Immunosuppression by adenosine is an important cancer immune checkpoint. Extracellular adenosine signals through specific receptors and can be transported across the cell membrane through nucleoside transporters. While adenosine receptors are well-known to regulate tumor immunity, the impact of adenosine transporters remains unexplored. In this study, we investigated the effect on tumor immunity of equilibrative nucleoside transporter-1 (ENT1), the major regulator of extracellular adenosine concentrations. Blocking or deleting host ENT1 significantly enhanced CD8+ T cell-dependent antitumor responses. Tumors inoculated into ENT1-deficient mice showed increased infiltration of effector CD8+ T cells with an enhanced cytotoxic transcriptomic profile and significant upregulation of granzyme B, IFN-γ, IL-2, TNF-α, and CXCL10. ENT1-deficiency was further associated with decreased tumor-infiltrating T regulatory cells and CD206high macrophages and suppressed CCL17 production. ENT1-deficiency notably potentiated the therapeutic activity of PD-1 blockade. T cells upregulated ENT1 upon activation, and blocking ENT1 enhanced their function when co-cultured with cognate antigen/HLA-matched melanoma cells. Mechanistically, ENT1-mediated adenosine uptake inhibited the activity of phosphoribosyl pyrophosphate synthetase (PRPS) in activated T cells, thereby suppressing production of uridine 5′-monophosphate (UMP) and its derivatives required for DNA and RNA synthesis. In summary, this study identified ENT1-mediated adenosine uptake as an important mechanism of adenosine-mediated immunosuppression and pyrimidine starvation that can be targeted to enhance antitumor T cell responses.

中文翻译：

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通过核苷转运蛋白 ENT1 摄取腺苷抑制抗肿瘤免疫和 T 细胞嘧啶合成


腺苷的免疫抑制是一个重要的癌症免疫检查点。细胞外腺苷通过特异性受体发出信号，并可通过核苷转运蛋白穿过细胞膜运输。虽然腺苷受体可调节肿瘤免疫，但腺苷转运蛋白的影响仍未得到探索。在这项研究中，我们研究了平衡核苷转运蛋白 1 （ENT1） 对肿瘤免疫的影响，ENT1 是细胞外腺苷浓度的主要调节因子。阻断或删除宿主 ENT1 显著增强了 CD8+ T 细胞依赖性抗肿瘤反应。接种到 ENT1 缺陷小鼠中的肿瘤显示效应 CD8+ T 细胞浸润增加，细胞毒性转录组谱增强，颗粒酶 B 、 IFN-γ、IL-2 、 TNF-α 和 CXCL10 显著上调。ENT1 缺陷进一步与肿瘤浸润 T 调节细胞和 CD206 高巨噬细胞减少相关，并抑制 CCL17 的产生。ENT1 缺陷显着增强了 PD-1 阻断的治疗活性。T 细胞在激活时上调 ENT1，阻断 ENT1 在与同源抗原/HLA 匹配的黑色素瘤细胞共培养时增强了它们的功能。从机制上讲，ENT1 介导的腺苷摄取抑制活化 T 细胞中磷酸核糖焦磷酸合成酶 （PRPS） 的活性，从而抑制 DNA 和 RNA 合成所需的尿苷 5′-单磷酸 （UMP） 及其衍生物的产生。综上所述，本研究发现 ENT1 介导的腺苷摄取是腺苷介导的免疫抑制和嘧啶饥饿的重要机制，可以靶向增强抗肿瘤 T 细胞反应。