Characterization of HBV surface antigen isoforms in the natural history and treatment of HBV infection.

BACKGROUND: The loss of HBV HBsAg or functional cure is a desirable goal of hepatitis B management. The relative abundances of HBsAg isoforms may offer additional diagnostic and predicting values. To evaluate the clinical utility of HBsAg isoforms, we developed novel prototype assays on the ARCHITECT automated serology platform that specifically detects total-HBsAg (T-HBsAg), large (L-HBsAg), and middle (M-HBsAg) products of the S gene to determine the isoform composition of human specimens from acute and chronic HBV infection and during long-term nucleos(t)ide analog therapy. RESULTS: In the early phase of acute HBV infection, L-HBsAg and M-HBsAg emerged within days and were in parallel to T-HBsAg during the entire course of infection. M-HBsAg levels were consistently higher than L-HBsAg levels. Patients with HBeAg(+) chronic hepatitis B had higher T-HBsAg, M-HBsAg, and L-HBsAg levels compared with HBeAg(-) patients. Correlations of M-HBsAg and L-HBsAg to T-HBsAg were similar in both. In contrast, there was no strong correlation between L-HBsAg or M-HBsAg with HBV DNA levels. During long-term nucleos(t)ide analog treatment, changes in HBsAg isoform abundance were proportional to T-HBsAg regardless of treatment responses for both HBeAg(+) and HBeAg(-) chronic hepatitis B. A larger sample size may be necessary to detect a significant difference. CONCLUSION: HBsAg isoform compositions parallel T-HBsAg levels in both acute and chronic hepatitis B infection. L-HBsAg and M-HBsAg individual biomarkers do not appear to provide an additional diagnostic benefit for staging chronic disease or monitoring response to treatment with current therapies.