STAT3 gain-of-function syndrome

A human STAT3 gain-of-function variant drives local Th17 dysregulation and skin inflammation in mice

Germline gain-of-function (GOF) variants in STAT3 cause an inborn error of immunity associated with early-onset poly-autoimmunity and immune dysregulation. To study tissue-specific immune dysregulation, we used a mouse model carrying a missense variant (p.G421R) that causes human disease. We observed spontaneous and imiquimod (IMQ)-induced skin inflammation associated with cell-intrinsic local Th17 responses in STAT3 GOF mice. CD4+ T cells were sufficient to drive skin inflammation and showed increased Il22 expression in expanded clones. Certain aspects of disease, including increased epidermal thickness, also required the presence of STAT3 GOF in epithelial cells. Treatment with a JAK inhibitor improved skin disease without affecting local Th17 recruitment and cytokine production. These findings collectively support the involvement of Th17 responses in the development of organ-specific immune dysregulation in STAT3 GOF and suggest that the presence of STAT3 GOF in tissues is important for disease and can be targeted with JAK inhibition.

Stat3 Regulates Developmental Hematopoiesis and Impacts Myeloid Cell Function via Canonical and Non-Canonical Modalities

INTRODUCTION

Signal transducer and activator of transcription (STAT) 3 is extensively involved in the development, homeostasis, and function of immune cells, with STAT3 disruption associated with human immune-related disorders. The roles ascribed to STAT3 have been assumed to be due to its canonical mode of action as an inducible transcription factor downstream of multiple cytokines, although alternative noncanonical functional modalities have also been identified. The relative involvement of each mode was further explored in relevant zebrafish models.

METHODS

Genome editing with CRISPR/Cas9 was used to generate mutants of the conserved zebrafish Stat3 protein: a loss of function knockout (KO) mutant and a mutant lacking C-terminal sequences including the transactivation domain (ΔTAD). Lines harboring these mutations were analyzed with respect to blood and immune cell development and function in comparison to wild-type zebrafish.

RESULTS

The Stat3 KO mutant showed perturbation of hematopoietic lineages throughout primitive and early definitive hematopoiesis. Neutrophil numbers did not increase in response to lipopolysaccharide (LPS) or granulocyte colony-stimulating factor (G-CSF) and their migration was significantly diminished, the latter correlating with abrogation of the Cxcl8b/Cxcr2 pathway, with macrophage responses perturbed. Intriguingly, many of these phenotypes were not shared by the Stat3 ΔTAD mutant. Indeed, only neutrophil and macrophage development were disrupted in these mutants with responsiveness to LPS and G-CSF maintained, and neutrophil migration actually increased.

CONCLUSION

This study has identified roles for zebrafish Stat3 within hematopoietic stem cells impacting multiple lineages throughout primitive and early definitive hematopoiesis, myeloid cell responses to G-CSF and LPS and neutrophil migration. Many of these roles showed conservation, but notably several involved noncanonical modalities, providing additional insights for relevant diseases.

Th17/1 and ex-Th17 cells are detected in patients with polyarticular juvenile arthritis and increase following treatment

BACKGROUND

A better understanding of the pathogenesis of polyarticular juvenile idiopathic arthritis (polyJIA) is needed to aide in the development of data-driven approaches to guide selection between therapeutic options. One inflammatory pathway of interest is JAK-STAT signaling. STAT3 is a transcription factor critical to the differentiation of inflammatory T helper 17 cells (Th17s). Previous studies have demonstrated increased STAT3 activation in adult patients with rheumatoid arthritis, but less is known about STAT3 activation in polyJIA. We hypothesized that Th17 cells and STAT3 activation would be increased in treatment-naïve polyJIA patients compared to pediatric controls.

METHODS

Blood from 17 patients with polyJIA was collected at initial diagnosis and again if remission was achieved (post-treatment). Pediatric healthy controls were also collected. Peripheral blood mononuclear cells were isolated and CD4 + T cell subsets and STAT activation (phosphorylation) were evaluated using flow cytometry. Data were analyzed using Mann-Whitney U and Wilcoxon matched-pairs signed rank tests.

