Molecular feature and therapeutic perspectives of immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome

A splice of life: the discovery, function, and clinical implications of FOXP3 isoforms in autoimmune disease

Regulatory T cells (Tregs) are a specialized subset of CD4+ T cells essential for the maintenance of immune homeostasis and prevention of autoimmunity. Treg lineage and functions are programmed by the X-chromosome encoded transcription factor forkhead box P3 (FOXP3). In humans, multiple FOXP3 isoforms are generated through alternative splicing. A full-length isoform containing all coding exons (FOXP3-FL) and a version lacking the second exon (FOXP3-ΔE2) are the predominant FOXP3 isoforms. Additionally, there are two minor isoforms lacking either exon 7 (FOXP3-ΔE7) and both exons 2 and 7 (FOXP3-ΔE2ΔE7). Although healthy humans express approximately equal levels of the FOXP3-FL and FOXP3-ΔE2 isoforms, sole expression of FOXP3-ΔE2 results in the development of a systemic autoimmune disease that resembles immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. These clinical observations strongly suggest functional defects in suppression by Tregs programmed by the FOXP3-ΔE2 isoform. Work from the past two decades has provided phenotypic and functional evidence of differences between Tregs programmed by the FOXP3-FL, FOXP3-ΔE2, and FOXP3-ΔE7 isoforms. In this review, we discuss the discovery of the FOXP3 isoforms, differences in the phenotype and function of Tregs programmed by different FOXP3 isoforms, and the role that these isoforms are known to play in autoimmunity.

Development of Chronic Thyroiditis During Cyclosporin A Treatment

Cyclosporin A (CsA) is a calcineurin inhibitor used as an immunosuppressant. Although CsA effectively suppresses T cells, excessive suppression of regulatory T cells may exacerbate autoimmune diseases. Here, we report a case of chronic thyroiditis developing during CsA treatment. A 64-year-old woman, on CsA for 2 years for aplastic anemia, presented with a nodule in the right thyroid lobe, raising concern for malignant lymphoma. Right hemithyroidectomy confirmed mucosa-associated lymphoid tissue lymphoma without chronic thyroiditis in the adjacent normal tissue. Owing to the localized lesion, the patient was monitored with a reduced dose of CsA. Initial thyroid ultrasonography showed a normal left lobe; however, hypoechoic areas appeared 1-year postsurgery, followed by diffuse thyroid enlargement and further expansion of these hypoechoic areas. Postoperative fluorodeoxyglucose positron emission tomography showed progressive uptake in the left lobe, and thyroid autoantibodies, initially negative, became positive. Five years later, suspected lymphoma recurrence prompted a residual thyroidectomy, which confirmed mucosa-associated lymphoid tissue lymphoma with chronic thyroiditis. This case suggests that excessive suppression of regulatory T cells by CsA may induce chronic thyroiditis. Further studies on chronic thyroiditis in patients treated with CsA may enhance our understanding of its pathogenesis.

Research Progress of Alternative Polyadenylation in Diseases Related to Glycolipid Metabolism

With changes in lifestyle, sedentary behavior or lack of physical exercise increases the risk of various glycolipid metabolic disorders. Glycolipid metabolic dysregulation refers to abnormalities in the metabolism of carbohydrates and lipids, including diseases such as diabetes, obesity, and metabolic syndrome. In-depth research into the molecular mechanisms of glycolipid metabolic dysregulation can help develop more effective treatment strategies and preventive measures to prevent the occurrence of long-term complications such as cardiovascular diseases. Alternative polyadenylation (APA) is an important form of RNA modification that helps regulate gene expression and generate protein diversity. This modification can affect processes such as RNA stability, post-transcriptional modification, and translational regulation. Recent studies have confirmed that APA can influence the expression of genes involved in glucose and lipid metabolism, increasing the probability of developing immune, endocrine, and metabolic diseases. The review explains the research progress of APA involvement in various metabolic diseases and explores these mechanisms, providing new insights and directions for novel metabolic disorder treatment strategies.

