Pro- and anti-inflammatory cytokine production by autoimmune T cells against preproinsulin in HLA-DRB1*04, DQ8 Type 1 diabetes

Immunopeptidomic Analysis Reveals That Deamidated HLA-bound Peptides Arise Predominantly from Deglycosylated Precursors

The presentation of post-translationally modified (PTM) peptides by cell surface HLA molecules has the potential to increase the diversity of targets for surveilling T cells. Although immunopeptidomics studies routinely identify thousands of HLA-bound peptides from cell lines and tissue samples, in-depth analyses of the proportion and nature of peptides bearing one or more PTMs remains challenging. Here we have analyzed HLA-bound peptides from a variety of allotypes and assessed the distribution of mass spectrometry-detected PTMs, finding deamidation of asparagine or glutamine to be highly prevalent. Given that asparagine deamidation may arise either spontaneously or through enzymatic reaction, we assessed allele-specific and global motifs flanking the modified residues. Notably, we found that the N-linked glycosylation motif NX(S/T) was highly abundant across asparagine-deamidated HLA-bound peptides. This finding, demonstrated previously for a handful of deamidated T cell epitopes, implicates a more global role for the retrograde transport of nascently N-glycosylated polypeptides from the ER and their subsequent degradation within the cytosol to form HLA-ligand precursors. Chemical inhibition of Peptide:N-Glycanase (PNGase), the endoglycosidase responsible for the removal of glycans from misfolded and retrotranslocated glycoproteins, greatly reduced presentation of this subset of deamidated HLA-bound peptides. Importantly, there was no impact of PNGase inhibition on peptides not containing a consensus NX(S/T) motif. This indicates that a large proportion of HLA-I bound asparagine deamidated peptides are generated from formerly glycosylated proteins that have undergone deglycosylation via the ER-associated protein degradation (ERAD) pathway. The information herein will help train deamidation prediction models for HLA-peptide repertoires and aid in the design of novel T cell therapeutic targets derived from glycoprotein antigens.

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.

DRB4*01:01 Has a Distinct Motif and Presents a Proinsulin Epitope That Is Recognized in Subjects with Type 1 Diabetes

DRB4*01:01 (DRB4) is a secondary HLA-DR product that is part of the high-risk DR4/DQ8 haplotype that is associated with type 1 diabetes (T1D). DRB4 shares considerable homology with HLA-DR4 alleles that predispose to autoimmunity, including DRB1*04:01 and DRB1*04:04. However, the DRB4 protein sequence includes distinct residues that would be expected to alter the characteristics of its binding pockets. To identify high-affinity peptides that are recognized in the context of DRB4, we used an HLA class II tetramer-based approach to identify epitopes within multiple viral Ags. We applied a similar approach to identify antigenic sequences within glutamic acid decarboxylase 65 and pre-proinsulin that are recognized in the context of DRB4. Seven sequences were immunogenic, eliciting high-affinity T cell responses in DRB4⁺ subjects. DRB1*04:01-restricted responses toward many of these peptides have been previously described, but responses to a novel pre-proinsulin 9-28 peptide were commonly observed in subjects with T1D. Furthermore, T cells that recognized this peptide in the context of DRB4 were present at significantly higher frequencies in patients with T1D than in healthy controls, implicating this as a disease-relevant specificity that may contribute to the breakdown of β cell tolerance in genetically susceptible individuals. We then deduced a DRB4 motif and confirmed its key features through structural modeling. This modeling suggested that the core epitope within the pre-proinsulin 9-28 peptide has a somewhat unusual binding motif, with tryptophan in the fourth binding pocket of DRB4, perhaps influencing the availability of this complex for T cell selection.

The Clinical Course of Patients with Preschool Manifestation of Type 1 Diabetes Is Independent of the HLA DR-DQ Genotype

Introduction: Major histocompatibility complex class II genes are considered major genetic risk factors for autoimmune diabetes. We analysed Human Leukocyte Antigen (HLA) DR and DQ haplotypes in a cohort with early-onset (age < 5 years), long term type 1 diabetes (T1D) and explored their influence on clinical and laboratory parameters. Methods: Intermediate resolution HLA-DRB1, DQA1 and DQB1 typing was performed in 233 samples from the German Paediatric Diabetes Biobank and compared with a local control cohort of 19,544 cases. Clinical follow-up data of 195 patients (diabetes duration 14.2 ± 2.9 years) and residual C-peptide levels were compared between three HLA risk groups using multiple linear regression analysis. Results: Genetic variability was low, 44.6% (104/233) of early-onset T1D patients carried the highest-risk genotype HLA-DRB1*03:01-DQA1*05:01-DQB1*02:01/DRB1*04-DQA1*03:01-DQB1*03:02 (HLA-DRB1*04 denoting 04:01/02/04/05), and 231 of 233 individuals carried at least one of six risk haplotypes. Comparing clinical data between the highest (n = 83), moderate (n = 106) and low risk (n = 6) genotypes, we found no difference in age at diagnosis (mean age 2.8 ± 1.1 vs. 2.8 ± 1.2 vs. 3.2 ± 1.5 years), metabolic control, or frequency of associated autoimmune diseases between HLA risk groups (each p > 0.05). Residual C-peptide was detectable in 23.5% and C-peptide levels in the highest-risk group were comparable to levels in moderate to high risk genotypes. Conclusion: In this study, we saw no evidence for a different clinical course of early-onset T1D based on the HLA genotype within the first ten years after manifestation.

Narrowing in on the anti-β cell-specific T cells: looking 'where the action is'

PURPOSE OF REVIEW

By necessity, the vast majority of information we have on autoreactive T cells in human type 1 diabetes (T1D) has come from the study of peripheral blood of donors with T1D. It is not clear how representative the peripheral autoreactive T-cell repertoire is of the autoreactive T cells infiltrating the islets in T1D. We will summarize and discuss what is known of the immunohistopathology of insulitis, the T-cell receptor repertoire expressed by islet-infiltrating T cells, and the autoreactivity and function of islet-infiltrating T cells in T1D.

RECENT FINDINGS

Recovery and analysis of live, islet-infiltrating T cells from the islets of cadaveric donors with T1D revealed a broad repertoire and proinflammatory phenotype of CD4 T-cell autoreactivity to peptide targets from islet proteins, including proinsulin, as well as CD4 T-cell reactivity to a number of post-translationally modified peptides, including peptides with citrullinations and hybrid insulin peptide fusions. Islet-infiltrating CD8 T cells were also derived and required further isolation and characterization.

SUMMARY

The recovery of live, islet-infiltrating T cells from donors with T1D, reactive with a broad range of known targets and post-translationally modified peptides, allows for the specific functional analysis of islet-infiltrating T cells for the development of antigen-specific immunotherapies.

