Previously, RNA transcripts of cDNA clones of hepatitis C virus (HCV) genotypes 1a (strains H77, HCV-1, and HC-TN), 1b (HC-J4, Con1, and HCV-N), and 2a (HC-J6 and JFH1) were found to be infectious in chimpanzees. However, only JFH1 was infectious in human hepatoma Huh7 cells. We performed genetic analysis of HCV genotype 3a (strain S52) and 4a (strain ED43) prototype strains and generated full-length consensus cDNA clones (pS52 and pED43). Transfection of Huh7.5 cells with RNA transcripts of these clones did not yield cells expressing HCV Core. However, intrahepatic transfection of chimpanzees resulted in robust infection with peak HCV RNA titers of ϳ5.5 log 10 international units (IU)/ml. Genomic consensus sequences recovered from serum at the times of peak viral titers were identical to the sequences of the parental plasmids. Both chimpanzees developed acute hepatitis with elevated liver enzymes and significant necroinflammatory liver changes coinciding with detection of gamma interferon-secreting, intrahepatic T cells. However, the onset and broadness of intrahepatic T-cell responses varied greatly in the two animals, with an early (week 4) multispecific response in the ED43-infected animal (3 weeks before the first evidence of viral control) and a late (week 11) response with limited breadth in the S52-infected animal (without evidence of viral control). Autologous serum neutralizing antibodies were not detected during the acute infection in either animal. Both animals became persistently infected. In conclusion, we generated fully functional infectious cDNA clones of HCV genotypes 3a and 4a. Proof of functionality of all genes might further the development of recombinant cell culture systems for these important genotypes.Hepatitis C virus (HCV) is a small, enveloped virus with a single-stranded RNA genome, approximately 9.6 kb in length. The genome consists of 5Ј and 3Ј untranslated regions (UTRs) and a single open reading frame (ORF), encoding structural proteins (Core, E1, and E2), p7, and nonstructural proteins (NS2, NS3, NS4A, NS4B, NS5A, and NS5B) (22). Due to significant genetic heterogeneity, HCV was classified into 7 major genotypes and numerous subtypes, differing Ͼ30% and Ͼ20%, respectively, at the nucleotide level and at the amino acid level. Strains/isolates differ in 2 to 10% at the nucleotide/ amino acid level, and quasispecies typically differ in up to 2% at the nucleotide/amino acid level (70). As a main cause of liver cirrhosis and hepatocellular carcinoma, chronic HCV infection poses a major public health burden. There is no vaccine available, and combination therapy with alpha interferon and ribavirin is characterized by many side effects and contraindications, as well as low efficacy (22). Research on the HCV life cycle and new therapeutics requires well-characterized experimental models and reagents representing the different virus variants.Chimpanzees, the only animal model of HCV infection mirroring immunopathogenesis and viral persistence observed in human infections (4, 80), can be ...

Hepatitis C virus (HCV) persistence is facilitated by exhaustion of CD8+ T cells that express the inhibitory receptor programmed cell death 1 (PD-1). Blockade of PD-1 signaling improves in vitro proliferation of HCV-specific T lymphocytes, but whether antiviral function can be restored in infected individuals is unknown. To address this question, chimpanzees with persistent HCV infection were treated with anti-PD-1 antibodies. A significant reduction in HCV viremia was observed in one of three treated animals without apparent hepatocellular injury. Viremia rebounded in the responder animal when antibody treatment was discontinued. Control of HCV replication was associated with restoration of intrahepatic CD4+ and CD8+ T-cell immunity against multiple HCV proteins. The responder animal had a history of broader T-cell immunity to multiple HCV proteins than the two chimpanzees that did not respond to PD-1 therapy. The results suggest that successful PD-1 blockade likely requires a critical threshold of preexisting virus-specific T cells in liver and warrants consideration of therapeutic vaccination strategies in combination with PD-1 blockade to broaden narrow responses. Anti-PD-1 immunotherapy may also facilitate control of other persistent viruses, notably the hepatitis B virus where options for long-term control of virus replication are limited.

