IL-4Rα Blockade by Dupilumab Decreases Staphylococcus aureus Colonization and Increases Microbial Diversity in Atopic Dermatitis

Dupilumab for Atopic Dermatitis-From Clinical Trials to Molecular and Cellular Mechanisms

Dupilumab is a monoclonal antibody that represents the first approved targeted biological therapy for adults, adolescents, and children older than 6 years with moderate-to-severe atopic dermatitis (AD). Dupilumab binds the shared chain of the interleukin-4 and interleukin-13 receptor blocking the downstream signaling of these cytokines. The clinical improvements induced by dupilumab were associated with remission of the dysregulated immune mechanisms linked with AD. Dupilumab reversed the epidermal barrier defects and improved the global molecular signature of AD. This review seeks to provide an overview on the development of dupilumab as the first target-specific biological treatment for AD, with a description of the clinical trials that have been performed in different age groups, their outcomes, and reported adverse effects. Novel aspects of dupilumab treatment, as well as the current knowledge on the molecular and cellular mechanisms underlying the treatment of AD with dupilumab, are summarized and discussed.

Altered Maturation of the Skin Microbiome in Infants with Atopic Dermatitis

The aim of this study was to investigate the early-life development of the skin microbiome in atopic dermatitis. Nineteen infants with atopic dermatitis and 19 healthy infants were evaluated 3 times, at 3 months intervals, within the first 30 months of life. Tape-strips were collected from volar forearms, cheeks, and eczema lesions, and the skin microbiome was assessed by 16S rRNA sequencing. Both the community structure and richness of the skin microbiome of infants with atopic dermatitis differed significantly from that of healthy infants, with greater richness in healthy infants. For infants with atopic dermatitis, the community composition was not dominated by Staphylococci. For healthy infants, community composition and richness correlated significantly with age, while such a pattern was not revealed in infants with atopic dermatitis. This suggests a slower maturation of the skin microbiome in atopic dermatitis, which precedes the staphylococcal predominance observed in older children and adults.

Uptake of Staphylococcus aureus by keratinocytes is reduced by interferon-fibronectin pathway and filaggrin expression

Staphylococcus aureus (S. aureus) is frequently detected in the skin of patients with atopic dermatitis (AD). AD skin-derived strains of S. aureus (AD strain) are selectively internalized into keratinocytes (HaCaT cells) compared to standard strains. However, the mechanism of AD strain internalization by keratinocytes and effect of the skin environment on internalization remain unclear. HaCaT cells were exposed to heat-killed AD or standard strains of fluorescently labeled S. aureus, with or without interferon (IFN)-γ, interleukin (IL)-4, and IL-13 cytokines, for 24 h. Filaggrin and fibronectin expression in HaCaT cells was knocked down using small interfering RNA. The amount of internalized S. aureus was evaluated using a cell imaging system. The effects of INF-γ, IL-4, and S. aureus exposure on mRNA expression in HaCaT cells were analyzed using single-cell RNA sequencing. AD strains adhered to HaCaT cells in approximately 15 min and were increasingly internalized for up to 3 h (2361 ± 467 spots/100 cells, mean ± SD), whereas the standard strain was not (991 ± 71 spots/100 cells). In the presence of IFN-γ, both the number of internalized strains and fibronectin expression significantly decreased compared to in the control, whereas Th2 cytokines had no significant effects. The number of internalized AD strains was significantly higher in filaggrin knockdown and lower in fibronectin knockdown HaCaT cells compared to in the control. RNA sequencing revealed that IFN-γ decreased both fibronectin and filaggrin expression. Keratinocyte internalization of the AD strain may be predominantly mediated by the INF-γ-fibronectin pathway and partially regulated by filaggrin expression.

An Overview of the Latest Metabolomics Studies on Atopic Eczema with New Directions for Study

Atopic eczema (AE) is an inflammatory skin disorder affecting approximately 20% of children worldwide and early onset can lead to asthma and allergies. Currently, the mechanisms of the disease are not fully understood. Metabolomics, the analysis of small molecules in the skin produced by the host and microbes, opens a window to observe the mechanisms of the disease which then may lead to new drug targets for AE treatment. Here, we review the latest advances in AE metabolomics, highlighting both the lipid and non-lipid molecules, along with reviewing the metabolites currently known to reside in the skin.

Single-cell transcriptome profile of mouse skin undergoing antigen-driven allergic inflammation recapitulates findings in atopic dermatitis skin lesions

BACKGROUND

Allergic skin inflammation elicited in mice by epicutaneous (EC) sensitization with antigen shares characteristics with human atopic dermatitis (AD).

OBJECTIVE

We characterized gene expression by single cells in mouse skin undergoing antigen-driven allergic inflammation and compared the results with findings in AD skin lesions.

METHODS

Mice were EC sensitized by application of ovalbumin (OVA) or saline to tape-stripped skin. Single-cell RNA sequencing was performed on skin cells 12 days later. Flow cytometry analysis was performed to validate results.

RESULTS

Sequencing identified 7 nonhematopoietic and 6 hematopoietic cell subsets in EC-sensitized mouse skin. OVA sensitization resulted in the expansion in the skin of T cells, dendritic cells, macrophages, mast cells/basophils, fibroblasts, and myocytes cell clusters, and in upregulation of T_H2 cytokine gene expression in CD4⁺ T cells and mast cells/basophils. Genes differentially expressed in OVA-sensitized skin included genes important for inflammation in dendritic cells and macrophages, collagen deposition, and leukocyte migration in fibroblasts, chemotaxis in endothelial cells and skin barrier integrity, and differentiation in KCs-findings that recapitulate those in AD skin lesions. Unexpectedly, mast cells/basophils, rather than T cells, were the major source of Il4 and ll13 in OVA-sensitized mouse skin. In addition, our results suggest novel pathways in fibroblast and endothelial cells that may contribute to allergic skin inflammation.

CONCLUSION

The gene expression profile of single cells in mouse skin undergoing antigen-driven shares many features with that in AD skin lesions and unveils novel pathways that may be involved in allergic skin inflammation.

