Cellular immune response to diverse islet cell antigens in IDDM

Autoreactive T cells in type 1 diabetes

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

Avidity-dependent programming of autoreactive T cells in T1D

Fate determination for autoreactive T cells relies on a series of avidity-dependent interactions during T cell selection, represented by two general types of signals, one based on antigen expression and density during T cell development, and one based on genes that interpret the avidity of TCR interaction to guide developmental outcome. We used proinsulin-specific HLA class II tetramers to purify and determine transcriptional signatures for autoreactive T cells under differential selection in type 1 diabetes (T1D), in which insulin (INS) genotypes consist of protective and susceptible alleles that regulate the level of proinsulin expression in the thymus. Upregulation of steroid nuclear receptor family 4A (NR4A) and early growth response family genes in proinsulin-specific T cells was observed in individuals with susceptible INS-VNTR genotypes, suggesting a mechanism for avidity-dependent fate determination of the T cell repertoire in T1D. The NR4A genes act as translators of TCR signal strength that guide central and peripheral T cell fate decisions through transcriptional modification. We propose that maintenance of an NR4A-guided program in low avidity autoreactive T cells in T1D reflects their prior developmental experience influenced by proinsulin expression, identifying a pathway permissive for autoimmunity.

Antigen targets of type 1 diabetes autoimmunity

Type 1 diabetes is characterized by recognition of one or more β-cell proteins by the immune system. The list of target antigens in this disease is ever increasing and it is conceivable that additional islet autoantigens, possibly including pivotal β-cell targets, remain to be discovered. Many knowledge gaps remain with respect to the disorder's pathogenesis, including the cause of loss of tolerance to islet autoantigens and an explanation as to why targeting of proteins with a distribution of expression beyond β cells may result in selective β-cell destruction and type 1 diabetes. Yet, our knowledge of β-cell autoantigens has already led to translation into tissue-specific immune intervention strategies that are currently being assessed in clinical trials for their efficacy to halt or delay disease progression to type 1 diabetes, as well as to reverse type 1 diabetes. Here we will discuss recently gained insights into the identity, biology, structure, and presentation of islet antigens in relation to disease heterogeneity and β-cell destruction.

Humoral autoimmunity in type 1 diabetes: prediction, significance, and detection of distinct disease subtypes

Type 1 diabetes mellitus (T1D) is an autoimmune disease encompassing the T-cell-mediated destruction of pancreatic β cells and the production of autoantibodies against islet proteins. In humoral autoimmunity in T1D, the detection of islet autoantibodies and the examination of their associations with genetic factors and cellular autoimmunity constitute major areas in both basic research and clinical practice. Although insulin is a key autoantigen and may be primus inter pares in importance among T1D autoantigens, an abundant body of research has also revealed other autoantigens associated with the disease process. Solid evidence indicates that autoantibodies against islet targets serve as key markers to enroll newly diagnosed T1D patients and their family members in intervention trials aimed at preventing or halting the disease process. The next challenge is perfecting mechanistic bioassays to be used as end points for disease amelioration following immunomodulatory therapies aimed at blocking immune-mediated β-cell injury and, in turn, preserving β-cell function in type 1 diabetes mellitus.

Beyond the hormone: insulin as an autoimmune target in type 1 diabetes

Insulin is not only the hormone produced by pancreatic β-cells but also a key target antigen of the autoimmune islet destruction leading to type 1 diabetes. Despite cultural biases between the fields of endocrinology and immunology, these two facets should not be regarded separately, but rather harmonized in a unifying picture of diabetes pathogenesis. There is increasing evidence suggesting that metabolic factors (β-cell dysfunction, insulin resistance) and immunological components (inflammation and β-cell-directed adaptive immune responses) may synergize toward islet destruction, with insulin standing at the crossroad of these pathways. This concept further calls for a revision of the classical dichotomy between type 1 and type 2 diabetes because metabolic and immune mechanisms may both contribute to different extents to the development of different forms of diabetes. After providing a background on the mechanisms of β-cell autoimmunity, we will explain the role of insulin and its precursors as target antigens expressed not only by β-cells but also in the thymus. Available knowledge on the autoimmune antibody and T-cell responses against insulin will be summarized. A unifying scheme will be proposed to show how different aspects of insulin biology may lead to β-cell destruction and may be therapeutically exploited. We will argue about possible reasons why insulin remains the mainstay of metabolic control in type 1 diabetes but has so far failed to prevent or halt β-cell autoimmunity as an immune modulatory reagent.

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.

An update on the use of NOD mice to study autoimmune (Type 1) diabetes

The widely used nonobese diabetic (NOD) mouse model of autoimmune (Type 1) diabetes mellitus shares multiple characteristics with the human disease, and studies employing this model continue to yield clinically relevant and important information. Here, we review some of the recent key findings obtained from NOD mouse investigations that have both advanced our understanding of disease pathogenesis and suggested new therapeutic targets and approaches. Areas discussed include antigen discovery, identification of genes and pathways contributing to disease susceptibility, development of strategies to image islet inflammation and the testing of therapeutics. We also review recent technical advances that, combined with an improved understanding of the NOD mouse model's limitations, should work to ensure its popularity, utility and relevance in the years ahead.

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.

Latent autoimmune diabetes in adults

CONTEXT

Autoantibodies that are reactive to islet antigens are present at the time of diagnosis in most patients with type 1 diabetes. Additionally, approximately 10% of phenotypic type 2 diabetic patients are positive for at least one of the islet autoantibodies, and this group is often referred to as "latent autoimmune diabetes in adults (LADA)." These patients share many genetic and immunological similarities with type 1 diabetes, suggesting that LADA, like type 1 diabetes, is an autoimmune disease. However, there are differences in autoantibody clustering, T cell reactivity, and genetic susceptibility and protection between type 1 diabetes and LADA, implying important differences in the underlying disease processes.

EVIDENCE ACQUISITION AND SYNTHESIS

In this clinical review, we will summarize the current understanding of LADA based on the MEDLINE search of all peer-reviewed publications (original articles and reviews) on this topic between 1974 and 2009.

CONCLUSIONS

In LADA, diabetes occurs earlier in the beta-cell-destructive process because of the greater insulin resistance. Complexities arise also because of variable definitions of LADA and type 1 diabetes in adults. As immunomodulatory therapies that slow or halt the type 1 diabetes disease process are discovered, testing these therapies in LADA will be essential.

Genetic determinants of Type 1 diabetes: immune response genes

Type 1 diabetes (T1D) is a polygenic autoimmune disease. Susceptibility to T1D is strongly linked to a major genetic locus that is the MHC, and several other minor loci including insulin, cytotoxic T-lymphocyte-associated antigen-4, PTPN22 and others that contribute to diabetes risk in an epistatic way. We have observed that there are three sets of DR3-positive autoimmunity-favoring haplotypes in the north-Indian population, including B50-DR3, B58-DR3 and B8-DR3. The classical Caucasian autoimmunity favoring AH8.1 (HLA-A1-B8-DR3) is rare in the Indian population, and has been replaced by a variant AH8.1v, which differs from the Caucasian AH8.1 at several gene loci. Similarly, there are additional HLA-DR3 haplotypes, A26-B8-DR3 (AH8.2), A24-B8-DR3 (AH8.3), A3-B8-DR3 (AH8.4) and A31-B8-DR3 (AH8.5), of which AH8.2 is the most common. The fact that disease-associated DR3-positive haplotypes show heterogeneity in different populations suggests that these might possess certain shared components that are involved in the development of autoimmunity.

