Prevalent CD8(+) T cell response against one peptide/MHC complex in autoimmune diabetes

Structural plasticity in I-Ag7 links autoreactivity to hybrid insulin peptides in type I diabetes

We recently provided evidence for promiscuous recognition of several different hybrid insulin peptides (HIPs) by the highly diabetogenic, I-Ag7-restricted 4.1-T cell receptor (TCR). To understand the structural determinants of this phenomenon, we solved the structure of an agonistic HIP/I-Ag7 complex, both in isolation as well as bound to the 4.1-TCR. We find that HIP promiscuity of the 4.1-TCR is dictated, on the one hand, by an amino acid sequence pattern that ensures I-Ag7 binding and, on the other hand, by the presence of three acidic residues at positions P5, P7 and P8 that favor an optimal engagement by the 4.1-TCR’s complementary determining regions. Surprisingly, comparison of the TCR-bound and unbound HIP/I-Ag7 structures reveals that 4.1-TCR binding triggers several novel and unique structural motions in both the I-Ag7 molecule and the peptide that are essential for docking. This observation indicates that the type 1 diabetes-associated I-Ag7 molecule is structurally malleable and that this plasticity allows the recognition of multiple peptides by individual TCRs that would otherwise be unable to do so.

Role of Gut Microbiota in Multiple Sclerosis and Potential Therapeutic Implications

The role of gut microbiota in health and diseases has been receiving increased attention recently. Emerging evidence from previous studies on gut-microbiota-brain axis highlighted the importance of gut microbiota in neurological disorders. Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease of the central nervous system (CNS) resulting from T-cell-driven, myelin-directed autoimmunity. The dysbiosis of gut microbiota in MS patients has been reported in published research studies, indicating that gut microbiota plays an important role in the pathogenesis of MS. Gut microbiota have also been reported to influence the initiation of disease and severity of experimental autoimmune encephalomyelitis, which is the animal model of MS. However, the underlying mechanisms of gut microbiota involvement in the pathogenesis of MS remain unclear. Therefore, in this review, we summerized the potential mechanisms for gut microbiota involvement in the pathogenesis of MS, including increasing the permeability of the intestinal barrier, initiating an autoimmune response, disrupting the blood-brain barrier integrity, and contributing to chronic inflammation. The possibility for gut microbiota as a target for MS therapy has also been discussed. This review provides new insight into understanding the role of gut microbiota in neurological and inflammatory diseases.

Engineered RBCs Encapsulating Antigen Induce Multi-Modal Antigen-Specific Tolerance and Protect Against Type 1 Diabetes

Antigen-specific therapies that suppress autoreactive T cells without inducing systemic immunosuppression are a much-needed treatment for autoimmune diseases, yet effective strategies remain elusive. We describe a microfluidic Cell Squeeze^® technology to engineer red blood cells (RBCs) encapsulating antigens to generate tolerizing antigen carriers (TACs). TACs exploit the natural route of RBC clearance enabling tolerogenic presentation of antigens. TAC treatment led to antigen-specific T cell tolerance towards exogenous and autoantigens in immunization and adoptive transfer mouse models of type 1 diabetes (T1D), respectively. Notably, in several accelerated models of T1D, TACs prevented hyperglycemia by blunting effector functions of pathogenic T cells, particularly in the pancreas. Mechanistically, TACs led to impaired trafficking of diabetogenic T cells to the pancreas, induced deletion of autoreactive CD8 T cells and expanded antigen specific Tregs that exerted bystander suppression. Our results highlight TACs as a novel approach for reinstating immune tolerance in CD4 and CD8 mediated autoimmune diseases.

Antigen- and Epitope-Delivering Nanoparticles Targeting Liver Induce Comparable Immunotolerance in Allergic Airway Disease and Anaphylaxis as Nanoparticle-Delivering Pharmaceuticals

The targeting of natural tolerogenic liver sinusoidal endothelial cells (LSEC) by nanoparticles (NPs), decorated with a stabilin receptor ligand, is capable of generating regulatory T-cells (Tregs), which can suppress antigen-specific immune responses, including to ovalbumin (OVA), a possible food allergen. In this regard, we have previously demonstrated that OVA-encapsulating poly(lactic-co-glycolic acid) (PLGA) nanoparticles eliminate allergic airway inflammation in OVA-sensitized mice, prophylactically and therapeutically. A competing approach is a nanocarrier platform that incorporates pharmaceutical agents interfering in mTOR (rapamycin) or NF-κB (curcumin) pathways, with the ability to induce a tolerogenic state in nontargeted antigen-presenting cells system-wide. First, we compared OVA-encapsulating, LSEC-targeting tolerogenic nanoparticles (TNPs) with nontargeted NPs incorporating curcumin and rapamycin (Rapa) in a murine eosinophilic airway inflammation model, which is Treg-sensitive. This demonstrated roughly similar tolerogenic effects on allergic airway inflammation by stabilin-targeting NP^OVAversus nontargeted NPs delivering OVA plus Rapa. Reduction in eosinophilic inflammation and TH2-mediated immune responses in the lung was accompanied by increased Foxp3⁺ Treg recruitment and TGF-β production in both platforms. As OVA incorporates IgE-binding as well as non-IgE-binding epitopes, the next experiment explored the possibility of obtaining immune tolerance by non-anaphylactic T-cell epitopes. This was accomplished by incorporating OVA^323-339 and OVA^257-264 epitopes in liver-targeting NPs to assess the prophylactic and therapeutic impact on allergic inflammation in transgenic OT-II mice. Importantly, we demonstrated that the major histocompatibility complex (MHC)-II binding (former) but not the MHC-I binding (latter) epitope interfered in allergic airway inflammation, improving TNP^OVA efficacy. The epitope-specific effect was transduced by TGF-β-producing Tregs. In the final phase of experimentation, we used an OVA-induced anaphylaxis model to demonstrate that targeted delivery of OVA and its MHC-II epitope could significantly suppress the anaphylaxis symptom score, mast cell release, and the late-phase inflammatory response. In summary, these results demonstrate comparable efficacy of LSEC-targeting versus pharmaceutical PLGA nanoparticles, as well as the ability of T-cell epitopes to achieve response outcomes similar to those of the intact allergens.

