The impact of amino acids on tumor immunotherapy is gradually being uncovered. In this study, we screened various essential and non-essential amino acids and found that methionine enhances mRNA methylation and reduced the activation of Type I interferon pathway in bladder cancer. Through RNA sequencing, point mutations, MB49 mouse tumor models, and single-cell RNA sequencing, we demonstrated that high methionine levels elevate the expression of m⁶A reader YTHDF1, promoting the degradation of RIG-I, thereby inhibiting the RIG-I/MAVS-mediated IFN-I pathway and reducing the efficacy of tumor immunotherapy. Additionally, immunoprecipitation and mass spectrometry revealed that YTHDF1 binds to the eukaryotic translation initiation factor eIF5B, which acts on PD-L1 mRNA to enhance its translation and promote immune evasion. By intravesical administration of oncolytic bacteria VNP20009, we effectively depleted methionine locally, significantly prolonging mouse survival and enhancing immune cell infiltration and differentiation within tumors. Multiplex immunofluorescence assays in bladder cancer immunotherapy patients confirmed our findings. Our research elucidates two mechanisms by which methionine inhibits bladder cancer immunotherapy and proposes a targeted methionine depletion strategy that advances research while minimizing nutritional impact on patients.

氨基酸对肿瘤免疫治疗的影响正在逐渐被揭示。在这项研究中，我们筛选了各种必需和非必需氨基酸，发现蛋氨酸增强了膀胱癌中 mRNA 甲基化并减少了 I 型干扰素通路的激活。通过 RNA 测序、点突变、MB49 小鼠肿瘤模型和单细胞 RNA 测序，我们证明高蛋氨酸水平会提高 m⁶A 读取器 YTHDF1 的表达，促进 RIG-I 的降解，从而抑制 RIG-I/MAVS 介导的 IFN-I 通路，降低肿瘤免疫治疗的疗效。此外，免疫沉淀和质谱分析显示，YTHDF1 与真核翻译起始因子 eIF5B 结合，该因子作用于 PD-L1 mRNA 以增强其翻译并促进免疫逃逸。通过膀胱内施用溶瘤菌 VNP20009，我们有效地局部耗尽了蛋氨酸，显着延长了小鼠的存活时间并增强了肿瘤内免疫细胞的浸润和分化。膀胱癌免疫治疗患者的多重免疫荧光测定证实了我们的发现。我们的研究阐明了蛋氨酸抑制膀胱癌免疫治疗的两种机制，并提出了一种靶向蛋氨酸耗竭策略，该策略可推进研究，同时最大限度地减少对患者的营养影响。