Role of CD28 in fatal autoimmune disorder in scurfy mice

IL-27 Gene Therapy Ameliorates IPEX Syndrome Caused by Germline Mutation of Foxp3 Gene: A Major Role for Induction of IL-10

Inactivating mutations of Foxp3, the master regulator of regulatory T cell development and function, lead to immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome in mice and humans. IPEX is a fatal autoimmune disease, with allogeneic stem cell transplant being the only available therapy. In this study, we report that a single dose of adeno-associated virus (AAV)-IL-27 to young mice with naturally occurring Foxp3 mutation (Scurfy mice) substantially ameliorates clinical symptoms, including growth retardation and early fatality. Correspondingly, AAV-IL-27 gene therapy significantly prevented naive T cell activation, as manifested by downregulation of CD62L and upregulation of CD44, and immunopathology typical of IPEX. Because IL-27 is known to induce IL-10, a key effector molecule of regulatory T cells, we evaluated the contribution of IL-10 induction by crossing IL-10-null allele to Scurfy mice. Although IL-10 deficiency does not affect the survival of Scurfy mice, it largely abrogated the therapeutic effect of AAV-IL-27. Our study revealed a major role for IL-10 in AAV-IL-27 gene therapy and demonstrated that IPEX is amenable to gene therapy.

Perspectives on Psoriasiform Adverse Events from Immune Checkpoint Inhibitors: Lessons Learned from Our Practice

Background: New oncologic therapies, including immune checkpoint inhibitors (ICIs), have revolutionized the survival and prognosis of cancer patients. However, these therapies are often complicated by immune-related adverse effects (irAEs) that may impact quality of life and potentially limit their use. Among these adverse events are psoriasis and psoriatic arthritis that may develop de novo or flare under treatment with ICIs. Given the exceptional immune status of patients receiving ICIs, managing these conditions without interfering with the effect of the oncologic treatment may prove very challenging. Aim: To review the literature data on ICI-induced psoriasis exacerbation or development, to present our own experience, and to discuss the pathogenic mechanisms underlying this association and the optimal therapeutic approach for these patients. Case Reports: We report three cases of ICI-induced de novo psoriasis and two cases of ICI-induced psoriasis exacerbation that required systemic treatment. Oral acitretin treatment successfully controlled psoriasis lesions in three cases and allowed for the continuation of immunotherapy. Literature Review: We performed a medical literature search across several databases (PubMed, Medline, Google Scholar) using the search terms "immune checkpoint inhibitor-induced psoriasis/psoriasiform dermatitis/psoriasis arthritis". We identified and revised 80 relevant publications that reported 1102 patients with psoriasis and/or psoriasis arthritis induced or exacerbated by ICIs. We assessed the type of cancer, the therapeutic agent involved, the clinical form of psoriasis, the presence or absence of psoriatic arthritis, the personal and family history of psoriasis, the age, the gender, the time until onset or exacerbation of skin lesions, the specific treatment recommended, the need for ICI discontinuation, and the patient's outcome. Conclusions: As ICIs represent a fairly novel therapy, the association with several adverse effects is only now unraveling. Psoriasis exacerbation or onset following the initiation of immunotherapy is one such example, as more and more reports and case series are being published. Awareness of the relationship between psoriasis and treatment with ICIs, prompt recognition, and initiation of adequate skin-directed therapies are essential for the avoidance of skin lesions worsening, the need for systemic treatments that may interfere with ICIs' effects, or the discontinuation of the latter. In the absence of generally accepted guidelines, it is advisable to treat patients with severe, widespread psoriasis with drugs that do not impair the effects of immunotherapy and thus do not alter the patient's prognosis.