A guide to thymic selection of T cells

The thymus is an evolutionarily conserved organ that supports the development of T cells. Not only does the thymic environment support the rearrangement and expression of diverse T cell receptors but also provides a unique niche for the selection of appropriate T cell clones. Thymic selection ensures that the repertoire of available T cells is both useful (being MHC-restricted) and safe (being self-tolerant). The unique antigen-presentation features of the thymus ensure that the display of self-antigens is optimal to induce tolerance to all types of self-tissue. MHC class-specific functions of CD4+ T helper cells, CD8+ killer T cells and CD4+ regulatory T cells are also established in the thymus. Finally, the thymus provides signals for the development of several minor T cell subsets that promote immune and tissue homeostasis. This Review provides an introductory-level overview of our current understanding of the sophisticated thymic selection mechanisms that ensure T cells are useful and safe.

Regulatory T cells in gastric cancer: Key controllers from pathogenesis to therapy

Gastric cancer (GC) is a highly aggressive malignancy that remains a significant contributor to cancer-related mortality worldwide, despite a decline in incidence in recent years. Early-stage GC poses a diagnostic challenge due to its asymptomatic nature, leading to poor prognoses for most patients. Conventional treatment approaches, including chemotherapy and surgery, have shown limited efficacy in improving outcomes for GC patients. The advent of immune checkpoint inhibitors (ICIs) has revolutionized cancer therapy, yielding durable responses across various malignancies. However, the clinical benefits of ICIs in GC have been modest, underscoring the need for a comprehensive understanding of immune cell functions within the GC tumor microenvironment (TME). Regulatory T cells (Tregs), a subset of T lymphocytes, play a pivotal role in GC development and progression and serve as prognostic biomarkers for GC patients. This review aims to elucidate the multifaceted roles of Tregs in the pathogenesis, progression, and prognosis of gastric cancer, and establish their actual and future potential as therapeutic targets. By providing insights into the intricate interplay between Tregs and the TME, this review strives to stimulate further investigation and facilitate the development of targeted Treg-based therapeutic strategies for GC.

Metabolic regulation of forkhead box P3 alternative splicing isoforms and their impact on health and disease

Forkhead Box P3 (FOXP3) is crucial for the development and suppressive function of human regulatory T cells (Tregs). There are two predominant FOXP3 splicing isoforms in healthy humans, the full-length isoform and the isoform lacking exon 2, with different functions and regulation mechanisms. FOXP3 splicing isoforms show distinct abilities in the cofactor interaction and the nuclear translocation, resulting in different effects on the differentiation, cytokine secretion, suppressive function, linage stability, and environmental adaptation of Tregs. The balance of FOXP3 splicing isoforms is related to autoimmune diseases, inflammatory diseases, and cancers. In response to environmental challenges, FOXP3 transcription and splicing can be finely regulated by T cell antigen receptor stimulation, glycolysis, fatty acid oxidation, and reactive oxygen species, with various signaling pathways involved. Strategies targeting energy metabolism and FOXP3 splicing isoforms in Tregs may provide potential new approaches for the treatment of autoimmune diseases, inflammatory diseases, and cancers. In this review, we summarize recent discoveries about the FOXP3 splicing isoforms and address the metabolic regulation and specific functions of FOXP3 splicing isoforms in Tregs.

The forkhead box protein P3 gene rs3761548 promoter polymorphism confers a genetic contribution to the risk of preeclampsia: A systematic review and meta-analysis

Various studies have investigated the risk of preeclampsia with the forkhead box protein P3 (FOXP3) gene rs2232365 and rs3761548 polymorphisms. However, the results remained contradictory. A comprehensive literature search was conducted using the Cochrane Library, PubMed, and Web of Science (up to Oct 11, 2021). Meta-analysis was carried out in the R language environment for statistical computing and graphics. A fixed-effect or random-effects model was used according to the statistical significance of heterogeneity among included studies. The pooled odds ratios and corresponding 95% confidence intervals were calculated to estimate the strength of the effect. For the rs2232365 polymorphism, statistical significance was detected neither in the overall population nor among the East Asian and West Asian subgroups. However, for rs3761548, the summarized statistics revealed a significant association between the C allele carriage and preeclampsia risk in the homozygote, heterozygote, and dominant models. The further stratified analysis found this effect might be specific to West-South Asian ethnic subgroups. To sum up, this meta-analysis showed that the FOXP3 rs3761548 polymorphism was significantly associated with preeclampsia susceptibility, and it had a deleterious effect especially in the West-South Asian population. In contrast, rs2232365 may serve as neither a protective nor a risk factor for preeclampsia onset.

