肝细胞癌肿瘤突变负荷与肿瘤微环境免疫浸润细胞关联性研究

Identification of the Relationships between Tumor Mutation Burden with Immune Infiltrates in Liver Hepatocellular Carcinoma

摘要: 目的：肝细胞癌是我国常见肿瘤之一，并占癌症死亡人数的第二位。随着免疫治疗的普及，免疫检查点抑制剂也逐步应用于肝癌，部分患者取得了良好的治疗效果。但是目前仍缺少准确地预测免疫检查点抑制剂的生物标志物。肿瘤突变负荷及免疫浸润细胞是常用的免疫检查点抑制剂的生物标志物，可以有效预测其疗效，在恶性黑色素瘤及非小细胞肺癌中已经得到证实。但在肝癌中此类研究尚少，为了探究肿瘤突变负荷及免疫浸润细胞之间是否存在协同关系以便更好预测免疫检查点抑制剂在肝癌中的疗效，我们展开了本次研究。方法：从TCGA数据库中下载肝癌患者的基因表达数据、基因突变数据及临床数据。将所有患者根据肿瘤突变负荷分为高突变负荷组及低突变负荷组，从两组患者的数据中鉴定出差异表达最明显的基因。利用功能富集分析及蛋白质–蛋白质相互作用网络分析差异基因的生物学功能。CIBERSORT算法用于分析两组患者之间肿瘤微环境免疫浸润细胞的特征，Kaplan-Meier生存分析用以分析两组之间患者的生存时间有无差别。结果：TP53是肝细胞癌中突变频率最高的基因，在高肿瘤突变负荷组及低肿瘤突变复合组中，MAGEA3、MAGEA6及MAGEA12基因表达差异最为显著，其功能与细胞增殖、上皮–间质转化等恶性表型密切相关。在肿瘤微环境免疫浸润细胞差别中，低肿瘤突变复合组的记忆性CD4+ T细胞数量显著高于高肿瘤突变复合组，且生存期明显延长。结论：在肝细胞癌患者中，低肿瘤突变负荷组的CD4+ T细胞数量显著高于高肿瘤突变复合组，并且有更好的临床预后。这显示在肝细胞癌中，以TMB高低作为判断肝细胞癌免疫检查点抑制剂的唯一生物标志物尚有待商榷，应结合更多指标综合评估。

Abstract: Background: Hepatocellular carcinoma (HCC) is one of the most common tumors in China, and accounts for the second largest number of cancer deaths. With the popularity of immunotherapy, immune checkpoint inhibitors are gradually applied to liver cancer, and some patients have achieved good therapeutic effects. However, there is still a lack of accurate biomarkers to predict immune checkpoint inhibitors. Tumor mutation load and immune infiltrating cells are commonly used as biomarkers of immune checkpoint inhibitors, which can effectively predict efficacy. It has been confirmed in malignant melanoma and non-small cell lung cancer. In order to explore whether there is a synergistic relationship between tumor mutation load and immune infiltrating cells, so as to better predict the efficacy of immune checkpoint inhibitors in liver cancer, we launched this study. Methods: The mutation data, clinical data and gene expression data of liver hepatocellular carcinoma patients were downloaded from TCGA database. Differentially expressed genes were identified from high and low TMB groups. Functional enrichment analyses and protein-protein interaction (PPI) network analysis were used to identify the functions and pathway of the DEGs. And immune cell infiltration signatures were evaluated by CIBERSORT algorithm. Results: TP53 is the gene with the highest mutation frequency in hepatocellular carcinoma. The expression of magea3, magea6 and magea12 genes is the most significant in high tumor mutation load group and low tumor mutation complex group. Its function is closely related to cell proliferation, epithelial mesenchymal transition and other malignant phenotypes. The number of memory CD4+ T cells in low mutation group was significantly higher than that in high mutation group, and the survival time was significantly longer. Conclusion: In HCC patients, the number of CD4+ T cells in low mutation load group was significantly higher than that in high mutation complex group, and the clinical prognosis was better. This suggests that high mutation load may not be a positive prognostic marker of immunosuppressive agents in HCC.