DOCK8 Deficiency Presenting as an IPEX-Like Disorder

Primary atopic disorders: inborn errors of immunity causing severe allergic disease

Allergic diseases, including asthma, allergic rhinitis, atopic dermatitis, and food allergies, are driven by dysregulated immune responses, often involving IgE-mediated mast cell and basophil activation, Th2 inflammation, and epithelial dysfunction. While environmental factors are well-known contributors, the genetic components underpinning these conditions are increasingly understood. Traditionally viewed as polygenic multifactorial disorders, allergic diseases can also be caused by single-gene defects affecting the immune system and skin epithelial barrier, leading to profoundly dysregulated allergic responses. These monogenic allergic disorders are collectively referred to as primary atopic disorders or PADs. To date, over 48 single-gene defects have been established to cause PADs. This review highlights (i) the significance of PADs, (ii) the biological pathways involved in the pathogenesis of PADs, (iii) clinical strategies to differentiate PADs from their much more common polygenic counterparts, and (iv) diagnostic strategies for PADs.

Case report: Advanced age at transplantation and pre-emptive treatment with dupilumab in DOCK8 deficiency

Dedicator of cytokinesis 8 (DOCK8) deficiency is a combined immunodeficiency (CID) due to biallelic mutations in the gene encoding DOCK8. Major clinical phenomena are recurrent severe infections of the lungs and skin, atopic eczema, and predisposition to malignancy leading to a poor prognosis. Typical findings include highly elevated IgE and eosinophilia. Allogeneic hematopoietic stem cell transplantation (alloHSCT) is indicated as the only curative treatment option. We present a patient with advanced disease undergoing alloHSCT at the age of 11 years after individualized pre-treatment using dupilumab and rituximab resulting in a decrease in IgE levels and clinical improvement of the skin condition. Additionally, in a review of the literature, we summarize morbidity and outcome in DOCK8-deficient patients older than 8 years of age receiving alloHSCT. Life-threatening infections, malignancy, and disease-related complications with organ damage pre-transplant are challenging in older DOCK8-deficient patients. The therapeutic role of dupilumab in DOCK8 deficiency should be evaluated in larger studies.

DOCK8 deficiency due to a deep intronic variant in two kindreds with hyper-IgE syndrome

Dedicator of cytokinesis 8 (DOCK8) deficiency underlies the majority of cases of patients with autosomal recessive form of the hyper-immunoglobulin E syndrome (HIES). Most DOCK8 mutations involve deletions and splice junction mutations that abrogate protein expression. However, a few patients whose presentation is reminiscent of DOCK8 deficiency have no identifiable mutations. Using Whole Exome Sequencing (WES), we identified a deep intronic homozygous DOCK8 variant located in intron 36 (c.4626 + 76 A > G) in two unrelated patients with features of HIES that resulted in an in-frame 75 base pair intronic sequence insertion in DOCK8 cDNA, resulting in a premature stop codon (p.S1542ins6Ter). This variant resulted in variable decrease in DOCK8 expression that was associated with impaired T cell receptor-triggered actin polymerization, decreased IL-6-induced STAT3 phosphorylation, reduced expression of the Th17 cell markers CCR6 and IL-17, and higher frequencies of GATA3+ T cells indicative of Th2 skewing. Our approach extends the reach of WES in identifying disease-related intronic variants. It highlights the role of non-coding mutations in immunodeficiency disorders, including DOCK8 deficiency, and emphasizes the need to explore these mutations in unexplained inborn errors of immunity.

Pathophysiology of Congenital High Production of IgE and Its Consequences: A Narrative Review Uncovering a Neglected Setting of Disorders

Elevated serum IgE levels serve as a critical marker for uncovering hidden immunological disorders, particularly inborn errors of immunity (IEIs), which are often misdiagnosed as common allergic conditions. IgE, while typically associated with allergic diseases, plays a significant role in immune defense, especially against parasitic infections. However, extremely high levels of IgE can indicate more severe conditions, such as Hyper-IgE syndromes (HIES) and disorders with similar features, including Omenn syndrome, Wiskott-Aldrich syndrome, and IPEX syndrome. Novel insights into the genetic mutations responsible for these conditions highlight their impact on immune regulation and the resulting clinical features, including recurrent infections, eczema, and elevated IgE. This narrative review uniquely integrates recent advances in the genetic understanding of IEIs and discusses how these findings impact both diagnosis and treatment. Additionally, emerging therapeutic strategies, such as hematopoietic stem cell transplantation (HSCT) and gene therapies, are explored, underscoring the potential for personalized treatment approaches. Emphasizing the need for precise diagnosis and tailored interventions aims to enhance patient outcomes and improve the quality of care for those with elevated IgE levels and associated immunological disorders.

