ICOS通过促进Th1细胞极化抑制结直肠癌发生发展的机制研究

Colorectal cancer (CRC) is a very common cancer with a high mortality and incidence rate. Recently, the role of B7-CD28 family in tumor immunology has gradually been recognized and the inducible T-cell co-stimulator (ICOS), the one of new members of these family, has the ability of maintaining T cell activity. However, the role of ICOS played in CRC remains poorly understood. Our previous study showed that ICOS is mainly expressed on CD4+ T cells, and ICOS expression is positively associated with the progress of CRC patients. By using flow cytometry and CCK-8 assays, we found that ICOS+CD4+ T cells have the molecular characteristics of Th1 cells, and inhibit the growth of tumor cells in CRC, suggesting that ICOS may be one of the markers of Th1 cells and plays an important role in the CD4+ T cells to Th1 polarization in CRC. Therefore, this projects will confirm the association in a large sample size and verify ICOS+CD4+ T cells belonging to Th1 cells which have the effect of killing tumor cells in CRC. Furthermore, we will study the mechanism on ICOS promoting the CD4+ T cells to Th1 polarization in CRC and explore the posibility of Akt/mTOR/STAT1 signaling pathway involved in ICOS-induced Th1 polarization. More importantly, by using mouse xenograft model of CRC, our study will evaluate that the antitumor activity of ICOS in CD4+ T cells by promoting Th1 polarization, which provides a new target for CRC cellular immunotherapy.

结直肠癌（CRC）发病率和死亡率居高不下。近年来B7-CD28家族在肿瘤免疫中的作用逐渐被关注，ICOS作为其家族新成员之一，具有维持T细胞活性的特点，在CRC中作用机制尚不清楚。我们前期研究已发现，在CRC中ICOS主要表达在CD4+T细胞中，并且与患者预后呈正相关。在此研究基础上，通过预实验发现ICOS+CD4+T细胞具有Th1细胞的分子特性，且可以抑制肿瘤细胞的生长。上述结果提示ICOS在CRC中可能是Th1细胞的标记物之一，并在CD4+T细胞向Th1极化中发挥重要作用。因此，本研究拟在CRC大样本中进一步明确ICOS+CD4+T细胞是一群Th1细胞，且具有杀伤肿瘤细胞的作用；揭示ICOS可能通过Akt/mTOR/STAT1通路促进Th1极化的分子机制；更为重要的是，在CRC小鼠移植瘤中评价ICOS通过促进Th1极化来发挥抗肿瘤活性作用，为CRC临床细胞免疫治疗提供新靶标。

在我国结直肠癌发病率和死亡率居高不下。ICOS作为B7-CD28家族族新成员，具有维持T细胞活性的特点，但在CRC中作用机制尚不清楚。本课题首先在324例结直肠癌组织样本中进行ICOS免疫组织实验，结果表明，ICOS高表达的结直肠癌患者5年总生存率和5年无病生存率相对较高，尤其是对于中晚期结直肠癌患者ICOS的表达水平与结直肠癌患者预后呈正相关性；接着，通过构建结直肠癌类器官模型与免疫细胞共培养体系，发现高表达的ICOS可以抑制结直肠肿瘤细胞的生长；通过Transwell实验，在结直肠癌原代细胞与免疫细胞共培养发现，高表达的ICOS可以抑制结直肠癌细胞的侵袭能力；在机制上，我们首先通过RNA测序等生物信息学技术发现，高表达的ICOS可以激活PI3K/Akt/mTOR信号通路；接着，课题组通过流式细胞学技术分选出肿瘤细胞和ICOS+CD4+ T细胞或ICOS+CD4- T细胞，通过western blotting实验发现，高表达的ICO激活CD4+ T细胞内的PI3K/Akt/mTOR信号通路，而肿瘤细胞中该信号通路无统计学差异；课题组进一步发现高表达的ICOS可以促进CD4+ T细胞内的STAT1磷酸化，促进T-bet的表达，促进CD4+ T细胞分泌INF-γ、TNF-α、IN-12细胞因子杀伤肿瘤细胞。最后在结直肠癌类器官模型中，阐述ICOS联合anti-PD-1的免疫治疗可以抑制结直肠癌细胞的生长。总之，本课题的研究结果将有助于加深理解免疫微环境在结直肠癌发生发展中的作用，为今后结直肠癌的临床细胞免疫治疗提供新的潜在靶点和依据。