Functional defects of peripheral regulatory T lymphocytes in patients with progressive vitiligo

Pediatric vitiligo

Vitiligo is a disease of pigment loss. Most investigators currently consider vitiligo to be a disorder that occurs as a result of autoimmune destruction of melanocytes, supported by identification of antimelanocyte antibodies in many patients, and the presence of comorbid autoimmune disease in patients with and family members of individuals with vitiligo. One-half of vitiligo cases are of childhood onset. This article presents a current overview of pediatric vitiligo including comorbidities of general health, psychological factors, therapeutic options, and long-term health considerations.

A comprehensive association analysis confirms ZMIZ1 to be a susceptibility gene for vitiligo in Chinese population

BACKGROUND

ZMIZ1 has been shown to be associated with multiple autoimmune diseases and play a role in the development of melanocyte. The association of ZMIZ1 with vitiligo was also suggested, but the evidence did not reach genome-wide significance and has not been confirmed by independent studies.

METHODS

A fine mapping analysis of the ZMIZ1 locus was carried out in the dataset of 1117 vitiligo patients and 3437 controls through deep imputation. Ten suggestive SNPs were then analysed in an independent validation cohort of 7458 cases and 7542 controls. SNPs within ZMIZ1 locus were functionally annotated using the ENCODE and RegulomeDB databases and published eQTL dataset of primary immune cells.

RESULTS

A genome-wide significant association was discovered at rs1408944 (OR(combined)=1.18, p(combined)=1.38E-09) that locates at a DNAse hypersensitivity site and within a Myb_1 motif carried by the binding sites of six overlapping transcription factors (TFs) within the region. Gene Relationships Across Implicated Loci (GRAIL) analysis revealed biological connectivity between ZMIZ1 and previously discovered susceptibility loci for vitiligo as well as the six TFs.

CONCLUSIONS

Our study has confirmed ZMIZ1 as a novel susceptibility locus for vitiligo and further suggested rs1408944 to be the putative causal variant that potentially interrupts TF binding and thus the transcriptional regulation of ZMIZ1.

Autoimmune vitiligo does not require the ongoing priming of naive CD8 T cells for disease progression or associated protection against melanoma

Vitiligo is a CD8 T cell-mediated autoimmune disease that has been shown to promote the longevity of memory T cell responses to melanoma. However, mechanisms whereby melanocyte/melanoma Ag-specific T cell responses are perpetuated in the context of vitiligo are not well understood. These studies investigate the possible phenomenon of naive T cell priming in hosts with melanoma-initiated, self-perpetuating, autoimmune vitiligo. Using naive pmel (gp10025-33-specific) transgenic CD8 T cells, we demonstrate that autoimmune melanocyte destruction induces naive T cell proliferation in skin-draining lymph nodes, in an Ag-dependent fashion. These pmel T cells upregulate expression of CD44, P-selectin ligand, and granzyme B. However, they do not downregulate CD62L, nor do they acquire the ability to produce IFN-γ, indicating a lack of functional priming. Accordingly, adult thymectomized mice exhibit no reduction in the severity or kinetics of depigmentation or long-lived protection against melanoma, indicating that the continual priming of naive T cells is not required for vitiligo or its associated antitumor immunity. Despite this, depletion of CD4 T cells during the course of vitiligo rescues the priming of naive pmel T cells that are capable of producing IFN-γ and persisting as memory, suggesting an ongoing and dominant mechanism of suppression by regulatory T cells. This work reveals the complex regulation of self-reactive CD8 T cells in vitiligo and demonstrates the overall poorly immunogenic nature of this autoimmune disease setting.

A quantitative increase in regulatory T cells controls development of vitiligo

T cell cytolytic activity targeting epidermal melanocyte is shown to cause progressive depigmentation and autoimmune vitiligo. Using the recently developed transgenic mice h3TA2 that carry T cell with a HLA-A2 restricted human tyrosinase reactive TCR and develop spontaneous vitiligo from an early age, we addressed the mechanism regulating autoimmune vitiligo. Depigmentation was significantly impaired only in IFN-γ knockout h3TA2 mice but not in TNF-α or perforin knockout h3TA2 mouse strains, confirming a central role for IFN-γ in vitiligo development. Additionally, the regulatory T cells (Treg) were relatively abundant in h3TA2-IFN-γ^−/− mice, and depletion of Treg employing anti-CD25 antibody fully restored the depigmentation phenotype in h3TA2-IFN-γ^−/− mice mediated in part through upregulation of pro-inflammatory cytokines as IL-17and IL-22. Further therapeutic potential of Treg abundance in preventing progressive depigmentation was evaluated by adoptively transferring purified Treg or using rapamycin. Both adoptive transfer of Treg and rapamycin induced lasting remission of vitiligo in mice treated at the onset of disease, or in mice with established disease. This leads us to conclude that reduced regulatory responses are pivotal to the development of vitiligo in disease-prone mice, and that a quantitative increase in the Treg population may be therapeutic for vitiligo patients with active disease.

