Identification of a CD8 T cell that can independently mediate autoimmune diabetes development in the complete absence of CD4 T cell helper functions

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

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

Nfkbid Overexpression in Nonobese Diabetic Mice Elicits Complete Type 1 Diabetes Resistance in Part Associated with Enhanced Thymic Deletion of Pathogenic CD8 T Cells and Increased Numbers and Activity of Regulatory T Cells

Type 1 diabetes (T1D) in both humans and NOD mice is caused by T cell-mediated autoimmune destruction of pancreatic β cells. Increased frequency or activity of autoreactive T cells and failures of regulatory T cells (Tregs) to control these pathogenic effectors have both been implicated in T1D etiology. Due to the expression of MHC class I molecules on β cells, CD8 T cells represent the ultimate effector population mediating T1D. Developing autoreactive CD8 T cells normally undergo extensive thymic negative selection, but this process is impaired in NOD mice and also likely T1D patients. Previous studies identified an allelic variant of Nfkbid, a NF-κB signal modulator, as a gene strongly contributing to defective thymic deletion of autoreactive CD8 T cells in NOD mice. These previous studies found ablation of Nfkbid in NOD mice using the clustered regularly interspaced short palindromic repeats system resulted in greater thymic deletion of pathogenic CD8 AI4 and NY8.3 TCR transgenic T cells but an unexpected acceleration of T1D onset. This acceleration was associated with reductions in the frequency of peripheral Tregs. In this article, we report transgenic overexpression of Nfkbid in NOD mice also paradoxically results in enhanced thymic deletion of autoreactive CD8 AI4 T cells. However, transgenic elevation of Nfkbid expression also increased the frequency and functional capacity of peripheral Tregs, in part contributing to the induction of complete T1D resistance. Thus, future identification of a pharmaceutical means to enhance Nfkbid expression might ultimately provide an effective T1D intervention approach.

Toll-Like Receptor 3 Is Critical to the Pancreatic Islet Milieu That Is Required for Coxsackievirus B4-Induced Type 1 Diabetes in Female Nonobese Diabetic Mice

OBJECTIVE

Genetic and environmental influences play a role as triggers of type 1 diabetes mellitus (T1DM). Female nonobese diabetic (NOD) mice are useful for studying T1DM as they spontaneously develop T1DM, which can be accelerated by some viruses. Toll-like receptor 3 (TLR3) is believed to play a critical role in viral-induced T1DM and β-cell destruction, because female Tlr3 knockout (Tlr3-/-) NOD mice are protected from Coxsackievirus B4 (CVB4)-induced acceleration of T1DM. However, the exact role(s) TLR3 plays in the pathogenesis of CVB4-induced T1DM remain unknown.

METHODS

This longitudinal study used immunostaining, laser capture microdissection, and reverse transcription real-time polymerase chain reaction of islets from female uninfected and CVB4-infected Tlr3+/+ and Tlr3-/- NOD mice.

RESULTS

Islets isolated from female Tlr3+/+ NOD mice 4 to 8 weeks of age had higher amounts of insulitis, Cxcl10, Il1b, Tnfa, and Tgfb1 expression compared with Tlr3-/- NOD mice. After CVB4 infection, Tlr3+/+ NOD mice had higher amounts of insulitis and T-cell infiltration at 3 days after infection compared with Tlr3-/- CVB4-infected NOD mice.

CONCLUSIONS

Toll-like receptor 3 is necessary for establishment of a pancreatic islet inflammatory microenvironment by increasing insulitis and cytokine expression that facilitates CVB4-induced T1DM in female NOD mice.

Noncontiguous T cell epitopes in autoimmune diabetes: From mice to men and back again

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that affects the insulin-producing beta cells of the pancreatic islets. The nonobese diabetic mouse is a widely studied spontaneous model of the disease that has contributed greatly to our understanding of T1D pathogenesis. This is especially true in the case of antigen discovery. Upon review of existing knowledge concerning the antigens and peptide epitopes that are recognized by T cells in this model, good concordance is observed between mouse and human antigens. A fascinating recent illustration of the contribution of the nonobese diabetic mouse in the area of epitope identification is the discovery of noncontiguous CD4+ T cell epitopes. This novel epitope class is characterized by the linkage of an insulin-derived peptide to, most commonly, a fragment of a natural cleavage product of another beta cell secretory granule constituent. These so-called hybrid insulin peptides are also recognized by T cells in patients with T1D, although the precise mechanism for their generation has yet to be defined and is the subject of active investigation. Although evidence from the tumor immunology arena documented the existence of noncontiguous CD8+ T cell epitopes, generated by proteasome-mediated peptide splicing involving transpeptidation, such CD8+ T cell epitopes were thought to be a rare immunological curiosity. However, recent advances in bioinformatics and mass spectrometry have challenged this view. These developments, coupled with the discovery of hybrid insulin peptides, have spurred a search for noncontiguous CD8+ T cell epitopes in T1D, an exciting frontier area still in its infancy.

CD226 Deletion Reduces Type 1 Diabetes in the NOD Mouse by Impairing Thymocyte Development and Peripheral T Cell Activation

The costimulatory molecule CD226 is highly expressed on effector/memory T cells and natural killer cells. Costimulatory signals received by T cells can impact both central and peripheral tolerance mechanisms. Genetic polymorphisms in CD226 have been associated with susceptibility to type 1 diabetes and other autoimmune diseases. We hypothesized that genetic deletion of Cd226 in the non-obese diabetic (NOD) mouse would impact type 1 diabetes incidence by altering T cell activation. CD226 knockout (KO) NOD mice displayed decreased disease incidence and insulitis in comparison to wild-type (WT) controls. Although female CD226 KO mice had similar levels of sialoadenitis as WT controls, male CD226 KO mice showed protection from dacryoadenitis. Moreover, CD226 KO T cells were less capable of adoptively transferring disease compared to WT NOD T cells. Of note, CD226 KO mice demonstrated increased CD8⁺ single positive (SP) thymocytes, leading to increased numbers of CD8⁺ T cells in the spleen. Decreased percentages of memory CD8⁺CD44⁺CD62L^- T cells were observed in the pancreatic lymph nodes of CD226 KO mice. Intriguingly, CD8⁺ T cells in CD226 KO mice showed decreased islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-tetramer and CD5 staining, suggesting reduced T cell receptor affinity for this immunodominant antigen. These data support an important role for CD226 in type 1 diabetes development by modulating thymic T cell selection as well as impacting peripheral memory/effector CD8⁺ T cell activation and function.

Soluble CD137 Ameliorates Acute Type 1 Diabetes by Inducing T Cell Anergy

We show here that soluble CD137 (sCD137), the alternately spliced gene product of Tnfsfr9, effectively treats acute type 1 diabetes (T1D) in nonobese diabetic (NOD) mice. sCD137 significantly delayed development of end-stage disease, preserved insulin+ islet beta cells, and prevented progression to end-stage T1D in some mice. We demonstrate that sCD137 induces CD4+ T cell anergy, suppressing antigen-specific T cell proliferation and IL-2/IFN-γ secretion. Exogenous IL-2 reversed the sCD137 anergy effect. sCD137 greatly reduces inflammatory cytokine production by CD8 effector memory T cells, critical mediators of beta cell damage. We demonstrate that human T1D patients have decreased serum sCD137 compared to age-matched controls (as do NOD mice compared to NOD congenic mice expressing a protective Tnfsfr9 allele), that human sCD137 is secreted by regulatory T cells (Tregs; as in mice), and that human sCD137 induces T cell suppression in human T cells. These findings provide a rationale for further investigation of sCD137 as a treatment for T1D and other T cell-mediated autoimmune diseases.

