Where CD4+CD25+ T reg cells impinge on autoimmune diabetes

The potential therapeutic role of IL-35 in pathophysiological processes in type 1 diabetes mellitus

A chronic autoimmune condition known as type 1 diabetes mellitus (T1DM) has characteristics marked by a gradual immune-mediated deterioration of the β-cells that produce insulin and causes overt hyperglycemia. it affects more than 1.2 million kids and teenagers (0-19 years old). In both, the initiation and elimination phases of T1DM, cytokine-mediated immunity is crucial in controlling inflammation. T regulatory (Treg) cells, a crucial anti-inflammatory CD4+ T cell subset, secretes interleukin-35 (IL-35). The IL-35 has immunomodulatory properties by inhibiting pro-inflammatory cells and cytokines, increasing the secretion of interleukin-10 (IL-10) as well as transforming Growth Factor- β (TGF-β), along with stimulating the Treg and B regulatory (Breg) cells. IL-35, it is a possible target for cutting-edge therapies for cancers, inflammatory, infectious, and autoimmune diseases, including TIDM. Unanswered questions surround IL-35's function in T1DM. Increasing data suggests Treg cells play a crucial role in avoiding autoimmune T1DM. Throughout this review, we will explain the biological impacts of IL-35 and highlight the most recently progresses in the roles of IL-35 in treatment of T1DM; the knowledge gathered from these findings might lead to the development of new T1DM treatments. This review demonstrates the potential of IL-35 as an effective autoimmune diabetes inhibitor and points to its potential therapeutic value in T1DM clinical trials.

Selective ablation of thymic and peripheral Foxp3+ regulatory T cell development

Foxp3+ regulatory T (Treg) cells of thymic (tTreg) and peripheral (pTreg) developmental origin are thought to synergistically act to ensure immune homeostasis, with self-reactive tTreg cells primarily constraining autoimmune responses. Here we exploited a Foxp3-dependent reporter with thymus-specific GFP/Cre activity to selectively ablate either tTreg (ΔtTreg) or pTreg (ΔpTreg) cell development, while sparing the respective sister populations. We found that, in contrast to the tTreg cell behavior in ΔpTreg mice, pTreg cells acquired a highly activated suppressor phenotype and replenished the Treg cell pool of ΔtTreg mice on a non-autoimmune C57BL/6 background. Despite the absence of tTreg cells, pTreg cells prevented early mortality and fatal autoimmunity commonly observed in Foxp3-deficient models of complete Treg cell deficiency, and largely maintained immune tolerance even as the ΔtTreg mice aged. However, only two generations of backcrossing to the autoimmune-prone non-obese diabetic (NOD) background were sufficient to cause severe disease lethality associated with different, partially overlapping patterns of organ-specific autoimmunity. This included a particularly severe form of autoimmune diabetes characterized by an early onset and abrogation of the sex bias usually observed in the NOD mouse model of human type 1 diabetes. Genetic association studies further allowed us to define a small set of autoimmune risk loci sufficient to promote β cell autoimmunity, including genes known to impinge on Treg cell biology. Overall, these studies show an unexpectedly high functional adaptability of pTreg cells, emphasizing their important role as mediators of bystander effects to ensure self-tolerance.

The beta cell-immune cell interface in type 1 diabetes (T1D)

BACKGROUND

T1D is an autoimmune disease in which pancreatic islets of Langerhans are infiltrated by immune cells resulting in the specific destruction of insulin-producing islet beta cells. Our understanding of the factors leading to islet infiltration and the interplay of the immune cells with target beta cells is incomplete, especially in human disease. While murine models of T1D have provided crucial information for both beta cell and autoimmune cell function, the translation of successful therapies in the murine model to human disease has been a challenge.

SCOPE OF REVIEW

Here, we discuss current state of the art and consider knowledge gaps concerning the interface of the islet beta cell with immune infiltrates, with a focus on T cells. We discuss pancreatic and immune cell phenotypes and their impact on cell function in health and disease, which we deem important to investigate further to attain a more comprehensive understanding of human T1D disease etiology.

MAJOR CONCLUSIONS

The last years have seen accelerated development of approaches that allow comprehensive study of human T1D. Critically, recent studies have contributed to our revised understanding that the pancreatic beta cell assumes an active role, rather than a passive position, during autoimmune disease progression. The T cell-beta cell interface is a critical axis that dictates beta cell fate and shapes autoimmune responses. This includes the state of the beta cell after processing internal and external cues (e.g., stress, inflammation, genetic risk) that that contributes to the breaking of tolerance by hyperexpression of human leukocyte antigen (HLA) class I with presentation of native and neoepitopes and secretion of chemotactic factors to attract immune cells. We anticipate that emerging insights about the molecular and cellular aspects of disease initiation and progression processes will catalyze the development of novel and innovative intervention points to provide additional therapies to individuals affected by T1D.

Pancreatic draining lymph nodes (PLNs) serve as a pathogenic hub contributing to the development of type 1 diabetes

Type 1 diabetes (T1D) is a chronic, progressive autoinflammatory disorder resulting from the breakdown of self-tolerance and unrestrained β cell-reactive immune response. Activation of immune cells is initiated in islet and amplified in lymphoid tissues, especially those pancreatic draining lymph nodes (PLNs). The knowledge of PLNs as the hub of aberrant immune response is continuously being replenished and renewed. Here we provide a PLN-centered view of T1D pathogenesis and emphasize that PLNs integrate signal inputs from the pancreas, gut, viral infection or peripheral circulation, undergo immune remodeling within the local microenvironment and export effector cell components into pancreas to affect T1D progression. In accordance, we suggest that T1D intervention can be implemented by three major ways: cutting off the signal inputs into PLNs (reduce inflammatory β cell damage, enhance gut integrity and control pathogenic viral infections), modulating the immune activation status of PLNs and blocking the outputs of PLNs towards pancreatic islets. Given the dynamic and complex nature of T1D etiology, the corresponding intervention strategy is thus required to be comprehensive to ensure optimal therapeutic efficacy.

Splicing factor SRSF1 controls autoimmune-related molecular pathways in regulatory T cells distinct from FoxP3

Regulatory T cells (Tregs) are vital for maintaining immune self-tolerance, and their impaired function leads to autoimmune disease. Mutations in FoxP3, the master transcriptional regulator of Tregs, leads to immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome in humans and the early lethal "scurfy" phenotype with multi-organ autoimmune disease in mice. We recently identified serine/arginine-rich splicing factor 1 (SRSF1) as an indispensable regulator of Treg homeostasis and function. Intriguingly, Treg-conditional SRSF1-deficient mice exhibit early lethal systemic autoimmunity with multi-organ inflammation reminiscent of the scurfy mice. Importantly, SRSF1 is decreased in T cells from patients with the autoimmune disease systemic lupus erythematosus (SLE), and low SRSF1 levels inversely correlate with disease severity. Given that the Treg-specific deficiency of SRSF1 causes similarly profound autoimmune disease outcomes in mice as the deficiency/mutation in FoxP3, we aimed to evaluate the genes and molecular pathways controlled by these two indispensable regulatory proteins. We performed comparative bioinformatic analyses of transcriptomic profiles of Tregs from Srsf1-knockout mice and two Foxp3 mutant mice--the FoxP3-deficient ΔFoxp3 and the Foxp3 M370I mutant mice. We identified 132 differentially expressed genes (DEGs) unique to Srsf1-ko Tregs, 503 DEGs unique to Foxp3 M370I Tregs, and 1367 DEGs unique to ΔFoxp3 Tregs. Gene set enrichment and pathway analysis of DEGs unique to Srsf1-ko Tregs indicate that SRSF1 controls cytokine and immune response pathways. Conversely, FoxP3 controls pathways involved in DNA replication and cell cycle. Besides the distinct gene signatures, we identified only 30 shared genes between all three Treg mutants, mostly contributing to cytokine and immune defense pathways. Prominent genes included the chemokines CXCR6 and CCL1 and the checkpoint inhibitors FASLG and PDCD1. Thus, we demonstrate that SRSF1 and FoxP3 control common and distinct molecular pathways implicated in autoimmunity. Our analyses suggest that SRSF1 controls crucial immune functions in Tregs contributing to immune tolerance, and perturbations in its levels lead to systemic autoimmunity via mechanisms that are largely distinct from FoxP3.