Mutations from patients with IPEX ported to mice reveal different patterns of FoxP3 and Treg dysfunction

Mutations of the transcription factor FoxP3 in patients with "IPEX" (immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome) disrupt regulatory T cells (Treg), causing an array of multiorgan autoimmunity. To understand the functional impact of mutations across FoxP3 domains, without genetic and environmental confounders, six human FOXP3 missense mutations are engineered into mice. Two classes of mutations emerge from combined immunologic and genomic analyses. A mutation in the DNA-binding domain shows the same lymphoproliferation and multiorgan infiltration as complete FoxP3 knockouts but delayed by months. Tregs expressing this mutant FoxP3 are destabilized by normal Tregs in heterozygous females compared with hemizygous males. Mutations in other domains affect chromatin opening differently, involving different cofactors and provoking more specific autoimmune pathology (dermatitis, colitis, diabetes), unmasked by immunological challenges or incrossing NOD autoimmune-susceptibility alleles. This work establishes that IPEX disease heterogeneity results from the actual mutations, combined with genetic and environmental perturbations, explaining then the intra-familial variation in IPEX.

Metabolism along the life journey of T cells

T cells are one of few cell types in adult mammals that can proliferate extensively and differentiate diversely upon stimulation, which serves as an excellent example to dissect the metabolic basis of cell fate decisions. During the last decade, there has been an explosion of research into the metabolic control of T-cell responses. The roles of common metabolic pathways, including glycolysis, lipid metabolism, and mitochondrial oxidative phosphorylation, in T-cell responses have been well characterized, and their mechanisms of action are starting to emerge. In this review, we present several considerations for T-cell metabolism-focused research, while providing an overview of the metabolic control of T-cell fate decisions during their life journey. We try to synthesize principles that explain the causal relationship between cellular metabolism and T-cell fate decision. We also discuss key unresolved questions and challenges in targeting T-cell metabolism to treat disease.

Molecular and Functional Analyses of the Primordial Costimulatory Molecule CD80/86 and Its Receptors CD28 and CD152 (CTLA-4) in a Teleost Fish

The moderate activation of T cells in mammals requires the costimulatory molecules, CD80 and CD86, on antigen-presenting cells to interact with their respective T cell receptors, CD28 and CD152 (CTLA-4), to promote costimulatory signals. In contrast, teleost fish (except salmonids) only possess CD80/86 as their sole primordial costimulatory molecule. However, the mechanism, which underlies the interaction between CD80/86 and its receptors CD28 and CD152 still requires elucidation. In this study, we cloned and identified the CD80/86, CD28, and CD152 genes of the grass carp (Ctenopharyngodon idella). The mRNA expression analysis showed that CD80/86, CD28, and CD152 were constitutively expressed in various tissues. Further analysis revealed that CD80/86 was highly expressed in IgM⁺ B cells. Conversely, CD28 and CD152 were highly expressed in CD4⁺ and CD8⁺ T cells. Subcellular localization illustrated that CD80/86, CD28, and CD152 are all located on the cell membrane. A yeast two-hybrid assay exhibited that CD80/86 can bind with both CD28 and CD152. In vivo assay showed that the expression of CD80/86 was rapidly upregulated in Aeromonas hydrophila infected fish compared to the control fish. However, the expression of CD28 and CD152 presented the inverse trend, suggesting that teleost fish may regulate T cell activation through the differential expression of CD28 and CD152. Importantly, we discovered that T cells were more likely to be activated by A. hydrophila after CD152 was blocked by anti-CD152 antibodies. This suggests that the teleost CD152 is an inhibitory receptor of T cell activation, which is similar to the mammalian CD152. Overall, this study begins to define the interaction feature between primordial CD80/86 and its receptors CD28 and CD152 in teleost fish, alongside providing a cross-species understanding of the evolution of the costimulatory signals throughout vertebrates.

Druggable monogenic immune defects hidden in diverse medical specialties: Focus on overlap syndromes

In the last two decades two new paradigms changed our way of perceiving primary immunodeficiencies: An increasing number of immune defects are more associated with inflammatory or autoimmune features rather than with infections. Some primary immune defects are due to hyperactive pathways that can be targeted by specific inhibitors, providing innovative precision treatments that can change the natural history of diseases. In this article we review some of these “druggable” inborn errors of immunity and describe how they can be suspected and diagnosed in diverse pediatric and adult medicine specialties. Since the availability of precision treatments can dramatically impact the course of these diseases, preventing the development of organ damage, it is crucial to widen the awareness of these conditions and to provide practical hints for a prompt detection and cure.

