A Defect in Thymic Tolerance Causes T Cell-Mediated Autoimmunity in a Murine Model of COPA Syndrome

The pathogenesis, clinical presentations and treatment of monogenic systemic vasculitis

Many monogenic autoinflammatory diseases, including DADA2 (deficiency of adenosine deaminase 2), HA20 (haploinsufficiency of A20), SAVI (STING-associated vasculopathy with onset in infancy), COPA syndrome, LAVLI (LYN kinase-associated vasculopathy and liver fibrosis) and VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome, present predominantly with vasculitis and constitute a substantial subgroup of vasculitic conditions associated with a 'probable aetiology'. The spectrum of monogenic vasculitis encompasses all sizes and types of blood vessel, ranging from large vessels to medium-size and small vessels, and from the arterial side to the venous side of the vasculature. Monogenic vasculitis typically starts early in life during infancy or childhood; VEXAS syndrome, which presents in late adulthood, is an exception. The activation of myeloid cells via inflammasome and nuclear factor-κB pathways, type I interferon-enhanced autoimmune mechanisms and/or dysregulated adaptive immune responses have an important role in the development of immune-mediated endothelial dysfunction and vascular damage. Genetic testing is essential for the diagnosis of underlying monogenic autoinflammatory diseases; however, the penetrance of genetic variants can vary. Increased awareness and recognition of distinctive clinical findings could facilitate earlier diagnosis and allow for more-targeted treatments.

COPA Syndrome-From Pathogenesis to Treatment

Coatomer subunit α (COPA) syndrome is a mendelian autosomal dominant immune dysregulation disease characterized by early onset lung disease in the form of diffuse alveolar hemorrhaging or interstitial lung disease, frequently associated with arthritis, glomerulonephritis, and high titer autoantibodies usually mimicking other autoimmune diseases. While immunosuppressive medication has been effective in controlling arthritis, data on long-term lung disease control remains scarce, which poses a real challenge as the progression of lung disease is the main cause of poor life expectancy in COPA patients. Nevertheless, JAK inhibitor therapy seems to be the most promising therapeutic choice now.

Non-infectious mixed cryoglobulinemia as a new clinical presentation of mutation in the gene encoding coatomer subunit alpha: a case report of two adult sisters

Cryoglobulinemia is a rare disease characterized by the presence of cryoglobulins in the blood serum. It is usually caused by autoimmune, lymphoproliferative, or infectious factors. The pathogenesis of cryoglobulinemia is not well understood, therefore, genetic testing is very important. We present the case of two adult sisters with different clinical phenotypes of non-infectious cryoglobulinemic vasculitis associated with a rare genetic variant [(Hg38) 1:160323529 C>G, NP_004362.2:p.(Gly203Ala)]. One of the sisters suffered from essential mixed cryoglobulinemia, while the other suffered from cryoglobulinemia associated with systemic connective tissue disease. In both cases, genetic tests revealed a variant in the COPA gene, encoding coatomer subunit alpha. Mutations in the COPA gene are associated with COPA syndrome, an autoimmune interstitial lung, joint, and kidney monogenic disease, found mainly in children. Only 15 pathogenic COPA variants have been reported thus far which suggests that the full spectrum of disease manifestations remains unknown. Ours is the first report of the association of the COPA gene with non-infectious cryoglobulinemic vasculitis in adults. This unexpected finding may direct research into the pathogenesis of cryoglobulinemia and new treatment strategies for this rare disease.

Activation of autoreactive lymphocytes in the lung by radioresistant cells expressing a STING gain-of-function mutation

Gain-of-function mutations in the dsDNA sensing adaptor STING lead to a severe autoinflammatory syndrome known as STING-associated vasculopathy with onset in infancy (SAVI). Patients with SAVI develop interstitial lung disease (ILD) and produce autoantibodies that are commonly associated with systemic autoimmune diseases. Mice expressing the most common SAVI mutation, STING V154M (VM), similarly develop ILD but exhibit severe T and B cell lymphopenia and low serum Ig titers, and they lack autoantibodies. Importantly, lethally irradiated VM hosts reconstituted with WT stem cells (WT→VM) still develop ILD. In this study, we find that WT→VM chimeras had restored B cell function, produced autoantibodies, and thereby recapitulated the loss of tolerance seen in patients with SAVI. Lymphocytes derived from both WT and BCR or TCR transgenic (Tg) donors accumulated in the extravascular lung tissue of WT+Tg→VM mixed chimeras, but lymphocyte activation and germinal center formation required WT cells with a diverse repertoire. Furthermore, when T cells isolated from the WT→VM chimeras were adoptively transferred to naive Rag1-deficient secondary hosts, they trafficked to the lung and recruited neutrophils. Overall, these findings indicated that VM expression by radioresistant cells promoted the activation of autoreactive B cells and T cells that then differentiated into potentially pathogenic effector subsets.