DIAPH1-Deficiency is Associated with Major T, NK and ILC Defects in Humans

Loss of function mutations in Diaphanous related formin 1 (DIAPH1) are associated with seizures, cortical blindness, and microcephaly syndrome (SCBMS) and are recently linked to combined immunodeficiency. However, the extent of defects in T and innate lymphoid cells (ILCs) remain unexplored. Herein, we characterized the primary T, natural killer (NK) and helper ILCs of six patients carrying two novel loss of function mutation in DIAPH1 and Jurkat cells after DIAPH1 knockdown. Mutations were identified by whole exome sequencing. T-cell immunophenotyping, proliferation, migration, cytokine signaling, survival, and NK cell cytotoxicity were studied via flow cytometry-based assays, confocal microscopy, and real-time qPCR. CD4+ T cell proteome was analyzed by mass spectrometry. p.R351* and p.R322*variants led to a significant reduction in the DIAPH1 mRNA and protein levels. DIAPH1-deficient T cells showed proliferation, activation, as well as TCR-mediated signaling defects. DIAPH1-deficient PBMCs also displayed impaired transwell migration, defective STAT5 phosphorylation in response to IL-2, IL-7 and IL-15. In vitro generation/expansion of Treg cells from naïve T cells was significantly reduced. shRNA-mediated silencing of DIAPH1 in Jurkat cells reduced DIAPH1 protein level and inhibited T cell proliferation and IL-2/STAT5 axis. Additionally, NK cells from patients had diminished cytotoxic activity, function and IL-2/STAT5 axis. Lastly, DIAPH1-deficient patients' peripheral blood contained dramatically reduced numbers of all helper ILC subsets. DIAPH1 deficiency results in major functional defects in T, NK cells and helper ILCs underlining the critical role of formin DIAPH1 in the biology of those cell subsets.

Regulatory T-cell dysfunction and cutaneous exposure to Staphylococcus aureus underlie eczema in DOCK8 deficiency

BACKGROUND

Dedicator of cytokinesis 8 (DOCK8)-deficient patients have severe eczema, elevated IgE, and eosinophilia, features of atopic dermatitis (AD).

OBJECTIVE

We sought to understand the mechanisms of eczema in DOCK8 deficiency.

METHODS

Skin biopsy samples were characterized by histology, immunofluorescence microscopy, and gene expression. Skin barrier function was measured by transepidermal water loss. Allergic skin inflammation was elicited in mice by epicutaneous sensitization with ovalbumin (OVA) or cutaneous application of Staphylococcus aureus.

RESULTS

Skin lesions of DOCK8-deficient patients exhibited type 2 inflammation, and the patients' skin was colonized by Saureus, as in AD. Unlike in AD, DOCK8-deficient patients had a reduced FOXP3:CD4 ratio in their skin lesions, and their skin barrier function was intrinsically intact. Dock8-/- mice exhibited reduced numbers of cutaneous T regulatory (Treg) cells and a normal skin barrier. Dock8-/- and mice with an inducible Dock8 deletion in Treg cells exhibited increased allergic skin inflammation after epicutaneous sensitization with OVA. DOCK8 was shown to be important for Treg cell stability at sites of allergic inflammation and for the generation, survival, and suppressive activity of inducible Treg cells. Adoptive transfer of wild-type, but not DOCK8-deficient, OVA-specific, inducible Treg cells suppressed allergic inflammation in OVA-sensitized skin of Dock8-/- mice. These mice developed severe allergic skin inflammation and elevated serum IgE levels after topical exposure to Saureus. Both were attenuated after adoptive transfer of WT but not DOCK8-deficient Treg cells.

CONCLUSION

Treg cell dysfunction increases susceptibility to allergic skin inflammation in DOCK8 deficiency and synergizes with cutaneous exposure to Saureus to drive eczema in DOCK8 deficiency.

T-helper-2 cells and atopic disease: lessons learnt from inborn errors of immunity

Inborn errors of immunity (IEI) are caused by monogenic variants that affect the host response to bacterial, viral, and fungal pathogens. As such, individuals with IEI often present with severe, recurrent, and life-threatening infections. However, the spectrum of disease due to IEI is very broad and extends to include autoimmunity, malignancy, and atopic diseases such as eczema, atopic dermatitis, and food and environmental allergies. Here, I review IEI that affect cytokine signaling pathways that dysregulate CD4⁺ T-cell differentiation, resulting in increased T-helper-2 (Th2) cell development, function, and pathogenicity. These are elegant examples of how rare IEI can provide unique insights into more common pathologies such as allergic disease that are impacting the general population at increased frequency.

Treg specialization and functions beyond immune suppression

The actions of the immune system are finely tuned, involving complex communication and coordination between diverse immune and non-immune cells across the tissues of the body. A healthy immune system requires a precise balance between immunity and tolerance. Regulatory T cells (Tregs) have long been appreciated as one of the master regulators of this balance; their importance is underscored by the autoimmunity that develops in mice and humans when Tregs are missing or dysfunctional. In addition to the immunoregulatory roles of Tregs in suppressing autoimmunity and inflammation via control of adaptive and innate immune responses, several non-immune modulatory functions of Tregs have been identified in recent years. In this review, we have highlighted the growing literature on the action of Tregs in metabolism, stem cell maintenance, tissue repair, and angiogenesis. Alongside Tregs' immune suppressive role, these non-suppressive activities comprise a key function of Tregs in regulating health and disease. As Tregs receive increasing attention as therapeutic targets, understanding their non-canonical functions may become an important feature of Treg-directed interventions.