Atopic dermatitis: Is innate or adaptive immunity in control? A clinical perspective

Atopic dermatitis (AD) is a chronic inflammatory skin disease with barrier defects and immune dysregulations. The pathogenesis of AD involves the physical barrier as well as epithelial cells, which are considered a vital part of the innate immunity of the skin. The importance of filaggrin mutations in the pathogenesis of AD has also been well-established with reproducible results around the world in multiple studies and ethnic groups. This protein plays an important role in skin barrier functions and further reaffirms barrier defects as one of the primary causes of AD. The main epithelial cells, keratinocytes, function as a major sentinel for the skin in detecting danger signals or microbial pathogens, and trigger downstream immune responses. In AD, these cells express TSLP, IL-33 and IL-25, which lead to downstream systemic production of type 2 cytokines. In spite of major advances in our understanding of the innate immunity of AD, recent success in the systemic therapeutics of AD have focused on targeting the products of the adaptive immunity, particularly cytokines produced by T cells. In addition to type 2 cytokines, type 17 cytokines have also been implicated in the pathogenesis of AD. The current review examines the implications of these cytokines in AD from clinical perspectives.

Dysbiosis of Skin Microbiota with Increased Fungal Diversity is Associated with Severity of Disease in Atopic Dermatitis

Background

Atopic dermatitis (AD) is a multifactorial inflammatory skin disease and an altered skin microbiota with an increase of Staphylococcus aureus has been reported. However, the role of fungi remains poorly investigated.

Objectives

We aimed to improve the understanding of the fungal skin microbiota, the mycobiota, in AD in relation to the bacterial colonization.

Methods

Skin swabs of 16 AD patients and 16 healthy controls (HC) from four different skin sites, that is antecubital crease, dorsal neck, glabella and vertex from multiple time points were analysed by DNA sequencing of the internal transcribed spacer region 1 (ITS1) and 16S rRNA gene for fungi and bacteria, respectively.

Results

Malassezia spp. were the predominant fungi in all subjects but with a decreased dominance in severe AD patients in favour of non‐Malassezia fungi, for example Candida spp. For bacteria, a decrease of Cutibacterium spp. in AD patients in favour of Staphylococcus spp., particularly S. aureus, was observed. Further, both bacterial and fungal community compositions of severe AD patients significantly differed from mild‐to‐moderate AD patients and HC with the latter two having overall similar microbiota showing some distinctions in bacterial communities.

Conclusions

We conclude that severe AD is associated with a pronounced dysbiosis of the microbiota with increased fungal diversity. Potentially infectious agents, for example Staphylococcus and Candida, were increased in severe AD.

Dupilumab for Atopic Dermatitis-From Clinical Trials to Molecular and Cellular Mechanisms

Dupilumab is a monoclonal antibody that represents the first approved targeted biological therapy for adults, adolescents, and children older than 6 years with moderate-to-severe atopic dermatitis (AD). Dupilumab binds the shared chain of the interleukin-4 and interleukin-13 receptor blocking the downstream signaling of these cytokines. The clinical improvements induced by dupilumab were associated with remission of the dysregulated immune mechanisms linked with AD. Dupilumab reversed the epidermal barrier defects and improved the global molecular signature of AD. This review seeks to provide an overview on the development of dupilumab as the first target-specific biological treatment for AD, with a description of the clinical trials that have been performed in different age groups, their outcomes, and reported adverse effects. Novel aspects of dupilumab treatment, as well as the current knowledge on the molecular and cellular mechanisms underlying the treatment of AD with dupilumab, are summarized and discussed.

From Skin Barrier Dysfunction to Systemic Impact of Atopic Dermatitis: Implications for a Precision Approach in Dermocosmetics and Medicine

: Atopic dermatitis (AD) affects up to 20% of children and is considered the starting point of the atopic march with the development of food allergy, asthma, and allergic rhinitis. The heterogeneous phenotype reflects distinct and/or overlapping pathogenetic mechanisms with varying degrees of epidermal barrier disruption, activation of different T cell subsets and dysbiosis of the skin microbiome. Here, we review current evidence suggesting a systemic impact of the cutaneous inflammation in AD together with a higher risk of asthma and other comorbidities, especially in severe and persistent AD. Thus, early therapy of AD to restore the impaired skin barrier, modified microbiome, and target type 2 inflammation, depending on the (endo)phenotype, in a tailored approach is crucial. We discuss what we can learn from the comorbidities and the implications for preventive and therapeutic interventions from precision dermocosmetics to precision medicine. The stratification of AD patients into biomarker-based endotypes for a precision medicine approach offers opportunities for better long-term control of AD with the potential to reduce the systemic impact of a chronic skin inflammation and even prevent or modify the course, not only of AD, but possibly also the comorbidities, depending on the patient’s age and disease stage.

Role of Basophils in a Broad Spectrum of Disorders

Basophils are the rarest granulocytes and have long been overlooked in immunological research due to their rarity and similarities with tissue-resident mast cells. In the last two decades, non-redundant functions of basophils have been clarified or implicated in a broad spectrum of immune responses, particularly by virtue of the development of novel analytical tools for basophils. Basophils infiltrate inflamed tissues of patients with various disorders, even though they circulate in the bloodstream under homeostatic conditions. Depletion of basophils results in the amelioration or exaggeration of inflammation, depending on models of disease, indicating basophils can play either beneficial or deleterious roles in a context-dependent manner. In this review, we summarize the recent findings of basophil pathophysiology under various conditions in mice and humans, including allergy, autoimmunity, tumors, tissue repair, fibrosis, and COVID-19. Further mechanistic studies on basophil biology could lead to the identification of novel biomarkers or therapeutic targets in a broad range of diseases.