Tissue-specific autoimmunity controlled by Aire in thymic and peripheral tolerance mechanisms

Tissue-specific autoimmune diseases are assumed to arise through malfunction of two checkpoints for immune tolerance: defective elimination of autoreactive T cells in the thymus and activation of these T cells by corresponding autoantigens in the periphery. However, evidence for this model and the outcome of such alterations in each or both of the tolerance mechanisms have not been sufficiently investigated. We studied these issues by expressing human AIRE (huAIRE) as a modifier of tolerance function in NOD mice wherein the defects of thymic and peripheral tolerance together cause type I diabetes (T1D). Additive huAIRE expression in the thymic stroma had no major impact on the production of diabetogenic T cells in the thymus. In contrast, huAIRE expression in peripheral antigen-presenting cells (APCs) rendered the mice resistant to T1D, while maintaining other tissue-specific autoimmune responses and antibody production against an exogenous protein antigen, because of the loss of Xcr1+ dendritic cells, an essential component for activating diabetogenic T cells in the periphery. These results contrast with our recent demonstration that huAIRE expression in both the thymic stroma and peripheral APCs resulted in the paradoxical development of muscle-specific autoimmunity. Our results reveal that tissue-specific autoimmunity is differentially controlled by a combination of thymic function and peripheral tolerance, which can be manipulated by expression of huAIRE/Aire in each or both of the tolerance mechanisms.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Deciphering CD4+ T cell specificity using novel MHC-TCR chimeric receptors

αβ T cell antigen receptors (TCRs) bind complexes of peptide and major histocompatibility complex (pMHC) with low affinity, which poses a considerable challenge for the direct identification of αβ T cell cognate peptides. Here we describe a platform for the discovery of MHC class II epitopes based on the screening of engineered reporter cells expressing novel pMHC-TCR (MCR) hybrid molecules carrying cDNA-derived peptides. This technology identifies natural epitopes of CD4⁺ T cells in an unbiased and efficient manner and allows detailed analysis of TCR cross-reactivity that provides recognition patterns beyond discrete peptides. We determine the cognate peptides of virus- and tumor-specific T cells in mouse disease models and present a proof of concept for human T cells. Furthermore, we use MCR to identify immunogenic tumor neo-antigens and show that vaccination with a peptide naturally recognized by tumor-infiltrating lymphocytes efficiently protects mice from tumor challenge. Thus, the MCR technology holds promise for basic research and clinical applications, allowing the personalized identification of T cell-specific neo-antigens in patients.

Antigen-specific therapeutic approaches for autoimmunity

The main function of the immune system in health is to protect the host from infection by microbes and parasites. Because immune responses to nonself bear the risk of unleashing accidental immunity against self, evolution has endowed the immune system with central and peripheral mechanisms of tolerance, including regulatory T and B cells. Although the past two decades have witnessed the successful clinical translation of a whole host of novel therapies for the treatment of chronic inflammation, the development of antigen-based approaches capable of selectively blunting autoimmune inflammation without impairing normal immunity has remained elusive. Earlier autoantigen-specific approaches employing peptides or whole antigens have evolved into strategies that seek to preferentially deliver these molecules to autoreactive T cells either indirectly, via antigen-presenting cells, or directly, via major histocompatibility complex molecules, in ways intended to promote clonal deletion and/or immunoregulation. The disease specificity, mechanistic underpinnings, developability and translational potential of many of these strategies remain unclear.

Prenatal Betamethasone interferes with immune system development and alters target cells in autoimmune diabetes

Non-genetic factors are crucial in the pathogenesis of type 1 diabetes (T1D), a disease caused by autoimmunity against insulin-producing β-cells. Exposure to medications in the prenatal period may influence the immune system maturation, thus altering self-tolerance. Prenatal administration of betamethasone –a synthetic glucocorticoid given to women at risk of preterm delivery– may affect the development of T1D. It has been previously demonstrated that prenatal betamethasone administration protects offspring from T1D development in nonobese diabetic (NOD) mice. The direct effect of betamethasone on the immature and mature immune system of NOD mice and on target β-cells is analysed in this paper. In vitro, betamethasone decreased lymphocyte viability and induced maturation-resistant dendritic cells, which in turn impaired γδ T cell proliferation and decreased IL-17 production. Prenatal betamethasone exposure caused thymus hypotrophy in newborn mice as well as alterations in immune cells subsets. Furthermore, betamethasone decreased β-cell growth, reduced C-peptide secretion and altered the expression of genes related to autoimmunity, metabolism and islet mass in T1D target tissue. These results support the protection against T1D in the betamethasone-treated offspring and demonstrate that this drug alters the developing immune system and β-cells. Understanding how betamethasone generates self-tolerance could have potential clinical relevance in T1D.

Advances in immunotherapy of type I diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease affecting 3 million individuals in the U.S. The pathogenesis of T1DM is driven by immune-mediated destruction of pancreatic β cells, the source of glucose regulator insulin. While T1DM can be successfully managed with insulin replacement therapy, approaches that can modify the underlying immuno-pathology of β cell destruction has been long sought after. Immunotherapy can attenuate T cell responses against β cell antigens. Given the detailed cellular and molecular definitions of T1DM immune responses, rational immunomodulation can be and have been developed in mouse models, and in some instances, tested in humans. The possibility of identifying individuals who are predisposed to T1DM through genotyping lend to the possibility of preventive vaccines. While much has been accomplished in delineating the mechanisms of immunotherapies, some of which are being tested in humans, long-term preservation of β cells and insulin independency has not been achieved. In this regard, the drug delivery field has much to offer in maximizing the benefits of immune modulators by optimizing spatiotemporal presentation of antigens and costimulatory signals. In this review, we attempt to capture the current state of T1DM immunotherapy by highlighting representative studies.

Naringenin Modifies the Development of Lineage-Specific Effector CD4+ T Cells

Disrupted balance in the lineages of CD4⁺ T cell subsets, including pro-inflammatory T helper (Th) cells and anti-inflammatory regulatory T cells (Treg), is a primary pathogenic factor for developing autoimmunity. We have found that this immunomodulatory effect of naringenin on effector T cells and T-cell mediated experimental autoimmune encephalomyelitis (EAE). We therefore explored the effects of naringenin on the development of different effector CD4⁺ T cells. Naïve CD4⁺ T cells were differentiated under respective Th1, Th2, Th17, and Treg polarizing conditions with naringenin. Percent populations of each differentiated CD4⁺ T cell subsets were determined and the corresponding regulating pathways were investigated as underlying mechanisms. Naringenin mainly inhibited CD4⁺ T cell proliferation and differentiation to Th1 and Th17, but did not affect Th2 cells. Impeded Th1 polarization was associated with inhibition of its specific regulator proteins T-bet, p-STAT1, and p-STAT4 by naringenin. Likewise, Th17 regulator proteins RORγt, p-STAT3, and Ac-STAT3 were also inhibited by naringenin. In addition, naringenin promoted Treg polarization and also prevented IL-6-induced suppression of Treg development via down-regulation of p-Smad2/3 as well as inhibition of IL-6 signaling, and the latter was further supported by the in vivo results showing lower soluble IL-6R but higher soluble gp130 levels in plasma of naringenin-fed compared to the control EAE mice. Naringenin impacts CD4⁺ T cell differentiation in a manner that would explain its beneficial effect in preventing/mitigating T cell-mediated autoimmunity.