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.

CD8+ suppressor-mediated regulation of human CD4+ T cell responses to glutamic acid decarboxylase 65

Although potentially autoreactive T cells are present even in healthy subjects, most individuals do not develop autoimmune disease. It has been well demonstrated that CD4+ CD25+ regulatory T cells play a significant role in controlling the expansion of autoreactive T cells in the periphery. However, some healthy individuals exhibit measurable responses to self peptide even in the presence of CD4+ CD25+ regulatory cells. This article describes the regulation of human CD4+ T cell responses to glutamic acid decarboxylase 65 (GAD65), an autoantigen implicated in type-1 diabetes, by autologous CD8+ suppressor T cells. In cells cultured from healthy individuals, the inclusion of autologous CD8+ T cells at physiological levels resulted in a dramatic decrease in the magnitude of in vitro CD4+ T cell responses to GAD65 peptide. Based on transwell experiments, the observed suppression was cell contact-dependent. However, antibody blocking studies indicated that suppression was mediated by IL-10. Cell fractionation studies suggested that CD8+ suppressor T cells originate from the CD45RA+ CD27- population. The suppression of CD4+ T cell responses to GAD65 in healthy individuals raises the possibility that CD8+ suppressor T cells play an important role in controlling potentially autoreactive T cells in the general population.

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.

Diminished Th1-Like Response to Autoantigens in Children with a High Risk of Developing Type 1 Diabetes

The exact role of T-helper (Th) cells that precede the clinical manifestation of type 1 diabetes remains unclear. The aim of this investigation was to study the Th1- and Th2-like profile in children and adults with high risk of developing the disease. Peripheral blood mononuclear cells were collected from high-risk children and adults and from healthy individuals matched for age and gender. Using the sensitive enzyme-linked immunospot (ELISPOT) technique to divide Th1- from Th2-like lymphocytes, secretion of interferon-gamma (IFN-gamma) and interleukin-4 was analysed from lymphocytes spontaneously and after in vitro stimulation with different antigens, based on present paradigms regarding the pathogenesis of type 1 diabetes. Compared to the response observed in healthy individuals, we found that individuals with a high risk of developing type 1 diabetes, especially children, responded with less IFN-gamma secretion to the three autoantigens glutamic acid decarboxylase 65 (GAD65), insulin and tyrosinphosphatase (IA-2). Thus, a diminished Th1-like response by in vitro autoantigen stimulation was observed in especially children with a high risk of developing type 1 diabetes. Reduced Th1/Th2 response was related to signs of beta cell exhaustion.

Mapping of epitopes for autoantibodies to the type 1 diabetes autoantigen IA-2 by peptide phage display and molecular modeling: overlap of antibody and T cell determinants

IA-2 is a major target of autoimmunity in type 1 diabetes. IA-2 responsive T cells recognize determinants within regions represented by amino acids 787-817 and 841-869 of the molecule. Epitopes for IA-2 autoantibodies are largely conformational and not well defined. In this study, we used peptide phage display and homology modeling to characterize the epitope of a monoclonal IA-2 Ab (96/3) from a human type 1 diabetic patient. This Ab competes for IA-2 binding with Abs from the majority of patients with type 1 diabetes and therefore binds a region close to common autoantibody epitopes. Alignment of peptides obtained after screening phage-displayed peptide libraries with purified 96/3 identified a consensus binding sequence of Asn-x-Glu-x-x-(aromatic)-x-x-Gly. The predicted surface on a three-dimensional homology model of the tyrosine phosphatase domain of IA-2 was analyzed for clusters of Asn, Glu, and aromatic residues and amino acids contributing to the epitope investigated using site-directed mutagenesis. Mutation of each of amino acids Asn(858), Glu(836), and Trp(799) reduced 96/3 Ab binding by >45%. Mutations of these residues also inhibited binding of serum autoantibodies from IA-2 Ab-positive type 1 diabetic patients. This study identifies a region commonly recognized by autoantibodies in type 1 diabetes that overlaps with dominant T cell determinants.

T lymphocyte response against pancreatic beta cell antigens in fulminant Type 1 diabetes

AIMS/HYPOTHESIS

Fulminant Type 1 diabetes is a novel subtype of Type 1 diabetes that involves the abrupt onset of insulin-deficient hyperglycaemia. This subtype appears to be non-autoimmune because of the absence of diabetes-related autoantibodies in the serum, and of insulitis in pancreatic biopsy specimens. The pathogenesis of the disease is still unknown. In this study, we investigated whether T cell autoimmune responses are involved in fulminant Type 1 diabetes.

METHODS

Cellular immune responses to beta cell autoantigens were studied by enzyme-linked immunospot (ELISPOT) assay in 13 fulminant Type 1 diabetic patients and 49 autoantibody-positive autoimmune Type 1 diabetic patients. Results were compared with those of 18 Type 2 diabetic patients, six secondary diabetic patients (diabetes due to chronic pancreatitis) and 35 healthy controls.

RESULTS

Nine of 13 (69.2%) GAD-reactive Th1 cells, and three of 12 (25%) insulin-B9-23-reactive Th1 cells were identified in fulminant Type 1 diabetic patients by ELISPOT, as in autoantibody-positive Type 1 diabetic patients. Four fulminant Type 1 diabetic patients possessed the highly diabetes-resistant allele DR2, three of whom had GAD-reactive Th1 cells in the periphery.

CONCLUSIONS/INTERPRETATION

Peripheral immune reaction was observed in 69.2% of fulminant Type 1 diabetic patients, indicating that autoreactive T cells might contribute, at least in part, to the development of fulminant Type 1 diabetes.

A comprehensive guide to antibody and T-cell responses in type 1 diabetes

Type 1 diabetes (T1D) is an organ-specific autoimmune disease in which the insulin-producing beta cells in the pancreatic islets are selectively eliminated. T cells specific for beta-cell antigens are the mediators of this precise cellular destruction. However, antibodies to beta-cell proteins are also generated and may be used for predicting disease in at-risk populations. Over the past two decades, numerous beta-cell proteins and lipids have been implicated as autoantigens in patients or in non-obese diabetic (NOD) mice, a well-studied animal model of T1D. Here, we present a review of these antigens, accompanied by their T-cell epitopes, where known, and a discussion of our current understanding of why particular self-proteins become disease-inciting antigens. Although two dozen beta-cell antigens have been identified to date, few of these have been confirmed to be recognized by pathogenic T cells early in the disease process. Further identification and characterization of initiating beta-cell antigens targeted by pathogenic T cells should be a priority for future studies.

Cytokine Profile in Children During the First 3 Months after the Diagnosis of Type 1 Diabetes

Type 1 diabetes is an autoimmune disease with an inflammatory process directed against the beta cells in pancreas. This investigation aimed at studying the immune response during the first 3 months after the diagnosis of type 1 diabetes, with focus on the balance of T-helper 1 (Th1)- and Th2-like cytokines, produced spontaneously and in response to relevant autoantigens. Peripheral blood mononuclear cells (PBMCs) were collected from type 1 diabetic children (10-17 years) at 5, 20, 35 and 90 days after diagnosis. Expression of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) mRNA were detected by real-time reverse transcriptase polymerase chain reaction and IFN-gamma, IL-10 and IL-13 by enzyme-linked immunosorbent assay in cell supernatant after stimulation with a glutamic acid decarboxylase 65 (GAD(65))-peptide [amino acid (a.a.) 247-279], insulin, the ABBOS-peptide (a.a. 152-169), phytohaemagglutinin and keyhole limpet haemocyanin. Spontaneous and antigen-induced expression and secretion of cytokines were low at the diagnosis of type 1 diabetes. During the first month, after diagnosis, the GAD(65)-peptide caused an increased ratio of IFN-gamma/IL-4 mRNA expression (P < 0.05) and increased secretion of IFN-gamma (P = 0.07). Expression of IFN-gamma mRNA did also increase from stimulation with insulin (P < 0.05), even though cytokine secretion remained low. Thus, duration after diagnosis as well as metabolic state should be carefully considered both in studies of the pathogenesis of type 1 diabetes and in immune intervention studies at onset.