Dendritic Cells Guide Islet Autoimmunity through a Restricted and Uniquely Processed Peptidome Presented by High-Risk HLA-DR

Identifying T cell epitopes of islet autoantigens is important for understanding type 1 diabetes (T1D) immunopathogenesis and to design immune monitoring and intervention strategies in relationship to disease progression. Naturally processed T cell epitopes have been discovered by elution from HLA-DR4 of pulsed B lymphocytes. The designated professional APC directing immune responses is the dendritic cell (DC). To identify naturally processed epitopes, monocyte-derived DC were pulsed with preproinsulin (PPI), glutamic acid decarboxylase (65-kDa isoform; GAD65), and insulinoma-associated Ag-2 (IA-2), and peptides were eluted of HLA-DR3 and -DR4, which are associated with highest risk for T1D development. Proteome analysis confirmed uptake and processing of islet Ags by DC. PPI peptides generated by DC differed from those processed by B lymphocytes; PPI signal-sequence peptides were eluted from HLA-DR4 and -DR3/4 that proved completely identical to a primary target epitope of diabetogenic HLA-A2-restricted CD8 T cells. HLA-DR4 binding was confirmed. GAD65 peptides, eluted from HLA-DR3 and -DR4, encompassed two core regions overlapping the two most immunodominant and frequently studied CD4 T cell targets. GAD65 peptides bound to HLA-DR3. Strikingly, the IA-2 ligandome of HLA-DR was exclusively generated from the extracellular part of IA-2, whereas most previous immune studies have focused on intracellular IA-2 epitopes. The newly identified IA-2 peptides bound to HLA-DR3 and -DR4. Differential T cell responses were detected against the newly identified IA-2 epitopes in blood from T1D patients. The core regions to which DC may draw attention from autoreactive T cells are largely distinct and more restricted than are those of B cells. GAD65 peptides presented by DC focus on highly immunogenic T cell targets, whereas HLA-DR-binding peptides derived from IA-2 are distinct from the target regions of IA-2 autoantibodies.

T cell epitopes and post-translationally modified epitopes in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease in which progressive loss of self-tolerance, evidenced by accumulation of auto-antibodies and auto-reactive T cells that recognize diverse self-proteins, leads to immune-mediated destruction of pancreatic beta cells and loss of insulin secretion. In this review, we discuss antigens and epitopes in T1D and the role that post-translational modifications play in circumventing tolerance mechanisms and increasing antigenic diversity. Emerging data suggest that, analogous to other autoimmune diseases such as rheumatoid arthritis and celiac disease, enzymatically modified epitopes are preferentially recognized in T1D. Modifying enzymes such as peptidyl deiminases and tissue transglutaminase are activated in response to beta cell stress, providing a mechanistic link between post-translational modification and interactions with the environment. Although studies of such responses in the at-risk population have been limited, current data suggests that breakdown in tolerance through post-translational modification represents an important checkpoint in the development of T1D.

Spontaneous complete remission of type 1 diabetes mellitus in an adult - review and case report

Type 1 diabetes mellitus (T1DM) is an autoimmune condition that results in low plasma insulin levels by destruction of beta cells of the pancreas. As part of the natural progression of this disease, some patients regain beta cell activity transiently. This period is often referred to as the ‘honeymoon period’ or remission of T1DM. During this period, patients manifest improved glycemic control with reduced or no use of insulin or anti-diabetic medications. The incidence rates of remission and duration of remission is extremely variable. Various factors seem to influence the remission rates and duration. These include but are not limited to C-peptide level, serum bicarbonate level at the time of diagnosis, duration of T1DM symptoms, haemoglobin A1C (HbA1C) levels at the time of diagnosis, sex, and age of the patient. Mechanism of remission is not clearly understood. Extensive research is ongoing in regard to the possible prevention and reversal of T1DM. However, most of the studies that showed positive results were small and uncontrolled. We present a 32-year-old newly diagnosed T1DM patient who presented with diabetic ketoacidosis (DKA) and HbA1C of 12.7%. She was on basal bolus insulin regimen for the first 4 months after diagnosis. Later, she stopped taking insulin and other anti-diabetic medications due to compliance and logistical issues. Eleven months after diagnosis, her HbA1C spontaneously improved to 5.6%. Currently (14 months after T1DM diagnosis), she is still in complete remission, not requiring insulin therapy.

Follicular helper T cell signature in type 1 diabetes

The strong genetic association between particular HLA alleles and type 1 diabetes (T1D) indicates a key role for CD4+ T cells in disease; however, the differentiation state of the responsible T cells is unclear. T cell differentiation originally was considered a dichotomy between Th1 and Th2 cells, with Th1 cells deemed culpable for autoimmune islet destruction. Now, multiple additional T cell differentiation fates are recognized with distinct roles. Here, we used a transgenic mouse model of diabetes to probe the gene expression profile of islet-specific T cells by microarray and identified a clear follicular helper T (Tfh) cell differentiation signature. Introduction of T cells with a Tfh cell phenotype from diabetic animals efficiently transferred diabetes to recipient animals. Furthermore, memory T cells from patients with T1D expressed elevated levels of Tfh cell markers, including CXCR5, ICOS, PDCD1, BCL6, and IL21. Defects in the IL-2 pathway are associated with T1D, and IL-2 inhibits Tfh cell differentiation in mice. Consistent with these previous observations, we found that IL-2 inhibited human Tfh cell differentiation and identified a relationship between IL-2 sensitivity in T cells from patients with T1D and acquisition of a Tfh cell phenotype. Together, these findings identify a Tfh cell signature in autoimmune diabetes and suggest that this population could be used as a biomarker and potentially targeted for T1D interventions.

HLA-DR4-associated T and B cell responses to specific determinants on the IA-2 autoantigen in type 1 diabetes

Autoantibodies to IA-2 in type 1 diabetes are associated with HLA-DR4, suggesting influences of HLA-DR4-restricted T cells on IA-2-specific B cell responses. The aim of this study was to investigate possible T-B cell collaboration by determining whether autoantibodies to IA-2 epitopes are associated with T cell responses to IA-2 peptides presented by DR4. T cells secreting the cytokines IFN-γ and IL-10 in response to seven peptides known to elicit T cell responses in type 1 diabetes were quantified by cytokine ELISPOT in HLA-typed patients characterized for Abs to IA-2 epitopes. T cell responses were detected to all peptides tested, but only IL-10 responses to 841-860 and 853-872 peptides were associated with DR4. Phenotyping by RT-PCR of FACS-sorted CD45RO(hi) T cells secreting IL-10 in response to these two peptides indicated that these expressed GATA-3 or T-bet, but not FOXP3, consistent with these being Th2 or Th1 memory T cells rather than of regulatory phenotype. T cell responses to the same two peptides were also associated with specific Abs: those to 841-860 peptide with Abs to juxtamembrane epitopes, which appear early in prediabetes, and those to peptide 853-872 with Abs to an epitope located in the 831-862 central region of the IA-2 tyrosine phosphatase domain. Abs to juxtamembrane and central region constructs were both DR4 associated. This study identifies a region of focus for B and T cell responses to IA-2 in HLA-DR4 diabetic patients that may explain HLA associations of IA-2 autoantibodies, and this region may provide a target for future immune intervention to prevent disease.

RNA-seq methods for identifying differentially expressed gene in human pancreatic islet cells treated with pro-inflammatory cytokines

Type 1 diabetes is a chronic autoimmune disease in which pancreatic beta cells are killed by the infiltrating immune cells as well as the cytokines released by these cells. Many studies indicate that inflammatory mediators have an essential role in this disease. In the present study, we profiled the transcriptome in human islets of langerhans under control conditions or following exposure to the pro-inflammatory cytokines based on the RNA sequencing dataset downloaded from SRA database. After filtered the low-quality ones, the RNA readers was aligned to human genome hg19 by TopHat and then assembled by Cufflinks. The expression value of each transcript was calculated and consequently differentially expressed genes were screened out. Finally, a total of 63 differentially expressed genes were identified including 60 up-regulated and three down-regulated genes. GBP5 and CXCL9 stood out as the top two most up-regulated genes in cytokines treated samples with the log2 fold change of 12.208 and 10.901, respectively. Meanwhile, PTF1A and REG3G were identified as the top two most down-regulated genes with the log2 fold change of -3.759 and -3.606, respectively. Of note, we also found 262 lncRNAs (long non-coding RNA), 177 of which were inferred as novel lncRNAs. Further in-depth follow-up analysis of the transcriptional regulation reported in this study may shed light on the specific function of these lncRNA.

