Treatment-related restoration of Langerhans cell migration in psoriasis

Phospholipase activity of acyloxyacyl hydrolase induces IL-22-producing CD1a-autoreactive T cells in individuals with psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by Th17 responses. Recent evidence has identified Langerhans cells to have a key role in disease pathogenesis, with constitutive high expression of CD1a and capacity to present lipid antigens to T cells. Phospholipase A2 enzymes generate neolipid antigens for recognition by CD1a-reactive T cells; however, the broader enzymatic pathways of CD1a lipid ligand generation have not been thoroughly investigated. In this study, we used immunofluorescence of skin and ELISpot analyses of CD1a-reactive T cells to investigate the role of the lipase acyloxyacyl hydrolase (AOAH) in CD1a ligand generation with relevance to the pathogenesis of psoriasis. We found that the PLA2 activity of rAOAH leads to the activation of circulating CD1a auto-reactive T cells, leading to the production of IFN-γ and IL-22. Circulating AOAH-responsive CD1a-reactive T cells from patients with psoriasis showed elevated IL-22 production. We observed that AOAH is highly expressed in psoriatic lesions compared to healthy skin. Overall, these data present a role for AOAH in generating antigens that activate circulating lipid-specific CD1a-restricted T cells and, thus, contribute to psoriatic inflammation. These findings suggest that inhibition of PLA2 activity of AOAH may have therapeutic potential for individuals with psoriasis.

Immunological Memory of Psoriatic Lesions

The natural course of psoriasis is the appearance of new lesions in the place of previous ones, which disappeared after a successful therapy. Recent studies of psoriasis etiopathogenesis showed that after psoriatic plaques have disappeared, in healthy skin we can still find a trace of inflammation in the form of tissue resident memory cells (TRM). They are originally responsible for protection against viral and bacterial infections in non-lymphatic tissues. In psoriatic inflammation, they are characterized by heterogeneity depending on their origin. CD8+ T cells TRM are abundantly present in psoriatic epidermis, while CD4+ TRM preferentially populate the dermis. In psoriasis, epidermal CD8+ TRM cells express CLA, CCR6, CD103 and IL-23R antigen and produce IL-17A during ex vivo stimulation. However, CD4+ CD103+ TRM can also colonize the epidermis and produce IL-22 during stimulation. Besides T cells, Th22 and epidermal DCs proved that epidermal cells in healed skin were still present and functioning after several years of disease remission. It explains the clinical phenomenon of the tendency of psoriatic lesions to relapse in the same location and it allows to develop new therapeutic strategies in the future.

Discovery of super soft-drug modulators of sphingosine-1-phosphate receptor 1

The oral S1PR1 agonist ponesimod demonstrated substantial efficacy in a phase II clinical trial of psoriasis. Unfortunately, systemic side effects were observed, which included lymphopenia and transient bradycardia. We sought to develop a topical soft-drug S1PR1 agonist with an improved therapeutic index. By modifying ponesimod, we discovered an ester series of S1PR agonists. To increase metabolic instability in plasma we synthesised esters described as specific substrates for paraoxonase and butyrylcholinesterases, esterases present in human plasma.

T cell ignorance is bliss: T cells are not tolerized by Langerhans cells presenting human papillomavirus antigens in the absence of costimulation

Human papillomavirus type 16 (HPV16) infections are intra-epithelial, and thus, HPV16 is known to interact with Langerhans cells (LCs), the resident epithelial antigen-presenting cells (APCs). The current paradigm for APC-mediated induction of T cell anergy is through delivery of T cell receptor signals via peptides on MHC molecules (signal 1), but without costimulation (signal 2). We previously demonstrated that LCs exposed to HPV16 in vitro present HPV antigens to T cells without costimulation, but it remained uncertain if such T cells would remain ignorant, become anergic, or in the case of CD4+ T cells, differentiate into Tregs. Here we demonstrate that Tregs were not induced by LCs presenting only signal 1, and through a series of in vitro immunizations show that CD8⁺ T cells receiving signal 1+2 from LCs weeks after consistently receiving signal 1 are capable of robust effector functions. Importantly, this indicates that T cells are not tolerized but instead remain ignorant to HPV, and are activated given the proper signals.

Desired response to phototherapy vs photoaggravation in psoriasis: what makes the difference?

Psoriasis commonly responds beneficially to UV radiation from natural sunlight or artificial sources. Therapeutic mechanisms include the proapoptotic and immunomodulating effects of UV, affecting many cells and involving a variety of pro- and anti-inflammatory cytokines, downregulating the Th17/IL-23 response with simultaneous induction of regulatory immune cells. However, exposure to UV radiation in a subset of psoriasis patients leads to exacerbation of the disease. We herein shed light on the predisposing factors of photosensitive psoriasis, including genetics (such as HLA-Cw*0602 or CARD14), gender and coexisting photodermatoses such as polymorphic light eruption (PLE) in the context of potential molecular mechanisms behind therapeutic photoresponsiveness or photoaggravation. UV-induced damage/pathogen-associated molecular patterns, damage to self-coding RNA (signalling through Toll-like receptors), certain antimicrobial peptides and/or inflammasome activation may induce innate immunity, leading to psoriasis at the site of UV exposure when there is concomitant, predisposing resistance against UV-induced suppression of the adaptive immune response (like in PLE) that otherwise would act to reduce psoriasis.