Atopic dermatitis: pathomechanisms and lessons learned from novel systemic therapeutic options

Atopic dermatitis (AD) is a chronic, heterogenous, inflammatory skin disorder associated with a high skin-related health burden, typically starting in childhood and often persisting into adulthood. AD is characterized by a wide range of clinical phenotypes, reflecting multiple underlying pathophysiological mechanisms and interactions between genetics, immune system dysregulation, and environmental factors. In this review, we describe the diverse cellular and molecular mechanisms involved in AD, including the critical role of T cell-driven inflammation, primarily via T helper (Th) 2- and Th17-derived cytokines, many of which are mediated by the Janus kinase (JAK) signaling pathway. These local inflammatory processes interact with sensory neuronal pathways, contributing to the clinical manifestations of AD, including itch, pain, and sleep disturbance. The recent elucidation of the molecular pathways involved in AD has allowed treatment strategies to evolve from broad-acting systemic immunosuppressive therapies to more targeted agents, including JAK inhibitors and cytokine-specific biologic agents. Evidence from the clinical development of these targeted therapies has reinforced and expanded our understanding of the pathophysiological mechanisms underlying AD and holds promise for individualized treatment strategies tailored to specific AD subtypes.

Keratinocyte EGF signaling dominates in Atopic Dermatitis lesions: a comparative RNAseq analysis

Atopic dermatitis (AD) remains a highly heterogenous disorder with a multifactorial aetiology. Whilst keratinocytes are known to play a fundamental role in AD, their contribution to the overall immune landscape in moderate‐to‐severe AD is still poorly understood. In order to design new therapeutics, further investigation is needed into common disease pathways at the molecular level. We used publicly available whole‐tissue RNAseq data (4 studies) and single‐cell RNAseq keratinocyte data to identify genes/pathways that are involved in keratinocyte responses in AD and after dupilumab treatment. Transcripts present in both keratinocytes (single‐cell) and whole‐tissue, referred to as the keratinocyte‐enriched lesional skin (KELS) genes, were analysed using functional/pathway analysis. Following statistical testing, 2049 genes (16.8%) were differentially expressed in KELS. Enrichment analyses predicted increases in not only type‐1/type‐2 immune signalling and chemoattraction, but also in EGF‐dominated growth factor signalling. We identified complex crosstalk between keratinocytes and immune cells involving a dominant EGF family signature which converges on keratinocytes with potential immunomodulatory and chemotaxis‐promoting consequences. Although keratinocytes express the IL4R, we observed no change in EGF signalling in KELS after three‐month treatment with dupilumab, indicating that this pathway is not modulated by dupilumab immunotherapy. EGF family signalling is significantly dysregulated in AD lesions but is not associated with keratinocyte proliferation. EGF signalling pathways in AD require further study.

Optimizing topical management of atopic dermatitis

OBJECTIVE

Provide a review of atopic dermatitis management, focusing on optimizing topical therapy, creating a stepwise approach for treatment plans, and providing guidance on when to start systemic therapy.

DATA SOURCES

PubMed search of articles in the English language regarding atopic dermatitis in all ages.

STUDY SELECTION

Articles on the subject matter were selected and reviewed.

RESULTS

Topical corticosteroids are the first-line treatment for managing atopic dermatitis. Topical nonsteroidal agents, calcineurin inhibitors, crisaborole, and recently, ruxolitinib, which cause no cutaneous atrophy, are options for reducing the use of topical corticosteroids, including on sensitive sites. Emerging topical agents are in clinical trials. Proactive management, with continued application 2 to 3 times weekly of a midpotency topical corticosteroid or tacrolimus, may maintain control for clear (or almost clear) localized sites of dermatitis that rapidly recur when topical anti-inflammatory medication is stopped. If topical therapy alone cannot control disease and quality of life is impacted, reevaluation to confirm the diagnosis, manage comorbid conditions, address compliance and patient-specific concerns, and optimize topical therapy must be undertaken before deciding to advance to systemic medication. Dupilumab, an interleukin-4 receptor inhibitor, has become first-line systemic therapy given its efficacy and safety, allowing long-term treatment without laboratory monitoring. Other biologics and Janus kinase inhibitors are emerging as alternatives that could eliminate the need for immunosuppressants with their higher risks.

CONCLUSION

Several options are now available for topical treatment. A stepwise approach is needed to consider alternative therapies and diagnoses before advancing to systemic treatment, but the safety of newer immunomodulators will lower the threshold for more aggressive intervention.

Type 2 Inflammation Contributes to Skin Barrier Dysfunction in Atopic Dermatitis

Skin barrier dysfunction, a defining feature of atopic dermatitis (AD), arises from multiple interacting systems. In AD, skin inflammation is caused by host-environment interactions involving keratinocytes as well as tissue-resident immune cells such as type 2 innate lymphoid cells, basophils, mast cells, and T helper type 2 cells, which produce type 2 cytokines, including IL-4, IL-5, IL-13, and IL-31. Type 2 inflammation broadly impacts the expression of genes relevant for barrier function, such as intracellular structural proteins, extracellular lipids, and junctional proteins, and enhances Staphylococcus aureus skin colonization. Systemic anti‒type 2 inflammation therapies may improve dysfunctional skin barrier in AD.

Preventing allergies through the skin

OBJECTIVE

To inform readers of the current and forthcoming skin barrier interventions that have clinically relevant implications in the prevention of allergic sensitization and atopic diseases.

DATA SOURCES

Peer-reviewed journal articles indexed on PubMed and clinical trials referenced on clinicaltrials.gov were analyzed.

STUDY SELECTIONS

Literature searches from PubMed and clinicaltrials.gov were performed using combinations of the following search terms: prevention, allergy, atopy, skin, cutaneous, microbiome, microbiota, Staphylococcus aureus, atopic dermatitis, eczema, food allergy, and asthma.

RESULTS

The skin barrier represents an entry point for allergic sensitization and T_H2-mediated allergic disorders. Results from clinical trials designed to improve microbiome complexity and reduce S aureus colonization, provide skin barrier enhancement, and deliver epicutaneous immunotherapy are summarized and discussed in the context of primary, secondary, and tertiary prevention of allergic disease.

