Long-term follow-up of chimpanzees inoculated with the first infectious clone for hepatitis C virus

Two chimpanzees (Ch1535 and Ch1536) became infected with hepatitis C virus (HCV) following intrahepatic inoculation with RNA transcribed from a full-l ength cDNA clone of the virus. Both animals were persistently infected and have been followed for 60 weeks. They showed similar responses to infection , with transient liver enzyme elevations and liver inflammatory responses, which peaked at weeks 17 (Ch1535) and 12 (Ch1536) postinoculation (p.i.). A ntibody responses to structural and nonstructural proteins were first detec ted at weeks 13 (Ch1535) and 10 (Ch1536) p.i. Serum RNA titers increased st eadily during the first 10 to 13 weeks but decreased sharply in both animal s following antibody and inflammatory responses. Despite direct evidence of humoral immune responses to multiple viral antigens, including hypervariab le region 1 (HVR1), both animals remained chronically infected. Detailed se quence analysis of serum HCV RNA revealed no change in the majority HVR1 se quence in Ch1535 and a single-amino-acid mutation in Ch1536, with very litt le clonal variation in either animal. Full-length genome analysis at week 6 0 revealed several amino acid substitutions localized to antigens E1, E2, p 7, NS3, and NS5. Of these, 55.6 and 40% were present as the majority sequen ce in serum RNA isolated at week 26 p.i. (Ch1535) and week 22 p.i. (Ch1536) , respectively, and could represent immune escape mutations. Mutations accu mulated at a rate of 1.57 x 10(-3) and 1.48 x 10(-3) nucleotide substitutio ns/site/year for Ch1535 and Ch1536, respectively. Taken together, these dat a indicate that establishment of a persistent HCV infection in these chimpa nzees is not due to changes in HVR1; however, the possibility remains that mutations arising in other parts of the genome contributed to this persiste nce.