Staphylococcus aureus-Specific Tissue-Resident Memory CD4+ T Cells Are Abundant in Healthy Human Skin

Staphylococcus aureus-specific skin resident memory T cells protect against bacteria colonization but exacerbate atopic dermatitis-like flares in mice

BACKGROUND

The contribution of Staphylococcus aureus to the exacerbation of atopic dermatitis (AD) is widely documented, but its role as a primary trigger of AD skin symptoms remains poorly explored.

OBJECTIVES

This study sought to reappraise the main bacterial factors and underlying immune mechanisms by which S aureus triggers AD-like inflammation.

METHODS

This study capitalized on a preclinical model, in which different clinical isolates were applied in the absence of any prior experimental skin injury.

RESULTS

The development of S aureus-induced dermatitis depended on the nature of the S aureus strain, its viability, the concentration of the applied bacterial suspension, the production of secreted and nonsecreted factors, as well as the activation of accessory gene regulatory quorum sensing system. In addition, the rising dermatitis, which exhibited the well-documented AD cytokine signature, was significantly inhibited in inflammasome adaptor apoptosis-associated speck-like protein containing a CARD domain- and monocyte/macrophage-deficient animals, but not in T- and B-cell-deficient mice, suggesting a major role for the innate response in the induction of skin inflammation. However, bacterial exposure generated a robust adaptive immune response against S aureus, and an accumulation of S aureus-specific γδ and CD4+ tissue resident memory T cells at the site of previous dermatitis. The latter both contributed to worsen the flares of AD-like dermatitis on new bacteria exposures, but also, protected the mice from persistent bacterial colonization.

CONCLUSIONS

These data highlight the induction of unique AD-like inflammation, with the generation of proinflammatory but protective tissue resident memory T cells in a context of natural exposure to pathogenic S aureus strains.

Linking S. aureus Immune Evasion Mechanisms to Staphylococcal Vaccine Failures

Vaccination arguably remains the only long-term strategy to limit the spread of S. aureus infections and its related antibiotic resistance. To date, however, all staphylococcal vaccines tested in clinical trials have failed. In this review, we propose that the failure of S. aureus vaccines is intricately linked to prior host exposure to S. aureus and the pathogen's capacity to evade adaptive immune defenses. We suggest that non-protective immune imprints created by previous exposure to S. aureus are preferentially recalled by SA vaccines, and IL-10 induced by S. aureus plays a unique role in shaping these non-protective anti-staphylococcal immune responses. We discuss how S. aureus modifies the host immune landscape, which thereby necessitates alternative approaches to develop successful staphylococcal vaccines.

T cell and bacterial microbiota interaction at intestinal and skin epithelial interfaces

Graphical Abstract.

Resident cutaneous memory T cells: a clinical review of their role in chronic inflammatory dermatoses and potential as therapeutic targets

Resident memory T cells (T-RMs) remain in epithelial barrier tissues after antigen exposure and the initial effector phase. These T-RMs provide effective antimicrobial and anticancer immunity; however, pathogenic T-RMs have been shown to mediate various chronic inflammatory disorders in a variety of tissue types. In the skin, T-RMs are referred to as resident cutaneous memory T cells (cT-RMs). Understanding the mechanisms leading to the development and establishment of these cT-RMs populations may allow for targeted treatments that provide durable responses in chronic immune-mediated skin diseases, even after cessation. In this review, we summarize the evidence on cT-RMs as drivers of chronic inflammatory dermatoses, including psoriasis, vitiligo, atopic dermatitis, cutaneous lupus erythematosus and alopecia areata, among others. Data from in vitro, animal model and ex vivo human studies are presented, with a focus on the potential for cT-RMs to trigger acute disease flares, as well as recurrent disease, by establishing an immune 'memory' in the skin. Furthermore, the available data on the potential for existing and novel treatments to affect the development or survival of cT-RMs in the skin are synthesized. The data suggest a dynamic and rapidly growing area in the field of dermatology; however, we also discuss areas in need of greater research to allow for optimal treatment selection for long-term disease control.

