Single-cell RNA sequencing defines disease-specific differences between chronic nodular prurigo and atopic dermatitis

The big four in the pathogenesis and pathophysiology of prurigo nodularis: Interplay among type 2 inflammation, epidermal hyperplasia, dermal fibrosis, and itch from neuroimmune dysregulation

Prurigo nodularis (PN) is a distinct inflammatory dermatosis. It is characterized by intensely pruritic, firm nodules, typically 1 to 2 cm in diameter, which usually develop on the extensor surfaces of the extremities. Histopathologically, the following characteristics are observed in PN lesions: (1) dermal cellular infiltrates composed of type 2 inflammation-associated immune cells with lesional overexpression of type 2 cytokines (including interleukin [IL]-4, IL-13, and IL-31), (2) dermal fibrosis, and (3) epidermal hyperplasia with hyperkeratosis. Additionally, functional and structural alterations of cutaneous sensory nerve fibers profoundly contribute to itch in cooperation with type 2 inflammation. This abnormal interaction is referred to as neuroimmune dysregulation. The scratching behavior induced by itching from neuroimmune dysregulation initiates the development of prurigo nodules. This distinctive pathogenic feature of "itch-first" in PN is distinct from "inflammation-first" in atopic dermatitis, where the skin initially exhibits type 2 inflammation, which is subsequently followed by itching. The interplay between the four elements, namely type 2 inflammation, epidermal hyperplasia, dermal fibrosis, and itch resulting from neuroimmune dysregulation, appears to be pivotal in the pathogenesis and pathophysiology of PN.

Single-cell RNA sequencing of chronic idiopathic erythroderma defines disease-specific markers

BACKGROUND

Chronic erythroderma is a potentially life-threatening condition that can be caused by various diseases, but approximately 30% of cases remain idiopathic, often with insufficient treatment options.

OBJECTIVE

We sought to establish a molecular disease map of chronic idiopathic erythroderma (CIE).

METHODS

We performed single-cell RNA sequencing combined with T-cell receptor sequencing of blood and skin from 5 patients with CIE and compared results with 8 cases of erythrodermic cutaneous T-cell lymphoma (eCTCL), 15 cases of moderate to severe atopic dermatitis, 10 cases of psoriasis, and 20 healthy control individuals.

RESULTS

In eCTCL, we found strong expansion of CD4+ malignant clones with a CCR7+SELL+ central memory phenotype. In contrast, CIE exhibited a pattern of low-level, but consistent, expansion of CD8A+KLRK1+ T-cell clones, both in blood and in skin. KLRK1 was also expressed by CCR10+FUT7+ skin-homing CIE blood T cells that had increased proliferation rates and were absent in all other conditions. While patients with CIE and eCTCL lacked the strong type 2 or type 17 immune skewing typically found in atopic dermatitis or psoriasis, respectively, they were characterized by upregulation of MHC II genes (HLA-DRB1, HLA-DRA, and CD74) in keratinocytes and fibroblasts, most likely in an IFN-γ-dependent fashion. Overall, we found the strongest upregulation of type 1 immune mediators in CIE samples, both in the expanded CD8A+ clones and in the tissue microenvironment.

CONCLUSIONS

Despite the notion that CIE might be a mere bundle of various yet uncharacterized disease processes, we found specific pathogenic signatures in these patients, which were different from other forms of erythroderma. These data might help to improve our pathogenic understanding of the blood and skin compartments of CIE, aiding in discovery of future treatment targets.

Type 2 immunity in allergic diseases

Significant advancements have been made in understanding the cellular and molecular mechanisms of type 2 immunity in allergic diseases such as asthma, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis (EoE), food and drug allergies, and atopic dermatitis (AD). Type 2 immunity has evolved to protect against parasitic diseases and toxins, plays a role in the expulsion of parasites and larvae from inner tissues to the lumen and outside the body, maintains microbe-rich skin and mucosal epithelial barriers and counterbalances the type 1 immune response and its destructive effects. During the development of a type 2 immune response, an innate immune response initiates starting from epithelial cells and innate lymphoid cells (ILCs), including dendritic cells and macrophages, and translates to adaptive T and B-cell immunity, particularly IgE antibody production. Eosinophils, mast cells and basophils have effects on effector functions. Cytokines from ILC2s and CD4+ helper type 2 (Th2) cells, CD8 + T cells, and NK-T cells, along with myeloid cells, including IL-4, IL-5, IL-9, and IL-13, initiate and sustain allergic inflammation via T cell cells, eosinophils, and ILC2s; promote IgE class switching; and open the epithelial barrier. Epithelial cell activation, alarmin release and barrier dysfunction are key in the development of not only allergic diseases but also many other systemic diseases. Recent biologics targeting the pathways and effector functions of IL4/IL13, IL-5, and IgE have shown promising results for almost all ages, although some patients with severe allergic diseases do not respond to these therapies, highlighting the unmet need for a more detailed and personalized approach.

