HLA-DQ8-Associated T Cell Responses to the Diabetes Autoantigen Phogrin (IA-2β) in Human Prediabetes

T Cell-Mediated Beta Cell Destruction: Autoimmunity and Alloimmunity in the Context of Type 1 Diabetes

Type 1 diabetes (T1D) results from destruction of pancreatic beta cells by T cells of the immune system. Despite improvements in insulin analogs and continuous blood glucose level monitoring, there is no cure for T1D, and some individuals develop life-threatening complications. Pancreas and islet transplantation have been attractive therapeutic approaches; however, transplants containing insulin-producing cells are vulnerable to both recurrent autoimmunity and conventional allograft rejection. Current immune suppression treatments subdue the immune system, but not without complications. Ideally a successful approach would target only the destructive immune cells and leave the remaining immune system intact to fight foreign pathogens. This review discusses the autoimmune diabetes disease process, diabetic complications that warrant a transplant, and alloimmunity. First, we describe the current understanding of autoimmune destruction of beta cells including the roles of CD4 and CD8 T cells and several possibilities for antigen-specific tolerance induction. Second, we outline diabetic complications necessitating beta cell replacement. Third, we discuss transplant recognition, potential sources for beta cell replacement, and tolerance-promoting therapies under development. We hypothesize that a better understanding of autoreactive T cell targets during disease pathogenesis and alloimmunity following transplant destruction could enhance attempts to re-establish tolerance to beta cells.

Novel diabetes autoantibodies and prediction of type 1 diabetes

Autoantibodies are currently the most robust biomarkers of type 1 diabetes and are frequently used to establish entry criteria for the participation of genetically at-risk individuals in secondary prevention/intervention clinical trials. Since their original description almost 40 years ago, considerable efforts have been devoted toward identifying the precise molecular targets that are recognized. Such information can have significant benefit for developing improved metrics for identifying/stratifying of at-risk subjects, developing potential therapeutic targets, and advancing understanding of the pathophysiology of the disease. Currently, four major molecular targets ([pro]insulin, GAD65, IA-2, and ZnT8) have been confirmed, with approximately 94% of all subjects with a clinical diagnosis of type 1 diabetes expressing autoantibodies to at least one of these molecules at clinical onset. In this review, we summarize some of the salient properties of these targets that might contribute to their autoantigenicity and methods that have been used in attempts to identify new components of the humoral autoresponse.

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.

Tolerogenic vaccination reduced effector memory CD4 T cells and induced effector memory Treg cells for type I diabetes treatment

Background

Vaccination could induce immune tolerance and protected NOD mice from the development of type I diabetes (T1D). We previously demonstrated that insulin peptide (B9-23) combined with dexamethasone (DEX) stimulated the expansion of antigen specific regulatory T (Treg) cells which in turn effectively prevented T1D in NOD mice. Here, we aimed to investigate the therapeutic effect of tolerogenic vaccination for T1D treatment.

Methodology/Principal Findings

The diabetic NOD mice (Blood glucose level ≧250 mg/dl) were treated with B9-23 and DEX twice. The tolerance was restored by blocking maturation of dendritic cells (DCs) and inducing Treg cells in treated NOD mice. Remarkably, the reduction of autoreactive effector memory CD4 T (Tm) cells and the induction of functional effector memory Treg (mTreg) cells contributed to the improvement of T1D in treated NOD mice.

Conclusions/Significance

Tolerogenic vaccination restored tolerance and ameliorated T1D by suppressing effector CD4 Tm cells and inducing effector mTreg cells. Our findings implicate the potential of tolerogenic vaccination for T1D treatment.

Mapping I-A(g7) restricted epitopes in murine G6PC2

G6PC2, also known as islet-specific glucose 6-phosphatase catalytic subunit-related protein (IGRP), is a major target of autoreactive CD8(+) T cells in both diabetic human subjects and the non-obese diabetic (NOD) mouse. However, in contrast to the abundant literature regarding the CD8(+) response to this antigen, much less is known about the potential involvement of IGRP-reactive CD4(+) T cells in diabetogenesis. The single previous study that examined this question in NOD mice was based upon a candidate epitope approach and identified three I-A(g7)-restricted epitopes that each elicited spontaneous responses in these animals. However, given the known inaccuracies of MHC class II epitope prediction algorithms, we hypothesized that additional specificities might also be targeted. To address this issue, we immunized NOD mice with membranes from insect cells overexpressing full-length recombinant mouse IGRP and measured recall responses of purified CD4(+) T cells using a library of overlapping peptides encompassing the entire 355-aa primary sequence. Nine peptides representing 8 epitopes gave recall responses, only 1 of which corresponded to any of the previously reported sequences. In each case proliferation was blocked by a monoclonal antibody to I-A(g7), but not the appropriate isotype control. Consistent with a role in diabetogenesis, proliferative responses to 4 of the 9 peptides (3 epitopes) were also detected in CD4(+) T cells purified from the pancreatic draining lymph nodes of pre-diabetic female animals, but not from peripheral lymph nodes or spleens of the same animals. Intriguingly, one of the newly identified spontaneously reactive epitopes (P8 [IGRP(55-72)]) is highly conserved between mice and man, suggesting that it might also be a target of HLA-DQ8-restricted T cells in diabetic human subjects, an hypothesis that we are currently testing.