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

AIMS/HYPOTHESIS

Preproinsulin is a target T cell autoantigen in human Type 1 diabetes. This study analyses the phenotype and epitope recognition of preproinsulin reactive T cells in subjects with a high genetic risk of diabetes [HLA-DRB1*04, DQ8 with Ab+ (autoantibody-positive) or without islet autoantibodies (control subjects)], and in HLA-matched diabetic patients.

METHODS

A preproinsulin peptide library approach was used to screen for cytokine profiles and epitope specificities in human peripheral blood lymphocytes, and CD4(+)CD45RA(-) and CD4(+)CD45RA(+) T cell subfractions, representing memory and naive and recently primed T cells respectively.

RESULTS

In CD4(+) T cell subsets we identified immunodominant epitopes and cytokine production patterns that differed profoundly between patients, Ab+ subjects and non-diabetic HLA-matched control subjects. In Ab+ subjects, a C-peptide epitope C13-29 and insulin B-chain epitope B11-27 were preferentially recognised, whereas insulin-treated Type 1 diabetic patients reacted to native insulin and B-chain epitope B1-16. In peripheral blood lymphocytes of Ab+ subjects, an increase in T helper (Th) 1 (IFNgamma, IL-2) and Th2 (IL-4) cytokines was detectable, wheras in CD45RA(+) and CD45RA(-) subsets, IL-4 and IL-10 phenotypes dominated, compatible with the contribution of non-CD4 cells to IFNgamma content. In insulin-treated Type 1 diabetic patients, naive and recently primed CD4(+) cells were characterised by increasd IFNgamma, TNFalpha, and IL-5.

CONCLUSIONS/INTERPRETATION

Our data show that T cell reactivity to preproinsulin in CD45RA subsets is Th2-dominant in Ab+ subjects, challenging the Th1 paradigm in Type 1 diabetes. Characteristic immunodominant epitopes and cytokine patterns distinguish diabetic patients and Ab+ subjects from HLA-matched healthy individuals. This could prove useful in monitoring of T-cell immunity in clinical diabetes intervention trials.

Relationship between T and B Cell Responses to Proinsulin in Human Type 1 Diabetes

In type 1 diabetes, humoral and cell-mediated responses to insulin and proinsulin are detectable. Autoantibodies to insulin are associated with impending disease in young individuals and are used as predictive markers to determine disease risk. The aim of this study was to investigate whether different cytokine patterns of cellular reactivity to insulin might serve as additional specific markers of disease maturation and might improve disease prediction in individuals at risk. We correlated T and B cell responses to insulin in subjects with increased genetic risk (HLA-DRB1*04, DQB1*0302) for diabetes with or without islet autoantibodies (Ab+ subjects and controls, respectively) and HLA-matched patients. Peripheral blood mononuclear cells were stimulated with 15 overlapping proinsulin peptides (16-mer), and proinflammatory Th1 (IFNgamma) and anti-inflammatory Th2 (IL-4) cytokines were analyzed. We observed a simultaneous increase in IL-4 and IFNgamma secretion in early islet autoimmunity of Ab+ subjects, but not in insulin-treated T1D patients. Furthermore, the increase in IL-4 secretion in Ab+ subjects was associated with insulin autoantibody responses. There was no correlation of either IFNgamma or IL-4 secretion with insulin antibody responses in patients already treated with exogenous insulin. In conclusion, our findings reveal that quantification of cytokine responses to proinsulin in peripheral blood may prove to be a promising specific marker of diabetes progression and could, in addition to insulin autoantibodies, be used in the prediction of type 1 diabetes.

Human T-cells recognise N-terminally Fmoc-modified peptide

We aimed to generate T-cell clones specific for human pre-proinsulin. An HLA DQ8, CD4+ T-cell clone that recognised a 10mer (C65-A9) peptide from pre-proinsulin was isolated. Further analysis revealed that the clone responded neither to recombinant proinsulin nor to re-synthesised C65-A9 peptide. Analysis of the original peptide revealed minor contamination (<0.5%) with an N-terminal Fmoc adduct. This peptide was synthesised and shown to stimulate the clone. Thus, Fmoc-modified peptides, which are common contaminants in synthetic peptides, can stimulate human CD4+ T-cells. This finding has important implications for the use of synthetic peptides in screening and epitope mapping studies and their use as vaccines in humans.

Prospects for the prevention and reversal of type 1 diabetes mellitus

Type 1 (insulin-dependent) diabetes mellitus results from selective immune-mediated destruction of pancreatic islet beta cells. Strategies to prevent or reverse the development of diabetes can be divided into three groups, depending on whether they focus on beta-cell protection, regeneration or replacement. Prevention of immune beta-cell destruction involves either halting the immune attack directed against beta cells or making beta cells better able to withstand immune attack, for example, by making them resistant to free radical damage. The recent identification of beta-cell growth factors and development of stem cell technologies provides an alternative route to the reversal of diabetes, namely beta-cell regeneration. Interestingly, stem cell-derived islets appear to be less sensitive to recurrent immune destruction that is normally seen in response to islet transplantation. The last alternative is beta-cell replacement or substitution. This covers a wide range of interventions including human whole pancreas transplantation, xenotransplantation, genetically modified beta cells, mechanical insulin sensing and delivery devices, and the artificial pancreas. This review describes recent advances in each of these research areas and aims to provide clinicians with an idea of where and when an effective strategy to prevent or reverse diabetes development will become available.

Spontaneous peripheral T-cell responses to the IA-2beta (phogrin) autoantigen in young nonobese diabetic mice

Phogrin (IA-2beta), a major autoantigen in type 1 diabetes in man is recognized by peripheral T cells in the nonobese diabetic (NOD) mouse. CD4(+) T-cell clones derived from immunized NOD animals elicit islet destruction in a disease transfer model. Spontaneous proliferative responses to the protein and derived peptide epitopes were detected in peripheral lymph node cells (LNC) of unprimed NOD mice but not BALB/c controls as early as 4 weeks of age at a time point when insulitis in NOD animals is minimal. Responses to irradiated NOD islet cells but not irradiated NOD spleen cells were observed for both male and female NOD animals. Insulin, phogrin and phogrin-peptide 7 (aa 755-777) but not phogrin-peptide 2 (aa 640-659) or tetanus toxin peptide were recognized as antigens. Islet cell-reactive and phogrin peptide 7-specific CD4(+) T-cell lines were generated from splenocytes of unprimed 4-week-old NOD females and shown to secrete Th1-type cytokines. The results show that the phogrin molecule is targeted early in the course of disease in NOD animals at a time when circulating autoantibodies are absent and insulitis is minimal.