Molecular profiling of skin cells identifies distinct cellular signatures in radiation-induced skin injury across various stages in the murine dataset

BACKGROUND

Radiation-induced skin injury (RISI) commonly manifests in cancer patients undergoing radiotherapy (RT). However, a universally accepted standard for treating radiation injury has not yet been established. Our objective was to provide a detailed molecular overview of skin pre- and post-radiation therapy, aiming to enhance our understanding of the subclusters and molecular mechanisms contributing to radiodermatitis.

METHODS

C57BL/6 mice were subjected to a single fraction (20 Gy) of RT targeting the right dorsal skin. We then employed integrated single-cell RNA sequencing (scRNA-seq) to analyze skin samples from mice at 7 and 30 days after radiation exposure, as well as from non-irradiated mice. The Seurat analysis pipeline, Cellchat, SCP, and ssGSEA were used to define the cell types and mechanisms involved in radiation-induced skin injury. Reverse transcription polymerase chain reaction (RT-PCR), multiplex immunofluorescent staining, and other datasets (GSE130183, GSE193564, and GSE193807) were used to validate our findings.

RESULTS

Thirty-two distinct cell clusters encompassing 71,412 cells were identified. We discovered that cycling keratinocytes (KCs), with the BMP signaling pathway enriched, could activate the Wnt pathway, as well as the SMAD pathways, driving the wound healing and fibrosis processes in RISI. Terminally differentiated secretory-papillary fibroblasts (Fibs) are capable of attracting immune cells, which contributes to the pathogenesis of RISI. Lymphatic endothelial cells (ECs) with pro-inflammatory properties play a critical role in the pathogenesis of RISI by facilitating leukocyte migration. Our analysis also highlighted enhanced ligand-receptor interactions, notably the interactions between chemokines like CXCL10, CCL2, and ACKR1, across subclusters of inflammatory KCs, Fibs, ECs, and immune cells, underscoring their pivotal role in leukocyte recruitment in RISI.

CONCLUSIONS

Cycling KCs, secretory-papillary Fibs, and lymphatic ECs play critical roles in RISI progression. Targeting the interactions of these subclusters with immune cells might help improve the severity of RISI. Furthermore, our study provides a valuable resource for understanding the interactions among immune cells in the context of RISI.

IL-9 sensitizes human TH2 cells to proinflammatory IL-18 signals in atopic dermatitis

BACKGROUND

TH2 cells crucially contribute to the pathogenesis of atopic dermatitis (AD) by secreting high levels of IL-13 and IL-22. Yet the upstream regulators that activate TH2 cells in AD skin remain unclear. IL-18 is a putative upstream regulator of TH2 cells because it is implicated in AD pathogenesis and has the capacity to activate T cells.

OBJECTIVE

We sought to decipher the role of IL-18 in TH2 responses in blood and skin of AD patients.

METHODS

Peripheral blood mononuclear cells and skin biopsy samples from AD patients and healthy donors were used. Functional assays were performed ex vivo using stimulation or blocking experiments. Analysis was performed by flow cytometry, bead-based multiplex assays, RT-qPCR, RNA-Seq, Western blot, and spatial sequencing.

RESULTS

IL-18Rα+ TH2 cells were enriched in blood and lesional skin of AD patients. Of all the cytokines for which TH2 cells express the receptor, only IL-9 was able to induce IL-18R via an IL-9R-JAK1/JAK3-STAT1 signaling pathway. Functionally, stimulation of circulating TH2 cells with IL-18 induced secretion of IL-13 and IL-22, an effect that was enhanced by costimulation with IL-9. Mechanistically, IL-18 induced TH2 cytokines via activation of IRAK4, NF-κB, and AP-1 signaling in TH2 cells, and neutralization of IL-18 inhibited these cytokines in cultured explants of AD skin lesions. Finally, IL-18 protein levels correlated positively with disease severity in lesional AD skin.

CONCLUSION

Our data identify a novel IL-9/IL-18 axis that contributes to TH2 responses in AD. Our findings suggest that both IL-9 and IL-18 could represent upstream targets for future treatment of AD.

Single-cell sequencing delineates T-cell clonality and pathogenesis of the parapsoriasis disease group

BACKGROUND

Mycosis fungoides (MF), the most common cutaneous T-cell lymphoma, is often underdiagnosed in early stages because of similarities with benign dermatoses such as atopic dermatitis (AD). Furthermore, the delineation from what is called "parapsoriasis en plaque", a disease that can appear either in a small- or large-plaque form, is still controversial.

