Type-2 immunity associated with type-1 related skin inflammatory diseases: friend or foe?

Chronic inflammatory skin diseases are multifactorial diseases that combine genetic predisposition, environmental triggers, and metabolic disturbances associated with abnormal immune responses. From an immunological perspective, the better understanding of their physiopathology has demonstrated a large complex network of immune cell subsets and related cytokines that interact with both epidermal and dermal cells. For example, in type-1-associated diseases such as alopecia areata, vitiligo, and localized scleroderma, recent evidence suggests the presence of a type-2 inflammation that is well known in atopic dermatitis. Whether this type-2 immune response has a protective or detrimental impact on the development and chronicity of these diseases remains to be fully elucidated, highlighting the need to better understand its involvement for the management of patients. This mini-review explores recent insights regarding the potential role of type-2-related immunity in alopecia areata, vitiligo, and localized scleroderma.

Evaluation of Facial Vitiligo Severity with a Mixed Clinical and Artificial Intelligence Approach.

Vitiligo is the most common depigmenting skin disorder. Given the ongoing development of new targeted therapies, it has become important to evaluate adequately the surface area involved. Assessment of vitiligo scores can be time consuming, with variations between investigators. Therefore, the aim of this study was to build an artificial intelligence system capable of assessing facial vitiligo severity. One hundred pictures of faces of patients with vitiligo were used to train and validate the artificial intelligence model. Sixty-nine additional pictures of facial vitiligo were then used as a final dataset. Three expert physicians scored the facial vitiligo on the same 69 pictures. Inter and intrarater performances were evaluated by comparing the scores between raters and artificial intelligence. Algorithm assessment achieved an accuracy of 93%. Overall, the scores reached a good agreement between vitiligo raters and the artificial intelligence model. Results demonstrate the potential of the model. It provides an objective evaluation of facial vitiligo and could become a complementary/alternative tool to human assessment in clinical practice and/or clinical research.

Resident memory T cells in nonlesional skin and healed lesions of patients with chronic inflammatory diseases: Appearances can be deceptive.

Tissue-resident memory T (TRM) cells serve as a first line of defense in peripheral tissues to protect the organism against foreign pathogens. However, autoreactive TRM cells are increasingly implicated in autoimmunity, as evidenced in chronic autoimmune and inflammatory skin conditions. This highlights the need to characterize their phenotype and understand their role for the purpose of targeting them specifically without affecting local immunity. To date, the investigation of TRM cells in human skin diseases has focused mainly on lesional tissues of patients. Accumulating evidence suggests that self-reactive TRM cells are still present in clinically healed lesions of patients and play a role in disease flares, but TRM cells also populate skin that is apparently normal. This review discusses the ontogeny of TRM cells in the skin as well as recent insights regarding the presence of self-reactive TRM cells in both clinically healed skin and nonlesional skin of patients with autoimmune and inflammatory skin conditions, with a particular focus on psoriasis, atopic dermatitis, and vitiligo.

Impact of house dust mite in vitiligo skin: environmental contribution to increased cutaneous immunity and melanocyte detachment.

BACKGROUND: Vitiligo is an autoimmune skin disorder characterized by loss of melanocytes. Protease-mediated disruption of junctions between keratinocytes and/or keratinocyte intrinsic dysfunction may directly contribute to melanocyte loss. House dust mite (HDM), an environmental allergen with potent protease activity, contributes to respiratory and gut disease but also to atopic dermatitis and rosacea. OBJECTIVES: To verify if HDM can contribute to melanocyte detachment in vitiligo and if so, by which mechanism(s). METHODS: Using primary human keratinocytes, human skin biopsies from healthy donors and patients with vitiligo, and 3D reconstructed human epidermis, we studied the effect of HDM on cutaneous immunity, tight and adherent junction expression and melanocyte detachment. RESULTS: HDM increased keratinocyte production of vitiligo-associated cytokines and chemokines and increased expression of toll-like receptor (TLR)-4. This was associated with increased in situ matrix-metalloproteinase (MMP)-9 activity, reduced cutaneous expression of adherent protein E-cadherin, increased soluble E-cadherin in culture supernatant and significantly increased number of suprabasal melanocytes in the skin. This effect was dose-dependent and driven by cysteine protease Der p1 and MMP-9. Selective MMP-9 inhibitor, Ab142180, restored E-cadherin expression and inhibited HDM-induced melanocyte detachment. Keratinocytes from patients with vitiligo were more sensitive to HDM-induced changes than healthy keratinocytes. All results were confirmed in a 3D model of healthy skin and in human skin biopsies. CONCLUSIONS: Our results highlight that environmental mite may act as an external source of pathogen-associated molecular pattern molecules in vitiligo and topical MMP-9 inhibitors may be useful therapeutic targets. Whether HDM contributes to the onset of flares in vitiligo remains to be tested in carefully controlled trials.

