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High-grade gliomas (HGGs) are the most common and deadliest of malignant primary brain tumors. Additionally, brain and central nervous system tumors are the leading cause of cancer-related morbidity and mortality in infants and children. Tumors, including HGGs, co-opt immune checkpoint molecules to evade T-cell killing, and targeting these pathways has led to cures in some patients with cancers. Immunotherapy trials, including the use of checkpoint blockade therapies, have been conducted with limited success in brain tumor patients. Our analysis of data from The Cancer Genome Atlas identified that of over 30 assessed checkpoint molecules, only expression of the genes coding for PD1 and TIGIT, within the tumor, were associated with shorter overall survival and progression-free survival times. Furthermore, using published pediatric glioma resources, we found that TIGIT expression is elevated in pediatric HGGs compared with lower-grade pediatric gliomas, and TIGIT expression was inversely associated with overall survival in children with HGGs. These data led us to hypothesize that glioma-associated T-cells express PD-1 and TIGIT, which can be targeted to reduce glioma growth. To test this, we assessed whether mono/combination therapies with anti-PD-1 and anti-TIGIT could improve survival and immune function in a syngeneic orthotopic GL261 glioma mouse model. Although anti-TIGIT therapy alone failed to prolong survival, mice treated with both anti-PD1 and anti-TIGIT demonstrated improved survival compared with mice receiving anti-PD1 alone. Immunologic analysis of tumor-infiltrating cells in our mouse model revealed high expression levels of PVR, the TIGIT ligand, on cells resembling myeloid-derived suppressor cells (MDSCs), within the tumor. Additionally, TIGIT treatment led to the reduction of a subset of T-regulatory cells and cells resembling MDSCs. Overall, our data suggest that anti-TIGIT may reduce immunosuppressive cells at the tumor site and improve the efficacy of anti-PD1 trials in adults and children with HGGs.

BACKGROUND: Most diffuse gliomas are characterized by mutations in isocitrate dehydrogenase 1 or 2 (IDH1/2). Among its many effects, these mutations drive specific epigenetic programs that result in tumor cell intrinsic resistance to innate lymphoid cells. Here, we define a central role for retinoic acid signaling in mediating immune resistance to innate anti-tumor immunity in IDH mutant tumors. IDH mutations in gliomas suppress retinoic acid signaling through transcriptional repression of Retinol Binding Protein 1 (RBP1), a key chaperone protein in retinoic acid biosynthesis. Loss of retinoic acid signaling results in diminished expression of retinoic-acid-responsive genes, including activating NKG2D ligands ULBP1 and ULBP3 and results in resistance to natural killer (NK cells). METHODS: We evaluated the efficacy of all-trans retinoic acid (ATRA) as a therapeutic adjuvant for IDH mutant gliomas. In a series of in vitro and in vivo experiments, we assessed the ability of ATRA to increase NKG2D ligand expression in IDH mutant cells, and its ability to increase NK-mediated recognition and killing. We also looked at the impact of ATRA on the tumor immune microenvironment and its underlying mechanisms RESULTS: ATRA treatment led to increased recognition and killing of IDH mutant glioma cells by NK cells, by increasing NKG2D ligand expression. In vivo, ATRA treatment led to significantly slower tumor growth in IDH mutant tumor-bearing mice. Importantly, we made the unexpected finding that restoration of retinoic acid signaling dramatically reshapes the landscape of the immune microenvironment by permitting infiltration of NK cells and CD8 T cells in a manner dependent on the chemokine CCL2. CONCLUSIONS: Retinoic acid therapy using ATRA results in marked suppression of IDH mutant glioma tumor growth in an NK cell-dependent fashion in preclinical animal models of glioma. These findings have important therapeutic implications for the treatment of IDH mutant diffuse glioma.

A significant number of patients with high-grade gliomas do not respond to standard therapy. For relapsed bevacizumab refractory Glioblastoma (GBM), no effective treatment options exist. Recently, BRAF V600 mutations have been recognized in higher frequency in younger patients with epithelioid GBM (E-GBM) and other primary brain tumors. We describe the case of a 40 year old Caucasian woman with left temporal epithelioid GBM who originally presented at age 39 with seizures. She underwent gross total resection followed by external beam radiation with concurrent temozolomide and two cycles of adjuvant temozolomide. Her tumor recurred 5 months from diagnosis and she underwent radiosurgery followed by bevacizumab. Four months later she developed marked interval radiographic progression associated with a severe non-fluent aphasia. Because molecular analysis of the primary tumor revealed a BRAF V600E mutation, she was placed on the BRAF inhibitor vemurafenib. After only two months of vemurafenib therapy we observed a robust partial radiographic response along with complete recovery of language and return to near normal neurologic function. While not a common mutation, there may be a role for BRAF inhibitors in a subset of GBM with BRAF V600 mutations. BRAF V600E mutational analyses should be performed on GBMs, and prospective trials are warranted.

Chemokines are known to play an integral role in the cellular trafficking of the immune system, which has important implications in immunotherapy of cancers. Expression of CXCL10/IP10 and CCL5/RANTES has been shown to correlate with increased infiltration of effector T cells and natural killer (NK) cells; conversely expression of CCL22/MDC has been associated with suppression of the adaptive immune response through recruitment of regulatory T cells. Our study evaluated the effects of polyinosinic polycytidylic acid stabilized with lysine and carboxymethylcellulose (poly-ICLC) and IFN-alpha individually and in combination on the expression of chemokines in glioma tissue samples and in glioma cell lines cocultured with myeloid cells to simulate the tumor microenvironment. We found that IFNα as a single agent produced the greatest increase in the expression of CCL5 and CXCL10 while minimizing the expression of CCL22. The addition of poly-ICLC further increased expression of CCL5 and CXCL10. Patient glioma samples had heterogeneous chemokine expression but demonstrated a similar pattern of expression of chemokines to the coculture and cell lines examined. Our findings support the use of IFN-alpha with poly-ICLC as a potential immunotherapy adjuvant for patients with gliomas.