Expression analysis of PD‐1 and Tim‐3 immune checkpoint receptors in patients with vitiligo; positive association with disease activity

Abstract

The contribution of immune checkpoint receptors in the immunopathogenesis of various autoimmune diseases has been addressed in previous reports. In this study, the expression profile of T‐cell immunoglobulin and mucin‐domain containing‐3 (Tim‐3) and programmed cell death‐1 (PD‐1) checkpoint molecules was investigated in CD8+ T cells of Vitiligo patients. The association of Tim‐3 and PD‐1 expression with disease activity was also explored. The frequency of Tim‐3+/PD‐1+/CD8+ T cells in 30 patients with vitiligo and 30 sex‐ and age‐matched controls was determined by flow cytometry. CD8+ T cells were then positively isolated by magnetic beads, and the mRNA expression of PD‐1 and Tim‐3 was determined by TaqMan‐based real‐time PCR. To measure the cytokines production, PBMCs were stimulated with PMA/ionomycin and concentrations of IL‐4, IFN‐γ and TNF‐α were measured in culture supernatants by ELISA. Disease activity of patients with vitiligo was determined using the Vitiligo Area Severity Index. Patients with vitiligo have significantly shown more expression of Tim‐3 and PD‐1 on their CD8+ T cells compared with controls. Expression analysis of Tim‐3 mRNA, but not PD‐1, confirmed the results obtained from flow cytometry. While the production levels of TNF‐α and IFN‐γ were found higher by patients with vitiligo, IL‐4 production was lower in patients compared with controls. A direct association was observed between the Tim‐3 and PD‐1 expression and also the production of pro‐inflammatory cytokines with disease activity of patients with vitiligo. Our results indicate that Tim‐3 and PD‐1 are involved in immune dysregulation mechanisms of CD8+ T cells in vitiligo and may introduce as potential biomarkers for disease progression and targeted immunotherapy.

Mechanisms of melanocyte death in vitiligo

“…Recently, programmed cell death protein (PD)‐1 and T‐cell immunoglobulin and mucin‐domain containing‐3 molecules, which serve as immune checkpoints to mediate braking of cytotoxic response, are found to be highly expressed on vitiligo CD8 + T cells. This is surmised to be a compensation mechanism of the immune system to keep peripheral tolerance towards self‐tissue, in face of hyperactivated CD8 + T cells 163 . A study administrating programmed death‐ligand 1 on vitiligo mice successfully reversed the depigmentation also endorses the participation of immune checkpoint in self‐immunoresponse against melanocytes 164 …”

Melanoma and Vitiligo: In Good Company

“…A study of patients with metastatic melanoma showed that exosomes released from melanoma cells carry PD-L1 on their surface, and that the increase in levels of circulating exosomal PD-L1 correlates with tumor response to anti-PD-1 therapy [87]. In vitiligo, PD-1 expression in CD8+ T cells is positively associated with disease activity [90].…”

Targeting the PD-1/PD-L1 Axis in Human Vitiligo

“…PD-L1 expression by autoreactive T cells, however, has not been shown. Similarly, vitiligo patients show increased PD-1 expression on CD8 + T cells compared to healthy donor CD8 + T cells ( 47 ), implying that PD-1 expression is due to excessive activation of autoreactive CD8 + T cells. PD-1 expression on CD8 + T cells appears to positively correlate with disease activity ( 47 ), suggesting a more vigorous attempt to control the inflammatory situation by increasing PD-1 expression.…”

“…Similarly, vitiligo patients show increased PD-1 expression on CD8 + T cells compared to healthy donor CD8 + T cells ( 47 ), implying that PD-1 expression is due to excessive activation of autoreactive CD8 + T cells. PD-1 expression on CD8 + T cells appears to positively correlate with disease activity ( 47 ), suggesting a more vigorous attempt to control the inflammatory situation by increasing PD-1 expression. In situ , PD-1 is significantly expressed in marginal and lesional infiltrates when compared to non-lesional skin in patients with active non-segmental vitiligo ( 48 ).…”