A major problem in hepatitis C virus (HCV) immunotherapy or vaccine design is the extreme variability of the virus. We identified human monoclonal antibodies (mAbs) that neutralize genetically diverse HCV isolates and protect against heterologous HCV quasispecies challenge in a human liver-chimeric mouse model. The results provide evidence that broadly neutralizing antibodies to HCV protect against heterologous viral infection and suggest that a prophylactic vaccine against HCV may be achievable.

Hepatitis C virus (HCV), a Hepacivirus, is a major cause of viral hepatitis, liver cirrhosis and hepatocellular carcinoma. HCV envelope glycoproteins E1 and E2 mediate fusion and entry into host cells and are the primary targets of the humoral immune response. The crystal structure of the E2 core bound to broadly neutralizing antibody AR3C at 2.65 Å reveals a compact architecture composed of a central Ig-fold β-sandwich flanked by two additional protein layers. The CD81 receptor-binding site was identified by EM and by site-directed mutagenesis and overlaps with the AR3C epitope. The x-ray and EM E2 structures differ markedly from predictions of an extended, three-domain, class II fusion protein fold and therefore provide invaluable information for HCV drug and vaccine design.

Hepatitis C virus (HCV) infects ∼2% of the world's population. It is estimated that there are more than 500,000 new infections annually in Egypt, the country with the highest HCV prevalence. An effective vaccine would help control this expanding global health burden. HCV is highly variable, and an effective vaccine should target conserved T- and B-cell epitopes of the virus. Conserved B-cell epitopes overlapping the CD81 receptor-binding site (CD81bs) on the E2 viral envelope glycoprotein have been reported previously and provide promising vaccine targets. In this study, we isolated 73 human mAbs recognizing five distinct antigenic regions on the virus envelope glycoprotein complex E1E2 from an HCV-immune phage-display antibody library by using an exhaustive-panning strategy. Many of these mAbs were broadly neutralizing. In particular, the mAb AR4A, recognizing a discontinuous epitope outside the CD81bs on the E1E2 complex, has an exceptionally broad neutralizing activity toward diverse HCV genotypes and protects against heterologous HCV challenge in a small animal model. The mAb panel will be useful for the design and development of vaccine candidates to elicit broadly neutralizing antibodies to HCV.

Hepatitis C virus (HCV) establishes a chronic infection in the majority of exposed individuals and can cause cirrhosis and hepatocellular carcinoma. The role of antibodies directed against HCV in disease progression is poorly understood. Neutralizing antibodies (nAbs) can prevent HCV infection in vitro and in animal models. However, the effects of nAbs on an established HCV infection are unclear. Here, we demonstrate that three broadly nAbs, AR3A, AR3B and AR4A, delivered with adeno-associated viral (AAV) vectors can confer protection against viral challenge in humanized mice. Furthermore, we provide evidence that nAbs can abrogate an ongoing HCV infection in primary hepatocyte cultures and in a human liver chimeric mouse model. These results showcase a novel therapeutic approach to interfere with HCV infection exploiting a previously unappreciated need for HCV to continuously infect new hepatocytes in order to sustain chronicity.

Hepatitis C virus (HCV) infects more than 2% of the global population and is a leading cause of liver cirrhosis, hepatocellular carcinoma, and end-stage liver diseases. Circulating HCV is genetically diverse, and therefore a broadly effective vaccine must target conserved T-and Bcell epitopes of the virus. Human mAb HCV1 has broad neutralizing activity against HCV isolates from at least four major genotypes and protects in the chimpanzee model from primary HCV challenge. The antibody targets a conserved antigenic site (residues 412-423) on the virus E2 envelope glycoprotein. Two crystal structures of HCV1 Fab in complex with an epitope peptide at 1.8-Å resolution reveal that the epitope is a β-hairpin displaying a hydrophilic face and a hydrophobic face on opposing sides of the hairpin. The antibody predominantly interacts with E2 residues Leu 413 and Trp 420 on the hydrophobic face of the epitope, thus providing an explanation for how HCV isolates bearing mutations at Asn 415 on the same binding face escape neutralization by this antibody. The results provide structural information for a neutralizing epitope on the HCV E2 glycoprotein and should help guide rational design of HCV immunogens to elicit similar broadly neutralizing antibodies through vaccination.neutralizing determinant | protective determinant | antigen-antibody complex | type I' β-turn H epatitis C virus (HCV) infects >2% of the world population, with an estimated >500,000 new infections annually in the highest endemic country, Egypt (1, 2). In the United States, the rate of symptomatic HCV infection declined over the last decade and began to level out at ∼4 million cases around 2005 (3). Alarmingly, however, in developed countries, new cases are often associated with the younger age group (15-24 y) because of illegal injection drug use (4). Although some HCV-infected individuals can resolve infection without drug treatment, ∼70% develop chronic hepatitis and, over a period of 20-30 y, 20-30% will develop liver cirrhosis and 1-5% hepatocellular carcinoma (5). Furthermore, HCV infection is associated with several extrahepatic manifestations, neuropathy, and autoimmune diseases including mixed cryoglobulinemia and Sjögren's syndrome (6). The standard-of-care treatment for HCV infection uses a combination of pegylated IFN-α and ribavirin, which is effective in approximately 50% of treated patients but has many side effects. Two direct-acting antiviral drugs targeting the virus protease NS3 have recently been approved in the United States for triple therapy with IFN-α and ribavirin to improve success rates and to shorten treatment (7). To solve the global HCV problem and to eradicate the virus, more effective, tolerable, and affordable drugs against HCV, as well as a vaccine, are needed. Potent direct-acting antiviral drugs against additional viral targets are currently under development and show promise in IFN-free treatments (8). In the past few years, progress has also been made in vaccine development for prophylaxis and therapeutic purposes (9, 1...