Bioengineering strategies for inducing tolerance in autoimmune diabetes

Type 1 diabetes is an autoimmune disease marked by the destruction of insulin-producing beta cells in the pancreatic islets. Strategies to delay onset or prevent the autoimmune recognition of beta cell antigens or T cell-mediated killing of beta cells have mainly focused on systemic immunomodulation and antigen-specific immunotherapy. To bridge the fields of type 1 diabetes immunology and biomaterials engineering, this article will review recent trends in the etiology of type 1 diabetes immunopathology and will focus on the contributions of emerging bioengineered strategies in the fight against beta cell autoimmunity in type 1 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.

Microbial antigen mimics activate diabetogenic CD8 T cells in NOD mice

Both animal model and human studies indicate that commensal bacteria may modify type 1 diabetes (T1D) development. However, the underlying mechanisms by which gut microbes could trigger or protect from diabetes are not fully understood, especially the interaction of commensal bacteria with pathogenic CD8 T cells. In this study, using islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-reactive CD8 T cell receptor NY8.3 transgenic nonobese diabetic mice, we demonstrated that MyD88 strongly modulates CD8(+) T cell-mediated T1D development via the gut microbiota. Some microbial protein peptides share significant homology with IGRP. Both the microbial peptide mimic of Fusobacteria and the bacteria directly activate IGRP-specific NY8.3 T cells and promote diabetes development. Thus, we provide evidence of molecular mimicry between microbial antigens and an islet autoantigen and a novel mechanism by which the diabetogenicity of CD8(+) T cells can be regulated by innate immunity and the gut microbiota.

Elevated IFN-alpha/beta levels in a streptozotocin-induced type I diabetic mouse model promote oxidative stress and mediate depletion of spleen-homing CD8+ T cells by apoptosis through impaired CCL21/CCR7 axis and IL-7/CD127 signaling

Type 1 diabetes mellitus (T1D) is associated with increased type 1 interferon (IFN) levels and subsequent severe defects in lymphocyte function, which increase susceptibility to infections. The blockade of type 1 IFN receptor 1 (IFNAR1) in non-obese diabetic mice has been shown to delay T1D onset and decrease T1D incidence by enhancing spleen CD4+ T cells and restoring B cell function. However, the effect of type 1 IFN blockade during T1D on splenic CD8+ T cells has not previously been studied. Therefore, we investigated, for the first time, the effect of IFNAR1 blockade on the survival and architecture of spleen-homing CD8+ T cells in a streptozotocin-induced T1D mouse model. Three groups of mice were examined: a non-diabetic control group; a diabetic group; and a diabetic group treated with an anti-IFNAR1 blocking antibody. We observed that T1D induction was accompanied by a marked destruction of β cells followed by a marked reduction in insulin levels and increased IFN-α and IFN-β levels in the diabetic group. The diabetic mice also exhibited many abnormal changes including an elevation in blood and spleen free radical (reactive oxygen species and nitric oxide) and pro-inflammatory cytokine (IL-6 and TNF-α) levels, a significant decrease in IL-7 levels, and subsequently, a significant decrease in the numbers of spleen-homing CD8+ T cells. This decrease in spleen-homing CD8+ T cells resulted from a marked reduction in the CCL21-mediated entry of CD8+ T cells into the spleen and from increased apoptosis due to a marked reduction in IL-7-mediated STAT5 and AKT phosphorylation. Interestingly, type 1 IFN signaling blockade in diabetic mice significantly restored the numbers of splenic CD8+ T cells by restoring free radical, pro-inflammatory cytokine and IL-7 levels. These effects subsequently rescued splenic CD8+ T cells from apoptosis through a mechanism that was dependent upon CCL21- and IL-7-mediated signaling. Our data suggest that type 1 IFN is an essential mediator of pathogenesis in T1D and that this role results from the negative effect of IFN signaling on the survival of splenic CD8+ T cells.

NOD mice are functionally deficient in the capacity of cross-presentation

Cross-presentation by CD8(+) conventional dendritic cells (cDCs) is involved in the maintenance of peripheral tolerance and this process is termed cross-tolerance. Previous reports showed that non-obese diabetic (NOD) mice have reduced number of splenic CD8(+) cDCs compared with non-diabetic strains, and that the administration of Flt3L to enhance DC development resulted in reduced diabetes incidence. As CD8(+) cDCs are the most efficient antigen cross-presenting cells, it was assumed that reduced cross-presentation by non-activated, tolerogenic CD8(+) cDC predisposes to autoimmune diabetogenesis. Here we show for the first time that indeed NOD mice have a defect in autoantigen cross-presentation capacity. First, we showed that NOD CD8(+) cDCs were less sensitive to iatrogenic cytochrome c, which had previously been shown to selectively deplete CD8(+) cDCs that functionally cross-present. Second, we found that proliferation of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific CD8(+) T cells was impaired in NOD compared with non-obese diabetes resistant mice after immunization with cell associated recombinant fusion protein containing the cognate IGRP peptide. This study, therefore, suggests that the reduced number of CD8(+) cDCs in NOD mice, coupled with the reduced capacity to cross-present self-antigens, reduces the overall capacity to maintain peripheral tolerance in the spontaneous autoimmune type 1 diabetes mice.

The cross-priming capacity and direct presentation potential of an autoantigen are separable and inversely related properties

We investigated whether a prevalent epitope of the β-cell-specific autoantigen islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP206-214) reaches regional Ag-presentation pathways via unprocessed polypeptide chains, as free IGRP206-214 peptide or via preformed IGRP206-214/K(d) complexes. This was accomplished by expressing bacterial artificial chromosome transgenes encoding wild-type (stable) or ubiquitinated (unstable) forms of IGRP in IGRP-deficient NOD mice carrying MHC class I-deficient β-cells, dendritic cells, or B cells. We investigated the ability of the pancreatic lymph nodes of these mice to prime naive IGRP206-214-reactive CD8(+) T cells in vivo, either in response to spontaneous Ag shedding, or to synchronized forms of β-cell necrosis or apoptosis. When IGRP was made unstable by targeting it for proteasomal degradation within β-cells, the cross-priming, autoimmune-initiating potential of this autoantigen (designated autoantigenicity) was impaired. Yet at the same time, the direct presentation, CTL-targeting potential of IGRP (designated pathogenicity) was enhanced. The appearance of IGRP206-214 in regional Ag-presentation pathways was dissociated from transfer of IGRP206-214 or IGRP206-214/K(d) from β cells to dendritic cells. These results indicate that autoantigenicity and pathogenicity are separable and inversely related properties and suggest that pathogenic autoantigens, capable of efficiently priming CTLs while marking target cells for CTL-induced killing, may have a critical balance of these two properties.

