Jillian M. Richmond

CXCL10 Is Critical for the Progression and Maintenance of Depigmentation in a Mouse Model of Vitiligo

Neutralizing CXCL10 reverses established vitiligo. New Skin in the Game of Vitiligo Therapy The immune system is tasked with protecting the body from invading pathogens. Yet, sometimes, immune cells themselves attack the tissues they are supposed to protect. One such autoimmune disease is vitiligo, where immune cells are thought to attack melanocytes—the pigment-producing cells in the skin. Individuals with vitiligo have depigmented areas in their skin, which is disfiguring and also increases the risk of skin damage. Now, Rashighi et al. suggest that blocking the chemokine CXCL10 may restore pigmentation in patients with vitiligo. The authors examined gene expression in lesional skin from vitiligo patients and found an interferon-γ–specific signature, including differential expression of the chemokine CXCL10. They found that CXCL10 was up-regulated in vitiligo patients; its receptor CXCR3 was up-regulated in T cells from these patients as well. The authors then looked in a mouse model of vitiligo to determine the functional relevance of this observation. Mice with CXCR3-deficient T cells developed a much less severe form of vitiligo, as did mice lacking CXCL10 or treated with a CXCL10-neutralizing antibody. What’s more, this CXCL10-neutralizing antibody resulted in repigmentation in mice with already established vitiligo lesions. These data suggest that CXCL10 neutralization should be considered as a potential treatment for vitiligo. Vitiligo is an autoimmune disease of the skin that results in disfiguring white spots. There are no U.S. Food and Drug Administration–approved treatments for vitiligo, and most off-label treatments yield unsatisfactory results. Vitiligo patients have increased numbers of autoreactive, melanocyte-specific CD8+ T cells in the skin and blood, which are directly responsible for melanocyte destruction. We report that gene expression in lesional skin from vitiligo patients revealed an interferon-γ (IFN-γ)–specific signature, including the chemokine CXCL10. CXCL10 was elevated in both vitiligo patient skin and serum, and CXCR3, its receptor, was expressed on pathogenic T cells. To address the function of CXCL10 in vitiligo, we used a mouse model of disease that also exhibited an IFN-γ–specific gene signature, expression of CXCL10 in the skin, and up-regulation of CXCR3 on antigen-specific T cells. Mice that received Cxcr3−/− T cells developed minimal depigmentation, as did mice lacking Cxcl10 or treated with CXCL10-neutralizing antibody. CXCL9 promoted autoreactive T cell global recruitment to the skin but not effector function, whereas CXCL10 was required for effector function and localization within the skin. Surprisingly, CXCL10 neutralization in mice with established, widespread depigmentation induces reversal of disease, evidenced by repigmentation. These data identify a critical role for CXCL10 in both the progression and maintenance of vitiligo and thereby support inhibiting CXCL10 as a targeted treatment strategy.

Innate immune mechanisms in vitiligo: danger from within

Vitiligo is an autoimmune disease of the skin in which melanocytes are destroyed by antigen-specific T cells, resulting in patchy depigmentation. Although adaptive immunity plays a clear role in disease progression, initiating factors are largely unknown. Many studies report that cellular stress pathways are dysregulated in melanocytes from vitiligo patients, suggesting that melanocyte-intrinsic defects participate in disease pathogenesis. Recent studies reveal that melanocyte stress generates damage-associated molecular patterns that activate innate immunity, thus connecting stress to organ-specific inflammation. Genetic studies in vitiligo support a role for stress, innate immunity, and adaptive mechanisms. Here, we discuss advances in the field that highlight how cellular stress, endogenous danger signals, and innate immune activation promote the onset of vitiligo.

