Hepatitis C virus (HCV) is

The tight junction protein claudin-1 (CLDN1) has been shown to be essential for hepatitis C virus (HCV) entry-the first step of viral infection. Due to the lack of neutralizing anti-CLDN1 antibodies, the role of CLDN1 in the viral entry process is poorly understood. In this study, we produced antibodies directed against the human CLDN1 extracellular loops by genetic immunization and used these antibodies to investigate the mechanistic role of CLDN1 for HCV entry in an infectious HCV cell culture system and human hepatocytes. Antibodies specific for cell surface-expressed CLDN1 specifically inhibit HCV infection in a dose-dependent manner. W ith an estimated 170 million infected individuals, hepatitis C virus (HCV) has a major impact on public health. HCV is a hepatotropic virus that causes persistent infection in the majority of infected individuals. 1 Therapeutic options for chronic infection are limited, and a vaccine is not available. 2 HCV entry into hepatocytes is the first step of the viral life cycle resulting in productive viral infection. 3

End-stage liver disease caused by chronic hepatitis C virus (HCV) infection is a leading cause for liver transplantation (LT). Due to viral evasion from host immune responses and the absence of preventive antiviral strategies, reinfection of the graft is universal. The mechanisms by which the virus evades host immunity to reinfect the liver graft are unknown. In a longitudinal analysis of six HCV-infected patients undergoing LT, we demonstrate that HCV variants reinfecting the liver graft were characterized by efficient entry and poor neutralization by antibodies present in pretransplant serum compared with variants not detected after transplantation. Monoclonal antibodies directed against HCV envelope glycoproteins or a cellular entry factor efficiently cross-neutralized infection of human hepatocytes by patient-derived viral isolates that were resistant to autologous host-neutralizing responses. These findings provide significant insights into the molecular mechanisms of viral evasion during HCV reinfection and suggest that viral entry is a viable target for prevention of HCV reinfection of the liver graft.