Single-cell analysis implicates Th17 to Th2 cell plasticity in the pathogenesis of palmoplantar pustulosis

Expanding the therapeutic horizons of spesolimab: a review of off-label applications for inflammatory skin diseases

PURPOSE

This review aims to outline the crucial role of IL-36 signaling in inflammatory skin diseases and summarize the therapeutic potential of spesolimab. Our goal is to provide insights into the off-label applications of spesolimab and future directions for its use in treating other challenging skin diseases.

MATERIALS AND METHODS

We conducted a comprehensive literature search across PubMed, Embase, Web of Science, MEDLINE, Scopus, and the Cochrane Library to identify relevant studies. For RCTs, we additionally searched the ClinicalTrials.gov database.

RESULTS

In this review, we examine its off-label applications for conditions such as palmoplantar pustulosis, acrodermatitis continua of Hallopeau, hidradenitis suppurativa, pyoderma gangrenosum, and acute generalized exanthematous pustulosis. This review also explores the role of IL-36 in the pathophysiology of these disorders and discusses how spesolimab may address the limitations of current therapies for refractory cases. Randomized controlled trials and case reports are summarized to highlight the efficacy and tolerability of spesolimab across various inflammatory skin conditions. We highlight the challenges presented by the absence of standardized treatment guidelines and the need for larger clinical trials.

CONCLUSIONS

This review underscores the potential of spesolimab to enhance treatment strategies for inflammatory skin diseases.

Emerging Therapies for Palmoplantar Pustulosis with a Focus on IL-23 Inhibitors

Palmoplantar pustulosis (PPP) is a chronic inflammatory skin disease characterized by recurrent pustules, erythema, and scaling on the palms and soles, leading to a significantly reduced quality of life. Although PPP shares some immunopathological features with psoriasis vulgaris, it is distinguished by unique genetic predispositions, including a higher prevalence in East Asian populations, and a complex immune profile, particularly dysregulation of the IL-23/Th17 axis and IL-36 cytokines. Recent advances in psoriasis treatment have highlighted IL-23 inhibitors, which target the p19 subunit to suppress Th17 activation and inflammatory cytokines. Clinical trials show that IL-23 inhibitors significantly improve disease severity and patient-reported outcomes in PPP while maintaining favorable safety profiles. Notably, guselkumab and risankizumab have recently been approved for PPP treatment in Japan and Korea. In contrast, IL-17 inhibitors and IL-36 blockers have yielded mixed results. A recent phase 3 trial in Japan demonstrated the significant efficacy of apremilast in treating PPP, with a favorable safety profile, suggesting that apremilast may be a promising treatment option for PPP. Due to PPP's lower prevalence compared with psoriasis vulgaris, clinical trials remain limited. Further large-scale, controlled studies are needed to clarify the efficacy and long-term safety of these therapies in diverse populations. This review summarizes emerging evidence on IL-23 inhibitors and other treatments for PPP, detailing their mechanisms of action, clinical efficacy, safety profiles, current challenges, and future perspectives in optimizing therapy.

Palmoplantar Pustulosis as an Immune-Mediated Inflammatory Disease with a Possible Relevance of Th17 Cell Plasticity: A Narrative Review

Palmoplantar pustulosis (PPP) is an immune-mediated inflammatory disease (IMID) of the skin that causes the formation of sterile pustules on the palms and soles. The clinical course of PPP is variable, with some patients having persistent skin lesions and others having lesions that wax and wane repeatedly. PPP has been treated with drugs such as those used for plaque psoriasis. The efficacy of biologics targeting the interleukin (IL)-23-helper T (Th)17 axis is not as conspicuous in PPP as in plaque psoriasis. Traditionally, CD4+ Th cell subsets have been defined by the expression of a small number of cytokines; however, recent advances in immunology have shown that some Th cell subsets can express cytokines of other Th subsets in response to changes in the environment. Recent studies have suggested the involvement of unique Th17 cells with Th2 cell characteristics in the pathogenesis of PPP. Thus, the insufficient efficacy of biologics targeting the IL-23-Th17 axis in PPP raises the question of whether Th17 cell plasticity is involved in the pathogenesis of PPP. In this review, we discuss the complexity of PPP pathogenesis with some speculation, compare the new knowledge obtained by other IMIDs or their mouse models with that of PPP elucidated thus far, and contribute to the development of future research.

Biologic Treatment Adherence and Persistence in Patients with Palmoplantar Pustulosis: A Real-World, Claims-Based Study

INTRODUCTION

Palmoplantar pustulosis (PPP) is a debilitating skin condition characterized by pustules, erythema, and scales on the palms and soles. Treatment adherence in psoriatic diseases is suboptimal.