The targeting of β-cells by T lymphocytes in human type 1 diabetes: clinical perspectives

This review focuses on genes that control β-cell targeting in autoimmune, type 1-dependent, diabetes (T1D) and on insulin as the major autoantigen recognized by T lymphocytes throughout the disease process. T1D associates with multiple gene variants. Beyond genes that predispose to general failure of immune tolerance to self, loci identified by the analysis of crosses between non-obese diabetic (NOD) and conventional mouse strains harbour genes that control β-cell targeting or the deviation of autoimmunity towards other tissues. We report here the role of genes encoding co-activation molecules involved in the activation of T lymphocytes, ICOS and ICOS ligand (B7RP1). NOD mice which are deficient in either of these two molecules are protected from diabetes, but instead develop a neuromuscular autoimmune disease. We also report the characterization in humans of T lymphocytes that are specific for major β-cell autoantigens, especially insulin. This opens the way towards new bioassays in the diagnosis of autoimmunity and towards autoantigen-specific immunotherapy in T1D. In order to develop a new preclinical model of T1D that would allow testing insulin epitopes to induce immune tolerance in vivo, we developed a mouse that is deficient in endogenous major histocompatibility complex class I and class II genes and deficient for the two murine insulin genes and that express human class I, class II and insulin genes.

Targeting regulatory T cells in the treatment of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease resulting in islet β cell destruction, hypoinsulinemia, and severely altered glucose homeostasis. T1DM has classically been attributed to the pathogenic actions of auto-reactive effector T cells(Teffs) on the β cell. Recent literature now suggests that a failure of a second T cell subtype, known as regulatory T cells (Tregs), plays a critical role in the development of T1DM. During immune homeostasis, Tregs counterbalance the actions of autoreactive Teff cells, thereby participating in peripheral tolerance. An imbalance in the activity between Teff and Tregs may be crucial in the breakdown of peripheral tolerance, leading to the development of T1DM. In this review, we summarize our current understanding of Treg function in health and in T1DM, and examine the effect of experimental therapies for T1DM on Treg cell number and function in both mice and humans.

Pancreatic islet autoimmunity

Type 1 diabetes (T1D) represents 10 to 15% of all forms of diabetes. Its incidence shows a consistent rise in all countries under survey. Evidence for autoimmunity in human T1D relies on the detection of insulitis, of islet cell antibodies, of activated β-cell-specific T lymphocytes and on the association of T1D with a restricted set of class II major histocompatibility complex (MHC) alleles. However, mechanisms that initiate the failure of immune tolerance to β-cell autoantigens remain elusive in common forms of T1D. T1D commonly develop as a multifactorial disease in which environmental factors concur with a highly multigenic background. The disease is driven by the activation of T-lymphocytes against pancreatic β-cells. Several years elapse between initial triggering of the autoimmune response to β cells, as evidenced by the appearance or islet cell autoantibodies, and the onset of clinical diabetes, defining a prediabetes stage. Active mechanisms hold back autoreactive effector T-cells in prediabetes, in particular a subset of CD4+ T-cells (T(reg)) and other regulatory T-cells, such as invariant NKT cells. There is evidence in experimental models that systemic or local infections can trigger autoimmune reactions to β-cells. However, epidemiological observations that have accumulated over years have failed to identify undisputable environmental factors that trigger T1D. Moreover, multiple environmental factors may intervene in the disease evolution and protective as weel as triggering environmental factors may be involved. Available models also indicate that local signals within the islets are required for full-blown diabetes to develop. Many autoantigens that are expressed by β-cells but also by the other endocrine islet cells and by neurons are recognized by lymphocytes along the development of T1D. The immune image of β-cells is that of native components of the β-cell membrane, as seen by B-lymphocytes, and of fragments of intracellular β-cell proteins in the form of peptides loaded onto class I MHC molecules on the β-cell surface and class I and class II molecules onto professional antigen presenting cells. Given the key role of T lymphocytes in T1D, the cartography of autoantigen-derived peptides that are presented to class I-restricted CD8(+) T-cells and class II-restricted CD4(+) T-cells is of outmost importance and is a necessary step in the development of diagnostic T-cell assays and of immunotherapy of T1D.

Cathepsin S dominates autoantigen processing in human thymic dendritic cells

The interaction of developing thymocytes with peptide-MHC complexes on thymic antigen presenting cells (APC) is crucial for T cell development, both for positive selection of "useful" thymocytes as well as negative selection of autoreactive thymocytes to prevent autoimmunity. The peptides presented on MHC II molecules are generated by lysosomal proteases such as the cathepsins. At the same time, lysosomal proteases will also destroy other potential T cell epitopes from self-antigens. This will lead to a lack of presentation on negatively selecting thymic antigen presenting cells and consequently, escape of autoreactive T cells recognizing these epitopes. In order to understand the processes that govern generation or destruction of self-epitopes in thymic APC, we studied the antigen processing machinery and epitope processing in the human thymus. We find that each type of thymic APC expresses a different signature of lysosomal proteases, providing indirect evidence that positive and negative selection of CD4(+) T cells might occur on different sets of peptides, in analogy to what has been proposed for CD8(+) T cells. We also find that myeloid dendritic cells (DC) are more efficient in processing autoantigen than plasmacytoid DC. In addition, we observed that cathepsin S plays a central role in processing of the autoantigens myelin basic protein and proinsulin in thymic dendritic cells. Cathepsin S destroyed a number of known T cell epitopes, which would be expected to result in lack of presentation and consequently, escape of autoreactive T cells. Cathepsin S therefore appears to be an important factor that influences selection of autoreactive T cells.

Etiopathogenesis of insulin autoimmunity

Autoimmunity against pancreatic islet beta cells is strongly associated with proinsulin, insulin, or both. The insulin autoreactivity is particularly pronounced in children with young age at onset of type 1 diabetes. Possible mechanisms for (pro)insulin autoimmunity may involve beta-cell destruction resulting in proinsulin peptide presentation on HLA-DR-DQ Class II molecules in pancreatic draining lymphnodes. Recent data on proinsulin peptide binding to type 1 diabetes-associated HLA-DQ2 and -DQ8 is reviewed and illustrated by molecular modeling. The importance of the cellular immune reaction involving cytotoxic CD8-positive T cells to kill beta cells through Class I MHC is discussed along with speculations of the possible role of B lymphocytes in presenting the proinsulin autoantigen over and over again through insulin-carrying insulin autoantibodies. In contrast to autoantibodies against other islet autoantigens such as GAD65, IA-2, and ZnT8 transporters, it has not been possible yet to standardize the insulin autoantibody test. As islet autoantibodies predict type 1 diabetes, it is imperative to clarify the mechanisms of insulin autoimmunity.

Prediction of HLA class I-restricted T-cell epitopes of islet autoantigen combined with binding and dissociation assays

Identification of cognate peptides recognized by human leucocyte antigen (HLA)/T cell receptor (TCR) complex provides insight into the pathogenic process of type 1 diabetes (T1D). We hypothesize that HLA-binding assays alone are inadequate metrics for the affinity of peptides. Zinc transporter-8 (ZnT8) has emerged in recent years as a novel, major, human autoantigen. Therefore, we aim to identify the HLA-A2-restricted ZnT8 epitopes using both binding and dissociation assays. HLA class I peptide affinity algorithms were used to predict candidate ZnT8 peptides that bind to HLA-A2. We analyzed 15 reported epitopes of seven β-cell candidate autoantigens and eight predicted candidate ZnT8 peptides using binding and dissociation assays. Using IFN-γ ELISpot assay, we tested peripheral blood mononuclear cells (PBMCs) from recent-onset T1D patients and healthy controls for reactivity to seven reported epitopes and eight candidate ZnT8 peptides directly ex vivo. We found five of seven recently reported epitopes in Chinese T1D patients. Of the eight predicted ZnT8 peptides, ZnT8(153-161) had a strong binding affinity and the lowest dissociation rate to HLA-A*0201. We identified it as a novel HLA-A*0201-restricted T-cell epitope in three of eight T1D patients. We conclude that ZnT8(153-161) is a novel HLA-A*0201-restricted T-cell epitope. We did not observe a significant correlation (P = 0.3, R = - 0.5) between cytotoxic T cell (CTL) response and peptide/HLA*0201 complex stability. However, selection of peptides based on affinity and their dissociation rate may be helpful for the identification of candidate CTL epitopes. Thus, we can minimize the number of experiments for the identification of T-cell epitopes from interesting antigens.