The potential role of dendritic cells in the therapy of Type 1 diabetes

Type 1 diabetes (T1D) is the result of T-cell mediated autoimmune destruction of pancreatic islet β-cells. The two current treatments for T1D are based on insulin or islet-cell replacement rather than the pathogenesis of T1D and remain problematic. Islet/pancreas transplantation does not cater for the majority of sufferers due to the lack of supply of organs and the need for continuous immunosuppression regimens. The mainstay treatment is insulin replacement, but this is disruptive to lifestyle and does not protect against severe long-term complications. An early vaccination and long-term restoration of immune tolerance to self-antigens in T1D patients (reversing the immunopathogenesis of the disease) would be preferable. Dendritic cells (DCs) are potent APCs and play an important role in inducing and maintaining immune tolerance. Targeting DCs through different DC surface molecules shows effective modulation of immune responses. Their feasibility for immunotherapy to prolong transplant survival and cancer immunotherapy has been demonstrated. Therefore, DCs could potentially be used in the treatment of autoimmune diseases. This review summarizes new insights into DCs as a potential therapeutic target for the treatment of T1D.

Nanomedicine in autoimmunity

The application of nanotechnology to the diagnosis and therapy of human diseases is already a reality and is causing a real revolution in how we design new therapies and vaccines. In this review we focus on the applications of nanotechnology in the field of autoimmunity. First, we review scenarios in which iron oxide nanoparticles have been used in the diagnosis of autoimmune diseases, mostly through magnetic resonance imaging (MRI), both in animal models and patients. Second, we discuss the potential of nanoparticles as an immunotherapeutic platform for autoimmune diseases, for now exclusively in pre-clinical models. Finally, we discuss the potential of this field to generate the 'perfect drug' with the capacity to report on its therapeutic efficacy in real time, that is, the birth of theranostics in autoimmunity.

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.

B7-H4.Ig inhibits the development of type 1 diabetes by regulating Th17 cells in NOD mice

Type 1 diabetes (T1D) is an autoimmune disease characterized by immunological destruction of insulin-producing pancreatic β-cells and subsequent hyperglycemia. The non-obese diabetic (NOD) mouse strain spontaneously develops a disease similar to human T1D and is commonly used as an animal model for studying this disease. We have previously shown that the administration of B7-H4-immunoglobulin fusion protein (B7-H4.Ig), a newly identified T-cell co-inhibitory signaling molecule, blocks the onset of diabetes in NOD mice. However, the mechanism(s) by which B7-H4 protects NOD mice from T1D is not fully understood. IL-17 is a pro-inflammatory cytokine, produced by Th17 cells, that activates T cells and other immune cells to produce a variety of cytokines and chemokines. Increasing evidence has shown that therapeutic agents targeting the IL-17 molecule or directly inhibiting IL-17-producing cells regulate autoimmune diabetes in NOD mice, suggesting that IL-17 is involved in the pathogenesis of this disease. In this study, we investigate whether B7-H4.Ig treatment inhibits the generation of Th17 cells which subsequently decreases IL-17 production and prevents the onset of T1D in NOD mice. Pre-diabetic female NOD mice were injected intraperitoneally with control mouse IgG or B7-H4.Ig starting at 4 weeks of age for 12 weeks. Our data showed that the frequency of Th17 cells in B7-H4.Ig-treated mice was significantly decreased. In addition, our data showed that B7-H4.Ig-treated mice had decreased levels of pro-inflammatory cytokines and Th17-associated cytokines, and an increased level of the potent Th17 inhibitor IFN-γ. To further investigate the effect of B7-H4.Ig on differentiation of Th17 cells, we co-cultured splenocytes with Th17-polarizing cytokines in the absence or presence of B7-H4.Ig. Our results indicated that splenocytes, under the Th17 driving conditions in the presence of B7-H4.Ig, had significantly decreased the numbers of Th17 cells compared to cells co-cultured in the absence of B7-H4.Ig. Together, this study suggests that blocking the generation of Th17 cells with the administration of B7-H4.Ig effectively inhibits the development of T1D in NOD mice.

Antibody combination therapy targeting CD25, CD70 and CD8 reduces islet inflammation and improves glycaemia in diabetic mice

Destruction of pancreatic islets in type 1 diabetes is caused by infiltrating, primed and activated T cells. In a clinical setting this autoimmune process is already in an advanced stage before intervention therapy can be administered. Therefore, an effective intervention needs to reduce islet inflammation and preserve any remaining islet function. In this study we have investigated the role of targeting activated T cells in reversing autoimmune diabetes. A combination therapy consisting of CD25-, CD70- and CD8-specific monoclonal antibodies was administered to non-obese diabetic (NOD) mice with either new-onset diabetes or with advanced diabetes. In NOD mice with new-onset diabetes antibody combination treatment reversed hyperglycaemia and achieved long-term protection from diabetes (blood glucose <13·9 mmol/l) in >50% of mice. In contrast, in the control, untreated group blood glucose levels continued to increase and none of the mice were protected from diabetes (P < 0·0001). Starting therapy early when hyperglycaemia was relatively mild proved critical, as the mice with advanced diabetes showed less efficient control of blood glucose and shorter life span. Histological analysis (insulitis score) showed islet preservation and reduced immune infiltration in all treated groups, compared to their controls. In conclusion, antibody combination therapy that targets CD25, CD70 and CD8 results in decreased islet infiltration and improved blood glucose levels in NOD mice with established diabetes.

