Constitutive IFN signaling to modulate the immunogenicity of glioma cells.

Abstract

e13528 Background: Interferons (IFN) are cytokines that might be constitutively expressed also in the absence of acute infection and thereby regulate various physiological processes such as cellular proliferation and differentiation, cell viability or immune cell function. Alterations in IFN signaling have been observed in numerous malignancies, but their role in glioblastoma, particularly in glioma-initiating cells, has not been investigated in detail. Methods: We characterized constitutive type I IFN signaling and its functional impact in glioma cells using expression analyses, RNA interference-mediated silencing of various genes involved in the IFN signaling pathway and immune cell lysis assays. Results: We found constitutive expression of pSTAT1 and Myxovirus A (MxA), a classical IFN-response marker, in the absence of exogenous IFN-β in vitro and higher MxA expression in gliomas than in normal tissue in vivo, indicating that IFN signaling is constitutively active in these tumors. Silencing of the type I IFN receptor, IFNAR1/2, or its ligands, IFN-α or IFN-β, decreased MxA levels, providing evidence for the existence of an autocrine type I IFN signaling loop. On a functional level, we observed reduced PD-L1, MHC class I and class II expression and increased susceptibility to immune cell-mediated lysis upon disruption of IFN signaling, suggesting that constitutive IFN signaling in gliomas contributes to the immune evasion of glioma cells. Conclusions: Our findings point to an important role of constitutive IFN signaling in glioma cells in the regulation of anti-tumor immune responses.