CONCLUSION

The skin barrier is a promising target for prevention of allergic disease, though clinical trial results thus far have been mixed, at best.

The role of the skin microbiome in atopic dermatitis - correlations and consequences

The physical barrier function of the skin is significantly supported by the (epi-)dermal immune system and the skin's own microbiome. Atopic dermatitis is characterized by an imbalance of all these three factors. The skin microbiome establishes itself immediately after birth and plays an important role in the development and maintenance of immune homeostasis. The clinical picture of atopic dermatitis shows, among other things, changes in the skin microbiome. Particularly during an acute phase, a strongly reduced bacterial diversity as well as the dominance of a single pathogen, Staphylococcus aureus, is observed. Staphylococcus aureus exacerbates the inflammatory process; furthermore, the bacteria produce proteases and toxins that further weaken the already severely compromised barrier function of the skin of patients with atopic dermatitis. However, knowledge of dermal dysbiosis also yields new treatment options for the therapy of the disease. In particular, the application of active bacteria represents a direct influence on the skin microbiome. Results of initial clinical studies on various approaches demonstrate promising results; this article provides an overview of work in this area.

Infections in children and adolescents treated with dupilumab in pediatric clinical trials for atopic dermatitis-A pooled analysis of trial data

BACKGROUND/OBJECTIVE

Patients with moderate-to-severe atopic dermatitis (AD) have increased risk of cutaneous and extracutaneous infections. Dupilumab has previously been associated with reduced risk of serious/severe infections and non-herpetic skin infections in adults with moderate-to-severe AD. This analysis assessed infection rates with dupilumab versus placebo in pediatric patients with moderate-to-severe and severe AD participating in clinical trials.

METHODS

This is a pooled analysis from two 16-week, randomized, placebo-controlled, phase 3 clinical trials of dupilumab: monotherapy in adolescents aged 12-17 years with moderate-to-severe AD (LIBERTY AD ADOL, NCT03054428) and with concomitant topical corticosteroids in children aged 6-11 years with severe AD (LIBERTY AD PEDS, NCT03345914). Data were pooled according to treatment received: placebo/approved dupilumab doses/other studied dupilumab doses/all dupilumab doses. Exposure-adjusted rates (patients with ≥1 event per 100 patient-years [nP/100 PY]) were used to compare treatment groups.

RESULTS

Overall, 612 patients were included: 205 received placebo and 407 received dupilumab (261 received approved dupilumab doses and 146 received other studied dupilumab doses). Overall infection rates were numerically lower with dupilumab versus placebo (nP/100 PY: placebo, 227; approved dupilumab, 173; other dupilumab, 206; all dupilumab, 184). Total skin infections were numerically less frequent in all dupilumab-treated groups versus placebo (nP/100 PY: placebo, 67; approved dupilumab, 30; other dupilumab, 46; all dupilumab, 36).

CONCLUSIONS

These data suggest that dupilumab treatment in children and adolescents with AD does not increase infection risk overall and is associated with lower rates of skin infections compared with placebo.

Model-based meta-analysis to optimise S. aureus-targeted therapies for atopic dermatitis

Several clinical trials of Staphylococcus aureus (S. aureus)‒targeted therapies for atopic dermatitis (AD) have shown conflicting results about whether they improve AD severity scores. This study performs a model-based meta-analysis to investigate the possible causes of these conflicting results and suggests how to improve the efficacies of S. aureus‒targeted therapies. We developed a mathematical model that describes systems-level AD pathogenesis involving dynamic interactions between S. aureus and coagulase-negative Staphylococcus (CoNS). Our model simulation reproduced the clinically observed detrimental effects of the application of S. hominis A9 and flucloxacillin on AD severity and showed that these effects disappeared if the bactericidal activity against CoNS was removed. A hypothetical (modeled) eradication of S. aureus by 3.0 log₁₀ colony-forming unit per cm² without killing CoNS achieved Eczema Area and Severity Index 75 comparable with that of dupilumab. This efficacy was potentiated if dupilumab was administered in conjunction with S. aureus eradication (Eczema Area and Severity Index 75 at week 16) (S. aureus eradication: 66.7%, dupilumab 61.6% and combination 87.8%). The improved efficacy was also seen for virtual dupilumab poor responders. Our model simulation suggests that killing CoNS worsens AD severity and that S. aureus‒specific eradication without killing CoNS could be effective for patients with AD, including dupilumab poor responders. This study will contribute to designing promising S. aureus‒targeted therapy.

Early intervention and prevention of allergic diseases

Food allergy (FA) is now one of the most common chronic diseases of childhood often lasting throughout life and leading to significant worldwide healthcare burden. The precise mechanisms responsible for the development of this inflammatory condition are largely unknown; however, a multifactorial aetiology involving both environmental and genetic contributions is well accepted. A precise understanding of the pathogenesis of FA is an essential first step to developing comprehensive prevention strategies that could mitigate this epidemic. As it is frequently preceded by atopic dermatitis and can be prevented by early antigen introduction, the development of FA is likely facilitated by the improper initial presentation of antigen to the developing immune system. Primary oral exposure of antigens allowing for presentation via a well-developed mucosal immune system, rather than through a disrupted skin epidermal barrier, is essential to prevent FA. In this review, we present the data supporting the necessity of (1) an intact epidermal barrier to prevent epicutaneous antigen presentation, (2) the presence of specific commensal bacteria to maintain an intact mucosal immune system and (3) maternal/infant diet diversity, including vitamins and minerals, and appropriately timed allergenic food introduction to prevent FA.