Lower levels of interleukin-1β gene expression are associated with impaired Langerhans' cell migration in aged human skin

Langerhans' cells (LC) play pivotal roles in skin immune responses, linking innate and adaptive immunity. In aged skin there are fewer LC and migration is impaired compared with young skin. These changes may contribute to declining skin immunity in the elderly, including increased skin infections and skin cancer. Interleukin-1β (IL-1β) and tumour necrosis factor-α (TNF-α) are mandatory signals for LC migration and previous studies suggest that IL-1β signalling may be dysregulated in aged skin. Therefore, we sought to explore the mechanisms underlying these phenomena. In skin biopsies of photoprotected young (< 30 years) and aged (> 70 years) human skin ex vivo, we assessed the impact of trauma, and mandatory LC mobilizing signals on LC migration and gene expression. Biopsy-related trauma induced LC migration from young epidermis, whereas in aged skin, migration was greatly reduced. Interleukin-1β treatment restored LC migration in aged epidermis whereas TNF-α was without effect. In uncultured, aged skin IL-1β gene expression was lower compared with young skin; following culture, IL-1βmRNA remained lower in aged skin under control and TNF-α conditions but was elevated after culture with IL-1β. Interleukin-1 receptor type 2 (IL1R2) gene expression was significantly increased in aged, but not young skin, after cytokine treatment. Keratinocyte-derived factors secreted from young and aged primary cells did not restore or inhibit LC migration from aged and young epidermis, respectively. These data suggest that in aged skin, IL-1β signalling is diminished due to altered expression of IL1B and decoy receptor gene IL1R2.

First-in-human studies of seletalisib, an orally bioavailable small-molecule PI3Kδ inhibitor for the treatment of immune and inflammatory diseases

PURPOSE

PI3Ks are potential therapeutic targets in immune-inflammatory diseases. These studies aimed to investigate the safety, tolerability and PK profile of seletalisib, a selective inhibitor of PI3Kδ in humans.

METHODS

These phase I, randomised, double-blind, placebo-controlled, single-centre studies (NCT02303509, NCT02207595) evaluated single and multiple oral doses of seletalisib (5-90 mg QD and 30 mg BID) in healthy adults and subjects with mild-to-moderate psoriasis (Study-1). Pharmacodynamic effects on markers of inflammation were assessed via changes in ex vivo basophil degranulation and histological assessment of psoriatic skin biopsies.

RESULTS

Seletalisib was well tolerated at doses ≤15 mg (Study-1) and ≤45 mg QD (Study-2) for 14 days. No safety concerns or dose-limiting toxicities were identified (Study-1). Incidence of gastrointestinal-related AEs was not dose related but higher incidences of rash AEs were associated with higher-dose seletalisib (Study-2 rash AEs: 18 in 12 seletalisib-treated subjects versus 1 in 1 placebo-treated subject). Mean seletalisib plasma concentration-time profiles increased with increasing doses after single and multiple dosing, with no major deviations from dose-proportionality. There was no unexpected accumulation or loss of exposure after multiple dosing (time-independent pharmacokinetic profile). Apparent t 1/2 values were supportive of once-daily dosing (geometric mean t1/2: Study-1, 17.7-21.1 h; Study-2, 18.1-22.4 h). No clinically significant food effect was observed (Study-1). Pharmacodynamic findings demonstrated ex vivo inhibition of basophil degranulation, improvements in histological assessment of skin biopsies and other markers of psoriatic biology and preliminary evidence of target engagement in psoriatic skin tissue.

CONCLUSIONS

Seletalisib safety, tolerability and pharmacokinetic/pharmacodynamic profiles support its continued clinical development in immune-inflammatory diseases.

Langerhans cell markers CD1a and CD207 are the most rapidly responding genes in lesional psoriatic skin following adalimumab treatment

TNFα-, IL-23- and IL-17-targeting drugs are highly effective in the treatment of psoriasis. However, the precise molecular mechanism remains unknown. In psoriatic skin, the presence of Langerhans cells (LCs) is reduced, but the role of LC is poorly understood. The purpose of this study was to investigate the impact of TNFα and IL-23/IL-17 on the presence of LC in the skin during treatment. Therefore, psoriatic skin was investigated before and after 4 days of adalimumab or ustekinumab treatment. Furthermore, TNFα and IL-17A stimulation was investigated in an ex vivo model of epidermis and dermis from healthy normal skin kept in cultures at an air-liquid interphase for 4 days. In a gene array analysis, we found that the two LC markers, CD1a and CD207, were among the most up- or downregulated genes in psoriatic skin after anti-TNFα therapy. Validation showed that both mRNA expression and protein level followed the same pattern and became significantly upregulated after 4 days of treatment. No changes were seen after ustekinumab treatment. In the ex vivo skin model, a decrease in the CD1a level was seen after TNFα stimulation and it was caused by LC migration from epidermis. No response in LC migration was seen after IL-17A stimulation. Taken together, we demonstrated that changes in the LC level in epidermis precede the histological and clinical changes during adalimumab treatment in psoriatic skin. Furthermore, TNFα plays a prominent role in orchestrating LC migration in the skin. This seems not to be the true for the IL-23/IL-17A pathway.

