| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1995: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1994: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
We have previously demonstrated that sensitivity to interferon is different among hepatitis C virus (HCV) quasispecies simultaneously detected in same individuals and that interferon-resistant HCV quasispecies are selected during the treatment. To determine the genetic basis of their resistance to interferon, HCV genotype-1b was obtained from serum of three patients before and during interferon therapy, and their full-length nucleotide and deduced amino acid sequences were determined. Comparison of the paris of interferon-resistant and interferon-sensitive HCV isolates in respective individuals demonstrated clusters of amino acid differences in the C-terminal half of the NS5A region (codon 2154-2383), which contained a common unique amino acid difference at codon 2218. Additional sequence data of the C-terminal half of the NS5A region obtained from six interferon-resistant and nine interferon-sensitive HCV confirmed the exclusive existence of missense mutations in a 40 amino acid stret
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ch of the NS5A region around codon 2218 (from codon 2209 to codon 2248) in interferon-sensitive HCV.On the other hand, this region of interferon-resistant HCV was identical to that of prototype HCV genotype-1b (HCV-J,HCV-JTa or HC-J4). We designated this region as the interferon sensitivity determining region. Thus, HCV genotype-1b with the prototype-interferon sensitivity determining region appears to be interferon-resistant strains. The specific nature of these mutations would make it possible to predict prognostic effects of interferon treatment.
Subsequently, we evaluated the possibility for predicting the response to interferon by examining the NS5A2209-2248 of pretherapy HCV.Eighty-four patients with chronic hepatitis C infected with HCV-1b were treated with high doses of interferon-alpha. The deduced amino acid sequence of the NS5A2209-2248 was determined by direct sequencing of the NS5A2209-2248 amplified from serum RNA by polymerase chain reaction. Complete responses with negative serum HCV-RNA for six months after the cessation of interferon were observed in 0 percent of 30 patients with the wild type NS5A2209-2248 (no amino acid substitution compared to the prototype HCV-1b), 13 percent of 38 patients with the intermediate type (1-3 amino acid substitutions), and 100percent of 16 patients with the mutant type (4 or more amino acid substitutions), indicating that the mutant type was significantly associated with the complete response (P<0.001). Although serum HCV-RNA level was lower in the mutant type than the others (P<0.001), multivariate analyzes revealed that the number of amino acid substitutions in the NS5A2209-2248 was the only independent predictor of the complete response (odds ratio 5.4, P=0.007). Responses to interferon are closely related to the structure of the NS5A2209-2248, which is predictive for the outcome of interferon therapy in chronic HCV-1b infection. Less
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