Evaluation of hepatitis C virus envelope proteins expressed in E. coli and insect cells for use as tools for antibody screening

Background/Methods: The two envelope proteins of hepatitis C virus, E1 and E2, were expressed in E. coli and, as secretory proteins, in Sf9 insect cells using recombinant baculoviruses. Co-infection of insect cells with E1 and E2-recombinant baculoviruses was performed, which has been shown to result in formation of E1–E2 dimers. All envelope proteins were purified by Ni2+-NTA chromatography and used for screening of serum samples in a HCV EIA assay. Serum samples of normal blood donors, chronically HCV-infected patients, a mixed titer panel and several sero-conversion panels were screened and compared to test results with Cobas Core Anti-HCV EIA. Results: Screening of the sera of chronically HCV-infected patients (100% positive in Cobas Core Anti-HCV EIA) revealed 10–40% anti-E1 positive sera using different Sf9-expressed, glycosylated proteins and 93% using E. coli-expressed, non-glycosylated E1 protein. When the same sera were tested with different E2 proteins expressed in Sf9 cells and in E. coli, about 70–73% showed anti-E2 reactivity. When the proteins from Sf9 cells co-infected with E1- and E2-recombinant baculoviruses were tested, 70–80% of the same sera showed anti-envelope reactivity. Conclusions: Testing of these patient antisera, and those from the well-characterized mixed titer panel BBI-PHV203, showed that recombinant E1 expressed in E. coli and co-expressed E1 and E2 proteins from Sf9 cells could be used as additional tools for anti-HCV antibody screening.