Authors:

Yinmeng Li

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About Paper:

Glioblastoma (GBM) is the most aggressive primary brain tumor, with patient median survival under 15 months despite standard therapy. Its therapy resistance is driven by a profoundly immunosuppressive tumor microenvironment (TME), in which tumor-associated myeloid cells (TAMCs) adopt an anti-inflammatory, tumor-promoting phenotype that suppresses antitumor immunity. Among the key mediators of this process is osteopontin (Secreted Phosphoprotein 1, SPP1), an immunoregulatory protein highly expressed in TAMCs and implicated in driving T cell exhaustion and immune evasion. Our single-cell RNA sequencing analysis validated high SPP1 expression in TAMCs in GBM models, suggesting that SPP1 may sustain the immunosuppressive polarization of TAMCs. Based on these findings, we hypothesized that silencing SPP1 in TAMCs may shift them toward a pro-inflammatory state, and thereby remodel the GBM microenvironment to enhance anti-tumor immune responses. To test this hypothesis, we have engineered lipid nanoparticles (LNPs) to deliver small interfering RNA (siRNA) against SPP1 in vitro. Knockdown kinetics revealed efficient transcription reduction, with qPCR showing rapid downregulation of SPP1 within 6 hours and nearly complete silencing within 24 hours. Functionally, SPP1 silencing reprogrammed TAMCs as characterized by upregulated expression of pro-inflammatory genes such as interferon beta (IFNB) and C-C motif chemokine ligand 5 (CCLS5). In addition, IncuCyte live-cell imaging revealed that SPP1-deficient TAMCs exhibited enhanced phagocytic activity, which may accelerate clearance of apoptotic tumor cells. When co-cultured with CD8* T cells, these reprogrammed TAMCs no longer exerted strong immunosuppressive effects and thus T cell proliferation was rescued, as demonstrated by flow cytometry. Altogether, these findings suggest that SPP1 inhibition via sIRNA/LNP reprograms TAMCs from an immunosuppressive to a pro-inflammatory state, enhancing anti-tumor immune functions. This nanotherapy approach may offer a novel route to remodel the GBM microenvironment with translational potential to synergize with current standard-of-care treatments.

Source:

Northwestern University

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Co-authors:

Yinmeng Li