Immunology of Diabetes Society T-Cell Workshop: HLA class II tetramer-directed epitope validation initiative

BACKGROUND

Islet-antigen-specific CD4+ T cells are known to promote auto-immune destruction in T1D. Measuring T-cell number and function provides an important biomarker. In response to this need, we evaluated responses to proinsulin and GAD epitopes in a multicentre study.

METHODS

A tetramer-based assay was used in five participating centres to measure T-cell reactivities to DR0401-restricted epitopes. Three participating centres concurrently performed ELISPOT or immunoblot assays. Each centre used blind-coded, centrally distributed peptide and tetramer reagents.

RESULTS

All participating centres detected responses to auto-antigens and the positive control antigen, and in some cases cloned the corresponding T cells. However, response rates varied among centres. In total, 74% of patients were positive for at least one islet epitope. The most commonly recognized epitope was GAD270-285. Only a minority of the patients tested by tetramer and ELISPOT were concordant for both assays.

CONCLUSIONS

This study successfully detected GAD and proinsulin responses using centrally distributed blind-coded reagents. Centres with little previous experience using class II tetramer reagents implemented the assay. The variability in response rates observed for different centres suggests technical difficulties and/or heterogeneity within the local patient populations tested. Dual analysis by tetramer and ELISPOT or immunoblot assays was frequently discordant, suggesting that these assays detect distinct cell populations. Future efforts should investigate shared blood samples to evaluate assay reproducibility and longitudinal samples to identify changes in T-cell phenotype that correlate with changes in disease course.

T cell recognition of autoantigens in human type 1 diabetes: clinical perspectives

Type 1 diabetes (T1D) is an autoimmune disease driven by the activation of lymphocytes against pancreatic β-cells. Among β-cell autoantigens, preproinsulin has been ascribed a key role in the T1D process. The successive steps that control the activation of autoreactive lymphocytes have been extensively studied in animal models of T1D, but remains ill defined in man. In man, T lymphocytes, especially CD8⁺ T cells, are predominant within insulitis. Developing T-cell assays in diabetes autoimmunity is, thus, a major challenge. It is expected to help defining autoantigens and epitopes that drive the disease process, to pinpoint key functional features of epitope-specific T lymphocytes along the natural history of diabetes and to pave the way towards therapeutic strategies to induce immune tolerance to β-cells. New T-cell technologies will allow defining autoreactive T-cell differentiation programs and characterizing autoimmune responses in comparison with physiologically appropriate immune responses. This may prove instrumental in the discovery of immune correlates of efficacy in clinical trials.

Functional consequences of HLA-DQ8 homozygosity versus heterozygosity for islet autoimmunity in type 1 diabetes

Human leukocyte antigen (HLA) class II haplotypes are established risk factors in type 1 diabetes (T1D). The heterozygous DQ2/8 genotype confers the highest risk, whereas the DQ6/8 genotype is protective. We hypothesized that DQ2/8 trans-molecules composed of α and β chains from DQ2 and DQ8 express unique β-cell epitopes, whereas DQ6 may interfere with peptide binding to DQ8. Here we show that a single insulin epitope (InsB13-21) within the T1D prototype antigenic InsB6-22 peptide can bind to both cis- and trans-dimers, although these molecules display different peptide binding patterns. DQ6 binds a distinct insulin epitope (InsB6-14). The phenotype of DQ8-restricted T cells from a T1D patient changed from proinflammatory to anti-inflammatory in the presence of DQ6. Our data provide new insights into both susceptible and protective mechanism of DQ, where protecting HLA molecules bind autoantigens in a different (competing) binding register leading to 'epitope stealing', thereby inducing a regulatory, rather than a pathogenic immune response.

Intramuscular delivery of a naked DNA plasmid encoding proinsulin and pancreatic regenerating III protein ameliorates type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is an autoimmune disease characterized by inflammation of pancreatic islets and destruction of β cells. Up to now, there is still no cure for this devastating disease and alternative approach should be developed. To explore a novel gene therapy strategy combining immunotherapy and β cell regeneration, we constructed a non-viral plasmid encoding proinsulin (PI) and pancreatic regenerating (Reg) III protein (pReg/PI). Therapeutic potentials of this plasmid for T1DM were investigated. Intramuscular delivery of pReg/PI resulted in a significant reduction in hyperglycemia and diabetes incidence, with an increased insulin contents in the serum of T1DM mice model induced by STZ. Treatment with pReg/PI also restored the balance of Th1/Th2 cytokines and expanded CD4(+)CD25(+)Foxp3(+) T regulatory cells, which may attribute to the establishment of self-immune tolerance. Additionally, in comparison to the mice treated with empty vector pBudCE4.1 (pBud), attenuated insulitis and apoptosis achieved by inhibiting activation of NF-κB in the pancreas of pReg/PI treated mice were observed. In summary, these results indicate that intramuscular delivery of pReg/PI distinctly ameliorated STZ-induced T1DM by reconstructing the immunological self-tolerance and promoting the regeneration of β cells, which might be served as a promising candidate for the gene therapy of T1DM.

IFN-gamma and IL-10 islet-antigen-specific T cell responses in autoantibody-negative first-degree relatives of patients with type 1 diabetes

AIMS/HYPOTHESIS

Islet antibody-negative first-degree relatives of type 1 diabetes patients have a very low risk of developing diabetes. We studied the balance between IFN-gamma (proinflammatory) and IL-10 (regulatory) T cell responses in these participants.

METHODS

Peripheral blood T cells from adult (18-50 years old, n = 40) DRB1*0401-positive first-degree relatives negative for GAD and tyrosine phosphatase-like insulinoma antigen 2 (IA-2) antibodies were tested for IFN-gamma and IL-10 responses in a sensitive cytokine enzyme-linked immunospot assay against a panel of seven peptide epitopes derived from IA-2 and proinsulin. Comparison was made with HLA-matched newly diagnosed type 1 diabetic patients (n = 42) and healthy controls (n = 39).

RESULTS

First-degree relatives and newly diagnosed type 1 diabetic patients displayed a similar frequency of IFN-gamma responses to the peptide panel and both were significantly greater than in healthy controls (relatives 9.6%, patients 11.8%, controls 4.0%, p = 0.003). First-degree relatives and newly diagnosed type 1 diabetic patients also showed similar frequencies of IL-10 responses, which were significantly lower than in healthy controls (relatives 7.1%, patients 9.0%, controls 15.8%, p = 0.003). However, individual IL-10 responses of first-degree relatives were similar in size to those in healthy controls and larger than those in newly diagnosed type 1 diabetic patients (relatives median 29 spot-forming cells/1 x 10(6) peripheral blood mononuclear cells, controls 33, patients 11, p = 0.02).

CONCLUSIONS/INTERPRETATION

Taken together, these results suggest that antibody-negative first-degree relatives have a balance of proinflammatory and regulatory T cells, which is intermediate between that of newly diagnosed type 1 diabetic patients and healthy controls. This suggests that even a moderate regulatory response may be sufficient to prevent the development of clinical type 1 diabetes in genetically predisposed individuals.