Emerging Trends and Focus in Human Skin Microbiome Over the Last Decade: A Bibliometric Analysis and Literature Review

Background

Human skin microbiome is the first barrier against exogenous attack and is associated with various skin disease pathogenesis and progression. Advancements in high-throughput sequencing technologies have paved the way for a deeper understanding of this field. Based on the bibliometric analysis, this investigation aimed to identify the hotspots and future research trends associated with human skin microbiomes studied over the past decade.

Methods

The published research on skin microbiome from January 2013 to January 2023 was retrieved from the Web of Science Core Collection. Data cleaning processes to ensure robust data and the bibliometrix packages R, CiteSpace, VOSviewer, Origin, and Scimago Graphica for bibliometric and visual analyses were utilized.

Results

A total of 1629 published documents were analyzed. The overall publication trend steadily increased, with relatively fast growth in 2017 and 2020. The United States of America has the highest number of publications and citations and shows close collaborations with China and Germany. The University of California, San Diego, indicated a higher number of publications than other institutions and the fastest growth rate. The top three most publishing journals on this topic are Microorganisms, Frontiers in Microbiology, and Experimental dermatology. Gallo RL is the most influential author with the highest h- and g-index and most publications in skin microecology, followed by Grice EA and Kong HH. The top 10 most frequently used keywords in recent years included skin microbiome, microbiome, staphylococcus aureus, diversity, atopic dermatitis, skin, bacteria, infections, gut microbiota, and disease.

Conclusion

The skin microbiome is an area of research that requires continuous analysis, and even with much-achieved progress, future research will further be aided as technology develops.

Challenges in development of vaccines directed toward antimicrobial resistant bacterial species

Antimicrobial resistance (AMR) is considered by WHO one of the top ten public health threats. New control strategies involving concerted actions of both public and private sectors need to be developed. Vaccines play a major role in controlling the spread of AMR pathogens by decreasing transmission and limiting the use of antibiotics, reducing at the end the selective pressure for the emergence of new resistant strains. In this review, by using as example some of the most serious AMR pathogens, we highlighted the major hurdles from a research and development point of view. New approaches to better understand the immunological mechanisms of response to both natural infections and vaccines that aimed to identify correlates of protection, together with the application of new technologies for vaccine design and delivery are discussed as potential solutions.

Anti-staphylococcus aureus adaptive immunity is impaired in end-stage renal disease patients on hemodialysis: one-year longitudinal study

Introduction

Patients with end-stage renal disease (ESRD) display defects in adaptive and innate immunity, increasing susceptibility to infection. Staphylococcus aureus (S. aureus) is a major cause of bacteraemia in this population and is associated with increased mortality. More information on the immune response to S. aureus in these patients is needed to inform effective vaccine development.

Methods

A longitudinal prospective study was carried out at two medical centers and included 48 ESRD patients who started chronic hemodialysis (HD) treatment ≤3 months before inclusion. Control samples were taken from 62 consenting healthy blood donors. Blood samples were obtained from ESRD patients at each visit, on month (M) 0 (beginning of HD), M6 and M12. Around 50 immunological markers of adaptive and innate immunity were assessed to compare immune responses to S. aureus in ESRD patients versus controls to document the changes on their immune profile during HD.

Results

S. aureus survival in whole blood was significantly higher in ESRD patients than in controls at M0 (P=0.049), while impaired oxidative burst activity was observed in ESRD patients at all timepoints (P<0.001). S. aureus-specific immunoglobulin G (IgG) responses to iron surface determinant B (IsdB) and S. aureus α hemolysin (Hla) antigens were lower in ESRD patients than in healthy donors at M0 (P=0.003 and P=0.007, respectively) and M6 (P=0.05 and P=0.03, respectively), but were restored to control levels at M12. Moreover, S. aureus-specific T-helper cell responses were comparable to controls for IsdB but were impaired for Hla antigen at all timepoints: 10% of ESRD patients responded to Hla at M0, increasing to 30% at M12, compared with 45% of healthy donors. B-cell and T-cell concentrations in blood were significantly reduced (by 60% and 40%, respectively) compared with healthy controls. Finally, upregulation of Human Leucocyte Antigen-DR (HLA-DR) and C-C chemokine Receptor type 2 (CCR2) was impaired at M0 but was restored during the first year of HD.

