Interferon-β signal may up-regulate PD-L1 expression through IRF9-dependent and independent pathways in lung cancer cells.

The programmed death ligand-1 (PD-L1) (also called B7-H1 and CD274) belonging to the CD28 family of co-stimulatory molecules is ectopically expressed on the surface of various cancer cells. PD-L1 interacts with programmed death-1 (PD-1) on T cells to trigger an inhibitory signal that suppresses anti-tumor T cell responses as an important mechanism of tumor escape from anti-tumor immune response. Recent development of PD-1/PD-L1 blockades has provided novel immunotherapy strategies for cancers including non-small cell lung cancer (NSCLC). Although the therapy is quite effective for some patients with NSCLC, others are resistant to the treatment, so that regulatory mechanisms of PD-L1 in lung cancer cells need to be understood in detail. Here we analyzed effect of interferon-β (IFN-β) that can be produced in cancer microenvironment on PD-L1 expression in lung tumor cells. An addition of IFN-β elevated PD-L1 expression in mouse and human lung cancer cell lines in culture. This phenomenon was totally dependent on JAK signaling molecules, while IRF9 deficiency in murine lung cancer cells partially attenuated the IFN-β-induced increase in PD-L1. mTOR may not be significantly involved in the regulation of PD-L1, whereas PI3-K pathway played differential roles on PD-L1 mRNA and cell-surface PD-L1 expression, in the cells treated with IFN-β. These results strongly suggest that the type I IFN receptor signal elicits an increase in PD-L1 expression in lung cancer cells through IRF9-dependent and independent pathways.