Complexity of human immune response profiles for CD4+ T cell epitopes from the diabetes autoantigen GAD65

Complex protein antigens contain multiple potential T cell recognition epitopes, which are generated through a processing pathway involving partial antigen degradation via proteases, binding to MHC molecules, and display on the APC surface, followed by recognition via the T cell receptor. We have investigated recognition of the GAD65 protein, one of the well-characterized autoantigens in type I diabetes, among individuals carrying the HLA-DR4 haplotypes characteristic of susceptibility to IDDM. Using sets of 20-mer peptides spanning the GAD65 molecule, multiple immunostimulatory epitopes were identified, with diverse class II DR molecules functioning as the restriction element. The majority of T cell responses were restricted by DRB1 molecules; however, DRB4 restricted responses were also observed. Antigen-specific T cell clones and lines were derived from peripheral blood samples of pre-diabetic and IDDM patients and T cell recognition and response were measured. Highly variable proliferative and cytokine release profiles were observed, even among T cells specific for a single GAD65 epitope.

Th2 dominance of T helper cell response to preproinsulin in individuals with preclinical type 1 diabetes

In human type 1 diabetes (T1D) autoantibodies to insulin precede clinical disease, while little is known about the contribution of insulin-specific T lymphocytes-in particular, T helper (Th) subsets. Here we have studied the in vivo primed cytokine response to preproinsulin in peripheral blood mononuclear cells (PBMCs) and two major Th cell subsets-CD45RO+ memory cells and CD45RA+ naive/resting cells-in 35 individuals with HLA-DRB1*04, DQB1*0302 diabetes risk marker: 12 patients with T1D, 12 autoantibody-positive (Ab+) individuals, and 11 healthy controls. Cytokine secretion (TNF-alpha, IFN-gamma, IL-2, IL-4, IL-5, and IL-10) was measured in the supernatants of the cultures stimulated with 21 overlapping preproinsulin peptides as well as proinsulin and insulin. In Ab+ individuals our results reveal higher IL-4 levels in CD45RO+ memory cells and higher IL-5 levels in CD45RA+ naive/resting cells, while higher IL-2 production was found in PBMCs. In contrast, in PBMCs of T1D patients higher IFN-gamma and IL-10 secretion was found. Our data delineate characteristic cytokine patterns in peripheral T lymphocytes from patients at different stages of the T1D development.

Predominantly recognized proinsulin T helper cell epitopes in individuals with and without islet cell autoimmunity

Antibody response to insulin and to its precursor ProInsulin is associated with increased risk for type 1 diabetes (T1D), though little is known about T cell reactivity to this molecule. In the present study from peripheral blood mononuclear cells (PBMC), in vivo primed CD45RO+ memory T helper (Th) cells were enriched and their reactivity to eight overlapping ProInsulin peptides and to protein was analyzed. Individuals with high risk HLA-DRB1*04, DQB1*0302 alleles were investigated: relatives of patients with T1D having humoral markers of islet cell autoimmunity (autoantibody positive, Ab+; n=11), patients with T1D (n=8), and healthy control individuals (n=16). The ProInsulin epitope which was most frequently recognized in all the tested individuals was C-peptide (C) 18-A-chain (A)1. In Ab+ relatives the responses to this epitope and to two additional parts of the ProInsulin, B-chain (B) 11-C24 and C28-A21, was observed. In T1D patients who have already been treated with insulin, response to peptide B20-C4 and to the entire insulin molecule predominates. Our findings suggest that the spontaneous memory Th cell response to ProInsulin in individuals with high risk HLA alleles is predominantly directed to one epitope which maps to the central, C-peptide region. In individuals with humoral markers of islet cell autoimmunity and in patients with T1D, spread response to distinct ProInsulin regions was observed.

Effect of modified diabetic splenocytes on mice injected with splenocytes from multiple low-dose streptozotocin diabetic donors

Etiological agents of autoimmune processes that have been made nonvirulent by several treatments, i.e., mitomycin C (Mit C), can be used as a vaccine to protect against disease. In this work we studied the effects of splenocytes from diabetic mice on animals that had been injected with modified splenocytes (Mit C-treated splenocytes from multiple low-dose streptozotocin [mld-sz] mice) 15 days before. Splenocytes from mld-sz diabetic donors altered i.p. glucose tolerance and the first peak of insulin secretion pattern when injected into normal singeneic recipients. These effects can be prevented partially (one injection in a vaccine form) or completely (two injections with a 15-day interval) by a previous injection of Mit C-treated mononuclear splenocytes (MS) from mld-sz mice. The fact that control splenocytes previously treated with Mit C were not able to achieve similar results indicates that donor splenocytes have to be diabetic to prevent the disease. On the other hand, Mit C-treated diabetic MS were not effective in preventing the alterations in glucose tolerance and in the pattern of insulin secretion when injected into athymic mice. This suggests that the preventive effect of Mit C-treated diabetic MS injection also implies an active role of the T cells from the recipient mice. Mit C-treated diabetic splenocytes are preferentially trapped by the pancreas and the lymph nodes from recipient mice. Our results show that the impairment in glucose tolerance and in the insulin secretion pattern produced by diabetic splenocyte transfer can be prevented by one or two previous injections of Mit C-modified diabetic splenocytes.

Cytotoxic T cells to an epitope in the islet autoantigen IA-2 are not disease-specific

Cytotoxic CD8 T lymphocytes (CTL) are effectors of pancreatic islet beta-cell destruction in type 1 diabetes but, with the exception of a single report, CTL to islet antigen peptides have not been identified. We used autologous blood monocyte-derived dendritic cells to elicit HLA-A2-restricted CTL to a peptide, MVWESGCTV (aa 797-805), that is contiguous with a dominant CD4 T-cell epitope in the islet antigen tyrosine phosphatase IA-2. IA-2 peptide-specific CTL activity measured as 51Cr release from autologous lymphoblasts was detected in 2/6 islet antibody-positive relatives at high risk for type 1 diabetes but also in 2/6 closely HLA-matched controls. All subjects had CTL activity to an HLA-A2-restricted Epstein-Barr virus peptide. CTL to the IA-2 self-peptide were therefore not disease-specific, consistent with other evidence that autoreactive T cells are present in healthy individuals.

Intermolecular antigen spreading occurs during the preclinical period of human type 1 diabetes

Intra- and intermolecular spreading of T cell responses to autoantigens has been implicated in the pathogenesis of autoimmune diseases. Therefore, we questioned whether T cell responses from subjects identified as at-risk (positive for autoantibody reactivity to islet proteins) for the development of type 1 diabetes, a cell-mediated autoimmune disease, would demonstrate intermolecular Ag spreading of T cell responses to islet cell proteins. Previously, we have demonstrated that by the time subjects develop type 1 diabetes, they have T cell responses to numerous islet proteins, whereas T cells from normal controls respond to a limited number of islet proteins. Initial testing of PBMC responses from 25 nondiabetic at-risk subjects demonstrated that 16 of the 25 subjects have PBMC responses to islet proteins similar to controls. Fourteen of these 16 subjects were available for follow-up. Eleven of the 14 developed T cell responses to increasing numbers of islet proteins, and 6 of these subjects developed type 1 diabetes. In the nine subjects who already demonstrated T cell Ag spreading at the initial visit, four were available for follow-up. Of these four, two had increases in T cell reactivity to islet proteins, while two maintained their initial levels of T cell reactivity. We also observed Ag spreading in autoantibody reactivity to islet proteins in nine of the 18 at-risk subjects available for follow-up. Our data strongly support the conclusion that intermolecular spreading of T cell and Ab responses to islet proteins occurs during the preclinical period of type 1 diabetes.