Conclusion

All together, these results show that adaptive immunity was largely impaired in ESRD patients, whereas innate immunity was less impacted and tended to be restored by HD.

NOD2 Agonism Counter-Regulates Human Type 2 T Cell Functions in Peripheral Blood Mononuclear Cell Cultures: Implications for Atopic Dermatitis

Atopic dermatitis (AD) is known as a skin disease; however, T cell immunopathology found in blood is associated with its severity. Skin Staphylococcus aureus (S. aureus) and associated host-pathogen dynamics are important to chronic T helper 2 (Th2)-dominated inflammation in AD, yet they remain poorly understood. This study sought to investigate the effects of S. aureus-derived molecules and skin alarmins on human peripheral blood mononuclear cells, specifically testing Th2-type cells, cytokines, and chemokines known to be associated with AD. We first show that six significantly elevated Th2-related chemokine biomarkers distinguish blood from adult AD patients compared to healthy controls ex vivo; in addition, TARC/CCL17, LDH, and PDGF-AA/AB correlated significantly with disease severity. We then demonstrate that these robust AD-associated biomarkers, as well as associated type 2 T cell functions, are readily reproduced from healthy blood mononuclear cells exposed to the alarmin TSLP and the S. aureus superantigen SEB in a human in vitro model, including IL-13, IL-5, and TARC secretion as well as OX-40-expressing activated memory T cells. We further show that the agonism of nucleotide-binding oligomerization domain-containing protein (NOD)2 inhibits this IL-13 secretion and memory Th2 and Tc2 cell functional activation while inducing significantly increased pSTAT3 and IL-6, both critical for Th17 cell responses. These findings identify NOD2 as a potential regulator of type 2 immune responses in humans and highlight its role as an endogenous inhibitor of pathogenic IL-13 that may open avenues for its therapeutic targeting in AD.

Toxin expression during Staphylococcus aureus infection imprints host immunity to inhibit vaccine efficacy

Staphylococcus aureus infections are a major public health issue, and a vaccine is urgently needed. Despite a considerable promise in preclinical models, all vaccines tested thus far have failed to protect humans against S. aureus. Unlike laboratory mice, humans are exposed to S. aureus throughout life. In the current study, we hypothesized that prior exposure to S. aureus "imprints" the immune response to inhibit vaccine-mediated protection. We established a mouse model in which S. aureus skin and soft tissue infection (SSTI) is followed by vaccination and secondary SSTI. Unlike naïve mice, S. aureus-sensitized mice were incompletely protected against secondary SSTI by vaccination with the inactivated α-hemolysin (Hla) mutant Hla_H35L. Inhibition of protection was specific for the Hla_H35L vaccine and required hla expression during primary SSTI. Surprisingly, inhibition occurred at the level of vaccine-elicited effector T cells; hla expression during primary infection limited the expansion of T cells and dendritic cells and impaired vaccine-specific T cell responses. Importantly, the T cell-stimulating adjuvant CAF01 rescued inhibition and restored vaccine-mediated protection. Together, these findings identify a potential mechanism for the failure of translation of promising S. aureus vaccines from mouse models to clinical practice and suggest a path forward to prevent these devastating infections.

T-cell receptor sequencing specifies psoriasis as a systemic and atopic dermatitis as a skin-focused, allergen-driven disease

BACKGROUND

Atopic dermatitis (AD) and psoriasis represent two of the most common inflammatory skin diseases in developed countries. A hallmark of both diseases is T-cell infiltration into the skin. However, it is still not clarified to what extent these infiltrating T cells are antigen-specific skin-homing T cells or unspecific heterogeneous bystander cells.

METHODS

To elucidate this, T cells from lesional skin and from blood of 9 AD and 10 psoriasis patients were compared by receptor (TCR) sequencing. Therefore, peripheral blood mononuclear cells (PBMC) were cell-sorted according to expression of the cutaneous leukocyte antigen (CLA) into skin-homing (CLA⁺ ) and non-skin-homing (CLA^- ) subfractions. Aeroallergen-specific T-cell lines were grown from AD patients' PBMC in parallel.

