Conventional immunotherapy in the treatment of glioblastoma (GBM) has essentially produced no significant advantage over the use of chemotherapeutic drugs. A strongly immunosuppressive tumor microenvironment and lack of antigen-presenting major histocompatibility expression on tumor cells have made GBM a poor immunological target. Molecular heterogeneity of GBMs, both within the tumor and across patients, results in the immunological escape of tumors that do not express target antigens. Therefore, the development of nonconventional immunotherapy for GBM is continuously being sought. γδ T cells are a minor subset of the human T-cell repertoire with unique antitumor properties that have been shown to be functionally superior to conventional αβ T-cell receptor expressing T cell-based immunotherapy for cancer, including GBM. Unlike, the more abundant αβ T cells, γδ T cells do not require major histocompatibility proteins for activation. In addition to the γδ T-cell receptor, these cells express a plethora of other antigenic receptors that recognize external stimuli, as well as several self-peptides, which make these cells a strong candidate for the development of cancer immunotherapeutics. A higher threshold of activation-induced cell death and resistance to inducing graft-versus-host disease are also characteristics of these T cells. In this review, we discuss the biology and immunological characteristics of γδ T cells and review current research using γδ T cells in GBM immunotherapy to explore whether these cells can be the potential next-gen immunotherapeutic candidate for this dreadful disease.

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Glioblastoma is associated with poor prognosis with a mean survival of 15 months after diagnosis. The current standard of care includes surgery, radiation, and temozolomide with the use of tumor-treating fields in select patient population. The past decade has witnessed a convergence in our understanding of tumor biology and the role of the immune system in fighting cancer. The highly immunosuppressive tumor microenvironment exerted by glioblastoma cells has contributed to the lack of success of novel immunotherapies till date (including checkpoint inhibitors). Oncolytic viral-based approaches are of renewed interest given advances in tumor cell tropism, pathogenicity, and immunogenicity. More importantly, oncolytic viruses have been shown to initiate a broad immune response through various mechanisms including dual activation of the innate and adaptive arms of the host immune system. Because the initial clinical studies with monotherapy checkpoint inhibition in glioblastoma have failed to demonstrate a survival advantage, most trials in glioblastoma are testing combinations that seek to augment the immune response through mutually reinforcing approaches that can overcome the immunosuppressive milieu. Preclinical data in glioblastoma models with combined oncolytic viruses therapy and checkpoint blockade are favorable and provide rationale to initiate first-in-human trials. Even though the number of clinical trials testing this combination in glioblastoma is limited, more studies are expected in the future.

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Glioblastoma (GBM) is the most common primary central nervous system tumor, and despite advances made in traditional chemotherapy and radiation, it continues to carry a poor prognosis. The discovery of the profound immunosuppressive microenvironment created by GBM has given insight on the aggressiveness of this recalcitrant disease. This has led many to believe that immune therapy may yield the improvement in survival that the neuro-oncology community is seeking. In other cancers, the targeting of immune checkpoints has been the most promising immunotherapeutic strategy to date. Immune checkpoints modulate the function of the immune system by increasing or decreasing immune activity. Checkpoint inhibitors and more recently agonists target molecules that regulate immune response to increase immune function either directly or by removal of inhibitory signals. These molecules modulate immunity in the physiologic state to maintain homeostasis, but they are co-opted by cancer to avoid immune detection and attack. The use of checkpoint inhibition to improve cancer therapy has revolutionized the field of oncology, leading to unprecedented improvements in survival from many systemic malignancies. Utilizing PubMed and ClinicalTrials.gov to compile published findings and ongoing trials, we review immune checkpoints and their modulators from bench to bedside over several decades. In this review, the discovery of different checkpoint molecules and the development of drugs used to target them are addressed. In addition, the current state of checkpoint inhibition in GBM, presenting completed and ongoing preclinical and clinical studies utilizing these therapies, is discussed. Finally, we conclude by reviewing the current limitations and potential future directions for the use of checkpoint blockade in the treatment of GBM.

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Treatment-related lymphopenia is a poor prognostic factor for overall survival in patients with high-grade glioma and predicts suboptimal response to immune therapies. Immunotherapy is conceptually an appealing approach in adults with high-grade glioma given that effector lymphocytes are capable of penetrating the blood–brain barrier. However, 40% of these patients develop severe lymphopenia (CD4 counts <200) following concurrent radiation and temozolomide. These low lymphocyte counts are associated with inferior survival. Research suggests that this iatrogenic immunosuppression is attributed to the inadvertent radiation of circulating lymphocytes as they traverse the irradiated field. Lymphocyte subtypes are universally affected by this radiation toxicity. These findings have been reproduced in animal studies, and clinical correlations have been demonstrated in patients with various malignancies. This lymphopenia has been linked with failure to respond to immunologic interventions. Recent insights into the etiology of this radiation-induced lymphopenia have triggered a variety of novel approaches to prevent or restore immunologic function in this patient population. These include altering radiation plans, reducing the number of lymphocytes passing through the radiation field, harvesting lymphocytes before and reinfusing them after radiation, and using growth factors to restore lymphocyte counts. This manuscript reviews critical relationships between treatment-related lymphopenia and immunotherapy outcomes in patients with high-grade gliomas and novel approaches to these issues.

