RT Journal Article SR Electronic T1 Orphan nuclear receptor TLX promotes immunosuppression via its transcriptional activation of PD-L1 in glioma JF Journal for ImmunoTherapy of Cancer JO J Immunother Cancer FD BMJ Publishing Group Ltd SP e001937 DO 10.1136/jitc-2020-001937 VO 9 IS 4 A1 Jiayi Zhou A1 Xiaojuan Pei A1 Yingui Yang A1 Zhu Wang A1 Weijie Gao A1 Ran Ye A1 Xiantong Zhang A1 Jiangang Liu A1 Zhuohao Liu A1 Xinzhi Yang A1 Jingli Tao A1 Chunshan Gu A1 Wei Hu A1 Franky Lueng Chan A1 Xin Li A1 Jie Mao A1 Dinglan Wu YR 2021 UL http://jitc.bmj.com/content/9/4/e001937.abstract AB Background High-grade gliomas are rapidly progressing tumors of the central nervous system, and are associated with poor prognosis and highly immunosuppressive microenvironments. Meanwhile, a better understanding of PD-L1, a major prognostic biomarker for checkpoint immune therapy, regulation may provide insights for developing novel immunotherapeutic strategies for treating gliomas. In the present study, we elucidate the functional significance of the orphan nuclear receptor TLX in human glioma, and its functional role in immune suppression through regulation of PD-L1/PD-1 axis.Methods TLX and PD-L1 expression patterns, and their association with clinicopathological parameters and immune phenotypes of glioma were analysed using CIBERSORT algorithm and single-sample gene-set enrichment analysis from The Cancer Genome Atlas (n=695) and Chinese Glioma Genome Atlas (n=1018) databases. Protein expression and cellular localization of TLX, PD-L1, and PD-1, as well as the prevalence of cytotoxic tumor-infiltrating lymphocytes (TILs), and tumor-associated macrophages (TAMs), in the glioma immune microenvironment were analyzed via tissue microarray by immunohistochemistry and multiplex immunofluorescence. Glioma allografts and xenografts with TLX manipulation (knockdown/knockout or reverse agonist) were inoculated subcutaneously, or orthotopically into the brains of immunodeficient and immunocompetent mice to assess tumor growth by imaging, and the immune microenvironment by flow cytometry. PD-L1 transcriptional regulation by TLX was analyzed by chromatin immunoprecipitation and luciferase reporter assays.Results TLX and PD-L1 expression was positively associated with macrophage-mediated immunosuppressive phenotypes in gliomas. TLX showed significant upregulation and positive correlation with PD-L1. Meanwhile, suppression of TLX significantly inhibited in vivo growth of glioma allografts and xenografts (p<0.05), rescued the antitumoral immune response, significantly decreased the PD-L1+, and glioma-associated macrophage population, and increased cytotoxic lymphocyte infiltration (p<0.05). Mechanistically, TLX binds directly to CD274 (PD-L1) gene promoter and activates CD274 transcription.Conclusions TLX contributes to glioma malignancy and immunosuppression through transcriptional activation of PD-L1 ligands that bind to PD-1 expressed on both TILs and TAMs. Thus, targeting the druggable TLX may have potential therapeutic significance in glioma immune therapy.Data are available in a public, open access repository. Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplemental information. Yes.