RESULTS

Intra-individual comparison of TCRB CDR3 regions revealed that clonally expanded T cells in skin lesions of both AD and psoriasis patients corresponded to skin-homing circulating T cells. However, in psoriasis patients, these T-cell clones were also detectable to a larger extent among CLA^- circulating T cells. Up to 28% of infiltrating cells in AD skin were identified as allergen-specific by overlapping TCR sequences.

CONCLUSIONS

Our data show that in line with the systemic nature of psoriasis, T-cell clones that infiltrate psoriatic skin lesions do not exclusively possess skin-homing ability and are therefore most probably specific to antigens that are not exclusively expressed or located in the skin. T cells driving AD skin inflammation appear to home nearly exclusively to the skin and are, to a certain extent, specific to aeroallergens.

Skin Deep: The Role of the Microbiota in Cutaneous Autoimmunity

The skin microbiota is thought to possibly contribute to the pathogenesis of skin autoimmune diseases. The gut microbiota affects systemically the development and function of the immune system, thereby potentially influencing cutaneous autoimmunity as well. In this paper, we review the role of the gut and skin microbiota in cutaneous autoimmune diseases. Besides direct inflammatory effects at the skin barrier, microbiota may contribute to the pathogenesis of skin autoimmune diseases by metabolites, recall immune cell responses, and permeation of antigens to the subepidermal space. Skin and gut barrier dysfunction may represent a common pathophysiologic process allowing microbiota or its particles to promote autoimmune diseases at barrier surfaces.

Staphylococcus aureus adaptive evolution: Recent insights on how immune evasion, immunometabolic subversion and host genetics impact vaccine development

Despite meritorious attempts, a S. aureus vaccine that prevents infection or mitigates severity has not yet achieved efficacy endpoints in prospective, randomized clinical trials. This experience underscores the complexity of host-S. aureus interactions, which appear to be greater than many other bacterial pathogens against which successful vaccines have been developed. It is increasingly evident that S. aureus employs strategic countermeasures to evade or exploit human immune responses. From entering host cells to persist in stealthy intracellular reservoirs, to sensing the environmental milieu and leveraging bacterial or host metabolic products to reprogram host immune responses, S. aureus poses considerable challenges for the development of effective vaccines. The fact that this pathogen causes distinct types of infections and can undergo transient genetic, transcriptional or metabolic adaptations in vivo that do not occur in vitro compounds challenges in vaccine development. Notably, the metabolic versatility of both bacterial and host immune cells as they compete for available substrates within specific tissues inevitably impacts the variable repertoire of gene products that may or may not be vaccine antigens. In this respect, S. aureus has chameleon phenotypes that have alluded vaccine strategies thus far. Nonetheless, a number of recent studies have also revealed important new insights into pathogenesis vulnerabilities of S. aureus. A more detailed understanding of host protective immune defenses versus S. aureus adaptive immune evasion mechanisms may offer breakthroughs in the development of effective vaccines, but at present this goal remains a very high bar. Coupled with the recent advances in human genetics and epigenetics, newer vaccine technologies may enable such a goal. If so, future vaccines that protect against or mitigate the severity of S. aureus infections are likely to emerge at the intersection of precision and personalized medicine. For now, the development of S. aureus vaccines or alternative therapies that reduce mortality and morbidity must continue to be pursued.

Assessment of patient-to-patient and intra-individual human abdominal skin immune cell variability

INTRODUCTION

The objective of the study was to characterize the baseline intra-individual and inter-individual variability of immune cell subsets within abdominoplasty skin specimens.

METHODS

Abdominoplasty biopsies were taken from 5 patients and analysed using the Vectra 3 automated quantitative pathology imaging system with inForm software.

RESULTS

Adjacent skin regions demonstrated intra-patient variability in immune subset counts ranging from 1- to 5-fold. Inter-variability between patients was approximately 2- to 7-fold for most subsets, except for HLA-DR⁺ antigen presenting cells, which varied 19-fold.

