Spatial characterization of interface dermatitis in cutaneous lupus reveals novel chemokine ligand-receptor pairs that drive disease

Chemokines play critical roles in the recruitment and activation of immune cells in both homeostatic and pathologic conditions. Here, we examined chemokine ligand-receptor pairs to better understand the immunopathogenesis of cutaneous lupus erythematosus (CLE), a complex autoimmune connective tissue disorder. We used suction blister biopsies to measure cellular infiltrates with spectral flow cytometry in the interface dermatitis reaction, as well as 184 protein analytes in interstitial skin fluid using Olink targeted proteomics. Flow and Olink data concordantly demonstrated significant increases in T cells and antigen presenting cells (APCs). We also performed spatial transcriptomics and spatial proteomics of punch biopsies using digital spatial profiling (DSP) technology on CLE skin and healthy margin controls to examine discreet locations within the tissue. Spatial and Olink data confirmed elevation of interferon (IFN) and IFN-inducible CXCR3 chemokine ligands. Comparing involved versus uninvolved keratinocytes in CLE samples revealed upregulation of essential inflammatory response genes in areas near interface dermatitis, including AIM2. Our Olink data confirmed upregulation of Caspase 8, IL-18 which is the final product of AIM2 activation, and induced chemokines including CCL8 and CXCL6 in CLE lesional samples. Chemotaxis assays using PBMCs from healthy and CLE donors revealed that T cells are equally poised to respond to CXCR3 ligands, whereas CD14+CD16+ APC populations are more sensitive to CXCL6 via CXCR1 and CD14+ are more sensitive to CCL8 via CCR2. Taken together, our data map a pathway from keratinocyte injury to lymphocyte recruitment in CLE via AIM2-Casp8-IL-18-CXCL6/CXCR1 and CCL8/CCR2, and IFNG/IFNL1-CXCL9/CXCL11-CXCR3.

Lesional CD8+ T-Cell Number Predicts Surgical Outcomes of Melanocyte-Keratinocyte Transplantation Surgery for Vitiligo

The melanocyte-keratinocyte transplantation procedure (MKTP) treats stable and recalcitrant vitiligo. Despite careful selection of candidates based on clinical stability, the success of the procedure is unpredictable. The aim of our study was to define the immunological profile of stable vitiligo lesions undergoing MKTP and correlate them with clinical outcomes. We included 20 MKTP candidates with vitiligo and a patient with piebaldism as a control. Prior to MKTP, T-cell subsets and chemokines in the recipient skin were measured by flow cytometry and ELISA. During MKTP, melanocytes in the donor skin were quantified by flow cytometry. After MKTP, patients were followed for 12 months and repigmentation was assessed clinically and by ImageJ analysis of clinical photographs. Baseline immunologic biomarkers, duration of clinical stability, and transplanted melanocyte number were correlated to postsurgical repigmentation scores. CD8+ T cells were elevated in 43% of the clinically stable vitiligo lesions. CD8+ T-cell number negatively correlated with postsurgical repigmentation scores (r = -0.635, P = 0.002). Duration of clinical stability, skin chemokines, and transplanted melanocyte number did not influence postsurgical repigmentation. This study demonstrates that CD8+ T-cell number correlates negatively with success of postsurgical repigmentation and can be a biomarker to identify ideal surgical candidates.

Regulatory T Cells Require CCR6 for Skin Migration and Local Suppression of Vitiligo

Vitiligo is an autoimmune skin disease caused by melanocyte-targeting autoreactive CD8+ T cells. Regulatory T cells (Tregs) have been implicated in restraining vitiligo severity in both mouse models and human patients; however, whether they must be present in the skin for their suppressive function is still unclear. We observed uneven distribution of Tregs within different anatomical locations of mouse skin, which correlated with reduced depigmentation after vitiligo induction. We specifically depleted Tregs in our mouse model of vitiligo and observed increased disease. Next, we found that Tregs contact CD8+ T effector cells in vitiligo lesional skin and that Treg recruitment to the skin inversely correlated with disease severity, suggesting a critical role for Treg suppression within the skin. When we investigated the signals facilitating Treg migration to the skin, we found that although CXCR3 was dispensable for Treg migration and function in vitiligo, Tregs lacking CCR6 exhibited a reduced capacity to migrate to the skin and suppress depigmentation, despite normal systemic numbers in the skin-draining lymph nodes. Our observations highlight a key role for cutaneous Tregs in disease suppression during vitiligo and identify CCR6 as a chemokine receptor that contributes to Treg migration to the skin.

scRNA-seq of human vitiligo reveals complex networks of subclinical immune activation and a role for CCR5 in Treg function

[Figure: see text].