Intradermal skin test with diabetes specific antigens in patients with type 1 diabetes

Cell mediated immune response in vitro to a number of antigens has been reported in patients with Type 1 diabetes. The aim of the present study was to develop an in vivo intradermal (delayed type hypersensitivity) skin test using antigens known to be recognized by lymphocytes of patients with Type 1 diabetes and to compare, where possible, the in vivo response to the in vitro T cell proliferation to the same antigens. The skin test was performed in the following group of patients: 55 with recent onset Type 1 diabetes; 16 patients with Type 1 diabetes of longer duration; 10 patients with autoimmune thyroid disease and 20 patients with Latent Autoimmune Diabetes in Adults (LADA). Type 1 diabetes specific antigens for the skin test included glutamic acid decarboxilase (GAD65), insulin and beta casein, whereas diabetes non specific antigens included tetanus toxoid, diphteria, proteus, tubercolin, streptococcus, and glycerol as control. A multitest device consisting of heads delivering intradermally 10 microl of solution containing the antigens was applied to the forearms; the specific antigens were injected in one forearm whereas the non specific antigens were injected in the other forearm. Reading of the reaction, which was considered positive in the presence of a nodule of 2 mm diameter was performed 48 h after the multitest application. The in vitro T cell response to diabetes specific antigens used in the multitest was studied using conventional proliferation assays in patients with recent onset Type 1 diabetes and in age matched normal subjects. Only recent onset Type 1 diabetes patients showed an in vivo positive response to GAD65, such response being detectable in 10 patients (18%). Two patients reacted also to beta casein and insulin, all other patient groups resulted negative but 2 patients with longer duration of Type 1 diabetes. There was no apparent link between the in vivo skin test and in vitro T cell proliferation to GAD65. We conclude that in vivo cell mediated immune reaction to GAD65, insulin and beta casein can be visualized in a minority of patients with recent onset Type 1 diabetes. Further studies are required to determine specificity and whether altering the dose can improve the sensitivity of the test.

Type I diabetes and multiple sclerosis patients target islet plus central nervous system autoantigens; nonimmunized nonobese diabetic mice can develop autoimmune encephalitis

Type I diabetes and multiple sclerosis (MS) are distinct autoimmune diseases where T cells target either islet or CNS self-proteins. Unexpectedly, we found that autoreactive T cells in diabetic patients, relatives with high diabetes risk, nonobese diabetic (NOD) mice, and MS patients routinely target classical islet as well as CNS autoantigens. The pathogenic potential of CNS autoreactivity was testable in NOD mice. Pertussis holotoxin, without additional Ags or adjuvants, allowed development of an NOD mouse-specific, autoimmune encephalitis with variable primary-progressive, monophasic, and relapsing-remitting courses. T cells from diabetic donors transferred CNS disease to pertussis toxin-pretreated NOD.scid mice, with accumulation of CD3/IFN-gamma transcripts in the brain. Diabetes and MS appear more closely related than previously perceived. NOD mouse-specific, autoimmune encephalitis provides a new MS model to identify factors that determine alternative disease outcomes in hosts with similar autoreactive T cell repertoires.

Antidiabetogenic effect of pentoxifylline is associated with systemic and target tissue modulation of cytokines and nitric oxide production

We have shown recently that xanthine derivative pentoxifylline (PTX) downregulates an inflammatory autoimmune process triggered in genetically susceptible Dark Agouti rats by multiple low doses of streptozotocin (MLD-SZ, 20 mg/kg/day ip for 5 days). We studied the cellular and molecular consequences of PTX treatment during MLD-SZ-induced diabetes with special emphasis on local vs. systemic production of inflammatory mediators. Administration of PTX (200 mg/kg/day for 10 days) during induction of the disease reduced clinical signs of diabetes and protected rats from development of destructive intrainsulitis. Pentoxifylline did not affect diabetogenic effect of single high dose of SZ (100 mg/kg SZ). Ex vivo analysis of the islets of Langerhans performed in early disease development revealed that PTX downregulates production of proinflammatory cytokines IFN-gamma and TNF, as well as inducible nitric oxide synthase (iNOS) expression and NO production. In addition, PTX treatment suppressed splenocyte autoreactivity, as well as the frequency of cells expressing IL-2R and MHC class II antigens. There was no evidence of any changes in proportion of ICAM-1 and LFA-1 expressing splenocytes in comparison to control MLD-SZ-treated animals. In contrast to suppressed intraislet production, high peripheral expression of both iNOS mRNA and NO was found in MLD-SZ rats treated with PTX. Taken together, the data indicate that the effect on both systemic and intra-islet production of NO, suppression of autoreactive cell activation and of local type 1 cytokine release may contribute to the therapeutic benefit achieved by PTX in the rat.

A disease-associated cellular immune response in type 1 diabetics to an immunodominant epitope of insulin

The 9-23 amino acid region of the insulin B chain (B9-23) is a dominant epitope recognized by pathogenic T lymphocytes in nonobese diabetic mice, the animal model for type 1 diabetes. We describe herein similar (B9-23)-specific T-cell responses in peripheral lymphocytes obtained from patients with recent-onset type 1 diabetes and from prediabetic subjects at high risk for disease. Short-term T-cell lines generated from patient peripheral lymphocytes showed significant proliferative responses to (B9-23), whereas lymphocytes isolated from HLA and/or age-matched nondiabetic normal controls were unresponsive. Antibody-mediated blockade demonstrated that the response was HLA class II restricted. Use of the highly sensitive cytokine-detection ELISPOT assay revealed that these (B9-23)-specific cells were present in freshly isolated lymphocytes from only the type 1 diabetics and prediabetics and produced the proinflammatory cytokine IFN-gamma. This study is, to our knowledge, the first demonstration of a cellular response to the (B9-23) insulin epitope in human type 1 diabetes and suggests that the mouse and human diseases have strikingly similar autoantigenic targets, a feature that should facilitate development of antigen-based therapeutics.

Early Th1 response in unprimed nonobese diabetic mice to the tyrosine phosphatase-like insulinoma-associated protein 2, an autoantigen in type 1 diabetes

The insulinoma-associated protein 2 (IA-2) is a phosphatase-like autoantigen inducing T and B cell responses associated with human insulin-dependent diabetes mellitus (IDDM). We now report that T cell responses to IA-2 can also be detected in the nonobese diabetic (NOD) mouse, a model of human IDDM. Cytokine secretion in response to purified mouse rIA-2, characterized by high IFN-gamma and relatively low IL-10 and IL-6 secretion, was elicited in spleen cells from unprimed NOD mice. Conversely, no response to IA-2 was induced in spleen cells from BALB/c, C57BL/6, or Biozzi AB/H mice that express, like NOD, the I-A(g7) class II molecule, but are not susceptible to spontaneous IDDM. The IA-2-induced IFN-gamma response in NOD spleen cells could already be detected at 3 wk and peaked at 8 wk of age, whereas the IL-10 secretion was maximal at 4 wk of age and then waned. IA-2-dependent IFN-gamma secretion was induced in CD4(+) cells from spleen as well as pancreatic and mesenteric lymph nodes. It required Ag presentation by I-A(g7) molecules and engagement of the CD4 coreceptor. Interestingly, cytokines were produced in the absence of cell proliferation and IL-2 secretion. The biological relevance of the response to IA-2 is indicated by the enhanced IDDM following a single injection of the recombinant protein emulsified in IFA into 18-day-old NOD mice. In addition, IFN-gamma production in response to IA-2 and IDDM acceleration could be induced by IL-12 administration to 12-day-old NOD mice. These results identify IA-2 as an early T cell-inducing autoantigen in the NOD mouse and indicate a role for the IA-2-induced Th1 cell response in IDDM pathogenesis.