Development and Characterization of a Preclinical Model for the Evaluation of CD205-Mediated Antigen Delivery Therapeutics in Type 1 Diabetes

Dendritic cells (DCs) are crucial for the production of adaptive immune responses to disease-causing microbes. However, in the steady state (i.e., in the absence of an infection or when Ags are experimentally delivered without a DC-activating adjuvant), DCs present Ags to T cells in a tolerogenic manner and are important for the establishment of peripheral tolerance. Delivery of islet Ags to DCs using Ag-linked Abs to the DC endocytic receptor CD205 has shown promise in the NOD mouse model of type 1 diabetes (T1D). It is important to note, however, that all myeloid DCs express CD205 in humans, whereas in mice, only one of the classical DC subsets does (classical DC1; CD8α⁺ in spleen). Thus, the evaluation of CD205-targeted treatments in mice will likely not accurately predict the results observed in humans. To overcome this challenge, we have developed and characterized a novel NOD mouse model in which all myeloid DCs transgenically express human CD205 (hCD205). This NOD.hCD205 strain displays a similar T1D incidence profile to standard NOD mice. The presence of the transgene does not alter DC development, phenotype, or function. Importantly, the DCs are able to process and present Ags delivered via hCD205. Because Ags taken up via hCD205 can be presented on both class I and class II MHC, both CD4⁺ and CD8⁺ T cells can be modulated. As both T cell subsets are important for T1D pathogenesis, NOD.hCD205 mice represent a unique, patient-relevant tool for the development and optimization of DC-directed T1D therapies.

eIF5A inhibition influences T cell dynamics in the pancreatic microenvironment of the humanized mouse model of Type 1 Diabetes

We have developed a transgenic mouse model of Type 1 Diabetes (T1D) in which human GAD65 is expressed in pancreatic β-cells, and human MHC-II is expressed on antigen presenting cells. Induced GAD65 antigen presentation activates T-cells, which initiates the downstream events leading to diabetes. In our humanized mice, we have shown downregulation of eukaryotic translation initiation factor 5 A (elF5A), expressed only in actively dividing mammalian cells. In-vivo inhibition of elF5A hypusination by deoxyhypusine synthase (DHS) inhibitor "GC7" was studied; DHS inhibitor alters the pathophysiology in our mouse model by catalyzing the crucial hypusination and the rate-limiting step of elF5A activation. In our mouse model, we have shown that inhibition of eIF5A resets the pro-inflammatory bias in the pancreatic microenvironment. There was: (a) reduction of Th1/Th17 response, (b) an increase in Treg numbers, (c) debase in IL17 and IL21 cytokines levels in serum, (d) lowering of anti-GAD65 antibodies, and (e) ablation of the ER stress that improved functionality of the β-cells, but minimal effect on the cytotoxic CD8 T-cell (CTL) mediated response. Conclusively, immune modulation, in the case of T1D, may help to manipulate inflammatory responses, decreasing disease severity, and may help manage T1D in early stages of disease. Our study also demonstrates that without manipulating the CTLs mediated response extensively, it is difficult to treat T1D.

Antigen recognition in autoimmune diabetes: a novel pathway underlying disease initiation

Development of human autoimmune disorders results from complex interplay among genetic, environmental, and immunological risk factors. Despite much heterogeneity in environmental triggers, the leading genes that give the propensity for tissue-specific autoimmune diseases, such as type 1 diabetes, are those associated with particular class II major histocompatibility complex alleles. Such genetic predisposition precipitates presentation of tissue antigens to MHC-II-restricted CD4 T cells. When properly activated, these self-reactive CD4 T cells migrate to the target tissue and trigger the initial immune attack. Using the non-obese diabetic mouse model of spontaneous autoimmune diabetes, much insight has been gained in understanding how presentation of physiological levels of self-antigens translates into pathological outcomes. In this review, we summarize recent advances illustrating the features of the antigen presenting cells, the sites of the antigen recognition, and the nature of the consequent T cell responses. We emphasize emerging evidence that highlights the importance of systemic presentation of catabolized tissue antigens in mobilization of pathogenic T cells. The implication of these studies in therapeutic perspectives is also discussed.

A Hypermorphic Nfkbid Allele Contributes to Impaired Thymic Deletion of Autoreactive Diabetogenic CD8+ T Cells in NOD Mice

In both NOD mice and humans, the development of type 1 diabetes (T1D) is dependent in part on autoreactive CD8+ T cells recognizing pancreatic β cell peptides presented by often quite common MHC class I variants. Studies in NOD mice previously revealed that the common H2-Kd and/or H2-Db class I molecules expressed by this strain aberrantly lose the ability to mediate the thymic deletion of pathogenic CD8+ T cell responses through interactions with T1D susceptibility genes outside the MHC. A gene(s) mapping to proximal chromosome 7 was previously shown to be an important contributor to the failure of the common class I molecules expressed by NOD mice to mediate the normal thymic negative selection of diabetogenic CD8+ T cells. Using an inducible model of thymic negative selection and mRNA transcript analyses, we initially identified an elevated Nfkbid expression variant as a likely NOD-proximal chromosome 7 region gene contributing to impaired thymic deletion of diabetogenic CD8+ T cells. CRISPR/Cas9-mediated genetic attenuation of Nfkbid expression in NOD mice resulted in improved negative selection of autoreactive diabetogenic AI4 and NY8.3 CD8+ T cells. These results indicated that allelic variants of Nfkbid contribute to the efficiency of intrathymic deletion of diabetogenic CD8+ T cells. However, although enhancing thymic deletion of pathogenic CD8+ T cells, ablating Nfkbid expression surprisingly accelerated T1D onset that was associated with numeric decreases in both regulatory T and B lymphocytes in NOD mice.

Combinatorial detection of autoreactive CD8+ T cells with HLA-A2 multimers: a multi-centre study by the Immunology of Diabetes Society T Cell Workshop

AIMS/HYPOTHESIS

Validated biomarkers are needed to monitor the effects of immune intervention in individuals with type 1 diabetes. Despite their importance, few options exist for monitoring antigen-specific T cells. Previous reports described a combinatorial approach that enables the simultaneous detection and quantification of multiple islet-specific CD8⁺ T cell populations. Here, we set out to evaluate the performance of a combinatorial HLA-A2 multimer assay in a multi-centre setting.

METHODS

The combinatorial HLA-A2 multimer assay was applied in five participating centres using centralised reagents and blinded replicate samples. In preliminary experiments, samples from healthy donors were analysed using recall antigen multimers. In subsequent experiments, samples from healthy donors and individuals with type 1 diabetes were analysed using beta cell antigen and recall antigen multimers.

RESULTS

The combinatorial assay was successfully implemented in each participating centre, with CVs between replicate samples that indicated good reproducibility for viral epitopes (mean %CV = 33.8). For beta cell epitopes, the assay was very effective in a single-centre setting (mean %CV = 18.4), but showed sixfold greater variability across multi-centre replicates (mean %CV = 119). In general, beta cell antigen-specific CD8⁺ T cells were detected more commonly in individuals with type 1 diabetes than in healthy donors. Furthermore, CD8⁺ T cells recognising HLA-A2-restricted insulin and glutamate decarboxylase epitopes were found to occur at higher frequencies in individuals with type 1 diabetes than in healthy donors.

CONCLUSIONS/INTERPRETATION

Our results suggest that, although combinatorial multimer assays are challenging, they can be implemented in multiple laboratories, providing relevant T cell frequency measurements. Assay reproducibility was notably higher in the single-centre setting, suggesting that biomarker analysis of clinical trial samples would be most successful when assays are performed in a single laboratory. Technical improvements, including further standardisation of cytometry platforms, will likely be necessary to reduce assay variability in the multi-centre setting.

The Type 1 Diabetes-Resistance Locus Idd22 Controls Trafficking of Autoreactive CTLs into the Pancreatic Islets of NOD Mice

Type 1 diabetes (T1D) has a strong genetic component. The insulin dependent diabetes (Idd)22 locus was identified in crosses of T1D-susceptible NOD mice with the strongly T1D-resistant ALR strain. The NODcALR-(D8Mit293-D8Mit137)/Mx (NOD-Idd22) recombinant congenic mouse strain was generated in which NOD mice carry the full Idd22 confidence interval. NOD-Idd22 mice exhibit almost complete protection from spontaneous T1D and a significant reduction in insulitis. Our goal was to unravel the mode of Idd22-based protection using in vivo and in vitro models. We determined that Idd22 did not impact immune cell diabetogenicity or β cell resistance to cytotoxicity in vitro. However, NOD-Idd22 mice were highly protected against adoptive transfer of T1D. Transferred CTLs trafficked to the pancreatic lymph node and proliferated to the same extent in NOD and NOD-Idd22 mice, yet the accumulation of pathogenic CTLs in the islets was significantly reduced in NOD-Idd22 mice, correlating with disease resistance. Pancreatic endothelial cells from NOD-Idd22 animals expressed lower levels of adhesion molecules, even in response to inflammatory stimuli. Lower adhesion molecule expression resulted in weaker adherence of T cells to NOD-Idd22 endothelium compared with NOD-derived endothelium. Taken together, these results provide evidence that Idd22 regulates the ability of β cell-autoreactive T cells to traffic into the pancreatic islets and may represent a new target for pharmaceutical intervention to potentially prevent T1D.

