补体C3a/C3aR途径调节Tregs功能及其在抗肿瘤免疫中的作用机制

Blocking PD1 / PDL1 to rescue the exhaustion of CD8+ T cells can improve the antitumor effect in patients with a broad spectrum of cancers. However, this improvement is only observed in a subset of patients. To explore the mechanism of the inhibited anti-tumor immune by tumor microenvironment remains a central theme. We found that the complement C3 produced by the tumor itself significantly inhibited the anti-tumor response of CD8+ T cells, and decreased the anti-PDL1 treatment sensitivity, which was related to the complement C3aR. We further found that the local Tregs from the tumor microenviroment expressed C3aR, and their inhibitory function was enhanced. In this study we will identify C3aR+ Tregs phenotype, and the related signaling pathways, etc., to research the roles of C3a/C3aR pathway on the enhanced immunosuppressive function of Tregs in vivo and in vitro.The correlation between C3a/C3aR pathway and the clinical PDL1 therapy will be evaluated as well. In addition, we will map the chromatin accessibility of Tregs with positive and negative expression of C3aR,respectively, and explore the regulatory mechanism for C3aR expression by using transcriptome study, quantitative PCR, ChIP and reporter assay.The expected results not only help to understand the mechanism of C3aR expression in tregs,and the roles of C3aR in the immunosuppressive function of Tregs in tumor microenvironment, but also help to find new drug targets for anti-tumor treatment.

阻断PD1/PDL1来挽救耗竭CD8+T细胞已取得令人鼓舞的临床抗肿瘤效果，但仅对部分患者有效。探讨肿瘤微环境抑制抗肿瘤免疫的机制仍是当前研究重点。动物荷瘤实验中，我们发现：肿瘤自身产生的补体C3能显著抑制CD8+T细胞的抗肿瘤免疫，降低anti-PDL1治疗敏感性，且与补体C3aR相关。进一步发现，肿瘤局部的Tregs表达C3aR，且抑制功能更强。本项目拟从C3aR+Tregs表型、信号通路等方面，体内外、正反向探讨该群Tregs抑制功能增强的原因；进而研究C3a/C3aR途径与临床PDL1治疗的相关性。另外，拟绘制C3aR+和C3aR-Tregs染色质可接近性图谱，结合转录组学、定量PCR、ChIP、报告基因等手段研究C3aR表达的调控机理。预期结果不但可理解肿瘤微环境影响C3aR表达及C3aR调节Tregs免疫抑制功能的机制，同时可能发现新的抗肿瘤药物靶标。

近年来，针对PD-1/PD-L1等免疫检查点的抗体药物在肿瘤的免疫治疗中有重要进展。然而，其仅在部分病人有效。肿瘤微环境和宿主的异质性是导致疗效差异的重要原因。补体是天然免疫的重要组成成分，但在肿瘤微环境形成中的作用和机制仍不清楚。我们发现肿瘤细胞自身表达的补体C3能在其细胞内活化，产生的活化片段C3a可与表达其受体C3aR的Treg、CAF和TAM等细胞结合，激活相关的信号通路，促进肿瘤微环境的形成，阻断抗肿瘤免疫。阻断C3a/C3aR途径能有效解除抗PD-L1抗体的免疫耐受，显著改善其治疗效果。此外，我们利用ATAC-seq和CUT&Tag技术同时整合转录组数据，探讨了肿瘤局部Treg免疫抑制功能强于外周血Treg的可能机制，我们发现在肿瘤浸润Treg中存在两种类型的活性增强子；AP-1家族基序在肿瘤浸润Treg的增强子区域富集。最后，我们验证了AP-1在调控区域结合以调节肿瘤浸润Treg的特征基因，并且Ap-1是体外Treg细胞激活所必需的。Ap-1家族的c-Jun高表达与人类肝细胞肝癌患者的生存率相关。总的来说，我们的研究结果为c- jun介导的肿瘤浸润Treg激活机制提供了深入的了解，并有望用于开发新的靶向肿瘤浸润Treg的治疗策略。