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Midline astrocytic neoplasms have distinct molecular characteristics, quite different from astrocytic neoplasms with similar morphology but not located in the midline. It is imperative that neuropathologists should be aware of the existence of these tumors, so they can be correctly diagnosed. Here, we discuss the case of a 14-year-old boy who presented with acute onset of vomiting followed by loss of consciousness. Subsequent magnetic resonance imaging revealed an ill-defined exophytic lesion arising from the brainstem and extending into the left cerebellopontine angle, with areas of hemorrhage and patchy restricted diffusion. The tumor was resected. Microscopy revealed medium-sized tumor cells in diffuse sheets, having round nuclei, granular chromatin, and scant cytoplasm. Microvascular and endothelial cell proliferation in small necrotic areas were seen. Mitosis was 0–1 per high-power field. By routine histopathological analysis, all features were consistent with the diagnosis of glioblastoma. Tumor cells were immunopositive for glial fibrillary acidic protein and isocitrate dehydrogenase-1 mutation (R132H), immunonegative for p53, and retained alpha thalassemia/mental retardation syndrome X-linked. It also showed a strong immunopositivity for H3-K27M mutation. A diagnosis of a diffuse midline glioma with H3-K27M mutation corresponding to the World Health Organization Grade IV was made. This case highlights the importance of exploring signature mutations in well-defined tumor categories such as H3-K27M-mutant diffuse midline glioma.

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Background and Aim: Mechanisms of glioma progression are poorly understood. Upregulation of calcium-activated potassium channel subunit alpha-1 (KCNMA1), which encodes the α-subunit of maxi-calcium-activated potassium (BK_Ca) channels, is shown to be a novel mechanism for the malignant phenotype of brain tumor cells. The aim of this study was to establish the functional role of KCNMA1 in glioma biology. Materials and Methods: U-87-MG (U-87) cells were transfected to increase BK_Ca channel expression and activity. Glioma cell proliferation, invasiveness, and transendothelial migration were then measured. BK_Ca channels were blocked with iberiotoxin or short hairpin RNA (shRNA), which significantly inhibited K+ currents and growth of U-87 cells. It was tested whether KCNMA1 overexpression enhanced tumorogenecity in glioma xenograft mouse models by injecting wild-type and KCNMA1- overexpressing U87-MG cells. In parallel experiment, it was studied whether shRNA KCNMA1-expressing U-87 cells show attenuated glioma growth in mice. The study protocol was approved by the Institutional Animal Care and Use Committee, Mercer University (A0706007_01), Atlanta, GA, USA on July 20, 2007. Results: The effect of KCNMA1 overexpression in glioma growth as well as on associated cell biology functions such as proliferation, invasion, and migration was presented in this study. Messenger RNA and protein analyses revealed that KCNMA1 was amplified in 90% of high-grade gliomas and in high-grade glioma cell line U-87. In contrast, KCNMA1 amplification was not found in normal brain tissues. These data indicate that KCNMA1 plays critical role in glioma biology by interacting with several cellular processes. The data demonstrate that KCNMA1 amplification drives glioma cell proliferation and growth, which can be attenuated by its downregulation. Conclusion: KCNMA1 is a regulator of glioma cell proliferation and growth and thus qualifies as a promising diagnostic and therapeutic target in the treatment of glioma.

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Background and Aim: Gliomas carrying mutated isocitrate dehydrogenase 1 (IDH1) have an improved prognosis, but how this mutation improves survival is not known. In this study, we evaluated the correlation of expression of the gene transcriptional coactivator with PDZ-binding motif (TAZ) with IDH1 mutation in astrocytomas of different grades. Materials and Methods: We analyzed the expression of TAZ by immunohistochemistry in a cohort of 90 formalin-fixed paraffin-embedded human astrocytoma samples. A human glioblastoma cell line (U87) was transfected with mutated IDH1^R132H; the expression and subcellular location of TAZ were analyzed by western blot assay, quantitative real-time polymerase chain reaction, and immunofluorescence staining. We detected activation of the Hippo signaling pathway by western blot. Octyl-2-hydroxyglutarate (Octyl-2-HG), an analog of 2-HG, was used to treat IDH1 wild-type U87 cells to determine its influence on the expression of TAZ. Cell viability assay, flow cytometry, Transwell migration assay, and scratch assay were used to analyze cell proliferation and invasive capacity. To verify that those changes were caused by the expression of TAZ, we did a rescue experiment by transfecting TAZ in the IDH1^R132H cells. The study was approved by the Ethics Committee of Fudan University (approval No. 2016-Y013) on January 18, 2016. Results: TAZ expression was significantly lower in IDH1-mutated astrocytoma than the wild type in the same tumor grade. In IDH1-mutant cells, the nuclear TAZ location was decreased and the Hippo signaling pathway was activated as determined by TAZ phosphorylation and increased 14-3-3e expression. Treatment with Octyl-2-HG reduced the expression of TAZ. IDH1^R132H cells showed decreased invasion proliferation compared with IDH1 wild-type cells. Overexpression of TAZ rescued cell migration and invasion capacity. Conclusion: In glioma, IDH1^R132H mutation decreases TAZ expression and significantly reduces the invasive character of glioma cells.

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