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.

Type 1 diabetes-associated HLA-DQ8 transdimer accommodates a unique peptide repertoire

HLA-DQ2 and HLA-DQ8 are strongly predisposing haplotypes for type 1 diabetes (T1D). Yet HLA-DQ2/8 heterozygous individuals have a synergistically increased risk compared with HLA-DQ2 or HLA-DQ8 homozygote subjects that may result from the presence of a transdimer formed between the α-chain of HLA-DQ2 (DQA1*05:01) and the β-chain of HLA-DQ8 (DQB1*03:02). We generated cells exclusively expressing this transdimer (HLA-DQ8trans), characterized its peptide binding repertoire, and defined a unique transdimer-specific peptide binding motif that was found to be distinct from those of HLA-DQ2 and HLA-DQ8. This motif predicts an array of peptides of islet autoantigens as candidate T cell epitopes, many of which selectively bind to the HLA transdimer, whereas others bind to both HLA-DQ8 and transdimer with similar affinity. Our findings provide a molecular basis for the association between HLA-DQ transdimers and T1D and set the stage for rational testing of potential diabetogenic peptide epitopes.

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.

Type 1 diabetes patients born to immigrants to Sweden increase their native diabetes risk and differ from Swedish patients in HLA types and islet autoantibodies

AIM

To determine whether type 1 diabetes mellitus (T1DM) patients, having parents who immigrated to Sweden, have increased T1DM risk before 18 yr compared with countries of origin. We also determined whether they have different human leukocyte antigen (HLA) genetic markers and islet autoantibodies at diagnosis compared with Swedish patients.

METHODS

A total of 1988 (53% males) newly diagnosed and confirmed T1DM patients <18 yr registered within the Better Diabetes Diagnosis (BDD) study (May 2005 to September 2008) were included. Participants were classified into three groups: Swedish, non-Swedish, and Mixed-origin patients according to country of origin of two generations (parents and grandparents). These groups were compared with respect to T1DM HLA markers and islet autoantibodies [glutamic acid decarboxylase autoantibodies (GAD65Ab), insulin autoantibodies (IAA), and islet antigen-2 autoantibodies (IA-2Ab)].

RESULTS

Only 30 (1.5%) patients were born outside Sweden. Swedish patients constituted 66%, non-Swedish patients 8%, Mixed origins 17%, and 9% were of uncertain origin. Confirmed T1DM in patients within the study was 22 (95% CI: 21-23) patients/10(5)/yr rate for Swedish patients compared with 14 (95% CI: 13-15) among non-Swedish patients. The HLA-DQ8 haplotype (p < 0.0001) and DQ2/8 genotype (p < 0.02) predominated among Swedish compared with non-Swedish patients. In contrast, DQ2 was the most frequent haplotype among non-Swedish patients [OR = 1.5 (95% CI: 1.0-2.0), p < 0.04]. Multiple (≥2) autoantibodies (p < 0.04) and specifically IA-2Ab (p < 0.001) were most prevalent among the Swedish patients. Multiple autoantibodies were associated with DQ8 among the Swedish patients only (p < 0.001).

CONCLUSION

Patients born to parents who had immigrated to the high T1DM incidence environment of Sweden have, compared with Swedish patients, more frequent HLA-DQ2 genetic markers and are diagnosed more often with GAD65Ab.

