First published October 11, 2018 - More info
Glioblastoma is highly enriched with macrophages, and osteopontin (OPN) expression levels correlate with glioma grade and the degree of macrophage infiltration, thus we studied whether OPN plays a crucial role in immune modulation. Quantitative PCR, immune blotting, and ELISA were used to determine OPN expression. Knockdown of OPN was achieved using complementary siRNA, shRNA and CRISPR/CAS9 techniques followed by a series of in vitro functional migration and immunological assays. OPN gene-deficient mice were used to examine the roles of non-tumor-derived OPN on survival of mice harboring intracranial gliomas. Patients with mesenchymal GBM show high OPN expression, a negative survival prognosticator. OPN is a potent chemokine for macrophages, and its blockade significantly impaired the ability of glioma cells to recruit macrophages. Integrin αVβ5 (ITGαVβ5) is highly expressed on glioblastoma-infiltrating macrophages and constitutes a major OPN receptor. OPN maintains the M2 macrophage gene signature and phenotype. Both tumor-derived OPN and host-derived OPN was critical for glioma development. OPN deficiency in either the innate immune or glioma cells demonstrated a marked reduction of M2 macrophages and elevated T cell effector activity infiltrating the glioma. Furthermore, OPN deficiency in the glioma cells sensitized them to direct CD8+ T cell cytotoxicity. OPN can be exploited as an immune modulatory target, with efficacious therapeutic results using systemically administered OPN-4-1BB bispecific aptamers, increasing median survival time by 68% (P < 0.05). OPN is an important chemokine for recruiting macrophages to glioblastoma, mediates crosstalk between tumor cells and the innate immune system, and can be exploited as a therapeutic target.