Gastrointestinal manifestations in children with primary immune deficiencies: A case series

Gastrointestinal (GI) manifestations are the second most common complications of primary immune deficiencies (PIDs) after pulmonary disease, affecting up to one-half of children with PIDs. Non-infectious GI manifestations such as allergic, autoimmune, and inflammatory disorders can be the predominant manifestations of PIDs. We present a series of five children who presented predominantly with these GI manifestations of PID, not attributable to infections. Very early age of onset (infancy), parental consanguinity, and failure to respond to hypoallergenic formula led to strong suspicion for underlying PIDs. Next-generation sequencing led to the underlying genetic diagnosis. Early diagnosis and hematopoietic stem cell transplantation could be life-saving in these children.

Inborn Errors of the Immune System Associated With Atopy

Atopic disorders, including atopic dermatitis, food and environmental allergies, and asthma, are increasingly prevalent diseases. Atopic disorders are often associated with eosinophilia, driven by T helper type 2 (Th2) immune responses, and triggered by disrupted barrier function leading to abnormal immune priming in a susceptible host. Immune deficiencies, in contrast, occur with a significantly lower incidence, but are associated with greater morbidity and mortality. A subset of atopic disorders with eosinophilia and elevated IgE are associated with monogenic inborn errors of immunity (IEI). In this review, we discuss current knowledge of IEI that are associated with atopy and the lessons these immunologic disorders provide regarding the fundamental mechanisms that regulate type 2 immunity in humans. We also discuss further mechanistic insights provided by animal models.

Treg-associated monogenic autoimmune disorders and gut microbial dysbiosis

Primary immunodeficiency diseases (PIDs) caused by a single-gene defect generally are referred to as monogenic autoimmune disorders. For example, mutations in the transcription factor autoimmune regulator (AIRE) result in a condition called autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy; while mutations in forkhead box P3 lead to regulatory T cell (Treg)-deficiency-induced multiorgan inflammation, which in humans is called "immune dysregulation, polyendocrinopathy, enteropathy with X-linked inheritance" (or IPEX syndrome). Previous studies concluded that monogenic diseases are insensitive to commensal microbial regulation because they develop even in germ-free (GF) animals, a conclusion that has limited the number of studies determining the role of microbiota in monogenic PIDs. However, emerging evidence shows that although the onset of the disease is independent of the microbiota, several monogenic PIDs vary in severity in association with the microbiome. In this review, we focus on monogenic PIDs associated with Treg deficiency/dysfunction, summarizing the gut microbial dysbiosis that has been shown to be linked to these diseases. From limited studies, we have gleaned several mechanistic insights that may prove to be of therapeutic importance in the early stages of life. IMPACT: This review paper serves to refute the concept that monogenic PIDs are not linked to the microbiome. The onset of monogenic PIDs is independent of microbiota; single-gene mutations such as AIRE or Foxp3 that affect central or peripheral immune tolerance produce monogenic diseases even in a GF environment. However, the severity and outcome of PIDs are markedly impacted by the microbial composition. We suggest that future research for these conditions may focus on targeting the microbiome.

Cellular and molecular mechanisms breaking immune tolerance in inborn errors of immunity

In addition to susceptibility to infections, conventional primary immunodeficiency disorders (PIDs) and inborn errors of immunity (IEI) can cause immune dysregulation, manifesting as lymphoproliferative and/or autoimmune disease. Autoimmunity can be the prominent phenotype of PIDs and commonly includes cytopenias and rheumatological diseases, such as arthritis, systemic lupus erythematosus (SLE), and Sjogren's syndrome (SjS). Recent advances in understanding the genetic basis of systemic autoimmune diseases and PIDs suggest an at least partially shared genetic background and therefore common pathogenic mechanisms. Here, we explore the interconnected pathogenic pathways of autoimmunity and primary immunodeficiency, highlighting the mechanisms breaking the different layers of immune tolerance to self-antigens in selected IEI.

