Hepatitis C virus NS5A protein inhibits inteferon antiviral activity, but the effects do not correlate with clinical response

Background & Aims: Patients with chronic hepatitis C virus infection are commonly treated with interferon alfa (IFN-alpha), but the long-term response rate is poor. A region of NS5A of hepatitis C virus genotype 1 (the ISDR) has been associated with treatment outcome in some patients. NS5A binds to and inhibits PKR in vitro and inhibits IFN-alpha in human cells. We examined the effects of the NS5A protein from patients who did or did not respond to IFN-alpha to determine whether NS5A from IFN-alpha nonresponders inhibited the effects of IFN-alpha in vitro. Methods: We cloned NS5A from patients who had well-characterized responses to IFN-alpha and expressed them in a human fibroblast cell line under the control of an inducible promoter. The NS5A expression levels were controlled, and the effects of different proteins on the protective actions of IFN-alpha against encephalomyocarditis virus were investigated. Results: NS5A expression blocked the antiviral effects of IFN-alpha in human cells, This inhibition was dependent on the level of NS5A expression. Although ISDR changes gave only small differences in IFN-alpha inhibition, clones derived from a patient who did not respond to IFN-alpha and one who did respond to treatment differed greatly: the clones from a patient with response to IFN-alpha were much more inhibitory than those derived from the patient with no response. Conclusions: The inhibition of the antiviral effects of IFN-alpha by NS5A is not regulated exclusively by the ISDR, and the effects of NS5A in vitro do not correlate with treatment outcomes.