OBJECTIVE

We sought to characterize the parapsoriasis disease spectrum.

METHODS

We performed single-cell RNA sequencing of skin biopsies from patients within the parapsoriasis-to-early-stage MF spectrum, stratified for small and large plaques, and compared them to AD, psoriasis, and healthy control skin.

RESULTS

Six of 8 large-plaque lesions harbored either an expanded alpha/beta or gamma/delta T-cell clone with downregulation of CD7 expression, consistent with a diagnosis of early-stage MF. In contrast, 6 of 7 small-plaque lesions were polyclonal in nature, thereby lacking a lymphomatous phenotype, and also revealed a less inflammatory microenvironment than early-stage MF or AD. Of note, polyclonal small- and large-plaque lesions characteristically harbored a population of NPY+ innate lymphoid cells and displayed a stromal signature of complement upregulation and antimicrobial hyperresponsiveness in fibroblasts and sweat gland cells, respectively. These conditions were clearly distinct from AD or psoriasis, which uniquely harbored CD3+CRTH2+ IL-13 expressing "TH2A" cells, or strong type 17 inflammation, respectively.

CONCLUSION

These data position polyclonal small- and large-plaque parapsoriasis lesions as a separate disease entity that characteristically harbors a so far undescribed innate lymphoid cell population. We thus propose a new term, "polyclonal parapsoriasis en plaque", for this kind of lesion because they can be clearly differentiated from early- and advanced-stage MF, psoriasis, and AD on several cellular and molecular levels.

Thymus and activation-regulated chemokine (CCL17) as a clinical biomarker in atopic dermatitis: significance and limitations in the new treatment era

Thymus and activation-regulated chemokine (TARC; CCL17) is a T-helper-2 chemokine that reflects atopic dermatitis (AD) disease activity. Since 2008, serum TARC levels have been commercially measured in Japan, and clinical experience has shown the usefulness of TARC. The fallacy that eczema is always visible often hinders successful treatment, when there is subclinical inflammation which is inferable from the TARC level. AD treatment has entered a new era with higher therapeutic efficacy. TARC has a different meaning than it did previously, and its significance and limitations are discussed. First, a more appropriate topical therapy monitoring TARC would be useful in selecting truly necessitated patients for expensive new therapies. Dupilumab quickly lowers serum TARC before clinical improvement, and its normalization is not a criterion for dose reduction. However, in some severe cases, TARC may help determine whether to continue treatment. During treatment with JAK inhibitors, serum TARC levels are often elevated and may be abnormally high, leading to the exacerbation of dermatitis. Prurigo nodularis is divided into two types associated with elevated and normal TARC levels, which may aid in the selection of therapeutic agents. In this new era, TARC remains a useful biomarker for more accurate drug selection and the determination of therapeutic efficacy; Currently, in clinical trials of AD, all outcome measurements depend on the clinical score; however the use of a biomarker, such as TARC, as a secondary outcome measure will clarify the characteristics of each drug and the pathophysiological conditions for which it is expected to be effective.

Translating tissue expression of STAT 1, 3 and 6 in prurigo nodularis to clinical efficacy of oral tofacitinib - A prospective single-arm investigational study

Background Interleukin (IL)-4, IL-13, IL-17, IL-22 and IL-3 are overexpressed in prurigo nodularis (PN). They mediate their action via the Janus Kinase (JAK) Signal transducer and activator of transcription (STAT) pathway. Objectives Our aim was to study the expression of tissue STAT1, STAT3, and STAT6, as well as the efficacy of the JAK-STAT inhibitor, tofacitinib, in PN. Methods A prospective study was conducted in a tertiary care hospital. Patients with PN were recruited after excluding secondary causes. Pruritus was graded using Pruritus Grading System Score (PGSS). All cases underwent histological assessment using immunohistochemical markers for STAT1, STAT3, and STAT6 in both lesional and perilesional skin. Tofacitinib was initiated at a dose of 5 mg twice daily or 11 mg once daily and then tapered to a maintenance dose. The final PGSS at the time of data evaluation, as well as the occurrence of remissions and relapses, was assessed. Results The majority of the 17 patients included in the study had moderate to severe disease. Immunohistochemical analysis revealed marked tissue expression of STAT6 in 13 and STAT3 in 10 patients, while STAT1 expression was seen in only 4 patients [p < 0.05], suggesting a Th2/Th17 tissue response. The mean onset of action of tofacitinib was 11.2 ± 6.44 days and the mean duration of treatment was 5.6 ± 2.2 months. A significant reduction in PGSS was noted after treatment (66.1%, P value 0.0004). Fourteen of the patients maintained remission on low-dose therapy (5 mg OD or A/D) while one patient experienced a relapse. No serious adverse effects were noted. Limitation We could not study the tissue cytokines and the expression of STATs after achieving clinical response on oral tofacitinib. Conclusion The efficacy of tofacitinib in PN is based on its inhibitory effect on Th2 and Th17 cytokines, which is dependent on STAT6 and STAT3.