METHODS

A retrospective cohort study, using healthcare claims data from patients aged ≥ 18 years with newly diagnosed PPP (selected between October 1, 2016 and March 31, 2020 from IBM® MarketScan® Commercial and the Optum® Clinformatics® Data Mart databases), was conducted to investigate adherence to and persistence with biologics in patients with PPP.

RESULTS

Biologics were dispensed to 114/840 (13.6%) MarketScan and 76/750 (10.1%) Optum patients. Mean proportion of days covered (PDC; range) for biologics was similar between databases (MarketScan, 66% [8-100%]; Optum, 61% [8-99%]), and good adherence (≥ 80% PDC) was infrequent (MarketScan, 42.1%; Optum, 34.2%). Mean (standard deviation) persistence was slightly longer in MarketScan (283 [121] days) versus Optum (275 [133] days). Mean (range) adherence was similar between ages, although persistence was longer in patients aged 18-64 versus ≥ 65 years (279 [132] vs 258 [140] days).

CONCLUSION

In patients with PPP, adherence to biologics was poor and persistence was variable; understanding and addressing the reasons behind these observations may improve treatment outcomes.

Blood Single-Cell Transcriptomic and Proteomic Signatures of Paradoxical Eczema in Patients with Psoriasis Treated with Biologics

Biologics targeting the TNF and IL-17/23 axis are highly effective treatments for psoriasis but can result in cutaneous adverse events. The pathogenesis of paradoxical eczema, the occurrence of an atopic dermatitis phenotype after biologic initiation in people with psoriasis, is unknown. Using single-cell RNA sequencing and mass cytometry, we found increased expression of TNF, IFN-γ, and IFN-α and their signaling pathways in paradoxical eczema case cell clusters compared with that in matched psoriasis controls. Genetic variants influencing the expression of chemokine signaling and TNF pathway genes were associated with paradoxical eczema in a separate genotyped cohort, and this association was independent of known atopic risk loci. This suggests that paradoxical eczema has a predominantly type 1 systemic inflammatory signature and that genetic susceptibility to aberrant chemokine and TNF pathway signaling could contribute to development of this phenotype during biologic treatment.

Off-label use of JAK1 inhibitor upadacitinib in dermatology

Upadacitinib, a selective Janus kinase 1 (JAK1) inhibitor, has gained FDA approval for conditions such as rheumatoid arthritis and atopic dermatitis. Emerging studies suggest its potential for off-label use in various dermatological disorders. This review systematically explores the off-label dermatological applications of upadacitinib. We conducted a comprehensive literature search across MEDLINE, EMBASE, SCOPUS, and ClinicalTrials.gov. Studies on alopecia areata, hidradenitis suppurativa, vitiligo, and other conditions were included. The review identified two randomized controlled trials (RCTs) evaluating upadacitinib's efficacy in hidradenitis suppurativa and vitiligo. Both trials demonstrated promising improvements in clinical outcomes, though some results were not statistically significant. Additionally, case reports and series highlight its efficacy in alopecia areata and lichen planus. These findings suggest upadacitinib as a viable option for refractory dermatological conditions. However, the limited sample sizes and short follow-up periods underscore the need for further large-scale, long-term studies.

A Case of Allergic Contact Dermatitis Due to Chrysanthemum After Guselkumab Therapy for Palmoplantar Pustulosis

Eczematous paradoxical reactions are commonly associated with anti-interleukin-17A (anti-IL-17A) antibodies. However, IL-23 p19 inhibitors can also cause similar cutaneous manifestations. We present a case of a 77-year-old Japanese woman with palmoplantar pustulosis (PPP), who developed eczematous lesions on her face, neck, and dorsum of the hands 10 weeks after initiating guselkumab treatment. Patch tests revealed a positive reaction to Chrysanthemum flowers and leaves, confirming a diagnosis of contact dermatitis. This was notable, as the patient had routine contact with Chrysanthemum every morning for years without prior allergic reactions, until after initiating anti-IL-23 p19 antibody treatment. Given the temporal association and potential causal link with guselkumab administration, the treatment was discontinued, and avoiding contact with the plant improved the contact dermatitis eruptions. Concurrently, PPP lesions remained unchanged. IL-23 inhibition is known to skew the IL-12/T-helper 1 (Th1) axis, resulting in increased interferon-γ (IFN-γ) production, a cytokine implicated in the early sensitization phase of allergic contact dermatitis (ACD). Despite prior tolerance, this case report highlights the importance of considering drug-induced ACD in patients presenting with new-onset eczema while on biologic therapy, particularly in susceptible individuals.

A systematic review of recent randomized controlled trials for palmoplantar pustulosis

Background: Palmoplantar pustulosis (PPP) is a chronic inflammatory condition, that leads to significant functional impairment and reduced quality of life. Despite its low incidence, treatment options are diverse and often ineffective, necessitating a review of recent therapeutic advances.