Beyond IBD: the genetics of other early-onset diarrhoeal disorders

Diarrhoeal disorders in childhood extend beyond the inflammatory bowel diseases. Persistent and severe forms of diarrhoea can occur from birth and are associated with significant morbidity and mortality. These disorders can affect not only the gastrointestinal tract but frequently have extraintestinal manifestations, immunodeficiencies and endocrinopathies. Genomic analysis has advanced our understanding of these conditions and has revealed precision-based treatment options such as potentially curative haematopoietic stem cell transplant. Although many new mutations have been discovered, there is frequently no clear genotype-phenotype correlation. The functional effects of gene mutations can be studied in model systems such as patient-derived organoids. This allows us to further characterise these disorders and advance our understanding of the pathophysiology of the intestinal mucosa. In this review, we will provide an up to date overview of genes involved in diarrhoeal disorders of early onset, particularly focussing on the more recently described gene defects associated with protein loosing enteropathy.

Immune dysregulation, polyendocrinopathy and enteropathy, X-linked (IPEX) syndrome due to a mutation in FOXP3, modified by a pathogenic variant in SON (SON DNA-binding protein)

Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked, known as IPEX syndrome, is a rare heterogeneous condition. Zhu-Tokita-Takenouchi-Kim Syndrome (ZTTK) is an autosomal dominant condition arising from a mutation in the SON gene, which is involved in mRNA splicing. A case showing interactions of mutations in these two genes is described in which both conditions become non-typical.

Case report: Dupilumab treatment improved type 2 disorders in a patient with IPEX syndrome diagnosis

We described a case of IPEX syndrome successfully controlled with dupilumab, an anti-IL4 receptor alpha subunit inhibitor. IPEX syndrome is a rare and generally fatal genetic disorder characterized by immune dysregulation, polyendocrinopathy and enteropathy, mostly diagnosed in early childhood. Nonetheless, cases reported in the last 20 years demonstrated that IPEX clinical spectrum encompasses more than the classical triad of early-onset intractable diarrhea, type 1 diabetes and eczema. Atypical cases of IPEX include patients with late-onset of symptoms, single-organ involvement, mild disease phenotypes or rare clinical features. A 21-year-old caucasian man presented with immune dysregulation (hypereosinophilia and elevated IgE), protein-losing enteropathy, polyendocrinopathy (thyroiditis, osteoporosis, delayed puberty), weight loss, eczema manifestations and celiac disease. IPEX syndrome was diagnosed because of the presence of a hemizygous mutation in FOXP3 gene (c.543C>T (p.S181S) in the exon 5). During the course of the disease, the patient developed erosive proctitis, pyoderma gangrenosum, and erythema nodosum. Symptoms improved only after enteral and parenteral corticosteroid therapy and the patient soon developed steroid-dependence. Notwithstanding various therapies including azathioprine, sirolimus, tacrolimus, adalimumab, vedolizumab, the patient failed to achieve a good control of symptoms without steroids. Almost exclusive enteral nutrition with a hypoallergenic, milk-protein free, amino acid-based food for special medical purposes. He continued to lose weight (BMI 14.5 kg/m2) with a consequent high limitation of physical activity and a progressive worsening of the quality of life. In consideration of the poor response to conventional immunosuppressants and the presence of type 2 inflammatory manifestations, treatment with dupilumab at an initial dose of 600 mg, followed by a maintenance dose of 300 mg every other week, according to atopic dermatitis labeled dose, was started and combined to oral budesonide 6 mg/day and 6-mercaptopurine 75 mg/day. The patient experienced a rapid improvement in bowel and skin symptoms, leading to a progressive tapering of steroids. By our knowledge, this is the first report of IPEX syndrome successfully treated by antiIL-4/IL-13 therapy. In this case dupilumab demonstrated to be an effective, safe and steroid-sparing option.

