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Glial cells suppress postencephalitic CD8+ T lymphocytes through PD-L1.

ABSTRACT: Engagement of the programmed death (PD)-1 receptor on activated cells by its ligand (PD-L1) is a mechanism for suppression of activated T-lymphocytes. Microglia, the resident inflammatory cells of the brain, are important for pathogen detection and initiation of innate immunity, however, a novel role for these cells as immune regulators has also emerged. PD-L1 on microglia has been shown to negatively regulate T-cell activation in models of multiple sclerosis and acute viral encephalitis. In this study, we investigated the role of glial cell PD-L1 in controlling encephalitogenic CD8(+) T-lymphocytes, which infiltrate the brain to manage viral infection, but remain to produce chronic neuroinflammation. Using a model of chronic neuroinflammation following murine cytomegalovirus (MCMV)-induced encephalitis, we found that CD8(+) T-cells persisting within the brain expressed PD-1. Conversely, activated microglia expressed PD-L1. In vitro, primary murine microglia, which express low basal levels of PD-L1, upregulated the co-inhibitory ligand on IFN-γ-treatment. Blockade of the PD-1: PD-L1 pathway in microglial: CD8(+) T-cell co-cultures increased T-cell IFN-γ and interleukin (IL)-2 production. We observed a similar phenomenon following blockade of this co-inhibitory pathway in astrocyte: CD8(+) T-cell co-cultures. Using ex vivo cultures of brain leukocytes, including microglia and CD8(+) T-cells, obtained from mice with MCMV-induced chronic neuroinflammation, we found that neutralization of either PD-1 or PD-L1 increased IFN-γ production from virus-specific CD8(+) T-cells stimulated with MCMV IE1168-176 peptide. These data demonstrate that microglia and astrocytes control antiviral T-cell responses and suggest a therapeutic potential of PD1: PD-L1 modulation to manage the deleterious consequences of uncontrolled neuroinflammation.

SUBMITTER: Schachtele SJ

PROVIDER: S-EPMC4141010 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Based on preclinical findings, programmed death-ligand 1 (PD-L1) can substantially attenuate CD8+ T-cell-mediated anti-tumoral immune responses. However, clinical studies have reported controversial results regarding the significance of the tumor-infiltrating CD8+ T-cells/PD-L1 axis on the clinical picture and the response rate of patients with high-grade glial tumors to anti-cancer therapies. Herein, we conducted a systematic review according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statements to clarify the clinical significance of the tumor-infiltrating CD8+ T-cells/PD-L1 axis and elucidate the impact of this axis on the response rate of affected patients to anti-cancer therapies. Indeed, a better understanding of the impact of this axis on the response rate of affected patients to anti-cancer therapies can provide valuable insights to address the futile response rate of immune checkpoint inhibitors in patients with high-grade glial tumors. For this purpose, we systematically searched Scopus, Web of Science, Embase, and PubMed to obtain peer-reviewed studies published before 1 January 2021. We have observed that PD-L1 overexpression can be associated with the inferior prognosis of glioblastoma patients who have not been exposed to chemo-radiotherapy. Besides, exposure to anti-cancer therapies, e.g., chemo-radiotherapy, can up-regulate inhibitory immune checkpoint molecules in tumor-infiltrating CD8+ T-cells. Therefore, unlike unexposed patients, increased tumor-infiltrating CD8+ T-cells in anti-cancer therapy-exposed tumoral tissues can be associated with the inferior prognosis of affected patients. Because various inhibitory immune checkpoints can regulate anti-tumoral immune responses, the single-cell sequencing of the cells residing in the tumor microenvironment can provide valuable insights into the expression patterns of inhibitory immune checkpoints in the tumor micromovement. Thus, administrating immune checkpoint inhibitors based on the data from the single-cell sequencing of these cells can increase patients' response rates, decrease the risk of immune-related adverse events development, prevent immune-resistance development, and reduce the risk of tumor recurrence.

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Glial cells suppress postencephalitic CD8+ T lymphocytes through PD-L1.

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