Vitiligo: Current Therapies and Future Treatments.

The current management of vitiligo remains challenging; however, different strategies can be proposed to patients with a good efficacy in many cases. First, it is important to identify patients in the active phase of the disease because treatment should start as soon as possible to halt its progression. For patients with a stable disease, the treatment strategy is now well-stratified and is based on a combination of phototherapy (natural or in a cabin) and topical immunomodulatory agents. Surgical treatments are useful for localized and stable vitiligo, as well as for segmental vitiligo. Depigmentation remains indicated in very extensive forms. The recent approval of topical ruxolitinib cream in both the US and Europe brings new approaches for the management of vitiligo and paves the way for the development of new topical or oral targeted drugs.

Aetiopathogenesis of Vitiligo.

Vitiligo is a chronic auto-immune disease characterized by skin depigmentation due to the loss of melanocytes. The better understanding of the disease mechanisms is currently undergoing a significant dynamism, opening a new era in therapeutic development. The pathophysiology of vitiligo has attracted the attention of researchers for years and many advances have been made in clarifying the crosstalk between the cellular players involved in the development of vitiligo lesions. The understanding of the complex interactions between epidermal cells (i.e. melanocytes and keratinocytes), dermal fibroblasts, and immune cells, led to a better characterization of the signals leading to the loss of melanocytes. Recent advances highlighted the role resident T memory cells in the development and recurrence of lesions. This narrative review aims to give an overview of the mechanisms leading to melanocyte disappearance in vitiligo, with a focus on the intercellular interaction network involved in the activation of the local skin immune response.

Cytokine-Mediated Crosstalk Between Keratinocytes and T Cells in Atopic Dermatitis.

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction, dysregulated immune response, and dysbiosis with increased Staphylococcus aureus colonization. Infiltration of various T helper cell subsets into lesional skin and subsequent cytokine release are a hallmark of AD. Release of cytokines by both T cells and keratinocytes plays a key role in skin inflammation and drives many AD features. This review aims to discuss cytokine-mediated crosstalk between T cells and keratinocytes in AD pathogenesis and the potential impact of virulence factors produced by Staphylococcus aureus on these interactions.

Vitiligo Skin T Cells Are Prone to Produce Type 1 and Type 2 Cytokines to Induce Melanocyte Dysfunction and Epidermal Inflammatory Response Through Jak Signaling.

Vitiligo is a T cell-mediated inflammatory skin disorder characterized by the loss of epidermal melanocytes. However, the contribution of melanocytes to the physiopathology of the disease in response to the T-cell microenvironment remains unclear. Here, using NanoString technology and multiplex ELISA, we show that active vitiligo perilesional skin is characterized by prominent type 1 and 2 associated immune responses. The vitiligo skin T-cell secretome downregulated melanocyte function and adhesion while increasing melanocyte mitochondrial metabolism and expression of inflammatory cytokines and chemokines by epidermal cells. The Jak1/2 inhibitor ruxolitinib strongly inhibited such effects on epidermal cells. Our data highlight that vitiligo is more complex than previously thought, with prominent combined activities of both T helper type 1- and T helper type 2-related cytokines inducing inflammatory responses of epidermal cells. Melanocytes do not appear only to be a target of T cells in vitiligo but could actively contribute to perpetuate inflammation. Jak inhibitors could prevent the impact of T cells on epidermal cells and pigmentation, highlighting their potential clinical benefit in vitiligo.

Analysis of tumor response and clinical factors associated with vitiligo in patients receiving anti-programmed cell death-1 therapies for melanoma: A cross-sectional study.