Endothelial cell expression of a STING gain-of-function mutation initiates pulmonary lymphocytic infiltration

Patients afflicted with Stimulator of interferon gene (STING) gain-of-function mutations frequently present with debilitating interstitial lung disease (ILD) that is recapitulated in mice expressing the STINGV154M mutation (VM). Prior radiation chimera studies revealed an unexpected and critical role for non-hematopoietic cells in initiating ILD. To identify STING-expressing non-hematopoietic cell types required for the development of ILD, we use a conditional knockin (CKI) model and direct expression of the VM allele to hematopoietic cells, fibroblasts, epithelial cells, or endothelial cells. Only endothelial cell-targeted VM expression results in enhanced recruitment of immune cells to the lung associated with elevated chemokine expression and the formation of bronchus-associated lymphoid tissue, as seen in the parental VM strain. These findings reveal the importance of endothelial cells as instigators of STING-driven lung disease and suggest that therapeutic targeting of STING inhibitors to endothelial cells could potentially mitigate inflammation in the lungs of STING-associated vasculopathy with onset in infancy (SAVI) patients or patients afflicted with other ILD-related disorders.

Activated STING in the thymus alters T cell development and selection leading to autoimmunity

Classifying systemic inflammatory disorders as autoinflammatory or autoimmune provides insight into disease pathogenesis and whether treatment should target innate molecules and their signaling pathways or the adaptive immune response. COPA syndrome is a monogenic disorder of immune dysregulation that leads to interstitial lung disease and high-titer autoantibodies. Studies show constitutive activation of the innate immune molecule STING is centrally involved in disease. However, the mechanisms by which STING results in loss of T cell tolerance and autoimmunity in COPA syndrome or more common autoimmune diseases is not understood. Using CopaE241K/+ mice, we uncovered a functional role for STING in the thymus. Single cell data of human thymus demonstrates STING is highly expressed in medullary thymic epithelial cells (mTECs) involved in processing and presenting self-antigens to thymocytes. In CopaE241K/+ mice, activated STING in mTECs triggered interferon signaling, impaired macroautophagy and caused a defect in negative selection of T cells. Wild-type mice given a systemic STING agonist phenocopied the selection defect and showed enhanced thymic escape of a T cell clone targeting a self-antigen also expressed in melanoma. Our work demonstrates STING activation in TECs shapes the T cell repertoire and contributes to autoimmunity, findings important for settings that activate thymic STING.

Autoinflammatory Diseases Due to Defects in Degradation or Transport of Intracellular Proteins

The number of human inborn errors of immunity has now gone beyond 430. The responsible gene variants themselves are apparently the cause for the disorders, but the underlying molecular or cellular mechanisms for the pathogenesis are often unclear. In order to clarify the pathogenesis, the mutant mice carrying the gene variants are apparently useful and important. Extensive analysis of those mice should contribute to the clarification of novel immunoregulatory mechanisms or development of novel therapeutic maneuvers critical not only for the rare monogenic diseases themselves but also for related common polygenic diseases. We have recently generated novel model mice in which complicated manifestations of human inborn errors of immunity affecting degradation or transport of intracellular proteins were recapitulated. Here, we review outline of these disorders, mainly based on the phenotype of the mutant mice we have generated.

COPI coatomer subunit α-COP interacts with the RNA binding protein Nucleolin via a C-terminal dilysine motif

The COPI coatomer subunit α-COP has been shown to co-precipitate mRNA in multiple settings, but it was unclear whether the interaction with mRNA was direct or mediated by interaction with an adapter protein. The COPI complex often interacts with proteins via C-terminal dilysine domains. A search for candidate RNA binding proteins with C-terminal dilysine motifs yielded Nucleolin, which terminates in a KKxKxx sequence. This protein was an especially intriguing candidate as it has been identified as an interacting partner for Survival Motor Neuron protein (SMN). Loss of SMN causes the neurodegenerative disease Spinal Muscular Atrophy. We have previously shown that SMN and α-COP interact and co-migrate in axons, and that overexpression of α-COP reduced phenotypic severity in cell culture and animal models of SMA. We show here that in an mRNA independent manner, endogenous Nucleolin co-precipitates endogenous α-COP and ε-COP but not β-COP which may reflect an interaction with the so-called B-subcomplex rather a complete COPI heptamer. The ability of Nucleolin to bind to α-COP requires the presence of the C-terminal KKxKxx domain of Nucleolin. Furthermore, we have generated a point mutant in the WD40 domain of α-COP which eliminates its ability to co-precipitate Nucleolin but does not interfere with precipitation of partners mediated by non-KKxKxx motifs such as the kainate receptor subunit 2. We propose that via interaction between the C-terminal dilysine motif of Nucleolin and the WD40 domain of α-COP, Nucleolin acts an adaptor to allow α-COP to interact with a population of mRNA.