FoxP3 deficiency causes no inflammation or neurodegeneration in the murine brain

Regulatory T cells (Treg) maintain immunological self-tolerance and their functional or numerical deficits are associated with progression of several neurological diseases. We examined the effects of Treg absence on the structure and integrity of the unchallenged murine brain. When compared to control, Treg-deficient FoxP3sf mutant mice showed no differences in brain size, myelin amount and oligodendrocyte numbers. FoxP3sf strain displayed no variations in quantity of neurons and astrocytes, whereas microglia numbers were slightly reduced. We demonstrate lack of neuroinflammation and parenchymal responses in the brains of Treg-deficient mice, suggesting a minor Treg role in absence of blood-brain barrier breakdown.

Refractory hypotension with fever revealing checkpoint inhibitor-induced hypophysitis

The new era of immunotherapy in cancer has led to a dramatical increase in patients survival but also to the emergence of a new type of immune-mediated toxicities mimicking known diseases but with special features. As the spectrum of checkpoint inhibitors is widening to many types of cancer expressing histological signs of immune blockade, new subtypes of immune-related adverse events are meant to be discovered and classified and among them new life-threatening situations that need to be quickly identified and require urgent treatment. We here report a case of refractory arterial hypotension with fever leading to diagnosis of combined immune-related adverse events associating hypophysitis, thyroiditis and colitis complicated by refractory arterial hypotension with fever.

Unregulated antigen-presenting cell activation by T cells breaks self tolerance

T cells proliferate vigorously following acute depletion of CD4⁺ Foxp3⁺ T regulatory cells [natural Tregs (nTregs)] and also when naive T cells are transferred to syngeneic, nTreg-deficient Rag1 ^-/- hosts. Here, using mice raised in an antigen-free (AF) environment, we show that proliferation in these two situations is directed to self ligands rather than food or commensal antigens. In both situations, the absence of nTregs elevates B7 expression on host dendritic cells (DCs) and enables a small subset of naive CD4 T cells with high self affinity to respond overtly to host DCs: bidirectional T/DC interaction ensues, leading to progressive DC activation and reciprocal strong proliferation of T cells accompanied by peripheral Treg (pTreg) formation. Likewise, high-affinity CD4 T cells proliferate vigorously and form pTregs when cultured with autologous DCs in vitro in the absence of nTregs: this anti-self response is MHCII/peptide dependent and elicited by the raised level of B7 on cultured DCs. The data support a model in which self tolerance is imposed via modulation of CD28 signaling and explains the pathological effects of superagonistic CD28 antibodies.

Adenosine A2A Receptor Deletion Blocks the Beneficial Effects of Lactobacillus reuteri in Regulatory T-Deficient Scurfy Mice

The lack of a functional Foxp3 transcription factor and regulatory T (Treg) cells causes lethal, CD4⁺ T cell-driven autoimmune diseases in scurfy (SF) mice and humans. Recent studies have shown that adenosine A_2A receptor activation limits inflammation and tissue damage, thereby playing an anti-inflammatory role. However, the role of the adenosine A_2A receptor in the development of disease in SF mice remains unclear. Using a genetic approach, we found that adenosine A_2A receptor deletion in SF mice (SF⋅A2A-/-) does not affect early life events, the development of a lymphoproliferative disorder, or hyper-production of pro-inflammatory cytokines seen in the Treg-deficiency state. As shown previously, Lactobacillus reuteri DSM 17938 treatment prolonged survival and reduced multiorgan inflammation in SF mice. In marked contrast, A_2A receptor deletion completely blocked these beneficial effects of L. reuteri in SF mice. Altogether, these results suggest that although absence of the adenosine A_2A receptor does not affect the development of disease in SF mice, it plays a critical role in the immunomodulation by L. reuteri in Treg-deficiency disease. The adenosine A_2A receptor and its activation may have a role in treating other Treg dysfunction-mediated autoimmune diseases.