Case Report: Hypomorphic Function and Somatic Reversion in DOCK8 Deficiency in One Patient With Two Novel Variants and Sclerosing Cholangitis

DOCK8 deficiency is a combined immunodeficiency due to biallelic variants in dedicator of cytokinesis 8 (DOCK8) gene. The disease has a wide clinical spectrum encompassing recurrent infections (candidiasis, viral and bacterial infections), virally driven malignancies and immune dysregulatory features, including autoimmune (cytopenia and vasculitis) as well as allergic disorders (eczema, asthma, and food allergy). Hypomorphic function and somatic reversion of DOCK8 has been reported to result in incomplete phenotype without IgE overproduction. Here we describe a case of DOCK8 deficiency in a 8-year-old Caucasian girl. The patient's disease was initially classified as autoimmune thrombocytopenia, which then evolved toward a combined immunodeficiency phenotype with recurrent infections, persistent EBV infection and lymphoproliferation. Two novel variants (one deletion and one premature stop codon) were characterized, resulting in markedly reduced, but not absent, DOCK8 expression. Somatic reversion of the DOCK8 deletion was identified in T cells. Hypomorphic function and somatic reversion were associated with restricted T cell repertoire, decreased STAT5 phosphorylation and impaired immune synapse functioning in T cells. Although the patient presented with incomplete phenotype (absence of markedly increase IgE and eosinophil count), sclerosing cholangitis was incidentally detected, thus indicating that hypomorphic function and somatic reversion of DOCK8 may delay disease progression but do not necessarily prevent from severe complications.

Novel CARMIL2 loss-of-function variants are associated with pediatric inflammatory bowel disease

CARMIL2 is required for CD28-mediated co-stimulation of NF-κB signaling in T cells and its deficiency has been associated with primary immunodeficiency and, recently, very early onset inflammatory bowel disease (IBD). Here we describe the identification of novel biallelic CARMIL2 variants in three patients presenting with pediatric-onset IBD and in one with autoimmune polyendocrine syndrome (APS). None manifested overt clinical signs of immunodeficiency before their diagnosis. The first patient presented with very early onset IBD. His brother was found homozygous for the same CARMIL2 null variant and diagnosed with APS. Two other IBD patients were found homozygous for a nonsense and a missense CARMIL2 variant, respectively, and they both experienced a complicated postoperative course marked by severe infections. Immunostaining of bowel biopsies showed reduced CARMIL2 expression in all the three patients with IBD. Western blot and immunofluorescence of transfected cells revealed an altered expression pattern of the missense variant. Our work expands the genotypic and phenotypic spectrum of CARMIL2 deficiency, which can present with either IBD or APS, aside from classic immunodeficiency manifestations. CARMIL2 should be included in the diagnostic work-up of patients with suspected monogenic IBD.

FOXP3 and Tip60 Structural Interactions Relevant to IPEX Development Lead to Potential Therapeutics to Increase FOXP3 Dependent Suppressor T Cell Functions

Regulatory T (Treg) cells play a role in the maintenance of immune homeostasis and are critical mediators of immune tolerance. The Forkhead box P3 (FOXP3) protein acts as a regulator for Treg development and function. Mutations in the FOXP3 gene can lead to autoimmune diseases such as Immunodysregulation, polyendocrinopathy, enteropathy, and X-linked (IPEX) syndrome in humans, often resulting in death within the first 2 years of life and a scurfy like phenotype in Foxp3 mutant mice. We discuss biochemical features of the FOXP3 ensemble including its regulation at various levels (epigenetic, transcriptional, and post-translational modifications) and molecular functions. The studies also highlight the interactions of FOXP3 and Tat-interacting protein 60 (Tip60), a principal histone acetylase enzyme that acetylates FOXP3 and functions as an essential subunit of the FOXP3 repression ensemble complex. Lastly, we have emphasized the role of allosteric modifiers that help stabilize FOXP3:Tip60 interactions and discuss targeting this interaction for the therapeutic manipulation of Treg activity.

Immune Monitoring of Patients With Primary Immune Regulation Disorders Unravels Higher Frequencies of Follicular T Cells With Different Profiles That Associate With Alterations in B Cell Subsets

Primary immune regulation disorders lead to autoimmunity, allergy and inflammatory conditions due to defects in the immune homeostasis affecting different T, B and NK cell subsets. To improve our understanding of these conditions, in this work we analyzed the T and B cell compartments of 15 PID patients with dysregulation, including 3 patients with STAT1 GOF mutation, 7 patients with CVID with dysregulation, 3 patients with mutations in CTLA4, 1 patient with CD25 mutation and 1 patient with STAT5b mutation and compared them with healthy donors and with CVID patients without dysregulation. CD4⁺ and CD8⁺ T cells from the patients exhibited a significant decreased frequency of naïve and regulatory T cells with increased frequencies of activated cells, central memory CD4⁺ T cells, effector memory CD8⁺ T cells and terminal effector CD8⁺ T cells. Patients also exhibited a significantly increased frequency of circulating CD4⁺ follicular helper T cells, with altered frequencies of cTfh cell subsets. Such cTfh cells were skewed toward cTfh1 cells in STAT1 GOF, CTLA4, and CVID patients, while the STAT5b deficient patient presented a skew toward cTfh17 cells. These alterations confirmed the existence of an imbalance in the cTfh1/cTfh17 ratio in these diseases. In addition, we unraveled a marked dysregulation in the B cell compartment, characterized by a prevalence of transitional and naïve B cells in STAT1 GOF and CVID patients, and of switched-memory B cells and plasmablast cells in the STAT5b deficient patient. Moreover, we observed a significant positive correlation between the frequencies cTfh17 cells and switched-memory B cells and between the frequency of switched-memory B cells and the serum IgG. Therefore, primary immunodeficiencies with dysregulation are characterized by a skew toward an activated/memory phenotype within the CD4⁺ and CD8⁺ T cell compartment, accompanied by abnormal frequencies of Tregs, cTfh, and their cTfh1 and cTfh17 subsets that likely impact on B cell help for antibody production, which likely contributes to their autoimmune and inflammatory conditions. Therefore, assessment of these alterations by flow cytometry constitutes a simple and straightforward manner to improve diagnosis of these complex clinical entities that may impact early diagnosis and patients' treatment. Also, our findings unravel phenotypic alterations that might be associated, at least in part, with some of the clinical manifestations observed in these patients.

