The aim of the study was to assess the role of different viral strains of hepatitis C virus (HCV) in determining the outcome of the alpha-interferon (IFN) therapy. Fifty-seven patients (34 from Italy and 23 from Japan) with HCV-positive liver disease were enrolled in the study. The NS4 region of HCV was amplified in sera by "nested" polymerase chain reaction (PCR) using a primer pair synthesized according to the sequence of JK-1. The NS4 region was positive in 14 (41%) Italian and in 13 (56%) Japanese patients. In positive patients the sequence of the NS4 region was also obtained. Subsequently, HCV genotype was determined in all patients by PCR amplification of the core region. All patients received recombinant alpha2a-interferon (IFN), 6 million units 3 times a week for 1 month followed by 3 million units 3 times a week for 5 months. The patients were followed for 1 year after the end of treat- ment. At the end of the follow-up, 17 (30%) had sustained normal levels of serum alanine aminotransferase (ALT). The outcome of treatment was not correlated with race, age, sex, histology, and pretreatment ALT level, but was significantly (P < 0.00001) associated with the presence of both the NS4-JK-1 region and HCV type II. Among the 27 NS4-positive patients, only 1 patient (3.7%) achieved a complete response, whereas the remaining 26 patients (96.3%) either were non-responders or relapsed after IFN was discontinued. In contrast, among the 30 NS4-JK-I-negative patients, 15 (53%) had a sustained remission. HCV genotyping showed type I in 3 (So/,), type II in 40 (74%), type Ill in 4 (7%), and type IV in 3 (6%) cases. Coinfection was present in 4 (7%), while in 3 cases amplification was not obtained. Patients with type II were all non-responders or relapsers, while a response to the treatment was oberved in 17 of 17 (100%) of the remaining patients. These data indicate that the presence of JK-1 variant of HCV or HCV type II is
almost always predictive of a poor response rate of IFN therapy.