Atopic dermatitis: pathogenesis and therapeutic intervention

The skin serves as the first protective barrier for nonspecific immunity and encompasses a vast network of skin-associated immune cells. Atopic dermatitis (AD) is a prevalent inflammatory skin disease that affects individuals of all ages and races, with a complex pathogenesis intricately linked to genetic, environmental factors, skin barrier dysfunction as well as immune dysfunction. Individuals diagnosed with AD frequently exhibit genetic predispositions, characterized by mutations that impact the structural integrity of the skin barrier. This barrier dysfunction leads to the release of alarmins, activating the type 2 immune pathway and recruiting various immune cells to the skin, where they coordinate cutaneous immune responses. In this review, we summarize experimental models of AD and provide an overview of its pathogenesis and the therapeutic interventions. We focus on elucidating the intricate interplay between the immune system of the skin and the complex regulatory mechanisms, as well as commonly used treatments for AD, aiming to systematically understand the cellular and molecular crosstalk in AD-affected skin. Our overarching objective is to provide novel insights and inform potential clinical interventions to reduce the incidence and impact of AD.

Skin microdialysis detects distinct immunologic patterns in chronic inflammatory skin diseases

BACKGROUND

Insight into the pathophysiology of inflammatory skin diseases, especially at the proteomic level, is severely hampered by the lack of adequate in situ data.

OBJECTIVE

We characterized lesional and nonlesional skin of inflammatory skin diseases using skin microdialysis.

METHODS

Skin microdialysis samples from patients with atopic dermatitis (AD, n = 6), psoriasis vulgaris (PSO, n = 7), or prurigo nodularis (PN, n = 6), as well as healthy controls (n = 7), were subjected to proteomic and multiplex cytokine analysis. Single-cell RNA sequencing of skin biopsy specimens was used to identify the cellular origin of cytokines.

RESULTS

Among the top 20 enriched Gene Ontology (GO; geneontology.org) annotations, nicotinamide adenine dinucleotide metabolic process, regulation of secretion by cell, and pyruvate metabolic process were elevated in microdialysates from lesional AD skin compared with both nonlesional skin and controls. The top 20 enriched Kyoto Encyclopedia of Genes and Genomes (KEGG; genome.jp/kegg) pathways in these 3 groups overlapped almost completely. In contrast, nonlesional skin from patients with PSO or PN and control skin showed no overlap with lesional skin in this KEGG pathway analysis. Lesional skin from patients with PSO, but not AD or PN, showed significantly elevated protein levels of MCP-1 compared with nonlesional skin. IL-8 was elevated in lesional versus nonlesional AD and PSO skin, whereas IL-12p40 and IL-22 were higher only in lesional PSO skin. Integrated single-cell RNA sequencing data revealed identical cellular sources of these cytokines in AD, PSO, and PN.

CONCLUSION

On the basis of microdialysates, the proteomic data of lesional PSO and PN skin, but not lesional AD skin, differed significantly from those of nonlesional skin. IL-8, IL-22, MCP-1, and IL-12p40 might be suitable markers for minimally invasive molecular profiling.

Omics in allergy and asthma

This review explores the transformative impact of omics technologies on allergy and asthma research in recent years, focusing on advancements in high-throughput technologies related to genomics and transcriptomics. In particular, the rapid spread of single-cell RNA sequencing has markedly advanced our understanding of the molecular pathology of allergic diseases. Furthermore, high-throughput genome sequencing has accelerated the discovery of monogenic disorders that were previously overlooked as ordinary intractable allergic diseases. We also introduce microbiomics, proteomics, lipidomics, and metabolomics, which are quickly growing areas of research interest, although many of their current findings remain inconclusive as solid evidence. By integrating these omics data, we will gain deeper insights into disease mechanisms, leading to the development of precision medicine approaches that promise to enhance treatment outcomes.