The long and winding road: From mouse linkage studies to a novel human therapeutic pathway in type 1 diabetes

Autoimmunity involves a loss of immune tolerance to self-proteins due to a combination of genetic susceptibility and environmental provocation, which generates autoreactive T and B cells. Genetic susceptibility affects lymphocyte autoreactivity at the level of central tolerance (e.g., defective, or incomplete MHC-mediated negative selection of self-reactive T cells) and peripheral tolerance (e.g., failure of mechanisms to control circulating self-reactive T cells). T regulatory cell (Treg) mediated suppression is essential for controlling peripheral autoreactive T cells. Understanding the genetic control of Treg development and function and Treg interaction with T effector and other immune cells is thus a key goal of autoimmunity research. Herein, we will review immunogenetic control of tolerance in one of the classic models of autoimmunity, the non-obese diabetic (NOD) mouse model of autoimmune Type 1 diabetes (T1D). We review the long (and still evolving) elucidation of how one susceptibility gene, Cd137, (identified originally via linkage studies) affects both the immune response and its regulation in a highly complex fashion. The CD137 (present in both membrane and soluble forms) and the CD137 ligand (CD137L) both signal into a variety of immune cells (bi-directional signaling). The overall outcome of these multitudinous effects (either tolerance or autoimmunity) depends upon the balance between the regulatory signals (predominantly mediated by soluble CD137 via the CD137L pathway) and the effector signals (mediated by both membrane-bound CD137 and CD137L). This immune balance/homeostasis can be decisively affected by genetic (susceptibility vs. resistant alleles) and environmental factors (stimulation of soluble CD137 production). The discovery of the homeostatic immune effect of soluble CD137 on the CD137-CD137L system makes it a promising candidate for immunotherapy to restore tolerance in autoimmune diseases.

CD103 integrin identifies a high IL-10-producing FoxP3+ regulatory T-cell population suppressing allergic airway inflammation

BACKGROUND

Although FoxP3⁺ regulatory T (Treg) cells constitute a highly heterogeneous population, with different regulatory potential depending on the disease context, distinct subsets or phenotypes remain poorly defined. This hampers the development of immunotherapy for allergic and autoimmune disorders. The present study aimed at characterizing distinct FoxP3⁺ Treg subpopulations involved in the suppression of Th2-mediated allergic inflammation in the lung.

METHODS

We used an established mouse model of allergic airway disease based on ovalbumin sensitization and challenge to analyze FoxP3⁺ Tregs during the induction and resolution of inflammation, and identify markers that distinguish their most suppressive phenotypes. We also developed a new knock-in mouse model (Foxp3^cre Cd103^dtr ) enabling the specific ablation of CD103⁺ FoxP3⁺ Tregs for functional studies.

RESULTS

We found that during resolution of allergic airway inflammation in mice >50% of FoxP3⁺ Treg cells expressed the integrin CD103 which marks FoxP3⁺ Treg cells of high IL-10 production, increased expression of immunoregulatory molecules such as KLRG1, ICOS and CD127, and enhanced suppressive capacity for Th2-mediated inflammatory responses. CD103⁺ FoxP3⁺ Tregs were essential for keeping allergic inflammation under control as their specific depletion in Foxp3^cre Cd103^dtr mice lead to severe alveocapillary damage, eosinophilic pneumonia, and markedly reduced lifespan of the animals. Conversely, adoptive transfer of CD103⁺ FoxP3⁺ Tregs effectively treated disease, attenuating Th2 responses and allergic inflammation in an IL-10-dependent manner.

CONCLUSIONS

Our study identifies a novel regulatory T-cell population, defined by CD103 expression, programmed to prevent exuberant type 2 inflammation and keep homeostasis in the respiratory tract under control. This has important therapeutic implications.

Splicing factor SRSF1 controls distinct molecular programs in regulatory and effector T cells implicated in systemic autoimmune disease

Systemic autoimmune diseases are characterized by hyperactive effector T cells (Teffs), aberrant cytokines and chemokines, and dysfunctional regulatory T cells (Tregs). We previously uncovered new roles for serine/arginine-rich splicing factor 1 (SRSF1) in the control of genes involved in T cell signaling and cytokine production in human T cells. SRSF1 levels are decreased in T cells from patients with systemic lupus erythematosus (SLE), and low levels correlate with severe disease. Moreover, T cell-conditional Srsf1-deficient mice recapitulate the autoimmune phenotype, exhibiting CD4 T cell hyperactivity, dysfunctional Tregs, systemic autoimmunity, and tissue inflammation. However, the role of SRSF1 in controlling molecular programs in Teffs and Tregs and how these pathways are implicated in autoimmunity is not known. Here, by comparative bioinformatics analysis, we demonstrate that SRSF1 controls largely distinct gene programs in Tregs and Teffs in vivo. SRSF1 regulates 189 differentially expressed genes (DEGs) unique to Tregs, 582 DEGs unique to Teffs, and 29 DEGs shared between both. Shared genes included IL-17A, IL-17F, CSF1, CXCL10, and CXCR4, and were highly enriched for inflammatory response and cytokine-cytokine receptor interaction pathways. SRSF1 controls distinct pathways in Tregs, which include chemokine signaling and immune cell differentiation, compared with pathways in Teffs, which include cytokine production, T cell homeostasis, and activation. We identified putative mRNA binding targets of SRSF1 which include CSF1, CXCL10, and IL-17F. Finally, comparisons with transcriptomics profiles from lupus-prone MRL/lpr mice reveal that SRSF1 controls genes and pathways implicated in autoimmune disease. The target genes of SRSF1 and putative binding targets we discovered, have known roles in systemic autoimmunity. Our findings suggest that SRSF1 controls distinct molecular pathways in Tregs and Teffs and aberrant SRSF1 levels may contribute to their dysfunction and immunopathogenesis of systemic autoimmune disease.

Tetrahedral Framework Nucleic Acids Reverse New-Onset Type 1 Diabetes

Type 1 diabetes (T1D) is caused by breakdowns of central and peripheral immune tolerance and destructions of insulin-producing β-cells. Conventional insulin injection cannot cure the disease. Regulatory immune cells, including regulatory T-cells (Tregs) and regulatory B-cells (Bregs), play critical roles in immune tolerance. Inducing regulatory immune cells to halt the progress of T1D and restore immune tolerance is the promising approach in T1D immunotherapy. Here, tetrahedral framework nucleic acids (tFNAs) were utilized to treat T1D in non-obese diabetic (NOD) mice. 250 nM tFNA treatment was adopted in the experiment to reverse hyperglycemia and protect insulin-secreting β-cells in diabetic NOD mice. In addition, 250 nM tFNA treatment could induce Tregs and Bregs and suppress helper T (Th)-cells in the pancreas. In the pancreas, cytokines, as a significant signal during CD4⁺ T-cell differentiation, directly direct the differentiation programs. Apart from cytokines directing the differentiation of T-cells, the signal transducer and activator of transcription (STAT) signal is strongly associated with T-cell differentiation and T1D progression. We demonstrated tFNA treatment inducing regulatory immune cells probably by increasing TGF-β levels and the STAT signal. To sum up, 250 nM tFNA treatment could protect the diabetic NOD mice from hyperglycemia and preserve the functions of β-cells by restoring peripheral immune tolerance. The possible mechanism of inducing immune tolerance was related to the STAT signal and cytokine changes in the pancreas. Moreover, immunoregulation capabilities of tFNAs were demonstrated in the experiment, which set the foundation of tFNAs participating in further antigen-specific immunotherapies.

