乏氧微环境下PD-L1参与胰腺癌免疫逃逸的分子机制及联合治疗策略研究

Checkpoint-targeted immune therapy has breaked through in multiple clinical trials of refractory tumors, but it didn't improve prognosis in pancreatic cancer. We believed a complex nature of tumor immunity rebuilding served as the key of therapy efficacy. Hypoxia played an important part in the progression and the radio-chemotherapy resistance in pancreatic cancer, while its role in local immunity-rebuilding still remain to be elucidated. Previous study showed that checkpoint PD-L1 expression increased in pancreatic cancer. In our experiments, we discovered that patients with high expression of PD-L1 associated with a poor prognosis, and that PD-L1 expression under hypoxia positively correlated with FOXP3 expression and Treg infiltration. Transcription factor FOXP3 participates in the immunology escape in pancreatic cancer under hypoxia. This study aims to clarify the regulation mechanism of PD-L1 by FOXP3 under hypoxia condition, and further investigates the function and mechanism of PD-L1-Treg network exerted on the immune escape in pancreatic cancer. We explore new combination immune therapy based on the hypoxia and immunology rebuilding microenvironment of pancreatic cancer, thus providing theory evidence for the basic research and clinical translation for future treatment of pancreatic cancer.

以免疫检查点为靶标的免疫调节治疗在多种难治性肿瘤的临床试验中获得突破，然而在胰腺癌的研究中却未能改善预后。深入分析，我们认为不同微环境中肿瘤免疫重塑的差异是影响治疗效果的关键。乏氧微环境在胰腺癌的进展及放化疗抵抗中发挥重要作用，然而乏氧微环境对胰腺癌局部免疫重塑的影响及机制尚未阐明。文献报道免疫检查点PD-L1在胰腺癌中表达增加。我们研究发现高表达PD-L1的胰腺癌患者预后差，乏氧状态下胰腺癌细胞PD-L1表达与Foxp3表达以及肿瘤局部Treg细胞浸润呈显著正相关。转录因子Foxp3参与乏氧状态下胰腺癌免疫逃逸，本研究拟阐明乏氧环境中胰腺癌细胞Foxp3对PD-L1表达的调控机制；探讨乏氧微环境下胰腺癌细胞PD-L1与Treg细胞间的交互网络在胰腺癌免疫逃逸中的作用及内在机制；进而针对胰腺癌乏氧微环境和免疫重塑特征，探索新的联合免疫治疗方案，为胰腺癌治疗的基础研究与临床转化提供理论依据。

胰腺癌是预后最差的消化道恶性肿瘤，其发病率和死亡率近年来在我国呈现逐年上升的趋势。局部免疫微环境重塑(immunoediting) 在胰腺癌进展及放化疗抵抗中发挥重要作用。传统放化疗手段缺乏对胰腺癌肿瘤微环境尤其是免疫微环境的有效干预，常常导致治疗失败。随着分子生物学和肿瘤免疫学的发展，以肿瘤微环境为靶向的联合免疫治疗正在成为胰腺癌基础和临床研究关注的焦点。我们近年来围绕胰腺癌复杂的免疫微环境开展研究，以期在免疫治疗方向为胰腺癌患者带来福音。围绕前期工作基础提出胰腺癌细胞发挥类免疫调节细胞功能的新概念，明确了转录因子FOXP3在胰腺癌细胞中异常表达及其生物学功能。通过系列功能实验验研究阐明了胰腺癌细胞C-FOXP3参与肿瘤免疫微环境调节的内在机制：一方面CCL5的启动子区存在FOXP3转录调控的靶序列，胰腺癌细胞中FOXP3可以直接结合到CCL5启动子区的特定把序列，胰腺癌细胞C-FOXP3转录调控CCL5分泌，趋化Treg至肿瘤局部，协同发挥免疫抑制（Oncogene. 2017;36(21):3048-3058.）；另一方面，与正常胰腺导管上皮细胞比较，PD-L1蛋白在部分胰腺导管腺癌细胞中表达升高，肿瘤细胞高表达PD-L1提示胰腺导管腺癌患者的不良预后，PD-L1表达水平与肿瘤细胞FOXP3表达水平呈现正相关，同时肿瘤细胞高表达PD-L1的胰腺导管腺癌局部Treg细胞浸润增多，患者预后相对较差。上皮源性FOXP3可促进肿瘤细胞PD-L1表达上调（Signal transduction and targeted therapy, 2020, 5(1): 1-12.）。FOXP3通过促进Tregs细胞以及PD-L1的表达的双重作用抑制CD8+杀伤T细胞的活性。临床前研究发现，利用多种胰腺肿瘤模型，采取PD-L1和CCL5抗体联合阻断，可在上皮细胞FOXP3阳性的胰腺肿瘤中产生良好的抗肿瘤效果，从而为胰腺个体化免疫治疗提供了一种潜在的新策略。