The effect of dexamethasone on the microenvironment and efficacy of checkpoint inhibitors in glioblastoma: A systematic review

Background: Checkpoint inhibitor immunotherapy has not proven clinically effective in glioblastoma. This lack of effectiveness may be partially attributable to the frequent administration of dexamethasone in glioblastoma patients. In this systematic review, we assess whether dexamethasone (1) affects the glioblastoma microenvironment and (2) interferes with checkpoint inhibitor immunotherapy efficacy in the treatment of glioblastoma. Methods: PubMed and Embase were systematically searched for eligible articles published up to September 15, 2021. Both in vitro and in vivo preclinical studies, as well as clinical studies were selected. The following information was extracted from each study: Tumor model, corticosteroid treatment, and effects on individual immune components or checkpoint inhibitor immunotherapy. Results: Twenty-one preclinical studies in cellular glioma models (n = 10), animal glioma models (n = 6), and glioblastoma patient samples (n = 7), and 3 clinical studies were included. Preclinical studies show that dexamethasone decreases the presence of microglia and other macrophages as well as the number of T lymphocytes in both tumor tissue and periphery. Dexamethasone abrogates the antitumor effects of checkpoint inhibitors on T lymphocytes in preclinical studies. Although randomized studies directly addressing our research question are lacking, clinical studies suggest a negative association between corticosteroids and survival outcomes in glioblastoma patients receiving checkpoint inhibitors after adjustment for relevant prognostic factors. Conclusions: Preclinical research shows that dexamethasone inhibits the antitumor immune response in glioma, thereby promoting a protumorigenic microenvironment. The efficacy of checkpoint inhibitor immunotherapy in glioblastoma patients may therefore be negatively affected by the use of dexamethasone. Future research could investigate the potential of edema-reducing alternatives to dexamethasone.