Lymph Node Stromal Cell-Intrinsic MHC Class II Expression Promotes MHC Class I-Restricted CD8 T Cell Lineage Conversion to Regulatory CD4 T Cells

MHC class I (MHC-I)-restricted CD4⁺ T cells have long been discovered in the natural repertoire of healthy humans as well as patients with autoimmune diseases or cancer, but the exact origin of these cells remains to be fully characterized. In mouse models, mature peripheral CD8⁺ T cells have the potential to convert to CD4⁺ T cells in the mesenteric lymph nodes. This conversion can produce a unique population of MHC-I-restricted CD4⁺ T cells including Foxp3⁺ regulatory T cells termed MHC-I-restricted CD4⁺Foxp3⁺ T (CI-T_reg) cells. In this study we examined the cellular and molecular elements that promote CD8-to-CD4 lineage conversion and the development of CI-T_reg cells in mice. Using adoptive transfer and bone marrow chimera experiments, we found that the differentiation of CI-T_reg cells was driven by lymph node stromal cell (LNSC)-intrinsic MHC-II expression as opposed to transcytosis of MHC-II from bone marrow-derived APCs. The lineage conversion was accompanied by Runx3 versus ThPOK transcriptional switch. This finding of a new role for LNSCs in vivo led us to develop an efficient tissue culture method using LNSCs to generate and expand CI-T_reg cells in vitro. CI-T_reg cells expanded in vitro with LNSCs effectively suppressed inflammatory tissue damage caused by pathogenic CD4⁺ T cells in mouse models of colitis. This study identified a novel role of MHC-II expressed by LNSCs in immune regulation and the potential utilization of LNSCs to generate novel subsets of immune regulatory cells for therapeutic applications.

Transient Depletion of Foxp3+ Regulatory T Cells Selectively Promotes Aggressive β Cell Autoimmunity in Genetically Susceptible DEREG Mice

Type 1 diabetes (T1D) represents a hallmark of the fatal multiorgan autoimmune syndrome affecting humans with abrogated Foxp3⁺ regulatory T (Treg) cell function due to Foxp3 gene mutations, but whether the loss of Foxp3⁺ Treg cell activity is indeed sufficient to promote β cell autoimmunity requires further scrutiny. As opposed to human Treg cell deficiency, β cell autoimmunity has not been observed in non-autoimmune-prone mice with constitutive Foxp3 deficiency or after diphtheria toxin receptor (DTR)-mediated ablation of Foxp3⁺ Treg cells. In the spontaneous nonobese diabetic (NOD) mouse model of T1D, constitutive Foxp3 deficiency did not result in invasive insulitis and hyperglycemia, and previous studies on Foxp3⁺ Treg cell ablation focused on Foxp3^DTR NOD mice, in which expression of a transgenic BDC2.5 T cell receptor (TCR) restricted the CD4⁺ TCR repertoire to a single diabetogenic specificity. Here we revisited the effect of acute Foxp3⁺ Treg cell ablation on β cell autoimmunity in NOD mice in the context of a polyclonal TCR repertoire. For this, we took advantage of the well-established DTR/GFP transgene of DEREG mice, which allows for specific ablation of Foxp3⁺ Treg cells without promoting catastrophic autoimmune diseases. We show that the transient loss of Foxp3⁺ Treg cells in prediabetic NOD.DEREG mice is sufficient to precipitate severe insulitis and persistent hyperglycemia within 5 days after DT administration. Importantly, DT-treated NOD.DEREG mice preserved many clinical features of spontaneous diabetes progression in the NOD model, including a prominent role of diabetogenic CD8⁺ T cells in terminal β cell destruction. Despite the severity of destructive β cell autoimmunity, anti-CD3 mAb therapy of DT-treated mice interfered with the progression to overt diabetes, indicating that the novel NOD.DEREG model can be exploited for preclinical studies on T1D under experimental conditions of synchronized, advanced β cell autoimmunity. Overall, our studies highlight the continuous requirement of Foxp3⁺ Treg cell activity for the control of genetically pre-installed autoimmune diabetes.

The Role of Programmed Death-1 in Type 1 Diabetes

PURPOSE OF REVIEW

Programmed death-1 (PD-1) is an inhibitory receptor that controls T and B cell proliferation and function through interacting with its ligand PD-L1 or PD-L2. PD-1/PD-L1 blockade reboots anti-tumor immunity and is currently used to treat > 15 different types of cancer. However, the response rate is not at 100% and some patients relapse. Importantly, up to 37% of patients treated with PD-1/PD-L1 blocking antibodies develop immune-related adverse events, including overt autoimmunity, such as type 1 diabetes (T1D). Herein, we discuss the role of PD-1, PD-L1, and PD-L2 signaling in pre-clinical models of T1D, including recent work from our laboratory.

RECENT FINDINGS

We highlight ongoing efforts to harness PD-1/PD-L1 signaling and treat autoimmunity. We also evaluate studies aimed at defining biomarkers that could reliably predict the development of immune-related adverse events after clinical PD-1/PD-L1 blockade. With increasing use of PD-1 blockade in the clinic, onset of autoimmunity is a growing health concern. In this review, we discuss what is known about the role of PD-1 pathway signaling in T1D and comment on ongoing efforts to identify patients at risk of T1D development after PD-1 pathway blockade.

T Cell Abnormalities in the Pathogenesis of Systemic Lupus Erythematosus: an Update

PURPOSE OF REVIEW

Systemic lupus erythematosus is a complex disease with broad spectrum of clinical manifestations. In addition to abnormal B cell responsive leading to autoantibody production, various T cells also play different roles in promoting systemic autoimmunity and end organ damage. We aim to provide a review on recent developments in how abnormalities in different T cells subsets contribute to systemic lupus erythematosus pathogenesis and how they inform the consideration of new promising therapeutics.

RECENT FINDINGS

Distinct subsets of T cells known as T follicular helper cells enable the production of pathogenic autoantibodies. Detailed understanding of the B cell helping T cell subsets should improve the performance of clinical trials targeting the cognate T:B cell interaction. CD8⁺ T cells play a role in peripheral tolerance and reversal of its exhausted phenotype could potentially alleviate both systemic autoimmunity and the risk of infection. Research on the abnormal lupus T cell signaling also leads to putative therapeutic targets able to restore interleukin-2 production and suppress the production of the pathogenic IL-17 cytokine. Recently, several studies have focused on dissecting T cell populations located in the damaged organs, aiming to target the pathogenic processes specific to each organ. Numerous T cell subsets play distinct roles in SLE pathogenesis and recent research in understanding abnormal signaling pathways, cellular metabolism, and environmental cues pave the way for the development of novel therapeutics.

Negative regulation of FOXP3 expression by c-Rel O-GlcNAcylation

O-GlcNAcylation is a reversible post-translational protein modification that regulates fundamental cellular processes including immune responses and autoimmunity. Previously, we showed that hyperglycemia increases O-GlcNAcylation of the transcription factor, nuclear factor kappaB c-Rel at serine residue 350 and enhances the transcription of the c-Rel-dependent proautoimmune cytokines interleukin-2, interferon gamma and granulocyte macrophage colony stimulating factor in T cells. c-Rel also plays a critical role in the transcriptional regulation of forkhead box P3 (FOXP3)-the master transcription factor that governs development and function of Treg cells. Here we show that the regulatory effect of c-Rel O-GlcNAcylation is gene-dependent, and in contrast to its role in enhancing the expression of proautoimmune cytokines, it suppresses the expression of FOXP3. Hyperglycemia-induced O-GlcNAcylation-dependent suppression of FOXP3 expression was found in vivo in two mouse models of autoimmune diabetes; streptozotocin-induced diabetes and spontaneous diabetes in nonobese diabetic mice. Mechanistically, we show that both hyperglycemia-induced and chemically enhanced cellular O-GlcNAcylation decreases c-Rel binding at the FOXP3 promoter and negatively regulates FOXP3 expression. Mutation of the O-GlcNAcylation site in c-Rel, (serine 350 to alanine), augments T cell receptor-induced FOXP3 expression and resists the O-GlcNAcylation-dependent repression of FOXP3 expression. This study reveals c-Rel S350 O-GlcNAcylation as a novel molecular mechanism inversely regulating immunosuppressive FOXP3 expression and proautoimmune gene expression in autoimmune diabetes with potential therapeutic implications.

