Quasispecies analysis and in vitro susceptibility of HBV strains isolated from HIV-HBV-coinfected patients with delayed response to tenofovir.

BACKGROUND Among 141 HIV-HBV-coinfected patients treated with tenofovir in our centre, 87% were good-responders to therapy. Seven patients showed a delayed response to tenofovir. The present study was performed to evaluate the quasispecies variability and the in vitro drug susceptibility to approved antiviral drugs of HBV genomes directly isolated from patients' sera. METHODS After purification of DNA from serum samples, full-length HBV DNA was amplified by PCR, cloned and sequenced. Drug sensitivity of HBV strains isolated from four delayed responders and five good-responders was assessed and compared to a wild-type HBV strain after transfection of the full genome into HepG2 cells. RESULTS Delayed responders, compared with good responders, showed a higher incidence of lamivudine-resistant mutations (71% and 35%, respectively; P=0.021) and a higher proportion of HBV genotype G (57% versus 16%, respectively; P=0.026). Clonal analysis demonstrated a higher variability of HBV quasispecies in delayed reponders than in good responders. In vitro analysis showed a lower efficacy of adefovir and tenofovir in delayed reponders. Furthermore, HBV genotype G strains showed a mild to weak susceptibility to tenofovir. CONCLUSIONS The reason for the slow decline in HBV DNA level observed during therapy in delayed responders is not clear. Delayed responders showed higher quasispecies variability, a higher proportion of HBV genotype G and a mild in vitro decreased susceptibility to tenofovir and adefovir. A combination of these factors in heavily treatment-experienced HIV-infected patients could explain the lower tenofovir activity. These patients must be closely monitored to prevent prospective emergence of resistance to approved antiviral drugs.