Unique features in the presentation of insulin epitopes in autoimmune diabetes: an update

Although an autoimmune disease involves diverse self-antigens, the initiation stage may require recognition of a limited number. This concept is verified in the non-obese diabetic (NOD) mouse model of autoimmune diabetes, in which strong evidence points to insulin as the prime antigen. The NOD mouse bears the I-A^g7 class II-MHC molecules (MHCII) that share common biochemical features and peptidome selection with the human diabetes-susceptible HLA-DQ8. Furthermore, both NOD mice and patients with type 1 diabetes (T1D) display an early appearance of insulin autoantibodies (IAAs) and subsequent insulin-reactive T cell infiltration into the islets. Therefore, a better understanding of insulin presentation is crucial for assessing disease pathogenesis and therapeutic intervention. Here, we summarize recent advances in insulin presentation events that underlie the essential role of this autoantigen in driving autoimmune diabetes.

Adoptive Transfer of mRNA-Transfected T Cells Redirected against Diabetogenic CD8 T Cells Can Prevent Diabetes

Chimeric major histocompatibility complex (MHC) molecules supplemented with T cell receptor (TCR) signaling motifs function as activation receptors and can redirect gene-modified T cells against pathogenic CD8 T cells. We have shown that β₂ microglobulin (β₂m) operates as a universal signaling component of MHC-I molecules when fused with the CD3-ζ chain. Linking the H-2K^d-binding insulin B chain peptide insulin B chain, amino acids 15-23 (InsB_15-23) to the N terminus of β₂m/CD3-ζ, redirected polyclonal CD8 T cells against pathogenic CD8 T cells in a peptide-specific manner in the non-obese diabetic (NOD) mouse. Here, we describe mRNA electroporation for delivering peptide/β₂m/CD3-ζ genes to a reporter T cell line and purified primary mouse CD8 T cells. The peptide/β₂m/CD3-ζ products paired with endogenous MHC-I chains and transmitted strong activation signals upon MHC-I cross-linking. The reporter T cell line transfected with InsB_15-23/β₂m/CD3-ζ mRNA was activated by an InsB_15-23-H-2K^d-specific CD8 T cell hybrid only when the transfected T cells expressed H-2K^d. Primary NOD CD8 T cells expressing either InsB_15-23/β₂m/CD3-ζ or islet-specific glucose-6-phosphatase catalytic subunit-related protein, amino acids 206-214 (IGRP_206-214)/β₂m/CD3-ζ killed their respective autoreactive CD8 T cell targets in vitro. Furthermore, transfer of primary CD8 T cells transfected with InsB_15-23/β₂m/CD3-ζ mRNA significantly reduced insulitis and protected NOD mice from diabetes. Our results demonstrate that mRNA encoding chimeric MHC-I receptors can redirect effector CD8 against diabetogenic CD8 T cells, offering a new approach for the treatment of type 1 diabetes.

Fresh Ideas, Foundational Experiments (FIFE): Immunology and Diabetes 2016 FIFE Symposium

The first Fresh Ideas, Foundational Experiments (FIFE): Immunology and Diabetes symposia workshop took place in 2016 and exemplified the active interest of a number of several investigators interested the global rise in the incidence of type 1 diabetes (T1D). This increase does not correlate with genetic drift and indicates that environmental exposures are playing an increasingly significant role. Despite major biomedical and technological advances in diagnosis and treatment, treatments are frequently insufficient as they do not inhibit the progression of the underlying autoimmune response and often fail to prevent life-threatening complications. T1D is the result of autoimmune destruction of the insulin-producing beta cells of the pancreas, and the precise, mechanistic contribution of the immune system to disease pathogenesis and progression remains to be fully characterized. Ultimately, the combinatorial effect of concurrent factors, including beta cell fragility, exogenous stressors, and genetic priming of the innate and adaptive immune system, work together to induce T1D autoimmunity. Thus, T1D is the result of immunological defects and environmental pathogens, requiring the sustained attention of collaborative research teams such as FIFE: I & D with varied perspectives, unified by the universally held goal of finding a sustainable, life-long cure. Herein, the authors provide perspective on various fields in T1D research highlighted by speakers participating in the inaugural FIFE symposium.

Understanding Autoimmune Diabetes through the Prism of the Tri-Molecular Complex

The strongest susceptibility allele for Type 1 Diabetes (T1D) is human leukocyte antigen (HLA), which supports a central role for T cells as the drivers of autoimmunity. However, the precise mechanisms that allow thymic escape and peripheral activation of beta cell antigen-specific T cells are still largely unknown. Studies performed with the non-obese diabetic (NOD) mouse have challenged several immunological dogmas, and have made the NOD mouse a key experimental system to study the steps of immunodysregulation that lead to autoimmune diabetes. The structural similarities between the NOD I-A^g7 and HLA-DQ8 have revealed the stability of the T cell receptor (TCR)/HLA/peptide tri-molecular complex as an important parameter in the development of autoimmune T cells, as well as afforded insights into the key antigens targeted in T1D. In this review, we will provide a summary of the current understanding with regard to autoimmune T cell development, the significance of the antigens targeted in T1D, and the relationship between TCR affinity and immune regulation.

IDO-Expressing Fibroblasts Protect Islet Beta Cells From Immunological Attack and Reverse Hyperglycemia in Non-Obese Diabetic Mice

Indoleamine 2,3-dioxygenase (IDO) induces immunological tolerance in physiological and pathological conditions. Therefore, we used dermal fibroblasts with stable IDO expression as a cell therapy to: (i) Investigate the factors determining the efficacy of this cell therapy for autoimmune diabetes in non-obese diabetic (NOD) mice; (ii) Scrutinize the potential immunological mechanisms. Newly diabetic NOD mice were randomly injected with either 10 × 10(6) (10M) or 15 × 10(6) (15M) IDO-expressing dermal fibroblasts. Blood glucose levels (BGLs), body weight, plasma kynurenine levels, insulitis severity, islet beta cell function, autoreactive CD8(+) T cells, Th17 cells and regulatory T cells (Tregs) were then investigated in these mice. IL-1β and cleaved caspase-3 levels were assessed in islets co-cultured with IDO-expressing fibroblasts. BGLs in 83% mice treated with 15M IDO-expressing fibroblasts recovered to normal up to 120 days. However, only 17% mice treated with 10M IDO-expressing cells were reversed to normoglycemia. A 15M IDO-expressing fibroblasts significantly reduced infiltrated immune cells in islets and recovered the functionality of remaining islet beta cells in NOD mice. Additionally, they successfully inhibited autoreactive CD8(+) T cells and Th17 cells as well as increased Tregs in different organs of NOD mice. Islet beta cells co-cultured with IDO-expressing fibroblasts had reduced IL-1β levels and cell apoptosis. Both cell number and IDO enzymatic activity contributes to the efficiency of IDO cell therapy. Optimized IDO-expressing fibroblasts successfully reverse the progression of diabetes in NOD mice through induction of Tregs as well as inhibition of beta cell specific autoreactive CD8(+) T cells and Th17 cells. J. Cell. Physiol. 231: 1964-1973, 2016. © 2016 Wiley Periodicals, Inc.

The Presence and Preferential Activation of Regulatory T Cells Diminish Adoptive Transfer of Autoimmune Diabetes by Polyclonal Nonobese Diabetic (NOD) T Cell Effectors into NSG versus NOD-scid Mice

NOD-scid.Il2rg(null) (NSG) mice are currently being used as recipients to screen for pathogenic autoreactive T cells in type 1 diabetes (T1D) patients. We questioned whether the restriction of IL-2R γ-chain (Il-2rγ)-dependent cytokine signaling only to donor cells in NSG recipients differently influenced the activities of transferred diabetogenic T cells when they were introduced as a monoclonal/oligoclonal population versus being part of a polyclonal repertoire. Unexpectedly, a significantly decreased T1D transfer by splenocytes from prediabetic NOD donors was observed in Il-2rγ(null)-NSG versus Il-2rγ-intact standard NOD-scid recipients. In contrast, NOD-derived monoclonal/oligoclonal TCR transgenic β cell-autoreactive T cells in either the CD8 (AI4, NY8.3) or CD4 (BDC2.5) compartments transferred disease significantly more rapidly to NSG than to NOD-scid recipients. The reduced diabetes transfer efficiency by polyclonal T cells in NSG recipients was associated with enhanced activation of regulatory T cells (Tregs) mediated by NSG myeloid APC. This enhanced suppressor activity was associated with higher levels of Treg GITR expression in the presence of NSG than NOD-scid APC. These collective results indicate NSG recipients might be efficiently employed to test the activity of T1D patient-derived β cell-autoreactive T cell clones and lines, but, when screening for pathogenic effectors within polyclonal populations, Tregs should be removed from the transfer inoculum to avoid false-negative results.