Prognostic factors for the course of beta cell function in autoimmune diabetes

This study presents a 2-yr follow-up of 281 patients, aged 15-34 yr, diagnosed with diabetes between 1992 and 1993. At diagnosis, 224 (80%) patients were positive for at least one of the following autoantibodies: islet cell antibodies (ICAs), glutamic acid decarboxylase antibodies (GADAs), or tyrosine phosphatase antibodies (IA-2As); the remaining 57 (20%) patients were negative for all three autoantibodies. At diagnosis, C-peptide levels were lower (0. 27; 0.16-0.40 nmol/L) in autoantibody-positive patients compared with autoantibody-negative patients (0.51; 0.28-0.78 nmol/L; P: < 0. 001). After 2 yr, C-peptide levels had decreased significantly in patients with autoimmune diabetes (0.20; 0.10-0.37 nmol/L; P: = 0. 0018), but not in autoantibody-negative patients. In patients with autoimmune diabetes, a low initial level of C-peptide (odds ratio, 2. 6; 95% confidence interval, 1.7-4.0) and a high level of GADAs (odds ratio, 2.5; 95% confidence interval, 1.1-5.7) were risk factors for a C-peptide level below the reference level of 0.25 nmol/L 2 yr after diagnosis. Body mass index had a significant effect in the multivariate analysis only when initial C-peptide was not considered. Factors such as age, gender, levels of ICA or IA-2A or insulin autoantibodies (analyzed in a subset of 180 patients) had no effect on the decrease in beta-cell function. It is concluded that the absence of pancreatic islet autoantibodies at diagnosis were highly predictive for a maintained beta-cell function during the 2 yr after diagnosis, whereas high levels of GADA indicated a course of decreased beta-cell function with low levels of C-peptide. In autoimmune diabetes, an initial low level of C-peptide was a strong risk factor for a decrease in beta-cell function and conversely high C-peptide levels were protective. Other factors such as age, gender, body mass index, levels of ICA, IA-2A or IAA had no prognostic importance.

Evidence for recognition of novel islet T cell antigens by granule-specific T cell lines from new onset type 1 diabetic patients

Type 1 diabetes is a T cell-mediated autoimmune disease where a number of islet beta-cell target autoantigens have been characterized on the basis of reactivity with autoantibodies. Nevertheless, there remains uncertainty of the nature of another group of autoantigens associated with the secretory granule fraction of islet beta-cells that appear to be targeted predominantly by autoreactive T cells. We have previously characterized CD4+, HLA-DR-restricted T cell lines from new onset type 1 diabetic patients that are specific for the secretory granule fraction of rat tumour insulinoma, RIN. The T cell line from the first patient, HS, proliferates in response to crude microsomal membranes prepared from a recently established, pure human islet beta-cell line NES2Y. In addition, the HS line also responds to secretory granule fractions prepared from a murine tumour insulinoma grown in RIP-Tag mice, showing the recognition of species-conserved antigen(s) in beta-cells. Using partially matched antigen-presenting cells, the HS T cells and another line derived from a second patient, MR, were shown to be restricted by disease-associated DRB1*0101 and DRB1*0404 alleles, respectively. Neither the HS or MR T cell lines proliferate in response to a large panel of candidate islet cell antigens, including insulin, proinsulin, glutamic acid decarboxylase, the protein tyrosine phosphatase IA-2/phogrin, imogen-38, ICA69 or hsp60. Our data provide compelling evidence of the presence of a group of antigens associated with the secretory granule fraction of islet beta-cells recognized by the T cell lines, whose definition may contribute to our knowledge of disease induction as well as to diagnosis.

Reactivation of type 1 diabetes in patients receiving human fetal pancreatic tissue transplants without immunosuppression

BACKGROUND

Type 1 diabetes is a cell-mediated autoimmune disease. Successful transplantation of human fetal pancreatic tissue into type 1 diabetic patients must address both autoimmunity and allograft rejection. We investigated whether humoral and cellular responses to islet antigens could be demonstrated in the peripheral blood of type 1 diabetic subjects receiving human fetal pancreatic tissue transplants.

METHODS

We investigated peripheral blood mononuclear cell (PBMC) responses, using cellular immunoblotting, and autoantibody responses to islet proteins, before transplant and at 3-month intervals after transplant, of nine long-term type 1 diabetes patients (mean disease duration of 21 years) receiving human fetal pancreatic tissue subcutaneously into the abdominal wall without immunosuppression.

RESULTS

Before transplant, all nine subjects were islet cell autoantibody (ICA)-negative and seven out of nine subjects were glutamic acid decarboxylase autoantibody (GADAb)-positive. After transplant, all subjects became ICA(+) and the two patients who were GADAb(-) before transplant became GADAb(+) after transplant. Maximum PBMC reactivity to separated human fetal pancreatic proteins was observed in four patients 3 months after transplant, in one patient at 6 months, in two patients at 9 months, and in one patient at 12 months after transplant. One subject, who had PBMC reactivity to multiple islet proteins before transplant, continued to respond to multiple islet proteins throughout the study.

CONCLUSIONS

We conclude that the development in the peripheral blood of ICA, GADAb, and PBMC reactivity to human fetal pancreatic proteins in the trans plant recipients is most consistent with reactivation of the type 1 diabetes disease process.

Peripheral blood mononuclear cell responses from type 1 diabetic patients and subjects at-risk for type 1 diabetes to human fetal pancreatic tissue proteins

BACKGROUND

Fetal pancreatic tissue has been suggested to be less immunogenic than adult islets. Thus, transplantation of human fetal pancreatic tissue as treatment for type 1 diabetes has been gaining interest. To investigate this question, we tested the peripheral blood mononuclear cell (PBMC) responses from different subject populations to human adult islet proteins (AIP) versus human fetal pancreatic proteins (FPP).

METHODS

PBMC responses to FPP and AIP from normal controls (n=14), newly diagnosed type 1 diabetes patients (n=5), long-term type 1 diabetes patients (n=9), and subjects at-risk for development of type 1 diabetes (n=3) were studied.

RESULTS

We observed that normal controls demonstrated PBMC reactivity to 0-3 molecular weight regions (mwr) for both the AIP (mean+/-SD, 0.8+/-1.1) and the FPP (0.6+/-0.7). In contrast, newly diagnosed type 1 diabetic patients (<1 year) demonstrated PBMC responses to 9-16 mwr for the AIP (12.8+/-2.5) and 0-14 mwr for the FPP (6.8+/-5.0). The PBMCs from long-term type 1 diabetes patients (> 3 years) were responsive to 2-11 mwr for AIP (6.0+/-2.8) and 0-11 mwr for FPP (4.9+/-4.0). Three nondiabetic ICA positive subjects at-risk for development of type 1 diabetes demonstrated positive PBMC reactivity to 9-18 mwr for the AIP (12.7+/-3.9) and 4-18 mwr for the FPP (10.0+/-5.9).

CONCLUSIONS

We conclude that human fetal pancreatic proteins are not significantly less stimulatory than human adult islet proteins to PBMCs of subjects with or at risk for type 1 diabetes.

Proliferative responses to selected peptides of IA-2 in identical twins discordant for Type 1 diabetes

BACKGROUND

The aim of the study was to define T lymphocyte reactivity to selected peptides of an islet antigen IA-2, associated with Type 1 diabetes.