Use of gene-modified regulatory T-cells to control autoimmune and alloimmune pathology: is now the right time?

Adoptive immunotherapy using genetically targeted T-cells has recently begun to achieve impressive clinical impact in selected tumor types. Furthermore, long-term follow-up studies indicate thus far that integrating viral vectors do not elicit clinically evident genotoxicity in T-cells, unlike hematopoietic stem cells. The optimism engendered by this clinical experience provides a platform for consideration of the extended use of this technology in other disease types. One area of particular interest entails the harnessing of regulatory T-cells (Tregs) in order to down-regulate unwanted immune responses. Increasing evidence supports the efficacy of this approach in pre-clinical models of autoimmune disease and allograft rejection. Nonetheless, questions remain about optimal host cell, transgene cargo, phenotypic stability of engineered cells in vivo and potential for toxicity. Here, we review the evidence that genetically engineered Tregs can effectively dampen pathogenic immune responses and critically evaluate the prospects for clinical development of this approach.

Inflammatory monocytes are potent antitumor effectors controlled by regulatory CD4+ T cells

The present study evaluates the impact of immune cell populations on metastatic development in a model of spontaneous melanoma [mice expressing the human RET oncogene under the control of the metallothionein promoter (MT/ret mice)]. In this model, cancer cells disseminate early but remain dormant for several weeks. Then, MT/ret mice develop cutaneous metastases and, finally, distant metastases. A total of 35% of MT/ret mice develop a vitiligo, a skin depigmentation attributable to the lysis of normal melanocytes, associated with a delay in tumor progression. Here, we find that regulatory CD4(+) T cells accumulate in the skin, the spleen, and tumor-draining lymph nodes of MT/ret mice not developing vitiligo. Regulatory T-cell depletion and IL-10 neutralization led to increased occurrence of vitiligo that correlated with a decreased incidence of melanoma metastases. In contrast, inflammatory monocytes/dendritic cells accumulate in the skin of MT/ret mice with active vitiligo. Moreover, they inhibit tumor cell proliferation in vitro through a reactive oxygen species-dependent mechanism, and both their depletion and reactive oxygen species neutralization in vivo increased tumor cell dissemination. Altogether, our data suggest that regulatory CD4(+) T cells favor tumor progression, in part, by inhibiting recruitment and/or differentiation of inflammatory monocytes in the skin.

Decreased regulatory T-cells and CD4(+) /CD8(+) ratio correlate with disease onset and progression in patients with generalized vitiligo

The aim of present study was to evaluate CD4(+) /CD8(+) ratio and CD4(+) CD25(hi) FoxP3(+) Tregs in GV patients with reference to their effect on disease onset and progression. Flow cytometry was used for determination of CD4(+) /CD8(+) ratio and Tregs in 82 patients and 50 controls. CD8(+) T-cell counts were significantly higher in GV patients as compared with controls (p = 0.003). Active GV patients showed higher CD8(+) T-cell counts compared with stable GV patients (p = 0.001). The CD4(+) /CD8(+) ratio decreased significantly in patients as compared with controls (p = 0.001). Moreover, the ratio in active GV patients significantly lowered as compared with stable GV patients (p = 0.002). Significant decrease in Treg cell percentage and counts in GV patients was observed compared with controls (p = 0.009, p = 0.008) with significant reduction in FoxP3 expression (p = 0.024). Treg cell percentage and counts were significantly decreased in active GV patients compared with stable GV patients (p = 0.007, p = 0.002). Our results suggest that an imbalance of CD4(+) /CD8(+) ratio and natural Tregs in frequency and function might be involved in the T-cell mediated pathogenesis of GV and its progression.

Vitiligo: interplay between oxidative stress and immune system

Vitiligo is a multifactorial polygenic disorder with a complex pathogenesis, linked with both genetic and non-genetic factors. The precise modus operandi for vitiligo pathogenesis has remained elusive. Theories regarding loss of melanocytes are based on autoimmune, cytotoxic, oxidant-antioxidant and neural mechanisms. Reactive oxygen species (ROS) in excess have been documented in active vitiligo skin. Numerous proteins in addition to tyrosinase are affected. It is possible that oxidative stress is one among the main principal causes of vitiligo. However, there also exists ample evidence for altered immunological processes in vitiligo, particularly in chronic and progressive conditions. Both innate and adaptive arms of the immune system appear to be involved as a primary event or as a secondary promotive consequence. There is speculation on the interplay, if any, between ROS and the immune system in the pathogenesis of vitiligo. The article focuses on the scientific evidences linking oxidative stress and immune system to vitiligo pathogenesis giving credence to a convergent terminal pathway of oxidative stress-autoimmunity-mediated melanocyte loss.

Association of FOXP3 (rs3761548) promoter polymorphism with nondermatomal vitiligo: A study from India

BACKGROUND

The rs3761548 polymorphism (-3279 C>A) of FOXP3 gene is associated with several autoimmune disorders.

OBJECTIVE

We sought to determine whether rs3761548 polymorphism is associated with nondermatomal vitiligo in Indian subjects.