Antibody blockade of IL-15 signaling has the potential to durably reverse vitiligo

Vitiligo is an autoimmune disease of the skin mediated by CD8⁺ T cells that kill melanocytes and create white spots. Skin lesions in vitiligo frequently return after discontinuing conventional treatments, supporting the hypothesis that autoimmune memory is formed at these locations. We found that lesional T cells in mice and humans with vitiligo display a resident memory (T_RM) phenotype, similar to those that provide rapid, localized protection against reinfection from skin and mucosal-tropic viruses. Interleukin-15 (IL-15)-deficient mice reportedly have impaired T_RM formation, and IL-15 promotes T_RM function ex vivo. We found that both human and mouse T_RM express the CD122 subunit of the IL-15 receptor and that keratinocytes up-regulate CD215, the subunit required to display the cytokine on their surface to promote activation of T cells. Targeting IL-15 signaling with an anti-CD122 antibody reverses disease in mice with established vitiligo. Short-term treatment with anti-CD122 inhibits T_RM production of interferon-γ (IFNγ), and long-term treatment depletes T_RM from skin lesions. Short-term treatment with anti-CD122 can provide durable repigmentation when administered either systemically or locally in the skin. On the basis of these data, we propose that targeting CD122 may be a highly effective and even durable treatment strategy for vitiligo and other tissue-specific autoimmune diseases involving T_RM.

T-cell positioning by chemokines in autoimmune skin diseases

Autoimmune skin diseases are complex processes in which autoreactive cells must navigate through the skin tissue to find their targets. Regulatory T cells in the skin help to mitigate autoimmune inflammation and may in fact be responsible for the patchy nature of these conditions. In this review, we will discuss chemokines that are important for global recruitment of T cell populations to the skin during disease, as well as signals that fine-tune their localization and function. We will describe prototypical disease responses and chemokine families that mediate these responses. Lastly, we will include an overview of chemokine-targeting drugs that have been tested as new treatment strategies for autoimmune skin diseases.

Resident Memory and Recirculating Memory T Cells Cooperate to Maintain Disease in a Mouse Model of Vitiligo

Tissue resident memory T cells (Trm) form in the skin in vitiligo and persist to maintain disease, as white spots often recur rapidly after discontinuing therapy. We and others have recently described melanocyte-specific autoreactive Trm in vitiligo lesions. Here, we characterize the functional relationship between Trm and recirculating memory T cells (Tcm) in our vitiligo mouse model. We found that both Trm and Tcm sensed autoantigen in the skin long after stabilization of disease, producing IFN-γ, CXCL9, and CXCL10. Blockade of Tcm recruitment to the skin with FTY720 or depletion of Tcm with low-dose Thy1.1 antibody reversed disease, indicating that Trm cooperate with Tcm to maintain disease. Taken together, our data provide characterization of skin memory T cells in vitiligo, demonstrate that Trm and Tcm work together during disease, and indicate that targeting their survival or function may provide novel, durable treatment options for patients.

