负向免疫调控分子TREM-2在肺癌发病中的作用及机制研究

Overexpression of negative regulatory molecules contribute to the defective immune responses and the promotion of immune escape in tumor microenvironment. Recent studies indicated that TREM-2 paired with DAP12 had a critical role in negative regulation of DC and Mφ activation upon TLR ligation during inflammation. Dispite of the distinctions in the initiation and sustainment of immune response,there were strong similarities between inflammaiton and tumor in immunoregulation,suggesting that TREM-2 might exert as a inhibitory receptor in tumor immunity.Our previous study showed that TREM-2 expression on monocytes was up-regulated in lung cancer patients compared with that of healthy controls, and TREM-2 levels of macrophages increased in malignance in contrast to benign diseases. Moreover, TREM-2 can be induced through mimicking tumor microevironment. Next,we will investigate the effect of TREM-2 on metastasis,chemotherapy and survival among patients,and explore the further mechanism of TREM-2 mediated immune evasion in vitro and in vivo. This study will provide new mechanism for tumor immune escape and inhibitory checkpoint for immunotherapy.

诱导免疫细胞过度表达负向免疫调控分子进而抑制荷瘤机体的免疫功能是肺癌细胞实现免疫逃逸的重要机制之一。TREM-2能够抑制树突状细胞（DC）和巨噬细胞（Mφ）的吞噬功能以及促炎细胞因子的释放而下调炎症反应。肿瘤与炎症尽管在免疫应答的启动和持续方面有着本质区别，但在免疫调节方面存在着不少相似并可互为借鉴之处，因此，我们推测 TREM-2可能参与了肺癌免疫逃逸的发生。先期研究发现肺癌患者外周血中单核细胞表达TREM-2的比例及丰度均较健康者增高、恶性病变者手术标本切片中Mφ的TREM-2表达高于良性者以及肿瘤微环境可以诱导DC过表达TREM-2。本项目拟进一步分析TREM-2与肺癌转移、化疗疗效以及患者远期生存的关系；通过体内外实验探讨TREM-2介导的肺癌免疫逃逸发生的分子机制以及所需的下游信号通路。该项目的完成有望为肺癌免疫逃逸机制增添新的认识，为筛选肺癌免疫治疗的新靶点提供一定的理论依据。

诱导免疫细胞过度表达负向免疫调控分子进而抑制荷瘤机体的免疫功能是肺癌细胞实现免疫逃逸的重要机制之一。在炎症过程中，髓系细胞触发受体-2（TREM-2）能够结合接头蛋白DAP-12启动免疫抑制性信号通路来抑制DC和巨噬细胞的吞噬功能以及促炎因子的释放而下调炎症反应。在本研究中，我们发现在肺癌患者和荷瘤小鼠的外周血单核细胞表面TREM-2的表达明显增高；荷瘤小鼠肺组织中TREM-2+DC数量明显多于正常小鼠；另一方面，肺癌患者的肺组织中巨噬细胞表面TREM-2表达高于良性疾病的患者，并且TREM-2的表达水平与病理分期呈正相关；通过手术和化疗手段减轻肿瘤负荷可以明显降低TREM-2的表达。在体外条件下，3LL肺腺癌细胞上清可以诱导骨髓来源的DC和巨噬细胞表达更多的TREM-2，而这些来自于肿瘤上清或者荷瘤小鼠肺组织的TREM-2+DC表现为CD80LowCD86LowMHCIILowDC表型，并伴随着功能受损，比如IL-12分泌减少，IL-10分泌增高和OVA内吞能力减弱。更重要的是，这些肿瘤微环境来源的TREM-2+DC可以明显抑制T细胞的增殖，并且这种作用可以被抗TREM-2的抗体部分逆转；进一步地，我们还发现Syk抑制剂可以减少TREM-2+DC分泌IL-10，而IL-10中和抗体和Syk抑制剂R406均可减轻TREM-2+ DC对T细胞增殖的抑制作用。荷瘤小鼠过继回输TREM-2+DC可以加速肿瘤的生长，但对小鼠的生存期没有影响。综上所述，我们认为TREM-2在肺癌发病中通过Syk-IL-10途径发挥负向免疫调控作用。