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Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. Development of vaccines to prevent HCV infection, or at least prevent progression to chronicity, is a major goal. In mice and rhesus macaques, a DNA vaccine encoding cell-surface HCV-envelope 2 (E2) glycoprotein stimulated stronger immune responses than a vaccine encoding intracellular E2. Therefore, we used DNA encoding surface-expressed E2 to immunize chimpanzees 2768 and 3001. Chimpanzee 3001 developed anti-E2 after the second immunization and antibodies to hypervariable region 1 (HVR1) after the third immunization. Although chimpanzee 2768 had only low levels of anti-E2 after the third immunization, an anamnestic response occurred after HCV challenge. CTL responses to E2 were not detected before challenge, but a strong response was detected after HCV challenge in chimpanzee 2768. An E2-specific CD4؉ response was detected in chimpanzee 2768 before challenge and in both chimpanzees postchallenge. Three weeks after the last immunization, animals were challenged with 100 50% chimpanzee-infectious doses (CID 50 ) of homologous monoclonal HCV. As a control, a naive chimpanzee was inoculated with 3 CID 50 of the challenge virus. The vaccine did not generate sterilizing immunity because both vaccinated chimpanzees were infected. However, both vaccinated chimpanzees resolved the infection early whereas the control animal became chronically infected. Compared with the control animal, hepatitis appeared earlier in the course of the infection in both vaccinated chimpanzees. Therefore, DNA vaccine encoding cell surface-expressed E2 did not elicit sterilizing immunity in chimpanzees against challenge with a monoclonal homologous virus, but did appear to modify the infection and might have prevented progression to chronicity. (HEPATOLOGY 2000;32:618-625.)Hepatitis C virus (HCV) is a major cause of chronic liver disease worldwide. 1 More than 2% of the entire world population is chronically infected with this virus; liver cirrhosis and hepatocellular carcinoma are recognized long-term sequelae of chronic HCV infection. 1 Chronic HCV infection has been treated with interferon but less than 20% of patients achieve a sustained response with this drug. 2 Combination therapy of interferon and the nucleoside analog ribavirin has increased the rate of sustained response to more than 30%, [3][4][5] and it is expected that in the next few years, new antiviral agents will further improve the response rate in chronically infected patients. The combination of more effective antiviral drugs and the lower incidence of new HCV infections since the introduction of anti-HCV screening of blood products will eventually reduce the prevalence of HCV infection in industrialized countries. However, HCV still causes at least 30,000 new cases of hepatitis in the United States each year. 6 In developing countries, where the prevalence of HCV infection in the general population can be as high as 30%, 7 strategies to prevent HCV transmission are not universally implement...

Protective immunity after resolved hepatitis C virus (HCV) infection has been reported. However, the breadth of this immunity has remained controversial, and the role of neutralizing antibodies has not been well-defined. In the present study, two chimpanzees (CH96A008 and CH1494) with resolved monoclonal H77C (genotype 1a) infection were rechallenged with low-dose homologous H77C virus about 12 months after viral clearance; CH96A008 became persistently infected, and CH1494 had transient viremia lasting 2 weeks. CH1494 was subsequently either partially or completely protected following five homologous rechallenges with monoclonal H77C or polyclonal H77 and after six heterologous rechallenges with HC-J4 (genotype 1b) or HC-J6 (genotype 2a) viruses. Subsequently, a final challenge with H77C resulted in persistent HCV infection. In both chimpanzees, serum neutralizing antibodies against retroviral pseudoparticles bearing the H77C envelope proteins were not detected during the initial infection or during rechallenge. However, anamnestic cellular immune responses developed during the initial homologous rechallenge, in particular in CH96A008, which developed a persistent infection. Polyprotein sequences of viruses recovered from CH1494 after the two homologous rechallenges that resulted in transient viremia were identical with the H77C virus. In contrast, the polyprotein sequences of viruses recovered from both chimpanzees after homologous rechallenge resulting in persistent infection had numerous changes. These findings have important implications for our understanding of immunity against HCV; even in the best-case scenario with autologous rechallenge, low-level viral persistence was seen in the presence of primed T-cell responses.