Validation and discovery of mechanisms that promote vitiligo pathogenesis using single-cell RNA-sequencing of cells isolated from skin interstitial fluid

Vitiligo is an autoimmune disease in which CD8+ T cells destroy melanocytes, leading to patchy, depigmented lesions of the skin. To investigate possible immune processes in the skin that could explain the patchy appearance of vitiligo inflammation, we performed single-cell RNA-sequencing on cells isolated from the skin using a modified suction blistering technique. We compared the transcriptomes of cells isolated from lesional and non-lesional skin of six vitiligo subjects with active, spreading lesions as well as normal skin from six healthy subjects. Using differential gene analysis to cluster more than 18,000 cell transcriptomes in an unbiased fashion, we were able to identify the cellular components of the skin: melanocytes, keratinocytes, and Langerhans cells, as well as subgroups of immune cells. Consistent with previous findings by our group and others, this approach revealed an IFNγ signature in vitiligo lesions. This method identified 87 ligand-receptor pairs that may promote vitiligo pathogenesis, including CXCR6 and CXCL16 that were just recently implicated in vitiligo. The data set also revealed that Langerhans cells actively express many genes which have known risk alleles for vitiligo, highlighting a potential pivotal role in the development of vitiligo. Overall, single-cell RNA-sequencing of the skin infiltrate in vitiligo lesions is providing robust data that confirms many previous findings, but adds additional layers of nuance missed by conventional studies of bulk material. This level of resolution will yield powerful insight into the identification of novel drug targets in previously unknown signaling pathways in vitiligo and other diseases of the skin.

Autoreactive T cells use IFNγ and Fas Ligand to clear melanocytes in vitiligo

Vitiligo is an autoimmune disease of the skin in which melanocytes are selectively destroyed, leading to a disfiguring depigmentation. Studies by our group and others demonstrated that IFNγ-induced chemokines drive pathogenesis through the recruitment of CD8+ T cells that kill melanocytes. We examined potential mechanisms of melanocyte killing by T cells in our mouse model by performing adoptive transfer of autoreactive cells lacking IFNγ, perforin, or Fas ligand. We found that disease severity and T cell accumulation in the skin was reduced in mice that received either IFNγ KO or Fas ligand KO melanocyte-specific T cells; however, perforin was not required. We partially rescued the disease phenotype by performing 50:50 co-injections of effector molecule KO T cells with WT T cells, however KO T cells outcompeted WT cells in recruitment to the epidermis, suggesting IFNγ and Fas Ligand are needed in situ to cause disease. To determine if IFNγ signaling was directly cytotoxic to melanocytes, we used a Cre-Lox system in which the IFNγR was specifically deleted in melanocytes. Floxed/Floxed Cre+ littermates were not protected from disease, suggesting IFNγ signaling in melanocytes is dispensable for melanocyte clearance. In summary, IFNγ has pleiotropic effects in vitiligo, required both for T cell recruitment and functional killing of melanocytes. This further supports targeting IFNγ signaling for the treatment of vitiligo. In addition to IFNγ, Fas ligand is a new potential target for therapy that warrants further investigation.

Repigmentation in vitiligo using the Janus kinase inhibitor tofacitinib may require concomitant light exposure

BACKGROUND

Vitiligo is an autoimmune disease in which cutaneous depigmentation occurs. Existing therapies are often inadequate. Prior reports have shown benefit of the Janus kinase (JAK) inhibitors.

OBJECTIVE

To evaluate the efficacy of the JAK 1/3 inhibitor tofacitinib in the treatment of vitiligo.

METHOD

This is a retrospective case series of 10 consecutive patients with vitiligo treated with tofacitinib. Severity of disease was assessed by body surface area of depigmentation.

RESULTS

Ten consecutive patients were treated with tofacitinib. Five patients achieved some repigmentation at sites of either sunlight exposure or low-dose narrowband ultraviolet B phototherapy. Suction blister sampling revealed that the autoimmune response was inhibited during treatment in both responding and nonresponding lesions, suggesting that light rather than immunosuppression was primarily required for melanocyte regeneration.

LIMITATIONS

Limitations include the small size of the study population, retrospective nature of the study, and lack of a control group.

CONCLUSION

Treatment of vitiligo with JAK inhibitors appears to require light exposure. In contrast to treatment with phototherapy alone, repigmentation during treatment with JAK inhibitors may require only low-level light. Maintenance of repigmentation may be achieved with JAK inhibitor monotherapy. These results support a model wherein JAK inhibitors suppress T cell mediators of vitiligo and light exposure is necessary for stimulation of melanocyte regeneration.

