Development of a hypersensitive digital ELISA system for hepatitis B core antigen

Chronic hepatitis B (CHB) is a global health threat caused by the hepatitis B virus (HBV). Nucleos(t)ide analogs (NUCs) are the standard treatment for CHB patients with HBV replication. However, NUCs cannot eliminate covalently closed circular DNA (cccDNA), the template for HBV replication, from the nuclei of hepatocytes; hence, patients with CHB need life-long treatment with NUCs because HBV relapses easily upon cessation of NUCs because of the residual cccDNA. However, NUCs can be terminated by accurately monitoring the activity of the cccDNA. Despite the recent development of highly sensitive detection systems for HBV biomarkers, the detection accuracy remains poor, especially at lower concentrations. Therefore, it is desirable to develop more sensitive and reliable biomarkers that have a good correlation with cccDNA, even at lower concentrations. In this study, we developed a digital enzyme-linked immunosorbent assay (ELISA) system for detecting hepatitis B core antigen (HBcAg) using a pair of monoclonal antibodies. The digital ELISA system successfully detected 2.9 pg/mL, which can be converted to 58 aM HBcAg, and the sensitivity was approximately 1000 times higher than that of conventional ELISA. Furthermore, the influence of plasma and serum matrices on the sensitivity can be ignored if the concentrations of the matrices are 1% or less. In addition, the antibody-blocking assay indicated that the digital ELISA system reacted specifically with HBcAg, even in the presence of serum or plasma. Collectively, our highly sensitive digital ELISA system for detecting HBcAg is a potentially new approach for evaluating therapeutic strategies for CHB.