COPA Syndrome from Diagnosis to Treatment: A Clinician's Guide

COPA syndrome is a recently described autosomal dominant inborn error of immunity characterized by high titer autoantibodies and interstitial lung disease, with many individuals also having arthritis and nephritis. Onset is usually in early childhood, with unique disease features including alveolar hemorrhage, which can be insidious, pulmonary cyst formation, and progressive pulmonary fibrosis in nonspecific interstitial pneumonia or lymphocytic interstitial pneumonia patterns. This review explores the clinical presentation, genetics, molecular mechanisms, organ manifestations, and treatment approaches for COPA syndrome, and presents a diagnostic framework of suggested indications for patient testing.

Targeting STING-mediated pro-inflammatory and pro-fibrotic effects of alveolar macrophages and fibroblasts blunts silicosis caused by silica particles

Silica is utilized extensively in industrial and commercial applications as a chemical raw material, increasing its exposure and hazardous potential to populations, with silicosis serving as an important representative. Silicosis is characterized by persistent lung inflammation and fibrosis, for which the underlying pathogenesis of silicosis is unclear. Studies have shown that the stimulating interferon gene (STING) participates in various inflammatory and fibrotic lesions. Therefore, we speculated that STING might also play a key role in silicosis. Here we found that silica particles drove the double-stranded DNA (dsDNA) release to activate the STING signal pathway, contributing to alveolar macrophages (AMs) polarization by secreting diverse cytokines. Then, multiple cytokines could generate a micro-environment to exacerbate inflammation and promote the activation of lung fibroblasts, hastening fibrosis. Intriguingly, STING was also crucial for the fibrotic effects induced by lung fibroblasts. Loss of STING could effectively inhibit silica particles-induced pro-inflammatory and pro-fibrotic effects by regulating macrophages polarization and lung fibroblasts activation to alleviate silicosis. Collectively, our results have revealed a novel pathogenesis of silica particles-caused silicosis mediated by the STING signal pathway, indicating that STING may be regarded as a promising therapeutic target in the treatment of silicosis.

Activation of Autoreactive Lymphocytes in the Lung by STING Gain-of-function Mutation Radioresistant Cells

Gain-of-function mutations in the dsDNA sensing adaptor STING lead to a severe autoinflammatory syndrome known as STING-associated vasculopathy with onset in Infancy (SAVI). SAVI patients develop interstitial lung disease (ILD) and commonly produce anti-nuclear antibodies (ANAs), indicative of concomitant autoimmunity. Mice heterozygous for the most common SAVI mutation, V154M (VM), also develop ILD, triggered by nonhematopoietic VM cells, but exhibit severe peripheral lymphopenia, low serum Ig titers and fail to produce autoantibodies. In contrast, we now show that lethally irradiated VM mice reconstituted with WT stem cells (WT→VM chimeras) develop ANAs and lung-reactive autoantibodies associated with accumulation of activated lymphocytes and formation of germinal centers in lung tissues. Moreover, when splenocytes from WT→VM chimeras were adoptively transferred into unmanipulated Rag1 -/- mice, donor T cells accumulated in the lung. Overall, these findings demonstrate that expression of the VM mutation in non-hematopoietic cells can promote the activation of immunocompetent autoreactive lymphocytes.

Summary

Chimeric mice expressing STING only in non-hematopoietic cells develop systemic and lung directed autoimmunity which recapitulates what is seen in pediatric patients with SAVI disease.