METHODS

Genomic DNA was isolated from blood samples of 303 patients and 305 control subjects and genotyping was done by allele-specific primers. Data analysis was carried out for the entire cohort and separately for male and female participants as FOXP3 is an X-linked marker. Statistics were performed using software.

RESULTS

The genotype frequencies differed significantly from patients to control subjects (P = .002). Further analysis demonstrated female participants with CC genotype were protected (CC vs CA+AA; odds ratio 0.38, 95% confidence interval 0.238-0.615) and those with CA genotype were at higher risk to develop vitiligo (CA vs CC+AA; odds ratio 2.634, 95% confidence interval 1.604-4.325). However, no such statistical difference was observed in male participants.

LIMITATIONS

Our study is, to our knowledge, the first report from India with respect to vitiligo and rs3761548; however, we lack adequate literature assistance.

CONCLUSIONS

The rs3761548 of FOXP3 gene in our population may be associated with susceptibility to vitiligo because of altered expression. CC genotype appears to be protective and CA genotype seems to impart nearly 3-fold risk to develop vitiligo in women and girls.

Vitiligo: an update on current pharmacotherapy and future directions

INTRODUCTION

Vitiligo is a common pigmentary skin disorder, characterized by the appearance of white macules on the skin, mucosal or hair. Treatment is often a tough challenge and involves a wide range of therapies.

AREAS COVERED

This review focuses on available first- and second-line pharmacological treatments for vitiligo. In particular, the mechanisms of action, the main indications, the efficacy and the most important side effects are reviewed. Moreover, a brief discussion is provided, regarding other nonpharmacological treatments, such as phototherapy and surgical options, due to their importance and successful outcomes in vitiligo treatment. Finally, a concise overview regarding the future directions in vitiligo therapy is presented.

EXPERT OPINION

The promising outcomes reported here demonstrate that it is possible to achieve a satisfactory and often stable repigmentation of vitiligo lesions. Topical corticosteroids, calcineurin inhibitors, phototherapy and photochemotherapy represent the first-line therapeutic options, due to their safety and efficacy, whereas vitamin D analogues, targeted phototherapy, oral corticosteroids and surgery should be used as second-line therapies. Other therapies, such as antioxidants, can be used in association with other therapeutic options, whereas depigmenting agents should be used only in cases of extensive vitiligo, recalcitrant to other treatments.

Systemic analyses of immunophenotypes of peripheral T cells in non-segmental vitiligo: implication of defective natural killer T cells

Although it is widely believed that non-segmental vitiligo (NSV) results from the autoimmune destruction of melanocytes, a clear understanding of defects in immune tolerance, which mediate this uncontrolled self-reactivity, is still lacking. In the present study, we systemically evaluated circulating regulatory T (Treg) cells, including CD4(+) CD25(+) FoxP3(+) Treg cells and invariant natural killer T (iNKT) cells, as well as naïve and memory CD4(+) and CD8(+) T cells and their cytokine production, in a cohort of 43 progressive NSV patients with race-, gender-, and age-matched healthy controls. We found that the general immunophenotypes of CD4(+) and CD8(+) T cells and the percentage of CD4(+) CD25(+) FoxP3(+) Tregs were comparable between NSV and healthy controls. However, percentages of peripheral iNKT cells were significantly decreased in NSV patients compared to that in healthy controls. Our data confirm the previous notion that the percentage of peripheral CD4(+) CD25(+) FoxP3(+) Tregs remains unaltered in NSV and suggests the involvement of defective iNKT cells in the pathogenesis of NSV.

Global activation of CD8+ cytotoxic T lymphocytes correlates with an impairment in regulatory T cells in patients with generalized vitiligo

Melanocyte-specific CD8⁺ cytotoxic T lymphocytes (CTLs) play a pivotal role in vitiligo-induced depigmentation. Yet, the mechanisms underlying the high frequency of generalized autoimmune disorders associated with generalized vitiligo (GV) are unknown. We hypothesized that an imbalance between activated CD8⁺ CTLs and regulatory T cells (Tregs) exists in patients with GV . Assessment of the circulating CD8⁺ CTLs and Tregs by flow cytometric analysis revealed an obvious expansion of CD8⁺ CTLs and a concomitant decrease in Treg cells in GV patients. The percentages of skin infiltrating CD8⁺ CTLs and Tregs were evaluated by immunohistochemistry and revealed dramatically increased numbers of both CD8⁺ CTLs and Tregs in the perilesional skin of GV patients. However, peripheral Tregs were impaired in their ability to suppress the proliferation and cytolytic capacity of autologous CD8⁺ T cells, suggesting that a functional failure of Tregs and the hyper-activation of CD8⁺ CTLs may contribute to progressive GV. Our data indicate that reduced numbers and impaired function of natural Tregs fail to control the widespread activation of CD8⁺ CTLs, which leads to the destruction of melanocytes and contributes to the elevated frequency of various associated autoimmune diseases. This knowledge furthers our understanding of the mechanisms of immune tolerance that are impaired in GV patients and may aid in the future development of effective immunotherapy for GV patients.