BackgroundPD-L1 is an immune inhibitory receptor ligand that leads to T cell dysfunction and apoptosis by binding to its receptor PD-1, which works in braking inflammatory response and conspiring tumor immune evasion. However, in gliomas, the cause of PD-L1 expression in the tumor microenvironment is not yet clear. Besides, auxiliary biomarkers are urgently needed for screening possible responsive glioma patients for anti-PD-1/PD-L1 therapies.MethodsThe distribution of tumor-infiltrating T cells and PD-L1 expression was analyzed via immunofluorescence in orthotopic murine glioma model. The expression of PD-L1 in immune cell populations was detected by flow cytometry. Data excavated from TCGA LGG/GBM datasets and the Ivy Glioblastoma Atlas Project was used for in silico analysis of the correlation among genes and survival.ResultsThe distribution of tumor-infiltrating T cells and PD-L1 expression, which parallels in murine orthotopic glioma model and human glioma microdissections, was interrelated. The IFN-γ level was positively correlated with PD-L1 expression in murine glioma. Further, IFN-γ induces PD-L1 expression on primary cultured microglia, bone marrow-derived macrophages, and GL261 glioma cells in vitro. Seven IFN-γ-induced genes, namely GBP5, ICAM1, CAMK2D, IRF1, SOCS3, CD44, and CCL2, were selected to calculate as substitute indicator for IFN-γ level. By combining the relative expression of the listed IFN-γ-induced genes, IFN-γ score was positively correlated with PD-L1 expression in different anatomic structures of human glioma and in glioma of different malignancies.ConclusionOur study identified the distribution of tumor-infiltrating T cells and PD-L1 expression in murine glioma model and human glioma samples. And we found that IFN-γ is an important cause of PD-L1 expression in the glioma microenvironment. Further, we proposed IFN-γ score aggregated from the expressions of the listed IFN-γ-induced genes as a complementary prognostic indicator for anti-PD-1/PD-L1 therapy.Electronic supplementary materialThe online version of this article (10.1186/s12974-018-1330-2) contains supplementary material, which is available to authorized users.

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Dendritic cell (DC)-based vaccination is a promising approach for active-specific immunotherapy, but is currently of limited efficacy. The safety and effectiveness of a DC vaccine (DCV) loaded with glioblastoma stem cell-like (GSC) antigens was assessed in glioblastoma multiforme (GBM) patients. In this double-blind, placebo-controlled phase II clinical trial, 43 GBM patients were randomized after surgery at a 1:1 ratio to receive either DCV (n = 22) or normal saline placebo (n = 21). Overall survival (OS) and progression-free survival (PFS) were analysed. Participants were stratified into different molecular subgroups based on the mutation (MT) status of isocitrate dehydrogenase (IDH1/2) and telomerase reverse transcriptase (TERT). Plasma cytokine levels, tumor-infiltrating lymphocyte numbers and immune co-inhibitory molecules PD-L1 and B7-H4 were also assessed. Multivariate Cox regression analysis revealed that DCV treatment significantly prolonged OS (p = 0.02) after adjusting for IDH1 and TERT promoter MT and B7-H4 expression, primary vs recurrent GBM. Among IDH1 TERT patients, DCV treatment significantly prolonged OS (p < 0.01) and PFS (p = 0.03) and increased plasma levels of cytokines CCL22 and IFN-γ compared with placebo. Patients with low B7-H4 expression showed significantly prolonged OS (p = 0.02) after DCV treatment. Therefore, IDH1TERT and low B7-H4 expression identified subgroups of GBM patients more responsive to GSC DCV-based specific active-immunotherapy.

Gliomas, the most common primary neoplasms in the brain, are notorious for their ability to evade the immune response. Despite microglial infiltration in gliomas, expression of MHC class II molecules in those microglia is compromised. Here, we report that Toll-like receptor 2 (TLR2) activation downregulated expression of MHC class II molecules in microglia in an orthotopic murine glioma model. TLR2-induced microglial impairment hindered the proliferation and activation of CD4 T cells, which facilitated glioma immune evasion. TLR2-induced downregulation of MHC class II molecules was caused by suppression of the master regulator of MHC class II molecule transcription, TLR2 activation triggered downstream MAPK/ERK1/2 signaling and loss of histone H3 acetylation at promoters, which in turn inhibited expression. In glioblastoma tissues, various endogenous TLR2 ligands, including the heat shock proteins that are endogenous TLR2 ligands, were upregulated, a response that correlated with inhibition. Thus, TLR2 promotes glioma immune-system evasion. These results advance our understanding of microglia as antigen-presenting cells in the context of glioma. In the glioma tumor microenvironment, TLR2 activation of microglia induces downregulation of microglial MHC class II expression. Impaired MHC class II expression limits T-cell-dependent antitumor immunity. .

MiR-15a/16, a miRNA cluster located at chromosome 13q14, has been reported to act as an immune regulator in inflammatory disorders besides its aberrant expression in cancers. However, little is known about its regulation in tumor-infiltrating immune cells. In our study, using an orthotropic GL261 mouse glioma model, we found that miR-15a/16 deficiency in host inhibited tumor growth and prolonged mice survival, which might be associated with the accumulation of tumor-infiltrating CD8+ T cells. More importantly, tumor-infiltrating CD8+ T cells without miR-15a/16 showed lower expression of PD-1, Tim-3 and LAG-3, and stronger secretion of IFN-γ, IL-2 and TNF-α than WT tumor-infiltrating CD8+ T cells. Also, our in vitro experiments further confirmed that miR-15a/16 CD8+ T displayed higher active phenotypes, more cytokines secretion and faster expansion, compared to WT CD8+ T cells. Mechanismly, mTOR was identified as a target gene of miR-15a/16 to negatively regulate the activation of CD8+ T cells. Taken together, these data suggest that miR-15a/16 deficiency resists the exhaustion and maintains the activation of glioma-infiltrating CD8+ T cells to alleviate glioma progression via targeting mTOR. Our findings provide evidence for the potential immunotherapy through targeting miR-15a/16 in tumor-infiltrating immune cells.