Objective: This review aims to evaluate the efficacy and safety of recent therapeutic options for the treatment of PPP, focusing on phototherapy, systemic therapies, and biologics.

Materials and methods: A systematic literature search identified 13 studies evaluating phototherapy and systemic therapies, including biologics. Inclusion criteria focused on randomized controlled trials with participants diagnosed with PPP.

Results: Phototherapy showed success: excimer laser demonstrated high efficacy for severe disease [PPP Area and Severity Index (PPPASI)-75 of 95.0%], while psoralen plus ultraviolet A therapy with retinoids or fumaric acid esters worked well in milder disease (PPPASI-90 of 90.0 and 81.8%, respectively). Evidence supports the efficacy and safety of guselkumab, brodalumab, and apremilast over a range of disease severity (PPPASI-50 ranged from 57.4 to 78.3% at week 16). Agents including anakinra, secukinumab, spesolimab, and RIST4721 (primary outcomes not achieved) may not be first-line treatments. By targeting multiple inflammatory pathways in PPP, JAK inhibitors may be more effective than biologics in treating PPP; however, more research is needed to confirm their safety and appropriate use.

Conclusions: Multiple new treatments exist for PPP with promising results, however longer-term studies with standardized outcome reporting are needed to determine optimal treatment strategies and their comparative efficacy.

Systematic analysis of human colorectal cancer scRNA-seq revealed limited pro-tumoral IL-17 production potential in gamma delta T cells

Gamma delta T cells play a crucial role in anti-tumor immunity due to their cytotoxic properties. However, the role and extent of γδ T cells in production of pro-tumorigenic interleukin-17 (IL-17) within the tumor microenvironment of colorectal cancer (CRC) remains controversial. In this study, we re-analyzed nine published human CRC whole-tissue single-cell RNA sequencing datasets, identifying 18,483 γδ T cells out of 951,785 total cells, in the neoplastic or adjacent normal tissue of 165 human CRC patients. Our results confirm that tumor-infiltrating γδ T cells exhibit high cytotoxicity-related transcription in both tumor and adjacent normal tissues, but critically, none of the γδ T cell clusters showed IL-17 production potential. We also identified various γδ T cell subsets, including poised effector-like T cells, tissue-resident memory T cells, progenitor exhausted-like T cells, and exhausted T cells, and noted an increased expression of cytotoxic molecules in tumor-infiltrating γδ T cells compared to their normal area counterparts. We proposed anti-tumor γδ T effector cells may arise from tissue-resident progenitor cells based on the trajectory analysis. Our work demonstrates that γδ T cells in CRC primarily function as cytotoxic effector cells rather than IL-17 producers, mitigating the concerns about their potential pro-tumorigenic roles in CRC, highlighting the importance of accurately characterizing these cells for cancer immunotherapy research and the unneglectable cross-species discrepancy between the mouse and human immune system in the study of cancer immunology.

Paradoxical Psoriasis: An Updated Review of Clinical Features, Pathogenesis, and Treatment Options

The definition of paradoxical psoriasis (PP) encompasses 2 main scenarios, namely, (i) new-onset psoriasis in patients treated for a different disease and (ii) worsening as well as phenotypical change of pre-existing psoriasis. Originally restricted to the appearance of an untoward psoriasiform reaction under TNF inhibitors, the term has gained new meaning, with the progressive observation of psoriasis-like eruptions also with other medications. Although the conceptual framework of PP has expanded, a molecular and clinicotherapeutic classification is still lacking. In addition, a certain degree of confusion surrounds the correct terminology to indicate these eruptions. In this paper, evidence on the epidemiology, clinical features, pathogenesis, and treatment of PP is reviewed, providing a perspective on possible pathogenesis-driven therapeutic approaches.

Disease heterogeneity and molecular classification of inflammatory palmoplantar diseases

BACKGROUND

Palmoplantar pustulosis (PPP) is an inflammatory disease characterized by relapsing eruptions of neutrophil-filled, sterile pustules on the palms and soles that can be clinically difficult to differentiate from non-pustular palmoplantar psoriasis (palmPP) and dyshidrotic palmoplantar eczema (DPE).

OBJECTIVE

We sought to identify overlapping and unique PPP, palmPP, and DPE drivers to provide molecular insight into their pathogenesis.

METHODS

We performed bulk RNA sequencing of lesional PPP (n = 33), palmPP (n = 5), and DPE (n = 28) samples, as well as 5 healthy nonacral and 10 healthy acral skin samples.