Expression of a STING Gain-of-function Mutation in Endothelial Cells Initiates Lymphocytic Infiltration of the Lungs

Patients afflicted with STING gain-of-function mutations frequently present with debilitating interstitial lung disease ( ILD ) that is recapitulated in mice expressing the STING V154M mutation ( VM ). Prior radiation chimera studies revealed an unexpected and critical role for non-hematopoietic cells in the initiation of ILD. To identify STING-expressing non-hematopoietic cell types relevant to ILD, we generated a conditional knock-in ( CKI ) model in which expression of the VM allele was directed to hematopoietic cells, fibroblasts, epithelial cells, or endothelial cells. Only endothelial cell-targeted expression of the mutant allele resulted in the recruitment of immune cells to the lung and the formation of bronchus-associated lymphoid tissue, as seen in the parental VM strain. These findings reveal the importance of endothelial cells as instigators of STING-driven lung disease and suggest that therapeutic targeting of STING inhibitors to endothelial cells could potentially mitigate inflammation in the lungs of SAVI patients or patients afflicted with other ILD-related disorders.

Summary

Patients with STING gain-of-function (GOF) mutations develop life-threatening lung autoinflammation. In this study, Gao et al. utilize a mouse model of conditional STING GOF to demonstrate a role for endothelial STING GOF in initiating immune cell recruitment into lung tissues of SAVI mice.

STING trafficking as a new dimension of immune signaling

The cGAS-STING pathway is an evolutionarily conserved immune signaling pathway critical for microbial defense. Unlike other innate immune pathways that largely rely on stationary cascades of signaling events, STING is highly mobile in the cell. STING is activated on the ER, but only signals after it arrives on the Golgi, and then it is quickly degraded by the lysosome. Each step of STING trafficking through the secretory pathway is regulated by host factors. Homeostatic STING trafficking via COPI-, COPII-, and clathrin-coated vesicles is important for maintaining baseline tissue and cellular immunity. Aberrant vesicular trafficking or lysosomal dysfunction produces an immune signal through STING, which often leads to tissue pathology in mice and humans. Many trafficking-mediated diseases of STING signaling appear to impact the central nervous system, leading to neurodegeneration. Therefore, STING trafficking introduces a new dimension of immune signaling that likely has broad implications in human disease.

Depletion of COPI in cancer cells: the role of reactive oxygen species in the induction of lipid accumulation, noncanonical lipophagy and apoptosis

The coatomer protein complex 1 (COPI) is a multisubunit complex that coats intracellular vesicles and is involved in intracellular protein trafficking. Recently we and others found that depletion of COPI complex subunits zeta (COPZ1) and delta (ARCN1) preferentially kills tumor cells relative to normal cells. Here we delineate the specific cellular effects and sequence of events of COPI complex depletion in tumor cells. We find that this depletion leads to the inhibition of mitochondrial oxidative phosphorylation and the elevation of reactive oxygen species (ROS) production, followed by accumulation of lipid droplets (LDs) and autophagy-associated proteins LC3-II and SQSTM1/p62 and, finally, apoptosis of the tumor cells. Inactivation of ROS in COPI-depleted cells with the mitochondrial-specific quencher, mitoquinone mesylate, attenuated apoptosis and markedly decreased both the size and the number of LDs. COPI depletion caused ROS-dependent accumulation of LC3-II and SQSTM1 which colocalizes with LDs. Lack of double-membrane autophagosomes and insensitivity to Atg5 deletion suggested an accumulation of a microlipophagy complex on the surface of LDs induced by depletion of the COPI complex. Our findings suggest a sequence of cellular events triggered by COPI depletion, starting with inhibition of oxidative phosphorylation, followed by ROS activation and accumulation of LDs and apoptosis.

STING Targeting in Lung Diseases

The cGAS-STING pathway displays important functions in the regulation of innate and adaptive immunity following the detection of microbial and host-derived DNA. Here, we briefly summarize biological functions of STING and review recent literature highlighting its important contribution in the context of respiratory diseases. Over the last years, tremendous progress has been made in our understanding of STING activation, which has favored the development of STING agonists or antagonists with potential therapeutic benefits. Antagonists might alleviate STING-associated chronic inflammation and autoimmunity. Furthermore, pharmacological activation of STING displays strong antiviral properties, as recently shown in the context of SARS-CoV-2 infection. STING agonists also elicit potent stimulatory activities when used as an adjuvant promoting antitumor responses and vaccines efficacy.