Consensus on the Diagnostic Algorithm for Chronic Nodular Prurigo

Chronic nodular prurigo (CNP) is a chronic dermatological disease characterized by the presence of chronic pruritus and pruritic nodular lesions. The aim of this study was to reach consensus among a group of experts based on a non-systematic literature review and an algorithm for the clinical diagnosis of CNP. The resulting algorithm is structured in 3 blocks: 1) early identification of the patient with a possible diagnosis of CNP; 2) diagnosis and assessment of CNP; and 3) categorization of CNP (identification of the underlying causes or associated comorbidities). We believe that this clinical algorithm can facilitate the correct diagnosis of patients with CNP. Additionally, it raises awareness on the need for a multidisciplinary approach and specific treatment of CNP, steps of paramount importance to make better therapeutic decisions.

[Translated article] Consensus on the Diagnostic Algorithm for Chronic Nodular Prurigo

Chronic nodular prurigo (CNP) is a chronic dermatological disease characterized by the presence of chronic pruritus and pruritic nodular lesions. The aim of this study was to reach consensus among a group of experts based on a non-systematic literature review and an algorithm for the clinical diagnosis of CNP. The resulting algorithm is structured in 3 blocks: 1) early identification of the patient with a possible diagnosis of CNP; 2) diagnosis and assessment of CNP; and 3) categorization of CNP (identification of the underlying causes or associated comorbidities). We believe that this clinical algorithm can facilitate the correct diagnosis of patients with CNP. Additionally, it raises awareness on the need for a multidisciplinary approach and specific treatment of CNP, steps of paramount importance to make better therapeutic decisions.

Single-cell analysis in rheumatic and allergic diseases: insights for clinical practice

Since the advent of single-cell RNA sequencing (scRNA-seq) methodology, single-cell analysis has become a powerful tool for exploration of cellular networks and dysregulated immune responses in disease pathogenesis. Advanced bioinformatics tools have enabled the combined analysis of scRNA-seq data and information on various cell properties, such as cell surface molecular profiles, chromatin accessibility and spatial information, leading to a deeper understanding of pathology. This Review provides an overview of the achievements in single-cell analysis applied to clinical samples of rheumatic and allergic diseases, including rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, allergic airway diseases and atopic dermatitis, with an expanded scope beyond peripheral blood cells to include local diseased tissues. Despite the valuable insights that single-cell analysis has provided into disease pathogenesis, challenges remain in translating single-cell findings into clinical practice and developing personalized treatment strategies. Beyond understanding the atlas of cellular diversity, we discuss the application of data obtained in each study to clinical practice, with a focus on identifying biomarkers and therapeutic targets.

Review of the potential value of serum interleukin levels as prognostic biomarkers of liver failure

Liver failure (LF) is prevalent in China and is characterized by complex pathogenesis, challenging clinical management, poor prognosis, and rising incidence and mortality rates. The immune status is an important factor affecting LF prognosis. Interleukins (Ils) are a type of cytokine that act and interact with multiple cells, including immune cells. These signaling molecules play important roles in intercellular information transmission, including the regulation of immune cells; mediation of the activation, proliferation, and differentiation of T and B cells; and orchestration of the inflammatory response. To date, many studies have explored the correlation between IL expression and liver disease prognosis, but few studies have evaluated Ils as the prognostic biomarkers of LF. This article reviews the potential use of Ils as the prognostic biomarkers of LF. Particularly, it evaluates the predictive values of IL-21, IL-22, and IL-31, the three often overlooked yet promising prognostic biomarkers, in predicting susceptibility to LF. Harnessing biomarkers for early prognostic insights can facilitate tailored treatment strategies and enhance patient survival. Thus, this article focuses on the identification of IL-21, IL-22, and IL-33 as biomarkers in preclinical and clinical studies on LF and reviews their role as biomarkers in the pathogenesis and diagnosis of LF.

Keratins 6, 16, and 17 in Health and Disease: A Summary of Recent Findings

Keratins 6, 16, and 17 occupy unique positions within the keratin family. These proteins are not commonly found in the healthy, intact epidermis, but their expression increases in response to damage, inflammation, and hereditary skin conditions, as well as cancerous cell transformations and tumor growth. As a result, there is an active investigation into the potential use of these proteins as biomarkers for different pathologies. Recent studies have revealed the role of these keratins in regulating keratinocyte migration, proliferation, and growth, and more recently, their nuclear functions, including their role in maintaining nuclear structure and responding to DNA damage, have also been identified. This review aims to summarize the latest research on keratins 6, 16, and 17, their regulation in the epidermis, and their potential use as biomarkers in various skin conditions.

[Treatment of chronic prurigo: update and perspectives]

BACKGROUND

Despite the high burden in patients with chronic prurigo (CPG), the first and so far only approved systemic therapy for this disease, dupilumab, has only been available since 2022. Therefore, treatment is mostly based on expert recommendations for off-label therapies. We aim to provide an overview of current therapies and possible future therapeutic drugs for CPG patients, which are currently in clinical trials.