Skin microbiome of atopic dermatitis

The skin microbiome is a key component of pathogenesis in atopic dermatitis (AD). The skin of AD patients is characterized by microbial dysbiosis, with a reduction of microbial diversity and overrepresentation of pathogenic Staphylococcus aureus (S. aureus). Recent exciting studies have elucidated an importance of establishing an appropriate immune response to microbes in early life and uncovered the new mechanisms of microbial community dynamics in modulating our skin microbiome. Several microbes are associated with AD pathogenesis, with proposed pathogenic effects from S. aureus and Malassezia. The complex relationships between microbes within the skin microbiome consortia includes various species, such as Staphylococcal, Roseomonas and Cutibacterium strains, that can inhibit S. aureus and are potential probiotics for AD skin. Numerous microbes are now also reported to modulate host response via communication with keratinocytes, specialized immune cells and adipocytes to improve skin health and barrier function. This increased understanding of skin microbiota bioactives has led to new biotherapeutic approaches that target the skin surface microenvironment for AD treatment.

Skin barrier defects in atopic dermatitis: From old idea to new opportunity

Atopic dermatitis (AD) is the most common chronic skin inflammatory disease, with a profound impact on patients’ quality of life. AD varies considerably in clinical course, age of onset and degree to which it is accompanied by allergic and non-allergic comorbidities. Skin barrier impairment in both lesional and nonlesional skin is now recognized as a critical and often early feature of AD. This may be explained by a number of abnormalities identified within both the stratum corneum and stratum granulosum layers of the epidermis. The goal of this review is to provide an overview of key barrier defects in AD, starting with a historical perspective. We will also highlight some of the commonly used methods to characterize and quantify skin barrier function. There is ample opportunity for further investigative work which we call out throughout this review. These include: quantifying the relative impact of individual epidermal abnormalities and putting this in a more holistic view with physiological measures of barrier function, as well as determining whether these barrier-specific endotypes predict clinical phenotypes (e.g. age of onset, natural history, comorbidities, response to therapies, etc). Mechanistic studies with new (and in development) AD therapies that specifically target immune pathways, Staphylococcus aureus abundance and/or skin barrier will help us understand the dynamic crosstalk between these compartments and their relative importance in AD.

Skin Microbiome in Patients with Hand Eczema and Healthy Controls: A Three-week Prospective Study

The pathogenesis of chronic hand eczema remains unclear. Insights into the skin microbiome in hand eczema and its potential relevance to disease severity may help to elucidate the underlying mechanisms of hand eczema. The aim of this study was to characterize the microbiome in patients with hand eczema and healthy controls. A 5-visit prospective study was conducted over a period of 3 weeks. At each visit, bacterial swabs were taken from the hands of patients with hand eczema and controls. The microbiome was examined using DNA extraction and 16S rRNA amplicon sequencing (V3–V4 regions). Fifty patients with hand eczema and 50 controls were included (follow-up rate=100%). The baseline bacterial α-diversity was reduced on the hands of patients with hand eczema compared with controls (effect size=–0.31; 95% confidence interval (95% CI) –0.50; –0.11; p = 0.003). The dysbiosis on the patients’ hands was stable over the study period, was associated with disease severity, and was characterized by reduced bacterial diversity and different bacterial community compositions.

Dysbiosis of skin mycobiome in atopic dermatitis

Atopic dermatitis (AD) is a chronic and relapsing inflammatory skin disease with an increasing prevalence worldwide. The aetiology and pathogenesis of AD have not been fully elucidated. Previous studies have suggested the role of fungi as a triggering factor in the development AD. Here we conducted a systematic review to investigate the skin mycobiome profiles in AD and to address whether there is an association between fungal dysbiosis and AD. We searched Medline/PubMed, Embase and Web of Science for research studies published in English between January 1st, 2010 and April 21st, 2021. A total of 11 human studies and 3 animal studies were included in this analysis. Fungal dysbiosis was observed in AD lesions with a depleted amount of Malassezia and a higher abundance of filamentous fungi. A positive correlation between Candida and Staphylococcus was also demonstrated in AD. We supposed that specific species of Malassezia spp. and Candida spp. may play a role in the pathogenesis of AD by interacting with the pathogenic bacteria. Topical application of emollients could improve the skin barrier function and restore the skin fungal flora by increasing the amount of Malassezia. Further studies focusing on the complex interplay between specific skin fungi and the host can provide better insight into the role of microorganisms in the pathogenesis of AD.

Basophil-derived IL-4 promotes cutaneous Staphylococcus aureus infection

Superficial cutaneous Staphylococcus aureus (S. aureus) infection in humans can lead to soft tissue infection, an important cause of morbidity and mortality. IL-17A production by skin TCRγδ+ cells in response to IL-1 and IL-23 produced by epithelial and immune cells is important for restraining S. aureus skin infection. How S. aureus evades this cutaneous innate immune response to establish infection is not clear. Here we show that mechanical injury of mouse skin by tape stripping predisposed mice to superficial skin infection with S. aureus. Topical application of S. aureus to tape-stripped skin caused cutaneous influx of basophils and increased Il4 expression. This basophil-derived IL-4 inhibited cutaneous IL-17A production by TCRγδ+ cells and promoted S. aureus infection of tape-stripped skin. We demonstrate that IL-4 acted on multiple checkpoints that suppress the cutaneous IL-17A response. It reduced Il1 and Il23 expression by keratinocytes, inhibited IL-1+IL-23-driven IL-17A production by TCRγδ+ cells, and impaired IL-17A-driven induction of neutrophil-attracting chemokines by keratinocytes. IL-4 receptor blockade is shown to promote Il17a expression and enhance bacterial clearance in tape-stripped mouse skin exposed to S. aureus, suggesting that it could serve as a therapeutic approach to prevent skin and soft tissue infection.

Immunological Targets of Biologic Drugs in Allergic Skin Diseases in Children

Atopic dermatitis and urticaria are two invalidating skin disorders that are very common in children. Recent advances in the understanding of their specific intracellular molecular pathways have permitted the development of precise biological molecules, targeting inflammatory mediators and arresting the pathogenetic pathways of skin diseases. Many biologics with promising results have been studied, although few are currently approved in children. In this review, we aim to provide the latest evidence about the use, indications, efficacy and safety of biologic therapies to treat atopic dermatitis and chronic urticaria in children and adolescents.

