The development of therapies for hepatitis C virus (HCV) infection has been hampered by the lack of a small-animal model of the disease. Now Alexander Ploss and colleagues describe the first immunocompetent rodent model for hepatitis C virus infection, using adenoviruses expressing four human factors to enable entry of HCV into mouse cells. These vectors were then used to transduce the livers of mice, which then became susceptible to HCV infection. Although the model does not enable a complete virus replication cycle, it should be useful for the evaluation of HCV vaccines and entry inhibitors. Hepatitis C virus (HCV) remains a major medical problem. Antiviral treatment is only partially effective and a vaccine does not exist. Development of more effective therapies has been hampered by the lack of a suitable small animal model. Although xenotransplantation of immunodeficient mice with human hepatocytes has shown promise, these models are subject to important challenges. Building on the previous observation that CD81 and occludin comprise the minimal human factors required to render mouse cells permissive to HCV entry in vitro4, we attempted murine humanization via a genetic approach. Here we show that expression of two human genes is sufficient to allow HCV infection of fully immunocompetent inbred mice. We establish a precedent for applying mouse genetics to dissect viral entry and validate the role of scavenger receptor type B class I for HCV uptake. We demonstrate that HCV can be blocked by passive immunization, as well as showing that a recombinant vaccinia virus vector induces humoral immunity and confers partial protection against heterologous challenge. This system recapitulates a portion of the HCV life cycle in an immunocompetent rodent for the first time, opening opportunities for studying viral pathogenesis and immunity and comprising an effective platform for testing HCV entry inhibitors in vivo.

The entire hepatitis C virus life cycle can be recapitulated in an inbred mouse model, allowing preclinical assessment of antiviral therapeutics and vaccines. In a 2009 Nature paper, Alexander Ploss and colleagues showed that transient expression of the human genes CD81 and occludin (OCLN) constituted a minimal set of cellular factors required for uptake of hepatitis C virus (HCV) into immune-competent mouse cells. Now they report that transgenic immune-deficient mice stably expressing CD81 and OCLN can sustain the complete HCV replication cycle with measurable viraemia. The availability of this genetically humanized mouse model opens the way to closer study of HCV infection in vivo and should provide a valuable platform for testing potential therapeutics. More than 130 million people worldwide chronically infected with hepatitis C virus (HCV) are at risk of developing severe liver disease. Antiviral treatments are only partially effective against HCV infection, 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 entry1, we previously showed that transient expression of these two human genes is sufficient to allow viral uptake into fully immunocompetent inbred mice2. 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 viraemia 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 evidence for the completion of the entire HCV life cycle in inbred mice. This genetically humanized mouse model opens new opportunities to dissect genetically HCV infection in vivo and provides an important preclinical platform for testing and prioritizing drug candidates and may also have utility for evaluating vaccine efficacy.

HCV-specific neutralizing antibodies protect humanized mice from challenge and suppress established infections.

Significance: Hepatitis E virus (HEV) is responsible for an estimated 20 million enterically transmitted cases of viral hepatitis globally. Here, we demonstrate that one of HEV’s three major gene products, ORF3, is an ion channel. Deletion of ORF3 abrogates release of infectious virions, and we show that viral egress can be rescued by expressing the influenza A virus (IAV) matrix-2 protein in trans . Expression of ORF3 facilitates ion flux across the plasma membrane, providing direct evidence for its viroporin activity. We identify regions within ORF3 abrogating both ion channel activity and particle release, thereby linking these two processes for a quasienveloped human virus and providing an attractive potential target for antiviral drug development.