MATERIALS AND METHODS

For this review, a systematic literature and clinical trial search was conducted via PubMed and Clinical Trials using the terms "chronic prurigo", "chronic nodular prurigo", "prurigo nodularis" and "therapy".

CONCLUSION

Multiple new therapeutic agents are currently under investigation in clinical trials, providing promising results for future treatment options. Moreover, an annotated checklist was developed recently to improve therapeutic decision-making in daily clinical practice with CPG patients.

Markers of Dermal Fibroblast Subpopulations for Viable Cell Isolation via Cell Sorting: A Comprehensive Review

Fibroblasts are among the most abundant cell types in the human body, playing crucial roles in numerous physiological processes, including the structural maintenance of the dermis, production of extracellular matrix components, and mediation of inflammatory responses. Despite their importance, fibroblasts remain one of the least characterized cell populations. The advent of single-cell analysis techniques, particularly single-cell RNA sequencing (scRNA-seq) and fluorescence-activated cell sorting (FACS), has enabled detailed investigations into fibroblast biology. In this study, we present an extensive analysis of fibroblast surface markers suitable for cell sorting and subsequent functional studies. We reviewed over three thousand research articles describing fibroblast populations and their markers, characterizing and comparing subtypes based on their surface markers, as well as their intra- and extracellular proteins. Our detailed analysis identified a variety of distinct fibroblast subpopulations, each with unique markers, characteristics dependent on their location, and the physiological or pathophysiological environment. These findings underscore the diversity of fibroblasts as a cellular population and could lead to the development of novel diagnostic and therapeutic tools.

Dupilumab Therapy Modulates Circulating Inflammatory Mediators in Patients with Prurigo Nodularis

Prurigo nodularis (PN) is a chronic inflammatory skin disease characterized by intense pruritus and skin nodules. Beyond the skin, PN involves circulating blood inflammation that may contribute to systemic disease comorbidities. Dupilumab was recently approved for treatment of PN, but its effects on systemic inflammation are unknown. Thus, we aimed to characterize changes in plasma concentrations of inflammatory proteins after dupilumab treatment. In this exploratory study, plasma samples were collected from 3 patients with moderate-to-severe PN before and after ≥6 months of dupilumab treatment. All patients exhibited clinically significant improvements after treatment. Of the 2569 proteins tested, 186 were differentially expressed after treatment (q < 0.1, fold change > 1.3). Downregulated proteins included cytokines associated with T helper (Th) 1 (IFN-γ, TNF-α), Th2 (IL-4, IL-13), and Th17/Th22 (IL-6, IL-22) signaling. Markers of innate immunity (IL-19, toll-like receptor 1, nitric oxide synthase 2), immune cell migration (CCL20, CD177), and fibrosis (IL-11, IL-22) were also decreased (q < 0.1). Gene set variation analysis of Th2, Th17, and epithelial-mesenchymal transition gene sets showed reduced pathway expression in the post-treatment cohort (P < .05). Plasma cytokine levels of IL-11, nitric oxide synthase 2, IL-13, IL-4, and IFNG (R2 > 0.75, q < 0.10) showed the strongest correlations with pruritus severity. Dupilumab may reduce systemic inflammatory proteins associated with multiple immune and fibrosis pathways in patients with PN, potentially modulating the development of systemic disease comorbidities.

Prurigo Nodularis: Pathogenesis and the Horizon of Potential Therapeutics

Chronic pruritus that lasts for over 6 weeks can present in various forms, like papules, nodules, and plaque types, with prurigo nodularis (PN) being the most prevalent. The pathogenesis of PN involves the dysregulation of immune cell-neural circuits and is associated with peripheral neuropathies, possibly due to chronic scratching. PN is a persistent and challenging condition, involving complex interactions among the skin, immune system, and nervous system. Lesional skin in PN exhibits the infiltration of diverse immune cells like T cells, eosinophils, macrophages, and mast cells, leading to the release of inflammatory cytokines and itch-inducing substances. Activated sensory nerve fibers aggravate pruritus by releasing neurotransmitters, perpetuating a vicious cycle of itching and scratching. Traditional treatments often fail, but recent advancements in understanding the inflammatory and itch transmission mechanisms of PN have paved the way for innovative therapeutic approaches, which are explored in this review.

