癌胚蛋白SALL4再激活诱导免疫细胞耗竭及机制探讨

SALL4 is a new-found oncofetal protein that is expressed in the human fetal liver and silenced in the adult liver, but it is reexpressed in patients who have hepatocellular carcinoma (HCC) and an unfavorable prognosis. Most recent researches focus on the role of SALL4 on tumorigenesis, proliferation, apoptosis, survival, invasive migration, and the maintenance of cancer stem cells (CSCs) of HCC; however, until now, there is no research on whether the reactivation of SALL4 impairs the function of immune cells in liver microenvironment. In our previous work, we have found the high expression of SALL4 in hepatocytes from both HBV-persistent mice and DEN/CCl4-induced HCC mice. Importantly, the levels of SALL4 positively correlates with PD-L1 expression and CD8+T cell exhaustion, while silencing SALL4 by RNAi significantly reverses the exhaustion of CD8+T cells. Based on these finding, we will confirm how the reactivated SALL4 inpairs the phenotype and function of hepatic immune cells (including CD8+T, CD4+T and NK cells) and finally leads to exhaustion through up-regulating the expression of inhibitory ligand PD-L1, Galectin-9 or HVEM. We will clarify the molecular mechanisms about how SALL4 induces immune cell exhaustion and how SALL4 is re-activated in adult hepatocytes. These investigations will provide novel SALL4-based therapeutic strategies for chronic HBV infection and liver cancer.

作为新发现的癌胚蛋白，SALL4高表达于胚胎肝脏，在健康成年肝脏基本沉默，却在肝癌中高表达，且预示着不良的预后。目前的研究多关注SALL4对肝癌发生发展的直接作用，但是SALL4的再激活是否会影响肝脏微环境中免疫细胞的功能及SALL4在成年肝脏再激活的机制尚属空白。我们在前期研究中初步发现HBV可诱导SALL4高表达、且SALL4表达水平与PD-L1表达及肝脏CD8+T细胞功能耗竭成正相关，本研究拟利用HBV感染的肝癌细胞系、HBV慢性持续性感染和肝癌小鼠模型，从免疫学的角度系统验证SALL4再激活通过上调肝细胞表面何种抑制性配体（PD-L1、Galectin-9、HVEM等）对肝脏微环境免疫细胞（CD8+T、CD4+T和NK细胞）表型和功能产生影响，最终诱导免疫细胞耗竭，并阐明SALL4再激活诱导免疫细胞耗竭及SALL4在成年肝脏再激活的分子机制，为慢性乙肝和肝癌的治疗提供新的策略。

SALL4为新发现的癌胚蛋白，高表达于胚胎肝脏，在健康成年肝脏基本沉默，却在肝癌中高表达，且预示着不良的预后。目前的研究多关注SALL4对肝癌发生发展的直接作用，但是SALL4的再激活是否会影响肝脏微环境中免疫细胞的功能及SALL4在成年肝脏再激活的机制尚属空白。. 本研究利用HBV感染的肝癌细胞系、HBV慢性持续性感染和肝癌小鼠模型及临床HBV+肝癌组织标本，系统验证了SALL4在HBV慢性感染和HBV+肝组织高表达，且与PD-L1等抑制性配体表达成正相关。通过HBV+肝癌患者队列进行肝癌组织的分子病理学研究，发现肝癌细胞SALL4和PD-L1的表达水平与miR-200c水平呈明显的负相关；通过大样本肝癌病人生存期回顾分析，发现低表达SALL4或PD-L1及高表达miR-200c的患者具有更长的生存期。而且，miR-200c和SALL4表达水平对HBV+肝癌患者的预后具有预测价值。. 通过对肝癌微环境免疫细胞状态的观察，发现SALL4再激活可上调肝细胞表面多种抑制性配体（PD-L1、Galectin-9、HVEM等）的表达，进而对肝脏微环境多种免疫细胞（CD8+T、CD4+T和NK细胞）的表型和功能产生影响，最终诱导免疫细胞耗竭。进一步以HBV+肝癌细胞为模型探讨其分子机制，发现HBV慢性持续性感染通过SALL4-miR200c-PD-L1调控轴促进肝脏微环境CD8+T细胞功能耗竭。本项目首次揭示在HBV感染和肝癌发展期间存在调节PD-L1表达的HBV-pSTAT3-SALL4-miR-200c-PDL1分子轴，阐明了SALL4在成年肝脏再激活及在HBV慢性感染存在下诱导免疫细胞耗竭的分子机制，基于该分子轴的干预策略对于逆转病毒或肿瘤诱导的免疫细胞功能衰竭具有重要意义，为慢性乙肝和肝癌的治疗提供了新的思路和策略。