Tracking the naturally occurring mutations across the full-length genome of hepatitis B virus of genotype D in different phases of chronic e-antigen-negative infection

Abstract

Clin Microbiol Infect 2012; 18: E412–E418 Abstract Hepatitis B e‐antigen (HBeAg)‐negative chronic HBV infection is highly prevalent in several parts of the world, including India, with the clinical spectrum ranging from inactive carrier (IC) state to chronic ‘e‐negative’ hepatitis B (CHB) and culminating in advanced liver disease such as cirrhosis (LC). The present study has for the first time investigated the natural diversity of HBV belonging to genotype D in treatment‐naïve Indian patients representing the above phases of HBeAg‐negative infection to identify candidate mutations associated with each disease state. Studies of full‐length HBV/D sequences revealed that the progressive accumulation and persistence of mutations in basal core promoter, negative regulatory element, Pre‐core region, the B‐ and T‐cell epitopes of X protein as well as deletions in the PreS region contribute significantly to disease progression from IC through CHB to LC. In addition, the development of CHB was associated with a significant increase in viral variants characterized by mutations in enhancer II, preS1 promoter, T‐cell epitope of core and B‐cell epitope region of PreS1. While few of the mutations were previously reported in the context of HBV genotypes B and C, others had not been documented before. Our results thus highlight a distinct pattern of mutation in HBV/D that may help in predicting clinical outcomes of HBeAg‐negative infection and have implications for better clinical management of the patients.

Immune-driven adaptation of hepatitis B virus genotype D involves preferential alteration in B-cell epitopes and replicative attenuation—an insight from human immunodeficiency virus/hepatitis B virus coinfection

“…We also included wellcharacterized, treatment-naive, immune-active EN-CHB patients (n = 13) from SDLD, who participated in our previous study [2]. In both cases, patients with HIV, hepatitis C virus or hepatitis δ virus infection, or possessing co-morbidities like diabetes mellitus, chronic alcoholism, intravenous drug abuse, or subjected to any prolonged (>7 days) drug therapy or showing evidence of cirrhosis and hepatocellular carcinoma were excluded.…”

“…HBV gene expression is controlled by two enhancers (Enh-I and Enh-II) and four promoters [2]. The basal core promoter (BCP) of HBV from EN-CHB, EP-CHB and HIV/HBV-coinfected subjects showed no significant difference with respect to the commonly described mutations, A1762T and G1764A that caused reduced HBeAg expression.…”

“…For all HBV ORFs, pairwise estimates of the number of synonymous substitutions/synonymous site (d S ) and the number of non-synonymous substitutions/non-synonymous site (d N ) were computed using a modified Nei-Gojobori model with Jukes-Cantor correction as implemented in MEGA5. Values of d S and d N were estimated for all published Tc-, Thand B-cell epitopes of HBV [2,[10][11][12], along with overlapping epitope and non-epitope regions. HBV sequence variability in different patient groups was analysed with the help of multiple alignment data.…”

“…The immune-active phase of CHI can be classified as hepatitis B e antigen (HBeAg)-positive (EP) or HBeAg-negative (EN) chronic hepatitis B (CHB) depending on HBeAg status and patients in either phase typically featured high HBV DNA and liver enzymes (alanine aminotransferase and aspartate aminotransferase) in sera and increased histological activity, reflecting immune-mediated lysis of infected hepatocytes [3]. High rates of nucleotide and amino acid changes had been reported in HBV from both EP-CHB and EN-CHB patients [2,4]; however, the extent of genetic diversity in HBV that results from host immune pressures remains unclear, unlike in human immunodeficiency virus (HIV) or hepatitis C virus infection, where immune-driven escape mutations have been well-studied [5,6]. Different studies suggest that approximately 10% of HIV-infected patients have chronic HBV coinfection because of shared transmission routes [7].…”

“…It replicates its genome via an error-prone reverse transcription that provides an increased opportunity for accumulation of mutations across its four overlapping open reading frames (ORFs), pre-S1/pre-S2/S, pre-C/C, P and X [2]. However, the appearance and persistence of these mutations is uniquely linked to the repertoire of antiviral responses exerted by the B-cell and T-cell arms of the host immune system, which favours the selection of viral variants that can escape immune recognition and have better adaptation in the host.…”