Commensal microbes drive intestinal inflammation by IL-17-producing CD4+ T cells through ICOSL and OX40L costimulation in the absence of B7-1 and B7-2

The costimulatory B7-1 (CD80)/B7-2 (CD86) molecules, along with T-cell receptor stimulation, together facilitate T-cell activation. This explains why in vivo B7 costimulation neutralization efficiently silences a variety of human autoimmune disorders. Paradoxically, however, B7 blockade also potently moderates accumulation of immune-suppressive regulatory T cells (Tregs) essential for protection against multiorgan systemic autoimmunity. Here we show that B7 deprivation in mice overrides the necessity for Tregs in averting systemic autoimmunity and inflammation in extraintestinal tissues, whereas peripherally induced Tregs retained in the absence of B7 selectively mitigate intestinal inflammation caused by Th17 effector CD4(+) T cells. The need for additional immune suppression in the intestine reflects commensal microbe-driven T-cell activation through the accessory costimulation molecules ICOSL and OX40L. Eradication of commensal enteric bacteria mitigates intestinal inflammation and IL-17 production triggered by Treg depletion in B7-deficient mice, whereas re-establishing intestinal colonization with Candida albicans primes expansion of Th17 cells with commensal specificity. Thus, neutralizing B7 costimulation uncovers an essential role for Tregs in selectively averting intestinal inflammation by Th17 CD4(+) T cells with commensal microbe specificity.

A transendocytosis perspective on the CD28/CTLA-4 pathway

T cell activation is a key event in the adaptive immune response and vital to the generation of both cellular and humoral immunity. Activation is required not only for effective CD4 T cell responses but also to provide help for B cells and the generation of cytotoxic T cell responses. Unsurprisingly, impaired T cell activation results in infectious pathology, whereas dysregulated activation can result in autoimmunity. The decision to activate is therefore tightly regulated and the CD28/CTLA-4 pathway represents this apical decision point at the molecular level. In particular, CTLA-4 (CD152) is an essential checkpoint control for autoimmunity; however, the molecular mechanism(s) by which CTLA-4 achieves its regulatory function are not well understood, especially how it functionally intersects with the CD28 pathway. In this chapter, we review the established molecular and cellular concepts relating to CD28 and CTLA-4 biology, and attempt to integrate these by discussing the transendocytosis of ligands as a new model of CTLA-4 function.

B cells are critical for autoimmune pathology in Scurfy mice

Impaired regulatory T-cell function results in a severe chronic autoimmune disease affecting multiple organs in Scurfy mice and humans with the immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. Previous studies have shown that T helper cells but not cytotoxic T cells are critical for the disease pathology. Whether this T-cell subset is responsible directly for tissue inflammation or rather indirectly via the interaction with B cells or myeloid cells is largely unknown. To study this and to identify potential therapeutic targets for this lethal disease we investigated the contribution of B cells to this complex autoimmune phenotype. We show that B cells and the production of autoantibodies plays a major role for skin, liver, lung, and kidney inflammation and therapeutic depletion of B cells resulted in reduced tissue pathology and in prolonged survival. In contrast, the absence of B cells did not impact systemic T-cell activation and hyperreactivity, indicating that autoantibody production by B cells may be a major factor for the autoimmune pathology in mice deficient for regulatory T cells.