Interleukin 10: the critical role of a pleiotropic cytokine in food allergy

Despite advances in research, the pathophysiology of food allergy has not yet been fully elucidated. IL-10 has both a pro- and anti-inflammatory effect on the development of food allergy and in order to understand its different immune-modulatory effects the factors that influence the inflammatory microenvironment need to be taken into account. Specific single nucleotide polymorphisms of the IL-10 gene seem to confer an increased risk of developing food allergy, but to date there is a substantial lack of genome- wide association studies regarding the genetic and epigenetic underpinnings of the disease. Special interest has been drawn to the development of allergen-specific regulatory CD4+CD25+ T-cells secreting IL-10 in the immunotherapy of allergic diseases. In addition, a distinct population of human tolerogenic dendritic cells (DC), DC-10 seems to hold great potential and could potentially serve as a therapeutic tool to improve the management of food allergy.

Clinical, Immunological, and Genetic Features in Patients with Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) and IPEX-like Syndrome

BACKGROUND

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inborn error of immunity caused by mutations in the forkhead box P3 (FOXP3) gene.

OBJECTIVE

In this study, we conducted a systematic review of patients with IPEX and IPEX-like syndrome to delineate differences in these 2 major groups.

METHODS

The literature search was performed in PubMed, Web of Science, and Scopus databases, and demographic, clinical, immunologic, and molecular data were compared between the IPEX and IPEX-like groups.

RESULTS

A total of 459 patients were reported in 148 eligible articles. Major clinical differences between patients with IPEX and IPEX-like syndrome were observed in rates of pneumonia (11% vs 31%, P < .001), bronchiectasis (0.3% vs 14%, P < .001), diarrhea (56% vs 42%, P = .020), and organomegaly (10% vs 23%, P = .001), respectively. Eosinophilia (95% vs 100%), low regulatory T-cell count (68% vs 50%), and elevated IgE (87% vs 61%) were the most prominent laboratory findings in patients with IPEX and IPEX-like syndrome, respectively. In the IPEX group, a lower mortality rate was observed among patients receiving hematopoietic stem cell transplantation (HSCT) (24%) compared with other patients (43%), P = .008; however, in the IPEX-like group, it was not significant (P = .189).

CONCLUSIONS

Patients with IPEX syndrome generally suffer from enteropathy, autoimmunity, dermatitis, eosinophilia, and elevated serum IgE. Despite similarities in their clinical presentations, patients with IPEX-like syndrome are more likely to present common variable immunodeficiency-like phenotype such as respiratory tract infections, bronchiectasis, and organomegaly. HSCT is currently the only curative therapy for both IPEX and IPEX-like syndrome and may result in favorable outcome.

Primary Atopic Disorders

Primary atopic disorders describes a series of monogenic diseases that have allergy- or atopic effector–related symptoms as a substantial feature. The underlying pathogenic genetic lesions help illustrate fundamental pathways in atopy, opening up diagnostic and therapeutic options for further study in those patients, but ultimately for common allergic diseases as well. Key pathways affected in these disorders include T cell receptor and B cell receptor signaling, cytokine signaling, skin barrier function, and mast cell function, as well as pathways that have not yet been elucidated. While comorbidities such as classically syndromic presentation or immune deficiency are often present, in some cases allergy alone is the presenting symptom, suggesting that commonly encountered allergic diseases exist on a spectrum of monogenic and complex genetic etiologies that are impacted by environmental risk factors.