Insulin gene VNTR genotype associates with frequency and phenotype of the autoimmune response to proinsulin

Immune responses to autoantigens are in part controlled by deletion of autoreactive cells through genetically regulated selection mechanisms. We have directly analyzed peripheral CD4+ proinsulin (PI) 76–90 (SLQPLALEGSLQKRG)-specific T cells using soluble fluorescent major histocompatibility complex class II tetramers. Subjects with type I diabetes and healthy controls with high levels of peripheral proinsulin-specific T cells were characterized by the presence of a disease-susceptible polymorphism in the insulin variable number of tandem repeats (INS-VNTR) gene. Conversely, subjects with a ‘protective' polymorphism in the INS-VNTR gene had nearly undetectable levels of proinsulin tetramer-positive T cells. These results strongly imply a direct relationship between genetic control of autoantigen expression and peripheral autoreactivity, in which proinsulin genotype restricts the quantity and quality of the potential T-cell response. Using a modified tetramer to isolate low-avidity proinsulin-specific T cells from subjects with the susceptible genotype, transcript arrays identified several induced pro-apoptotic genes in the control, but not diabetic subjects, likely representing a second peripheral mechanism for maintenance of tolerance to self antigens.

Autoantibodies and associated T-cell responses to determinants within the 831-860 region of the autoantigen IA-2 in Type 1 diabetes

B-cells influence T-cell reactivity by facilitating antigen presentation, but the role of autoantibody-secreting B-cells in regulating T-cell responses in Type 1 diabetes is poorly defined. The aims of this study were to characterise epitopes on the IA-2 autoantigen for three monoclonal antibodies from diabetic patients by amino acid substitutions of selected residues of IA-2, establish contributions of these epitopes to binding of serum antibodies in Type 1 diabetes and relate B- and T-cell responses to overlapping determinants on IA-2. The monoclonal antibodies recognised overlapping epitopes, with residues within the 831-860 region of IA-2 contributing to binding; substitution of Glu836 inhibited binding of all three antibodies. Monoclonal antibody Fab fragments and substitution of residues within the 831-836 region blocked serum antibody binding to an IA-2 643-937 construct. IL-10-secreting T-cells responding to peptides within the 831-860 region were detected by cytokine-specific ELISPOT in diabetic patients and responses to 841-860 peptide were associated with antibodies to the region of IA-2 recognised by the monoclonal antibodies. The study identifies a region of IA-2 frequently recognised by antibodies in Type 1 diabetes and demonstrates that these responses are associated with T-cells secreting IL-10 in response to a neighbouring determinant.

The sentinel role of CD8 T cells in regulating CD4 T cell responses to proinsulin in beta-islet cell autoimmunity

Circulating CD4 T cells specific for peptide epitopes of proinsulin and other autoantigens are markers of autoimmune beta cell destruction in type 1 diabetes, while the role of CD8 T cells is still largely unknown. Here we show that CD8 T cells of a diabetic patient--after rechallange with proinsulin peptides--secrete IFNgamma and granzyme B, markers of their effector capacity. On the other hand, CD8 T cells of the same patient in a "cross-talk" with proinsulin-specific CD4 T cells suppress their proliferation. If confirmed in larger numbers of subjects with beta-islet cell autoimmunity, these results may help us to understand the role of CD8 cells in disease progression and extend our knowledge of disease pathogenesis.

Recognition of human proinsulin leader sequence by class I-restricted T-cells in HLA-A*0201 transgenic mice and in human type 1 diabetes

OBJECTIVE

A restricted region of proinsulin located in the B chain and adjacent region of C-peptide has been shown to contain numerous candidate epitopes recognized by CD8(+) T-cells. Our objective is to characterize HLA class I-restricted epitopes located within the preproinsulin leader sequence.

RESEARCH DESIGN AND METHODS

Seven 8- to 11-mer preproinsulin peptides carrying anchoring residues for HLA-A1, -A2, -A24, and -B8 were selected from databases. HLA-A2-restricted peptides were tested for immunogenicity in transgenic mice expressing a chimeric HLA-A*0201/beta2-microglobulin molecule. The peptides were studied for binding to purified HLA class I molecules, selected for carrying COOH-terminal residues generated by proteasome digestion in vitro and tested for recognition by human lymphocytes using an ex vivo interferon-gamma (IFN-gamma) ELISpot assay.

RESULTS

Five HLA-A2-restricted peptides were immunogenic in transgenic mice. Murine T-cell clones specific for these peptides were cytotoxic against cells transfected with the preproinsulin gene. They were recognized by peripheral blood mononuclear cells (PBMCs) from 17 of 21 HLA-A2 type 1 diabetic patients. PBMCs from 25 of 38 HLA-A1, -A2, -A24, or -B8 patients produced IFN-gamma in response to six preproinsulin peptides covering residues 2-25 within the preproinsulin region. In most patients, the response was against several class I-restricted peptides. T-cells recognizing preproinsulin peptide were characterized as CD8(+) T-cells by staining with peptide/HLA-A2 tetramers.

CONCLUSIONS

We defined class I-restricted epitopes located within the leader sequence of human preproinsulin through in vivo (transgenic mice) and ex vivo (diabetic patients) assays, illustrating the possible role of preproinsulin-specific CD8(+) T-cells in human type 1 diabetes.

T-cell reactivity to insulin peptide A1-12 in children with recently diagnosed type 1 diabetes or multiple beta-cell autoantibodies

Insulin-specific immune responses appear early in preclinical type 1 diabetes (T1D), and bovine insulin in cow's milk-based infant formulas has been suggested to be of importance in induction of the primary response to insulin in humans. To characterize insulin-specific T-cell reactivity we studied T-cell responses to 10 insulin peptides derived from bovine (BI) and human insulin (HI) in 42 children with recently diagnosed T1D, 47 children with multiple autoantibodies and 111 autoantibody-negative control children with risk-associated HLA alleles. Proliferation responses detected in antigen-stimulated peripheral blood mononuclear cells did not differ between the three groups when the comparison was performed without considering HLA genotypes. However, significant differences were observed, when children with the high-risk genotype HLA (DRB1*03)-DQA1*05-DQB1*02/DRB1*0401-DQA1*03-DQB1*0302 were analyzed separately. The responses to the peptides including amino acids A1-12 derived from B1 and H1 were significantly higher in children with T1D (P=0.008, P=0.004, for B1 and H1, respectively) and in children with diabetes-associated autoantibodies (P=0.002 and P=0.001, respectively) than in control children. Positive responses (stimulation indices SI> or =3) were seen more frequently in T1D children than in controls (4/7 vs 2/19; P=0.03 and 4/7 vs 1/19; P=0.01 for B1 and H1, respectively). T-cell response to the insulin peptide A1-12 is enhanced in clinical and preclinical T1D associated with the high-risk HLA-genotype emphasizing the importance of this epitope.

CD4+ T cells from type 1 diabetic and healthy subjects exhibit different thresholds of activation to a naturally processed proinsulin epitope

Recent studies suggest that insulin is a primary autoantigen for type 1 diabetes. Several studies have identified preproinsulin (PPI) 76-90 as an immunodominant CD4+ T cell epitope. We developed a class II tetramer reagent using a modified PPI peptide with a lysine to serine substitution at position 88 (PPI 78-90(88S)) that has high binding affinity to DRA1*0101/DRB1*0401 (DR0401). Using this tetramer, positive responses were observed from both DR0401 healthy and type 1 diabetic subjects when T cells were stimulated with the PPI 78-90(88S) peptide. Seventy percent of these T cells proliferated in response to both the wild type PPI 76-90 and PPI 78-90(88S) peptides. However, when T cells were stimulated with wild type peptide and assayed with DR0401/PPI 78-90(88S), positive responses were only detected in the diabetic group but not in healthy subjects. When highly purified CD4+CD25-CD45RA+ T cells were stimulated with PPI 78-90(88S) peptide in the absence of antigen-presenting cells, T cells from the diabetic group were able to respond to peptide stimulation, while T cells from healthy subjects were not. These data suggest that T cells from type 1 diabetic subjects have a lower threshold of activation in response to PPI peptide stimulation as compared to healthy subjects.

