Ablation of cDC1 development by IL-6-induced C/EBPb support in the -165 kb Zeb2 enhancer

Type 1 conventional dendritic cells (cDC1) are required for effective CD8 T cell responses to many viruses and tumors and for effective checkpoint blockade immunotherapy. Recently, cytokines produced in association with certain tumors were reported to impair anti-tumor immune responses by reducing the abundance of cDC1. However, the reported mechanism of this reduction remains unclear, attributed either to reduced cDC1 development or decreased peripheral cDC1 survival. Here we show that tumor-derived IL-6 blocks cDC1 development from both in murine and human systems. We show that mechanism of this blockade is the IL-6-dependent increase in C/EBPß expression in the common dendritic cell progenitor (CDP). C/EBPß and NFIL3 compete for binding to sites in the -165 kb Zeb2 enhancer, and support or repress Zeb2 expression respectively. At homeostastis, pre-cDC1 specification occurs upon Nfil3 induction and consequent Zeb2 suppression. However, IL-6 strongly induces C/EBPß expression in CDPs, thereby preventing normal NFIL3-dependent pre-cDC1 specification. Importantly, the ability of IL-6 to block cDC1 development is dependent on the presence of C/EBPß binding sites in the -165 kb Zeb2 enhancer, as this effect is lost in ?1+2+3 mutnat mice in which these binding sites are mutated. These results explain how tumor-associated IL-6 suppresses cDC1 development and suggest therapeutic approaches preventing abnormal C/EBPß induction in CDPs may help reestablish cDC1 development to enhance anti-tumor immunity. Overall design: mRNA profiles of mouse bone marrow CDP treated with Flt3L alone or Flt3L plus IL-6 to examine transcriptional control mechanism of IL-6 for CDP specification toward cDC1 and cDC2

1型常规树突状细胞（cDC1）是介导针对多种病毒与肿瘤的有效CD8 T细胞应答、以及实现免疫检查点阻断免疫治疗的必需细胞。近期有研究报道，特定肿瘤伴随产生的细胞因子可通过降低cDC1的丰度，削弱抗肿瘤免疫应答。但目前该丰度降低的具体机制仍不明确，既往研究将其归因于cDC1发育受损或外周cDC1存活能力下降。本研究证实，肿瘤来源的白细胞介素6（IL-6）可在小鼠和人类体系中阻断cDC1的发育过程。进一步研究发现，该阻断作用的机制为：IL-6以依赖自身的方式上调常见树突状细胞祖细胞（CDP）内CCAAT增强子结合蛋白β（C/EBPβ）的表达。C/EBPβ与核因子白细胞介素3调控因子（NFIL3）竞争性结合位于-165 kb位点的Zeb2增强子区域，二者分别对Zeb2的表达起到抑制与促进作用。在生理稳态下，Nfil3的诱导可启动前cDC1特化过程，并伴随Zeb2表达的抑制。然而，IL-6可强烈诱导CDP内C/EBPβ的表达，从而阻断正常依赖NFIL3的前cDC1特化进程。值得注意的是，IL-6阻断cDC1发育的能力，依赖于-165 kb Zeb2增强子区域内的C/EBPβ结合位点：当该结合位点在Δ1+2+3突变小鼠中发生突变后，IL-6的该阻断效应便会消失。上述结果阐明了肿瘤相关IL-6抑制cDC1发育的分子机制，并提示：通过干预CDP内异常的C/EBPβ诱导过程，或可重建cDC1发育，从而增强抗肿瘤免疫应答。总体实验设计：将小鼠骨髓CDP分别用Flt3L单独处理，或Flt3L联合IL-6处理，随后进行mRNA转录组分析，以解析IL-6调控CDP向cDC1与cDC2分化的转录控制机制。