Identification of autoreactive CD8+ T cell responses targeting chromogranin A in humanized NOD mice and type 1 diabetes patients

ChgA has recently been identified as the autoantigen for diabetogenic CD4(+) T cells in NOD mice and T1D patients. However, autoreactive CD8(+) T-cell responses targeting ChgA haven't been studied yet. Here several HLA-A*0201-restricted peptides derived from mChgA and hChgA were selected by an integrated computational prediction approach, followed by an HLA-A*0201 binding assay. MChgA10-19 and mChgA(43-52) peptides, which bound well with HLA-A*0201 molecule, induced significant proliferation and IFN-γ-releasing of splenocytes from diabetic NOD.β2m(null).HHD mice. Notably, flow cytometry analysis found that mChgA(10-19) and mChgA(43-52) stimulated the production of IFN-γ, perforin, and IL-17 by splenic CD8(+) T cells of diabetic NOD.β2m(null).HHD mice. Furthermore, hChgA(10-19) and hChgA(43-52)-induced IFN-γ releasing by specific CD8(+) T cells were frequently detected in recent-onset HLA-A*0201-positive T1D patients. Thus, this study demonstrated that autoreactive CD8(+) T cells targeting ChgA were present in NOD.β2m(null).HHD mice and T1D patients, and might contribute to pathogenesis of T1D through secreting proinflammatory cytokines and cytotoxic molecules.

Immunomodulation therapy of diabetes by oral administration of a surfactin lipopeptide in NOD mice

Type 1 diabetes mellitus (T1DM) is considered an autoimmune disease, which can be attenuated by modulation of immune pathway from Th1- to Th2-type through vaccination. WH1fungin surfactin is a Bacillus-produced natural immunomodulator. NOD mice were orally treated with 5mg/kg or 25mg/kg WH1fungin once a week for total 4 weeks. After the final administration, the diabetes incidence and the anti-inflammatory roles of WH1fungin were investigated by immunohistochemistry, FACS and ELISA. The results showed oral WH1fungin obviously resulted in a WH1fungin-unspecific suppression of T1DM. Diabetes incidence was significantly reduced when compared to phosphate buffered saline (PBS) control. Mice in the control group began to be onset of diabetes at week 15, following with an increased mortality from week 16 to 28. At the end of observation, the diabetes incidence reached to 81% at week 30, while only 25% in WH1fungin groups. The splenocytes assay showed oral WH1fungin could suppress T cells proliferation, down-regulate amounts of activated CD8(+) T cells with the production of tumor necrosis factor (TNF)-α and interferon (IFN)-γ, and increase CD4(+)CD25(+)FOXP3(+) regulator T cells (Tregs). The serum assay revealed oral WH1fungin down-regulated TNF-α and IgG2a but increased interleukin (IL)-10 and IgG1 in mice. All of these data showed oral WH1fungin tended to switch the immune response from Th1- to Th2-type. The further surveys revealed that less IFN-γ but more transfer growth factor (TGF)-β were found in the islets of mice with oral WH1fungin when compared to that in the control group. As a result, the normal islet architecture and slight inflammatory cells infiltration was observed with a slight insulitis in the oral WH1fungin groups. These results demonstrate that oral WH1fungin might be a novel therapeutic approach for the prevention of T1DM.

Compensatory mechanisms allow undersized anchor-deficient class I MHC ligands to mediate pathogenic autoreactive T cell responses

Self-reactive T cells must escape thymic negative selection to mediate pathogenic autoimmunity. In the NOD mouse model of autoimmune diabetes, several β cell-cytotoxic CD8 T cell populations are known, with the most aggressive of these represented by AI4, a T cell clone with promiscuous Ag-recognition characteristics. We identified a long-elusive β cell-specific ligand for AI4 as an unusually short H-2D(b)-binding 7-mer peptide lacking a C-terminal anchor residue and derived from the insulin A chain (InsA14-20). Crystallography reveals that compensatory mechanisms permit peptides lacking a C-terminal anchor to bind sufficiently to the MHC to enable destructive T cell responses, yet allow cognate T cells to avoid negative selection. InsA14-20 shares two solvent-exposed residues with previously identified AI4 ligands, providing a structural explanation for AI4's promiscuity. Detection of AI4-like T cells, using mimotopes of InsA14-20 with improved H-2D(b)-binding characteristics, establishes the AI4-like T cell population as a consistent feature of the islet infiltrates of NOD mice. Our work establishes undersized peptides as previously unrecognized targets of autoreactive CD8 T cells and presents a strategy for their further exploration as Ags in autoimmune disease.

IGRP and insulin vaccination induce CD8+ T cell-mediated autoimmune diabetes in the RIP-CD80GP mouse

Autoimmune diabetes is characterized by autoantigen-specific T cell-mediated destruction of pancreatic islet beta cells, and CD8(+) T cells are key players during this process. We assessed whether the bitransgenic RIP-CD80 x RIP-LCMV-GP (RIP-CD80GP) mice may be a versatile antigen-specific model of inducible CD8(+) T cell-mediated autoimmune diabetes. Antigen-encoding DNA, peptide-loaded dendritic cells and antigen plus incomplete Freund's adjuvant were used for vaccination. Of 14 pancreatic proteins tested by DNA vaccination, murine pre-proinsulin 2 (100% of mice; median time after vaccination, 60 days) and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) (77%, 58 days) could induce diabetes. Vaccination with DNA encoding for zinc transporter 8, Ia-2, Ia-2β, glutamic acid decarboxylase 67 (Gad67), chromogranin A, insulinoma amyloid polypeptide and homeobox protein Nkx-2.2 induced diabetes development in 25-33% of mice. Vaccination with DNA encoding for Gad65, secretogranin 5, pancreas/duodenum homeobox protein 1 (Pdx1), carboxyl ester lipase, glucagon and control hepatitis B surface antigen (HBsAg) induced diabetes in <20% of mice. Diabetes induction efficiency could be increased by DNA vaccination with a vector encoding a ubiquitin-antigen fusion construct. Diabetic mice had florid T cell islet infiltration. CD8(+) T cell targets of IGRP were identified with a peptide library-based enzyme-linked immunospot assay, and diabetes could also be induced by vaccination with major histocompatibility complex (MHC) class I-restricted IGRP peptides loaded on mature dendritic cells. Vaccination with antigen plus incomplete Freund's adjuvant, which can prevent diabetes in other models, led to rapid diabetes development in the RIP-CD80GP mouse. We conclude that RIP-CD80GP mice are a versatile model of antigen specific autoimmune diabetes and may complement existing mouse models of autoimmune diabetes for evaluating CD8(+) T cell-targeted prevention strategies.

BAFF regulates activation of self-reactive T cells through B-cell dependent mechanisms and mediates protection in NOD mice

Targeting the BAFF/APRIL system has shown to be effective in preventing T-cell dependent autoimmune disease in the NOD mouse, a spontaneous model of type 1 diabetes. In this study we generated BAFF-deficient NOD mice to examine how BAFF availability would influence T-cell responses in vivo and the development of spontaneous diabetes. BAFF-deficient NOD mice which lack mature B cells, were protected from diabetes and showed delayed rejection of an allogeneic islet graft. Diabetes protection correlated with a failure to expand pathogenic IGRP-reactive CD8(+) T cells, which were maintained in the periphery at correspondingly low levels. Adoptive transfer of IGRP-reactive CD8(+) T cells with B cells into BAFF-deficient NOD mice enhanced IGRP-reactive CD8(+) T-cell expansion. Furthermore, when provoked with cyclophosphamide, or transferred to a secondary lymphopenic host, the latent pool of self-reactive T cells resident in BAFF-deficient NOD mice could elicit beta cell destruction. We conclude that lack of BAFF prevents the procurement of B-cell-dependent help necessary for the emergence of destructive diabetes. Indeed, treatment of NOD mice with the BAFF-blocking compound, BR3-Fc, resulted in a delayed onset and reduced incidence of diabetes.

