CCR2 and CCR5 co-inhibition modulates immunosuppressive myeloid milieu in glioma and synergizes with anti-PD-1 therapy.

Immunotherapy has revolutionized the treatment of cancers. Reinvigorating lymphocytes with checkpoint blockade has become a cornerstone of immunotherapy for multiple tumor types, but the treatment of glioblastoma has not yet shown clinical efficacy. A major hurdle to treat GBM with checkpoint blockade is the high degree of myeloid-mediated immunosuppression in brain tumors that limits CD8 T-cell activity. A potential strategy to improve anti-tumor efficacy against glioma is to use myeloid-modulating agents to target immunosuppressive cells, such as myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. We found that the co-inhibition of the chemokine receptors CCR2 and CCR5 in murine model of glioma improves the survival and synergizes robustly with anti-PD-1 therapy. Moreover, the treatment specifically reduced the infiltration of monocytic-MDSCs (M-MDSCs) into brain tumors and increased lymphocyte abundance and cytokine secretion by tumor-infiltrating CD8 T cells. The depletion of T-cell subsets and myeloid cells abrogated the effects of CCR2 and CCR5 blockade, indicating that while broad depletion of myeloid cells does not improve survival, specific reduction in the infiltration of immunosuppressive myeloid cells, such as M-MDSCs, can boost the anti-tumor immune response of lymphocytes. Our study highlights the potential of CCR2/CCR5 co-inhibition in reducing myeloid-mediated immunosuppression in GBM patients.

CCL5 of glioma-associated microglia/macrophages regulates glioma migration and invasion via calcium-dependent matrix metalloproteinase 2.

BACKGROUND: Glioma-associated microglia/macrophages (GAMs) comprise macrophages of peripheral origin and brain-intrinsic microglia, which support tumor progression. Chemokine C-C ligand 5 (CCL5) is an inflammatory mediator produced by immune cells and is involved in tumor growth and migration in several cancers, including glioma. However, the mechanisms detailing how CCL5 facilitates glioma invasion remain largely unresolved. METHODS: Glioma migration and invasion were determined by wound healing, transwell assay, and 3D µ-slide chemotaxis assay. The expression levels of CCL5, CD68, matrix metalloproteinase 2 (MMP2), phosphorylated Ca2+/calmodulin-dependent protein kinase II (p-CaMKII), p-Akt, and phosphorylated proline-rich tyrosine kinase 2 were determined by cytokine array, quantitative PCR, western blot, or immunohistochemistry. Zymography and intracellular calcium assays were used to analyze MMP2 activity and intracellular calcium levels, respectively. RESULTS: CCL5 modulated the migratory and invasive activities of human glioma cells in association with MMP2 expression. In response to CCL5, glioma cells underwent a synchronized increase in intracellular calcium levels and p-CaMKII and p-Akt expression levels. CCL5-directed glioma invasion and increases in MMP2 were suppressed after inhibition of p-CaMKII. Glioma cells tended to migrate toward GAM-conditioned media activated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in which CCL5 was abundant. This homing effect was associated with MMP2 upregulation, and could be ameliorated either by controlling intracellular and extracellular calcium levels or by CCL5 antagonism. Clinical results also revealed the associations between CCL5 and GAM activation. CONCLUSION: Our results suggest that modulation of glioma CaMKII may restrict the effect of CCL5 on glioma invasion and could be a potential therapeutic target for alleviating glioma growth.