Hepatitis C virus Broadly Neutralizing Monoclonal Antibodies Isolated 25 Years after Spontaneous Clearance

Hepatitis C virus (HCV) is world-wide a major cause of liver related morbidity and mortality. No vaccine is available to prevent HCV infection. To design an effective vaccine, understanding immunity against HCV is necessary. The memory B cell repertoire was characterized from an intravenous drug user who spontaneously cleared HCV infection 25 years ago. CD27+IgG+ memory B cells were immortalized using BCL6 and Bcl-xL. These immortalized B cells were used to study antibody-mediated immunity against the HCV E1E2 glycoproteins. Five E1E2 broadly reactive antibodies were isolated: 3 antibodies showed potent neutralization of genotype 1 to 4 using HCV pseudotyped particles, whereas the other 2 antibodies neutralized genotype 1, 2 and 3 or 1 and 2 only. All antibodies recognized non-linear epitopes on E2. Finally, except for antibody AT12-011, which recognized an epitope consisting of antigenic domain C /AR2 and AR5, all other four antibodies recognized epitope II and domain B. These data show that a subject, who spontaneously cleared HCV infection 25 years ago, still has circulating memory B cells that are able to secrete broadly neutralizing antibodies. Presence of such memory B cells strengthens the argument for undertaking the development of an HCV vaccine.

丙型肝炎病毒（Hepatitis C virus, HCV）是全球范围内引发肝脏相关疾病与死亡的主要病因之一，目前尚无可用疫苗可预防其感染。为研发有效疫苗，阐明机体针对HCV的免疫机制至关重要。本研究对一名25年前自发清除HCV感染的静脉吸毒者体内的记忆B细胞库进行了表征分析：采用BCL6与Bcl-xL对其CD27+IgG+记忆B细胞进行永生化构建，利用这批永生化B细胞开展针对HCV E1E2糖蛋白的抗体介导的免疫应答研究。研究团队共分离得到5株靶向E1E2的广谱反应性抗体：其中3株可通过丙型肝炎病毒假病毒颗粒（HCV pseudotyped particles）模型，强效中和基因型1至4型病毒；剩余2株则仅能中和基因型1、2、3型或仅1、2型病毒。所有抗体均识别E2蛋白上的非线性表位。最后，除抗体AT12-011识别由抗原结构域C/AR2与AR5构成的表位外，其余4株抗体均识别表位II与结构域B。上述实验数据表明，这名25年前自发清除HCV感染的受试者体内仍存在可分泌广谱中和抗体的循环记忆B细胞。这类记忆B细胞的存在，为HCV疫苗的研发提供了有力的理论支撑。