GB virus B (GBV-B), a flavivirus closely related to HCV, has previously been shown to infect and replicate to high titers in tamarins (Saguinus sp.). This study describes the use of GBV-B infection and replication in the common marmoset (Callithrix jacchus) for the successful development and validation of a surrogate animal model for hepatitis C virus (HCV). Infection of marmosets with GBV-B produced a viremia that peaked at 108 to 10 9 genome copies/ml for a period of 40 to 60 days followed by viral clearance at 60 to 80 days postinfection. Passage of the initial tamarin-derived GBV-B in marmosets produced an infectious stock that gave a more reproducible and consistent infection in the marmoset. Titration of the virus stocks in vivo indicated that they contained 1 infectious unit for every 1,000 genome copies. Cultures of primary marmoset hepatocytes were also successfully infected with GBV-B, with high levels of virus detected in supernatants and cells for up to 14 days postinfection. Treatment of GBV-B-infected hepatocyte cultures with a novel class of HCV protease inhibitor (pyrrolidine 5,5 trans-lactams) reduced viral levels by more than 2 logs. Treatment of GBV-B-infected marmosets with one such inhibitor resulted in a 3-log drop in serum viral titer over 4 days of therapy. These studies provide the first demonstration of the in vivo efficacy of a small-molecule inhibitor for HCV in an animal model and illustrate the utility of GBV-B as a surrogate animal model system for HCV.For many years the discovery and development of novel therapies for hepatitis C virus (HCV) has been hampered by a lack of both a small animal model and a robust in vitro viral replication system. Although the recently developed HCV replicon system (3, 20) has proven extremely valuable for preclinical testing of antiviral compounds, there is still a need for virus-based culture systems and animal models. The restricted host range of HCV means that apart from humans, it will only infect chimpanzees. However, ethical considerations and cost mitigate the use of chimpanzees in drug discovery programs. HCV murine models in which transgenic or mutant mice implanted with human hepatocytes were found to be able to support the replication of HCV have been described previously (16,21). However, these systems are laborious, require specialist expertise, and have yet to be reproduced. In the absence of an HCV animal model, researchers have looked to surrogate viruses (in particular, GB virus B [GBV-B]) to provide an alternative model system. GBV-B was first described over 30 years ago, following the inoculation of tamarins with sera from a patient suffering from acute hepatitis. Serial passage of sera from these animals into further tamarins resulted in hepatitis. Although initially thought to be a human pathogen, this "GB agent" is now known to be of primate origin (9). When the molecular sequence of the GB agent was first characterized, two separate but closely related viruses, GBV-A and GBV-B, were identified (22, 32). GBV-A appears to replic...

The TAATGARAT motif in the herpes simplex virus (HSV) immediate-early (IE) gene promoters plays a key role in their activation by the Oct-1–Vmw65 complex, but its role in mediating inhibitory effects of cellular octamer-binding proteins is less clear. We have used indicator viruses containing reporter constructs with different IE promoters driving a reporter β-galactosidase gene within the viral genome to investigate this. We showed that deletion of the upstream IE promoter region containing the TAATGARAT motifs abolishes the inhibitory effect of the cellular octamer-binding proteins Oct-2.4 and Oct-2.5 on the viral IE promoter. This inhibitory effect can be restored by addition of a single TAATGARAT motif to the minimal promoter within the viral genome. Hence, the TAATGARAT motif can indeed mediate both positive and negative effects of cellular transcription factors when it is located within the viral genome.

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