Background and aim: Since polymerase and surface genes overlap in hepatitis B virus (HBV), an antiviral-induced mutation in the polymerase gene may alter the surface antigenicity in patients with chronic hepatitis B (CHB), but this possibility has not been clearly confirmed. This study aimed to determine the drug susceptibility and surface antigenicity of the patient-derived mutants.
Patients and methods: Full-length HBV genomes isolated from four entecavir-resistant CHB patients were cloned and sequenced. Around 10 clones of full-length HBV obtained from each patient were analysed and registered in the NCBI GenBank. Representative clones were further characterized by in vitro drug susceptibility and surface antigenicity assays.
Results: The rtL180M + rtM204V mutations were common among all the clones analysed. Additionally, the ETV resistance mutations rtT184A/L, rtS202G and rtM250V were found among three patients. Most of the ETV-resistant mutants had amino acid alterations within the known epitopes recognized by T- and B-cells in the HBV surface and core antigens. The in vitro drug susceptibility assay showed that all tested clones were resistant to ETV treatment. However, they were all susceptible to ADV and TDF. More importantly, the rtI169T mutation in the RT domain, led to the sF161L mutation in the overlapping S gene, which decreased in surface antigenicity.
Conclusions: The ETV resistance mutations can affect the antigenicity of the HBsAg proteins due to changes in the overlapping sequence of this surface antigen. Thus, the apparent decline or disappearance of HBsAg needs to be interpreted cautiously in patients with previous or current antiviral resistance mutations.
Keywords: antivirals; drug resistance; entecavir; hepatitis B virus; surface antigenicity.
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