肿瘤相关巨噬细胞外泌体激活胃癌细胞干扰素信号通路在免疫检查点抑制剂治疗耐药中的作用和机制

Recent clinical trials using immune checkpoint blocking (ICB) antibodies have displayed durable clinical responses in various cancers including gastric cancer. Although these new immunotherapies have had a notable effect on cancer treatment, multiple mechanisms of immune resistance exist in tumors. Despite these impressive clinical results, the majority of patients are either resistant or relapse after therapy, highlighting the need to understand mechanisms that drive resistance. There is an urgent need to expand the proportion of patients that respond to immune checkpoint therapy. Growing evidences have suggested that tumor interferon signaling regulates a multigenic resistance program to immune checkpoint blockade. Interestingly, our preliminary data showed that tumor-associated macrophages (TAMs) derived exosome induce the activation of tumor interferon signaling pathway. In addition, the frequency of TAMs have been associated with the responsiveness to immune checkpoint blockade in gastric cancer. .Based on current progression and our preliminary data, we propose the hypothesis that induction of tumor interferon signaling by tumor-associated macrophages derived exosome regulate resistance program to immune checkpoint blockade. To accomplish this interesting project, we firstly will evaluate the effect of TAMs exosome on the responsive of ICB by in vivo gastric cancer model. Secondly, we will identify the functional microRNA or protein carried by exosome and intend to dissect the mechanism of TAMs-derived exosome to regulate IFN signaling pathway in tumor cells increases resistance to immune checkpoint blockade through multiple inhibitory pathways. Furthermore, selective pharmacologic targeting of PI3Kγ to repolarized TAMs, exosomes secreting inhibitor, and/or IFN signaling inhibitor were tested to check if these monotherapies or combination therapy restores sensitivity to immune checkpoint blockade.

免疫检查点抑制剂（ICB）对胃癌等多种肿瘤的临床疗效显著。然而大部分肿瘤患者对ICB治疗并不敏感，且部分敏感患者会逐渐出现耐药性，因此如何克服其耐药性是目前最大的挑战。最新研究证实肿瘤细胞干扰素信号通路持续活化介导ICB耐药性。我们前期研究意外发现肿瘤相关巨噬细胞（TAM）外泌体可刺激胃癌细胞IFN通路活化，且TAM影响胃癌ICB治疗抵抗。因此提出假说TAM通过外泌体调控胃癌细胞IFN通路活化抵抗ICB治疗。本项目拟首先通过体内外模型证实TAM外泌体对胃癌ICB治疗的抵抗作用。利用RNA表达谱/蛋白质谱鉴定调控IFN通路的TAM外泌体关键靶分子。然后体外沉默实验阐明该外泌体靶分子活化胃癌IFN通路诱导胃癌免疫逃逸的分子机制。最后应用巨噬细胞极化抑制剂、外泌体释放抑制剂、IFN信号抑制剂分别联合ICB治疗小鼠模型拟发现有效的、可用于临床转化的胃癌免疫治疗方案，使更多的胃癌患者受益于免疫治疗。

研究背景：靶向T免疫细胞的免疫检查点阻断剂（ICB）肿瘤治疗对部分患者临床效果显著，但目前大部分患者对ICB治疗耐药。其中重要的原因就是肿瘤微环境中大量存在免疫抑制性M2肿瘤相关巨噬细胞（TAMs) 可限制ICB的治疗疗效。然而，由于M2-TAMs在肿瘤发生发展中的功能和具体的分子特征尚不明确，因此目前临床还没有针对性的靶向调控巨噬细胞的治疗方案。为了提高ICB治疗的疗效，需要更好地理解M2-TAMs介导的免疫逃避机制并设计针对性的联合治疗方案。.研究内容和主要结果：通过本项目的实施，我们新发现免疫抑制性M2巨噬细胞可分泌外泌体诱导肿瘤细胞抵抗细胞毒性CD8+T细胞的杀伤，从而限制ICB的治疗疗效。蛋白质组学高通量筛选结合功能学实验研究证实，M2巨噬细胞外泌体（M2-Exo）通过下调肿瘤细胞MHC-I分子表达，降低肿瘤细胞自身免疫原性诱导免疫逃逸。具体的分子机制是M2巨噬细胞以M2-Exo外泌体形式传递载脂蛋白E（ApoE)到肿瘤细胞，通过直接结合并降低了肿瘤细胞的结合免疫球蛋白（BiP）ATP酶活性，触发内质网应激，从而降低肿瘤细胞MHC-I的表达。体内临床前动物模型发现，ApoE配体EZ-482可阻断M2-Exo的功能，增强BiP的ATP酶活性来提高肿瘤免疫原性，从而提高CD8+T细胞依赖性肿瘤杀伤活性，从而提高ICB疗效。因此，ApoE有望作为ICB治疗耐药的预测因子和潜在的治疗靶点。.结论和临床意义：该项目研究揭示了M2巨噬细胞调控免疫逃逸的新机制：M2巨噬细胞通过外泌体介导的功能性ApoE蛋白传递抑制肿瘤免疫原性，从而诱导ICB治疗抵抗。该项目的研究进一步确立了ApoE配体EZ-482联合ICB治疗用于富含肿瘤相关巨噬细胞的肿瘤免疫治疗的临床前理论基础。