North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition Position Paper on the Evaluation and Management for Patients With Very Early-onset Inflammatory Bowel Disease

The rate of pediatric inflammatory bowel disease (IBD) has been increasing over the last decade and this increase has occurred most rapidly in the youngest children diagnosed <6 years, known as very early-onset inflammatory bowel disease (VEO-IBD). These children can present with more extensive and severe disease than older children and adults. The contribution of host genetics in this population is underscored by the young age of onset and the distinct, aggressive phenotype. In fact, monogenic defects, often involving primary immunodeficiency genes, have been identified in children with VEO-IBD and have led to targeted and life-saving therapy. This position paper will discuss the phenotype of VEO-IBD and outline the approach and evaluation for these children and what factors should trigger concern for an underlying immunodeficiency. We will then review the immunological assays and genetic studies that can facilitate the identification of the underlying diagnosis in patients with VEO-IBD and how this evaluation may lead to directed therapies. The position paper will also aid the pediatric gastroenterologist in recognizing when a patient should be referred to a center specializing in the care of these patients. These guidelines are intended for pediatricians, allied health professionals caring for children, pediatric gastroenterologists, pediatric pathologists, and immunologists.

Gastrointestinal Disorders Associated with Primary Immunodeficiency Diseases

There are now 354 inborn errors of immunity (primary immunodeficiency diseases (PIDDs)) with 344 distinct molecular etiologies reported according to the International Union of Immunological Sciences (IUIS) (Clin Gastroenterol Hepatol 11: p. 1050-63, 2013, Semin Gastrointest Dis 8: p. 22-32, 1997, J Clin Immunol 38: p. 96-128, 2018). Using the IUIS document as a reference and cross-checking PubMed ( www.ncbi.nlm.nih.pubmed.gov ), we found that approximately one third of the 354 diseases of impaired immunity have a gastrointestinal component [J Clin Immunol 38: p. 96-128, 2018]. Often, the gastrointestinal symptomatology and pathology is the heralding sign of a PIDD; therefore, it is important to recognize patterns of disease which may manifest along the gastrointestinal tract as a more global derangement of immune function. As such, holistic consideration of immunity is warranted in patients with clinically significant gastrointestinal disease. Here, we discuss the manifold presentations and GI-specific complications of PIDDs which could lead patients to seek advice from a variety of clinician specialists. Often, patients with these medical problems will engage general pediatricians, surgeons, gastroenterologists, rheumatologists, and clinical immunologists among others. Following delineation of the presenting concern, accurate and often molecular diagnosis is imperative and a multi-disciplinary approach warranted for optimal management. In this review, we will summarize the current state of understanding of PIDD gastrointestinal disease involvement. We will do so by focusing upon gastrointestinal disease categories (i.e., inflammatory, diarrhea, nodular lymphoid hyperplasia, liver/biliary tract, structural disease, and oncologic disease) with an intent to aid the healthcare provider who may encounter a patient with an as-yet undiagnosed PIDD who presents initially with a gastrointestinal symptom, sign, or problem.

Treg cells in health and autoimmune diseases: New insights from single cell analysis

Autoimmune diseases, such as Systemic Lupus Erythematosus (SLE) or Rheumatoid Arthritis (RA) are characterized by the breakdown of immunological tolerance. Defects of regulatory T cells have been described among the various mechanisms, that are important for the development of autoimmune diseases, due to their critical role as regulators of peripheral immune tolerance and homeostasis. Initially T suppressor cells have been described as one population of peripheral T cells. Based on new technological advances a new understanding of the heterogeneity of different Treg cell populations in the lymphoid and non-lymphoid tissue has evolved over the last years. While initially Foxp3 has been defined as the main master regulator of Treg cells, we have learned that Treg cells from various tissue can be identified by a specific transcriptomic and epigenetic signature. Epigenetic mechanisms allow Treg cell stability, but we have also learned that certain Treg subsets are plastic and can under specific circumstances even enhance autoimmunity and inflammatory processes. Quantitative and functional defects of Treg cells have been observed in a variety of autoimmune diseases. Due to our understanding of the nature of this cell population, Treg cells have been a target of new Treg based therapies, such as low-dose IL-2. In addition, ongoing clinical trials aim to test safety and efficacy of transferred, in vitro expanded Treg cells in patients with autoimmune diseases and transplant patients.

Primary immunodeficiencies caused by mutations in actin regulatory proteins

The identification of patients with monogenic gene defects have illuminated the function of different proteins in the immune system, including proteins that regulate the actin cytoskeleton. Many of these actin regulatory proteins are exclusively expressed in leukocytes and regulate the formation and branching of actin filaments. Their absence or abnormal function leads to defects in immune cell shape, cellular projections, migration, and signaling. Through the study of patients' mutations and generation of mouse models that recapitulate the patients' phenotypes, our laboratory and others have gained a better understanding of the role these proteins play in cell biology and the underlying pathogenesis of immunodeficiencies and immune dysregulatory syndromes.

Recent developments in understanding the mechanisms of food allergy

PURPOSE OF REVIEW

The prevalence of food allergy is rising globally. This review will discuss recent discoveries regarding the immunologic mechanisms that drive the initial sensitization and allergic response to food antigens, which may inform prevention and treatment strategies.