Local autoantigen expression as essential gatekeeper of memory T-cell recruitment to islet grafts in diabetic hosts

It is generally believed that inflammatory cues can attract noncognate, "bystander" T-cell specificities to sites of inflammation. We have shown that recruitment of naive and in vitro activated autoreactive CD8⁺ T cells into endogenous islets requires local autoantigen expression. Here, we demonstrate that absence of an autoantigen in syngeneic extrapancreatic islet grafts in diabetic hosts renders the grafts "invisible" to cognate memory (and naive) T cells. We monitored the recruitment of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)₂₀₆₋₂₁₄-reactive CD8⁺ T cells into IGRP₂₀₆₋₂₁₄-competent and IGRP₂₀₆₋₂₁₄-deficient islet grafts in diabetic wild-type or IGRP₂₀₆₋₂₁₄(-/-) nonobese diabetic hosts (harboring either naive and memory T cells or only naive IGRP₂₀₆₋₂₁₄-specific T-cells, respectively). All four host-donor combinations had development of recurrent diabetes within 2 weeks. Wild-type hosts recruited IGRP₂₀₆₋₂₁₄-specific T cells into IGRP₂₀₆₋₂₁₄(+/+) but not IGRP₂₀₆₋₂₁₄(-/-) grafts. In IGRP₂₀₆₋₂₁₄(-/-) hosts, there was no recruitment of IGRP₂₀₆₋₂₁₄-specific T cells, regardless of donor type. Graft-derived IGRP₂₀₆₋₂₁₄ activated naive IGRP₂₀₆₋₂₁₄-specific T cells, but graft destruction invariably predated their recruitment. These results indicate that recurrent diabetes is exclusively driven by autoreactive T cells primed during the primary autoimmune response, and demonstrate that local antigen expression is a sine qua non requirement for accumulation of memory T cells into islet grafts. These findings underscore the importance of tackling autoreactive T-cell memory after β-cell replacement therapy.

Antidiabetogenic MHC class II promotes the differentiation of MHC-promiscuous autoreactive T cells into FOXP3+ regulatory T cells

Polymorphisms in MHC class II molecules, in particular around β-chain position-57 (β57), afford susceptibility/resistance to multiple autoimmune diseases, including type 1 diabetes, through obscure mechanisms. Here, we show that the antidiabetogenic MHC class II molecule I-A(b) affords diabetes resistance by promoting the differentiation of MHC-promiscuous autoreactive CD4(+) T cells into disease-suppressing natural regulatory T cells, in a β56-67-regulated manner. We compared the tolerogenic and antidiabetogenic properties of CD11c promoter-driven transgenes encoding I-A(b) or a form of I-A(b) carrying residues 56-67 of I-Aβ(g7) (I-A(b-g7)) in wild-type nonobese diabetic (NOD) mice, as well as NOD mice coexpressing a diabetogenic and I-A(g7)-restricted, but MHC-promiscuous T-cell receptor (4.1). Both I-A transgenes protected NOD and 4.1-NOD mice from diabetes. However, whereas I-A(b) induced 4.1-CD4(+) thymocyte deletion and 4.1-CD4(+)Foxp3(+) regulatory T-cell development, I-A(b-g7) promoted 4.1-CD4(+)Foxp3(+) Treg development without inducing clonal deletion. Furthermore, non-T-cell receptor transgenic NOD.CD11cP-I-A(b) and NOD.CD11cP-IA(b-g7) mice both exported regulatory T cells with superior antidiabetogenic properties than wild-type NOD mice. We propose that I-A(b), and possibly other protective MHC class II molecules, afford disease resistance by engaging a naturally occurring constellation of MHC-promiscuous autoreactive T-cell clonotypes, promoting their deviation into autoregulatory T cells.

Autoantigen recognition is required for recruitment of IGRP(206-214)-autoreactive CD8+ T cells but is dispensable for tolerance

The progression of autoimmune responses is associated with an avidity maturation process driven by preferential expansion of high avidity clonotypes at the expense of their low avidity counterparts. Central and peripheral tolerance hinder the contribution of high-avidity clonotypes targeting residues 206-214 of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP(206-214)) during the earliest stages of autoimmune diabetes. In this study, we probe the molecular determinants and biochemical consequences of IGRP(206-214)/K(d) recognition by high-, intermediate-, and low-avidity autoreactive CD8+ T cells, and we investigate the effects of genetic IGRP(206-214) silencing on their developmental biology. We find that differences in avidity for IGRP(206-214)/K(d) map to CDR1α and are associated with quantitative differences in CD3ε proline-rich sequence exposure and Nck recruitment. Unexpectedly, we find that tolerance of high-avidity CD8+ T cells, unlike their activation and recruitment into the pancreas, is dissociated from recognition of IGRP(206-214), particularly in adult mice. This finding challenges the view that tolerance of pathogenic autoreactive T cells is invariably triggered by recognition of the peptide-MHC complex that drives their activation in the periphery, indicating the existence of mechanisms of tolerance that are capable of sensing the avidity, hence pathogenicity of autoreactive T cells without the need to rely on local autoantigen availability.

The IL-2 diphtheria toxin fusion protein denileukin diftitox modulates the onset of diabetes in female nonobese diabetic animals in a time-dependent manner and breaks tolerance in male nonobese diabetic animals

Denileukin diftitox, also known as DAB(389)IL-2 or Ontak, is a fusion protein toxin consisting of the full-length sequence of the IL-2 protein and as toxophore the truncated diphtheria toxin. As a consequence, it delivers the toxic agent to CD25-bearing cells, whereby CD25 represents the high-affinity α-subunit of the IL-2 receptor. Initially it was developed for the treatment of patients with cutaneous T cell lymphoma. Meanwhile, denileukin diftitox is also used as an adjuvant in other tumor therapies and neoplastic disorders. In this study, to our knowledge we report for the first time that denileukin diftitox has also dramatic effects regarding the pathology of type 1 diabetes using the NOD mouse model. Repeated injections of denileukin diftitox into female NOD mice at 12 wk of age led to a clear acceleration of disease onset, whereas injection at 7 wk of age did not. Using male NOD mice, which are much less susceptible to diabetes, we demonstrate that the injection of denileukin diftitox leads to a dramatic development of type 1 diabetes within days after injection, thereby obviously breaking pre-existing tolerance mechanisms. This is accompanied by an increased IFN-γ production of autoreactive splenic cells and a decreased presence of regulatory CD4(+)CD25(+)Foxp3(+) T cells. In contrast, transfer of CD4(+)CD25(+)Foxp3(+) T cells could correct the defect after denileukin diftitox treatment. Furthermore, whereas IFN-γ production was increased in the pancreata of treated animals, insulin expression was strongly reduced. These finding should be considered when denileukin diftitox is used for the treatment of patients suffering from tumors and/or autoimmune disorders.