Amelioration of Autoimmune Diabetes of NOD Mice by Immunomodulating Probiotics

Type 1 autoimmune diabetes is an autoimmune disease characterized by specific destruction of pancreatic β-cells producing insulin. Recent studies have shown that gut microbiota and immunity are closely linked to systemic immunity, affecting the balance between pro-inflammatory and regulatory immune responses. Altered gut microbiota may be causally related to the development of immune-mediated diseases, and probiotics have been suggested to have modulatory effects on inflammatory diseases and immune disorders. We studied whether a probiotic combination that has immunomodulatory effects on several inflammatory diseases can reduce the incidence of diabetes in non-obese diabetic (NOD) mice, a classical animal model of human T1D. When Immune Regulation and Tolerance 5 (IRT5), a probiotic combination comprising Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus reuteri, Bifidobacterium bifidium, and Streptococcus thermophiles, was administered 6 times a week for 36 weeks to NOD mice, beginning at 4 weeks of age, the incidence of diabetes was significantly reduced. Insulitis score was also significantly reduced, and β-cell mass was conversely increased by IRT5 administration. IRT5 administration significantly reduced gut permeability in NOD mice. The proportion of total regulatory T cells was not changed by IRT5 administration; however, the proportion of CCR9⁺ regulatory T (Treg) cells expressing gut-homing receptor was significantly increased in pancreatic lymph nodes (PLNs) and lamina propria of the small intestine (SI-LP). Type 1 T helper (Th1) skewing was reduced in PLNs by IRT5 administration. IRT5 could be a candidate for an effective probiotic combination, which can be safely administered to inhibit or prevent type 1 diabetes (T1D).

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.

Attenuating Neurogenic Sympathetic Hyperreflexia Robustly Improves Antibacterial Immunity After Chronic Spinal Cord Injury

Spinal cord injury (SCI) disrupts critical physiological systems, including the cardiovascular and immune system. Plasticity of spinal circuits below the injury results in abnormal, heightened sympathetic responses, such as extreme, sudden hypertension that hallmarks life-threatening autonomic dysreflexia. Moreover, such sympathetic hyperreflexia detrimentally impacts other effector organs, including the spleen, resulting in spinal cord injury-induced immunodeficiency. Consequently, infection is a leading cause of mortality after SCI. Unfortunately, there are no current treatments that prophylactically limit sympathetic hyperreflexia to prevent subsequent effector organ dysfunction. The cytokine soluble tumor necrosis factor α (sTNFα) is upregulated in the CNS within minutes after SCI and remains elevated. Here, we report that commencing intrathecal administration of XPro1595, an inhibitor of sTNFα, at a clinically feasible, postinjury time point (i.e., 3 d after complete SCI) sufficiently diminishes maladaptive plasticity within the spinal sympathetic reflex circuit. This results in less severe autonomic dysreflexia, a real-time gauge of sympathetic hyperreflexia, for months postinjury. Remarkably, delayed delivery of the sTNFα inhibitor prevents sympathetic hyperreflexia-associated splenic atrophy and loss of leukocytes to dramatically improve the endogenous ability of chronic SCI rats to fight off pneumonia, a common cause of hospitalization after injury. The improved immune function with XPro1595 correlates with less noradrenergic fiber sprouting and normalized norepinephrine levels in the spleen, indicating that heightened, central sTNFα signaling drives peripheral, norepinephrine-mediated organ dysfunction, a novel mechanism of action. Thus, our preclinical study supports intrathecally targeting sTNFα as a viable strategy to broadly attenuate sympathetic dysregulation, thereby improving cardiovascular regulation and immunity long after SCI.SIGNIFICANCE STATEMENT Spinal cord injury (SCI) significantly disrupts immunity, thus increasing susceptibility to infection, a leading cause of morbidity in those living with SCI. Here, we report that commencing intrathecal administration of an inhibitor of the proinflammatory cytokine soluble tumor necrosis factor α days after an injury sufficiently diminishes autonomic dysreflexia, a real time gauge of sympathetic hyperreflexia, to prevent associated splenic atrophy. This dramatically improves the endogenous ability of chronically injured rats to fight off pneumonia, a common cause of hospitalization. This preclinical study could have a significant impact for broadly improving quality of life of SCI individuals.

Phenotypic characterisation of regulatory T cells in dogs reveals signature transcripts conserved in humans and mice

Regulatory T cells (Tregs) are a double-edged regulator of the immune system. Aberrations of Tregs correlate with pathogenesis of inflammatory, autoimmune and neoplastic disorders. Phenotypically and functionally distinct subsets of Tregs have been identified in humans and mice on the basis of their extensive portfolios of monoclonal antibodies (mAb) against Treg surface antigens. As an important veterinary species, dogs are increasingly recognised as an excellent model for many human diseases. However, insightful study of canine Tregs has been restrained by the limited availability of mAb. We therefore set out to characterise CD4+CD25high T cells isolated ex vivo from healthy dogs and showed that they possess a regulatory phenotype, function, and transcriptomic signature that resembles those of human and murine Tregs. By launching a cross-species comparison, we unveiled a conserved transcriptomic signature of Tregs and identified that transcript hip1 may have implications in Treg function.

Targeting Stem Cell-Derived Tissue-Associated Regulatory T Cells for Type 1 Diabetes Immunotherapy

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is an autoimmune disease in which the immune cells selectively destroy the pancreatic beta (β) cells and results in the deficiency of insulin production. The optimal treatment strategy for T1D should be preventing of β-cell destruction in the pancreas. The purpose of this review is to discuss the immunological therapeutic mechanisms that will help to understand the development and control of β-cell destruction. The review also presents a novel method for development of autoantigen (Ag)-specific regulatory T cells (Tregs) for T1D immunotherapy.

RECENT FINDINGS

Pancreatic-resident Tregs have the ability to dramatically suppress hyperactive immune cells. Islet cell transplantation is another attractive approach to replace the failed β cells. Due to the limited source of islet cells, research is going on in the use of animal cells and adult stem cells that may be derived from the patient's own body to produce β cells for transplantation. The mechanism behind the pancreatic β-cell destruction is largely unknown. In this review, a novel approach for the generation of tissue-associated Tregs from stem cells is considered. The stem cell-derived tissue-associated Tregs have the ability to home to the damaged pancreas to prevent the destruction. The review also provides new insights on the mechanism on how these suppressive immune cells protect the pancreas from the destruction of autoimmune cells. A novel method to develop functional auto Ag-specific Tregs that are derived from induced pluripotent stem cells (iPSCs), i.e., iPSC-Tregs, is discussed. Adoptive transfer of the iPSC-Tregs can substantially suppress T1D development in a murine model.

Genetic and functional data identifying Cd101 as a type 1 diabetes (T1D) susceptibility gene in nonobese diabetic (NOD) mice

Type 1 diabetes (T1D) is a chronic multi-factorial disorder characterized by the immune-mediated destruction of insulin-producing pancreatic beta cells. Variations at a large number of genes influence susceptibility to spontaneous autoimmune T1D in non-obese diabetic (NOD) mice, one of the most frequently studied animal models for human disease. The genetic analysis of these mice allowed the identification of many insulin-dependent diabetes (Idd) loci and candidate genes, one of them being Cd101. CD101 is a heavily glycosylated transmembrane molecule which exhibits negative-costimulatory functions and promotes regulatory T (Treg) function. It is abundantly expressed on subsets of lymphoid and myeloid cells, particularly within the gastrointestinal tract. We have recently reported that the genotype-dependent expression of CD101 correlates with a decreased susceptibility to T1D in NOD.B6 Idd10 congenic mice compared to parental NOD controls. Here we show that the knockout of CD101 within the introgressed B6-derived Idd10 region increased T1D frequency to that of the NOD strain. This loss of protection from T1D was paralleled by decreased Gr1-expressing myeloid cells and FoxP3+ Tregs and an enhanced accumulation of CD4-positive over CD8-positive T lymphocytes in pancreatic tissues. As compared to CD101+/+ NOD.B6 Idd10 donors, adoptive T cell transfers from CD101-/- NOD.B6 Idd10 mice increased T1D frequency in lymphopenic NOD scid and NOD.B6 Idd10 scid recipients. Increased T1D frequency correlated with a more rapid expansion of the transferred CD101-/- T cells and a lower proportion of recipient Gr1-expressing myeloid cells in the pancreatic lymph nodes. Fewer of the Gr1+ cells in the recipients receiving CD101-/- T cells expressed CD101 and the cells had lower levels of IL-10 and TGF-β mRNA. Thus, our results connect the Cd101 haplotype-dependent protection from T1D to an anti-diabetogenic function of CD101-expressing Tregs and Gr1-positive myeloid cells and confirm the identity of Cd101 as Idd10.

