IL-27 induces the expression of IDO and PD-L1 in human cancer cells

An IL-27/Stat3 axis induces expression of programmed cell death 1 ligands (PD-L1/2) on infiltrating macrophages in lymphoma

Immune escape and tolerance in the tumor microenvironment are closely involved in tumor progression, and are caused by T‐cell exhaustion and mediated by the inhibitory signaling of immune checkpoint molecules including programmed death‐1 (PD‐1), cytotoxic T‐lymphocyte associated protein 4, and T‐cell immunoglobulin and mucin domaincontaining molecule‐3. In the present study, we investigated the expression of the PD‐1 ligand 1 (PD‐L1) in a lymphoma microenvironment using paraffin‐embedded tissue samples, and subsequently studied the detailed mechanism of upregulation of PD‐L1 on macrophages using cultured human macrophages and lymphoma cell lines. We found that macrophages in lymphoma tissues of almost all cases of adult T‐cell leukemia/lymphoma (ATLL), follicular lymphoma and diffuse large B‐cell lymphoma expressed PD‐L1. Cell culture studies showed that the conditioned medium of ATL‐T and SLVL cell lines induced increased expression of PD‐L1/2 on macrophages, and that this PD‐L1/2 overexpression was dependent on activation of signal transducer and activator of transcription 3 (Stat3). In vitro studies including cytokine array analysis showed that IL‐27 (heterodimer of p28 and EBI3) induced overexpression of PD‐L1/2 on macrophages via Stat3 activation. Because lymphoma cell lines produced IL‐27B (EBI3) but not IL‐27p28, it was proposed that the IL‐27p28 derived from macrophages and the IL‐27B (EBI3) derived from lymphoma cells formed an IL‐27 (heterodimer) that induced PD‐L1/2 overexpression. Although the significance of PD‐L1/2 expressions on macrophages in lymphoma progression has never been clarified, an IL‐27‐Stat3 axis might be a target for immunotherapy for lymphoma patients.

Dual Roles of IL-27 in Cancer Biology and Immunotherapy

IL-27 is a pleiotropic two-chain cytokine, composed of EBI3 and IL-27p28 subunits, which is structurally related to both IL-12 and IL-6 cytokine families. IL-27 acts through a heterodimer receptor consisting of IL-27Rα (WSX1) and gp130 chains, which mediate signaling predominantly through STAT1 and STAT3. IL-27 was initially reported as an immune-enhancing cytokine that supports CD4+ T cell proliferation, T helper (Th)1 cell differentiation, and IFN-γ production, acting in concert with IL-12. However, subsequent studies demonstrated that IL-27 displays complex immune-regulatory functions, which may result in either proinflammatory or anti-inflammatory effects in relationship to the biological context and experimental models considered. Several pieces of evidence, obtained in preclinical tumor models, indicated that IL-27 has a potent antitumor activity, related not only to the induction of tumor-specific Th1 and cytotoxic T lymphocyte (CTL) responses but also to direct inhibitory effects on tumor cell proliferation, survival, invasiveness, and angiogenic potential. Nonetheless, given its immune-regulatory functions, the effects of IL-27 on cancer may be dual and protumor effects may also occur. Here, we will summarize IL-27 biological activities and its functional overlaps with the IFNs and discuss its dual role in tumors in the light of potential applications to cancer immunotherapy.

IL-27 Facilitates Skin Wound Healing through Induction of Epidermal Proliferation and Host Defense

Skin wound repair requires a coordinated program of epithelial cell proliferation and differentiation as well as resistance to invading microbes. However, the factors that trigger epithelial cell proliferation in this inflammatory process are incompletely understood. In this study, we demonstrate that IL-27 is rapidly and transiently produced by CD301b⁺ cells in the skin after injury. The functional role of IL-27 and CD301b⁺ cells is demonstrated by the finding that CD301b-depleted mice exhibit delayed wound closure in vivo, which could be rescued by topical IL-27 treatment. Furthermore, genetic ablation of the IL-27 receptor (Il27Ra^−/−) attenuates wound healing, suggesting an essential role for IL-27 signaling in skin regeneration in vivo. Mechanistically, IL-27 feeds back on keratinocytes to stimulate cell proliferation and re-epithelialization in the skin, whereas IL-27 leads to suppression of keratinocyte terminal differentiation. Finally, we identify that IL-27 potently increases expression of the antiviral oligoadenylate synthetase 2, but does not affect expression of antibacterial human beta defensin 2 or regenerating islet-derived protein 3-alpha. Together, our data suggest a previously unrecognized role for IL-27 in regulating epithelial cell proliferation and antiviral host defense during the normal wound healing response.

Elevated interleukin-27 levels in human neonatal macrophages regulate indoleamine dioxygenase in a STAT-1 and STAT-3-dependent manner

Microbial infections are a major cause of infant mortality as a result of limitations in immune defences. Interleukin-27 (IL-27) is a heterodimeric cytokine produced primarily by leucocytes and is immunosuppressive toward lymphocytes and leucocytes. Our laboratory demonstrated that human neonatal macrophages express IL-27 more abundantly than adult macrophages. Similarly in mice, IL-27 expression is elevated early in life and maintained through infancy. To determine IL-27-regulated mechanisms that may limit immunity, we evaluated the expression of a number of genes in response to this cytokine in primary human neonatal macrophages. Indoleamine 2,3-dioxygenase (IDO) gene expression was increased dose-responsively by IL-27. We have previously demonstrated inhibition of T-cell proliferation and cytokine production by neonatal macrophage-generated IL-27, and IDO is often implicated in this negative regulation. An increase in IDO protein was demonstrated by immunofluorescence microscopy and was consistent with increased enzyme activity following treatment with IL-27. Inclusion of a soluble receptor to neutralize endogenous IL-27, decreased IDO expression and activity compared with untreated macrophages. In response to IL-27, neonatal macrophages phosphorylate signal transdcuer and activator of transcription 1 (STAT-1) and STAT-3. Both transcription factors are recruited to the IDO regulatory region. STAT-3 dominates during steady-state regulation by lower levels of endogenous IL-27 production. A shift to enhanced STAT-1 recruitment occurs during increased levels of exogenously supplied IL-27. These data suggest an interesting interplay of STAT-1 and STAT-3 to regulate IDO activity and immunosuppression in response to different levels of IL-27 in the microenvironment of the immune response that may further our understanding of this interesting cytokine.