Association between barrier impairment and skin microbiota in atopic dermatitis from a global perspective: Unmet needs and open questions

Atopic diathesis encompassing atopic dermatitis (AD), allergic rhinoconjunctivitis, food allergy, eosinophilic esophagitis, and asthma is a widely prevalent condition with a broad heterogeneity in clinical course, age of onset, and lifespan persistence. A primary event in AD is the commonly inherited epidermal barrier dysfunction. Together with the host-microbiome interactions, barrier defect and allergen exposure modulate both innate and adaptive immunity, thus triggering and maintaining the inflammatory response. Microbiome diversity, together with the host's contact with nonpathogenic microbes in childhood, is a prerequisite for functional maturation of the immune system, which is in part mediated by microbiome-induced epigenetic changes. Yet, whether microbiome alterations are the result or the reason for barrier impairment and inflammatory response of the host is unclear. Exposure to locally prevalent microbial species could contribute to further modification of the disease course. The objective of this review is to reveal the link between changes in the skin microbiota, barrier dysfunction, and inflammation in AD. Addressing unmet needs includes determining the genetic background of AD susceptibility; the epigenetic modifications induced by the microbiota and other environmental factors; the role of globally diverse provoking factors; and the implementation of personalized, phenotype-specific therapies such as a epidermal barrier restoration in infancy and microbiota modulation via systemic or topical interventions, all of which open gaps for future research.

Early development of the skin microbiome: therapeutic opportunities

As human skin hosts a diverse microbiota in health and disease, there is an emerging consensus that dysregulated interactions between host and microbiome may contribute to chronic inflammatory disease of the skin. Neonatal skin is a unique habitat, structurally similar to the adult but with a different profile of metabolic substrates, environmental stressors, and immune activity. The surface is colonized within moments of birth with a bias toward maternal strains. Initial colonists are outcompeted as environmental exposures increase and host skin matures. Nonetheless, early life microbial acquisitions may have long-lasting effects on health through modulation of host immunity and competitive interactions between bacteria. Microbial ecology and its influence on health have been of interest to dermatologists for >50 years, and an explosion of recent interest in the microbiome has prompted ongoing investigations of several microbial therapeutics for dermatological disease. In this review, we consider how recent insight into the host and microbial factors driving development of the skin microbiome in early life offers new opportunities for therapeutic intervention. IMPACT: Advancement in understanding molecular mechanisms of bacterial competition opens new avenues of investigation into dermatological disease. Primary development of the skin microbiome is determined by immunological features of the cutaneous habitat. Understanding coordinated microbial and immunological development in the pediatric patient requires a multidisciplinary synthesis of primary literature.

Skin dysbiosis in the microbiome in atopic dermatitis is site-specific and involves bacteria, fungus and virus

BACKGROUND

Microbial dysbiosis with increased Staphylococcus aureus (S. aureus) colonization on the skin is a hallmark of atopic dermatitis (AD), however most microbiome studies focus on bacteria in the flexures and the microbial composition at other body sites have not been studied systematically.

OBJECTIVES

The aim of the study is to characterize the skin microbiome, including bacteria, fungi and virus, at different body sites in relation to AD, lesional state, and S. aureus colonization, and to test whether the nares could be a reservoir for S. aureus strain colonization.

METHODS

Using shotgun metagenomics we characterized microbial compositions from 14 well defined skin sites from 10 patients with AD and 5 healthy controls.

RESULTS

We found clear differences in microbial composition between AD and controls at multiple skin sites, most pronounced on the flexures and neck. The flexures exhibited lower alpha-diversity and were colonized by S. aureus, accompanied by S. epidermidis in lesions. Malassezia species were absent on the neck in AD. Virus mostly constituted Propionibacterium and Staphylococcus phages, with increased abundance of Propionibacterium phages PHL041 and PHL092 and Staphylococcus epidermidis phages CNPH82 and PH15 in AD. In lesional samples, both the genus Staphylococcus and Staphylococcus phages were more abundant. S. aureus abundance was higher across all skin sites except from the feet. In samples where S. aureus was highly abundant, lower abundances of S. hominis and Cutibacterium acnes were observed. M. osloensis and M. luteus were more abundant in AD. By single nucleotide variant analysis of S. aureus we found strains to be subject specific. On skin sites some S. aureus strains were similar and some dissimilar to the ones in the nares.

CONCLUSIONS

Our data indicate a global and site-specific dysbiosis in AD, involving both bacteria, fungus and virus. When defining targeted treatment clinicians should both consider the individual and skin site and future research into potential crosstalk between microbiota in AD yields high potential.

Mechanisms for control of skin immune function by the microbiome

The skin represents the largest area for direct contact between microbes and host immunocytes and is a site for constant communication between the host and this diverse and essential microbial community. Coagulase-negative staphylococci are an abundant bacterial genus on the human skin and are regulated through various mechanisms that include the epidermal barrier environment and innate and adaptive immune systems within the epidermis and dermis. In turn, some species and strains of these bacteria produce beneficial products that augment host immunity by exerting specifically targeted antimicrobial, anti-inflammatory, or anti-neoplastic activity while also promoting broad innate and adaptive immune responses. The use of selected skin commensals as a therapeutic has shown promise in recent human clinical trials. This emerging concept of bacteriotherapy is defining mechanisms of action and validating the dependence on the microbiome for maintenance of immune homeostasis.