RESULTS

Acral skin showed a unique immune environment, likely contributing to a unique niche for palmoplantar inflammatory diseases. Compared to healthy acral skin, PPP, palmPP, and DPE displayed a broad overlapping transcriptomic signature characterized by shared upregulation of proinflammatory cytokines (TNF, IL-36), chemokines, and T-cell-associated genes, along with unique disease features of each disease state, including enriched neutrophil processes in PPP and to a lesser extent in palmPP, and lipid antigen processing in DPE. Strikingly, unsupervised clustering and trajectory analyses demonstrated divergent inflammatory profiles within the 3 disease states. These identified putative key upstream immunologic switches, including eicosanoids, interferon responses, and neutrophil degranulation, contributing to disease heterogeneity.

CONCLUSION

A molecular overlap exists between different inflammatory palmoplantar diseases that supersedes clinical and histologic assessment. This highlights the heterogeneity within each condition, suggesting limitations of current disease classification and the need to move toward a molecular classification of inflammatory acral diseases.

Janus kinase inhibitor tofacitinib successfully treated palmoplantar pustulosis after switching from secukinumab: A case report and review of the literature

Palmoplantar pustulosis (PPP) is a chronic inflammatory recurrent disease characterized by sterile pustules involving palms and/or feet. Presently, there are no standard recommended treatment regimens. Tofacitinib is an oral Janus kinase (JAK) inhibitor, mainly acts on JAK 1 and 3 and has been approved for the treatment of rheumatoid arthritis in adults. Herein, we present a case of a patient with PPP who did not respond to IL-17A inhibitor secukinumab but was successfully treated by the JAK inhibitor tofacitinib.

A genome-wide meta-analysis of palmoplantar pustulosis implicates TH2 responses and cigarette smoking in disease pathogenesis

BACKGROUND

Palmoplantar pustulosis (PPP) is an inflammatory skin disorder that mostly affects smokers and manifests with painful pustular eruptions on the palms and soles. Although the disease can present with concurrent plaque psoriasis, TNF and IL-17/IL-23 inhibitors show limited efficacy. There is therefore a pressing need to uncover PPP disease drivers and therapeutic targets.

OBJECTIVES

We sought to identify genetic determinants of PPP and investigate whether cigarette smoking contributes to disease pathogenesis.

METHODS

We performed a genome-wide association meta-analysis of 3 North-European cohorts (n = 1,456 PPP cases and 402,050 controls). We then used the scGWAS program to investigate the cell-type specificity of the association signals. We also undertook genetic correlation analyses to examine the similarities between PPP and other immune-mediated diseases. Finally, we applied Mendelian randomization to analyze the causal relationship between cigarette smoking and PPP.

RESULTS

We found that PPP is not associated with the main genetic determinants of plaque psoriasis. Conversely, we identified genome-wide significant associations with the FCGR3A/FCGR3B and CCHCR1 loci. We also observed 13 suggestive (P < 5 × 10-6) susceptibility regions, including the IL4/IL13 interval. Accordingly, we demonstrated a significant genetic correlation between PPP and TH2-mediated diseases such as atopic dermatitis and ulcerative colitis. We also found that genes mapping to PPP-associated intervals were preferentially expressed in dendritic cells and often implicated in T-cell activation pathways. Finally, we undertook a Mendelian randomization analysis, which supported a causal role of cigarette smoking in PPP.

CONCLUSIONS

The first genome-wide association study of PPP points to a pathogenic role for deregulated TH2 responses and cigarette smoking.

Systematic Analysis of Human Colorectal Cancer scRNA-seq Revealed Limited Pro-tumoral IL-17 Production Potential in Gamma Delta T Cells

Gamma delta (γδ) T cells play a crucial role in anti-tumor immunity due to their cytotoxic properties. However, the role and extent of γδ T cells in production of pro-tumorigenic interleukin- 17 (IL-17) within the tumor microenvironment (TME) of colorectal cancer (CRC) remains controversial. In this study, we re-analyzed nine published human CRC whole-tissue single-cell RNA sequencing (scRNA-seq) datasets, identifying 18,483 γδ T cells out of 951,785 total cells, in the neoplastic or adjacent normal tissue of 165 human CRC patients. Our results confirm that tumor-infiltrating γδ T cells exhibit high cytotoxicity-related transcription in both tumor and adjacent normal tissues, but critically, none of the γδ T cell clusters showed IL-17 production potential. We also identified various γδ T cell subsets, including Teff, TRM, Tpex, and Tex, and noted an increased expression of cytotoxic molecules in tumor-infiltrating γδ T cells compared to their normal area counterparts. Our work demonstrates that γδ T cells in CRC primarily function as cytotoxic effector cells rather than IL-17 producers, mitigating the concerns about their potential pro-tumorigenic roles in CRC, highlighting the importance of accurately characterizing these cells for cancer immunotherapy research and the unneglectable cross-species discrepancy between the mouse and human immune system in the study of cancer immunology.