METHODS

We used 10 peptides selected from the IA-2 molecule due to their predicted ability to bind to HLA-DRB1*0401, a Type 1 diabetes-associated allele. We tested 21 identical twin pairs discordant for the disease and 15 control subjects and then followed them prospectively; seven non-diabetic twins developed diabetes.

RESULTS

Twins of identical pairs tended to respond to different peptides suggesting that the T cell response is, to a degree, shaped by non-genetically determined factors (p<0. 0001). However, there was no difference in the T cell responses between diabetic twins and either their non-diabetic identical twins or control subjects and the response was heterogenous. T cell responses did not differ in those seven non-diabetic twins who developed diabetes from those twins who did not. T cell responses to peptide 11 (amino acids 502-514) was immunodominant in diabetic twins as well as their non-diabetic twins and controls; responses were not correlated with HLA, IA-2 antibodies, age or duration of disease.

CONCLUSION

We conclude that T cell responses to selected IA-2 peptides are not genetically determined, heterogeneous, not strictly HLA controlled and did not distinguish diabetic or prediabetic twins from non-diabetic twins or controls. The identification of an immunodominant T cell response to IA-2 peptide 502-514 raises the possibility that this, or similar, epitopes may be of therapeutic value in disease prevention.

Reactivation of type 1 diabetes in patients receiving human fetal pancreatic tissue transplants without immunosuppression

BACKGROUND

Insulin-dependent (type 1) diabetes is a cell-mediated autoimmune disease. Successful transplantation of human fetal pancreatic tissue into type 1 diabetic patients must address both autoimmunity and allograft rejection. We investigated whether humoral and cellular responses to islet antigens could be demonstrated in the peripheral blood of type 1 diabetic subjects receiving human fetal pancreatic tissue transplants.

METHODS

We investigated peripheral blood mononuclear cell (PBMC) responses, using cellular immunoblotting, and autoantibody responses to islet proteins, before transplantation and at 3-month intervals after transplantation. Our study population included nine long-term type 1 diabetes patients (mean disease duration of 21 years) receiving human fetal pancreatic tissue subcutaneously into the abdominal wall without immunosuppression.

RESULTS

Before transplantation, all nine subjects tested negative for islet cell autoantibody (ICA), and seven of nine subjects tested positive for glutamic acid decarboxylase autoantibody (GADAb). After transplantation, all subjects became ICA(+), and the two patients who were GADAb(-) before transplantation, became GADAb(+) after transplantation. Maximum PBMC reactivity to separated human fetal pancreatic proteins was observed in four patients at 3 months, in one patient at 6 months, in two patients at 9 months, and in one patient at 12 months after transplantation. One subject, who had PBMC reactivity to multiple islet proteins before transplantation, continued to respond to multiple islet proteins throughout the study.

CONCLUSIONS

We conclude that the development in the peripheral blood of ICA, GADAb, and PBMC reactivity to human fetal pancreatic proteins in the transplant recipients is most consistent with reactivation of the type 1 diabetes disease process.

GAD65 and insulin B chain peptide (9-23) are not primary autoantigens in the type 1 diabetes syndrome of the BB rat

To investigate whether GAD65 whole molecule, GAD65 p35 or insulin B chain peptide (amino acids 9-23) play an essential role in the pathogenesis of type 1 diabetes in the BioBreeding (BB) rat, we gave serial injections of GAD65, p35 or insulin B chain (9-23) to six groups of BB/Worcester rats. The individual antigens were administered either intrathymically on day 2 and intraperitoneally in MF 59-0 adjuvant 5 times during the first 5 weeks, or by intranasal instillation once neonatally and 5 days/week for the following 6 weeks. Control groups were injected with vehicle only. Age of onset of diabetes and degree of insulitis were not different between controls and antigen-treated rats. Rats that received GAD65 intrathymically and intraperitoneally developed high GAD65-antibody titers without altering diabetes development. In GAD65-treated animals, serum antibodies recognized epitopes at 3 sites on GAD65 in diabetic animals but only at 1 site in non-diabetic animals. GAD65-injected animals also showed a significant reduction of IFN-gamma mRNA expression in the thymus. This study provides evidence against the hypothesis that GAD65 and insulin B chain peptide (9-23) are primary diabetogenic autoantigens in BB rats because immunizations with these antigens and GAD65-induced immune deviation did not alter the development of diabetes.

Autoreactive T cell responses in insulin-dependent (Type 1) diabetes mellitus. Report of the first international workshop for standardization of T cell assays

Type 1 diabetes is thought to result from a T cell-mediated destruction of the pancreatic beta-cells. Multiple and sometimes conflicting studies have identified a variety of aberrations in the cellular immune response to autoantigens in persons with the disease. Potential explanations for these discrepancies include incomparable techniques or culture conditions, diversity in the populations of patients or controls tested, and differences in autoantigen preparations. A T cell workshop was organized by the Immunology of Diabetes Society with the aim of appreciating and identifying problems associated with autoreactive T cell assays in type 1 diabetes. As a first phase, a series of candidate autoantigens were analysed by reference laboratories for quality. Subsequently, these preparations, as well as control stimuli, were distributed in a blind fashion to 26 laboratories worldwide, including all experienced centres, for analysis of T cell proliferation assays in 10 recent onset type 1 diabetes and 10 non-diabetic controls. For this analysis, participants used their own assays and references. The islet autoantigen quality control analyses performed prior to the distribution indicate that the quality of recombinant autoantigen preparations requires improvement. For example, several T cell clones specific for glutamic acid decarboxylase (GAD65) were unable to cross-react with GAD65 expressed in baculovirus, yeast or bacteria. Moreover, autoantigens expressed in E. coli interfered with autoantigen-specific proliferation of both T cell clones and peripheral blood mononuclear cells. Nonetheless, responses could be measured to all autoantigen preparations evaluated in the workshop. During the blind phase of the study, all centres were able to reproducibly measure T cell responses to two identical samples of tetanus toxoid, but there was significant interlaboratory variation in sensitivity and extent of the proliferative response measured. Third, the results using candidate autoantigens indicated that although a few laboratories could distinguish type 1 diabetes patients from non-diabetic controls in proliferative responses to individual islet autoantigens, in general, no differences in T cell proliferation between the two groups could be identified. This first T cell workshop on T cell autoreactivity in type 1 diabetes confirms that this was a difficult area for interlaboratory investigations, but provided insight towards future efforts focused on standardizing autoreactive T cell measurements. Some previously reported conflicting results can in part be explained by the observed interlaboratory variability. The inability to discriminate normal controls from new onset type 1 diabetes patients suggests that measuring proliferative responses in PBMC represents an incomplete picture of the immune response, perhaps complicated by difficulties in identifying suitable antigens and assays for standardized use.

Constitutive impaired TCR/CD3-mediated activation of T cells in IDDM patients co-exist with normal co-stimulation pathways

IDDM is a T cell-mediated autoimmune disease which is paradoxically associated with T cell functional deficiencies. The proliferative response of PBMC under CD3-, Vbeta2-, Vbeta8- and Vbeta7-stimulation was investigated in IDDM and NIDDM patients, non-diabetic first-degree relatives and control subjects. Despite normal surface expression of the TCR/CD3 complex, the TCR/CD3-mediated proliferation of PBMC from IDDM patients was significantly impaired compared to control subjects (P<0.05). This defect was specific for the autoimmune disease, constitutive and not linked to the class II MHC genotype, to metabolic disturbances or to presence of specific autoantibodies. Inefficient activation of T cells was not related to a lower capacity of CD28 to transduce co-stimulative signals because proliferative responses under CD2/CD28 stimulations were similar in IDDM and control groups. The IL-2/IL-2 receptor system was functional because unstimulated PBMC proliferated in response to increasing amounts of IL-2. Nevertheless, despite normal expression of CD25, addition of IL-2 did not normalize the proliferative defect linked to IDDM. In conclusion, excluding a faulty co-stimulation pathway, these results are in favour of a constitutive defect in the CD3/TCR transduction machinery, increasing sensitivity to apoptosis or anergy in T cells from IDDM patients.