Features of the Skin Microbiota in Common Inflammatory Skin Diseases

Many relatively common chronic inflammatory skin diseases manifest on the face (seborrheic dermatitis, rosacea, acne, perioral/periorificial dermatitis, periocular dermatitis, etc.), thereby significantly impairing patient appearance and quality of life. Given the yet unexplained pathogenesis and numerous factors involved, these diseases often present therapeutic challenges. The term “microbiome” comprises the totality of microorganisms (microbiota), their genomes, and environmental factors in a particular environment. Changes in human skin microbiota composition and/or functionality are believed to trigger immune dysregulation, and consequently an inflammatory response, thereby playing a potentially significant role in the clinical manifestations and treatment of these diseases. Although cultivation methods have traditionally been used in studies of bacterial microbiome species, a large number of bacterial strains cannot be grown in the laboratory. Since standard culture-dependent methods detect fewer than 1% of all bacterial species, a metagenomic approach could be used to detect bacteria that cannot be cultivated. The skin microbiome exhibits spatial distribution associated with the microenvironment (sebaceous, moist, and dry areas). However, although disturbance of the skin microbiome can lead to a number of pathological conditions and diseases, it is still not clear whether skin diseases result from change in the microbiome or cause such a change. Thus far, the skin microbiome has been studied in atopic dermatitis, seborrheic dermatitis, psoriasis, acne, and rosacea. Studies on the possible association between changes in the microbiome and their association with skin diseases have improved the understanding of disease development, diagnostics, and therapeutics. The identification of the bacterial markers associated with particular inflammatory skin diseases would significantly accelerate the diagnostics and reduce treatment costs. Microbiota research and determination could facilitate the identification of potential causes of skin diseases that cannot be detected by simpler methods, thereby contributing to the design and development of more effective therapies.

Dupilumab Therapy Improves Stratum Corneum Hydration and Skin Dysbiosis in Patients With Atopic Dermatitis

Purpose

We aimed to investigate the effects of dupilumab on 1) the permeability and antimicrobial barrier, 2) the composition of the skin microbiome, and 3) the correlation between changes in skin barrier properties and microbiota in atopic dermatitis (AD) patients.

Methods

Ten patients with severe AD were treated with dupilumab for 12 weeks. Disease severity was assessed using the Eczema Area and Severity Index (EASI). Skin barrier function was evaluated by measuring transepidermal water loss, stratum corneum (SC) hydration, and pH. The following parameters were analyzed in the pre- and post-treatment SC samples; 1) skin microbiota using 16S rRNA gene sequencing, 2) lipid composition using mass spectrometry, and 3) human β-defensin 2 (hBD-2) expression using quantitative reverse transcription polymerase chain reaction.

Results

SC hydration levels in the lesional and non-lesional skin increased after 12-week dupilumab therapy (24.2%, P < 0.001 and 59.9%, P < 0.001, respectively, vs. baseline) and correlated with EASI improvement (r = 0.90, P < 0.001 and r = 0.85, P = 0.003, respectively). Dupilumab increased the long-chain ceramide levels in atopic skin (118.4%, P = 0.028 vs. baseline) that correlated with changes in SC hydration (r = 0.81, P = 0.007) and reduced the elevated hBD-2 messenger RNA levels (−15.4%, P = 0.005 vs. baseline) in the lesional skin. Dupilumab decreased the abundance of Staphylococcus aureus. In contrast, the microbial diversity and the abundance of Cutibacterium and Corynebacterium species increased, which were correlated with an increase in SC hydration levels (Shannon diversity, r = 0.71, P = 0.027; Cutibacterium, r = 0.73, P = 0.017; Corynebacterium, r = 0.75, P = 0.012). Increased abundance of Cutibacterium species was also correlated with EASI improvement (r = 0.68, P = 0.032).

Conclusions

Th2 blockade-induced normalization of skin microbiome in AD patients is associated with increased SC hydration.

Impact of type 2 targeting biologics on acute exacerbations of chronic rhinosinusitis

Background: Acute exacerbations of chronic rhinosinusitis (AECRS) are associated with significant morbidity and decreased quality of life. There are sparse data assessing the real-world impact of biologics on AECRS. Objectives: We sought to determine the impact of type 2-targeting biologics on the frequency of medication use for AECRS episodes. Methods: Antibiotic and/or systemic corticosteroid courses for AECRS were identified in a retrospective study from November 2015 to February 2020, at a single academic health system. The estimated yearly rates for antibiotic and corticosteroid courses were evaluated before and after initiation of type 2 biologics. Results: One-hundred and sixty-five patients with chronic rhinosinusitis (CRS) had received either omalizumab (n = 12), mepolizumab (n = 42), benralizumab (n = 44), dupilumab (n = 61), or reslizumab (n = 6). Seventy percent had CRS with nasal polyps, and 30% had CRS without nasal polyps. All the patients had asthma. When all the biologics were combined, the estimated yearly rate for antibiotics for AECRS decreased from 1.34 (95% confidence interval [CI], 1.12-1.59) to 0.68 (95% CI, 0.52-0.88) with biologic use (49% reduction, p < 0.001). Those with frequent AECRS (three or more courses of antibiotics in the 1 year before biologic use) had a larger degree of reduction, with an estimated yearly rate of 4.15 (95% CI, 3.79-4.55) to 1.58 (95% CI, 1.06-2.35) with biologic use (n = 27; 62% reduction; p < 0.001). Within the total cohort, the estimated yearly rate for systemic corticosteroids for AECRS decreased from 1.69 (95% CI, 1.42-2.02) to 0.68 (95% CI, 0.53-0.88) with biologic use (60% reduction; p < 0.001). Conclusion: Type 2-targeting biologics reduced medication use for AECRS. This suggested that biologics may be a therapeutic option for patients with frequent AECRS.

Dupilumab: An Opportunity to Unravel In Vivo Actions of IL-4 and IL-13 in Humans

The application of biologics in clinical practice allows immunological observations under real-life conditions. In a new article in the Journal of Investigative Dermatology, Bakker et al. (2021) use deep immune cell phenotyping to demonstrate how dupilumab acts in a targeted fashion on skin-homing T cells, the driver cells of atopic dermatitis.

