Abstract
Though significant strides in tumorigenic comprehension and therapy modality have been witnessed over the past decades, glioma remains one of the most common and malignant brain tumors characterized by recurrence, dismal prognosis, and therapy resistance. Immunotherapy advance holds promise in glioma recently. However, the efficacy of immunotherapy varies among individuals with glioma, which drives researchers to consider the modest levels of immunity in the central nervous system, as well as the immunosuppressive tumor immune microenvironment (TIME). Considering the highly conserved property for sustaining energy homeostasis in mammalian cells and repeatedly reported links in malignancy and drug resistance, autophagy is determined as a cutting angle to elucidate the relations between glioma and the TIME. In this review, heterogeneity of TIME in glioma is outlined along with the reciprocal impacts between them. In addition, controversies on whether autophagy behaves cytoprotectively or cytotoxically in cancers are covered. How autophagy collapses from its homeostasis and aids glioma malignancy, which may depend on the cell type and the cellular context such as reactive oxygen species (ROS) and adenosine triphosphate (ATP) level, are briefly discussed. The consecutive application of autophagy inducers and inhibitors may improve the drug resistance in glioma after overtreatments. It also highlights that autophagy plays a pivotal part in modulating glioma and the TIME, respectively, and the intricate interactions among them. Specifically, autophagy is manipulated by either glioma or tumor-associated macrophages to conform one side to the other through exosomal microRNAs and thereby adjust the interactions. Given that some of the crosstalk between glioma and the TIME highly depend on the autophagy process or autophagic components, there are interconnections influenced by the status and well-being of cells presumably associated with autophagic flux. By updating the most recent knowledge concerning glioma and the TIME from an autophagic perspective enhances comprehension and inspires more applicable and effective strategies targeting TIME while harnessing autophagy collaboratively against cancer.
Highlights
Gliomas originate from supportive glial cells in people with dichotomy prognosis and limited treatment responses [1]
Autophagy represents not merely a way for cellular maintenance, and a key point of regulation in finely adjusting interplays between glioma and the tumor immune microenvironment (TIME). It supports glioma typically by enhancing the adaptability of glioma cells to the extent of progressive, invasive, and drug-resistant malignancy, and by rendering prevailing tumor-associated macrophages/microglia (TAM) differentiating towards the M2 phenotype through exosomes and reduce phagocytosis
The ultimate effect of autophagy in glioma and the TIME may highly depend on the cell type, the intensity of the surrounding signal, and the stage of the lesion and progression
Summary
Gliomas originate from supportive glial cells in people with dichotomy prognosis and limited treatment responses [1]. Recent advances have been made in exploring potential therapies by targeting the tumor immune microenvironment (TIME) in glioma. As immunotherapies prevail in cancers, the limited responses in glioma to treatment lead to a reexamination of the core of immunotherapy: the infiltrating immunocytes and their local microenvironment. The infiltrative immune cells, including tumor-associated macrophages/microglia (TAM), myeloid-derived suppressor cells (MDSCs), dendritic cells (DCs), neutrophils, and tumorinfiltrating lymphocytes, are meant to maintain intercellular homeostasis by eliminating abnormalities though the initial targets which somehow compromise [5, 9]. Together with a few exhausted T cells, nonfunctional natural killer cells (NK cells), inflammatory mast cells, cancer-associated fibroblasts, diffusely distributed astrocytes, immunosuppressive cytokines, insufficient nutrient supply, and hypoxia, the glioma immune microenvironment is roughly characterized [10]
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