Efficient Infectious Cell Culture Systems of the Hepatitis C Virus (HCV) Prototype Strains HCV-1 and H77

The first discovered and sequenced hepatitis C virus (HCV) genome and the first in vivo infectious HCV clones originated from the HCV prototype strains HCV-1 and H77, respectively, both widely used in research of this important human pathogen. In the present study, we developed efficient infectious cell culture systems for these genotype 1a strains by using the HCV-1/SF9_A and H77C in vivo infectious clones. We initially adapted a genome with the HCV-1 5=UTR-NS5A (where UTR stands for untrans-lated region) and the JFH1 NS5B-3=UTR (5-5A recombinant), including the genotype 2a-derived mutations F1464L/A1672S/ D2979G (LSG), to grow efficiently in Huh7.5 cells, thus identifying the E2mutation S399F. The combination of LSG/S399F and reported TNcc(1a)-adaptive mutations A1226G/Q1773H/N1927T/Y2981F/F2994S promoted adaptation of the full-length HCV-1 clone. An HCV-1 recombinant with 17 mutations (HCV1cc) replicated efficiently in Huh7.5 cells and produced superna-tant infectivity titers of 104.0 focus-forming units (FFU)/ml. Eight of these mutations were identified from passaged HCV-1 vi-ruses, and the A970T/I1312V/C2419R/A2919Tmutations were essential for infectious particle production. Using CD81-deficient Huh7 cells, we further demonstrated the importance of A970T/I1312V/A2919T or A970T/C2419R/A2919T for virus assembly and that the I1312V/C2419R combination played a major role in virus release. Using a similar approach, we found that NS5B mutation F2994R, identified here from culture-adapted full-length TN viruses and a common NS3 helicase mutation (S1368P) derived from viable H77C and HCV-1 5-5A recombinants, initiated replication and culture adaptation of H77C containing LSG and TNcc(1a)-adaptive mutations. An H77C recombinant harboring 19 mutations (H77Ccc) replicated and spread efficiently after transfection and subsequent infection of naive Huh7.5 cells, reaching titers of 103.5 and 104.4 FFU/ml, respectively