Stem cell-derived tissue-associated regulatory T cells suppress the activity of pathogenic cells in autoimmune diabetes

The autoantigen-specific Tregs from pluripotent stem cells (PSCs), i.e., PSC-Tregs, have the ability to suppress autoimmunity. PSC-Tregs can be programmed to be tissue associated and to infiltrate into local inflamed tissues to suppress autoimmune responses after adoptive transfer. Nevertheless, the mechanisms by which the autoantigen-specific PSC-Tregs suppress the autoimmune response remain to be fully elucidated. In this study, we generated functional autoantigen-specific Tregs from the induced PSC (iPSCs), i.e., iPSC-Tregs, and investigated the underlying mechanisms of autoimmunity suppression by these Tregs in a type 1 diabetes (T1D) murine model. A double-Tg mouse model of T1D was established in F1 mice, in which the first generation of RIP-mOVA Tg mice that were crossed with OT-I T cell receptor (TCR) Tg mice was challenged with vaccinia viruses expressing OVA (VACV-OVA). We show that adoptive transfer of OVA-specific iPSC-Tregs greatly suppressed autoimmunity in the animal model and prevented the insulin-secreting pancreatic β cells from destruction. Further, we demonstrate that the adoptive transfer significantly reduced the expression of ICAM-1 in the diabetic pancreas and inhibited the migration of pathogenic CD8+ T cells and the production of the proinflammatory IFN-γ in the pancreas. These results indicate that the stem cell-derived tissue-associated Tregs can robustly accumulate in the diabetic pancreas, and, through downregulating the expression of ICAM-1 in the local inflamed tissues and inhibiting the production of proinflammatory cytokine IFN-γ, suppress the migration and activity of the pathogenic immune cells that cause T1D.

FOXP3+ Regulatory T Cell Compartment Is Altered in Children With Newly Diagnosed Type 1 Diabetes but Not in Autoantibody-Positive at-Risk Children

The dysfunction of FOXP3-positive regulatory T cells (Tregs) plays a key role in the pathogenesis of autoimmune diseases, including type 1 diabetes (T1D). However, previous studies analyzing the peripheral blood Treg compartment in patients with T1D have yielded partially conflicting results. Moreover, the phenotypic complexity of peripheral blood Tregs during the development of human T1D has not been comprehensively analyzed. Here, we used multi-color flow cytometry to analyze the frequency of distinct Treg subsets in blood samples from a large cohort comprising of 74 children with newly diagnosed T1D, 76 autoantibody-positive children at-risk for T1D and 180 age- and HLA-matched control children. The frequency of CD4+CD25+CD127lowFOXP3+ Tregs was higher in children with T1D compared to control children, and this change was attributable to a higher proportion of naïve Tregs in these subjects. Further longitudinal analyses demonstrated that the increase in Treg frequency correlated with disease onset. The frequencies of the minor subsets of CD25+FOXP3low memory Tregs as well as CD25lowCD127lowFOXP3+ Tregs were also increased in children with T1D. Moreover, the ratio of CCR6-CXCR3+ and CCR6+CXCR3- memory Tregs was altered and the frequency of proliferating Ki67-positive and IFN-γ producing memory Tregs was decreased in children with T1D. The frequency of CXCR5+FOXP3+ circulating follicular T regulatory cells was not altered in children with T1D. Importantly, none of the alterations observed in children with T1D were observed in autoantibody-positive at-risk children. In conclusion, our study reveals multiple alterations in the peripheral blood Treg compartment at the diagnosis of T1D that appear not to be features of early islet autoimmunity.

Treatment of T1D via optimized expansion of antigen-specific Tregs induced by IL-2/anti-IL-2 monoclonal antibody complexes and peptide/MHC tetramers

Type 1 diabetes can be overcome by regulatory T cells (Treg) in NOD mice yet an efficient method to generate and maintain antigen-specific Treg is difficult to come by. Here, we devised a combination therapy of peptide/MHC tetramers and IL-2/anti-IL-2 monoclonal antibody complexes to generate antigen-specific Treg and maintain them over extended time periods. We first optimized treatment protocols conceived to obtain an improved islet-specific Treg/effector T cell ratio that led to the in vivo expansion and activation of these Treg as well as to an improved suppressor function. Optimized protocols were applied to treatment for testing diabetes prevention in NOD mice as well as in an accelerated T cell transfer model of T1D. The combined treatment led to robust protection against diabetes, and in the NOD model, to a close to complete prevention of insulitis. Treatment was accompanied with increased secretion of IL-10, detectable in total splenocytes and in Foxp3⁻ CD4 T cells. Our data suggest that a dual protection mechanism takes place by the collaboration of Foxp3⁺ and Foxp3⁻ regulatory cells. We conclude that antigen-specific Treg are an important target to improve current clinical interventions against this disease.

Hyaluronan in immune dysregulation and autoimmune diseases

The tissue microenvironment contributes to local immunity and to the pathogenesis of autoimmune diseases - a diverse set of conditions characterized by sterile inflammation, immunity against self-antigens, and destruction of tissues. However, the specific factors within the tissue microenvironment that contribute to local immune dysregulation in autoimmunity are poorly understood. One particular tissue component implicated in multiple autoimmune diseases is hyaluronan (HA), an extracellular matrix (ECM) polymer. HA is abundant in settings of chronic inflammation and contributes to lymphocyte activation, polarization, and migration. Here, we first describe what is known about the size, amount, and distribution of HA at sites of autoimmunity and in associated lymphoid structures in type 1 diabetes, multiple sclerosis, and rheumatoid arthritis. Next, we examine the recent literature on HA and its impact on adaptive immunity, particularly in regards to the biology of lymphocytes and Foxp3+ regulatory T-cells (Treg), a T-cell subset that maintains immune tolerance in healthy individuals. We propose that HA accumulation at sites of chronic inflammation creates a permissive environment for autoimmunity, characterized by CD44-mediated inhibition of Treg expansion. Finally, we address potential tools and strategies for targeting HA and its receptor CD44 in chronic inflammation and autoimmunity.

Unique Features of Pancreatic-Resident Regulatory T Cells in Autoimmune Type 1 Diabetes

Recent progress in regulatory T cells (Tregs) biology emphasizes the importance of understanding tissue-resident Tregs in response to tissue-specific environment. Now, emerging evidence suggests that pancreatic-resident forkhead box P3⁺ Tregs have distinguishable effects on the suppression of over-exuberant immune responses in autoimmune type 1 diabetes (T1D). Thus, there is growing interest in elucidating the role of pancreatic-resident Tregs that function and evolve in the local environment. In this review, we discuss the phenotype and function of Tregs residing in pancreatic tissues and pancreatic lymph nodes, with emphasis on the unique subpopulations of Tregs that control the disease progression in the context of T1D. Specifically, we discuss known and possible modulators that influence the survival, migration, and maintenance of pancreatic Tregs.

