Anti-PD-1 antibody-activated Th17 cells subvert re-invigoration of antitumor cytotoxic T-lymphocytes via myeloid cell-derived COX-2/PGE2.

Anti-PD-1 antibody-mediated activation of type 17 T-cells undermines checkpoint inhibitor therapy in the LSL-KrasG12D murine lung cancer model. Herein, we establish that the Th17 subset is the primary driver of resistance to therapy demonstrate that the ontogeny of dysplasia-associated Th17 cells is driven by microbiota-conditioned macrophages; and identify the IL-17-COX-2-PGE2 axis as the mediator of CD8+ cytotoxic T-lymphocyte de-sensitization to checkpoint inhibitor therapy. Specifically, anti-PD-1 treatment of LSL-KrasG12D mice, in which CD4+ T-cells were deficient for RORc, resulted in a 60% increase in CTL cytotoxicity and a 2.5-fold reduction in tumor burden confirming the critical role of Th17 cells in resistance to therapy. Lung-specific depletion of microbiota reduced Th17 cell prevalence and tumor burden by 5- and 2.5-fold, respectively; establishing a link between microbiota and Th17 cell-driven tumorigenesis. Importantly, lung macrophages from microbiota sufficient, but not from microbiota-deficient, mice polarized naïve CD4+ T-cells to a Th17 phenotype, highlighting their role in bridging microbiota and Th17 immunity. Further, treatment with anti-PD-1 enhanced COX-2 and PGE2 levels, whereas neutralization of IL-17 diminished this effect. In contrast, inhibition of COX-2 rescued CTL activity and restored tumor suppression in anti-PD-1-treated mice, revealing the molecular basis of IL-17-mediated resistance to checkpoint blockade. Clinical implications of these findings are discussed.

Spatially Resolved Microglia/Macrophages in Recurrent Glioblastomas Overexpress Fatty Acid Metabolism and Phagocytic Genes.

BACKGROUND: Glioblastoma (GBM) tumors are rich in tumor-associated microglia/macrophages. Changes associated with treatment in this specific cell population are poorly understood. Therefore, we studied changes in gene expression of tumor-associated microglia/macrophages (Iba1+) cells in de novo versus recurrent GBMs. METHODS: NanoString GeoMx® Digital Spatial Transcriptomic Profiling of microglia/macrophages (Iba1+) and glial cells (Gfap+) cells identified on tumor sections was performed on paired de novo and recurrent samples obtained from three IDH-wildtype GBM patients. The impact of differentially expressed genes on patient survival was evaluated using publicly available data. RESULTS: Unsupervised analyses of the NanoString GeoMx® Digital Spatial Profiling data revealed clustering based on the transcriptomic data from Iba1+ and Gfap+ cells. As expected, conventional differential gene expression and enrichment analyses revealed upregulation of immune-function-related genes in Iba1+ cells compared to Gfap+ cells. A focused differential gene expression analysis revealed upregulation of phagocytosis and fatty acid/lipid metabolism genes in Iba1+ cells in recurrent GBM samples compared to de novo GBM samples. Importantly, of these genes, the lipid metabolism gene PLD3 consistently correlated with survival in multiple different publicly available datasets. CONCLUSION: Tumor-associated microglia/macrophages in recurrent GBM overexpress genes involved in fatty acid/lipid metabolism. Further investigation is needed to fully delineate the role of PLD phospholipases in GBM progression.