Challenge pools of hepatitis C virus genotypes 1-6 prototype strains: replication fitness and pathogenicity in chimpanzees and human liver-chimeric mouse models

Abstract

Chimpanzees represent the only animal model for studies of the natural history of hepatitis C virus (HCV). To generate virus stocks of important HCV variants, we infected chimpanzees with HCV strains of genotypes 1-6 and determined the infectivity titer of acute-phase plasma pools in additional animals. The courses of first- and second-passage infections were similar, with early appearance of viremia, HCV RNA titers of >10(4.7) IU/mL, and development of acute hepatitis; the chronicity rate was 56%. The challenge pools had titers of 10(3)-10(5) chimpanzee infectious doses/mL. Human liver-chimeric mice developed high-titer infections after inoculation with the challenge viruses of genotypes 1-6. Inoculation studies with different doses of the genotype 1b pool suggested that a relatively high virus dose is required to consistently infect chimeric mice. The challenge pools represent a unique resource for studies of HCV molecular virology and for studies of pathogenesis, protective immunity, and vaccine efficacy in vivo.

Figure 1

Course of first-passage infection with hepatitis C virus (HCV) genotypes 1–6 in chimpanzees. Serum samples collected weekly during 24–29 weeks of follow-up were tested for HCV RNA by means of in-house reverse transcription–nested polymerase chain reaction (PCR) with 5′ untranslated region primers and/or by means of quantitative tests (see Materials and Methods) (black rectangles, positive by reverse transcription–nested PCR and/or quantitative test; white rectangles, negative by reverse transcription–nested PCR). The estimated HCV RNA titers (black circles), determined by means of an in-house TaqMan assay, were plotted against time; samples below the detection limit of ~10 IU/mL are shown as not detected (ND). Anti-HCV antibodies were detected in the second-generation enzyme-linked immunosorbent assay (plus signs, positive detections; minus signs, negative detections). The shaded area represents serum alanine aminotransferase (ALT) level. Weekly liver biopsy specimens were collected and examined for necroinflammatory changes (graded as 0 [normal], 1 [mild], 2 [mild-moderate], 3 [moderate-severe], or 4 [severe]).