B7-1/B7-2 blockade overrides the activation of protective CD8 T cells stimulated in the absence of Foxp3+ regulatory T cells

Although T cell activation has been classically described to require distinct, positive stimulation signals that include B7-1 (CD80) and B7-2 (CD86) costimulation, overriding suppression signals that avert immune-mediated host injury are equally important. How these opposing stimulation and suppression signals work together remains incompletely defined. Our recent studies demonstrate that CD8 Teff activation in response to cognate peptide stimulation is actively suppressed by the Foxp3(+) subset of CD4 cells, called Tregs. Here, we show that the elimination of Treg suppression does not bypass the requirement for positive B7-1/B7-2 costimulation. The expansion, IFN-γ cytokine production, cytolytic, and protective features of antigen-specific CD8 T cells stimulated with purified cognate peptide in Treg-ablated mice were each neutralized effectively by CTLA-4-Ig that blocks B7-1/B7-2. In turn, given the efficiency whereby CTLA-4-Ig overrides the effects of Treg ablation, the role of Foxp3(+) cell-intrinsic CTLA-4 in mitigating CD8 Teff activation was also investigated. With the use of mixed chimera mice that contain CTLA-4-deficient Tregs exclusively after the ablation of WT Foxp3(+) cells, a critical role for Treg CTLA-4 in suppressing the expansion, cytokine production, cytotoxicity, and protective features of peptide-stimulated CD8 T cells is revealed. Thus, the activation of protective CD8 T cells requires positive B7-1/B7-2 costimulation even when suppression by Tregs and in particular, Treg-intrinsic CTLA-4 is circumvented.

Bcl6 controls the Th2 inflammatory activity of regulatory T cells by repressing Gata3 function

The transcriptional repressor Bcl6 is a critical arbiter of Th cell fate, promoting the follicular Th lineage while repressing other Th cell lineages. Bcl6-deficient (Bcl6(-/-)) mice develop a spontaneous and severe Th2-type inflammatory disease, thus warranting assessment of Bcl6 in regulatory T cell (Treg) function. Bcl6(-/-) Tregs were competent at suppressing T cell proliferation in vitro and Th1-type colitogenic T cell responses in vivo. In contrast, Bcl6(-/-) Tregs strongly exacerbated lung inflammation in a model of allergic airway disease and promoted higher Th2 responses, including systemic upregulation of microRNA-21. Further, Bcl6(-/-) Tregs were selectively impaired at controlling Th2 responses, but not Th1 and Th17 responses, in mixed chimeras of Bcl6(-/-) bone marrow with Foxp3(-/-) bone marrow. Bcl6(-/-) Tregs displayed increased levels of the Th2 transcription factor Gata3 and other Th2 and Treg genes. Bcl6 potently repressed Gata3 transcriptional transactivation, providing a mechanism for the increased expression of Th2 genes by Bcl6(-/-) Tregs. Gata3 has a critical role in regulating Foxp3 expression and functional fitness of Tregs; however, the signal that regulates Gata3 and restricts its transactivation of Th2 cytokines in Tregs has remained unexplored. Our results identify Bcl6 as an essential transcription factor regulating Gata3 activity in Tregs. Thus, Bcl6 represents a crucial regulatory layer in the Treg functional program that is required for specific suppression of Gata3 and Th2 effector responses by Tregs.

Immune tolerance: are regulatory T cell subsets needed to explain suppression of autoimmunity?

The potential for self-reactive T cells to cause autoimmune disease is held in check by Foxp3(+) regulatory T cells (Tregs), essential mediators of peripheral immunological tolerance. Tregs have the capacity to suppress multiple branches of the immune system, tightly controlling the different subsets of effector T cells across multiple different tissue environments. Recent genetic experiments have found mutations that disrupt specific Treg: effector T cell relationships, leading to the possibility that subsets of Tregs are required to suppress each subset of effector T cells. Here we review the environmental factors and mechanisms that allow Tregs to suppress specific subsets of effector T cells, and find that a parsimonious explanation of the genetic data can be made without invoking Treg subsets. Instead, Tregs show a functional and chemotactic plasticity based on microenvironmental influences that allows the common pool of cells to suppress multiple distinct immune responses.