Regulation of Cellular Processes by Interleukin-16 in Homeostasis and Cancer

Interleukin‐16 (IL‐16) is generated as a precursor molecule that is cleaved by caspase‐3 to produce a pro‐IL‐16 molecule that functions as a regulator of T cell growth, and a secreted peptide that functions as a CD4 and/or CD9 ligand for induction of cell motility and activation. IL‐16 has been predominantly studied as a contributing factor in the orchestration of an immune response; however, more recently IL‐16 bioactivity has been closely associated with the progression of a number of different cancers. While the association between IL‐16 plasma levels and tumor progression has been reported for many types of cancer, the mechanism for IL‐16 involvement has been partially elucidated for three of the cancer types, cutaneous T cell lymphoma (CTCL), multiple myeloma (MM), and breast cancer. The mechanism for promoting cell growth is different in each of these cancers and involves a sequence mutation in the pro‐molecule facilitating decreased p27KIP1 levels in CTCL; over expression of the secreted IL‐16 molecule to induce proliferation in CTCL T cells, and plasma cells in MM; and increased secreted IL‐16 acting to recruit CD4+ pro‐tumor macrophages in breast cancer. This article will review the cellular process for generating IL‐16, the biological activities for both the pro‐ and secreted forms of the protein, and then the mechanism by which these forms contribute to cancer progression. As a soluble cytokine the ability to reduce or eliminate IL‐16 synthesis through siRNA approaches or bioactivity through the use of neutralizing antibody treatment may represent a novel therapeutic approach. J. Cell. Physiol. 229: 139–147, 2014.

Simvastatin prevents and reverses depigmentation in a mouse model of vitiligo

Vitiligo is a common autoimmune disease of the skin that results in disfiguring white spots. There are no FDA-approved treatments, and current treatments are time-consuming, expensive, and have low efficacy. We sought to identify new treatments for vitiligo, and first considered repurposed medications because of the availability of safety data and expedited regulatory approval. We previously reported that the IFN-γ-induced chemokine CXCL10 is expressed in lesional skin from vitiligo patients, and that it is critical for the progression and maintenance of depigmentation in our mouse model of vitiligo. We hypothesized that targeting IFN-γ signaling might be an effective new treatment strategy. STAT1 activation is required for IFN-γ signaling and recent studies revealed that simvastatin, an FDA-approved cholesterol-lowering medication, inhibited STAT1 activation in vitro. Therefore, we hypothesized that simvastatin may be an effective treatment for vitiligo. We found that simvastatin both prevented and reversed depigmentation in our mouse model of vitiligo, and reduced the number of infiltrating autoreactive CD8+ T cells in the skin. Treatment of melanocyte-specific, CD8+ T cells in vitro decreased proliferation and IFN-γ production, suggesting additional effects of simvastatin directly on T cells. Based on these data, simvastatin may be a safe, targeted treatment option for patients with vitiligo.

Keratinocyte-Derived Chemokines Orchestrate T-Cell Positioning in the Epidermis during Vitiligo and May Serve as Biomarkers of Disease.

Vitiligo is an autoimmune disease of the skin that results in the destruction of melanocytes and the clinical appearance of white spots. Disease pathogenesis depends on IFN-γ and IFN-γ-induced chemokines to promote T-cell recruitment to the epidermis where melanocytes reside. The skin is a complex organ, with a variety of resident cell types. We sought to better define the microenvironment and distinct cellular contributions during autoimmunity in vitiligo, and we found that the epidermis is a chemokine-high niche in both a mouse model and human vitiligo. Analysis of chemokine expression in mouse skin showed that CXCL9 and CXCL10 expression strongly correlate with disease activity, whereas CXCL10 alone correlates with severity, supporting them as potential biomarkers for following disease progression. Further studies in both our mouse model and human patients showed that keratinocytes were the major chemokine producers throughout the course of disease, and functional studies using a conditional signal transducer and activator of transcription (STAT)-1 knockout mouse showed that IFN-γ signaling in keratinocytes was critical for disease progression and proper autoreactive T-cell homing to the epidermis. In contrast, epidermal immune cell populations including endogenous T cells, Langerhans cells, and γδ T cells were not required. These results have important clinical implications, because topical therapies that target IFN-γ signaling in keratinocytes could be safe and effective new treatments, and skin expression of these chemokines could be used to monitor disease activity and treatment responses.

Immunology and Skin in Health and Disease

The skin is a complex organ that, in addition to providing a strong barrier against external insults, serves as an arena for a wide variety of inflammatory processes, including immunity against infections, tumor immunity, autoimmunity, and allergy. A variety of cells collaborate to mount functional immune responses, which are initiated by resident populations and evolve through the recruitment of additional cell populations to the skin. Inflammatory responses are quite diverse, resulting in a wide range of signs and symptoms that depend on the initiating signals, characteristics of the infiltrating cell populations, and cytokines that are produced (cytokines are secreted protein that allows for cell-cell communication; usually refers to communication between immune-immune cells or stromal-immune cells). In this work, we will review the skin architecture and resident and recruited cell populations and discuss how these populations contribute to inflammation using human diseases and treatments when possible to illustrate their importance within a clinical context.