The transcription factor FoxP3 can fold into two dimerization states with divergent implications for regulatory T cell function and immune homeostasis

FoxP3 is an essential transcription factor (TF) for immunologic homeostasis, but how it utilizes the common forkhead DNA-binding domain (DBD) to perform its unique function remains poorly understood. We here demonstrated that unlike other known forkhead TFs, FoxP3 formed a head-to-head dimer using a unique linker (Runx1-binding region [RBR]) preceding the forkhead domain. Head-to-head dimerization conferred distinct DNA-binding specificity and created a docking site for the cofactor Runx1. RBR was also important for proper folding of the forkhead domain, as truncation of RBR induced domain-swap dimerization of forkhead, which was previously considered the physiological form of FoxP3. Rather, swap-dimerization impaired FoxP3 function, as demonstrated with the disease-causing mutation R337Q, whereas a swap-suppressive mutation largely rescued R337Q-mediated functional impairment. Altogether, our findings suggest that FoxP3 can fold into two distinct dimerization states: head-to-head dimerization representing functional specialization of an ancient DBD and swap dimerization associated with impaired functions.

Transcriptional and posttranslational regulation of Th17/Treg balance in health and disease

Regulatory T (Treg) cells and T helper type 17 (Th17) cells play important roles in adaptive immune responses, antagonizing each other in immune disorders. Th17/Treg balance is critical to maintaining the immune homeostasis of human bodies and is tightly regulated under healthy conditions. The transcription factors that are required for driving Th17 and Treg cell lineages differentiation respectively, RORγt and FOXP3 are tightly regulated under different tissue microenvironment, especially the transcriptional induction, posttranslational modifications, and dynamic enzymatic cofactors binding. The imbalance caused by alteration of the quantity or properties of RORγt⁺ Th17 or FOXP3⁺ Treg can contribute to inflammatory disorders in humans. Restoring Th17/Treg balance by modifying the enzymatic activities of RORγt and FOXP3 binding partners may be therapeutically applied to treat severe immune disorders. In this review, we focus on the transcriptional and posttranslational regulations of Th17/Treg balance, immune disorders caused by Th17/Treg imbalance, and new therapeutic strategies for restoring immune homeostasis.

Familial Clustering of Juvenile Psoriatic Arthritis Associated with a Hemizygous FOXP3 Mutation

PURPOSE OF REVIEW

We describe the clinical and genetic findings in four patients from a single family who presented with refractory psoriatic arthritis and were hemizygous in the forkhead box protein 3 (FOXP3) gene (c.1222G>A).

RECENT FINDINGS

We report four siblings with hemizygous mutation in the FOXP3 gene (c.1222G>A) who presented with type 1 diabetes mellitus and psoriatic arthritis poorly responsive to treatment. Our findings expand the phenotype spectrum of FOXP3 mutations. Immune dysregulation, polyendocrinopathy, and enteropathy, X-linked (IPEX) syndrome is a rare disorder caused by mutations in FOXP3 gene, which lead to early onset of constellation of autoimmune manifestations. This report highlights the influence of immune dysregulation in juvenile arthritis.

Treatment of Intestinal Inflammation With Epicutaneous Immunotherapy Requires TGF-β and IL-10 but Not Foxp3+ Tregs

