HEPATOLOGY Elsewhere 461 of HCV, the major population represented is interferon-sensi-ferent responses to IFN treatment. There were two groups: one consisted of nonresponders (n Γ
63); the other consisted tive, but during or following IFN treatment in nonresponders, an IFN-resistant clone(s) constitutes the major population. of complete responders (n Γ
21). The amino acid sequence analysis of the NS5A-ISDR indicated that there were three The difference was seen mainly in the E2, NS2, and NS5A regions in patient 1, in the E2 and NS5A region in patient groups: (1) wild-type with sequences identical to that of prototype HCV-J (n Γ
30), (2) intermediate-type with only one to 2, and in the NS5A region in patient 3. Although there were other scattered differences, the main differences were consid-three amino acid substitutions (n Γ
38), and (3) mutant-type with more than four amino acid changes (n Γ
16). The results ered to be clustered in the C-terminal region of the NS5A, particularly codons 2154-2383, and in the E2-hypervariable were clear. All of the 30 patients infected with wild-type HCV were nonresponders, and all of the 16 mutant HCV-infected region (HVR). After further pairwise comparison, these three pairs were found to have unique amino acid substitutions at patients were complete responders. Only 5 of the 38 patients infected with intermediate-type HCV were complete respond-codon 2218. They were glutamine, arginine, and cysteine in patients 1, 2, and 3, respectively, pretreatment. All changed ers. This time, however, the striking difference was not observed between sensitive and resistant clones at codon 2218. to histidine posttreatment. The previously published HCV type 1b (HCV-J, HCV-J4, and HCV-JTa) possesses a histidine Statistical analysis revealed that HCV RNA levels in sera before treatment were significantly lower in the patient residue at 2218. This was the only commonly observed amino acid difference before and after IFN treatment in three nonre-group with mutant-type than those with wild or intermediate types. However, for each individual the amount of HCV RNA sponders. Amino acid differences were detected in other regions, particularly the E2 hypervariable region. However, did not correlate with IFN responsiveness. Thus, it seems likely that the HCV clones that have identical or very similar there were no common changes among the three HCV isolates obtained from patients 1, 2, and 3. The authors considered amino acid sequences to that of wild-type in the ISDR are resistant to IFN therapy. that the pretreatment HCV sequence represented IFN-sensitive HCV and the posttreatment sequence that of an IFN-Viruses of the Flaviviridae family have a similar region corresponding to HCV NS5A. However, the biological func-resistant clone. It should be cautioned that the nucleotide sequence was determined by the direct method, and it was tion of these NS5As is not yet known. It was recently shown that it is a hyperphosphorylated protein. The candidate hy-thus not clear whether the IFN-resistant clone was originally present in the pretreatment samples as a minor population. perphosphorylation site is positioned at serine residues located near the ISDR described by these papers. 5 These papers The above results were clear but not conclusive. The authors extended the study by examining HCV sequences from six IFN by Enomoto et al. 2 provide a potentially important new predictor of IFN responsiveness. They also may provide clues nonresponders and nine complete responders. This time, they only examined sequences of the C-terminal half of the NS5A. The regarding potential virus-cell interactions in HCV infection.
When an efficient in vitro replication system is developed, it 9 IFN-resistant clones were from ''after'' samples of the previous patients 1 through 3 and new nonresponder patients 4 through would be very interesting to compare the virological behavior between HCV clones with wild-type or mutant sequences in 9. The 12 IFN-sensitive clones were ''before'' samples of patients 1 through 3 and responder patients 10 through 18. The amino the ISDR, particularly with regard to their replication activity. acid sequences from 2209 to 2248 of the former group were identical to those of prototype HCV 1b. In contrast, clones obtained from the latter group had at least one amino acid change in this TATSUO MIYAMURA, M.D. region. The clone from patient 18 even had an eight-amino acid Department of Virology II insertion between codon 2221 and 2222. Particularly illuminat-National Institutes of Health ing findings were again revealed at codon 2218. Clones from the Tokyo, Japan former group and from previous isolates (HCV-J, HCV-J4, and HCV JTa) possessed histidine at 2218. However, the amino acid REFERENCES