BACKGROUND: Clinical factors associated with vitiligo in patients receiving anti-programmed cell death-1 (PD-1) remain unknown. OBJECTIVE: To better characterize the occurrence of vitiligo in patients receiving anti-PD-1. METHODS: The present single-center ambispective cohort study included patients with melanoma treated with anti-PD-1. Progression-free survival, overall survival, and objective tumor response were compared between patients with and those without vitiligo using Kaplan-Meier curves and the log-rank test. Demographic and clinical factors associated with vitiligo were evaluated using multivariate logistic regression. RESULTS: Of the 457 patients included in the study, vitiligo developed in 85 patients. The clinical presentation of vitiligo consisted of the presence of ovalar and multiple flecked white macules, mainly located on chronic sun-exposed areas. The presence of vitiligo was associated with a significant improvement in overall survival and progression-free survival (P < .001). A Cox proportional hazards model estimation demonstrated markedly improved survival in patients with vitiligo compared with those without vitiligo (aHR [overall survival], 0.20; 95% CI, 0.12-0.33; P < .001; and aHR [progression-free survival], 0.33; 95% CI, 0.23-0.47; P < .001). In the multivariate logistic regression analyses, men showed an independent increased risk of the development of vitiligo (odds ratio, 1.66). In contrast, the presence of pulmonary metastases was found to be an independent factor associated with a reduced risk of the development of vitiligo (odds ratio, 0.50). LIMITATIONS: Single-center ambispective cohort. CONCLUSION: Vitiligo in patients receiving anti-PD-1 for advanced melanoma is associated with a better outcome. A gender effect associated with the development of vitiligo will need further investigation.

Targeting Innate Immunity to Combat Cutaneous Stress: The Vitiligo Perspective.

Multiple factors are involved in the process leading to melanocyte loss in vitiligo including environmental triggers, genetic polymorphisms, metabolic alterations, and autoimmunity. This review aims to highlight current knowledge on how danger signals released by stressed epidermal cells in a predisposed patient can trigger the innate immune system and initiate a cascade of events leading to an autoreactive immune response, ultimately contributing to melanocyte disappearance in vitiligo. We will explore the genetic data available, the specific role of damage-associated-molecular patterns, and pattern-recognition receptors, as well as the cellular players involved in the innate immune response. Finally, the relevance of therapeutic strategies targeting this pathway to improve this inflammatory and autoimmune condition is also discussed.

An update on Vitiligo pathogenesis.

Vitiligo, the most common depigmenting disorder of the skin, is undergoing a period of intense advances in both disease understanding and therapeutic possibilities leading the way to the beginning of a new era for the disorder. Its pathophysiology has gathered the attention of researchers for years, and many advances have been made in the clarification of the interaction between different factors that result in depigmented macule formation. The complex interplay between non-immunological and immunological factors in vitiligo is key for the development of the disease, and the participation of cells other than melanocytes, such as keratinocytes, fibroblasts, natural killer cells, and innate lymphoid cells, has been shown. Recent advances have also brought to the understanding of the complex part played by a specific subtype of T cells: T-resident memory cells. This review analyzes some of the most recent insights in vitiligo pathogenesis underlining the interactions between different cell types, which are the basis for the therapeutic approaches under development.

Vitiligo, From Physiopathology to Emerging Treatments: A Review.

Vitiligo is a chronic inflammatory skin disease leading to the loss of epidermal melanocytes. To date, treatment options for vitiligo patients are limited, lack sustained efficacy, and are mainly based on off-label use of immunosuppressive agents, such as systemic or topical steroids or topical calcineurin inhibitors, in association with the use of ultraviolet light. However, recent insights into the understanding of the immune pathogenesis of the disease have led to the identification of several therapeutic targets and the development of targeted therapies that are now being tested in clinical trials. In this review, based on the physiopathology of the disease, we summarize emerging targets that could be developed for the treatment of vitiligo and discuss recent and ongoing developments of drugs for the management of the disease.

Type-1 cytokines regulate MMP-9 production and E-cadherin disruption to promote melanocyte loss in vitiligo.