Dominant dystrophic epidermolysis bullosa is associated with glycolytically active GATA3+ T helper 2 cells which may contribute to pruritus in lesional skin

BACKGROUND

Dominant dystrophic epidermolysis bullosa (DDEB) is characterized by trauma-induced blisters and, in some individuals, intense pruritus. Precisely what causes itch in DDEB and optimal ways to reduce it have not been fully determined.

OBJECTIVES

To characterize DDEB skin transcriptomes to identify therapeutic targets to reduce pruritus in patients.

METHODS

Using bulk RNA sequencing, we evaluated affected and unaffected skin biopsy samples from six patients with DDEB (all with the very itchy pruriginosa subtype) and four healthy individuals. Single-cell transcriptomes of affected (n = 2) and unaffected (n = 1) DDEB skin and healthy skin (n = 2) were obtained. Dupilumab treatment was provided for three patients.

RESULTS

The skin bulk transcriptome showed significant enrichment of T helper (Th)1/2 and Th17 pathways in affected DDEB skin compared with nonlesional DDEB skin and healthy skin. Single-cell transcriptomics showed an association of glycolytically active GATA3+ Th2 cells in affected DDEB skin. Treatment with dupilumab in three people with DDEB led to significantly reduced visual analogue scale (VAS) itch scores after 12 weeks (mean VAS 3.83) compared with pretreatment (mean VAS 7.83). Bulk RNAseq and quantitative polymerase chain reaction showed that healthy skin and dupilumab-treated epidermolysis bullosa (EB) pruriginosa skin have similar transcriptomic profiles and reduced Th1/Th2 and Th17 pathway enrichment.

CONCLUSIONS

Single-cell RNAseq helps define an enhanced DDEB-associated Th2 profile and rationalizes drug repurposing of anti-Th2 drugs in treating DDEB pruritus.

Apremilast is a potentially useful treatment for severe palmoplantar pustulosis with extra-palmoplantar symptoms

Palmoplantar pustulosis (PPP) is a chronic inflammatory skin disorder affecting the palms and soles. In rare cases, severe patients develop acute extra-palmoplantar lesions often accompanied by arthralgia. Such cases with extensive symptoms often necessitate systemic treatments with variable efficacy and potential side effects. Apremilast, known for its broad immune response modulation, presents promise as a therapeutic option for severe PPP with joint and extra-palmoplantar lesions. This case highlights apremilast as a potential systemic treatment for such cases with minimal side effects.

Pentraxin 3 exacerbates psoriasiform dermatitis through regulation of macrophage polarization

OBJECTIVE

To elucidate the mechanism of Pentraxin 3 (PTX3) in the pathogenesis of psoriasiform dermatitis using Ptx3-knockout (Ptx3-KO) background mice.

METHODS

An Imiquimod (IMQ)-induced murine psoriatic model was created using Ptx3-KO (Ptx3-/-) and wild-type (Ptx3+/+) mice. Skin lesion severity and expression of inflammatory mediators (IL-6 and TNFα) were assessed using PASI score and ELISA, respectively. Cutaneous tissues from the two mice groups were subjected to histological analyses, including HE staining, Masson staining, and Immunohistochemistry (IHC). The PTX3, iNOS, COX2, and Arg1 expressions were quantified and compared between the two groups. We used RNA-seq to clarify the underlying mechanisms of the disease. Flow cytometry was used to analyze systemic Th17 cell differentiation and macrophage polarization.

RESULT

The psoriatic region exhibited a higher PTX3 expression than the normal cutaneous area. Moreover, PTX3 was upregulated in HaCaT cells post-TNFα stimulation. Upon IMQ stimulation, Ptx3-/- mice displayed a lower degree of the psoriasiform dermatitis phenotype compared to Ptx3+/+ mice. Consistent with the RNA-seq results, further experiments confirmed that compared to the wild-type group, the PTX3-KO group exhibited a generally lower IL-6, TNFα, iNOS, and COX2 expression and a contrasting trend in macrophage polarization. However, no significant difference in Th17 cell activation was observed between the two groups.

CONCLUSIONS

This study revealed that PTX3 was upregulated in psoriatic skin tissues and TNFα-stimulated HaCaT cells. We also discovered that PTX3 deficiency in mice ameliorated the psoriasiform dermatitis phenotype upon IMQ stimulation. Mechanistically, PTX3 exacerbates psoriasiform dermatitis by regulating macrophage polarization rather than Th17 cell differentiation.

Single-cell sequencing analysis and multiple machine-learning models revealed the cellular crosstalk of dendritic cells and identified FABP5 and KLRB1 as novel biomarkers for psoriasis

Background

Psoriasis is an immune-mediated disorder influenced by environmental factors on a genetic basis. Despite advancements, challenges persist, including the diminishing efficacy of biologics and small-molecule targeted agents, alongside managing recurrence and psoriasis-related comorbidities. Unraveling the underlying pathogenesis and identifying valuable biomarkers remain pivotal for diagnosing and treating psoriasis.

