Application of the trak-C™ HCV core assay for monitoring antiviral activity in HCV replication systems

The Ortho ® trak-C™ immunoassay has recently established detection of the HCV core antigen as a viable indirect marker of HCV replication in clinical samples. In this study, trak-C™ is used to monitor HCV replication in three pre-clinical models: the cellular HCV replicon system, transient transfection of HCV genomes, and the murine Alb-uPa/SCID HCV infection model. All of these systems utilize full-length HCV genomes that direct the expression of core, facilitating its detection with monoclonal antibodies. When performed with purified protein, the assay detects HCV core with a lower limit of detection at 1.5 pg, and exhibits linear detection up to 100 pg. When assaying extracts prepared from Huh-7 clone 21-5 cells harboring a full-length HCV replicon, core is detectable from as few as 63 cell equivalents. The assay was used to determine the sensitivity of Huh 21-5 cells to the antiviral effects of interferon (IFN). Inhibition by IFN-α using core detection was comparable to that observed using branched-DNA (bDNA 3.0) detection of HCV RNA. Replication of transfected full-length HCV 1a Con1 genomes in Huh-7 cells was also detectable using the trak-C™ assay. Finally, in the transgenic murine HCV infection model, the course of viral amplification was detected from serum using trak-C™ with kinetics similar to those observed with RNA detection. Given its ease of use and the lack of requirement for RNA purification, the trak-C™ assay has several advantages over RNA-based methods of viral monitoring.