Background: Inflammatory bowel disease (IBD) involves an increase in T effector cells in the intestines that disrupts the normal balance with T regulatory cells (Tregs). A therapy that restores this balance has the potential to treat IBD. We have shown that epicutaneous exposure to OVA induces Tregs that are able to induce tolerance. The Tregs also migrate to the intestines where they alleviate colitis in mice, demonstrating the potential for skin induced Tregs to treat intestinal inflammation. We investigated the role of Foxp3, IL-10, and TGF-β in the suppression of colitis by epicutaneous immunotherapy (ET). Methods: RAG1^-/- mice were transferred with CD4⁺CD45RB^hi T cells from wild type mice to induce colitis. To determine whether Foxp3⁺ Tregs, IL-10-, or TGF-β-producing Tregs were necessary, Foxp3-DTR, IL-10^-/-, or CD4-dnTGFBRII mice were immunized with OVA and OVA TCR enriched T cells were added. As control groups, some mice were given OVA TCR enriched T cells from wild type mice or no OVA TCR enriched T cells. Half of the mice in each group were then exposed on the skin to Viaskin patches containing OVA weekly for 3 weeks. Mice given OVA TCR enriched T cells from Foxp3-DTR mice were given diphtheria toxin (DT) or not in addition to ET. Mice were assessed for weight loss, colon length, colonic cytokine production, and histological inflammation. Results: ET, after injection with OVA TCR enriched T cells derived from wild type mice, prevented weight loss, decreased colonic inflammatory cytokine production and histological colitis. ET in the absence of the OVA TCR enriched T cells did not alleviate colitis. ET, after injection with OVA TCR enriched T cells derived from Foxp3-DTR mice, prevented weight loss, decreased colonic inflammatory cytokine production, and histological colitis. Ablation with DT did not impair the ability of ET to alleviate colitis. ET failed to alleviate colitis when OVA TCR enriched T cells were derived from IL-10^-/- or CD4-dnTGFBRII mice. Conclusions: ET through induction of Tregs, which produce IL-10 and TGF-β, could be a promising treatment for IBD.

IPEX Syndrome: Genetics and Treatment Options

(1) Background: IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome characterizes a complex autoimmune reaction beginning in the perinatal period, caused by a dysfunction of the transcription factor forkhead box P3 (FOXP3). (2) Objectives: Studies have shown the clinical, immunological, and molecular heterogeneity of patients with IPEX syndrome. The symptoms, treatment, and survival were closely connected to the genotype of the IPEX syndrome. Recognition of the kind of mutation is important for the diagnostics of IPEX syndrome in newborns and young infants, as well as in prenatal screening. The method of choice for treatment is hematopoietic stem cell transplantation and immunosuppressive therapy. In children, supportive therapy for refractory diarrhea is very important, as well as replacement therapy of diabetes mellitus type 1 (DMT1) and other endocrinopathies. In the future, genetic engineering methods may be of use in the successful treatment of IPEX syndrome. (3) Conclusions: The genetic defects determine a diagnostic approach and prognosis, making the knowledge of the genetics of IPEX syndrome fundamental to introducing novel treatment methods.

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.

A critical role of foxp3a-positive regulatory T cells in maintaining immune homeostasis in zebrafish testis development

Suppressive regulatory T cells (Treg cells) play a vital role in preventing autoimmunity and restraining excessive immune response to both self- and non-self-antigens. Studies on humans and mice show that the Forkhead box p3 (Foxp3) is a key regulatory gene for the development and function of Treg cells. In zebrafish, Treg cells have been identified by using foxp3a as a reliable marker. However, little is known about the function of foxp3a and Treg cells in gonadal development and sex differentiation. Here, we show that foxp3a is essential for maintaining immune homeostasis in zebrafish testis development. We found that foxp3a was specifically expressed in a subset of T cells in zebrafish testis, while knockout of foxp3a led to deficiency of foxp3a-positive Treg cells in the testis. More than 80% of foxp3a^-/- mutants developed as subfertile males, and the rest of the mutants developed as fertile females with decreased ovulation. Further study revealed that foxp3a^-/- mutants had a delayed juvenile ovary-to-testis transition in definite males and sex reversal in about half of the definite females, which led to a dominance of later male development. Owing to the absence of foxp3a-positive Treg cells in the differentiating testis of foxp3a^-/- mutants, abundant T cells and macrophages expand to disrupt an immunosuppressive milieu, resulting in defective development of germ cells and gonadal somatic cells and leading to development of infertile males. Therefore, our study reveals that foxp3a-positive Treg cells play an essential role in the orchestration of gonadal development and sex differentiation in zebrafish.