Beta-cell autoimmunity

Beta cell destruction in autoimmune diabetes is accompanied by the presence of autoantibodies and autoreactive T cells against beta cell antigens. Autoantibodies to insulin are predictive of future diabetes in man and in the non-obese diabetic mouse model. Furthermore, the detection of peripheral autoreactive CD8(+) T cells in this mouse model is indicative of beta cell killing and correlates with the development of diabetes. We describe two protocols that are helpful for the detection of beta-cell autoimmunity in mice. The first protocol describes the detection of insulin-specific autoantibodies using a radio-binding assay. The other is a general CD8(+) T cell ELISpot protocol for the detection of peptide-specific responses of CD8(+) T cells from secondary lymphoid organs or pancreatic islets.

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.

Role of the mitochondria in immune-mediated apoptotic death of the human pancreatic β cell line βLox5

Mitochondria are indispensable in the life and death of many types of eukaryotic cells. In pancreatic beta cells, mitochondria play an essential role in the secretion of insulin, a hormone that regulates blood glucose levels. Unregulated blood glucose is a hallmark symptom of diabetes. The onset of Type 1 diabetes is preceded by autoimmune-mediated destruction of beta cells. However, the exact role of mitochondria has not been assessed in beta cell death. In this study, we examine the role of mitochondria in both Fas- and proinflammatory cytokine-mediated destruction of the human beta cell line, βLox5. IFNγ primed βLox5 cells for apoptosis by elevating cell surface Fas. Consequently, βLox5 cells were killed by caspase-dependent apoptosis by agonistic activation of Fas, but only after priming with IFNγ. This beta cell line undergoes both apoptotic and necrotic cell death after incubation with the combination of the proinflammatory cytokines IFNγ and TNFα. Additionally, both caspase-dependent and -independent mechanisms that require proper mitochondrial function are involved. Mitochondrial contributions to βLox5 cell death were analyzed using mitochondrial DNA (mtDNA) depleted βLox5 cells, or βLox5 ρ⁰ cells. βLox5 ρ⁰ cells are not sensitive to IFNγ and TNFα killing, indicating a direct role for the mitochondria in cytokine-induced cell death of the parental cell line. However, βLox5 ρ⁰ cells are susceptible to Fas killing, implicating caspase-dependent extrinsic apoptotic death is the mechanism by which these human beta cells die after Fas ligation. These data support the hypothesis that immune mediators kill βLox5 cells by both mitochondrial-dependent intrinsic and caspase-dependent extrinsic pathways.

Toll-like receptor 7 stimulation promotes autoimmune diabetes in the NOD mouse

AIMS/HYPOTHESIS

The role of Toll-like receptor 7 (TLR7), a sensor of viral and self RNA, in promoting autoimmune diabetes remains unclear. Our goal was to determine the effect of TLR7 stimulation on the priming and activation of diabetogenic CD8(+) T cells.

METHODS

We explored the effects of CL097 (TLR7/8 agonist) and immunoregulatory sequence 661 (IRS661, TLR7 inhibitor) on bone marrow-derived dendritic cells (BMDCs), diabetogenic CD8(+) T cell function and autoimmune diabetes onset in NOD and 8.3 NOD T cell receptor transgenic mice (8.3 NOD mice).

RESULTS

TLR7 stimulation of NOD BMDCs increased activation and production of proinflammatory cytokines. In vivo administration of CL097 activated T cells and dendritic cells and increased levels of proinflammatory cytokines and type 1/2 IFNs in NOD mice. In vivo antigen-specific cytotoxicity studies revealed enhanced cytotoxicity against islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP, an islet autoantigen) peptide pulsed targets in NOD mice treated with CL097 plus CD40 agonist. This combination treatment accelerated the onset of autoimmune diabetes in 8.3 NOD mice. Likewise, topical treatment of NOD mice with a TLR7 agonist accelerated diabetes onset. Spontaneous disease in 8.3 NOD mice and accelerated disease in CL097+CD40 agonist-treated 8.3 NOD mice were delayed by IRS661 treatment, which is associated with inhibition of the endogenous upregulation of IFN-α levels within the pancreatic lymph nodes.

CONCLUSIONS/INTERPRETATION

TLR7 stimulation accelerates the spontaneous onset of autoimmune diabetes in 8.3 NOD and NOD mice. Conversely, TLR7 inhibition prevents the early events associated with diabetogenesis.

Exposure to IL-15 and IL-21 enables autoreactive CD8 T cells to respond to weak antigens and cause disease in a mouse model of autoimmune diabetes

Autoreactive CD8(+) T lymphocytes play a key role in the pathogenesis of several autoimmune diseases. It is not yet well understood how autoreactive CD8(+) T cells, which express TCRs with low reactivity toward self-Ags, gain the ability to respond to autoantigens to cause disease. Previously, we have shown that prior stimulation of CD8(+) T cells with synergistic combinations of cytokines produced by the innate immune response, such as IL-21 and IL-15, induces Ag-independent proliferation. Such "cytokine-primed" CD8 T cells displayed increased responsiveness to limiting quantities of the cognate Ag. In this paper, we report that prior stimulation with IL-15 and IL-21 also enables CD8(+) T cells to respond to weakly agonistic TCR ligands, resulting in proliferation, cytokine secretion, and cytolytic activity. Using a transgenic mouse model of autoimmune diabetes, we show that cytokine-primed autoreactive CD8(+) T cells induce disease following stimulation by weak TCR ligands, but their diabetogenic potential is dependent on continuous availability of IL-15 in vivo. These findings suggest that inflammatory cytokines could facilitate the triggering of autoreactive CD8(+) T cells by weak autoantigens, and this mechanism may have important implications for autoimmune diseases associated with microbial infections and chronic inflammation.

Induction of pathogenic cytotoxic T lymphocyte tolerance by dendritic cells: a novel therapeutic target

IMPORTANCE OF THE FIELD

Dendritic cells (DCs) have an important role, both direct and indirect, in controlling the expansion and function of T cells. Of the different subsets of T cells, cytotoxic T lymphocytes (CTLs/CD8(+) T cells) have been implicated in the pathogenesis and development of many diseases, including various forms of autoimmunity and transplant rejection. It may therefore be of therapeutic benefit to control the function of CTL in order to modulate disease processes and to ameliorate disease symptoms. Currently, pharmacological approaches have been employed to either directly or indirectly modulate the function of T cells. However, these treatment strategies have many limitations. Many experimental data have suggested that it is possible to alter CTL activity through manipulation of DC.

AREAS COVERED IN THIS REVIEW

Novel strategies that condition DCs to influence disease outcome through manipulation of CTL activity, both directly and indirectly. This includes the modulation of co-stimulation, negative co-stimulation, as well as manipulation of the cytokine milieu during CTL generation. Furthermore, DCs may also impact CTL activity through effects on effector and regulatory cells, along with manipulation of bioenergetic regulation, apoptotic-cell mediated tolerance and through the generation of exosomes. The implications of related interventions in the clinical arena are in turn considered.