Loss of melanocytes is the pathological hallmark of vitiligo, a chronic inflammatory skin depigmenting disorder induced by exaggerated immune response, including autoreactive CD8 T cells producing high levels of type 1 cytokines. However, the interplay between this inflammatory response and melanocyte disappearance remains to be fully characterized. Here, we demonstrate that vitiligo skin contains a significant proportion of suprabasal melanocytes, associated with disruption of E-cadherin expression, a major protein involved in melanocyte adhesion. This phenomenon is also observed in lesional psoriatic skin. Importantly, apoptotic melanocytes were mainly observed once cells were detached from the basal layer of the epidermis, suggesting that additional mechanism(s) could be involved in melanocyte loss. The type 1 cytokines IFN-γ and TNF-α induce melanocyte detachment through E-cadherin disruption and the release of its soluble form, partly due to MMP-9. The levels of MMP-9 are increased in the skin and sera of patients with vitiligo, and MMP-9 is produced by keratinocytes in response to IFN-γ and TNF-α. Inhibition of MMP-9 or the JAK/STAT signaling pathway prevents melanocyte detachment in vitro and in vivo. Therefore, stabilization of melanocytes in the basal layer of the epidermis by preventing E-cadherin disruption appears promising for the prevention of depigmentation occurring in vitiligo and during chronic skin inflammation.

NKG2D Defines a Subset of Skin Effector Memory CD8 T Cells with Proinflammatory Functions in Vitiligo.

Vitiligo is an autoimmune disease that results from the loss of melanocytes, associated with skin infiltration of CD8+ effector memory T cells with a Tc1 skewed immune response. NKG2D is an activating receptor found on immune cells, in particular natural killer and activated CD8+ T cells, that are able to produce a high amount of IFN-γ. Here we found that NKG2D expression was increased in vitiligo skin CD8+ effector memory T cells and was promoted by IL-15. Phenotypic and functional analyses showed that NKG2D+ CD8+ skin effector memory T cells displayed an activated phenotype and produced elevated levels of both IFN-γ and tumor necrosis factor-α. Additional experiments revealed that vitiligo skin dendritic cells expressed the NKG2D ligands MICA-MICB, and in vitro experiments showed that these ligands could be induced on dendritic cells by IFN-α. Cultures of IFN-α-stimulated dendritic cells with skin NKG2D+ CD8+ T cells potentiated the production of type 1 cytokines, which was next inhibited by blocking the NKG2D/MICA-MICB interaction. These data show that NKG2D is a potential marker of pathogenic skin CD8+ effector memory T cells during vitiligo. Therefore, targeting NKG2D could be an attractive strategy in vitiligo, a disease for which there is a strong need of innovative treatments.

Disrupting the IL-36 and IL-23/IL-17 loop underlies the efficacy of calcipotriol and corticosteroid therapy for psoriasis.

Psoriasis is one of the most common skin inflammatory diseases worldwide. The vitamin D3 analog calcipotriol has been used alone or in combination with corticosteroids in treating plaque psoriasis, but how it suppresses psoriatic inflammation has not been fully understood. Using an experimental mouse psoriasis model, we show that topical calcipotriol inhibited the pivotal IL-23/IL-17 axis and neutrophil infiltration in psoriatic skin, and interestingly, such effects were mediated through the vitamin D receptor (VDR) in keratinocytes (KCs). We further reveal that IL-36α and IL-36γ, which have recently emerged as key players in psoriasis pathogenesis, were effectively repressed by calcipotriol via direct VDR signaling in mouse KCs. Accordingly, calcipotriol treatment suppressed IL-36α/γ expression in lesional skin from patients with plaque psoriasis, which was accompanied by a reduced IL-23/IL-17 expression. In contrast, dexamethasone indirectly reduced IL-36α/γ expression in mouse psoriatic skin through immune cells. Furthermore, we demonstrate that calcipotriol and dexamethasone, in combination, synergistically suppressed the expression of IL-36α/γ, IL-23, and IL-17 in the established mouse psoriasis. Our findings indicate that the combination of calcipotriol and corticosteroid efficiently disrupts the IL-36 and IL-23/IL-17 positive feedback loop, thus revealing a mechanism underlying the superior efficacy of calcipotriol and corticosteroid combination therapy for psoriasis.

Vitiligo as a skin memory disease: The need for early intervention with immunomodulating agents and a maintenance therapy to target resident memory T cells.

The understanding of the immune mechanisms of vitiligo has profoundly improved over the past years. The recent discovery of a new population of antigen-experienced memory T cells called resident memory T cells (TRM ) has changed the concept of immune surveillance in peripheral tissue as skin, and the presence of melanocyte-specific TRM is clearly demonstrated in vitiligo, a disease that could be now seen such as a memory skin disease. This review summarizes the recent knowledge on skin TRM and their role in vitiligo. Future management or therapies for this disease will have the goal to block their migration/differentiation, to dampen their activation and/or their accumulation in the vitiligo skin to prevent flare-up or to promote repigmentation.