High-throughput sequencing of islet-infiltrating memory CD4+ T cells reveals a similar pattern of TCR Vβ usage in prediabetic and diabetic NOD mice

Autoreactive memory CD4⁺ T cells play a critical role in the development of type 1 diabetes, but it is not yet known how the clonotypic composition and TCRβ repertoire of the memory CD4⁺ T cell compartment changes during the transition from prediabetes to diabetes. In this study, we used high-throughput sequencing to analyze the TCRβ repertoire of sorted islet-infiltrating memory CD4⁺CD44^high T cells in 10-week-old prediabetic and recently diabetic NOD mice. We show that most clonotypes of islet-infiltrating CD4⁺CD44^high T cells were rare, but high-frequency clonotypes were significantly more common in diabetic than in prediabetic mice. Moreover, although the CD4⁺CD44^high TCRβ repertoires were highly diverse at both stages of disease development, dominant use of TRBV1 (Vβ2), TRBV13-3 (Vβ8.1), and TRBV19 (Vβ6) was evident in both prediabetic and diabetic mice. Our findings strongly suggest that therapeutic targeting of cells specifically expressing the dominant TCRβ might reduce pancreatic infiltration in prediabetic mice and attenuate the progression to diabetes.

DEC-205-mediated antigen targeting to steady-state dendritic cells induces deletion of diabetogenic CD8⁺ T cells independently of PD-1 and PD-L1

CD8⁺ T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) have been implicated in type 1 diabetes in both humans and non-obese diabetic (NOD) mice, in which T cells specific for IGRP₂₀₆₋₂₁₄ are highly prevalent. We sought to manipulate these pathogenic T cells by exploiting the ability of steady-state dendritic cells (DCs) to present antigens in a tolerogenic manner. The endocytic receptor DEC-205 was utilized to deliver an IGRP₂₀₆₋₂₁₄ mimotope to DCs in NOD mice, and the impact of this delivery on a polyclonal population of endogenous islet-reactive cognate T cells was determined. Assessment of islet-infiltrating CD8⁺ T cells showed a decrease in the percentage, and the absolute number, of endogenous IGRP₂₀₆₋₂₁₄-specific T cells when the mimotope was delivered to DCs, compared with delivery of a specificity control. Employing an adoptive transfer system, deletion of CD8⁺ T cells as a result of DEC-205-mediated antigen targeting was found to occur independently of programmed death-1 (PD-1) and its ligand (PD-L1), both often implicated in the regulation of peripheral T-cell tolerance. Given its promise for the manipulation of self-reactive polyclonal T cells demonstrated here, the distinctive characteristics of this antigen delivery system will be important to appreciate as its potential as an intervention for autoimmune diseases continues to be investigated.

Cytotoxic effector function of CD4-independent, CD8(+) T cells is mediated by TNF-α/TNFR

BACKGROUND

Liver parenchymal cell allografts initiate both CD4-dependent and CD4-independent, CD8(+) T cell-mediated acute rejection pathways. The magnitude of allospecific CD8(+) T cell in vivo cytotoxic effector function is maximal when primed in the presence of CD4(+) T cells. The current studies were conducted to determine if and how CD4(+) T cells might influence cytotoxic effector mechanisms.

METHODS

Mice were transplanted with allogeneic hepatocytes. In vivo cytotoxicity assays and various gene-deficient recipient mice and target cells were used to determine the development of Fas-, TNF-α-, and perforin-dependent cytotoxic effector mechanisms after transplantation.

RESULTS

CD8(+) T cells maturing in CD4-sufficient hepatocyte recipients develop multiple (Fas-, TNF-α-, and perforin-mediated) cytotoxic mechanisms. However, CD8(+) T cells, maturing in the absence of CD4(+) T cells, mediate cytotoxicity and transplant rejection that is exclusively TNF-α/TNFR-dependent. To determine the kinetics of CD4-mediated help, CD4(+) T cells were adoptively transferred into CD4-deficient mice at various times posttransplant. The maximal influence of CD4(+) T cells on the magnitude of CD8-mediated in vivo allocytotoxicityf occurs within 48 hours.

CONCLUSION

The implication of these studies is that interference of CD4(+) T cell function by disease or immunotherapy will have downstream consequences on both the magnitude of allocytotoxicity as well as the cytotoxic effector mechanisms used by allospecific CD8(+) cytolytic T cells.

The role of reactive oxygen species and proinflammatory cytokines in type 1 diabetes pathogenesis

Type 1 diabetes (T1D) is a T cell–mediated autoimmune disease characterized by the destruction of insulin-secreting pancreatic β cells. In humans with T1D and in nonobese diabetic (NOD) mice (a murine model for human T1D), autoreactive T cells cause β-cell destruction, as transfer or deletion of these cells induces or prevents disease, respectively. CD4⁺ and CD8⁺ T cells use distinct effector mechanisms and act at different stages throughout T1D to fuel pancreatic β-cell destruction and disease pathogenesis. While these adaptive immune cells employ distinct mechanisms for β-cell destruction, one central means for enhancing their autoreactivity is by the secretion of proinflammatory cytokines, such as IFN-γ, TNF-α, and IL-1. In addition to their production by diabetogenic T cells, proinflammatory cytokines are induced by reactive oxygen species (ROS) via redox-dependent signaling pathways. Highly reactive molecules, proinflammatory cytokines are produced upon lymphocyte infiltration into pancreatic islets and induce disease pathogenicity by directly killing β cells, which characteristically possess low levels of antioxidant defense enzymes. In addition to β-cell destruction, proinflammatory cytokines are necessary for efficient adaptive immune maturation, and in the context of T1D they exacerbate autoimmunity by intensifying adaptive immune responses. The first half of this review discusses the mechanisms by which autoreactive T cells induce T1D pathogenesis and the importance of ROS for efficient adaptive immune activation, which, in the context of T1D, exacerbates autoimmunity. The second half provides a comprehensive and detailed analysis of (1) the mechanisms by which cytokines such as IL-1 and IFN-γ influence islet insulin secretion and apoptosis and (2) the key free radicals and transcription factors that control these processes.

Islet-specific CTL cloned from a type 1 diabetes patient cause beta-cell destruction after engraftment into HLA-A2 transgenic NOD/scid/IL2RG null mice

Despite increasing evidence that autoreactive CD8 T-cells are involved in both the initiation of type 1 diabetes (T1D) and the destruction of beta-cells, direct evidence for their destructive role in-vivo is lacking. To address a destructive role for autoreactive CD8 T-cells in human disease, we assessed the pathogenicity of a CD8 T-cell clone derived from a T1D donor and specific for an HLA-A2-restricted epitope of islet-specific glucose-6-phosphatase catalytic-subunit related protein (IGRP). HLA-A2/IGRP tetramer staining revealed a higher frequency of IGRP-specific CD8 T-cells in the peripheral blood of recent onset human individuals than of healthy donors. IGRP_265–273-specific CD8 T-cells that were cloned from the peripheral blood of a recent onset T1D individual were shown to secrete IFNγ and Granzyme B after antigen-specific activation and lyse HLA-A2-expressing murine islets in-vitro. Lytic capacity was also demonstrated in-vivo by specific killing of peptide-pulsed target cells. Using the HLA-A2 NOD-scid IL2rγ^null mouse model, HLA-A2-restricted IGRP-specific CD8 T-cells induced a destructive insulitis. Together, this is the first evidence that human HLA-restricted autoreactive CD8 T-cells target HLA-expressing beta-cells in-vivo, demonstrating the translational value of humanized mice to study mechanisms of disease and therapeutic intervention strategies.

B-cell cross-presentation of autologous antigen precipitates diabetes

For autoimmune conditions like type 1 diabetes to progress, self-reactive CD8⁺ T cells would need to interact with peptide-antigen cross-presented on the surface of antigen-presenting cells in a major histocompatibility complex (MHC) class I-restricted fashion. However, the mechanisms by which autoantigen is cross-presented remain to be identified. In this study, we show cross-presentation of islet-derived autoantigens by B cells. B cells engage self-reactive CD8⁺ T cells in the pancreatic lymph node, driving their proliferative expansion and differentiation into granzyme B⁺interferon-γ⁺lysosomal-associated membrane protein 1⁺ effector cells. B-cell cross-presentation of insulin required proteolytic cleavage and endosomal localization and was sensitive to inhibitors of protein trafficking. Absent B-cell MHC class I, or B-cell receptor restriction to an irrelevant specificity, blunted the expansion of self-reactive CD8⁺ T cells, suggesting B-cell antigen capture and presentation are critical in vivo events for CD8 activation. Indeed, the singular loss of B-cell MHC class I subverted the conversion to clinical diabetes in NOD mice, despite the presence of a pool of activated, and B cell-dependent, interleukin-21-expressing Vβ4⁺CD4⁺ T cells. Thus, B cells govern the transition from clinically silent insulitis to frank diabetes by cross-presenting autoantigen to self-reactive CD8⁺ T cells.