RESULTS

Treatment-naïve polyJIA patients had increased Th17 cells (CD3 + CD4 + interleukin(IL)-17 +) compared to controls (0.15% v 0.44%, p < 0.05), but Tregs (CD3 + CD4 + CD25 + FOXP3 +) from patients did not differ from controls. Changes in STAT3 phosphorylation in CD4 + T cells following ex vivo stimulation were not significantly different in patients compared to controls. We identified dual IL-17 + and interferon (IFN)γ + expressing CD4 + T cells in patients, but not controls. Further, both Th17/1 s (CCR6 + CD161 + IFNγ + IL-17 +) and ex-Th17s (CCR6 + CD161 + IFNγ + IL-17neg) were increased in patients' post-treatment (Th17/1: 0.3% v 0.07%, p < 0.05 and ex-Th17s: 2.3% v 1.4%, p < 0.05). The patients with the highest IL-17 expressing cells post-treatment remained therapy-bound.

CONCLUSIONS

Patients with polyJIA have increased baseline Th17 cells, potentially reflecting higher tonic STAT3 activation in vivo. These quantifiable immune markers may identify patients that would benefit upfront from pathway-focused biologic therapies. Our data also suggest that inflammatory CD4 + T cell subsets not detected in controls but increased in post-treatment samples should be further evaluated as a tool to stratify patients in remission on medication. Future work will explore these proposed diagnostic and prognostic biomarkers.

Treg in inborn errors of immunity: gaps, knowns and future perspectives

Regulatory T cells (Treg) are essential for immune balance, preventing overreactive responses and autoimmunity. Although traditionally characterized as CD4+CD25+CD127lowFoxP3hi, recent research has revealed diverse Treg subsets such as Tr1, Tr1-like, and CD8 Treg. Treg dysfunction leads to severe autoimmune diseases and immune-mediated inflammatory disorders. Inborn errors of immunity (IEI) are a group of disorders that affect correct functioning of the immune system. IEI include Tregopathies caused by genetic mutations affecting Treg development or function. In addition, Treg dysfunction is also observed in other IEIs, whose underlying mechanisms are largely unknown, thus requiring further research. This review provides a comprehensive overview and discussion of Treg in IEI focused on: A) advances and controversies in the evaluation of Treg extended subphenotypes and function; B) current knowledge and gaps in Treg disturbances in Tregopathies and other IEI including Treg subpopulation changes, genotype-phenotype correlation, Treg changes with disease activity, and available therapies, and C) the potential of Treg cell-based therapies for IEI with immune dysregulation. The aim is to improve both the diagnostic and the therapeutic approaches to IEI when there is involvement of Treg. We performed a non-systematic targeted literature review with a knowledgeable selection of current, high-quality original and review articles on Treg and IEI available since 2003 (with 58% of the articles within the last 6 years) in the PubMed database.

Signal Transducer and Activator of Transcription Proteins at the Nexus of Immunodeficiency, Autoimmunity and Cancer

The signal transducer and activator of transcription (STAT) family of proteins has been demonstrated to perform pivotal roles downstream of a myriad of cytokines, particularly those that control immune cell production and function. This is highlighted by both gain-of-function (GOF) and loss-of-function (LOF) mutations being implicated in various diseases impacting cells of the immune system. These mutations are typically inherited, although somatic GOF mutations are commonly observed in certain immune cell malignancies. This review details the growing appreciation of STAT proteins as a key node linking immunodeficiency, autoimmunity and cancer.

Transcription factors in the development and treatment of immune disorders

Immune function is highly controlled at the transcriptional level by the binding of transcription factors (TFs) to promoter and enhancer elements. Several TF families play major roles in immune gene expression, including NF-κB, STAT, IRF, AP-1, NRs, and NFAT, which trigger anti-pathogen responses, promote cell differentiation, and maintain immune system homeostasis. Aberrant expression, activation, or sequence of isoforms and variants of these TFs can result in autoimmune and inflammatory diseases as well as hematological and solid tumor cancers. For this reason, TFs have become attractive drug targets, even though most were previously deemed "undruggable" due to their lack of small molecule binding pockets and the presence of intrinsically disordered regions. However, several aspects of TF structure and function can be targeted for therapeutic intervention, such as ligand-binding domains, protein-protein interactions between TFs and with cofactors, TF-DNA binding, TF stability, upstream signaling pathways, and TF expression. In this review, we provide an overview of each of the important TF families, how they function in immunity, and some related diseases they are involved in. Additionally, we discuss the ways of targeting TFs with drugs along with recent research developments in these areas and their clinical applications, followed by the advantages and disadvantages of targeting TFs for the treatment of immune disorders.