RECENT FINDINGS

Tolerance to food antigens is antigen-specific and promoted by oral exposure early in life and maternal transfer of immune complexes via breast milk. IgG can inhibit both the initiation and effector phases of allergic responses to food antigens in mice, and high levels of food-specific IgG4 are associated with acquisition of tolerance in humans. Disruption of the skin barrier provides a route for food sensitization through the actions of mast cells, type 2 innate lymphoid cells, and IL-33 signaling. Regulatory T cells (Tregs) promote acquisition of oral tolerance, although defects in circulating allergen-specific Tregs are not evident in children with established food allergy. Certain microbes can offer protection against the development of IgE and food allergic responses, while dysbiosis increases susceptibility to food allergy.

SUMMARY

Tolerance to food antigens is antigen-specific and is promoted by oral exposure early in life, maternal transfer of immune complexes, food-specific IgG, Tregs, an intact skin barrier, and a healthy microbiome.

Regulatory T Cells: the Many Faces of Foxp3

Regulatory T (Treg) cells expressing the transcription factor forkhead box P3 (Foxp3) play a requisite role in the maintenance of immunological homeostasis and prevention of peripheral self-tolerance breakdown. Although Foxp3 by itself is neither necessary nor sufficient to specify many aspects of the Treg cell phenotype, its sustained expression in Treg cells is indispensable for their phenotypic stability, metabolic fitness, and regulatory function. In this review, we summarize recent advances in Treg cell biology, with a particular emphasis on the role of Foxp3 as a transcriptional modulator and metabolic gatekeeper essential to an effective immune regulatory response. We discuss these findings in the context of human inborn errors of immune dysregulation, with a focus on FOXP3 mutations, leading to Treg cell deficiency. We also highlight emerging concepts of therapeutic Treg cell reprogramming to restore tolerance in the settings of immune dysregulatory disorders.

What is new in HIES? Recent insights from the interface of primary immune deficiency and atopy

PURPOSE OF REVIEW

Understanding the pathophysiology of monogenic primary immunodeficiency (PID) with atopic presentation has pivotal implications for intervention strategies and potentially wider polygenic atopic-related traits. This review will discuss advances in gene discovery arising from monogenic defects at the interface between PID and atopy, notably the hyper-IgE syndromes.

RECENT FINDINGS

Key molecular pathways underlying development of primary atopic diseases have recently been proposed. We test this classification through reviewing novel genes reported in the last 2 years and compare insights from pathway-analysis of genome-wide association studies (GWAS) of atopic-related traits.Growing access to next-generation sequencing (NGS) has resulted in a surge in gene discovery, highlighting the utility and some pitfalls of this approach in clinical practice. The variability of presenting phenotypes reveals important gene-dosage effects. This has important implications for therapeutic strategies such as protein stabilization and modulators of JAK-STAT or TH2-cytokine signalling. We also consider the therapeutic implications raised by CARD11 deficiency, and wider applications of NGS including polygenic risk score in atopy.

SUMMARY

Disorders presenting at the interface between PID and allergy are often difficult to diagnose, with serious consequences if missed. Application of NGS has already provided critical insights to pathways enabling targeted therapeutic interventions, and potential wider translation to polygenic disorders.

A Unique Presentation of Infantile-Onset Colitis and Eosinophilic Disease without Recurrent Infections Resulting from a Novel Homozygous CARMIL2 Variant

PURPOSE

This study aimed to characterize the clinical phenotype, genetic basis, and consequent immunological phenotype of a boy with severe infantile-onset colitis and eosinophilic gastrointestinal disease, and no evidence of recurrent or severe infections.

METHODS

Trio whole-exome sequencing (WES) was utilized for pathogenic variant discovery. Western blot (WB) and immunohistochemical (IHC) staining were used for protein expression analyses. Immunological workup included in vitro T cell studies, flow cytometry, and CyTOF analysis.

RESULTS

WES revealed a homozygous variant in the capping protein regulator and myosin 1 linker 2 (CARMIL2) gene: c.1590C>A; p.Asn530Lys which co-segregated with the disease in the nuclear family. WB and IHC analyses demonstrated reduced protein levels in patient's cells compared with controls. Moreover, comprehensive immunological workup revealed severely diminished blood-borne regulatory T cell (T_reg) frequency and impaired in vitro CD4⁺ T cell proliferation and T_reg generation. CyTOF analysis showed significant shifts in the patient's innate and adaptive immune cells compared with healthy controls and ulcerative colitis patients.

CONCLUSIONS

Pathogenic variants in CARMIL2 have been implicated in an immunodeficiency syndrome characterized by recurrent infections, occasionally with concurrent chronic diarrhea. We show that CARMIL2-immunodeficiency is associated with significant alterations in the landscape of immune populations in a patient with prominent gastrointestinal disease. This case provides evidence that CARMIL2 should be a candidate gene when diagnosing children with very early onset inflammatory and eosinophilic gastrointestinal disorders, even when signs of immunodeficiency are not observed.