Intracellular Sensing of DNA in Autoinflammation and Autoimmunity

Evidence has shown that DNA is a pathogen-associated molecular pattern, posing a unique challenge in the discrimination between endogenous and foreign DNA. This challenge is highlighted by certain autoinflammatory diseases that arise from monogenic mutations and result in periodic flares of inflammation, typically in the absence of autoantibodies or antigen-specific T lymphocytes. Several autoinflammatory diseases arise due to mutations in genes that normally prevent the accrual of endogenous DNA or are due to mutations that cause activation of intracellular DNA-sensing pathway components. Evidence from genetically modified murine models further support an ability of endogenous DNA and DNA sensing to drive disease pathogenesis, prompting the question of whether endogenous DNA can also induce inflammation in human autoimmune diseases. In this review, we discuss the current understanding of intracellular DNA sensing and downstream signaling pathways as they pertain to autoinflammatory disease, including the development of monogenic disorders such as Stimulator of interferon genes-associated vasculopathy with onset in infancy and Aicardi-Goutières syndrome. In addition, we discuss systemic rheumatic diseases, including certain forms of systemic lupus erythematosus, familial chilblain lupus, and other diseases with established links to intracellular DNA-sensing pathways, and highlight the lessons learned from these examples as they apply to the development of therapies targeting these pathways.

MITA/STING-mediated antiviral immunity and autoimmunity: the evolution, mechanism, and intervention

Mediator of IRF3 activation (MITA, also known as stimulator of interferon genes (STING) and endoplasmic reticulum interferon stimulator (ERIS)) is an ER-associated protein that senses cellular and bacterium-derived cyclic dinucleotide (CDN), leading to induction of type-I interferons (IFNs) and innate immune responses against viruses and bacteria. Recently, it has become clear that sensing of CDN and induction of autophagy are two evolutionarily conserved functions of MITA, predating its role in mediating type-I IFN induction. Studies have shown that MITA-mediated signaling promotes a number of autoimmune disorders caused by gene mutations in human. Here, we summarize the most recent progress on MITA-mediated signaling in a view of evolution and highlight the roles of MITA in human inflammatory disorders caused by gene mutations and in genetically modified mouse models. We also briefly introduce the chemicals targeting MITA and discuss their potential in treatment of MITA-mediated inflammatory diseases. Finally, we propose several key questions that should be addressed for targeting MITA for treatment of related autoimmune diseases.

Genetic diagnosis of immune dysregulation can lead to targeted therapy for interstitial lung disease: A case series and single center approach

In recent years, a growing number of monogenic disorders have been described that are characterized by immune dysregulation. A subset of these "primary immune regulatory disorders" can cause severe interstitial lung disease, often recognized in late childhood or adolescence. Patients presenting to pulmonary clinic may have long and complex medical histories, but lack a unifying genetic diagnosis. It is crucial for pulmonologists to recognize features suggestive of multisystem immune dysregulation and to initiate genetic workup, since targeted therapies based on underlying genetics may halt or even reverse pulmonary disease progression. Through such an approach, our center has been able to diagnose and treat a cohort of patients with interstitial lung disease from gene defects that affect immune regulation. Here we present representative cases related to pathogenic variants in three distinct pathways and summarize disease manifestations and treatment approaches. We conclude with a discussion of our perspective on the outstanding challenges for diagnosing and managing these complex life-threatening and chronic disorders.

Dysregulation of the cGAS-STING Pathway in Monogenic Autoinflammation and Lupus

One of the oldest mechanisms of immune defense against pathogens is through detection of foreign DNA. Since human DNA is compartmentalized into the nucleus, its presence in the cytosol heralds a potential threat. The cGAS-STING pathway is one of the most important cytosolic DNA sensing pathways and leads to interferon signaling, inflammasome activation, autophagy, and cell death. While STING signaling is protective at physiologic levels, chronic activation of this pathway can instead drive autoinflammation and autoimmunity. Here we discuss several monogenic disorders of the STING pathway that highlight its impact on both innate and adaptive immunity in the progressive loss of tolerance. The potential relevance of STING signaling in systemic lupus erythematosus is then discussed with a focus on future avenues for monitoring and targeting this pathway.

Pathogenic insights from genetic causes of autoinflammatory inflammasomopathies and interferonopathies

A number of systemic autoinflammatory diseases arise from gain-of-function mutations in genes encoding IL-1-activating inflammasomes or cytoplasmic nucleic acid sensors including the receptor and sensor STING and result in increased IL-1 and type I interferon production, respectively. Blocking these pathways in human diseases has provided proof-of-concept, confirming the prominent roles of these cytokines in disease pathogenesis. Recent insights into the multilayered regulation of these sensor pathways and insights into their role in amplifying the disease pathogenesis of monogenic and complex genetic diseases spurred new drug development targeting the sensors. This review provides insights into the pathogenesis and genetic causes of these "prototypic" diseases caused by gain-of function mutations in IL-1-activating inflammasomes (inflammasomopathies) and in interferon-activating pathways (interferonopathies) including STING-associated vasculopathy with onset in infancy, Aicardi-Goutieres syndrome, and proteasome-associated autoinflammatory syndromes that link activation of the viral sensors STING, "self" nucleic acid metabolism, and the ubiquitin-proteasome system to "type I interferon production" and human diseases. Clinical responses and biomarker changes to Janus kinase inhibitors confirm a role of interferons, and a growing number of diseases with "interferon signatures" unveil extensive cross-talk between major inflammatory pathways. Understanding these interactions promises new tools in tackling the significant clinical challenges in treating patients with these conditions.