Psoriatic T cells recognize neolipid antigens generated by mast cell phospholipase delivered by exosomes and presented by CD1a

Psoriasis is a chronic inflammatory skin disease associated with a T helper 17 response. Yet, it has proved challenging to identify relevant peptide-based T cell antigens. Antigen-presenting Langerhans cells show a differential migration phenotype in psoriatic lesions and express constitutively high levels of CD1a, which presents lipid antigens to T cells. In addition, phospholipase A2 (PLA2) is highly expressed in psoriatic lesions and is known to generate neolipid skin antigens for recognition by CD1a-reactive T cells. In this study, we observed expression of a cytoplasmic PLA2 (PLA2G4D) in psoriatic mast cells but, unexpectedly, also found PLA2G4D activity to be extracellular. This was explained by IFN-α-induced mast cell release of exosomes, which transferred cytoplasmic PLA2 activity to neighboring CD1a-expressing cells. This led to the generation of neolipid antigens and subsequent recognition by lipid-specific CD1a-reactive T cells inducing production of IL-22 and IL-17A. Circulating and skin-derived T cells from patients with psoriasis showed elevated PLA2G4D responsiveness compared with healthy controls. Overall, these data present an alternative model of psoriasis pathogenesis in which lipid-specific CD1a-reactive T cells contribute to psoriatic inflammation. The findings suggest that PLA2 inhibition or CD1a blockade may have therapeutic potential for psoriasis.

Update on psoriasis immunopathogenesis and targeted immunotherapy

Over recent years, significant progress has been made in characterisation of the underlying pathogenic mechanisms in psoriasis, a common cutaneous disease that is associated with major systemic co-morbidity and reduced life expectancy. Basic science discoveries have informed the design of novel therapeutic approaches, many of which are now under evaluation in late-stage clinical trials. Here we describe the complex interplay between immune cell types and cytokine networks that acts within self-perpetuating feedback loops to drive cutaneous inflammation in psoriasis. Genetic studies have been pivotal in the construction of the disease model and more recently have uncovered a distinct aetiology for rare, pustular variants of psoriasis. The translation of mechanistic insights into potential advancements in clinical care will also be described, including several treatments that target the interleukin-23 (IL-23)/T17 immune axis.

The immunopathogenesis of psoriasis

Psoriasis vulgaris is a chronic inflammatory skin disease that results from the complex interplay between keratinocytes, dendritic cells, and T cells. Keratinocytes trigger innate and adaptive immune responses. Dermal myeloid dendritic cells regulate T cell activation and production of cytokines and chemokines that amplify inflammation. Most of the psoriatic T cells discretely produce interferon-γ, interleukin (IL)-17, and IL-22. The initiation phase of psoriasis involves Toll-like receptors, antimicrobial peptide LL37, and plasmacytoid dendritic cells. Keratinocytes are the main cutaneous cell type expressing IL-17 receptors and hence the immune circuit is amplified by keratinocytes upregulating mRNAs for a range of inflammatory products.

Guttate psoriasis is associated with an intermediate phenotype of impaired Langerhans cell migration

BACKGROUND

An episode of guttate psoriasis can be an isolated event, can recur as guttate episodes, or develop into chronic plaque psoriasis (CPP). A previous study revealed that early-onset (before age 40 years) CPP is associated with inhibition of epidermal Langerhans cell (LC) migration.

OBJECTIVES

To determine whether guttate psoriasis is also associated with abnormal LC mobilization.

METHODS

Three groups of patients were recruited: current guttate episode (n = 5); guttate psoriasis progressed to CPP (n = 6); and resolved guttate psoriasis (n = 2). Biopsies were taken from uninvolved skin and LC migration was measured ex vivo using an epidermal explant model.

RESULTS

Patients with a current episode of guttate psoriasis displayed epidermal LC migration, although the extent was significantly lower than in skin from healthy controls (P < 0·05). In contrast, in those patients in whom guttate psoriasis developed into CPP there was no mobilization of LC. Finally, in patients in whom guttate psoriasis had resolved, LC migration was normal.

CONCLUSIONS

We have shown that guttate psoriasis is associated with an abnormality of LC mobilization, but a less marked inhibition compared with that seen in CPP. In resolved guttate psoriasis LC function returns to normal. These data provide further evidence that the pathogenesis of psoriasis is characterized by significant changes in epidermal LC function.