TCF1-LEF1 co-expression identifies a multipotent progenitor cell (TH2-MPP) across human allergic diseases

Repetitive exposure to antigen in chronic infection and cancer drives T cell exhaustion, limiting adaptive immunity. In contrast, aberrant, sustained T cell responses can persist over decades in human allergic disease. To understand these divergent outcomes, we employed bioinformatic, immunophenotyping and functional approaches with human diseased tissues, identifying an abundant population of type 2 helper T (TH2) cells with co-expression of TCF7 and LEF1, and features of chronic activation. These cells, which we termed TH2-multipotent progenitors (TH2-MPP) could self-renew and differentiate into cytokine-producing effector cells, regulatory T (Treg) cells and follicular helper T (TFH) cells. Single-cell T-cell-receptor lineage tracing confirmed lineage relationships between TH2-MPP, TH2 effectors, Treg cells and TFH cells. TH2-MPP persisted despite in vivo IL-4 receptor blockade, while thymic stromal lymphopoietin (TSLP) drove selective expansion of progenitor cells and rendered them insensitive to glucocorticoid-induced apoptosis in vitro. Together, our data identify TH2-MPP as an aberrant T cell population with the potential to sustain type 2 inflammation and support the paradigm that chronic T cell responses can be coordinated over time by progenitor cells.

Dupilumab-associated head and neck dermatitis shows a pronounced type 22 immune signature mediated by oligoclonally expanded T cells

Dupilumab, an IL4R-blocking antibody, has shown clinical efficacy for atopic dermatitis (AD) treatment. In addition to conjunctivitis/blepharitis, the de novo appearance of head/neck dermatitis is now recognized as a distinct side effect, occurring in up to 10% of patients. Histopathological features distinct from AD suggest a drug effect, but exact underlying mechanisms remain unknown. We profiled punch biopsies from dupilumab-associated head and neck dermatitis (DAHND) by using single-cell RNA sequencing and compared data with untreated AD and healthy control skin. We show that dupilumab treatment was accompanied by normalization of IL-4/IL-13 downstream activity markers such as CCL13, CCL17, CCL18 and CCL26. By contrast, we found strong increases in type 22-associated markers (IL22, AHR) especially in oligoclonally expanded T cells, accompanied by enhanced keratinocyte activation and IL-22 receptor upregulation. Taken together, we demonstrate that dupilumab effectively dampens conventional type 2 inflammation in DAHND lesions, with concomitant hyperactivation of IL22-associated responses.

Single-cell analysis of psoriasis resolution demonstrates an inflammatory fibroblast state targeted by IL-23 blockade

Biologic therapies targeting the IL-23/IL-17 axis have transformed the treatment of psoriasis. However, the early mechanisms of action of these drugs remain poorly understood. Here, we perform longitudinal single-cell RNA-sequencing in affected individuals receiving IL-23 inhibitor therapy. By profiling skin at baseline, day 3 and day 14 of treatment, we demonstrate that IL-23 blockade causes marked gene expression shifts, with fibroblast and myeloid populations displaying the most extensive changes at day 3. We also identify a transient WNT5A+/IL24+ fibroblast state, which is only detectable in lesional skin. In-silico and in-vitro studies indicate that signals stemming from these WNT5A+/IL24+ fibroblasts upregulate multiple inflammatory genes in keratinocytes. Importantly, the abundance of WNT5A+/IL24+ fibroblasts is significantly reduced after treatment. This observation is validated in-silico, by deconvolution of multiple transcriptomic datasets, and experimentally, by RNA in-situ hybridization. These findings demonstrate that the evolution of inflammatory fibroblast states is a key feature of resolving psoriasis skin.

MHC-I upregulation safeguards neoplastic T cells in the skin against NK cell-mediated eradication in mycosis fungoides

Cancer-associated immune dysfunction is a major challenge for effective therapies. The emergence of antibodies targeting tumor cell-surface antigens led to advancements in the treatment of hematopoietic malignancies, particularly blood cancers. Yet their impact is constrained against tumors of hematopoietic origin manifesting in the skin. In this study, we employ a clonality-supervised deep learning methodology to dissect key pathological features implicated in mycosis fungoides, the most common cutaneous T-cell lymphoma. Our investigations unveil the prominence of the IL-32β-major histocompatibility complex (MHC)-I axis as a critical determinant in tumor T-cell immune evasion within the skin microenvironment. In patients' skin, we find MHC-I to detrimentally impact the functionality of natural killer (NK) cells, diminishing antibody-dependent cellular cytotoxicity and promoting resistance of tumor skin T-cells to cell-surface targeting therapies. Through murine experiments in female mice, we demonstrate that disruption of the MHC-I interaction with NK cell inhibitory Ly49 receptors restores NK cell anti-tumor activity and targeted T-cell lymphoma elimination in vivo. These findings underscore the significance of attenuating the MHC-I-dependent immunosuppressive networks within skin tumors. Overall, our study introduces a strategy to reinvigorate NK cell-mediated anti-tumor responses to overcome treatment resistance to existing cell-surface targeted therapies for skin lymphoma.

