Completion of the entire hepatitis C virus life-cycle in genetically humanized mice

More than 130 million people world-wide chronically infected with hepatitis C virus (HCV) are at risk of developing severe liver disease. Antiviral treatments are only partially effective and a vaccine is not available. Development of more efficient therapies has been hampered by the lack of a small animal model. Building on the observation that CD81 and occludin (OCLN) comprise the minimal set of human factors required to render mouse cells permissive to HCV entry(1) we previously showed that transient expression of these two human genes is sufficient to allow viral uptake into fully immunocompetent inbred mice(2). Here, we demonstrate that transgenic mice stably expressing human CD81 and OCLN also support HCV entry but innate and adaptive immune responses restrict HCV infection in vivo. Blunting antiviral immunity in genetically humanized mice infected with HCV results in measurable viremia over several weeks. In mice lacking the essential cellular co-factor cyclophilin A (CypA), HCV RNA replication is markedly diminished, providing genetic evidence that this process is faithfully recapitulated. Using a cell-based fluorescent reporter activated by the NS3-4A protease we visualize HCV infection in single hepatocytes in vivo. Persistently infected mice produce de novo infectious particles, which can be inhibited with directly acting antiviral drug treatment, thereby providing for the first time evidence for the completion of the entire HCV life-cycle in inbred mice. This genetically humanized mouse model opens new opportunities to genetically dissect HCV infection in vivo and provides an important preclinical platform for testing and prioritizing drug and vaccine candidates.