Insulin as an autoantigen in NOD/human diabetes

Although multiple islet autoantigens are recognized by T lymphocytes and autoantibodies before the development of type 1A (immune-mediated diabetes), there is increasing evidence that autoimmunity to insulin may be central to disease pathogenesis. Evidence is strongest for the NOD mouse model where blocking immune responses to insulin prevents diabetes, and insulin peptides can be utilized to induce diabetes. In man insulin gene polymorphisms are associated with disease risk, and autoantibodies and T cells reacting with multiple insulin/proinsulin epitopes are present. It is not currently clear why insulin autoimmunity is so prominent and frequent, and though insulin can be used to immunologically prevent diabetes of NOD mice, insulin-based preventive immunoregulation of diabetes in man is not yet possible.

Protein microarray analysis as a tool for monitoring cellular autoreactivity in type 1 diabetes patients and their relatives

BACKGROUND

Autoreactive T cells have a crucial role in type 1 diabetes (T1D) pathogenesis.

OBJECTIVES

The aim of our study was to monitor the in vitro production of cytokines by peripheral blood mononuclear cells (PBMCs) after stimulation with diabetogenic autoantigens.

SUBJECTS

Ten T1D patients (tested at the time of diagnosis and 6 and 12 months later), 10 first-degree relatives of the T1D patients, and 10 controls underwent the study.

METHODS

PBMCs were stimulated with glutamic acid decarboxylase 65 (GAD65) amino acids (a.a.) 247-279, 509-528, and 524-543; proinsulin a.a. 9-23; and tyrosine phosphatase (islet antigen-2)/R2 a.a. 853-872. Interleukin (IL)-2, IL-4, IL-5, IL-6, IL-10, IL-13, interferon (IFN)-gamma, tumor necrosis factor beta, transforming growth factor beta1, and granulocyte colony-stimulating factor (GCSF) were analyzed by protein microarray.

RESULTS

Differences in cytokine(s) poststimulatory and mainly in basal production were observed in all groups. The most prominent findings were in controls, the higher basal levels of IL-2, IL-4, IL-5, IL-13, and GCSF were observed when compared with relatives (p < 0.05, for all). After stimulation in controls, there was a significant decrease in IL-2, IL-13, GCSF, and IFN-gamma (p < 0.05, for all). The group of relatives was the most variable in poststimulatory production. A strong correlation between cytokines production was found but groups differed in this aspect.

CONCLUSION

By multiplex analysis, it may be possible, for example, to define the risk immunological response pattern among relatives or to monitor the immune response in patients on immune modulation therapy.

Translational mini-review series on type 1 diabetes: Systematic analysis of T cell epitopes in autoimmune diabetes

T cell epitopes represent the molecular code words through which the adaptive immune system communicates. In the context of a T cell-mediated autoimmune disease such as type 1 diabetes, CD4 and CD8 T cell recognition of islet autoantigenic epitopes is a key step in the autoimmune cascade. Epitope recognition takes place during the generation of tolerance, during its loss as the disease process is initiated, and during epitope spreading as islet cell damage is perpetuated. Epitope recognition is also a potentially critical element in therapeutic interventions such as antigen-specific immunotherapy. T cell epitope discovery, therefore, is an important component of type 1 diabetes research, in both human and murine models. With this in mind, in this review we present a comprehensive guide to epitopes that have been identified as T cell targets in autoimmune diabetes. Targets of both CD4 and CD8 T cells are listed for human type 1 diabetes, for humanized [human leucocyte antigen (HLA)-transgenic] mouse models, and for the major spontaneous disease model, the non-obese diabetic (NOD) mouse. Importantly, for each epitope we provide an analysis of the relative stringency with which it has been identified, including whether recognition is spontaneous or induced and whether there is evidence that the epitope is generated from the native protein by natural antigen processing. This analysis provides an important resource for investigating diabetes pathogenesis, for developing antigen-specific therapies, and for developing strategies for T cell monitoring during disease development and therapeutic intervention.

Combinations of common chronic paediatric diseases deviate the immune response in diverging directions

The cytokine pattern of T lymphocytes has not been characterized in children with combinations of paediatric immunological disorders. We describe cytokine secretion in children with type 1 diabetes, coeliac disease and allergy and combinations of two of these diseases after stimulation with 'disease-specific' antigens. Peripheral blood mononuclear cells (PBMC) were collected from 68 children with type 1 diabetes, allergy or coeliac disease, two of these diseases in combination or none of these diseases. Using the enzyme-linked immunospot (ELISPOT) technique, interferon (IFN)-gamma and interleukin (IL)-4 were analysed from fresh PBMC spontaneously and after in vitro stimulation with antigens associated with one or more of these diseases (insulin, gluten, birch and cat extract, beta-lactoglobulin, ovalbumin and phytohaemagglutinin) in order to divide T helper (Th)1- from Th2-like lymphocytes. Stimulation with birch and cat extract caused increased IL-4 secretion in allergic children. A low IFN-gamma response to insulin was found in type 1 diabetic children, whereas allergic children responded to insulin by increased IL-4 secretion. Children suffering from both type 1 diabetes (Th1-prone) and allergy (Th2-prone) reacted distinctly to general mitogen stimulation. Children suffering from two Th1-dominated diseases (type 1 diabetes and coeliac disease) showed hardly any response to either food or inhalation allergens. Our results indicate an important interplay between common immunological diseases in children. The combination of two Th1-deviated diseases is associated with a suppressed immune response, whereas a combination of Th1- and Th2-dominated diseases appears to increase the general immune response.

Insulin treatment in patients with type 1 diabetes induces upregulation of regulatory T-cell markers in peripheral blood mononuclear cells stimulated with insulin in vitro

Patients with type 1 diabetes are treated with daily injections of human insulin, an autoantigen expressed in thymus. Natural CD4(+)CD25(high) regulatory T-cells are derived from thymus, and accordingly human insulin-specific regulatory T-cells should exist. We had a chance to study peripheral blood mononuclear cells (PBMCs) from children with type 1 diabetes both before and after starting insulin treatment, and thus we could analyze the effects of insulin treatment on regulatory T-cells in children with type 1 diabetes. PBMCs were stimulated for 72 h with bovine/human insulin. The mRNA expression of regulatory T-cell markers (transforming growth factor-beta, Foxp3, cytotoxic T-lymphocyte antigen-4 [CTLA-4], and inducible co-stimulator [ICOS]) or cytokines (gamma-interferon [IFN-gamma], interleukin [IL]-5, IL-4) was measured by quantitative RT-PCR. The secretion of IFN-gamma, IL-2, IL-4, IL-5, and IL-10 was also studied. The expression of Foxp3, CTLA-4, and ICOS mRNAs in PBMCs stimulated with bovine or human insulin was higher in patients on insulin treatment than in patients studied before starting insulin treatment. The insulin-induced Foxp3 protein expression in CD4(+)CD25(high) cells was detectable in flow cytometry. No differences were seen in cytokine activation between the patient groups. Insulin stimulation in vitro induced increased expression of regulatory T-cell markers, Foxp3, CTLA-4, and ICOS only in patients treated with insulin, suggesting that treatment with human insulin activates insulin-specific regulatory T-cells in children with newly diagnosed type 1 diabetes. This effect of the exogenous autoantigen could explain the difficulties to detect in vitro T-cell proliferation responses to insulin in newly diagnosed patients. Furthermore, autoantigen treatment-induced activation of regulatory T-cells may contribute to the clinical remission of the disease.

