Naturally Occurring Mutations in the Nonstructural Region 5B of Hepatitis C Virus (HCV) from Treatment-Naïve Korean Patients Chronically Infected with HCV Genotype 1b

The nonstructural 5B (NS5B) protein of the hepatitis C virus (HCV) with RNA-dependent RNA polymerase (RdRp) activity plays a pivotal role in viral replication. Therefore, monitoring of its naturally occurring mutations is very important for the development of antiviral therapies and vaccines. In the present study, mutations in the partial NS5B gene (492 bp) from 166 quasispecies of 15 genotype-1b (GT) treatment-naïve Korean chronic patients were determined and mutation patterns and frequencies mainly focusing on the T cell epitope regions were evaluated. The mutation frequency within the CD8+ T cell epitopes was significantly higher than those outside the CD8+ T cell epitopes. Of note, the mutation frequency within predicted CD4+ T cell epitopes, a particular mutational hotspot in Korean patients was significantly higher than it was in patients from other areas, suggesting distinctive CD4+ T cell-mediated immune pressure against HCV infection in the Korean population. The mutation frequency in the NS5B region was positively correlated with patients with carrier-stage rather than progressive liver disease (chronic hepatitis, liver cirrhosis and hepatocellular carcinoma). Furthermore, the mutation frequency in four codons (Q309, A333, V338 and Q355) known to be related to the sustained virological response (SVR) and end-of treatment response (ETR) was also significantly higher in Korean patients than in patients from other areas. In conclusion, a high degree of mutation frequency in the HCV GT-1b NS5B region, particularly in the predicted CD4+ T cell epitopes, was found in Korean patients, suggesting the presence of distinctive CD4+ T cell pressure in the Korean population. This provides a likely explanation of why relatively high levels of SVR after a combined therapy of pegylated interferon (PEG-IFN) and ribavirin (RBV) in Korean chronic patients with GT-1b infections are observed.

丙型肝炎病毒（hepatitis C virus, HCV）的非结构蛋白5B（NS5B）具有RNA依赖的RNA聚合酶（RNA-dependent RNA polymerase, RdRp）活性，在病毒复制过程中发挥关键作用。因此，监测其天然存在的突变对于抗病毒治疗与疫苗研发均具有重要意义。本研究对15名初治基因型1b型（GT-1b）韩国慢性丙型肝炎患者的166个准种的部分NS5B基因（492 bp）序列进行突变鉴定，并重点评估了T细胞表位区域的突变模式与突变频率。研究发现，CD8+ T细胞表位内的突变频率显著高于CD8+ T细胞表位外的突变频率。值得注意的是，韩国患者中存在特定突变热点的预测CD4+ T细胞表位内的突变频率，显著高于其他地区患者，提示韩国人群中存在独特的CD4+ T细胞介导的抗HCV感染免疫压力。NS5B区域的突变频率与处于携带状态的患者呈正相关，而非与进展性肝病（慢性肝炎、肝硬化及肝细胞癌）患者呈正相关。此外，已知与持续病毒学应答（sustained virological response, SVR）和治疗结束应答（end-of treatment response, ETR）相关的四个密码子（Q309、A333、V338及Q355）的突变频率，在韩国患者中也显著高于其他地区患者。综上，韩国患者的HCV GT-1b型NS5B区域存在较高的突变频率，尤其是在预测的CD4+ T细胞表位内，这表明韩国人群中存在独特的CD4+ T细胞免疫压力，这或许可以合理解释为何韩国GT-1b型慢性感染患者在接受聚乙二醇干扰素（pegylated interferon, PEG-IFN）联合利巴韦林（ribavirin, RBV）治疗后，可获得相对较高的持续病毒学应答率。