Background:Glioblastoma (GBM) is the most common and aggressive form of primary brain tumor. Although numerous postoperative therapeutic strategies have already been developed, including radiotherapy, tumors inevitably recur after several years of treatment. The coinhibitory molecule B7-H4 negatively regulates T cell immune responses and promotes immune escape. Exosomes mediate intercellular communication and initiate immune evasion in the tumor microenvironment (TME). Objective:This study aimed to determine whether B7-H4 is upregulated by radiation and loaded into exosomes, thus contributing to immunosuppression and enhancing tumor growth. Methods:Iodixanol density-gradient centrifugation and flow cytometry were used to verify exosomal B7-H4. Naïve T cells were differentiated into Th1 cells, with or without exosomes. T cell-secreted cytokines and markers of T cell subsets were measured. Mechanistically, the roles of B7-H4, and ALIX in GBM were analyzed using databases and tissue samples. Co-immunoprecipitation, and pull-down assays were used to tested the direct interactions between ATM and ALIX or STAT3. In vitro ATM kinase assays, western blotting, and site-directed mutation were used to assess ATM-mediated STAT3 phosphorylation. Finally, the contribution of exosomal B7-H4 to immunosuppression and tumor growth was investigated in vivo. Results:Exosomes from irradiated GBM cells decreased the anti-tumor immune response of T cell in vitro and in vivo via delivered B7-H4. Mechanistically, irradiation promoted exosome biogenesis by increasing the ATM-ALIX interaction. Furthermore, the ATM-phosphorylated STAT3 was found to directly binds to the B7-H4 promoter to increase its expression. Finally, the radiation-induced increase in exosomal B7-H4 induced FoxP3 expression during Th1 cell differentiation via the activated STAT1 pathway. In vivo, exosomal B7-H4 decreased the radiation sensitivity of GBM cells, and reduced the survival of GBM mice model. Conclusion:This study showed that radiation-enhanced exosomal B7-H4 promoted immunosuppression and tumor growth, hence defining a direct link between irradiation and anti-tumor immune responses. Our results suggest that co-administration of radiotherapy with anti-B7-H4 therapy could improve local tumor control and identify exosomal B7-H4 as a potential tumor biomarker.Keywords:B7-H4; Exosome; Glioblastoma (GBM); Tumor microenvironment (TME).

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乐备实（上海优宁维生物科技股份有限公司旗下全资子公司），是国内专注于提供高质量蛋白检测以及组学分析服务的实验服务专家，自2018年成立以来，乐备实不断寻求突破，公司的服务技术平台已扩展到单细胞测序、空间多组学、流式检测、超敏电化学发光、Luminex多因子检测、抗体芯片、PCR Array、ELISA、Elispot、PLA蛋白互作、多色免疫组化、DSP空间多组学等30多个，建立起了一套涵盖基因、蛋白、细胞以及组织水平实验的完整检测体系。

 
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