NOD mice, susceptible to pancreatic autoimmunity, demonstrate delayed growth of pancreatic cancer

Pancreatic cancer is a high mortality form of cancer, with a median survival only six months. There are multiple associated risk factors associated, most importantly type 2 diabetes, obesity, pancreatitis and smoking. The relative rarity of the disease, however, has made it difficult to dissect causative risk factors, especially with related risk factors. A major unanswered question with important therapeutic implications is the effect of immunological responses on pancreatic cancer formation, with data from other cancers suggesting the potential for local immunological responses to either increase cancer development or increase cancer elimination. Due to the rarity and late diagnosis of pancreatic cancer direct epidemiological evidence is lacking, thus necessitating a reliance on animal models. Here we investigated the relationship between pancreatic autoimmunity and cancer by backcrossing the well characterised Ela1-Tag transgenic model of pancreatic cancer onto the pancreatic autoimmune susceptible NOD mouse strain. Through longitudinal magnetic resonance imaging we found that the NOD genetic background delayed the onset of pancreatic tumours and substantially slowed the growth rate of tumours after development. These results suggest that elevated autoimmune surveillance of the pancreas limits tumour formation and growth, identifying pancreatic cancer as a promising target for immune checkpoint blockade therapies that unleash latent autoimmunity.

KLRG1 expression identifies short-lived Foxp3+ Treg effector cells with functional plasticity in islets of NOD mice

A progressive waning in Foxp3⁺ regulatory T (T_reg) cell function provokes autoimmunity in the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D), a cellular defect rescued by prophylactic IL-2 therapy. We showed that most islet-infiltrating T_reg cells express inducible T-cell co-stimulator (ICOS) in pre-diabetic NOD mice, and that ICOS⁺ T_reg cells display enhanced fitness and suppressive function in situ. Moreover, T1D progression is associated with decreased expansion and suppressive activity of ICOS⁺Foxp3⁺ T_reg cells, in islets, an observation consistent with the exacerbated T1D seen in NOD.BDC2.5 mice in which the ICOS pathway is abrogated. Here, we show that a large proportion of islet-resident T_reg cells express the KLRG1 marker of terminally differentiation, in contrast to islet-infiltrating ICOS^- T_reg or T_eff cells. We hypothesized that KLRG1 expression designates a subpopulation of ICOS⁺ T_reg cells in islets that progressively loses function, and contributes to the immune dysregulation observed at T1D onset. Indeed, KLRG1-expressing ICOS⁺ T_reg cells are prone to apoptosis, and have an impaired proliferative capacity and suppressive function in vitro and in vivo. T1D protective low-dose IL-2 treatment in vivo could not rescue the loss of KLRG1-expressing T_reg cells in situ. While the global pool of Foxp3⁺ T_reg cells displays some degree of functional plasticity in vivo, the KLRG1⁺ ICOS⁺ T_reg cell subset is particularly susceptible to lose Foxp3 expression and reprogram into Th1- or Th17-like effector T (T_eff) cells in the pancreas microenvironment. Overall, KLRG1 expression delineates a subpopulation of dysfunctional T_reg cells during T1D progression in autoantigen-specific TCR transgenic NOD mice.

Foxp3-independent mechanism by which TGF-β controls peripheral T cell tolerance

Peripheral T cell tolerance is promoted by the regulatory cytokine TGF-β and Foxp3-expressing Treg cells. However, whether TGF-β and Treg cells are part of the same regulatory module, or exist largely as distinct pathways to repress self-reactive T cells remains incompletely understood. Using a transgenic model of autoimmune diabetes, here we show that ablation of TGF-β receptor II (TβRII) in T cells, but not Foxp3 deficiency, resulted in early-onset diabetes with complete penetrance. The rampant autoimmune disease was associated with enhanced T cell priming and elevated T cell expression of the inflammatory cytokine GM-CSF, concomitant with pancreatic infiltration of inflammatory monocytes that triggered immunopathology. Ablation of the GM-CSF receptor alleviated the monocyte response and inhibited disease development. These findings reveal that TGF-β promotes T cell tolerance primarily via Foxp3-independent mechanisms and prevents autoimmunity in this model by repressing the cross talk between adaptive and innate immune systems.

Are Regulatory T Cells Defective in Type 1 Diabetes and Can We Fix Them?

Regulatory T cells (Tregs) are critical regulators of peripheral immune tolerance. Treg insufficiency can lead to autoimmune disorders, including type 1 diabetes (T1D). Increasing evidence in mouse models of T1D, as well as other autoimmune disorders, suggests that there are defects in Treg-mediated suppression. Indeed, whereas Treg frequency in the peripheral blood of T1D patients is unaltered, their suppressive abilities are diminished compared with Tregs in healthy controls. Although expression of the transcription factor Foxp3 is a prerequisite for Treg development and function, there are many additional factors that can alter their stability, survival, and function. Much has been learned in other model systems, such as tumors, about the mechanism and pathways that control Treg stability and function. This review poses the question of whether we can use these findings to develop new therapeutic approaches that might boost Treg stability, survival, and/or function in T1D and possibly other autoimmune disorders.

Expansion of FasL-Expressing CD5+ B Cells in Type 1 Diabetes Patients

Fas ligand drives insulitis in the non-obese diabetic mouse model of type 1 diabetes (T1D) and negatively regulates IL-10-producing (IL-10^pos) CD5⁺ B cells in pancreata. Relevance of these phenomena to the human disease is poorly understood. Here, using splenocytes from T1D, autoantibody (Ab⁺), and non-diabetic (ND) human subjects, we show that a subpopulation of CD5⁺ B cells that is characterized by expression of FasL (FasL^hiCD5⁺) was significantly elevated in T1D subjects, many of whom had significantly reduced frequency of IL-10^posCD5⁺ B cells compared to Ab⁺ subjects. The majority of FasL^hiCD5⁺ B cells did not produce cytokines and were more highly resistant to activation-induced cell death than their IL-10^posCD5⁺ counterparts. These results associate expansion of FasL-expressing CD5⁺ B cells with T1D and lay the groundwork for future mechanistic studies to understand specific role in disease pathogenesis.

miRNAs: novel regulators of autoimmunity-mediated pancreatic β-cell destruction in type 1 diabetes

MicroRNAs (miRNAs) are a series of conserved, short, non-coding RNAs that modulate gene expression in a posttranscriptional manner. miRNAs are involved in almost every physiological and pathological process. Type 1 diabetes (T1D) is an autoimmune disease that is the result of selective destruction of pancreatic β-cells driven by the immune system. miRNAs are also important participants in T1D pathogenesis. Herein, we review the most recent data on the potential involvement of miRNAs in T1D. Specifically, we focus on two aspects: the roles of miRNAs in maintaining immune homeostasis and regulating β-cell survival and/or functions in T1D. We also discuss circulating miRNAs as potent biomarkers for the diagnosis and prediction of T1D and investigate potential therapeutic approaches for this disease.

Singular role for T-BET+CXCR3+ regulatory T cells in protection from autoimmune diabetes

Foxp3⁺ regulatory T (Treg) cells are crucial for restraining inflammation in a variety of autoimmune diseases, including type 1 diabetes (T1D). However, the transcriptional and functional phenotypes of Treg cells within the pancreatic lesion remain poorly understood. Here we characterized pancreas-infiltrating Treg cells in the NOD mouse model of T1D and uncovered a substantial enrichment of the Treg subpopulation expressing the chemokine receptor CXCR3. Accumulation of CXCR3⁺ Treg cells within pancreatic islets was dependent on the transcription factor T-BET, and genetic ablation of T-BET increased the onset and penetrance of disease, abrogating the sex bias normally seen in the NOD model. Both male and female mice lacking T-BET⁺ Treg cells showed a more aggressive insulitic infiltrate, reflected most prominently by elevated production of type 1 cytokines. Our results suggest the possibility of fine therapeutic targeting of Treg cells, in a tissue- and cell-subset-specific fashion, as a more focused immunotherapy for T1D.

Mechanisms of diabetic autoimmunity: II--Is diabetes a central or peripheral disorder of effector and regulatory cells?