Allograft Dysfunction After Lung Transplantation for COPA Syndrome: A Case Report and Literature Review

COPA syndrome is an autoinflammatory disease with autoimmune and autoinflammatory manifestations affecting lungs, joints, and kidneys. COPA syndrome is caused by heterozygous loss-of-function mutations in the coatmer subunit alpha (COPA) gene, encoding α subunit of coatmer protein complex I (COP-I) coated vesicles. Mutant COPA induces constitutive activation of stimulator of interferon (IFN) genes (STING), leading to systemic inflammation and elevated type I interferon response. We have previously reported a Japanese family of COPA syndrome with a novel V242G mutation. Two out of 4 patients required lung transplantation due to intractable interstitial lung disease (ILD) and respiratory failure. Both of them deceased after lung transplantation, one due to sepsis and the other due to allograft dysfunction possibly caused by the reccurent ILD. The literature review indentified unfavorable outcome of the solid organ transplant in COPA syndrome and its related disease, however, precise clinico-pathological description of these cases has been scarce. Here, we report in detail the clinical course of our cases to clarify the pathophysiology of allograft dysfunction in COPA syndrome and propose potential therapeutic approaches to improve post-transplant graft survival.

The cGAS-STING Pathway: A Promising Immunotherapy Target

With the continuous development of immunotherapy, researchers have paid more attention to the specific immune regulatory mechanisms of various immune responses in different diseases. As a novel and vital innate immune signal pathway, the cGAS-STING signal pathway activated by nucleic acid substances, interplays with other immune responses, by which it participates in regulating cancer, autoimmune and inflammatory diseases, microbial and parasitic infectious diseases, and other diseases. With the exception of its role in innate immunity, the growing list of researches demonstrated expanding roles of the cGAS-STING signal pathway in bridging the innate immunity (macrophage polarization) with the adaptive immunity (T lymphocytes differentiation). Macrophages and T lymphocytes are the most representative cells of innate immunity and adaptive immunity, respectively. Their polarization or differentiation are involved in the pathogenesis and progression of various diseases. Here we mainly summarized recent advanced discoveries of how the cGAS-STING signal pathway regulated macrophages polarization and T lymphocytes differentiation in various diseases and vaccine applications, providing a promising direction for the development and clinical application of immunotherapeutic strategies for related diseases.

Monogenic autoimmunity and infectious diseases: the double-edged sword of immune dysregulation

The study of monogenic autoimmune diseases has provided key insights into molecular mechanisms involved in development of autoimmunity and immune tolerance. It has also become clear that such inborn errors of immunity (IEIs) frequently present clinically not only with autoimmune diseases, but also frequently have increased susceptibility to infection. The genes associated with monogenic autoimmunity influence diverse functional pathways, and the resulting immune dysregulation also impacts the complex and coordinated immune response to pathogens, for example type I interferon and cytokine signaling, the complement pathway and proper differentiation of the immune response. The SARS-CoV-2 pandemic has highlighted how monogenic autoimmunity can increase risk for serious infection with the discovery of severe disease in patients with pre-existing antibodies to Type I IFNs. This review discusses recent insight into the relationship between monogenic autoimmunity and infectious diseases.

Augmentation of STING-induced type I interferon production in COPA syndrome

OBJECTIVES

COPA syndrome, also known as an autoinflammatory interstitial lung, joint, and kidney (AILJK) disease, is caused by heterozygous mutations in the coatomer subunit alpha (COPA) gene. We found a novel COPA variant in four patients in one family. We aimed to elucidate whether and how the variant causes manifestations of COPA syndrome by studying these four patients and in a gene-targeted mouse model.

METHOD

We performed whole exome sequencing in seven family members and measured type I interferon (IFN) signature of the peripheral blood cells. We analyzed the effects of COPA variants in in vitro experiments and Copa mutant mice we generated.

