Immunotherapy approaches for glioblastoma multiforme have been thus far largely unsuccessful, suggesting unappreciated complexity in glioma biology and immunology. The intra-tumoral heterogeneity of these intrinsic brain tumors results in therapies killing only a subset of the tumor cells; therefore, therapeutic success will require achieving and optimizing an abscopal effect where tumor cells not specifically targeted are recognized and attacked as bystanders by the immune system. We have modified an immune-competent, genetically-driven mouse glioma model where a portion of the tumor burden is treated and another untreated portion is used as a readout of therapeutic efficacy. We find that following radiation of one lesion, anti-PD-L1 therapy enhances the abscopal response (macrophages and T-cells) to the un-irradiated lesion.  In gliomas with few baseline T-cells, the anti-PD-L1-enhanced abscopal response occurs as an anti-PD-L1-driven, macrophage-mediated, and ERK-dependent increase in phagocytosis of tumor cells. Our results indicate that combined radiation and anti-PD-L1 therapy for gliomas results in peripherally-derived macrophages being responders in tumors with few baseline T-cells in the microenvironment. SOURCE: Sonali Arora (sarora@fredhutch.org) -  FHCRC

Pluto Bioinformatics

GSE111806: Anti-PD-L1 antibody direct activation of macrophages contributes to an abscopal response in murine brain tumors