The Biology of Autoimmune Response in the Scurfy Mice that Lack the CD4+Foxp3+ Regulatory T-Cells

Due to a mutation in the Foxp3 transcription factor, Scurfy mice lack regulatory T-cells that maintain self-tolerance of the immune system. They develop multi-organ inflammation (MOI) and die around four weeks old. The affected organs are skin, tail, lungs and liver. In humans, endocrine and gastrointestinal inflammation are also observed, hence the disease is termed IPEX (Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked) syndrome. The three week period of fatal MOI offers a useful autoimmune model in which the controls by genetics, T-cell subsets, cytokines, and effector mechanisms could be efficiently investigated. In this report, we will review published work, summarize our recent studies of Scurfy double mutants lacking specific autoimmune-related genes, discuss the cellular and cytokine controls by these genes on MOI, the organ-specificities of the MOI controlled by environments, and the effector mechanisms regulated by specific Th cytokines, including several newly identified control mechanisms for organ-specific autoimmune response.

OX40 and CD30 signals in CD4(+) T-cell effector and memory function: a distinct role for lymphoid tissue inducer cells in maintaining CD4(+) T-cell memory but not effector function

CD4(+) effector and memory T cells play a pivotal role in the development of both normal and pathogenic immune responses. This review focuses on the molecular and cellular mechanisms that regulate their development, with particular focus on the tumor necrosis factor superfamily members OX40 (TNFRSF4) and CD30 (TNFRSF8). We discuss the evidence that in mice, these molecular signaling pathways act synergistically to regulate the development of both effector and memory CD4(+) T cells but that the cells that regulate memory versus effector function are distinct, effectively allowing the independent regulation of the memory and effector CD4(+) T-cell pools.

Lymphoid tissue inducer cells: innate cells critical for CD4+ T cell memory responses?

Lymphoid tissue inducer cells (LTi) are a relatively new arrival on the immunological cellular landscape, having first been characterized properly only 15 years ago. They are members of an emerging family of innate lymphoid cells (ILCs). Elucidation of their function reveals links not only with the ancient innate immune system, but also with adaptive immune responses, in particular the development of lymph nodes and CD4(+) T cell memory immune responses, which on one hand underpin the success of vaccination strategies, and on the other hand drive many human immunologically mediated diseases. This perspective article is not an exhaustive account of the role of LTi in the development of lymphoid tissues, as there have been many excellent reviews published already. Instead, we combine current knowledge of genetic phylogeny and comparative immunology, together with classical mouse genetics, to suggest how LTi might have evolved from a primitive lymphocytic innate cell in the ancestral 500-million-year-old vertebrate immune system into a cell critical for adaptive CD4(+) T cell immune responses in mammals.

Foxp3⁺ regulatory T cells exert asymmetric control over murine helper responses by inducing Th2 cell apoptosis

Foxp3(+) regulatory T cells play a pivotal role in maintaining self-tolerance and immune homeostasis. In the absence of regulatory T cells, generalized immune activation and multiorgan T cell-driven pathology occurs. Although the phenomenon of immunologic control by Foxp3(+) regulatory T cells is well recognized, the comparative effect over different arms of the immune system has not been thoroughly investigated. Here, we generated a cohort of mice with a continuum of regulatory T-cell frequencies ranging from physiologic levels to complete deficiency. This titration of regulatory T-cell depletion was used to determine how different effector subsets are controlled. We found that in vivo Foxp3(+) regulatory T-cell frequency had a proportionate relationship with generalized T-cell activation and Th1 magnitude, but it had a surprising disproportionate relationship with Th2 magnitude. The asymmetric regulation was associated with efficient suppression of Th2 cells through additional regulations on the apoptosis rate in Th2 cells and not Th1 cells and could be replicated by CTLA4-Ig or anti-IL-2 Ab. These results indicate that the Th2 arm of the immune system is under tighter control by regulatory T cells than the Th1 arm, suggesting that Th2-driven diseases may be more responsive to regulatory T-cell manipulation.

Abrogation of CD30 and OX40 signals prevents autoimmune disease in FoxP3-deficient mice

FoxP3-deficient mice are rescued from tissue and organ destruction and subsequent lethal autoimmune disease by the combined absence of OX40 and CD30 signals.