RESULTS

We identified a heterozygous variant of COPA gene in the four affected members of the family (c.725T>G, p.Val242Gly). IFN score was high in the members carrying the variant. In vitro analysis revealed that COPA V242G as well as the previously reported disease-causing variants augmented the stimulator of interferon genes (STING)-induced type I IFN promoter activities. Copa^V242G/+ mice manifested interstitial lung disease and STING-dependent elevation of IFN-stimulated genes (ISGs) expression. In Copa^V242G/+ dendritic cells, the STING pathway was not constitutively activated, but hyperactivated upon stimulation and led to increased type I IFN production.

CONCLUSION

V242G, a novel COPA variant, was found in four patients from one family. The gene-targeted mice with V242G variant recapitulated the interstitial lung disease and showed augmented responses of the STING pathway leading to increase of type I IFN production.

Monogenic autoinflammatory disorders: Conceptual overview, phenotype, and clinical approach

Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.

Genetics of Pediatric Immune-Mediated Diseases and Human Immunity

Primary immunodeficiency diseases (PIDs) are a rapidly growing, heterogeneous group of genetically determined diseases characterized by defects in the immune system. While individually rare, collectively PIDs affect between 1/1,000 and 1/5,000 people worldwide. The clinical manifestations of PIDs vary from susceptibility to infections to autoimmunity and bone marrow failure. Our understanding of the human immune response has advanced by investigation and discovery of genetic mechanisms of PIDs. Studying patients with isolated genetic variants in proteins that participate in complex signaling pathways has led to an enhanced understanding of host response to infection, and mechanisms of autoimmunity and autoinflammation. Identifying genetic mechanisms of PIDs not only furthers immunological knowledge but also benefits patients by dictating targeted therapies or hematopoietic stem cell transplantation. Here, we highlight several of these areas in the field of primary immunodeficiency, with a focus on the most recent advances.

STING-Mediated Lung Inflammation and Beyond

Mendelian autoinflammatory diseases characterized by constitutive activation of the type I interferon pathway, the so-called type I interferonopathies, constitute a rapidly expanding group of inborn errors of immunity. Among the type I interferonopathies, STING-associated vasculopathy with onset in infancy (SAVI) and COPA syndrome were described in the last 6 years, both manifesting a major inflammatory lung component associated with significant morbidity and increased mortality. There is striking clinical and histopathological overlap between SAVI and COPA syndrome, although distinct features are also present. Of note, there is a remarkably high frequency of clinical non-penetrance among individuals harboring pathogenic COPA mutations. SAVI is caused by, principally heterozygous, gain-of-function mutations in STING1 (previously referred to as TMEM173) encoding STING, a key adaptor of the interferon signaling pathway induced by DNA. COPA syndrome results from heterozygous dominant-negative mutations in the coatomer protein subunit alpha, forming part of a complex involved in intracellular cargo protein transport between the Golgi and the endoplasmic reticulum (ER). Of importance, a role for COPA in regulating the trafficking of STING, an ER-resident protein which translocates to the Golgi during the process of its activation, was recently defined, thereby possibly explaining some aspects of the phenotypic overlap between SAVI and COPA syndrome. Here, we review the expanding phenotype of these diseases, highlighting common as well as specific features, and recent advances in our understanding of STING biology that have informed therapeutic decision-making in both conditions. Beyond these rare Mendelian disorders, DNA sensing through STING is likely relevant to the pathology of several diseases associated with lung inflammation, including systemic lupus erythematosus, dermatomyositis, environmental toxin exposure, and viral infection.

Thymic origins of autoimmunity-lessons from inborn errors of immunity

During their intrathymic development, nascent T cells are empowered to protect against pathogens and to be operative for a life-long acceptance of self. While autoreactive effector T (Teff) cell progenitors are eliminated by clonal deletion, the intrathymic mechanisms by which thymic regulatory T cell (tTreg) progenitors maintain specificity for self-antigens but escape deletion to exert their regulatory functions are less well understood. Both tTreg and Teff development and selection result from finely coordinated interactions between their clonotypic T cell receptors (TCR) and peptide/MHC complexes expressed by antigen-presenting cells, such as thymic epithelial cells and thymic dendritic cells. tTreg function is dependent on expression of the FOXP3 transcription factor, and induction of FOXP3 gene expression by tTreg occurs during their thymic development, particularly within the thymic medulla. While initial expression of FOXP3 is downstream of TCR activation, constitutive expression is fixed by interactions with various transcription factors that are regulated by other extracellular signals like TCR and cytokines, leading to epigenetic modification of the FOXP3 gene. Most of the understanding of the molecular events underlying tTreg generation is based on studies of murine models, whereas gaining similar insight in the human system has been very challenging. In this review, we will elucidate how inborn errors of immunity illuminate the critical non-redundant roles of certain molecules during tTreg development, shedding light on how their abnormal development and function cause well-defined diseases that manifest with autoimmunity alone or are associated with states of immune deficiency and autoinflammation.

