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.
Jun Wei, Anantha Marisetty, Brett Schrand, Konrad Gabrusiewicz, Yuuri Hashimoto, Martina Ott, Zacharia Grami, Ling-Yuan Kong, Xiaoyang Ling, Hillary G. Caruso, Shouhao Zhou, Y. Alan Wang, Gregory N. Fuller, Jason T. Huse, Eli Gilboa, Nannan Kang, Xingxu Huang, Roel Verhaak, Shulin Li, Amy B. Heimberger