负性共刺激分子B7H5(VISTA)在结直肠癌组织表达的临床意义及在肿瘤免疫逃逸中的作用机制

As an important immune checkpoint molecule, negative co-stimulatory molecule B7H5 plays a crucial role in the process of tumor immune escape. The B7H5 receptor has not yet been found, therefore the clinical significance and the exact mechanism of B7H5 in the tumor microenvironment remain to be discussed. Our preliminary experimental results show that: (1) B7H5 is abnormal expressed by tumor-associated macrophage (TAM) in the microenvironment of CRC; (2) The level of B7-H5 is correlated with the poor prognosis of CRC patients; (3) B7H5 could inhibit T cells proliferation and cytokines (IL-2, IFN-γ) secretion. To this end, we proposed the hypothesis that B7H5, which is abnormally expressed by TAM, promotes the tumor immune escape by inhibiting the function of immune cells such as T cells. To test this hypothesis, we analyze the clinical significance of B7H5 in CRC patients, and we certify the role of B7H5 at the cellular and molecular levels. In addition, we interfere the function of B7H5 by blocking antibody both in tumor-bearing animal model and in vitro experiment, further clear the role of B7H5 in tumor immune escape. This project not only clarifies the molecular mechanism of B7H5 playing a role in the process of CRC immune escape, but also provides a theoretical and practical basis for B7H5 as new therapeutic targets for cancer.

负性共刺激分子B7H5是新近倍受关注的免疫卡控点分子，参与肿瘤的免疫逃逸，但鉴于B7H5受体尚未发现，B7H5在肿瘤微环境中的临床意义和确切的作用机制尚待探讨。预实验发现B7H5在结直肠癌（CRC）组织肿瘤相关巨噬细胞（TAM）呈高水平表达，并与CRC患者不良预后密切相关。B7H5可有效抑制T细胞的增殖和细胞因子（IL-2、IFN-γ）分泌。为此我们提出假说，在CRC的肿瘤微环境中，B7H5异常表达于TAM，并通过抑制T细胞等免疫细胞的功能来促进肿瘤细胞的免疫逃逸。为此本项目以CRC为研究对象，B7H5为靶分子，TAM表达B7H5为切入点，通过临床样本分析并在细胞和分子水平验证，采用自主研发的阻断性抗体进行荷瘤动物和体外干预实验进一步证实B7H5阻断在肿瘤免疫逃逸中的作用。本项目不仅阐明在CRC中B7H5介导免疫逃逸的分子机制，同时也为B7H5作为肿瘤的新型治疗靶点提供了理论和实践依据。

B7-H5是重要的B7共信号分子超家族成员之一。本项目经过研究发现，结直肠癌患者癌组织中B7-H5表达显著升高，并与淋巴结转移、AJCC显著正相关而与CD8+T细胞浸润呈负相关性。此外，B7-H5高表达的患者生存预后相比于低表达患者更差。本项目为明确B7-H5信号对结直肠癌免疫逃逸的作用机制，我们利用B7-H5阻断抗体干预MC38小鼠荷瘤模型。结果表明B7-H5信号阻断可以显著抑制小鼠MC38异位肿瘤的生长以及CD8+T细胞的浸润，从而促进结直肠癌细胞的免疫逃逸。项目组还利用CD8+T细胞阻断抗体证实B7-H5信号促进结直肠癌细胞的免疫逃逸是通过调控CD8+T细胞浸润和功能实现的。此外，项目组通过生物信息学的方法发现B7-H5可能涉及细胞代谢、天然免疫和肿瘤免疫逃逸等过程。综上，本项目阐明了B7-H5调控结直肠癌免疫逃逸的作用和机制，为结直肠癌的免疫治疗提供新的候选靶点。