Single-cell profiling of prurigo nodularis demonstrates immune-stromal crosstalk driving profibrotic responses and reversal with nemolizumab

BACKGROUND

Prurigo nodularis (PN) is a chronic neuroimmune skin disease characterized by bilaterally distributed pruritic hyperkeratotic nodules on extremities and trunk. Neuroimmune dysregulation and chronic scratching are believed to both induce and maintain the characteristic lesions.

OBJECTIVES

This study sought to provide a comprehensive view of the molecular pathogenesis of PN at the single-cell level to identify and outline key pathologic processes and the cell types involved. Features that distinguish PN skin from the skin of patients with atopic dermatitis were of particular interest. We further aimed to determine the impact of the IL31RA antagonist, nemolizumab, and its specificity at the single-cell level.

METHODS

Single-cell RNA-sequencing of skin from 15 healthy donors and nonlesional and lesional skin from 6 patients each with PN and atopic dermatitis, combined with spatial-sequencing using the 10x Visium platform. Integration with bulk RNA-sequencing data from patients treated with nemolizumab.

RESULTS

This study demonstrates that PN is an inflammatory skin disease characterized by both keratinocyte proliferation and activation of profibrotic responses. This study also demonstrates that the COL11A1+ fibroblast subset is a major contributor to fibrosis and is predominantly found in the papillary dermis of PN skin. Activation of fibrotic responses is the main distinguishing feature between PN and atopic dermatitis skin. This study further shows the broad effect of nemolizumab on PN cell types, with a prominent effect driving COL11A1+ fibroblast and keratinocyte responses toward normal.

CONCLUSIONS

This study provides a high-resolution characterization of the cell types and cellular processes activated in PN skin, establishing PN as a chronic fibrotic inflammatory skin disease. It further demonstrates the broad effect of nemolizumab on pathological processes in PN skin.

Chronic Prurigo Including Prurigo Nodularis: New Insights and Treatments

Chronic prurigo (CPG) is a neuroinflammatory, fibrotic dermatosis that is defined by the presence of chronic pruritus (itch lasting longer than 6 weeks), scratch-associated pruriginous skin lesions and history of repeated scratching. Patients with CPG experience a significant psychological burden and a notable impairment in their quality of life. Chronic prurigo of nodular type (CNPG; synonym: prurigo nodularis) represents the most common subtype of CPG. As CNPG is representative for all CPG subtypes, we refer in this review to both CNPG and CPG. We provide an overview of the clinical characteristics and assessment of CPG, the burden of disease and the underlying pathophysiology including associated therapeutic targets. The information provided results from a PubMed search for the latest publications and a database search for current clinical trials (ClinicalTrials.gov, EU Clinical Trials Register [European Medicines Agency]; using the following terms or combinations of terms: 'chronic prurigo', 'prurigo', 'prurigo nodularis', 'pathophysiology', 'therapy', 'biologics', 'treatment'). Dupilumab is the first authorized systemic therapy by the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) for CNPG to date. Topical and systemic agents that are currently under investigation in clinical randomized, placebo-controlled phase II and III trials such as biologics (e.g., nemolizumab, vixarelimab/KPL-716, barzolvolimab/CDX-0159), small molecules (ruxolitinib cream, povorcitinib/INCB054707, abrocitinib) and the opioid modulator nalbuphine are highlighted. In the last past 15 years, several milestones have been reached regarding the disease understanding of CPG such as first transcriptomic analysis, first terminology, first guideline, and first therapy approval in 2022, which contributed to improved medical care of affected patients. The broad range of identified targets, current case observations and initiated trials offers the possibility of more drug approvals in the near future.

Molecular mechanisms of pruritus in prurigo nodularis

Pruritus is the most common symptom of dermatological disorders, and prurigo nodularis (PN) is notorious for intractable and severe itching. Conventional treatments often yield disappointing outcomes, significantly affecting patients' quality of life and psychological well-being. The pathogenesis of PN is associated with a self-sustained "itch-scratch" vicious cycle. Recent investigations of PN-related itch have partially revealed the intricate interactions within the cutaneous neuroimmune network; however, the underlying mechanism remains undetermined. Itch mediators play a key role in pruritus amplification in PN and understanding their action mechanism will undoubtedly lead to the development of novel targeted antipruritic agents. In this review, we describe a series of pruritogens and receptors involved in mediating itching in PN, including cytokines, neuropeptides, extracellular matrix proteins, vasculogenic substances, ion channels, and intracellular signaling pathways. Moreover, we provide a prospective outlook on potential therapies based on existing findings.