Insights into immunity from clinical and basic science studies of DOCK8 immunodeficiency syndrome

DOCK8 immunodeficiency syndrome (DIDS) is a progressive combined immunodeficiency that can be distinguished from other combined immunodeficiencies or hyperimmunoglobulinemia E syndromes in featuring (a) profound susceptibility to virus infections of the skin, with associated skin cancers, and (b) severe food allergies. The DOCK8 locus has many repetitive sequence elements that predispose to the generation of large germline deletions as well as recombination-mediated somatic DNA repair. Residual DOCK8 protein contributes to the variable disease phenotype. The severe virus infections of the skin, and probably also VZV-associated vasculopathy, reflect an important function of DOCK8, which is normally required to maintain lymphocyte shape integrity as the cells migrate through dense tissues. Loss of DOCK8 also causes immune deficits through other mechanisms including a milder generalized cell survival defect and skewing of T helper cell subsets. Recent work has uncovered the roles for DOCK8 in dendritic cell responses that can also help explain the virus susceptibility, as well as in regulatory T cells that might help explain autoimmunity in a minority of patients. Fortunately, hematopoietic stem cell transplantation cures the eczema and infection susceptibility of DIDS, but not necessarily the other disease manifestations including food allergies.

Clinical, Immunological, and Molecular Heterogeneity of 173 Patients With the Phenotype of Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-Linked (IPEX) Syndrome

Background: Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) Syndrome is a rare recessive disorder caused by mutations in the FOXP3 gene. In addition, there has been an increasing number of patients with wild-type FOXP3 gene and, in some cases, mutations in other immune regulatory genes. Objective: To molecularly asses a cohort of 173 patients with the IPEX phenotype and to delineate the relationship between the clinical/immunologic phenotypes and the genotypes. Methods: We reviewed the clinical presentation and laboratory characteristics of each patient and compared clinical and laboratory data of FOXP3 mutation-positive (IPEX patients) with those from FOXP3 mutation-negative patients (IPEX-like). A total of 173 affected patients underwent direct sequence analysis of the FOXP3 gene while 85 IPEX-like patients with normal FOXP3 were investigated by a multiplex panel of "Primary Immune Deficiency (PID-related) genes." Results: Forty-four distinct FOXP3 variants were identified in 88 IPEX patients, 9 of which were not previously reported. Among the 85 IPEX-like patients, 19 different disease-associated variants affecting 9 distinct genes were identified. Conclusions: We provide a comprehensive analysis of the clinical features and molecular bases of IPEX and IPEX-like patients. Although we were not able to identify major distinctive clinical features to differentiate IPEX from IPEX-like syndromes, we propose a simple flow-chart to effectively evaluate such patients and to focus on the most likely molecular diagnosis. Given the large number of potential candidate genes and overlapping phenotypes, selecting a panel of PID-related genes will facilitate a molecular diagnosis.

Monogenic polyautoimmunity in primary immunodeficiency diseases

Primary immunodeficiency diseases (PIDs) consist of a large group of genetic disorders that affect distinct components of the immune system. PID patients are susceptible to infection and non-infectious complications, particularly autoimmunity. A specific group of monogenic PIDs are due to mutations in genes that are critical for the regulation of immunological tolerance and immune responses. This group of monogenic PIDs is at high risk of developing polyautoimmunity (i.e., the presence of more than one autoimmune disease in a single patient) because of their impaired immunity. In this review, we discuss the mechanisms of autoimmunity in PIDs and the characteristics of polyautoimmunity in the following PIDs: IPEX; monogenic IPEX-like syndrome; LRBA deficiency; CTLA4 deficiency; APECED; ALPS; and PKCδ deficiency.

TCR Signaling Abnormalities in Human Th2-Associated Atopic Disease

Stimulation of naïve CD4 T cells with weak T cell receptor agonists even in the absence of T helper-skewing cytokines can result in IL-4 production which can drive a Th2 response. Evidence for the in vivo consequences of such a phenomenon can be found in a number of mouse models and, importantly, a series of monogenic human diseases associated with significant atopy which are caused by mutations in the T cell receptor signaling cascade. Such diseases can help understand how Th2 responses evolve in humans, and potentially provide insight into therapeutic interventions.

Primary atopic disorders

Important insights from monogenic disorders into the immunopathogenesis of allergic diseases and reactions are discussed.

Monogenic disorders have provided fundamental insights into human immunity and the pathogenesis of allergic diseases. The pathways identified as critical in the development of atopy range from focal defects in immune cells and epithelial barrier function to global changes in metabolism. A major goal of studying heritable single-gene disorders that lead to severe clinical allergic diseases is to identify fundamental pathways leading to hypersensitivity that can be targeted to provide novel therapeutic strategies for patients with allergic diseases, syndromic and nonsyndromic alike. Here, we review known single-gene disorders leading to severe allergic phenotypes in humans, discuss how the revealed pathways fit within our current understanding of the atopic diathesis, and propose how some pathways might be targeted for therapeutic benefit.