Cytotoxic mechanisms employed by mouse T cells to destroy pancreatic β-cells

Several cytotoxic mechanisms have been attributed to T cells participating in β-cell death in type 1 diabetes. However, sensitivity of β-cells to these mechanisms in vitro and in vivo is likely to be different. Moreover, CD4⁺ and CD8⁺ T cells may use distinct mechanisms to cause β-cell demise that possibly involve activation of third-party cytotoxic cells. We used the transfer of genetically modified diabetogenic T cells into normal, mutant, and bone marrow chimeric recipients to test the contribution of major cytotoxic mechanisms in β-cell death. We found that 1) the killing of β-cells by CD4⁺ T cells required activation of the recipient's own cytotoxic cells via tumor necrosis factor-α (TNF-α); 2) CD8⁺ T-cell cytotoxic mechanisms destroying β-cells were limited to perforin and Fas ligand, as double knockouts of these molecules abrogated the ability of T cells to cause diabetes; and 3) individual CD8⁺ T-cell clones chose their cytotoxic weaponry by a yet unknown mechanism and destroyed their targets via either Fas-independent or Fas-dependent (~40% of clones) pathways. Fas-dependent destruction was assisted by TNF-α.

B7x in the periphery abrogates pancreas-specific damage mediated by self-reactive CD8 T cells

B7x (B7-H4 or B7S1) is the seventh member of the B7 family, and its in vivo function remains largely unknown. Despite new genetic data linking the B7x gene with autoimmune diseases, how exactly it contributes to peripheral tolerance and autoimmunity is unclear. In this study, we showed that B7x protein was not detected on APCs or T cells in both human and mice, which is unique in the B7 family. Because B7x protein is expressed in some peripheral cells such as pancreatic β cells, we used a CD8 T cell-mediated diabetes model (AI4αβ) in which CD8 T cells recognize an endogenous self-Ag, and found that mice lacking B7x developed more severe diabetes than control AI4αβ mice. Conversely, mice overexpressing B7x in the β cells (Rip-B7xAI4αβ) were diabetes free. Furthermore, adoptive transfer of effector AI4αβ CD8 T cells induced diabetes in control mice, but not in Rip-B7xAI4αβ mice. Mechanistic studies revealed that pathogenic effector CD8 T cells were capable of migrating to the pancreas but failed to robustly destroy tissue when encountering local B7x in Rip-B7xAI4αβ mice. Although AI4αβ CD8 T cells in Rip-B7xAI4αβ and AI4αβ mice showed similar cytotoxic function, cell death, and global gene expression profiles, these cells had greater proliferation in AI4αβ mice than in RIP-B7xAI4αβ mice. These results suggest that B7x in nonlymphoid organs prevents peripheral autoimmunity partially through inhibiting proliferation of tissue-specific CD8 T cells, and that local overexpression of B7x on pancreatic β cells is sufficient to abolish CD8 T cell-induced diabetes.

Granzyme B is dispensable in the development of diabetes in non-obese diabetic mice

Pancreatic beta cell destruction in type 1 diabetes is mediated by cytotoxic CD8(+) T lymphoctyes (CTL). Granzyme B is an effector molecule used by CTL to kill target cells. We previously showed that granzyme B-deficient allogeneic CTL inefficiently killed pancreatic islets in vitro. We generated granzyme B-deficient non-obese diabetic (NOD) mice to test whether granzyme B is an important effector molecule in spontaneous type 1 diabetes. Granzyme B-deficient islet antigen-specific CD8(+) T cells had impaired homing into islets of young mice. Insulitis was reduced in granzyme B-deficient mice at 70 days of age (insulitis score 0.043±0.019 in granzyme B-deficient versus 0.139±0.034 in wild-type NOD mice p<0.05), but was similar to wild-type at 100 and 150 days of age. We observed a reduced frequency of CD3(+)CD8(+) T cells in the islets and peripheral lymphoid tissues of granzyme B-deficient mice (p<0.005 and p<0.0001 respectively), but there was no difference in cell proportions in the thymus. Antigen-specific CTL developed normally in granzyme B-deficient mice, and were able to kill NOD islet target cells as efficiently as wild-type CTL in vitro. The incidence of spontaneous diabetes in granzyme B-deficient mice was the same as wild-type NOD mice. We observed a delayed onset of diabetes in granzyme B-deficient CD8-dependent NOD8.3 mice (median onset 102.5 days in granzyme B-deficient versus 57.50 days in wild-type NOD8.3 mice), which may be due to the delayed onset of insulitis or inefficient priming at an earlier age in this accelerated model of diabetes. Our data indicate that granzyme B is dispensable for beta cell destruction in type 1 diabetes, but is required for efficient early activation of CTL.

Subcongenic analyses reveal complex interactions between distal chromosome 4 genes controlling diabetogenic B cells and CD4 T cells in nonobese diabetic mice

Autoimmune type 1 diabetes (T1D) in humans and NOD mice results from interactions between multiple susceptibility genes (termed Idd) located within and outside the MHC. Despite sharing ∼88% of their genome with NOD mice, including the H2(g7) MHC haplotype and other important Idd genes, the closely related nonobese resistant (NOR) strain fails to develop T1D because of resistance alleles in residual genomic regions derived from C57BLKS mice mapping to chromosomes (Chr.) 1, 2, and 4. We previously produced a NOD background strain with a greatly decreased incidence of T1D as the result of a NOR-derived 44.31-Mb congenic region on distal Chr. 4 containing disease-resistance alleles that decrease the pathogenic activity of autoreactive B and CD4 T cells. In this study, a series of subcongenic strains for the NOR-derived Chr. 4 region was used to significantly refine genetic loci regulating diabetogenic B and CD4 T cell activity. Analyses of these subcongenic strains revealed the presence of at least two NOR-origin T1D resistance genes within this region. A 6.22-Mb region between rs13477999 and D4Mit32, not previously known to contain a locus affecting T1D susceptibility and now designated Idd25, was found to contain the main NOR gene(s) dampening diabetogenic B cell activity, with Ephb2 and/or Padi2 being strong candidates as the causal variants. Penetrance of this Idd25 effect was influenced by genes in surrounding regions controlling B cell responsiveness and anergy induction. Conversely, the gene(s) controlling pathogenic CD4 T cell activity was mapped to a more proximal 24.26-Mb region between the rs3674285 and D4Mit203 markers.

The influence of the microbiota on type-1 diabetes: on the threshold of a leap forward in our understanding

The last several years have seen breakthroughs in techniques to track the symbiont communities that normally colonize mammals (the microbiota) and in cataloguing the universe of the genes they carry (the microbiome). Applying these methods to human patients and corresponding murine models should allow us to decipher just how the microbiota impacts type-1 diabetes, i.e. which particular microbes are responsible and the cellular and molecular processes that are involved. Here, at its threshold, we set the stage for what promises to be an exciting rejuvenated area of investigation.

Intracellular pathways of pancreatic β-cell apoptosis in type 1 diabetes

BACKGROUND

Apoptosis of β cells is a feature of type 1 diabetes. It is also increasingly recognized in type 2 diabetes and islet graft rejection.

METHODS

We have studied the intracellular pathways that regulate β-cell apoptosis in type 1 and 2 diabetes. We have examined the role of Bid, a pro-apoptotic member of the Bcl-2 family, using islets from mice deficient in Bid. We also studied the Bcl-2 family molecules involved in killing by using high concentrations of reducing sugars such as glucose or ribose.

RESULTS

We found that Bid-deficient islets are protected from recombinant human perforin and granzyme B, as well as from Fas-mediated killing. This makes Bid a target for protection of β cells from multiple insults relevant to type 1 diabetes. In contrast to granzyme B and death receptor signalling, we found that islets lacking Bim or Puma were protected from glucose toxicity.

CONCLUSIONS

Our data indicate that different stimuli activate different initiator molecules in the Bcl-2-regulated pathway in β cells.

