Entry and replication of positive-sense, RNA viruses

HCV是一个主要的全球公共卫生问题，感染了全世界约7000万人。目前还没有批准的疫苗来对抗HCV感染，据估计，仅在美国每年就有超过40，000例新感染，在世界其他地区每年还有300 - 400万例新感染（疾病控制中心）。慢性HCV感染可以通过有效但昂贵的抗病毒治疗（50，000美元/治疗患者）治愈。然而，药物治疗并不是在全球范围内根除HCV感染的可行途径，因为这样做的成本过高。此外，成功治疗感染一种病毒基因型的患者并不排除再次感染另一种病毒。药物治疗方法也很复杂，因为大多数受影响的人不知道他们被感染，许多人从事危险行为，如静脉注射毒品。简而言之，最好的长期解决方案是投入大量的智力和财力资源，发现和开发一种有效对抗大多数（如果不是全部）HCV病毒基因型的多价疫苗。 HCV病毒粒子是一种结构异质的颗粒，其浮力密度低于大多数其他病毒，使其在已知病毒中独一无二。病毒粒子与几种宿主衍生的载脂蛋白和两种表面糖蛋白E1和E2缔合。E2通过与细胞受体CD 81和清道夫受体B类I型（SR-BI）相互作用负责细胞靶向。E1的功能仍然知之甚少。我们和其他人发表了E2核心结构具有新的结构域组织，缺乏典型融合肽的标志，并且在暴露于低pH时不会发生大的构象或寡聚体变化。因此，E2似乎在膜融合中没有直接作用，这意味着E1单独或E1 E2异二聚体负责融合过程。这些全面的结构，生物化学和生物物理的结果建立了一个基础，以更好地确定包膜糖蛋白在HCV感染的功能作用。 通过删除或修饰病毒上存在的免疫逃避机制，可以使HCV表面上的保守病毒表位更容易接近免疫系统。与一个国际研究小组合作，我们删除了E2表面的高变区1和选择的糖基化位点，这些位点已被证明会干扰几种中和抗体的结合（Khera et al. J Hepatol 2019）。有趣的是，携带这些突变的重组E2蛋白不能引发交叉中和抗体，这表明保守表位的暴露不足以将抗体应答集中在交叉中和抗体的产生上。这项研究的结果突出了我们对HCV进入和中和的理解的不足，为继续研究HCV进入提供了动力。

HCV represents a major global public health problem, infecting approximately 70 million people worldwide. There is currently no approved vaccine to counter HCV infection, and it is estimated that there are more than 40,000 new infections annually in the US alone with an additional 3-4 million new infections per year in the rest of world (Center for Disease Control). Chronic HCV infection is curable by an effective, albeit expensive, antiviral therapy ($50,000/treated patient). Drug treatment is not, however, a feasible route to worldwide eradication of HCV infection, as the cost of doing so would prohibitive. Moreover, successful treatment of a patient infected with one viral genotype does not preclude re-infection with another. The drug treatment approach is also complicated by the fact that most affected individuals are unaware that they are infected, and many engage in risky behaviors, such as intravenous drug use. Simply put, the best long term solution is to invest considerable intellectual and financial resources in discovery and development of a polyvalent vaccine effective against most, if not all, HCV viral genotypes. HCVs virion is a structurally heterogeneous particle which harbors a buoyant density lower than that of most other viruses, making it unique among known viruses. The virion associates with several host derived apolipoproteins and two surface glycoproteins, E1 and E2. E2 is responsible for cell targeting by interacting with the cellular receptors CD81 and scavenger receptor class B, type I (SR-BI). The function of E1 remains poorly understood. We and others published that the E2 core structure has a novel domain organization, lacks the hallmarks of a typical fusion peptide, and does not undergo large conformational or oligomeric changes upon exposure to low pH. As a result, E2 does not appear to have a direct role in membrane fusion, implying that E1 alone or the E1E2 heterodimer is responsible for the fusion process. These comprehensive structural, biochemical, and biophysical results have established a foundation to better define the functional roles of the envelope glycoproteins in HCV infection. Conserved viral epitopes on the surface of HCV can be made considerably more accessible to the immune system by deletion or modifying the immune evasion mechanism present on the virus. Working with an international group of investigators we deleted the hypervariable region 1 and selected glycosylation sites on the surface of E2, which have been shown to interfere with binding of several neutralizing antibodies (Khera et al. J Hepatol 2019). Interestingly, recombinant E2 proteins carrying these mutations are unable to elicit cross-neutralizing antibodies, suggesting that exposure of conserved epitopes is not sufficient to focus antibody responses on production of cross-neutralizing antibodies. The results of this study highlights highlights deficiencies in our understanding of HCV entry and neutralization, providing the impetus for continued research on HCV entry.