Our previous studies have implicated signaling through the tumor necrosis family receptors OX40 and CD30 as critical for maintaining CD4 memory responses. We show that signals through both molecules are also required for CD4 effector-mediated autoimmune tissue damage. Under normal circumstances, male mice deficient in the forkhead transcription factor FoxP3, which lack regulatory CD4 T cells, develop lethal autoimmune disease in the first few weeks of life. However, in the combined absence of OX40 and CD30, FoxP3-deficient mice develop normally and breed successfully. The extensive tissue infiltration and organ destruction characteristic of FoxP3 disease does not appear in these mice, and their mortality is not associated with autoimmunity. Although the absence of OX40 plays the dominant role, FoxP3-deficient mice sufficient in CD30 but deficient in OX40 signals still eventually develop lethal disease. This result was supported by the observation that blocking antibodies to OX40 and CD30 ligands also abrogated disease mediated by FoxP3-deficient T cells. These observations identify OX40 and CD30 signals as essential for the development of clinically relevant CD4-dependent autoimmunity and suggest that combination therapies that abrogate these signals might be used to treat established human autoimmune diseases.

Genetic control of the inflammatory T-cell response in regulatory T-cell deficient scurfy mice

IPEX (Immunodysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome is a rare, recessive disorder in patients with mutations in the foxp3 gene, the normal expression of which is required for the generation of functional regulatory T-cells. Scurfy mice also bear a mutation in the foxp3, and like IPEX patients, spontaneously develop multi-organ inflammation. As reviewed herein, breeding immune response genes into Scurfy mice has provided useful insight into how the inflammatory T-cell response is regulated in the absence of regulatory T-cells and post regulatory T-cell checkpoint. Of particular interest are those that preferentially affect the inflammatory T-cell response in an "apparent" organ-specific manner, implying that specific mechanisms of control exist for individual organs during multi-organ inflammation.

Autoimmune polyglandular syndromes

The autoimmune polyglandular syndromes-a group of syndromes comprising a combination of endocrine and nonendocrine autoimmune diseases-differ in their component diseases and in the immunologic features of their pathogenesis. One of the three main syndromes, type 1 autoimmune polyglandular syndrome (APS-1), has a unique pathogenic mechanism owing to mutations in the autoimmune regulator (AIRE) gene, which results in the loss of central tolerance-a process by which developing T cells with potential reactivity for self-antigens are eliminated during early differentiation in the thymus. Patients with IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) syndrome harbor mutations in the forkhead box P3 (FOXP3) gene in regulatory T cells, which leads to severe autoimmunity and immune deficiency. Although both of these disorders are rare, their well-defined mechanisms of disease provide a basis for the understanding of the more common condition, APS-2. In this syndrome, alleles of human leukocyte antigens (HLAs) determine the targeting of specific tissues by autoreactive T cells, which leads to organ-specific autoimmunity as a result of this loss of tolerance. Non-HLA genes also contribute to autoimmunity in APS-2 and, depending on the polymorphism, potentially predispose to a loss of tolerance or influence which organ is specifically targeted. This Review discusses the genetic basis of APS-1, APS-2 and IPEX syndrome, with an emphasis on the mechanisms of autoimmunity and presents currently available therapies to treat their underlying autoimmune disorders.

Immunologic endocrine disorders

Autoimmunity affects multiple glands in the endocrine system. Animal models and human studies highlight the importance of alleles in HLA-like molecules determining tissue-specific targeting that, with the loss of tolerance, leads to organ-specific autoimmunity. Disorders such as type 1A diabetes, Graves disease, Hashimoto thyroiditis, Addison disease, and many others result from autoimmune-mediated tissue destruction. Each of these disorders can be divided into stages beginning with genetic susceptibility, environmental triggers, active autoimmunity, and finally metabolic derangements with overt symptoms of disease. With an increased understanding of the immunogenetics and immunopathogenesis of endocrine autoimmune disorders, immunotherapies are becoming prevalent, especially in patients with type 1A diabetes. Immunotherapies are being used more in multiple subspecialty fields to halt disease progression. Although therapies for autoimmune disorders stop the progress of an immune response, immunomodulatory therapies for cancer and chronic infections can also provoke an unwanted immune response. As a result, there are now iatrogenic autoimmune disorders arising from the treatment of chronic viral infections and malignancies.

