Six-year follow-up of hepatitis B surface antigen concentrations in tenofovir disoproxil fumarate treated HIV-HBV-coinfected patients

Background: Quantitative measurement of hepatitis B surface antigen (HBsAg) has been proposed as a surrogate marker of treatment efficacy when HBV DNA load becomes undetectable. Our main objective was to study the kinetics of HBsAg level in HIV-HBV-coinfected patients with undetectable HBV DNA load under treatment containing tenofovir disoproxil fumarate (TDF). Methods: A retrospective analysis was performed on frozen serum samples of 33 HIV-HBV-coinfected patients who were treated with TDF and had undetectable HBV DNA for >= 1 year. Baseline and serial follow-up samples were assayed for HBsAg levels. Results: The characteristics of the patients at TDF initiation were median age 43.6 years, median HBV DNA load 2 log(10) IU/ml and median HBsAg concentration 3.4 log(10) IU/ml. Ten patients were positive for hepatitis B e antigen. Baseline median HBsAg concentration, defined 1 year after HBV DNA became undetectable, was 3.1 log(10) IU/ml. Overall, from years 1 to 6 and a median duration of TDF treatment of 2.6 years, the median HBsAg concentration decreased slowly. Notably, only 13 (39%) patients presented a constant decrease of HBsAg concentration, whereas the remaining had fluctuating or increasing HBsAg concentrations. The slope was not influenced by HBeAg status, HIV infection duration and CD4(+) T-cell count at baseline or at nadir. Conclusions: Despite control of HBV DNA replication under efficient TDF treatment, HBsAg levels persistently decreased in only 39% of HIV-HBV-coinfected patients. Larger follow-up studies are needed to determine whether HBsAg concentration monitoring under analogue treatment can be used as a reliable marker for HBV clearance.