The relationship between expression of PD-L1 and HIF-1α in glioma cells under hypoxia.

Abstract

e14043 Background: Hypoxia inducible factor-1α (HIF-1α) up-regulates the expression of programmed death ligand-1 (PD-L1) in some extracranial malignancies. However, whether it also increases PD-L1 expression in intracranial tumor is still unknown. Here we explored the relationship between HIF-1α and PD-L1 expression in glioma, and investigated their clinical significance. Methods: Tumor tissues from 120 patients with glioma, were analyzed for PD-L1 and HIF-1α expression using immunohistochemistry. And results were verified in vitro, using U251, U343 glioma cell lines. Gene expression were evaluated by quantitative PCR; protein levels were analyzed by Western blot; ChIP-qPCR (chromatin immunoprecipitation coupled with quantitative PCR) analysis showed the relationship between HIF-1α and PD-L1. Glioma in situ model were used to explore whether HIF-1α inhibitor (PX-478) can enhance anti-PD-L1 therapy responses. Tumor volume was measured twice weekly. Immune data were further analyzed by FACS DIVA 7.0 or Flow Jo 7.6.5 software. Results: In glioma patients, HIF-1α and PD-L1 were markedly overexpressed in high grade glioma (HGG) tissues and were both associated with poorer overall survival(OS) (PD-L1( < 5% vs. ≥ 5%): 3, 5, 10-year OS: 78.1%, 50.5%, 27.2% vs. 45.4%, 11.8%, 0%, P = 0.0026; HIF-1α( < 1% vs. ≥ 1%): 3, 5, 10-year OS:74.2%, 66.8%, 53.4% vs. 61.6%, 21.0%, 0%, P = 0.001). And the expression of PD-L1 was significantly positively correlated with the expression of HIF-1α in glioma patients ( r = 0.412, P < 0.001). In glioma cell lines, PD-L1 expression was significantly induced under hypoxia condition, but the enhanced PD-L1 expression was abrogated by either HIF-1α knock-down or HIF-1α inhibitor treatment. Furthermore, ChIP-qPCR analysis showed the direct binding of HIF-1α to PD-L1 proximal promoter, providing evidence that HIF-1α up-regulate PD-L1 expression in glioma cells. In glioma murine model, combination treatment with HIF-1α inhibitor and anti-PD-L1 antibody caused a more pronounced suppressive effect on tumor growth compared to mice treated with either single agent. Immunologically, the combination treatment improved both dendritic cell (DC) and CD8+ T cell activation. Conclusions: Multiple findings demonstrated that positive relationship between HIF-1α and PD-L1 existed in glioma cells under hypoxia condition. These observations also provide invaluable information that hypoxia contributes to a key phase of glioma cells evading adaptive immunity, thereby promoting malignant progression and poorer clinical outcomes. Given these, it would be a potential strategy to target HIF-1α in combination with the blockage of PD-1/PD-L1 pathway for anti-cancer in the future.