Distinct quasispecies characteristics and positive selection within precore/core gene in hepatitis B virus HBV associated acute-on-chronic liver failure

Background and Aim The cause of hepatitis B virus associated acute-on-chronic liver failure (ACLF) remains unclear. Quasispecies can contribute to virus persistence and pathogenesis. We used a bioinformatics-based molecular evolution approach to compare quasispecies characteristics and positive selection sites within HBV precore/core gene between ACLF and chronic hepatitis B (CHB) patients. Methods HBV precore/core gene were amplified from 11 ACLF and 10 CHB patients harboring HBV genotype B; following DNA cloning and sequencing quasispecies complexity, diversity, and positive selection sites within the precore/core gene were determined by bioinformatics analysis, and compared between the patient groups. Results Both quasispecies complexity (P=0.022 at nucleotide level and 0.008 at amino acid level) and diversity (P<0.05) were found to be significantly greater in ACLF than in CHB. The frequency of G1896/A mutation in ACLF (175/298 clones, 58.7%) was also significantly higher than in CHB (100/230 clones, 43.5%) (P=0.0005). Moreover, analysis of positive selection revealed that significantly more patients with such sites were present in ACLF than in CHB (8/11 VS 2/10, P=0.03); the majority of these positive selection sites lay within HLA-restricted epitopes. Conclusions The ACLF patients showed distinct quasispecies characteristics with higher complexity and diversity within the HBV precore/core gene. The increased HBV quasispecies complexity and diversity, together with a distinct set of positive selection sites, is likely associated with the development of ACLF.