Recognition of HLA class I-restricted beta-cell epitopes in type 1 diabetes

Type 1 diabetes results from the autoimmune destruction of insulin-producing pancreatic beta-cells by cytotoxic T-lymphocytes (CTLs). In humans, few beta-cell epitopes have been reported, thereby limiting the study of beta-cell-specific CTLs in type 1 diabetes. To identify additional epitopes, HLA class I peptide affinity algorithms were used to identify a panel of peptides derived from the beta-cell proteins islet amyloid polypeptide (IAPP), islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), insulin, insulinoma-associated antigen 2 (IA-2), and phogrin that were predicted to bind HLA-A*0201. Peripheral blood mononuclear cells from 24 HLA-A*0201 recent-onset type 1 diabetic patients and 11 nondiabetic control subjects were evaluated for gamma-interferon secretion in response to peptide stimulation in enzyme-linked immunospot assays. We identified peptides IAPP9-17, IGRP215-223, IGRP152-160, islet IA-2(172-180), and IA-2(482-490) as novel HLA-A*0201-restricted T-cell epitopes in type 1 diabetic patients. Interestingly, we observed a strong inverse correlation between the binding affinity of beta-cell peptides to HLA-A*0201 and CTL responses against those peptides in recent-onset type 1 diabetic patients. In addition, we found that self-reactive CTLs with specificity for an insulin peptide are frequently present in healthy individuals. These data suggest that many beta-cell epitopes are recognized by CTLs in recent-onset type 1 diabetic patients. These epitopes may be important in the pathogenesis of type 1 diabetes.

HLA Class I Epitope Discovery in Type 1 Diabetes: Independent and Reproducible Identification of Proinsulin Epitopes of CD8 T Cells--Report of the IDS T Cell Workshop Committee

Islet autoreactive CD8 T cells are plausible candidates for direct beta cell toxicity in type 1 diabetes (T1DM). In 2005, cellular studies in the pathogenesis of this disease have reached a new milestone. Autoreactive CD8 T cells have been defined and several target islet epitopes of these have been discovered and validated simultaneously in three independent studies. The insulin B10-B18 peptide that displays exceptional binding affinity for HLA-A2 has been reported in all three studies, and its recognition shows an association with autoimmune beta cell destruction and T1DM. These studies imply that CD8 T cell-based HLA tetramers and ELISPOT analyses can be useful to monitor T1DM as well as islet transplantation, and may provide useful tools to assess immunological efficacy of immune intervention trials.

DRB1*0401-restricted human T cell clone specific for the major proinsulin73-90 epitope expresses a down-regulatory T helper 2 phenotype

Recently, we have identified proinsulin (P-Ins)(73-90) as an immunodominant T cell epitope of HLA-DRB1*0401 (DR4) subjects with beta-islet cell autoimmunity and of HLA-DR4/CD4 double-transgenic mice immunized with human P-Ins. We have compared the fine specificities of one human CD4 T cell clone and two mouse T cell hybridoma clones recognizing this epitope, and, although these three clones all recognized the same core region (LALEGSLQK), there were major differences in how they interacted with the peptide (p)/HLA complex, reflecting the fact that human P-Ins is a foreign antigen in the mouse and an autoantigen in the type 1 diabetes patient. The human T cell clone was forkhead transcription factor 3 (Foxp3)-positive, a marker for regulatory T cell lineages, and secreted predominantly IL-5, IL-10, and low levels of IFNgamma in response to P-Ins(73-90). This finding is compatible with the previously detected regulatory cytokine pattern in subjects with beta-cell autoimmunity. However, added N- or C-terminal amino acids drastically changed HLA and tetramer binding capacity as well as T cell reactivity and the cytokine phenotype of the P-Ins(73-90)-specific human CD4 T cell clone, suggesting a potential for this P-Ins epitope as a target for therapeutic intervention in HLA-DR4-positive humans with beta-islet cell autoimmunity or recent-onset type 1 diabetes.

TGF-beta signaling is required for the function of insulin-reactive T regulatory cells

We have previously isolated insulin-reactive Tregs from diabetic NOD mice designated 2H6, from which TCR transgenic mice were generated. The T cells from these 2H6 transgenic mice recognize insulin but have suppressive properties in vitro. They protect NOD mice in vivo from spontaneous development of diabetes and adoptive transfer of disease caused by polyclonal diabetogenic spleen cells as well as the highly diabetogenic monoclonal BDC2.5 TCR transgenic T cells that recognize an islet granule antigen. Using cells from both NOD and BDC2.5 mice that express a dominant-negative TGF-beta receptor type II (TGF-betaDNRII), we show that 2H6 T cells protected from disease by producing TGF-beta and that the ability of the target diabetogenic T cells to respond to TGF-beta was crucial. We further demonstrate that TGF-beta signaling in 2H6 cells was important for their protective properties, as 2H6 cells were unable to protect from adoptive transfer-induced diabetes if they were unable to respond to TGF-beta. Thus, our data demonstrate that insulin-specific regulatory cells protect from diabetes by virtue of their production of TGF-beta1 that acts in an autocrine manner to maintain their regulatory function and acts in a paracrine manner on the target cells.

Immunological mechanisms associated with long-term remission of human type 1 diabetes

BACKGROUND

Preservation of beta cell function is a central goal in type 1 diabetes (type 1 DM) immune intervention. The characterization of individuals with recovery from established type 1 DM should provide insight into regulatory mechanisms of beta cell autoimmunity.

METHODS

We studied a patient with antibody-positive type 1 DM with complete recovery of beta cell function for an observation period of 60 months. Using a preproinsulin (PPI) peptide library approach and in vitro cytokine profiling, cellular autoimmunity was characterized in peripheral blood mononuclear cells (PBMC) and CD4(+) T-helper cell subsets.

RESULTS

A predominant secretion of interleukin-10 (IL-10) was detected in the patient's PBMC, mostly attributable to naïve and recently primed CD45(+)RA(+) T cells, with limited PPI epitope recognition. In contrast to a cohort of patients with permanent type 1 DM, interferon-gamma secretion was low in PBMC and CD45(+)RA(+), but not in CD45(+)RA(-) insulin-reactive T lymphocytes. Autoantibodies against islet cells, tyrosine phosphatase IA-2, GAD65 and insulin were positive at diabetes onset, but gradually declined during follow-up.

CONCLUSIONS

Our observations support the concept that IL-10-dependent regulatory CD4(+) T-cell pathways are involved in beta cell recovery after the onset of hyperglycemia in autoimmune type 1 DM.

Islet-specific glucose-6-phosphatase catalytic subunit-related protein-reactive CD4+ T cells in human subjects

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is recognized as a major autoantigen for autoimmune type 1 diabetes (T1D) in the NOD mouse model. This study was undertaken to examine CD4+ T cell responses toward IGRP in human subjects. The tetramer-guided epitope mapping approach was used to identify IGRP-specific CD4+ T cell epitopes. IGRP(23-35) and IGRP(247-259) were identified as DRA1*0101/DRB1*0401-restricted epitopes. IGRP(13-25) and IGRP(226-238) were identified as DRA1*0101/DRB1*0301-restricted epitopes. IGRP-specific tetramers were used to evaluate the prevalence of IGRP-reactive T cells in healthy and T1D subjects. More than 80% of subjects with either DRB1*0401 or DRB1*0301 haplotype have IGRP-specific CD4+ T cell responses for at least one IGRP epitope. IGRP-specific T cells from both healthy and T1D groups produce both gamma-IFN and IL-10. DRA1*0101/DRB1*0401 IGRP(247-259)-restricted T cells also show cross-reactivity to an epitope derived from liver/kidney glucose-6-phosphatase. The detection of IGRP-reactive T cells in both type 1 diabetic subjects and healthy subjects and recent reports of other autoreactive T cells detected in healthy subjects underscore the prevalence of potentially autoreactive T cells in the peripheral immune system of the general population.