Homeostatic regulation of STING by retrograde membrane traffic to the ER

Coat protein complex I (COP-I) mediates the retrograde transport from the Golgi apparatus to the endoplasmic reticulum (ER). Mutation of the COPA gene, encoding one of the COP-I subunits (α-COP), causes an immune dysregulatory disease known as COPA syndrome. The molecular mechanism by which the impaired retrograde transport results in autoinflammation remains poorly understood. Here we report that STING, an innate immunity protein, is a cargo of the retrograde membrane transport. In the presence of the disease-causative α-COP variants, STING cannot be retrieved back to the ER from the Golgi. The forced Golgi residency of STING results in the cGAS-independent and palmitoylation-dependent activation of the STING downstream signaling pathway. Surf4, a protein that circulates between the ER/ ER-Golgi intermediate compartment/ Golgi, binds STING and α-COP, and mediates the retrograde transport of STING to the ER. The STING/Surf4/α-COP complex is disrupted in the presence of the disease-causative α-COP variant. We also find that the STING ligand cGAMP impairs the formation of the STING/Surf4/α-COP complex. Our results suggest a homeostatic regulation of STING at the resting state by retrograde membrane traffic and provide insights into the pathogenesis of COPA syndrome.

COPA regulates Golgi to ER transport, and mutations lead to autoinflammation and disease through poorly understood mechanisms. Here, the authors show that disease-causing COPA variants prevent STING transport from the Golgi to the ER, leading to cGAS-independent activation of the STING pathway.

A defect in COPI-mediated transport of STING causes immune dysregulation in COPA syndrome

Pathogenic COPA variants cause a Mendelian syndrome of immune dysregulation with elevated type I interferon signaling. COPA is a subunit of coat protein complex I (COPI) that mediates Golgi to ER transport. Missense mutations of the COPA WD40 domain impair binding and sorting of proteins targeted for ER retrieval, but how this causes disease remains unknown. Given the importance of COPA in Golgi-ER transport, we speculated that type I interferon signaling in COPA syndrome involves missorting of STING. We show that a defect in COPI transport causes ligand-independent activation of STING. Furthermore, SURF4 is an adapter molecule that facilitates COPA-mediated retrieval of STING at the Golgi. Activated STING stimulates type I interferon-driven inflammation in CopaE241K/+ mice that is rescued in STING-deficient animals. Our results demonstrate that COPA maintains immune homeostasis by regulating STING transport at the Golgi. In addition, activated STING contributes to immune dysregulation in COPA syndrome and may be a new molecular target in treating the disease.

COPA silences STING

Two studies published in this issue of JEM, by Lepelley et al. (https://doi.org/10.1084/jem.20200600) and Deng et al. (https://doi.org/10.1084/jem.20201045), and two additional manuscripts by Mukai et al. (https://doi.org/10.1101/2020.05.20.107664 Preprint v1) and Steiner et al. (https://doi.org/10.1101/2020.07.09.194399 Preprint v1) demonstrate that COPA syndrome-associated high interferon titers are linked to mutations in COPA preventing STING's retrieval from the Golgi back to the ER and thereby causing chronic immune activation.

COPA syndrome, 5 years after: Where are we?

Heterozygous missense mutations in COPA, encoding coatomer protein subunit alpha (COPA), cause an interferonopathy mainly associating lung, joint and kidney involvement. This rare autoinflammatory disease is characterised by variable expression and a remarkably high frequency of clinical non-penetrance. Lung features, predominantly chronic diffuse alveolar haemorrhage (DAH), are observed in almost patients and can result in end-stage respiratory insufficiency. The initially described phenotype was broadened to include isolated DAH or lupus nephritis. Rare manifestations reminiscent of other monogenic interferonopathies occur. This indicates the need for careful clinical evaluation in patients with suspicion or diagnosis of COPA syndrome. Considering the dominant inheritance model and the highly variable phenotype, ranging from severe multi-organic disorder to non-penetrance, a careful family screening is recommended. New insights in disease pathogenesis have linked COPA mutations to STING-mediated interferon signalling. Beside a variable efficacy of 'classical' immunosuppressive drugs, Janus kinase (JAK) inhibitors constitute a promising treatment in COPA syndrome, and further targeted therapies are awaited.