Role of genetics in resistance to type 1 diabetes

BACKGROUND

A single nucleotide polymorphism in the mitochondrial gene encoding NADH dehydrogenase subunit 2 (mt-ND2) has been associated with reduced incidence of human type 1 diabetes (T1D). We identified the orthologue of this mitochondrial single nucleotide polymorphism in mouse and using NOD mouse models linked this genetic polymorphism to T1D resistance. The mechanism how this single nucleotide polymorphism affects the development of diabetes is studied using mouse models and beta cell lines.

METHODS

The impact of this single nucleotide polymorphism on mitochondrial function and resistance to reactive oxygen species was assessed. For these studies we measured oxygen consumption by isolated mitochondria under different doses of nitric oxide. In addition, alloxan sensitivity of beta cell lines was tested using the MTT method to measure cell survival.

RESULTS

mt-Nd2a is associated with protection against mouse T1D and alloxan-induced diabetes. Mice with mt-Nd2a exhibited resistance to transfer of diabetes by single clone of diabetogenic CD4+ or CD8+ T cells. Beta cell line with mt-Nd2a resist in vitro attack of diabetogenic CD8+ cytotoxic T cells, as well as free radicals generated by alloxan; isolated mitochondria with mt-Nd2a showed lower reactive oxygen species production and were more resistant to nitric oxide.

CONCLUSION

mt-Nd2a protects against T1D in mouse models. The protection is at beta cell level and is associated with resistance against reactive oxygen species-mediated damage and death.

Structural and functional characterization of a single-chain peptide-MHC molecule that modulates both naive and activated CD8+ T cells

Peptide-MHC (pMHC) multimers, in addition to being tools for tracking and quantifying antigen-specific T cells, can mediate downstream signaling after T-cell receptor engagement. In the absence of costimulation, this can lead to anergy or apoptosis of cognate T cells, a property that could be exploited in the setting of autoimmune disease. Most studies with class I pMHC multimers used noncovalently linked peptides, which can allow unwanted CD8(+) T-cell activation as a result of peptide transfer to cellular MHC molecules. To circumvent this problem, and given the role of self-reactive CD8(+) T cells in the development of type 1 diabetes, we designed a single-chain pMHC complex (scK(d).IGRP) by using the class I MHC molecule H-2K(d) and a covalently linked peptide derived from islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP(206-214)), a well established autoantigen in NOD mice. X-ray diffraction studies revealed that the peptide is presented in the groove of the MHC molecule in canonical fashion, and it was also demonstrated that scK(d).IGRP tetramers bound specifically to cognate CD8(+) T cells. Tetramer binding induced death of naive T cells and in vitro- and in vivo-differentiated cytotoxic T lymphocytes, and tetramer-treated cytotoxic T lymphocytes showed a diminished IFN-γ response to antigen stimulation. Tetramer accessibility to disease-relevant T cells in vivo was also demonstrated. Our study suggests the potential of single-chain pMHC tetramers as possible therapeutic agents in autoimmune disease. Their ability to affect the fate of naive and activated CD8(+) T cells makes them a potential intervention strategy in early and late stages of disease.

Superoxide production by macrophages and T cells is critical for the induction of autoreactivity and type 1 diabetes

OBJECTIVE

The role of reactive oxygen species (ROS) and their dissipation in type 1 diabetes pathogenesis have garnered considerable controversy. Our recent work has demonstrated the importance of NADPH oxidase (NOX) activity for type 1 diabetes development and modulating T-cell autoreactivity. We previously linked decreased monocyte ROS with diabetes resistance in the alloxan-resistant mouse, and NOD-Ncf1(m1J) mice with a genetic ablation of NOX activity had reduced and delayed type 1 diabetes compared with NOD mice.

RESEARCH DESIGN AND METHODS

To determine the required cellular sources of ROS that are necessary for type 1 diabetes initiation, we used antibody depletion and adoptive transfer experiments into NOD and NOD-Scid females, respectively. After receiving treatment, female mice were monitored for hyperglycemia and overt diabetes.

RESULTS

Depletion of macrophages and neutrophils fully protected NOD mice from type 1 diabetes. However, elimination of neutrophils alone showed no significant reduction or delay. Type 1 diabetes induction in NOD-Scid mice by adoptive transfer with NOD-Ncf1(m1J) splenocytes was significantly delayed compared with NOD splenocytes, suggesting macrophage ROS and modulation of effector responses are critical for diabetes. The adaptive immune response was also altered by the absence of NOX activity, as purified T cells from NOD-Ncf1(m1J) mice exhibited delayed transfer kinetics. Cotransfer experiments demonstrated the defect was intrinsic to NOX-deficient CD8(+) T cells. After stimulation, cytotoxic T cells exhibited decreased effector function in the absence of superoxide production.

CONCLUSIONS

These data demonstrate that the impaired autoreactive response of NOX-deficient NOD-Ncf1(m1J) immune system results from an alteration in the antigen-presenting cell-T-cell axis rather than failure of neutrophils to act as effector cells and that ROS signaling is important for the initiation of β-cell-directed autoimmunity by T cells.

Discovery of low-affinity preproinsulin epitopes and detection of autoreactive CD8 T-cells using combinatorial MHC multimers

Autoreactive cytotoxic CD8 T-cells (CTLs) play a key pathogenic role in the destruction of insulin-producing beta-cells resulting in type 1 diabetes. However, knowledge regarding their targets is limited, restricting the ability to monitor the course of the disease and immune interventions. In a multi-step discovery process to identify novel CTL epitopes in human preproinsulin (PPI), PPI was digested with purified human proteasomes, and resulting COOH-fragments aligned with algorithm-predicted HLA-binding peptides to yield nine potential HLA-A1, -A2, -A3 or -B7-restricted candidates. An UV-exchange method allowed the generation of a repertoire of multimers including low-affinity HLA-binding peptides. These were labeled with quantum dot-fluorochromes and encoded in a combinatorial fashion, allowing parallel and sensitive detection of specific, low-avidity T-cells. Significantly increased frequencies of T-cells against four novel PPI epitopes (PPI(4-13)/B7, PPI(29-38)/A2, PPI(76-84)/A3 and PPI(79-88)/A3) were detected in stored blood of patients with recent onset diabetes but not in controls. Changes in frequencies of circulating CD8 T-cells against these novel epitopes were detected in blood of islet graft recipients at different time points after transplantation, which correlated with clinical outcome. In conclusion, our novel strategy involving a sensitive multiplex detection technology and requiring minimal volumes of stored blood represents a major improvement in the direct ex-vivo characterization and enumeration of immune cells in the pathogenesis of type 1 diabetes.

The development and functions of CD4(+) T cells expressing a transgenic TCR specific for an MHC-I-restricted tumor antigenic epitope

It has been reported that the ratio of CD4(+) to CD8(+) T cells has no bias in a few class I major histocompatibility complex (MHC-I)-restricted T-cell receptor (TCR)-transgenic mice specific for alloantigens or autoantigens, in which most CD4(+) T cells express an MHC-I-restricted TCR. In this study, we further showed that more than 50% of CD4(+) T cells in MHC-I-restricted P1A tumor antigen-specific TCR (P1ATCR)-transgenic mice could specifically bind to MHC-I/P1A peptide complex. P1A peptide could stimulate the transgenic CD4(+) T cells to proliferate and secrete both type 1 helper T cell and type 2 helper T cell cytokines. The activated CD4(+) T cells also showed cytotoxicity against P1A-expressing tumor cells. The analysis of TCR α-chains showed that these CD4(+) T cells were selected by co-expressing endogenous TCRs. Our results show that CD4(+) T cells from P1ATCR transgenic mice co-expressed an MHC-I-restricted transgenic TCR and another rearranged endogenous TCRs, both of which were functional.