T regulatory cells follow CXCL10 to suppress T effector cells through a contact-dependent mechanism in the skin during vitiligo

Vitiligo is an autoimmune disease of the skin driven by CD8+ T effector cells (Teffs) that infiltrate the epidermis to kill melanocytes, resulting in visible white spots. To investigate the role of T regulatory cells (Tregs) during vitiligo we depleted Tregs in our mouse model with CD4 depleting antibody or diphtheria toxin-treated Foxp3-DTR mice and saw increased disease (p<0.0001 and p<0.02, respectively) and increased Teff skin infiltration, suggesting that Tregs suppress Teffs during vitiligo. We investigated the kinetics of Treg and Teff migration to the skin in our mouse model and saw that both cell types accumulate in a similar pattern, suggesting that Tregs may follow the same signals that recruit Teffs to the skin. Previous studies revealed that CXCL10, which is upregulated in human patients as well as in our mouse model of disease, is primarily expressed in the epidermis and necessary for the migration of CXCR3+Teffs to the epidermis. Using flow cytometry we saw that both mouse and human Tregs in the skin express CXCR3 during vitiligo and confocal microscopy revealed that mouse Tregs co-localize with CXCL10 expression in the skin during vitiligo. Using confocal microscopy, we observed that Tregs directly contact Teffs in mouse skin, suggesting that Tregs may use contact-dependent mechanisms of suppression in the skin. We found similar interactions in human skin and hypothesize that Tregs follow CXCL10 to localize with Teffs in the epidermis where they suppress Teffs through a contact-dependent mechanism.

Suction blistering the lesional skin of vitiligo patients reveals useful biomarkers of disease activity

BACKGROUND

Vitiligo is an autoimmune disease of the skin with limited treatment options; there is an urgent need to identify and validate biomarkers of disease activity to support vitiligo clinical studies.

OBJECTIVE

To investigate potential biomarkers of disease activity directly in the skin of vitiligo subjects and healthy subjects.

METHODS

Patient skin was sampled via a modified suction-blister technique, allowing for minimally invasive, objective assessment of cytokines and T-cell infiltrates in the interstitial skin fluid. Potential biomarkers were first defined and later validated in separate study groups.

RESULTS

In screening and validation, CD8+ T-cell number and C-X-C motif chemokine ligand (CXCL) 9 protein concentration were significantly elevated in active lesional compared to nonlesional skin. CXCL9 protein concentration achieved greater sensitivity and specificity by receiver operating characteristic analysis. Suction blistering also allowed for phenotyping of the T-cell infiltrate, which overwhelmingly expresses C-X-C motif chemokine receptor 3.

LIMITATIONS

A small number of patients were enrolled for the study, and only a single patient was used to define the treatment response.

CONCLUSION

Measuring CXCL9 directly in the skin might be effective in clinical trials as an early marker of treatment response. Additionally, use of the modified suction-blister technique supports investigation of inflammatory skin diseases using powerful tools like flow cytometry and protein quantification.

Suction blistering of vitiligo lesional skin provides insights into the pathophysiology of organ specific autoimmunity

Vitiligo is an autoimmune disease of the skin in which CD8+ T cells destroy the pigment producing cells of the skin: melanocytes. To study the immune infiltrate that propagates vitiligo directly in human skin, we employed a novel suction blistering technique to study skin interstitial fluid by ELISA and flow cytometry. Consistent with previous publications demonstrating IFNγ signatures in vitiligo, CD8+ T cell number and CXCL9 protein concentration were elevated in vitiligo lesional skin compared to normal control skin. Receiver operator characteristic analysis revealed that these measurements may be used to distinguish active from stable disease. Phenotypic analysis of T cells in the skin interstitial fluid showed that the majority of CD4+ T cells in vitiligo skin express CXCR3, the receptor for CXCL9, whereas only 47% of CD4+ T cells expressing CXCR3 in the skin of healthy subjects. The frequency of CD8+ T cells expressing CXCR3 was high in both vitiligo patients and healthy donors. Higher CXCR3+ T cell recruitment via elevated CXCL9 expression may contribute to an observed increase in CD8+ T cell to Treg ratio observed active vitiligo skin (4.1 to 2.5 non-lesional). Additionally, all T cells in the skin microenvironment highly express PD-1. These results support the hypothesis that vitiligo is driven by IFNγ dependent signaling, and targeting components downstream of IFNγ may be useful in treating vitiligo. Moreover, suction blistering human skin is a powerful tool that can be used to aid the study of other inflammatory skin diseases.