Understanding the Spectrum of Immune Dysregulation Manifestations in Autoimmune Lymphoproliferative Syndrome and Autoimmune Lymphoproliferative Syndrome-like Disorders

As a disorder of immune dysregulation, autoimmune lymphoproliferative syndrome (ALPS) stems from pathogenic variants in the first apoptosis signal-mediated apoptosis (Fas) and Fas-ligand pathway that result in elevations of CD3+ TCRαβ+ CD4- CD8- T cells along with chronic lymphoproliferation, a heightened risk for malignancy, and importantly for the rheumatologist, increased risk of autoimmunity. While immune cytopenias are the most encountered autoimmune phenomena, there is increasing appreciation for ocular, musculoskeletal, pulmonary and renal inflammatory manifestations similar to more common rheumatology diseases. Additionally, ALPS-like conditions that share similar clinical features and opportunities for targeted therapy are increasingly recognized via genetic testing, highlighting the need for rheumatologists to be facile in the recognition and diagnosis of this spectrum of disorders. This review will focus on clinical and laboratory features of both ALPS and ALPS-like disorders with the intent to provide a framework for rheumatologists to understand the pathophysiologic drivers and discriminate between diagnoses.

Transcription factor defects in inborn errors of immunity with atopy

Transcription factors (TFs) are critical components involved in regulating immune system development, maintenance, and function. Monogenic defects in certain TFs can therefore give rise to inborn errors of immunity (IEIs) with profound clinical implications ranging from infections, malignancy, and in some cases severe allergic inflammation. This review examines TF defects underlying IEIs with severe atopy as a defining clinical phenotype, including STAT3 loss-of-function, STAT6 gain-of-function, FOXP3 deficiency, and T-bet deficiency. These disorders offer valuable insights into the pathophysiology of allergic inflammation, expanding our understanding of both rare monogenic and common polygenic allergic diseases. Advances in genetic testing will likely uncover new IEIs associated with atopy, enriching our understanding of molecular pathways involved in allergic inflammation. Identification of monogenic disorders profoundly influences patient prognosis, treatment planning, and genetic counseling. Hence, the consideration of IEIs is essential for patients with severe, early-onset atopy. This review highlights the need for continued investigation into TF defects to enhance our understanding and management of allergic diseases.

Activated PI3Kδ syndrome - reviewing challenges in diagnosis and treatment

Activated PI3Kδ syndrome (APDS) is a rare inborn error of immunity (IEI) characterized primarily by frequent infections, lymphoproliferation and autoimmunity. Since its initial description in 2013, APDS has become part of the growing group of nearly 500 IEIs affecting various components of the immune system. The two subtypes of APDS - APDS1 and APDS2 - are caused by variants in the PIK3CD and PIK3R1 genes, respectively. Due to the rarity of the disease and the heterogeneous clinical picture, many patients are not diagnosed until years after symptom onset. Another challenge is the large number of PIK3CD and PIK3R1 variants whose functional significance for developing APDS is inconclusive. Treatment of APDS has so far been mostly symptom-oriented with immunoglobulin replacement therapy, immunosuppressive therapies and antibiotic or antiviral prophylaxes. Additionally, allogeneic stem cell transplantation as well as new targeted therapies are options targeting the root cause that may improve patients' quality of life and life expectancy. However, the clinical course of the disease is difficult to predict which complicates the choice of appropriate therapies. This review article discusses diagnostic procedures and current and future treatment options, and highlights the difficulties that physicians, patients and their caretakers face in managing this complex disease. This article is based on cohort studies, the German and US guidelines on the management of primary immunodeficiencies as well as on published experience with diagnosis and compiled treatment experience for APDS.