Establishment of a new strategy for studying the phenotype resistance of hepatitis B virus isolates / 中华传染病杂志

ABSTRACT

Objective To establish a novel and convenient method to study the phenotype of drug resistant hepatitis B virus (HBV) isolates,and to analyze the drug susceptibility by replacing the reverse transcriptase (RT) domain of wild-type HBV with that of the drug resistant HBV isolates.Methods Full length of HBV isolates was amplified and cloned from the sera of patients prior to nucleoside/nucleotide analogues (NA) treatment.Wild-type full-length HBV genomes was used to construct the recombinant expression plasmids PHY536207 (genotype B) and PHY97 (genotype C).The restriction enzyme sites were introduced in the upstream and downstream region of reverse transeription (RT) domain to construct plasmid,which were named as mPHY536207 and mPHY97,respectively.Lamivudine (LAM) resistant mutant and adefovir (ADV) resistant mutant were isolated and cloned to construct recombinant expression plasmids PHY634 and PHY6923,respectively.Subsequently,the RT domain of mPHY536207 was replaced by that of drug resistant mutant to construct the plasmids RT634 (LAM-resistant) and RT6923 (ADVresistant).The HBV constructs were transfected into Huh7 cells.The HBsAg levels in supernatant were determined by enzyme-linked immunosobent assay (ELISA),and the amount of intracellular HBV DNA was assayed by real-time polymerase chain reaction and Southern blot analysis.Results The plasmids PHY536207 and PHY97 containing genotype B and genotype C wild-type fulllength HBV genomes were constructed successfully,both of which could replicate in Huh7 cells.Intracellular HBV DNA extracted from cells in each of six-well culture plates was more than 1 × 107 copy/ mL,and the introduction of Pst Ⅰ restriction enzyme site did not affect the viral replication and HBsAg secretion.PHY634 and RT634,in which mutant RT domain was replaced into a wild type HBV expressing vector,exhibited the same HBV DNA replication under the treatment with different doses of LAM,the value of 50％ inhibitory concentration (IC50) was ＞100 μmol/L,while the IC50 of mPHY536207 was 0.18μmol/L.Moreover,wild-type isolate was sensitive to ADV (IC50 =1.2 μmol/L),while PHY6923 and RT6923 were resistant to ADV treatment (IC50 ＞100 μmol/L).Conclusion The phenotypic assay is successfully developed in this study based on replacing RT domain of wild-type HBV strains with that of clinical isolated drug resistant strain.