CONCLUSIONS

Our data highlight the importance of including multiple patients and multiple patient samples when designing dermatological studies that utilise abdominoplasty skin.

Staphylococcus aureus specific lung resident memory CD4+ Th1 cells attenuate the severity of influenza virus induced secondary bacterial pneumonia

Staphylococcus aureus is a major cause of severe pulmonary infections. The evolution of multi-drug resistant strains limits antibiotic treatment options. To date, all candidate vaccines tested have failed, highlighting the need for an increased understanding of the immunological requirements for effective S. aureus immunity. Using an S. aureus strain engineered to express a trackable CD4⁺ T cell epitope and a murine model of S. aureus pneumonia, we show strategies that lodge Th1 polarised bacterium specific CD4⁺ tissue resident memory T cells (Trm) in the lung can significantly attenuate the severity of S. aureus pneumonia. This contrasts natural infection of mice that fails to lodge CD4⁺ Trm cells along the respiratory tract or provide protection against re-infection, despite initially generating Th17 bacterium specific CD4⁺ T cell responses. Interestingly, lack of CD4⁺ Trm formation after natural infection in mice appears to be reflected in humans, where the frequency of S. aureus reactive CD4⁺ Trm cells in lung tissue is also low. Our findings reveal the protective capacity of S. aureus specific respiratory tract CD4⁺ Th1 polarised Trm cells and highlight the potential for targeting these cells in vaccines that aim to prevent the development of S. aureus pneumonia.

B and T cell epitope-based peptides predicted from clumping factor protein of Staphylococcus aureus as vaccine targets

Staphylococcus aureus infection is emerging as a global threat because of the highly debilitating nature of the associated disease's unprecedented magnitude of its spread and growing global resistance to antimicrobial medicines. Recently WHO has categorized these bacteria under the high global priority pathogen list and is one of the six nosocomial pathogens termed as ESKAPE pathogens which have emerged as a serious threat to public health worldwide. The development of a specific vaccine can stimulate an optimal antibody response, thus providing immunity against it. Therefore, in the present study efforts have been made to identify potential vaccine candidates from the Clumping factor surface proteins (ClfA and ClfB) of S. aureus. Employing the immunoinformatics approach, fourteen antigenic peptides including T-cell, B-cell epitopes were identified which were non-toxic, non-allergenic, high antigenicity, strong binding efficiency with commonly occurring MHC alleles. Consequently, a multi-epitope vaccine chimera was designed by connecting these epitopes with suitable linkers an adjuvant to enhance immunogenicity. Further, homology modeling and molecular docking were performed to construct the three-dimensional structure of the vaccine and study the interaction between the modeled structure and immune receptor (TLR-2) present on lymphocyte cells. Consequently, molecular dynamics simulation for 100 ns period confirmed the stability of the interaction and reliability of the structure for further analysis. Finally, codon optimization and in silico cloning were employed to ensure the successful expression of the vaccine candidate. As the targeted protein is highly antigenic and conserved, hence the designed novel vaccine construct holds potential against emerging multi-drug-resistant organisms.

Staphylococcus aureus Vaccine Research and Development: The Past, Present and Future, Including Novel Therapeutic Strategies

Staphylococcus aureus is one of the most important human pathogens worldwide. Its high antibiotic resistance profile reinforces the need for new interventions like vaccines in addition to new antibiotics. Vaccine development efforts against S. aureus have failed so far however, the findings from these human clinical and non-clinical studies provide potential insight for such failures. Currently, research is focusing on identifying novel vaccine formulations able to elicit potent humoral and cellular immune responses. Translational science studies are attempting to discover correlates of protection using animal models as well as in vitro and ex vivo models assessing efficacy of vaccine candidates. Several new vaccine candidates are being tested in human clinical trials in a variety of target populations. In addition to vaccines, bacteriophages, monoclonal antibodies, centyrins and new classes of antibiotics are being developed. Some of these have been tested in humans with encouraging results. The complexity of the diseases and the range of the target populations affected by this pathogen will require a multipronged approach using different interventions, which will be discussed in this review.