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Recent clinical studies suggest that hepatitis B virus (HBV) load and genotype may be independent predictors of responses to antiviral therapies. However, it is difficult for clinicians to accurately determine viral loads in patient samples because results—both the values and the units of measure—can vary greatly among different tests. Accordingly, the World Health Organization (WHO) has produced the first international standard for HBV DNA for nucleic acid amplification technology (NAT) assays. In the present study, we describe the performance of the target-capture PCR HBV DNA quantitative assay for the quantitation of HBV DNA in clinical samples and reference panels. The range of quantitation was between 50 and 10 10 IU/ml. The sensitivity and accuracy of the target-capture PCR assay were demonstrated by using the HBV panel from Quality Control for Medical Diagnostics (QCMD) and the WHO HBV DNA standard. The target-capture PCR assay quantitated the six genotype A members of the QCMD panel and dilutions of the WHO HBV DNA standard within an accuracy of 74 to 142%. Compared to current serological methods, the assay offers window period reductions of 19 days prior to HBV surface antigen and 26 days prior to HBV e antigen detection. The target-capture PCR assay was also compared with four commercially available NAT assays, and the various units of measure were standardized with respect to the international units of the WHO HBV DNA standard. The target-capture PCR assay is a sensitive, accurate, high-throughput, rapid, and reproducible assay for the determination of HBV loads.

The current commercially licensed enzyme-linked immunosorbent assays (ELISAs) for hepatitis C virus (HCV) mainly use recombinant proteins containing linear epitopes. There is evidence, however, that conformational epitopes of HCV are more immunoreactive. Thus, we have designed an HCV antibody assay that employs a conformational protein, NS3NS4a PI (with functional protease and helicase activities), and a linear fusion protein, multiple-epitope fusion antigen 7.1 (MEFA 7.1) or MEFA 7.2. We have shown that NS3NS4a PI detects early-seroconversion conformation-sensitive antibodies better than c33c antigen. The correct conformation of NS3NS4a PI also cross-reacts with different genotype samples better than the c33c antigen. MEFA 7.1 and MEFA 7.2 incorporate all the major immunodominant and genotype-specific epitopes of HCV core, E1, E2 hypervariable region 1 (HVR1), E2 HVR1-plus-HVR2 consensus, NS3, NS4, and NS5. Since MEFA 7.1 is degraded by the active NS3NS4a PI protease, we designed a second MEFA 7.2 construct in which the six protease cleavage sites found in MEFA 7.1 were eliminated by amino acid mutation. We demonstrate here that MEFA 7.2 remains intact in the presence of NS3NS4a PI and preserves the epitopes present in MEFA 7.1. Compared to currently licensed assays, an ELISA incorporating a combination of the two antigens NS3NS4a PI and MEFA 7.1 or 7.2 demonstrates better serotype sensitivity and detects seroconversion earlier in many commercially available panels. We believe that an assay using NS3NS4a PI and MEFA 7.1 or 7.2 may have the potential to replace current HCV immunoassays for better sensitivity.