Methods

We employed a series of bioinformatics (including single-cell sequencing data analysis and machine learning techniques) and statistical methods to integrate and analyze multi-level data. We observed the cellular changes in psoriatic skin tissues, screened the key genes Fatty acid binding protein 5 (FABP5) and The killer cell lectin-like receptor B1 (KLRB1), evaluated the efficacy of six widely prescribed drugs on psoriasis treatment in modulating the dendritic cell-associated pathway, and assessed their overall efficacy. Finally, RT-qPCR, immunohistochemistry, and immunofluorescence assays were used to validate.

Results

The regulatory influence of dendritic cells (DCs) on T cells through the CD70/CD27 signaling pathway may emerge as a significant facet of the inflammatory response in psoriasis. Notably, FABP5 and KLRB1 exhibited up-regulation and co-localization in psoriatic skin tissues and M5-induced HaCaT cells, serving as potential biomarkers influencing psoriasis development.

Conclusion

Our study analyzed the impact of DC-T cell crosstalk in psoriasis, elucidated the characterization of two biomarkers, FABP5 and KLRB1, in psoriasis, and highlighted the promise and value of tofacitinib in psoriasis therapy targeting DCs.

Single-cell transcriptome landscape of circulating CD4+ T cell populations in autoimmune diseases

CD4+ T cells are key mediators of various autoimmune diseases; however, their role in disease progression remains unclear due to cellular heterogeneity. Here, we evaluated CD4+ T cell subpopulations using decomposition-based transcriptome characterization and canonical clustering strategies. This approach identified 12 independent gene programs governing whole CD4+ T cell heterogeneity, which can explain the ambiguity of canonical clustering. In addition, we performed a meta-analysis using public single-cell datasets of over 1.8 million peripheral CD4+ T cells from 953 individuals by projecting cells onto the reference and cataloging cell frequency and qualitative alterations of the populations in 20 diseases. The analyses revealed that the 12 transcriptional programs were useful in characterizing each autoimmune disease and predicting its clinical status. Moreover, genetic variants associated with autoimmune diseases showed disease-specific enrichment within the 12 gene programs. The results collectively provide a landscape of single-cell transcriptomes of CD4+ T cell subpopulations involved in autoimmune disease.

Hybrid lineages of CD4+ T cells: a handbook update

CD4+ T lymphocytes have been classified into several lineages, according to their gene expression profiles and their effector responses. Interestingly, recent evidence is showing that many lineages could yield hybrid phenotypes with unique properties and functions. It has been reported that such hybrid lineages might underlie pathologies or may function as effector cells with protection capacities against molecular threats. In this work, we reviewed the characteristics of the hybrid lineages reported in the literature, in order to identify the expression profiles that characterize them and the markers that could be used to identify them. We also review the differentiation cues that elicit their hybrid origin and what is known about their physiological roles.

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

The pathogenetic role of Th17 immune response in atopic dermatitis

PURPOSE OF REVIEW

As we continue to unravel the pathophysiology and immune mechanisms underlying atopic dermatitis (AD), the emergence of targeted treatments has provided new options for management. Although there are available therapies targeting various immune pathways in AD, the precise pathogenic role of interleukin (IL)-17 in AD pathogenesis remains unclear. The objective of this review is to examine the existing data pertaining to the role of IL-17 in AD and shed light on the potential of targeting this pathway as a therapeutic approach in AD treatment.

RECENT FINDINGS

IL-17 has a dual role of pro-inflammatory and immune protective function, making it an important player in several autoimmune and inflammatory conditions. The extent of IL-17 axis involvement in AD pathogenesis is still debatable. Emerging data show that Th17-related cytokines/chemokines are elevated in skin and sera samples of AD patients, with some articles reporting correlations with disease severity. Particularly increased Th17 signature in specific AD patient subsets, such as Asian-origin or pediatric patients, suggests that certain patients' disease presentations are more predominantly influenced by Th17, and, thus, they may benefit more from Th17 therapeutic targeting approaches. Lack of clinical efficacy with anti-Th17 biologics in AD patients, underscores the need to better elucidate the role of Th17 in AD pathogenesis, along with its utility in therapy.

SUMMARY

The well established role of IL-17 in autoimmune disorders hints for its possible participation in AD disease pathogenesis. Subsequent investigations are needed to assess whether the targeting of specific IL-17 isoforms, homodimers, or heterodimers in specific subpopulations of AD can modify treatment outcomes.