Understanding mechanisms of autoimmunity through translational research in vitiligo

Vitiligo is an autoimmune disease of the skin that leads to life-altering depigmentation and remains difficult to treat. However, clinical observations and translational studies over 30-40 years have led to the development of an insightful working model of disease pathogenesis: Genetic risk spanning both immune and melanocyte functions is pushed over a threshold by known and suspected environmental factors to initiate autoimmune T cell-mediated killing of melanocytes. While under cellular stress, melanocytes appear to signal innate immunity to activate T cells. Once the autoimmune T cell response is established, the IFN-γ-STAT1-CXCL10 signaling axis becomes the primary inflammatory pathway driving both progression and maintenance of vitiligo. This pathway is a tempting target for both existing and developing pharmaceuticals, but further detailing how melanocytes signal their own demise may also lead to new therapeutic targets. Research in vitiligo may be the future key to understand the pathogenesis of organ-specific autoimmunity, as vitiligo is common, reversible, progresses over the life of the individual, has been relatively well-defined, and is quite easy to study using translational and clinical approaches. What is revealed in these studies can lead to innovative treatments and also help elucidate the principles that underlie similar organ-specific autoimmune diseases, especially in cases where the target organ is less accessible.

Lung dendritic cells imprint T cell lung homing and promote lung immunity through the chemokine receptor CCR4

T cell trafficking into the lung is critical for lung immunity, but the mechanisms that mediate T cell lung homing are not well understood. Here, we show that lung dendritic cells (DCs) imprint T cell lung homing, as lung DC-activated T cells traffic more efficiently into the lung in response to inhaled antigen and at homeostasis compared with T cells activated by DCs from other tissues. Consequently, lung DC-imprinted T cells protect against influenza more effectively than do gut and skin DC-imprinted T cells. Lung DCs imprint the expression of CCR4 on T cells, and CCR4 contributes to T cell lung imprinting. Lung DC-activated, CCR4-deficient T cells fail to traffic into the lung as efficiently and to protect against influenza as effectively as lung DC-activated, CCR4-sufficient T cells. Thus, lung DCs imprint T cell lung homing and promote lung immunity in part through CCR4.

Compartmentalized chemokine-dependent regulatory T-cell inhibition of allergic pulmonary inflammation

BACKGROUND

Induction of endogenous regulatory T (Treg) cells represents an exciting new potential modality for treating allergic diseases, such as asthma. Treg cells have been implicated in the regulation of asthma, but the anatomic location in which they exert their regulatory function and the mechanisms controlling the migration necessary for their suppressive function in asthma are not known. Understanding these aspects of Treg cell biology will be important for harnessing their power in the clinic.

OBJECTIVE

We sought to determine the anatomic location at which Treg cells exert their regulatory function in the sensitization and effector phases of allergic asthma and to determine the chemokine receptors that control the migration of Treg cells to these sites in vivo in both mice and human subjects.

METHODS

The clinical efficacy and anatomic location of adoptively transferred chemokine receptor-deficient CD4(+)CD25(+) forkhead box protein 3-positive Treg cells was determined in the sensitization and effector phases of allergic airway inflammation in mice. The chemokine receptor expression profile was determined on Treg cells recruited into the human airway after bronchoscopic segmental allergen challenge of asthmatic patients.

RESULTS

We show that CCR7, but not CCR4, is required on Treg cells to suppress allergic airway inflammation during the sensitization phase. In contrast, CCR4, but not CCR7, is required on Treg cells to suppress allergic airway inflammation during the effector phase. Consistent with our murine studies, human subjects with allergic asthma had an increase in CCR4-expressing functional Treg cells in the lungs after segmental allergen challenge.

CONCLUSION

The location of Treg cell function differs during allergic sensitization and allergen-induced recall responses in the lung, and this differential localization is critically dependent on differential chemokine function.