CAMKK2 PROMOTES AN IMMUNOSUPPRESSIVE PROGRAM AND CHECKPOINT BLOCKADE RESISTANCE IN THE GLIOBLASTOMA TUMOR MICROENVIRONMENT

Abstract BACKGROUND Immunotherapy has demonstrated efficacy in several cancers but has shown only modest effects in Glioblastoma (GBM). This is linked to the anti-inflammatory nature of the tumor microenvironment (TME) and the pro-tumor functions of brain native cells. Targeting stromal cells, such as tumor associated macrophages (TAMs) and neurons, is a promising approach. Re-analysis of human and murine brain single cell-RNAseq (scRNAseq) datasets shows Calmodulin Dependent Kinase Kinase 2 (CaMKK2) is highly expressed in both neurons and TAMs. Loss of CaMKK2 polarizes TAMs to an immunostimulatory phenotype and reduces pro-tumor neuronal functions. Thus, we hypothesize that CaMKK2 promotes the pro-tumor nature of the GBM TME and immunotherapy resistance. RESULTS Murine GBM was orthotopically implanted into wild-type and CaMKK2-/- mice. CaMKK2-/- mice exhibited significantly prolonged survival. To determine if anti-tumor immune function was enhanced, we probed the TME using flow cytometry and scRNAseq. CaMKK2-/- mice showed increased abundance of precursor exhausted, potentially immune checkpoint blockade (ICB) responsive, CD8 T cells. Furthermore, T cell depletion abrogated the survival benefit observed in CaMKK2-/- mice. Considering these T cell phenotypes, we treated CaMKK2-/- mice with ICB, and indeed they were sensitive. To determine if the CaMKK2-/- survival phenotype and ICB response depended on CaMKK2 expression in hematopoietic or in non-hematopoietic cells, we utilized a reciprocal chimera model. Loss of CaMKK2 in the non-hematopoietic cells was more vital for survival and ICB response than in hematopoietic cells, suggesting a potential novel and unique role for CaMKK2 in brain native cells - potentially neurons - in coordinating ICB resistance. CONCLUSIONS We find that CaMKK2 exacerbates mortality and drives ICB resistance by limiting the anti-tumor response in GBM via both hematopoietic and brain native cells. Our findings identify a novel therapeutic target for GBM, and a unique role for CaMKK2 in the TME.