The paradigm of IL-23-independent production of IL-17F and IL-17A and their role in chronic inflammatory diseases

Interleukin-17 family (IL-17s) comprises six structurally related members (IL-17A to IL-17F); sequence homology is highest between IL-17A and IL-17F, displaying certain overlapping functions. In general, IL-17A and IL-17F play important roles in chronic inflammation and autoimmunity, controlling bacterial and fungal infections, and signaling mainly through activation of the nuclear factor-kappa B (NF-κB) pathway. The role of IL-17A and IL-17F has been established in chronic immune-mediated inflammatory diseases (IMIDs), such as psoriasis (PsO), psoriatic arthritis (PsA), axial spondylarthritis (axSpA), hidradenitis suppurativa (HS), inflammatory bowel disease (IBD), multiple sclerosis (MS), and asthma. CD4+ helper T cells (Th17) activated by IL-23 are well-studied sources of IL-17A and IL-17F. However, other cellular subtypes can also produce IL-17A and IL-17F, including gamma delta (γδ) T cells, alpha beta (αβ) T cells, type 3 innate lymphoid cells (ILC3), natural killer T cells (NKT), or mucosal associated invariant T cells (MAIT). Interestingly, the production of IL-17A and IL-17F by innate and innate-like lymphocytes can take place in an IL-23 independent manner in addition to IL-23 classical pathway. This would explain the limitations of the inhibition of IL-23 in the treatment of patients with certain rheumatic immune-mediated conditions such as axSpA. Despite their coincident functions, IL-17A and IL-17F contribute independently to chronic tissue inflammation having somehow non-redundant roles. Although IL-17A has been more widely studied, both IL-17A and IL-17F are overexpressed in PsO, PsA, axSpA and HS. Therefore, dual inhibition of IL-17A and IL-17F could provide better outcomes than IL-23 or IL-17A blockade.

Assessment of Treatment-Relevant Immune Biomarkers in Psoriasis and Atopic Dermatitis: Toward Personalized Medicine in Dermatology

Immunologically targeted therapies have revolutionized the treatment of inflammatory dermatoses, including atopic dermatitis and psoriasis. Although immunologic biomarkers hold great promise for personalized classification of skin disease and tailored therapy selection, there are no approved or widely used approaches for this in dermatology. This review summarizes the translational immunologic approaches to measuring treatment-relevant biomarkers in inflammatory skin conditions. Tape strip profiling, microneedle-based biomarker patches, molecular profiling from epidermal curettage, RNA in situ hybridization tissue staining, and single-cell RNA sequencing have been described. We discuss the advantages and limitations of each and open questions for the future of personalized medicine in inflammatory skin disease.

IL17A mRNA Staining Distinguishes Palmoplantar Psoriasis from Hyperkeratotic Palmoplantar Eczema in Diagnostic Skin Biopsies

Acral dermatoses, including hyperkeratotic palmoplantar eczema (HPE), palmoplantar psoriasis (PP), and mycosis fungoides palmaris et plantaris (MFPP), can be challenging to diagnose clinically and histopathologically. In this setting, cytokine biomarkers may be able to help provide diagnostic clarity. Therefore, we evaluated IL-17A, IFN-γ, and IL-13 expression in PP, HPE, and MFPP and compared their expression profiles with nonacral sites. We used biopsy specimens from the Yale Dermatopathology database, selecting cases of HPE (n = 12), PP (n = 8), MFPP (n = 8), normal acral skin (n = 9), nonacral eczema (n = 10), and nonacral psoriasis (n = 10) with classic clinical and histopathologic features. IL17A mRNA expression by RNA in situ hybridization differentiated PP (median score 63.1 [interquartile range 9.4-104.1]) from HPE (0.8 [0-6.0]; P = 0.003), MFPP (0.6 [0-2.6]; P = 0.003), and normal acral skin (0 [0-0]; P < 0.001). Unexpectedly, both PP and HPE showed co-expression of IFNG and IL13 mRNA. In contrast, nonacral psoriasis and eczema showed divergent patterns of IFNG and IL13 mRNA expression. Taken together, we show that IL17A mRNA expression may be a useful biomarker of PP, and we further show that acral dermatoses exhibit distinct immunology compared to nonacral sites, with implications for clinical management.

An update on therapeutic options for palmoplantar pustulosis: a narrative review and expert recommendations

INTRODUCTION

Palmoplantar pustulosis (PPP) is a chronic inflammatory skin disease belonging to the localized form of pustular psoriasis. It is characterized by sterile pustule formation in palms and soles and a recurrent disease course. Although we have many treatments for PPP, there is no authoritative guidance.

AREAS COVERED

A thorough search of PubMed was conducted to identify studies in PPP from 1973 onwards, with additional references to specific articles. Any treatment methods were outcomes of interest, including topical treatment, systemic treatment, biologics, other targeted treatments, phototherapy, and tonsillectomy.