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.

Mannose-Capped Lipoarabinomannan from Mycobacterium tuberculosis Preferentially Inhibits Sphingosine-1-Phosphate–Induced Migration of Th1 Cells

Chemokine receptor cross-desensitization provides an important mechanism to regulate immune cell recruitment at sites of inflammation. We previously reported that the mycobacterial cell wall glycophospholipid mannose-capped lipoarabinomannan (ManLAM) could induce human peripheral blood T cell chemotaxis. Therefore, we examined the ability of ManLAM to desensitize T cells to other chemoattractants as a potential mechanism for impaired T cell homing and delayed lung recruitment during mycobacterial infection. We found that ManLAM pretreatment inhibited in vitro migration of naive human or mouse T cells to the lymph node egress signal sphingosine-1-phosphate (S1P). Intratracheal administration of ManLAM in mice resulted in significant increases in T cells, primarily CCR5+ (Th1) cells, in lung-draining lymph nodes. To investigate the selective CCR5 effect, mouse T cells were differentiated into Th1 or Th2 populations in vitro, and their ability to migrate to S1P with or without ManLAM pretreatment was analyzed. ManLAM pretreatment of Th1 populations inhibited S1P-induced migration but had no effect on Th2 cell S1P-directed migration, suggesting a differential effect by S1P on the two subsets. The PI3K/AKT inhibitor Ly294002 inhibited S1P-directed migration by Th1 cells, whereas the ERK inhibitor U0126 inhibited Th2 cell S1P-directed migration. These observations demonstrate that S1P-induced migratory responses in Th1 and Th2 lymphocytes occurs via different signaling pathways and suggests further that the production of ManLAM during Mycobacterium tuberculosis infection may function to sequester Th1 cells in lung-draining lymph nodes, thereby delaying their recruitment to the lung.

CCR4 T cell recruitment to the skin in mycosis fungoides: potential contributions by thymic stromal lymphopoietin and interleukin-16

Abstract Mycosis fungoides (MF) is characterized by skin accumulation of CCR4+CCR7- effector memory T cells; however the mechanism for their recruitment is not clearly identified. Thymic Stromal Lymphopoietin (TSLP) is a keratinocyte-derived cytokine that triggers Th2 immunity and is associated with T cell recruitment to the skin in atopic dermatitis. Interleukin-16 (IL-16) is a chemoattractant and growth factor for CD4+ T cells. We hypothesized that TSLP and IL-16 could contribute to recruitment of malignant T cells in MF. We found elevated TSLP and IL-16 in very early stage patients’ plasma and skin biopsies, prior to elevation in CCL22. Both TSLP and IL-16 induced migratory responses of CCR4+TSLPR+CD4+CCR7−CD31+ cells, characteristic of malignant T cells in the skin. Co-stimulation also resulted in significant proliferative responses. We conclude that TSLP and IL-16, expressed at early stages of disease, function to recruit malignant T cells to the skin and contribute to their enhanced proliferation.

A double-blind, placebo-controlled, phase-II clinical trial to evaluate oral simvastatin as a treatment for vitiligo

To theEditor:Vitiligo is anautoimmunedisease caused by autoreactive CD8 T lymphocytes that target melanocytes, and interferon-induced CXCL10 plays an important role. Simvastatin inhibits interferonsignaling by blocking activation of STAT1 and prevented and reversed disease in our mouse model. A case report described a patient with vitiligo who repigmentedwith simvastatin.We conducted a small, randomized, double-blind, placebo-controlled, phase II clinical trial to test simvastatin as a treatment for vitiligo. After obtaining informed consent, we enrolled men ages 18 to 64 years with vitiligo affecting 3% to 50% of their body surface area (BSA). We excluded patients with a segmental presentation; those already taking a 3-hydroxy-3-methylglutarylcoenzyme A reductase inhibitor; those with existing thyroid disease; and women, based on their increased risk of simvastatin-induced myopathy. This study was approved by our institutional review board (Clinicaltrials.gov identifier number: NCT01517893). Fifteen patients were randomized to either 40 mg of simvastatin daily for the first month and 80 mg for the remaining 5 months of the study period, or placebo. Topicals were discontinued for at least 2 weeks, oral immunomodulators for 4 weeks, and