PD-L1 Expression Enhancement by Tumor-Associated Macrophages Derived Osteopontin Leads to Poor Non-Small Cell Lung Caner Prognosis

Background: In the tumor microenvironment, programmed death ligand 1(PD-L1) is a key protein upregulated by tumor cells in immune escape. Tumor-associated macrophages (TAMs) play a major role in this immunosuppression. Osteopontin (OPN) is related to tumor metastasis and proliferation and immunosuppression. OPN is expressed not only by tumor cells, but also by TAMs. However, little is known of the relationship between OPN expressed by TAMs(TOPN) and PD-L1 in non-small cell lung cancer. Methods: Tissue microarray was used to detect the expression of TOPN, TAMs and PD-L1 by multiple quantitative fluorescence staining in 509 NSCLC patients undergoing complete pulmonary resection. The correlations between TOPN, PD-L1 and clinicopathologic data were analyzed. And in vitro cell cocultures were further conducted to investigate the crosstalk between TOPN and Neoplastic PD-L1. The in vivo efficacy of TOPN was evaluated for PD-L1 expression in subcutaneous coculture mouse model of NSCLC. Results: We observed a positive association between the TOPN and PD-L1 expression in tumor tissues from 509 patients with NSCLC. In addition, survival analysis revealed that TOPN and PD-L1 were independent prognostic factors for overall survival(OS) and disease-free survival(DFS) of NSCLC patients. We further demonstrated that TOPN upregulated PD-L1 expression in NSCLC cells through NF-κB pathway in vitro . And the upregulation was inhibited by neutralization with anti-OPN antibody or NF-κB inhibitor after co-culture with macrophages. TOPN induced the PD-L1 expression in tumor-bearing mice, and promoted the tumor growth. Conclusions: TOPN/NF-κB axis plays a critical role in PD-L1 expression of NSCLC microenvironment. TOPN could be a potential therapeutic target for NSCLC.