Autoreactive CD8 T cells associated with beta cell destruction in type 1 diabetes

Type 1 diabetes is a T cell-mediated autoimmune disease, and insulin is an important target of the autoimmune response associated with beta cell destruction. The mechanism of destruction is still unknown. Here, we provide evidence for CD8 T cell autoreactivity associated with recurrent autoimmunity and loss of beta cell function in type 1 diabetic islet transplant recipients. We first identified an insulin B chain peptide (insB10-18) with extraordinary binding affinity to HLA-A2(*0201) that is expressed by the majority of type 1 diabetes patients. We next demonstrated that this peptide is naturally processed by both constitutive and immuno proteasomes and translocated to the endoplasmic reticulum by the peptide transporter TAP1 to allow binding to HLA-A2 in the endoplasmic reticulum and cell surface presentation. Peripheral blood mononuclear cells from a healthy donor were primed in vitro with this peptide, and CD8 T cells were isolated that specifically recognize target cells expressing the insulin B chain peptide. HLA-A2(insB10-18) tetramer staining revealed a strong association between detection of autoreactive CD8 T cells and recurrent autoimmunity after islet transplantation and graft failure in type 1 diabetic patients. We demonstrate that CD8 T cell autoreactivity is associated with beta cell destruction in type 1 diabetes in humans.

Class III alleles at the insulin VNTR polymorphism are associated with regulatory T-cell responses to proinsulin epitopes in HLA-DR4, DQ8 individuals

A variable number of tandem repeats (VNTR) polymorphism upstream of the insulin promoter is strongly associated with type 1 diabetes. The short class I alleles are predisposing and the long class III alleles are protective. As a possible mechanism for this effect, we previously reported a two- to threefold higher insulin transcription from class III than from class I chromosomes in thymus where insulin is expressed at low levels, presumably for the purpose of self-tolerance. In this article, we confirm this finding with independent methodology and report studies testing the hypothesis that class III alleles are associated with T-cell tolerance to (pro)insulin. Cytokine release in vitro after stimulation with 21 overlapping preproinsulin epitopes was assessed in blood mononuclear cells as well as naive and memory CD4+ T-cell subsets from 33 individuals with the high-risk DRB1*04, DQ8 haplotype (12 type 1 diabetic patients, 11 healthy control subjects, and 10 autoantibody-positive subjects). No significant differences between genotypes (24 I/I subjects versus 10 I/III or III/III subjects) were observed for gamma-interferon, tumor necrosis factor-alpha, or interleukin (IL)-4. By contrast, the I/III + III/III group showed a significant threefold higher IL-10 release in memory T-cells for whole proinsulin and the immunodominant region. Given that IL-10 is a marker of regulatory function, our data are consistent with the hypothesis that higher insulin levels in the thymus promote the formation of regulatory T-cells, a proposed explanation for the protective effect of the class III alleles.

Recognition of a subregion of human proinsulin by class I-restricted T cells in type 1 diabetic patients

Proinsulin is a key autoantigen in type 1 diabetes. Evidence in the mouse has underscored the importance of the insulin B chain region in autoimmunity to pancreatic beta cells. In man, a majority of proteasome cleavage sites are predicted by proteasome cleavage algorithms within this region. To study CD8+ T cell responses to the insulin B chain and adjacent C peptide, we selected 8- to 11-mer peptides according to proteasome cleavage patterns obtained by digestion of two peptides covering proinsulin residues 28 to 64. We studied their binding to purified HLA class I molecules and their recognition by T cells from diabetic patients. Peripheral blood mononuclear cells from 17 of 19 recent-onset and 12 of 13 long-standing type 1 diabetic patients produced IFN-gamma in response to proinsulin peptides as shown by using an ELISPOT assay. In most patients, the response was against several class I-restricted peptides. Nine peptides were recognized within the proinsulin region covering residues 34 to 61. Four yielded a high frequency of recognition in HLA-A1 and -B8 patients. Three peptides located in the proinsulin region 41-51 were shown to bind several HLA molecules and to be recognized in a high percentage of diabetic patients.

Preproinsulin-specific CD8+ T cells secrete IFNgamma in human type 1 diabetes

In animal models autoreactive CD8(+) T cells are crucial in the development of type 1 diabetes (T1D); however, their role in human T1D is still not known. To address the role of CD81 T cells we performed a pilot study by investigating CD8(+) T cell-mediated cytokine secretion after in vitro stimulation with 94 preproinsulin (PPI) peptides. We were able to show that CD8(+) T cells contribute to a strong IFNgamma reactivity against PPI in human T1D. Further investigations defining epitope specificity, cytokine secretion, and cytotoxic capacity are important to clarify their role in T1D development.

Mature high-affinity immune responses to (pro)insulin anticipate the autoimmune cascade that leads to type 1 diabetes

Children at risk for type 1 diabetes can develop early insulin autoantibodies (IAAs). Many, but not all, of these children subsequently develop multiple islet autoantibodies and diabetes. To determine whether disease progression is reflected by autoantibody maturity, IAA affinity was measured by competitive radiobinding assay in first and subsequent IAA-positive samples from children followed from birth in the BABYDIAB cohort. IAA affinity in first positive samples ranged from less than 10(6) l/mol to more than 10(11) l/mol. High affinity was associated with HLA DRB1*04, young age of IAA appearance, and subsequent progression to multiple islet autoantibodies or type 1 diabetes. IAA affinity in multiple antibody-positive children was on average 100-fold higher than in children who remained single IAA positive or became autoantibody negative. All high-affinity IAAs required conservation of human insulin A chain residues 8-13 and were reactive with proinsulin. In contrast, most lower-affinity IAAs were dependent on COOH-terminal B chain residues and did not bind proinsulin. These data are consistent with the concept that type 1 diabetes is associated with sustained early exposure to (pro)insulin in the context of HLA DR4 and show that high-affinity proinsulin-reactive IAAs identify children with the highest diabetes risk.

Precursor frequencies of T-cells reactive to insulin in recent onset type 1 diabetes mellitus

T-cell mediated autoimmune beta-cell destruction is an important component of type 1 diabetes (T1D) and insulin is a critical antigen recognized by autoreactive T-cells. The aim of this study was to investigate the precursor frequency of insulin reactive T-cells in type 1 diabetes. We studied 19 T1D patients, 12 age-matching non-diabetic healthy siblings and 12 non-diabetic healthy parents. Limiting dilution analysis (LDA) was performed to insulin and tetanus toxoid (TT). A progressive decrease in the number of negative cultures at increasing cell concentrations that is represented by a low goodness-of-fit (GoF, low Chi-square), was seen with the TT response in all three groups; precursor frequencies and GoF were similar in patients, siblings, and parents. Reactivity to insulin, however, showed low precursor frequencies in patients and siblings and the LDA to insulin demonstrated dramatic decreases in the number of positive cultures at higher cell concentrations leading to a high GoF in patients and siblings compared to parents. This saw-toothed pattern of reactivity to insulin is indicative of multiple hit kinetics and implies that the response is regulated. Consequently the precursor frequency of insulin autoreactive cells in patients and their siblings is probably much higher than calculated.