The Choice of Biologics in Patients with Severe Chronic Rhinosinusitis with Nasal Polyps

Patients with severe chronic rhinosinusitis with nasal polyps represent an unmet clinical need in terms of recurrent disease despite current medical and surgical therapy. Targeting type 2 inflammatory cytokines (IL4/5/13) appears to be a promising therapeutic approach for such patients akin to what has already been seen in severe asthma. An indirect comparison from phase 3 placebo-controlled trials has shown relative improvements in the coprimary end point of nasal polyp score (NPS) ranging from a 15% reduction (-0.8 units) with mepolizumab, 18% with omalizumab (-1.14 units), and 35% (-2.06 units) with dupilumab. This trend was mirrored by relative improvements in health status with the 22-item Sinonasal Outcome Test score showing a 21% reduction (-13.7 units) with mepolizumab, 27% (-16.1 units) with omalizumab, and 43% (-21.1 units) with dupilumab, all exceeding the minimal clinically important difference of 8.9 units. All biologics improved the coprimary end point of nasal airway blockage and also reduced the need for rescue medical and/or surgical polypectomy. We advocate performing real-life studies looking at the response to biologics in patients who are at increased risk for disease recurrence, including initial optimal medical and surgical polyp clearance before commencing biologics.

Updated understanding of Staphylococcus aureus in atopic dermatitis: From virulence factors to commensals and clonal complexes

Atopic dermatitis (AD) is a common inflammatory dermatosis that has multiple contributing factors including genetic, immunologic and environmental. Staphylococcus aureus (SA) has long been associated with exacerbation of AD. SA produces many virulence factors that interact with the human skin and immune system. These superantigens and toxins have been shown to contribute to adhesion, inflammation and skin barrier destruction. Recent advances in genome sequencing techniques have led to a broadened understanding of the multiple ways SA interacts with the cutaneous environment in AD hosts. For example, temporal shifts in the microbiome, specifically in clonal complexes of SA, have been identified during AD flares and remission. Herein, we review mechanisms of interaction between the cutaneous microbiome and SA and highlight known differences in SA clonal complexes that contribute to AD pathogenesis. Detailed knowledge of the genetic strains of SA and cutaneous dysbiosis is becoming increasingly relevant in paving the way for microbiome-modulating and precision therapies for AD.

The influence of biologics on the microbiome in immune-mediated inflammatory diseases: A systematic review

BACKGROUND

Immune-mediated inflammatory diseases (IMIDs) are a group of several chronic disorders with elusive pathogenesis that results in dysregulation of the normal immune response and leads to organ-specific or systemic inflammation. There are many reports on gastrointestinal or skin dysbiosis in patients with IMIDs; however, it is not clear whether dysbiosis is a cause or a result of the observed inflammation. We aimed to determine whether treatment of IMIDs patients with biologics affects their microbiota in comparison with baseline or placebo.

METHODS

We searched for studies in MEDLINE, Embase, Scopus, and Web of Science. Due to both high heterogeneity and lacking data, vote-counting and structured tables were used to summarize the data.

RESULTS AND LIMITATIONS

A total of 25 longitudinal human studies with 816 IMIDs patients receiving biologics were included. Data on α-diversity change are inconclusive. Most evidence supports the increase in all α-diversity metrics in responding inflammatory bowel disease (IBD) patients; however, vote counting did not confirm the significance of the directional change. In case of β-diversity, treatment with biologics made patients' microbiome more similar to the microbiome of healthy controls in 5 out of 7 studies. The changes in taxa abundance and predicted functionality of microbiome were systematically summarized. Limited number and quality of the included studies highly restricted the conclusions of the study.

CONCLUSIONS

Local inflammation may play pivotal role in the gut microbiome disruption in IMIDs patients. The effect of the biologics on human microbiota should be evaluated in randomized controlled trials and transparently reported.

Changes in Skin and Nasal Microbiome and Staphylococcal Species Following Treatment of Atopic Dermatitis with Dupilumab

Investigation of changes in the skin microbiome following treatment of atopic dermatitis (AD) with dupilumab may provide valuable insights into the skin microbiome as a therapeutic target. The aim of this study is to assess changes in the AD skin microbiome following treatment of AD with dupilumab (n = 27). E-swabs were collected from nose, lesional, and nonlesional skin before and after 16 weeks of dupilumab therapy, and the microbiome was analyzed by 16S rRNA and tuf gene sequencing. Data for 17 patients with milder disease receiving treatment with non-targeted therapies are also presented. The results show that both groups experienced clinical improvement (p < 0.001) following dupilumab therapy and that Shannon diversity increased and bacterial community structure changed. The relative abundance of the genus Staphylococcus (S.) and S. aureus decreased, while that of S. epidermidis and S. hominis increased. No significant changes were observed for patients receiving non-targeted treatments. The increases in S. epidermidis and S. hominis and the decrease in S. aureus correlated with clinical improvement. Furthermore, changes in S. hominis and S. epidermidis correlated inversely with S. aureus. In conclusion, treatment with dupilumab significantly changed the skin microbiome and decreased S. aureus. Our results suggest a favorable role of commensal staphylococci in AD.

[Dysbalance between the immune system and skin microbiome in chronic inflammatory dermatoses]

BACKGROUND

The skin is an organ frequently affected by chronic diseases. Inflammatory, immune-mediated dermatoses such as atopic dermatitis and psoriasis show a high prevalence as well as a significant impact on the quality of life of those affected. In a large proportion of cases, atopic dermatitis is associated with a marked change in microbial colonization of both clinically healthy and affected skin. In psoriasis, changes to this effect have been described, but clinical relevance remains elusive.

AIM

In recent years, increasing knowledge has been gained in microbiome research with resulting clinical relevance. The present article deals with the disturbed balance of the immune system and the skin microbiome in chronic inflammatory dermatoses on the basis of atopic dermatitis and psoriasis vulgaris.

MATERIALS AND METHODS

A literature search was performed in PubMed and Medline databases (entries until 09 April 2021).

RESULTS

Staphylococcus aureus is known to play a central pathophysiological role in atopic dermatitis. This is revisited in light of new insights regarding biodiversity and immunoregulatory processes. In psoriasis, a more heterogeneous body of data emerges regarding the microbiome and its contribution to disease development.

DISCUSSION

While topical applications to directly influence the microbiome are already being tested in atopic dermatitis, further knowledge regarding the pathophysiological significance of the microbiota is still needed in psoriasis.