice. Cotransfer of diabetogenic T cells and splenocytes of NOD mice treated with RGI-3100-iB, but not liposomal α-GalCer encapsulating an unrelated peptide, to NOD-SCID mice resulted in the prevention of diabetes and elevation of Foxp3 mRNA expression in the islets. These data indicate that the migration of insulin B-peptide-specific Tregs to islet of NOD mice that are involved in the suppression of pathogenic T cells related to diabetes onset and progression could be enhanced by the administration of liposomes containing α-GalCer and insulin B peptide.