Nonfunctional regulatory T cells and defective control of Th2 cytokine production in natural scurfy mutant mice

Foxp3(+) regulatory T cells (Tregs) are crucial for preventing autoimmunity. We have demonstrated that depletion of Foxp3(+) Tregs results in the development of a scurfy-like disease, indicating that Foxp3(-) effector T cells are sufficient to induce autoimmunity. It has been postulated that nonfunctional Tregs carrying potentially self-reactive T cell receptors may contribute to scurfy (sf) pathogenesis due to enhanced recognition of self. Those cells, however, could not be identified in sf mutants due to the lack of Foxp3 protein expression. To address this issue, we crossed the natural sf mouse mutant with bacterial artificial chromosome transgenic DEREG (depletion of regulatory T cells) mice. Since DEREG mice express GFP under the control of an additional Foxp3 promoter, those crossings allowed proving the existence of "would-be" Tregs, which are characterized by GFP expression in the absence of functional Foxp3. Sf Tregs lost their in vitro suppressive capacity. This correlated with a substantial reduction of intracellular cAMP levels, whereas surface expression of Treg markers was unaffected. Both GFP(+) and GFP(-) sf cells produced high amounts of Th2-type cytokines, reflected also by enhanced Gata-3 expression, when tested in vitro. Nevertheless, sf Tregs could be induced in vitro, although with lower efficiency than DEREG Tregs. Transfer of GFP(+) sf Tregs, in contrast to GFP(-) sf T cells, into RAG1-deficient animals did not cause the sf phenotype. Taken together, natural and induced Tregs develop in the absence of Foxp3 in sf mice, which lack both suppressive activity and autoreactive potential, but rather display a Th2-biased phenotype.

Regulation of multi-organ inflammation in the regulatory T cell-deficient scurfy mice

Scurfy mice display the most severe form of multi-organ inflammation due to total lack of the CD4+Foxp3+ regulatory T cells (Treg) resulted from a mutation of the X-linked transcription factor Foxp3. A large repertoire of Treg-suppressible, inflammation-inducing T cells was demonstrated by adoptive transfer experiments using Rag1-/- mice as recipients and by prolongation of lifespan through breeding with Faslpr/lpr mutant. Inflammation in the ear, eyes, skin, tail, salivary glands, lungs, stomach, pancreas, liver, small intestine, colon, skeletal muscle, and accessory reproductive organs are identified. Genetic and cellular regulations of specific organ inflammation are described. Sf mice may be useful for the identification of organ-specific antigens and Treg capable of suppressing inflammation in an organ-specific manner. Sf mice are also useful to determine the important inflammation process at the checkpoint after Treg regulation using genetic analysis through breeding.

Dicer-dependent microRNA pathway safeguards regulatory T cell function

Regulatory T (T reg) cells are indispensable for preventing autoimmunity. Incumbent to this role is the ability of T reg cells to exert their suppressor function under inflammatory conditions. We found that T reg cell–mediated tolerance is critically dependent on the Dicer-controlled microRNA (miRNA) pathway. Depletion of miRNA within the T reg cell lineage resulted in fatal autoimmunity indistinguishable from that in T reg cell–deficient mice. In disease-free mice lacking Dicer in all T cells or harboring both Dicer-deficient and -sufficient T reg cells, Dicer-deficient T reg cells were suppressive, albeit to a lesser degree, whereas their homeostatic potential was diminished as compared with their Dicer-sufficient counterparts. However, in diseased mice, Dicer-deficient T reg cells completely lost suppressor capacity. Thus, miRNA preserve the T reg cell functional program under inflammatory conditions.