Two competing hypotheses aiming to explain the onset of autoimmune reactions are discussed in the context of genetic and environmental predisposition to type 1 diabetes (T1D). The first hypothesis has evolved along characterization of the mechanisms of self-discrimination and attributes diabetic autoimmunity to escape of reactive T cells from central regulation in the thymus. The second considers frequent occurrence of autoimmune reactions within the immune homunculus, which are adequately suppressed by regulatory T cells originating from the thymus, and occasionally, insufficient suppression results in autoimmunity. Besides thymic dysfunction, deregulation of both effector and suppressor cells can in fact result from homeostatic aberrations at the peripheral level during initial stages of evolution of adaptive immunity. Pathogenic cells sensitized in the islets are efficiently expanded in the target tissue and pancreatic lymph nodes of lymphopenic neonates. In parallel, the same mechanisms of peripheral sensitization contribute to tolerization through education of naïve/effector T cells and expansion of regulatory T cells. Experimental evidence presented for each individual mechanism implies that T1D may result from a primary effector or suppressor immune abnormality. Disturbed self-tolerance leading to T1D may well result from peripheral deregulation of innate and adaptive immunity, with variable contribution of central thymic dysfunction.

Deficiency of Nuclear Factor-κB c-Rel Accelerates the Development of Autoimmune Diabetes in NOD Mice

The nuclear factor-κB protein c-Rel plays a critical role in controlling autoimmunity. c-Rel-deficient mice are resistant to streptozotocin-induced diabetes, a drug-induced model of autoimmune diabetes. We generated c-Rel-deficient NOD mice to examine the role of c-Rel in the development of spontaneous autoimmune diabetes. We found that both CD4(+) and CD8(+) T cells from c-Rel-deficient NOD mice showed significantly decreased T-cell receptor-induced IL-2, IFN-γ, and GM-CSF expression. Despite compromised T-cell function, c-Rel deficiency dramatically accelerated insulitis and hyperglycemia in NOD mice along with a substantial reduction in T-regulatory (Treg) cell numbers. Supplementation of isogenic c-Rel-competent Treg cells from prediabetic NOD mice reversed the accelerated diabetes development in c-Rel-deficient NOD mice. The results suggest that c-Rel-dependent Treg cell function is critical in suppressing early-onset autoimmune diabetogenesis in NOD mice. This study provides a novel natural system to study autoimmune diabetes pathogenesis and reveals a previously unknown c-Rel-dependent mechanistic difference between chemically induced and spontaneous diabetogenesis. The study also reveals a unique protective role of c-Rel in autoimmune diabetes, which is distinct from other T-cell-dependent autoimmune diseases such as arthritis and experimental autoimmune encephalomyelitis, where c-Rel promotes autoimmunity.

Exploring the induction of preproinsulin-specific Foxp3(+) CD4(+) Treg cells that inhibit CD8(+) T cell-mediated autoimmune diabetes by DNA vaccination

DNA vaccination is a promising strategy to induce effector T cells but also regulatory Foxp3⁺ CD25⁺ CD4⁺ Treg cells and inhibit autoimmune disorders such as type 1 diabetes. Little is known about the antigen requirements that facilitate priming of Treg cells but not autoreactive effector CD8⁺ T cells. We have shown that the injection of preproinsulin (ppins)-expressing pCI/ppins vector into PD-1- or PD-L1-deficient mice induced K^b/A12-21-monospecific CD8⁺ T cells and autoimmune diabetes. A pCI/ppinsΔA12-21 vector (lacking the critical K^b/A12-21 epitope) did not induce autoimmune diabetes but elicited a systemic Foxp3⁺ CD25⁺ Treg cell immunity that suppressed diabetes induction by a subsequent injection of the diabetogenic pCI/ppins. TGF-β expression was significantly enhanced in the Foxp3⁺ CD25⁺ Treg cell population of vaccinated/ppins-primed mice. Ablation of Treg cells in vaccinated/ppins-primed mice by anti-CD25 antibody treatment abolished the protective effect of the vaccine and enabled diabetes induction by pCI/ppins. Adoptive transfer of Treg cells from vaccinated/ppins-primed mice into PD-L1^−/− hosts efficiently suppressed diabetes induction by pCI/ppins. We narrowed down the Treg-stimulating domain to a 15-residue ppins76–90 peptide. Vaccine-induced Treg cells thus play a crucial role in the control of de novo primed autoreactive effector CD8⁺ T cells in this diabetes model.

PSG9 Stimulates Increase in FoxP3+ Regulatory T-Cells through the TGF-β1 Pathway

The pregnancy-specific glycoproteins (PSGs) are a family of proteins secreted by the syncytiotrophoblast of the placenta and are the most abundant trophoblastic proteins in maternal blood during the third trimester. The human PSG family consists of 10 protein-coding genes, some of which have a possible role in maintaining maternal immune tolerance to the fetus. PSG9 was reported as a potential predictive biomarker of pre-eclampsia, a serious complication of pregnancy that has been related to immunological dysfunction at the fetal-maternal interface. Therefore, we hypothesized that PSG9 may have an immunoregulatory role during pregnancy. We found that PSG9 binds to LAP and activates the latent form of TGF-β1. In addition, PSG9 induces the secretion of TGF-β1 from macrophages but not from CD4+ T-cells. TGF-β1 is required for the ex vivo differentiation of regulatory T-cells and, consistent with the ability of PSG9 to activate this cytokine, we observed that PSG9 induces the differentiation of FoxP3+ regulatory T-cells from naïve murine and human T-cells. Cytokines that are associated with inflammatory responses were also reduced in the supernatants of T-cells treated with PSG9, suggesting that PSG9, through its activation of TGFβ-1, could be a potent inducer of immune tolerance.

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.

B cell-targeted immunotherapy for type 1 diabetes: What can make it work?

Immunotherapy has revolutionized treatment of cancers and autoimmune diseases. Bucking the trend, however, is type 1 diabetes (T1D), although it is one of best understood autoimmune diseases and individuals at genetic risk are identifiable with high certainty. Here we review the major obstacles associated with pan-B-cell-depletion using rituximab (RTX) and discuss the notion that B cell-directed therapy may be most effective as a preventive measure. We suggest that it will be more productive to aim at identifying and targeting autoreactive B cells rather than making adjustments to pan-B cell depletion and that non-conventional alternative therapies such as antibody blockade of FasL to bolster IL-10-producing Breg cells, which work successfully in mice, should be considered.

Type 1 diabetes genetic susceptibility and dendritic cell function: potential targets for treatment

Type 1 diabetes is an autoimmune disease that results from the defective induction or maintenance of T cell tolerance against islet β cell self-antigens. Under steady-state conditions, dendritic cells with tolerogenic properties are critical for peripheral immune tolerance. Tolerogenic dendritic cells can induce T cell anergy and deletion and, in some contexts, induce or expand regulatory T cells. Dendritic cells contribute to both immunomodulatory effects and triggering of pathogenesis in type 1 diabetes. This immune equilibrium is affected by both genetic and environmental factors that contribute to the development of type 1 diabetes. Genome-wide association studies and disease association studies have identified >50 polymorphic loci that lend susceptibility or resistance to insulin-dependent diabetes mellitus. In parallel, diabetes susceptibility regions known as insulin-dependent diabetes loci have been identified in the nonobese diabetic mouse, a model for human type 1 diabetes, providing a better understanding of potential immunomodulatory factors in type 1 diabetes risk. Most genetic candidates have annotated immune cell functions, but the focus has been on changes to T and B cells. However, it is likely that some of the genomic susceptibility in type 1 diabetes directly interrupts the tolerogenic potential of dendritic cells in the pathogenic context of ongoing autoimmunity. Here, we will review how gene polymorphisms associated with autoimmune diabetes may influence dendritic cell development and maturation processes that could lead to alterations in the tolerogenic function of dendritic cells. These insights into potential tolerogenic and pathogenic roles for dendritic cells have practical implications for the clinical manipulation of dendritic cells toward tolerance to prevent and treat type 1 diabetes.