Autoimmunity in HLA-DQ8 transgenic mice expressing granulocyte/macrophage-colony stimulating factor in the beta cells of islets of langerhans

Type 1 diabetes (T1D) is a polygenic autoimmune disease with a strong HLA association particularly, HLA-DQ8. We investigated whether islet-specific expression of granulocyte/macrophage colony-stimulating factor (Ins.GM-CSF) in A Beta degrees.NOD.DQ8 mice (HLA-DQ8 transgenic mice on a NOD background lacking endogenous mouse MHC class II molecules) would predispose to development of spontaneous autoimmune diabetes. A Beta degrees.NOD.DQ8 mice expressing GM-CSF in the pancreatic ss cells (8+ G+) as well as litter mates lacking either HLA-DQ8 (8 - G+) or GM-CSF (8+ G -) or both (8 - G -) exhibited insulitis and sialadenitis of varying degrees. But none of the mice progressed to develop T1D. Other than the marked mononuclear cell infiltration in livers of mice expressing GM-CSF irrespective of HLA-DQ8 expression (8+ G+ or 8 - G+), no other changes were observed in the animals. Thus, we have shown for the first time that expression of HLA-DQ8 in the diabetes-predisposing mileu of NOD genetic background is not sufficient to predispose to development of autoimmune diabetes even when the potent immunostimulatory cytokine, GM-CSF is expressed in the pancreatic islets.

Evidence for in vivo primed and expanded autoreactive T cells as a specific feature of patients with type 1 diabetes

Identifying beta cell autoantigen-reactive T cells that are involved in the pathogenesis of type 1 diabetes has been troublesome for many laboratories. Disease-relevant autoreactive T cells should be in vivo Ag experienced. The aim of this study was to test this hypothesis and then use this principle as a strategy for identifying diabetes-relevant autoreactive T cells. In this study, a CSFE dilution assay was used to detect glutamic acid decarboxylase 65 (GAD65)- and insulin-responsive T cells and HLA-0201*-GAD65(114-122) pentamers were used to detect CD8(+) GAD-responsive T cells in memory CD45RO(+) and naive CD45RO(-) cell populations from patients with type 1 diabetes and healthy control subjects. T cell proliferative history was evaluated by flow cytometry telomere length measurement. CD4(+) and CD8(+) T cells specific for GAD65 and insulin were present in patients with type 1 diabetes and control subjects. Within the naive CD45RO(-) cells, CD4(+) and CD8(+) T cell responses were similar between patients and controls. Within the memory CD45RO(+) cells, CD4(+) T cell responses against whole GAD65 and insulin and HLA-0201*-GAD65(114-122) pentamer-positive CD8(+) T cells were found in patients with type 1 diabetes, but not in control subjects (p < 0.05 for all). Responding cells from the CD45RO(+) T cell population had substantially shorter telomere lengths than responding cells from the CD45RO(-) cell population. Diabetes-specific autoreactive T cells in the circulation have uniquely undergone sustained in vivo proliferation and differentiation into memory T cells. Prior selection of these cells is possible and is a way to identify diabetes-relevant target Ags and epitopes.

Initial results of screening of nondiabetic organ donors for expression of islet autoantibodies

CONTEXT

Type 1A diabetes is characterized by a long prodromal phase during which autoantibodies to islet antigens are present. Nevertheless, we lack data on the pancreatic pathology of subjects who are positive for islet autoantibodies (to islet autoantigens GAD65, insulin, and ICA512).

OBJECTIVE

In this manuscript, we describe a novel strategy in obtaining pancreata and pancreatic lymph nodes from islet autoantibody-positive organ donors that involves careful coordination among the laboratory and the organ donor provider organization.

DESIGN

We developed a rapid screening protocol for islet autoantibodies measurement of organ donors to allow identification of positive subjects before organ harvesting. In this way we were able to obtain pancreata and pancreatic lymph nodes from subjects with and without islet autoimmunity.

SETTING

The organ donors used in this study were obtained from the general community.

SUBJECTS

The population studied consisted of 112 organ donors (age range 1 month to 86 yr, mean age 39 yr).

MAIN OUTCOME MEASURE

The main outcome measure of this study consisted of evaluating the pancreatic histology and identify T cells autoreactive for islet antigens in the pancreatic lymph nodes.

RESULTS

To date we have identified three positive subjects and obtained the pancreas for histological evaluation from one of the autoantibody-positive donors who expressed ICA512 autoantibodies. Although this subject did not exhibit insulitis, lymphocytes derived from pancreatic lymph nodes reacted to the islet antigen phogrin.

CONCLUSION

In summary, these results indicate that it is possible to screen organ donors in real time for antiislet antibodies, characterize pancreatic histology, and obtain viable T cells for immunological studies.

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.