WHAT THE READER WILL GAIN

Insight into such indirect methods of controlling CTL activity allows for an understanding of how disease-specific T cells may be regulated, while also sparing other aspects of adaptive immunity for normal physiological function. Such an approach towards the treatment of disease represents an innovative therapeutic target in the clinical arena.

TAKE HOME MESSAGE

There are numerous innovative methods for using DCs to control CTL responses. Manipulation of this interaction is thus an attractive avenue for the treatment of disease, particularly those of immune dysregulation, such as seen in autoimmunity and transplantation. With the number of studies moving into clinical stages constantly increasing, further advances and successes in this area are inevitable.

On how monospecific memory-like autoregulatory CD8+ T cells can blunt diabetogenic autoimmunity: a computational approach

We have recently shown that during progression to autoimmune diabetes in NOD mice, memory autoreactive regulatory CD8(+) T cells arising from low-avidity precursors can be expanded to therapeutic levels using nanoparticles coated with disease-relevant peptide-major histocompatibility complexes (pMHCs). Here we examine the dynamics of memory autoregulatory CD8(+) T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214), a prevalent β cell autoantigen; their high-avidity counterparts (dominant effectors); and all other autoreactive non-islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214)-specific CD8(+) T cell specificities (subdominant effectors) in response to pMHC-coated nanoparticle (pMHC-nanoparticle) therapy. We combine experimental data with mathematical modeling to investigate the clonal competition dynamics of these T cell pools. To mimic the response diversity observed in NOD mice, we simulated many individual mice, using a wide range of parameters, and averaged the results as done experimentally. We find that under certain circumstances, pMHC-nanoparticle-induced expansion of autoregulatory CD8(+) T cells can effectively suppress the expansion of dominant and subdominant effectors simultaneously but, in some few cases, can lead to the substitution (or switching) of one effector population by another. The model supports the idea that disease suppression is based on the elimination of autoantigen-loaded APCs by the expanded autoregulatory CD8(+) T cells. The model also predicts that treatment strategies that operate by selectively inhibiting autoantigen-loaded APCs, such as the pMHC-nanoparticle approach, have the highest promise to blunt polyclonal, multiantigen-specific autoimmune responses in vivo without impairing systemic immunity.

Current approaches to measuring human islet-antigen specific T cell function in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the T cell-mediated destruction of the pancreatic insulin-producing beta cells. Currently there are no widely accepted and standardized assays available to analyse the function of autoreactive T cells involved in T1D. The development of such an assay would greatly aid efforts to understand the pathogenesis of T1D and is also urgently required to guide the development of antigen-based therapies intended to prevent, or cure, T1D. Here we describe some of the assays used currently to detect autoreactive T cells in human blood and review critically their strengths and weaknesses. The challenges and future prospects for the T cell assays are discussed.

The pathogenicity of self-antigen decreases at high levels of autoantigenicity: a computational approach

Recent experimental evidence suggests that antigenic stability facilitates antigen shuttling from target tissue to dendritic cells (DCs), enabling cross-priming of naive T cells. On the other hand, antigenic stability affects the efficiency of peptide-MHC (p-MHC) complex formation, altering a target cell's susceptibility to killing by the resulting CTLs. Using a mathematical model, we show how antigenic stability and p-MHC production efficiency interplay in autoantigenicity and pathogenic potential of target cell proteins in autoimmune disease. We consider protein allocated to both rapidly degraded versus stable functional pools [fractions f, 1 - f], contributing, with relative efficiency eta, to p-MHC presentation on a target cell, as well as to cross-presentation on a DC; we analyze the combined effect of these parameters. Our results suggest that autoantigenicity and pathogenicity (ability to elicit T cell activation versus target cell lysis) are not equivalent and that pathogenicity peaks at low to moderate levels of autoantigenicity.

The long and winding road to understanding and conquering type 1 diabetes

Autoimmune diseases with high population prevalence such as type 1 diabetes (T1D) develop as a result of ill-defined interactions between putative environmental triggers and a constellation of genetic elements scattered throughout the genome. In T1D, these interactions somehow trigger a loss of tolerance to pancreatic beta cells, manifested in the form of a chronic autoimmune response that mobilizes virtually every cell type of the immune system and progressively erodes the host's beta cell mass. The five accompanying review articles focus on key areas of T1D research, ranging from genetics and pathogenesis to prediction and therapy. Here, I attempt to integrate and bring into focus the most salient points of these reviews in the context of other findings, with an emphasis on identifying knowledge gaps and research opportunities.

In situ recognition of autoantigen as an essential gatekeeper in autoimmune CD8+ T cell inflammation

A current paradigm states that non-antigen-specific inflammatory cues attract noncognate, bystander T cell specificities to sites of infection and autoimmune inflammation. Here we show that cues emanating from a tissue undergoing spontaneous autoimmune inflammation cannot recruit naive or activated bystander T cell specificities in the absence of local expression of cognate antigen. We monitored the recruitment of CD8(+) T cells specific for the prevalent diabetogenic epitope islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)(206-214) in gene-targeted nonobese diabetic (NOD) mice expressing a T cell "invisible" IGRP(206-214) sequence. These mice developed islet inflammation and diabetes with normal incidence and kinetics, but their inflammatory lesions could recruit neither naive (endogenous or exogenous) nor ex vivo-activated IGRP(206-214)-reactive CD8(+) T cells. Conversely, IGRP(206-214)-reactive, but not nonautoreactive CD8(+) T cells rapidly homed to and accumulated in the inflamed islets of wild-type NOD mice. Our results indicate that CD8(+) T cell recruitment to a site of autoimmune inflammation results from an active process that is strictly dependent on local display of cognate pMHC and suggest that CD8(+) T cells contained in extralymphoid autoimmune lesions are largely autoreactive.