Autoimmune Diabetes: An Overview of Experimental Models and Novel Therapeutics

Type 1 diabetes (T1D) results from a chronic and selective destruction of insulin-secreting β-cells within the islets of Langerhans of the pancreas by autoreactive CD4(+) and CD8(+) T lymphocytes. The use of animal models of T1D was instrumental for deciphering the steps of the autoimmune process leading to T1D. The non-obese diabetic (NOD) mouse and the bio-breeding (BB) rat spontaneously develop the disease similar to the human pathology in terms of the immune responses triggering autoimmune diabetes and of the genetic and environmental factors influencing disease susceptibility. The generation of genetically modified models allowed refining our understanding of the etiology and the pathogenesis of the disease. In the present review, we provide an overview of the experimental models generated and used to gain knowledge on the molecular and cellular mechanisms underlying the breakdown of self-tolerance in T1D and the progression of the autoimmune response. Immunotherapeutic interventions designed in these animal models and translated into the clinical arena in T1D patients will also be discussed.

Regulatory T Cells in Autoimmune Diabetes: Mechanisms of Action and Translational Potential

Since the discovery of specialized T cells with regulatory function, harnessing the power of these cells to ameliorate autoimmunity has been a major goal. Here we collate the evidence that regulatory T cells (Treg) can inhibit Type 1 diabetes in animal models and humans. We discuss the anatomical sites and molecular mechanisms of Treg suppressive function in the Type 1 diabetes setting, citing evidence that Treg can function in both the pancreatic lymph nodes and within the pancreatic lesion. Involvement of the CTLA-4 pathway, as well as TGF-β and IL-2 deprivation will be considered. Finally, we summarize current efforts to manipulate Treg therapeutically in individuals with Type 1 diabetes. The translation of this research area from bench to bedside is still in its infancy, but the remarkable therapeutic potential of successfully manipulating Treg populations is clear to see.

BIM Deficiency Protects NOD Mice From Diabetes by Diverting Thymocytes to Regulatory T Cells

Because regulatory T-cell (Treg) development can be induced by the same agonist self-antigens that induce negative selection, perturbation of apoptosis will affect both negative selection and Treg development. But how the processes of thymocyte deletion versus Treg differentiation bifurcate and their relative importance for tolerance have not been studied in spontaneous organ-specific autoimmune disease. We addressed these questions by removing a critical mediator of thymocyte deletion, BIM, in the NOD mouse model of autoimmune diabetes. Despite substantial defects in the deletion of autoreactive thymocytes, BIM-deficient NOD (NODBim(-/-)) mice developed less insulitis and were protected from diabetes. BIM deficiency did not impair effector T-cell function; however, NODBim(-/-) mice had increased numbers of Tregs, including those specific for proinsulin, in the thymus and peripheral lymphoid tissues. Increased levels of Nur77, CD5, GITR, and phosphorylated IκB-α in thymocytes from NODBim(-/-) mice suggest that autoreactive cells receiving strong T-cell receptor signals that would normally delete them escape apoptosis and are diverted into the Treg pathway. Paradoxically, in the NOD model, reduced thymic deletion ameliorates autoimmune diabetes by increasing Tregs. Thus, modulating apoptosis may be one of the ways to increase antigen-specific Tregs and prevent autoimmune disease.

Treg Cell Differentiation: From Thymus to Peripheral Tissue

Regulatory T cells (Tregs) are crucial mediators of self-tolerance in the periphery. They differentiate in the thymus, where interactions with thymus-resident antigen-presenting cells, an instructive cytokine milieu, and stimulation of the T cell receptor lead to the selection into the Treg lineage and the induction of Foxp3 gene expression. Once mature, Treg cells leave the thymus and migrate into either the secondary lymphoid tissues, e.g., lymph nodes and spleen, or peripheral nonlymphoid tissues. There is growing evidence that Treg cells go beyond the classical modulation of immune responses and also play important functional roles in nonlymphoid peripheral tissues. In this review, we summarize recent findings about the thymic Treg lineage differentiation as well as the further specialization of Treg cells in the secondary lymphoid and in the peripheral nonlymphoid organs.

Activated regulatory T-cells attenuate myocardial ischaemia/reperfusion injury through a CD39-dependent mechanism

Regulatory T-cells (Tregs) are generally regarded as key immunomodulators that maintain immune tolerance and counteract tissue damage in a variety of immune-mediated disorders. However, its role in myocardial ischaemia/reperfusion injury (MIRI) remains unknown. The purpose of the present study was to determine whether Tregs exert a beneficial effect on mouse MIRI. We examined the role of Tregs in murine MIRI by depletion using 'depletion of regulatory T-cell' (DEREG) mice and adoptive transfer using Forkhead box P3 (Foxp3)-GFP knockin mice and the mechanisms of cardio protection were further studied in vivo and in vitro. Tregs rapidly accumulated in murine hearts following MIRI. Selective depletion of Tregs in the DEREG mouse model resulted in aggravated MIRI. In contrast, the adoptive transfer of in vitro-activated Tregs suppressed MIRI, whereas freshly isolated Tregs had no effect. Mechanistically, activated Treg-mediated protection against MIRI was not abrogated by interleukin (IL)-10 or transforming growth factor (TGF)-β1 inhibition but was impaired by the genetic deletion of cluster of differentiation 39 (CD39). Moreover, adoptive transfer of in vitro-activated Tregs attenuated cardiomyocyte apoptosis, activated a pro-survival pathway involving Akt and extracellular-signal-regulated kinase (ERK) and inhibited neutrophil infiltration, which was compromised by CD39 deficiency. Finally, the peripheral blood mononuclear cells of acute myocardial infarction (AMI) patients after primary percutaneous coronary intervention (PCI) revealed a decrease in CD4+CD25+CD127low Tregs and a relative increase in CD39+ cells within the Treg population. In conclusion, our data validated a protective role for Tregs in MIRI. Moreover, in vitro-activated Tregs ameliorated MIRI via a CD39-dependent mechanism, representing a putative therapeutic strategy.

Combination immunotherapies for type 1 diabetes mellitus

Immunotherapies for type 1 diabetes mellitus (T1DM) have been the focus of intense basic and clinical research over the past few decades. Restoring β-cell function is the ultimate goal of intervention trials that target the immune system in T1DM. In an attempt to achieve this aim, different combination therapies have been proposed over the past few years that are based on treatments tackling the various mechanisms involved in the destruction of β cells. The results of clinical trials have not matched expectations based on the positive results from preclinical studies. The heterogeneity of T1DM might explain the negative results obtained, but previous trials have not addressed this issue. However, novel promising combination therapies are being developed, including those that couple immunomodulators with drugs that stimulate β-cell regeneration in order to restore normoglycaemia. This strategy is an encouraging one to pursue the goal of finding a cure for T1DM. This Review summarizes the available data about combination immunotherapies in T1DM, particularly addressing their clinical importance. The available data supporting the use of registered drugs, such as proton pump inhibitors and incretin-based agents, that have been shown to induce β-cell regeneration will also be discussed.

Altered connexin 43 expression underlies age-dependent decrease of regulatory T cell suppressor function in nonobese diabetic mice

Type 1 diabetes is one of the most extensively studied autoimmune diseases, but the cellular and molecular mechanisms leading to T cell-mediated destruction of insulin-producing β cells are still not well understood. In this study, we show that regulatory T cells (T(regs)) in NOD mice undergo age-dependent loss of suppressor functions exacerbated by the decreased ability of activated effector T cells to upregulate Foxp3 and generate T(regs) in the peripheral organs. This age-dependent loss is associated with reduced intercellular communication mediated by gap junctions, which is caused by impaired upregulation and decreased expression of connexin 43. Regulatory functions can be corrected, even in T cells isolated from aged, diabetic mice, by a synergistic activity of retinoic acid, TGF-β, and IL-2, which enhance connexin 43 and Foxp3 expression in T(regs) and restore the ability of conventional CD4(+) T cells to upregulate Foxp3 and generate peripherally derived T(regs). Moreover, we demonstrate that suppression mediated by T(regs) from diabetic mice is enhanced by a novel reagent, which facilitates gap junction aggregation. In summary, our report identifies gap junction-mediated intercellular communication as an important component of the T(reg) suppression mechanism compromised in NOD mice and suggests how T(reg) mediated immune regulation can be improved.