Comparative study of GAD65-specific CD4+ T cells in healthy and type 1 diabetic subjects

Glutamic acid decarboxylase 65 (GAD65) is a putative autoantigen associated with the pathogenesis of type 1 diabetes (T1D). The prevalence of autoreactive CD4+ T cells towards the immunodominant GAD65(555-567) epitope in DR4 healthy and T1D subjects was investigated with class II tetramers. A slightly higher percentage of diabetic subjects had GAD65(555-567) tetramer-positive T cells upon GAD65(555-567) peptide stimulation on the total CD4+ T-cell populations compared to healthy subjects. In contrast, three quarters of subjects in both groups had tetramer-positive T cells resulting from stimulation of the CD4+CD25+ regulatory T-cell depleted CD4+ T cells. The frequencies and TCR Vbeta gene usages of GAD65(555-567) T cells were also similar in both groups. Experiments demonstrated that GAD65(555-567)-reactive T cells in healthy and diabetic subjects had different CD45RA phenotypes. For the healthy group, GAD65(555-567)-reactive T cells were generally found in the CD45RA+ naïve T-cell pool while GAD65(555-567)-reactive T cells from T1D subjects were present in both CD45RA+ naïve and CD45RA- memory T-cell pools. These findings suggested that there is no difference in thymic selection of DR4 restricted GAD-reactive T cells amongst healthy and T1D individuals but GAD65(555-567)-reactive T cells have been preferentially activated in diabetic patients.

Natural peptides selected by diabetogenic DQ8 and murine I-A(g7) molecules show common sequence specificity

In this study, a large number of naturally processed peptides was isolated and identified from the human diabetes-susceptible class II MHC molecules HLA-DQ8 (DQA1*0301,DQB1*0302) and from murine I-A species, both of which are expressed in genetically identical APC lines. The peptides presented during the processing of autologous proteins were highly selective in showing sequence specificity, mainly consisting of 1 or more acidic residues at their C terminus. Testing for binding to the MHC molecules revealed that the position 9 (P9) acidic residues of the peptides contributed decisively to binding. For HLA-DQ8, the P1 residue, which was also an acidic amino acid, influenced binding positively. Both HLA-DQ8 and I-A(g7) selected for common peptides that bound in the same register. There was no evidence for selection of peptides having nonspecific or promiscuous binding. Thus, diabetogenic class II MHC molecules are highly selective in terms of the peptides presented by their APCs, and this is governed by the features of their P9 anchor pocket. These results are in striking contrast to those from studies examining synthetic peptide or phage display libraries, in which many peptides were shown to bind.

The stages of type 1A diabetes: 2005

Type 1A diabetes is a chronic autoimmune disease usually preceded by a long prodrome during which autoantibodies to islet autoantigens are present. These antibodies are directed to a variety of antigens, but the best characterized are glutamic acid decarboxylase-65, insulinoma-associated antigen-2, and insulin. We hypothesize that the natural history of type 1A diabetes can be represented by several stages, starting from genetic susceptibility and ending in complete beta-cell destruction and overt diabetes. Type 1A diabetes probably results from a balance between genetic susceptibility and environmental influences. In both humans and animal models, the major determinants of the disease are genes within the major histocompatibility complex. The next best-characterized susceptibility locus is the insulin gene, the variable nucleotide tandem repeat locus. This gene affects the expression of insulin in the thymus and thus may play a role in the modulation of tolerance to this molecule. In a subset of genetically susceptible individuals, the activation of autoimmunity may be triggered by environmental factors such as viruses and/or diet. However, no conclusive association has been established between type 1A diabetes and specific environmental triggers. In this review, we provide evidence that insulin has a fundamental role in anti-islet autoimmunity.

Pathogenic T-cell clones in autoimmune diabetes: more lessons from the NOD mouse

T-cell clones that can efficiently transfer diabetes to prediabetic nonobese diabetic (NOD) mice provide a powerful approach to dissecting the autoimmune disease process and for investigating immunoregulation. Diabetogenic T-cell clones carried in culture allow for detailed analysis of T-cell effector function and in vivo activity, and thus the contribution of a single clonotype to pathogenesis can be studied. As T cells comprising most or all of the repertoire in T-cell receptor transgenic (TCR-Tg) mice, diabetogenic T-cell clones have led to new variations on the NOD mouse model of autoimmune disease. T-cell clones are being used to screen peptide libraries and proteomic arrays to identify the autoantigens that drive these clones in vivo and to extend our knowledge of the processes that give rise to these antigens. With the identification of peptide agonists and natural ligands, the development of MHC-peptide multimers has been possible. These reagents can track T cells in vivo and thus provide new approaches for disease diagnosis and therapy as well as a versatile set of tools for basic research on how T cells contribute to autoimmune disease.