CD8 T cells mediate direct biliary ductule damage in nonobese diabetic autoimmune biliary disease

We previously described the NOD.c3c4 mouse, which is protected from type 1 diabetes (T1D) because of protective alleles at multiple insulin-dependent diabetes (Idd) genes, but develops autoimmune biliary disease (ABD) resembling primary biliary cirrhosis (PBC). In this paper, we characterize the NOD.ABD strain, which is genetically related to the NOD.c3c4 strain but develops both ABD and T1D. Histologically, NOD.ABD biliary disease is indistinguishable from that in NOD.c3c4 mice. The frequency of effector memory (CD44(+)CD62L(-)) and central memory (CD44(+)CD62L(+)) CD8 T cells is significantly increased in the intrahepatic lymphocyte fraction of NOD.ABD mice, and NOD.ABD CD8 T cells produce more IFN-γ and TNF-α, compared with controls. NOD.ABD splenocytes can transfer ABD and T1D to NOD.c3c4 scid mice, but only T1D to NOD scid mice, suggesting that the genetic origin of the target organ and/or its innate immune cells is critical to disease pathogenesis. The disease transfer model, importantly, shows that biliary duct damage (characteristic of PBC) and inflammation precede biliary epithelial cell proliferation. Unlike T1D where both CD4 and CD8 T cells are required for disease transfer, purified NOD.ABD CD8 T cells can transfer liver inflammation into NOD.c3c4 scid recipients, and disease transfer is ameliorated by cotransferring T regulatory cells. Unlike NOD.c3c4 mice, NOD.ABD mice do not develop anti-nuclear or anti-Smith autoantibodies; however, NOD.ABD mice do develop the antipyruvate dehydrogenase Abs typical of human PBC. The NOD.ABD strain is a model of immune dysregulation affecting two organ systems, most likely by mechanisms that do not completely coincide.

Simultaneous detection of circulating autoreactive CD8+ T-cells specific for different islet cell-associated epitopes using combinatorial MHC multimers

OBJECTIVE

Type 1 diabetes results from selective T-cell-mediated destruction of the insulin-producing beta-cells in the pancreas. In this process, islet epitope-specific CD8(+) T-cells play a pivotal role. Thus, monitoring of multiple islet-specific CD8(+) T-cells may prove to be valuable for measuring disease activity, progression, and intervention. Yet, conventional detection techniques (ELISPOT and HLA tetramers) require many cells and are relatively insensitive.

RESEARCH DESIGN AND METHODS

Here, we used a combinatorial quantum dot major histocompatibility complex multimer technique to simultaneously monitor the presence of HLA-A2 restricted insulin B(10-18), prepro-insulin (PPI)(15-24), islet antigen (IA)-2(797-805), GAD65(114-123), islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)(265-273), and prepro islet amyloid polypeptide (ppIAPP)(5-13)-specific CD8(+) T-cells in recent-onset diabetic patients, their siblings, healthy control subjects, and islet cell transplantation recipients.

RESULTS

Using this kit, islet autoreactive CD8(+) T-cells recognizing insulin B(10-18), IA-2(797-805), and IGRP(265-273) were shown to be frequently detectable in recent-onset diabetic patients but rarely in healthy control subjects; PPI(15-24) proved to be the most sensitive epitope. Applying the "Diab-Q-kit" to samples of islet cell transplantation recipients allowed detection of changes of autoreactive T-cell frequencies against multiple islet cell-derived epitopes that were associated with disease activity and correlated with clinical outcome.

CONCLUSIONS

A kit was developed that allows simultaneous detection of CD8(+) T-cells reactive to multiple HLA-A2-restricted beta-cell epitopes requiring limited amounts of blood, without a need for in vitro culture, that is applicable on stored blood samples.

Molecular targeting of islet autoantigens

Type 1 diabetes of man and animal models results from immune-mediated specific beta cell destruction. Multiple islet antigens are targets of autoimmunity and most of these are not beta cell specific. Immune responses to insulin appear to be essential for the development of diabetes of the NOD mouse. In this review, we will emphasize the unusual manner in which selected autoantigenic peptides (particularly the recently discovered target of BDC2.5 T cells [chromagranin A]) are presented and recognized by autoreactive CD4(+) T cell receptors. We hypothesize that "unusual" structural interactions of specific trimolecular complexes (MHC class II, peptide, and T cell receptors) are fundamental to the escape from the thymus of autoreactive T cells able to cause type 1 diabetes.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

Immunology of beta-cell destruction

The pancreatic islet beta-cells are the target for an autoimmune process that eventually results in an inability to control blood glucose due to the lack of insulin. The different steps that eventually lead to the complete loss of the beta-cells are reviewed to include the very first step of a triggering event that initiates the development of beta-cell autoimmunity to the last step of appearance of islet-cell autoantibodies, which may mark that insulitis is about to form. The observations that the initial beta-cell destruction by virus or other environmental factors triggers islet autoimmunity not in the islets but in the draining pancreatic lymph nodes are reviewed along with possible basic mechanisms of loss of tolerance to islet autoantigens. Once islet autoimmunity is established the question is how beta-cells are progressively killed by autoreactive lymphocytes which eventually results in chronic insulitis. Many of these series of events have been dissected in spontaneously diabetic mice or rats, but controlled clinical trials have shown that rodent observations are not always translated into mechanisms in humans. Attempts are therefore needed to clarify the step 1 triggering mechanisms and the step to chronic autoimmune insulitis to develop evidence-based treatment approaches to prevent type 1 diabetes.

CD8(+) T cells specific for beta cells encounter their cognate antigens in the islets of NOD mice

CD8(+) T cells play a key role in the initiation of insulitis. However, the site(s) where naive CD8(+) T cells encounter beta-cell antigens and the mechanism(s) by which beta-cell autoimmunity is initiated remain to be determined. In the current study, an adoptive transfer model was employed assessing the initial site of priming and the nature of antigen recognition by naive beta-cell-specific CD8(+) T cells. Temporal analysis demonstrated that unlike CD4(+) T cells that are primed in the draining pancreatic lymph nodes, initial proliferation of transferred CD8(+) T cells was detected in the islets. These results indicate that in our model, naive beta-cell-specific CD8(+) T cells encounter beta-cell antigens in the islets. Furthermore, ectopic expression of CD80 by beta cells accelerated the onset of insulitis mediated by beta-cell-specific CD8(+) T cells, but had no effect on CD4(+) T-cell-mediated diabetes, suggesting an antigenic interaction between beta cells and naive CD8(+) T cells. However, it remains to be determined whether the initiation of insulitis in spontaneous diabetes is the result of a cognate interaction between naive CD8(+) T cells and islet beta cells.

Coxsackievirus B4 and type 1 diabetes pathogenesis: contribution of animal models

The role of enteroviruses, in particular type B coxsackieviruses (CV-B), in type 1 diabetes (T1D) pathogenesis is supported by epidemiological, clinical and experimental observations.The investigation of T1D pathogenesis benefits from the contribution of animal models called spontaneously diabetic. Among these animals the non-obese diabetic (NOD) mouse and the bio-breeding diabetes-prone (BBDP) rat present a genetic susceptibility manifested by the expression of an autoimmune diabetes similar to the pathology observed in human beings. Other models whose genetic predisposition is less known are of considerable contribution as well. Numerous major observations relative to several aspects of T1D pathogenesis in the context of CV-B infections, such as susceptibility, diabetogenicity, pancreatotropism, mechanisms of beta cells destruction and others, have been deduced thanks to investigations with animal models. Despite their limits, these models are necessary in improving our knowledge of the role of enteroviruses, like CV-B4, in the pathogenesis of T1D, and the recent advances ensuing from their contribution may have important therapeutic and preventive spin-offs.

Type 1 diabetes development requires both CD4+ and CD8+ T cells and can be reversed by non-depleting antibodies targeting both T cell populations

Type 1 diabetes development in NOD mice appears to require both CD4(+) and CD8(+) T cells. However, there are some situations where it has been suggested that either CD4(+) or CD8(+) T cells are able to mediate diabetes in the absence of the other population. In the case of transgenic mice, this may reflect the numbers of antigen-specific T cells able to access the pancreas and recruit other cell types such as macrophages leading to a release of high concentrations of damaging cytokines. Previous studies examining the requirement for CD8(+) T cells have used antibodies specific for CD8alpha. It is known that CD8alpha is expressed not only on alphabeta T cells, but also on other cell types, including a DC population that may be critical for presenting islet antigen in the pancreatic draining lymph nodes. Therefore, we have re-examined the need for both CD4(+) and CD8(+) T cell populations in diabetes development in NOD mice using an antibody to CD8beta. Our studies indicate that by using highly purified populations of T cells and antibodies specific for CD8(+) T cells, there is indeed a need for both cell types. In accordance with some other reports, we found that CD4(+) T cells appeared to be able to access the pancreas more readily than CD8(+) T cells. Despite the ability of CD4(+) T cells to recruit CD11b class II positive cells, diabetes did not develop in the absence of CD8(+) T cells. These studies support the observation that CD8(+) T cells may be final effector cells. As both T cell populations are clearly implicated in diabetes development, we have used a combination of non-depleting antibodies to target both CD4-positive and CD8-positive cells and found that this antibody combination was able to reverse diabetes onset in NOD mice as effectively as anti-CD3 antibodies.