EXPERT OPINION

Topical corticosteroids are suggested as first-line therapy. Oral acitretin has become the most applied systemic retinoid recommended in PPP without joint involvement. For patients with arthritis, immunosuppressants like cyclosporin A and methotrexate are more recommended. UVA1, NB-UVB, and 308-nm excimer laser are effective phototherapy options. The combinations of topical or systemic agents and phototherapy may enhance the efficacy, particularly in recalcitrant cases. Secukinumab, ustekinumab, and apremilast are the most investigated targeted therapies. However, heterogeneous reported outcomes in clinical trials provided low-to-moderate quality evidence of their efficacy. Future studies are required to address these evidence gaps. We suggest managing PPP based on the acute phase, maintenance phase, and comorbidities.

Interleukin-19 Levels Are Increased in Palmoplantar Pustulosis and Reduced following Apremilast Treatment

Palmoplantar pustulosis (PPP) is a chronic inflammatory skin disease characterised by neutrophilic granulocyte (neutrophil)-filled pustules on the palms and soles. The pathogenesis of PPP is poorly understood. This study conducted an identification of the immune mediators associated with PPP and an exploration of apremilast treatment effects on them. We screened for immune mediators elevated in blood taken from 68 patients with PPP versus control participants and included the most promising parameters in the protocol of phase the 2, multicentre study of apremilast (PDE4 inhibitor) in 21 patients with moderate-to-severe PPP (APLANTUS; EudraCT 2016-005122-11) for respective analysis of blood and skin samples of study patients. We investigated stimulated neutrophils and three-dimensional reconstituted epidermis cultures. Interleukin (IL)-19 was found to be the most upregulated immune mediator in the blood of PPP patients. IL-19 serum levels were independent of patients' age, gender, and BMI but were associated with strongly upregulated cutaneous IL-19 expression and correlated with the number of palmoplantar pustules. In patients participating in the APLANTUS study, apremilast reduced pustules more effectively than erythema and scaling. Moreover, this treatment significantly reduced IL-19 blood and skin levels. The reduction in IL-19 blood levels at week 4 correlated with the reduction in pustule counts at week 20 (end of treatment). IL-19 was expressed by neutrophils activated in vitro and induced CXCL6, a neutrophil-attracting chemokine, in epidermis models. This work demonstrates elevated IL-19 levels in the blood and skin of PPP patients and suggests a relevant role of this cytokine in the appearance of pustules in this disorder. It also suggests the suitability of IL-19 blood levels as a predictive biomarker for the treatment response of PPP patients, which should be validated in further studies.

Deep proteome profiling reveals signatures of age and sex differences in paw skin and sciatic nerve of naïve mice

The age and sex of studied animals profoundly impact experimental outcomes in biomedical research. However, most preclinical studies in mice use a wide-spanning age range from 4 to 20 weeks and do not assess male and female mice in parallel. This raises concerns regarding reproducibility and neglects potentially relevant age and sex differences, which are largely unknown at the molecular level in naïve mice. Here, we employed an optimized quantitative proteomics workflow in order to deeply profile mouse paw skin and sciatic nerves (SCN) - two tissues implicated in nociception and pain as well as diseases linked to inflammation, injury, and demyelination. Remarkably, we uncovered significant differences when comparing male and female mice at adolescent (4 weeks) and adult (14 weeks) age. Our analysis deciphered protein subsets and networks that were correlated with the age and/or sex of mice. Notably, among these were proteins/biological pathways with known (patho)physiological relevance, e.g., homeostasis and epidermal signaling in skin, and, in SCN, multiple myelin proteins and regulators of neuronal development. Extensive comparisons with available databases revealed that various proteins associated with distinct skin diseases and pain exhibited significant abundance changes in dependence on age and/or sex. Taken together, our study uncovers hitherto unknown sex and age differences at the level of proteins and protein networks. Overall, we provide a unique proteome resource that facilitates mechanistic insights into somatosensory and skin biology, and integrates age and sex as biological variables - a prerequisite for successful preclinical studies in mouse disease models.

Involvement of Molecular Mechanisms between T/B Cells and IL-23: From Palmoplantar Pustulosis to Autoimmune Diseases

Palmoplantar pustulosis (PPP) is a disease that causes recurrent blisters and aseptic pustules on the palms and soles. It has been suggested that both innate and acquired immunity are involved. In particular, based on the tonsils and basic experiments, it has been assumed that T and B cells are involved in its pathogenesis. In addition, the results of clinical trials have suggested that IL-23 is closely related to the pathogenesis. This review describes PPP and the genetic background, the factors involved in the onset and exacerbation of disease and its relation to the molecular mechanism. In addition, we describe the usefulness of biological therapy and its implications in relation to the importance in pathology, the pathogenesis of PPP, the importance of the role of the IL-23-Th17 axis and IL-36 in PPP. Furthermore, we describe an animal experimental model of PPP, the efficacy and mechanism of action of guselkumab, an anti-IL-23 antibody, the latest research, and finally the possibility for it to be effective for other autoimmune diseases.