Quasispecies and pre-existing drug-resistant mutations of hepatitis B virus in patients with chronic hepatitis B

Background/Aims: To investigate pre-existing hepatitis B virus (HBV) quasispecies and the genotypic evolution of several variants. Methods: From six patients with lamivudine (LAM) failure, serum samples at pretreatment, 6 months of LAM therapy, and virologic breakthrough were obtained. One hundred clones with HBV inserts in each patient were sequenced at each time point. Pretreatment serum samples were also analyzed from six patients who achieved good responses to LAM therapy. Results: Among the six patients with LAM failure, the analysis of 100 clones from patient 1 revealed the substitutions L180M in 1% of clones and V173L in 2% of clones. Patient 2 had substitutions of L80V, W153Q, and L180M. In patient 3, mutations conferring resistance to adefovir at V84I (5%), I169L (1%), and N236H (7%) and entecavir at S202G (2%) were detected. Patient 4 had mutations at T128N (1%), I169L (1%), V173L (2%), A181V (1%), and Q215H (1%). In patient 5, M204V/I was detected in 1% and 2% of clones, respectively. L80I and V173L were also identified in patient 6. In the six patients who responded to LAM, the degree of overall quasispecies was less than those with LAM failure. Conclusions: Various HBV quasispecies associated with drug resistance existed before treatment, and the quasispecies dynamically changed through LAM therapy.