巨噬细胞功能耗竭状态对肝癌微环境中抗肿瘤免疫的负向调控及其机制

Tumor-associated macrophages (TAMs) play an important role in the progression of hepatocellular carcinoma (HCC). However, except for changes in the polarization status and its paracrine effect on HCC, little is known about the functions (proliferation, migration, phagocytosis, antigen-presenting capacity and the cytokine secretion) of TAMs. Our previous studies showed that TAMs showed weak phagocytosis capacity, which was not recovered after reprogramming therapy (Transition from M2 phenotype to M1 phenotype). At the same time, after reprogramming, the migration capacity of TAMs was significantly deteriorated, which implied that part of the functions of TAMs were exhausted, and macrophage reprogramming aggregated the “functional exhaustion” of TAMs. It has been reported that PD-L1 expression is correlated with the “functional exhaustion” status of T cells and dendritic cells. We found that the PD-L1 expression was significantly higher in M1 macrophages than in M2 macrophages, which was consistent with MHC-II expression. PD-L1 monoclonal antibody therapy significantly inhibited the growth of mouse liver cancer. In the study, we aim to illustrate the correlation between PD-L1 and the “functional exhaustion” of TAMs and shed light on the potential value of macrophage reprogramming combining PD-L1 monoclonal antibody therapy in treating HCC.

肿瘤相关巨噬细胞（TAMs）在肝细胞癌（简称肝癌）进展中发挥重要作用。然而，除了极化以及通过旁分泌影响肿瘤的生物学行为以外，巨噬细胞的增殖、凋亡、迁移、吞噬、抗原提呈以及细胞因子分泌等功能在肝癌微环境中发生的变化并不清楚。我们前期研究发现，TAMs自身吞噬能力较弱，重编程(reprogramming)治疗（诱导M2向M1表型转化）后吞噬能力并无增强，同时迁移能力明显减弱，提示TAMs中存在某些功能的耗竭，重编程治疗可能加重巨噬细胞的“功能耗竭”。文献报道PD-L1表达与T细胞和树突状细胞的“功能耗竭”状态相关。我们的前期研究发现，PD-L1的表达在M1型巨噬细胞中显著增高，且显示出与MHC-II协同表达的特点；PD-L1单抗能够显著抑制小鼠肝癌生长。本课题拟探讨PD-L1表达与巨噬细胞的“功能耗竭”的关系，以及PD-L1单抗治疗联合巨噬细胞重编程在肝癌治疗中的价值。

前期研究发现，肝癌中肿瘤相关巨噬细胞（TAMs）存在“功能耗竭”状态，且M2向M1重编程可加重巨噬细胞“功能耗竭”；PD-L1等免疫抑制分子的表达水平与巨噬细胞“功能耗竭”的程度相关；肿瘤微环境中的巨噬细胞高表达MHC-Ⅱ分子，且与PD-L1呈同步表达的特征。本项目中，我们通过研究MHC-Ⅱ的伴侣分子CD74在巨噬细胞上的表达及其对肿瘤微环境的影响，为肝癌治疗提供潜在的干预手段。基于单细胞转录组测序和流式细胞检测的数据显示，肝癌组织中CD74+巨噬细胞中与抗肿瘤免疫反应相关的通路显著上调。CD74阳性细胞在肝癌间质组织低表达可提示肝癌患者术后的不良预后。进一步研究发现，CD74+巨噬细胞肿瘤内低浸润与肝癌CD8+T细胞功能受损有关。用CD74抗体竞争性阻断巨噬细胞上的CD74，会抑制CD8+T细胞的细胞毒性作用。我们的结果表明，CD74+巨噬细胞可促进抗肿瘤的免疫微环境。靶向CD74相关通路可调控抗肿瘤免疫反应，在肝癌药物治疗领域具有良好的干预价值。