IMMU-29. CSMD3 modulates the inflammatory induction of diffusely infiltrating low-grade gliomas in preclinical models

Abstract Well-regulated inflammation can control tumors by enhancing immune surveillance and clearance. Paradoxically, chronic inflammation can be a central mediator for the initiation and progression of cancers. Using a clinically relevant genetically engineered murine model of proneural low-grade diffusely infiltrative glioma (LGG) in various genetic immune backgrounds, including CD8+/+CX3CR1+/+ wildtype (WT), CD8-/- CX3CR1+/+ (CD8 KO), CD8+/+CX3CR1-/- (CX3CR1 KO), and CD8-/-CX3CR1-/- (DKO), inflammation was identified as an essential mediator in the initiation of LGG. DKO background mice had significantly prolonged survival (median survival (MS): undefined days; n=59; p = 0.0294) relative to WT (MS: 142 days; n=26), but CD8 KO (MS: 127 days; n=43; p = 0.8436) and CX3CR1 KO (MS: undefined days; n=45; p = 0.230) did not. There was no difference in grade, angiogenesis, proliferation, or invasion at endpoint between these backgrounds.Magnetic resonance imaging (MRI) during the first two months of glioma initiation confirmed that the DKO background mice had delayed T2/FLAIR abnormalities relative to the WT background. At early time points when the glioma is barely detectable on MRI (day 42-47), single-cell RNA sequencing (scRNA-seq) of the brain revealed that CSMD3 is a top upregulated gene in the immune cells in the DKO background relative to WT (log2FC = 1.54). Low CSMD3-expressing microglia are pro-inflammatory, as reflected by IFNγ and TNF gene signatures. In low-grade glioma patients, high expression of CSMD3 is correlated with better prognosis (high vs low: MS = 117.4 months and 50.9 months; hazard ratio=0.32; n=510; p<0.0001), and expression decreases as a function of grade (2 vs 3: p<0.0001). These findings identify CSMD3 as a novel regulator of immune reactivity, including microglia, that is associated with tumorigenesis in low-grade glioma.