T cell reactivity to human insulinoma cell line (CM) antigens in patients with type 1 diabetes

Autoimmune (type 1) diabetes mellitus results from a progressive destruction of insulin secreting beta cells operated by T lymphocytes in pancreatic islets. Circulating autoreactive T cells to specific beta cell antigens are detected in patients with type 1 diabetes. To date, several beta cell autoantigens have been identified in this disease (GAD, IA-2, 38kD secretory protein, insulin, ICA69 etc.), however, it is possible that also other unidentified self molecules contribute to trigger beta cell autoimmunity. In this study we used the human insulinoma cell line CM as source of beta cell antigens to detect reactive T lymphocytes in patients with type 1 diabetes mellitus. This cell line has been previously shown to express a number of recognized beta cell antigens. Since the expression of several beta cell antigens is affected by glucose stimulation we tested two preparations of CM cells cultured under different conditions containing low (0.8 mM) and high glucose concentration (11 mM). T cell proliferation was measured using cells from 32 patients with type 1 diabetes (19 of recent onset and 13 at 3 to 22 months from diagnosis) and 27 age-matched control subjects. A significant increase in T cell proliferation to CM cells grown in high glucose conditions (11 mM) (p < 0.05) was found in type 1 diabetic patients compared to controls. No significant differences were observed when using CM cells cultured at the low glucose concentration. Furthermore, the response to both extracts of CM cells was independent of disease duration (p = 0.6 for both CM cells cultured at 0.8 and 11 mM glucose). These data indicate that T cell reactivity to homogenates of CM cells is detectable in patients with type 1 diabetes and suggest that this human insulinoma cell line is an interesting potential source of beta cell material for immunological studies of autoimmune diabetes.

T cell response pattern to glutamic acid decarboxylase 65 (GAD65) peptides of newly diagnosed type 1 diabetic patients sharing susceptible HLA haplotypes

Autoantibodies and autoreactive T lymphocytes directed against several pancreatic beta cell proteins such as GAD65 have been identified in the circulation before and at the onset of clinical type 1 (insulin-dependent) diabetes. Using GAD65 synthetic peptides, we studied the proliferative response of peripheral blood mononuclear cells (PBMC) either from recently diagnosed type 1 diabetic patients, of whom the majority share the disease-associated HLA class II haplotype (DR4-DQB1*0201 or DR3-DQB1*0302), or from HLA-matched control subjects. We found that 67% (14/21) of the type 1 diabetic patients and 39% (9/23) of the control subjects exhibited a positive proliferative response. Compared with control subjects, however, PBMC from diabetic patients proliferated more frequently (P < 0.05) in the presence of peptide pools from the C-terminal region of GAD65 (amino acids 379-585). Diabetic patients with the same HLA-DQ or HLA-DR alleles showed partially identical T cell reactivity, but no clear correlation could be made between MHC class II specificity and T cell epitopes because of multiple combinations of class II alleles. In addition, by flow cytometry, we studied the direct binding of GAD65 peptides to MHC class II molecules of Epstein-Barr virus (EBV)-transformed B (EBV-B) cells obtained from a diabetic patient. We found that 11 GAD peptides were able to bind to the highly susceptible haplotype DRB1*0301/0401-DQA1*0301/0501-DQB1*0302/0201 on the surface of EBV-B cells in partial correlation with the results obtained in the proliferation assays.

T cell responses to enterovirus antigens and to beta-cell autoantigens in unaffected children positive for IDDM-associated autoantibodies

Enterovirus infections have been implicated in the pathogenesis of IDDM in a number of studies. The aim of the present study was to evaluate whether the cellular immune response to enterovirus antigens is abnormal in children who test positive for IDDM-associated autoantibodies. Lymphocyte proliferation responses were analysed to enterovirus antigens and to a panel of beta-cell autoantigen preparations in 31 non-diabetic ICA and/or GAD65 antibody-positive children and in 19 ICA/GAD65-negative control children. The responses to highly purified enteroviruses did not differ between autoantibody (AA)-positive and -negative subjects. However, proliferation responses to coxsackievirus-infected cell lysate, which also included non-structural proteins of the virus, were higher in AA-positive than in AA-negative subjects (P<0.05). This difference was most marked in children carrying the HLA-DQB1*02 allele (P=0.01). AA-positive subjects also had higher responses to one of the three GAD65 antigen preparations compared to AA-negative subjects (P<0.05). Proliferation responses to the adenovirus hexon protein did not differ between the groups. These results show that the increased responses to virus infected cell lysates are associated with early phases of beta-cell autoimmunity.

T cell autoreactivity to proinsulin epitopes in diabetic patients and healthy subjects

We investigated the immune response to proinsulin, a potential autoantigen in IDDM secreted exclusively by pancreatic beta-cells. A total of 2,142 short-term cell lines were generated from 19 individuals; seven IDDM patients at the disease onset and 12 control subjects. No increase in the frequency of proinsulin reactive cells was observed in the IDDM group. To define proinsulin epitopes, proliferative responses of proinsulin-specific lines were examined against 10 overlapping 15 amino acid peptides encompassing the human proinsulin sequence. The predominant immune response was directed against the proinsulin p35-50 peptide located in the (C) connecting peptide between the alpha- and beta-chain of insulin. Recognition of the proinsulin p35-50 peptide could be shown by generating specific T cell clones against the peptide. However, unlike responses to other tissue-specific autoantigens there were only low proliferative responses to proinsulin as measured by 3H-thymidine incorporation. This low reactivity may be partially explained by the location of the p35-50 peptide in the C-peptide which is released into the circulation and therefore, may induce a clonal anergy of T reactive cells. However, the significantly higher 3H-thymidine incorporation after CD3-CD28 triggering showed that peptide specific T cells were capable of a significant response with a stronger TCR signal.

T-cell response to proinsulin and insulin in type 1 and pretype 1 diabetes

Insulin-dependent diabetes mellitus (IDDM) results from the selective destruction of pancreatic beta cells by a T cell-mediated autoimmune process. Insulin and proinsulin are the only known beta cell-specific autoantigens. Using short-term cultures of freshly isolated peripheral blood mononuclear cells, we evaluated T-cell responses to proinsulin and to insulin in IDDM patients and individuals at risk for IDDM. A proliferative T-cell response to proinsulin was observed in only 2 of 26 recent-onset IDDM subjects and 2 of 12 long-standing IDDM subjects and was associated with a proliferative response to insulin. In contrast, 5 of 13 islet cell autoantibody-positive first-degree relatives of IDDM patients showed a proliferative response to proinsulin alone, 3 of 13 to insulin alone, and 1 of 13 to both insulin and proinsulin. Overall, 9 of 13 ICA-positive first-degree relatives responded to either proinsulin or insulin. We observed an inverse relationship between antiinsulin antibodies and T-cell responses to insulin in ICA-positive first-degree relatives but not in long-standing IDDM patients. Our data indicate that proinsulin is a major antigen in IDDM and, further, illustrate the difference between the autoimmune response to insulin and the immune response to exogenous insulin.