SLC38A2 and glutamine signaling in cDC1 dictate anti-tumor immunity [scRNA-Seq 2]

Cancer cells evade T-cell-mediated killing through poorly understood mechanisms of tumour–immune interactions. Dendritic cells (DCs), especially type-1 conventional DCs (cDC1), mediate T-cell priming and therapeutic efficacy against tumours. Besides pattern recognition receptors (PRRs), how DC functions are shaped by other environmental cues remains incompletely defined. Nutrients are emerging mediators of adaptive immunity, but whether nutrients impact DC function or innate–adaptive cell communication is largely unresolved. Here, we establish glutamine as an intercellular metabolic checkpoint to mediate tumour–cDC1 crosstalk and license cDC1 functionality for activating cytotoxic T cells. Intratumoral glutamine supplementation inhibits tumour growth by augmenting cDC1-mediated CD8+ T-cell immunity, and also overcomes therapeutic resistance to checkpoint blockade and T-cell-mediated immunotherapies. Mechanistically, tumour cells and cDC1 compete for glutamine uptake via transporter SLC38A2 to tune anti-tumour immunity. Nutrient screening and integrative analyses show that glutamine is the dominant amino acid for promoting cDC1 function, by signalling via FLCN to impinge upon TFEB function. Loss of FLCN in DCs selectively impairs cDC1 function in vivo in a TFEB-dependent manner, and phenocopies SLC38A2 deficiency by abrogating anti-tumour therapeutic effect of glutamine supplementation. Our findings establish glutamine-mediated intercellular metabolic crosstalk between tumour cells and cDC1 that underpins tumour immunoevasion, and reveal glutamine acquisition and signalling in cDC1 as limiting events for DC activation and putative targets for cancer treatment. Overall design: Wild-type mice were challenged with MC38 colon adenocarcinoma cells, and treated with PBS or glutamine daily starting from day 5. Anti-PD-1 antibody or rat IgG2b isotype control was injected intraperitoneally three times on day 7, 10 and 13. CD45- tumour cells, macrophages (CD45+CD64+), CD45+ non-macrophage immune cells (CD45+CD64-), and dendritic cells (CD45+CD64-CD11c+MHC-II+) in the tumour tissues were sorted at 15 d after tumour challenge and mixed at a 1:1:4:5 ratio (n = 2 biological replicates per group).

癌细胞通过尚未完全阐明的肿瘤-免疫互作机制逃逸T细胞介导的杀伤作用。树突状细胞（Dendritic cells, DCs），尤其是1型常规树突状细胞（type-1 conventional DCs, cDC1），介导T细胞致敏及抗肿瘤治疗效应。除模式识别受体（pattern recognition receptors, PRRs）外，其他环境信号如何调控DC功能仍未完全明确。
营养物质正逐渐被发现是适应性免疫的调控介质，但营养物质是否影响DC功能或先天-适应性细胞通信，在很大程度上仍未得到解决。
本研究确立谷氨酰胺作为一种细胞间代谢检查点，介导肿瘤与cDC1的互作，并赋予cDC1激活细胞毒性T细胞的功能。瘤内补充谷氨酰胺可通过增强cDC1介导的CD8+ T细胞免疫应答抑制肿瘤生长，同时还可克服对免疫检查点阻断及T细胞介导的免疫治疗的治疗抗性。
从机制上讲，肿瘤细胞与cDC1通过转运蛋白SLC38A2竞争摄取谷氨酰胺，以此调控抗肿瘤免疫。营养物质筛选与整合分析显示，谷氨酰胺是促进cDC1功能的核心氨基酸，其通过FLCN信号通路影响TFEB的功能。DC中FLCN的缺失会以TFEB依赖的方式在体内选择性损伤cDC1功能，并通过消除谷氨酰胺补充的抗肿瘤治疗效应，模拟SLC38A2缺陷的表型。
本研究揭示了肿瘤细胞与cDC1之间谷氨酰胺介导的细胞间代谢互作是肿瘤免疫逃逸的基础，并阐明了cDC1对谷氨酰胺的摄取与信号通路是DC激活的限制性事件，同时也是潜在的癌症治疗靶点。
总体实验设计：将野生型小鼠接种MC38结肠腺癌细胞，自第5天起每日以PBS或谷氨酰胺进行处理。分别于第7、10、13天三次腹腔注射抗PD-1抗体或大鼠IgG2b同型对照。于肿瘤接种后15天，分选肿瘤组织中的CD45-肿瘤细胞、巨噬细胞（CD45+CD64+）、CD45+非巨噬细胞免疫细胞（CD45+CD64-）以及树突状细胞（CD45+CD64-CD11c+MHC-II+），以1:1:4:5的比例混合（每组n=2个生物学重复）。