TLR2信号逆转MDSC介导的肝癌免疫抑制

Immunotherapy has become a new field for the treatment of hepatocellular carcinoma, among of which, Toll like receptors (TLR) have been proposed to play an important role in this area. In previous studies, TLR agonists have been indicated in the alleviation of the progression of cancer, but the mechanism is still not fully understood. Our previous data have shown that the deficiency of TLR2 signaling can aggravate the progression of hepatocellular carcinoma, which is accompanied by the notable increase of MDSC. In addition, TLR2 agonist can significantly slow down the progression of liver cancer, and the myeloid derived suppresser cells (MDSCs) are remarkably reduced. Therefore, we hypothesize that TLR2 may affect tumor progression by regulating the expression of MDSC or the polarization process in hepatocellular carcinoma. In this study, we intend to use animal models and clinical patients of liver cancer to explore the regulatory role of TLR2 agonist on MDSC. First, we will evaluate the effect of TLR2 on the polarization process of MDSC by TLR2 agonist through the spontaneous and tumor-bearing model of liver cancer and find the key molecules and signaling pathway in this process. Second, we will compare and analysis the number, phenotype and function of macrophages, dendritic cells, and MDSC, and make a conclusion about the correlation between them to identify the effect of TLR2 on MDSC. Overall, the study will clarify the regulatory mechanism of TLR2 on MDSC, improve the understanding of MDSC polarization, and provide theoretical basis and clinical basis for the immune therapy of liver cancer.

TLR家族在肿瘤免疫中发挥重要作用，活化后能够调控肿瘤进程，但其机制尚未完全揭示。本课题组前期研究表明，TLR2缺失导致肝癌进展加重，MDSC表达显著增加；TLR2激动剂则能够显著减缓肝癌进程，且MDSC明显减少，其下游分化成熟细胞呈活化表型。因此，我们推测TLR2通过上调细胞因子，激活相关信号通路调控MDSC极化过程进而影响肝癌发展。本课题拟分别采用小鼠模型和临床标本来探明TLR2激动剂对MDSC的调控作用，并揭示其作用机制。通过自发以及荷瘤肝癌模型，阐明TLR2是否能够调控MDSC的极化过程，并寻找其中行使调控作用的关键分子和信号通路；比较肝癌病人及健康人群在TLR2激动剂作用下MDSC与巨噬细胞，树突状细胞的数目，表型与功能，验证其表达相关性，同时验证关键靶点分子作用。通过上述研究阐明TLR2分子对MDSC的调控机制，完善MDSC的调控网络，并为肝癌免疫治疗提供理论基础和临床依据。

肝癌的发生发展是肝细胞突变与肿瘤抑制微环境共同作用的结果。MDSC是抑制环境形成的重要因素。靶向MDSC使其向成熟的树突状细胞，巨噬细胞发生分化，是肿瘤治疗的新方向。我们前期的结果发现TLR2激动剂可以减缓肝癌发生进程，并且MDSC数量明显降低，但其具体作用机制还不清楚。因此，我们提出假说，TLR2通过调控MDSC,促进细胞分化，向I型细胞成熟，发挥抗肿瘤作用。. 本研究分别进行了小鼠荷瘤模型，小鼠自发肝癌模型以及临床标本分析等三个层次的实验来进行相关研究。我们在小鼠荷瘤模型中发现TLR2激动剂能够减缓肿瘤发生。进一步的机制研究发现，小鼠荷瘤以后MDSC表达上调，Pam3CSK4处理后MDSC表达降低，同时MDSC中单核细胞样和粒细胞样两种亚群上的TLR2分子均上调表达，说明MDSC呈现出倾向于受TLR2信号调控的表现。与此一致地，我们检测到肿瘤小鼠中RUNX1，β-catenin，CD11C表达降低，而Pam3CSK4能够刺激上述三个分子表达水平恢复正常，以上结果提示我们TLR2可能是通过调节RUNX1/β-catenin相关信号通路使MDSC向DC发生转化。当在TLR2激活后，使用Ro5-3335阻断RUNX1作用，小鼠肿瘤的发展明显加重，MDSC增多，共刺激分子表达下调，初步说明TLR2激动剂通过RUNX1调节MDSC的极化。综上所述，我们发现TLR2激动剂可以减缓肿瘤的进展过程，这一过程是通过MDSC发生转化来实现的。RUNX1在MDSC的转化过程中发挥关键作用，阻断其活性使MDSC更多地停留在不成熟的细胞状态，从而发挥抑制功能。本研究阐明了TLR2激动剂减缓肝癌进展的机制，同时完善了Toll样受体对MDSC的调控网络，为Toll样受体激动剂应用于肝癌治疗提供了理论依据。