Toxin-coupled MHC class I tetramers can specifically ablate autoreactive CD8+ T cells and delay diabetes in nonobese diabetic mice

There is compelling evidence that self-reactive CD8(+) T cells are a major factor in development and progression of type 1 diabetes in animals and humans. Hence, great effort has been expended to define the specificity of autoimmune CD8(+) T cells and to alter their responses. Much work has focused on tolerization of T cells using proteins or peptides. A weakness in this approach is that residual autoreactive T cells may be activated and exacerbate disease. In this report, we use a novel approach, toxin-coupled MHC class I tetramers. Used for some time to identify Ag-specific cells, in this study, we use that same property to delete the Ag-specific cells. We show that saporin-coupled tetramers can delete islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-reactive T cells in vitro and in vivo. Sequence analysis of TCRbeta-chains of IGRP(+) cells reveals the repertoire complexity in the islets is markedly decreased as NOD mice age and significantly altered in toxic tetramer-treated NOD mice. Further tetramer(+) T cells in the islets are almost completely deleted, and, surprisingly, loss of tetramer(+) T cells in the islets is long lasting. Finally, we show deletion at 8 wk of age of IGRP(+) CD8(+) T cells, but not dystophia myotonica kinase- or insulin B-reactive cells, significantly delays diabetes in NOD mice.

Gut barrier disruption by an enteric bacterial pathogen accelerates insulitis in NOD mice

AIMS/HYPOTHESIS

Increased exposure to enteric microbes as a result of intestinal barrier disruption is thought to contribute to the development of several intestinal inflammatory diseases; however, it less clear whether such exposure modulates the development of extra-intestinal inflammatory and autoimmune diseases. The goal of this study was to examine the potential role of pathogenic enteric microbes and intestinal barrier dysfunction in the pathogenesis of type 1 diabetes.

METHODS

Using NOD mice, we assessed: (1) intrinsic barrier function in mice at different ages by measuring serum levels of FITC-labelled dextran; and (2) the impact on insulitis development of infection by strains of an enteric bacterial pathogen (Citrobacter rodentium) either capable (wild-type) or incapable (lacking Escherichia coli secreted protein F virulence factor owing to deletion of the gene [DeltaespF]) of causing intestinal epithelial barrier disruption.

RESULTS

Here we demonstrate that prediabetic (12-week-old) NOD mice display increased intestinal permeability compared with non-obese diabetes-resistant and C57BL/6 mice. We also found that young (4-week-old) NOD mice infected with wild-type C. rodentium exhibited accelerated development of insulitis in concert with infection-induced barrier disruption. In contrast, insulitis development was not altered in NOD mice infected with the non-barrier-disrupting DeltaespF strain. Moreover, C. rodentium-infected NOD mice demonstrated increased activation and proliferation of pancreatic-draining lymph node T cells, including diabetogenic CD8(+) T cells, compared with uninfected NOD mice.

CONCLUSIONS/INTERPRETATION

This is the first demonstration that a loss of intestinal barrier integrity caused by an enteric bacterial pathogen results in the activation of diabetogenic CD8(+) T cells and modulates insulitis.

Idd9.1 locus controls the suppressive activity of FoxP3+CD4+CD25+ regulatory T-cells

OBJECTIVE

The approximately 45-cM insulin-dependent diabetes 9 (Idd9) region on mouse chromosome 4 harbors several different type 1 diabetes-associated loci. Nonobese diabetic (NOD) mice congenic for the Idd9 region of C57BL/10 (B10) mice, carrying antidiabetogenic alleles in three different Idd9 subregions (Idd9.1, Idd9.2, and Idd9.3), are strongly resistant to type 1 diabetes. However, the mechanisms remain unclear. This study aimed to define mechanisms underlying the type 1 diabetes resistance afforded by B10 Idd9.1, Idd9.2, and/or Idd9.3.

RESEARCH DESIGN AND METHODS

We used a reductionist approach that involves comparing the fate of a type 1 diabetes-relevant autoreactive CD8(+) T-cell population, specific for residues 206-214 of islet-specific glucose 6 phosphatase catalytic subunit-related protein (IGRP(206-214)), in noncongenic versus B10 Idd9-congenic (Idd9.1 + Idd9.2 + Idd9.3, Idd9.2 + Idd9.3, Idd9.1, Idd9.2, and Idd9.3) T-cell receptor (TCR)-transgenic (8.3) NOD mice.

RESULTS

Most of the protective effect of Idd9 against 8.3-CD8(+) T-cell-enhanced type 1 diabetes was mediated by Idd9.1. Although Idd9.2 and Idd9.3 afforded some protection, the effects were small and did not enhance the greater protective effect of Idd9.1. B10 Idd9.1 afforded type 1 diabetes resistance without impairing the developmental biology or intrinsic diabetogenic potential of autoreactive CD8(+) T-cells. Studies in T- and B-cell-deficient 8.3-NOD.B10 Idd9.1 mice revealed that this antidiabetogenic effect was mediated by endogenous, nontransgenic T-cells in a B-cell-independent manner. Consistent with this, B10 Idd9.1 increased the suppressive function and antidiabetogenic activity of the FoxP3(+)CD4(+)CD25(+) T-cell subset in both TCR-transgenic and nontransgenic mice.

CONCLUSIONS

A gene(s) within Idd9.1 regulates the development and function of FoxP3(+)CD4(+)CD25(+) regulatory T-cells and, in turn, the activation of CD8(+) effector T-cells in the pancreatic draining lymph nodes, without affecting their development or intrinsic diabetogenic potential.

Activation of insulin-reactive CD8 T-cells for development of autoimmune diabetes

OBJECTIVE

We have previously reported a highly diabetogenic CD8 T-cell clone, G9C8, in the nonobese diabetic (NOD) mouse, specific to low-avidity insulin peptide B15-23, and cells responsive to this antigen are among the earliest islet infiltrates. We aimed to study the selection, activation, and development of the diabetogenic capacity of these insulin-reactive T-cells.

RESEARCH DESIGN AND METHODS

We generated a T-cell receptor (TCR) transgenic mouse expressing the cloned TCR Valpha18/Vbeta6 receptor of the G9C8 insulin-reactive CD8 T-cell clone. The mice were crossed to TCRCalpha-/- mice so that the majority of the T-cells expressed the clonotypic TCR, and the phenotype and function of the cells was investigated.

RESULTS

There was good selection of CD8 T-cells with a predominance of CD8 single-positive thymocytes, in spite of thymic insulin expression. Peripheral lymph node T-cells had a naïve phenotype (CD44lo, CD62Lhi) and proliferated to insulin B15-23 peptide and to insulin. These cells produced interferon-gamma and tumor necrosis factor-alpha in response to insulin peptide and were cytotoxic to insulin peptide-coated targets. In vivo, the TCR transgenic mice developed insulitis but not spontaneous diabetes. However, the mice developed diabetes on immunization, and the activated transgenic T-cells were able to transfer diabetes to immunodeficient NOD.scid mice.

CONCLUSIONS

Autoimmune CD8 T-cells responding to a low-affinity insulin B-chain peptide escape from thymic negative selection and require activation in vivo to cause diabetes.