Stromal CaMKK2 promotes immunosuppression and checkpoint blockade resistance in Glioblastoma

Abstract

Glioblastoma (GBM) is notorious for its immunosuppressive tumor microenvironment (TME). GBM is universally lethal and remains highly refractory to immunotherapy, including immune checkpoint blockade (ICB). Resistance to ICB is a central issue in GBM and is thought to be primarily driven by tumor-imposed immune dysfunction. Here, however, we identify calmodulin-dependent kinase kinase 2 (CaMKK2) as a novel driver of ICB resistance. CaMKK2 is highly expressed in myeloid cells and neurons and is associated with worsened survival in patients with GBM. Using CaMKK2-deficient preclinical murine models, we determine that host CaMKK2 expression reduces survival and promotes ICB resistance in a T cell-dependent manner. Single-cell RNA-sequencing, flow cytometric profiling, and immunofluorescence staining of immune cells in the tumor reveal that CaMKK2 expression is associated with several pro-tumor, ICB resistance-associated immune phenotypes. For instance, CaMKK2 promotes terminal exhaustion in CD8+ T cells and reduces the expansion of effector CD4+ T cells, additionally limiting their tumor penetrance and interactions with myeloid cells. CaMKK2 also maintains myeloid cells in an Apolipoprotein E+, disease-associated microglia-like phenotype, which is associated with ICB resistance. Conversely, CaMKK2 deficiency permits the programming of tumor-associated macrophages (TAMs) to a dendritic cell (DC)-like phenotype that is associated with ICB response. Finally, we determine that it is neuronal CaMKK2 expression, specifically, that is required for maintaining the ICB resistance-associated MHC-IIlow TAM phenotype. Our findings reveal CaMKK2 as a novel contributor to ICB resistance, primarily via non-hematopoietic cells, in GBM and additionally newly identify neurons as a critical driver of pro-tumor immune phenotypes within the GBM TME.