Hepatitis delta virus facilitates the selection of hepatitis B virus mutants in vivo and functionally impacts on their replicative capacity in vitro.

To identify molecular interactions between hepatitis B virus (HBV) and hepatitis delta virus (HDV), HBV sequences were analysed in HBV/HDV-infected patients. Characteristic amino acid substitutions were found in cytosolic domains of hepatitis B surface antigen (HBsAg), in contrast to HBV-mono-infected controls. The functional impact of HDV on the replication of wild-type and mutant HBV was assessed in vitro. HDV co-transfection significantly reduced the replication of HBV strains containing precore or basal core promoter mutations, and HBV polymerase or surface antigen mutants affected HDV replication in vitro. Conclusively, our study revealed distinct HBsAg mutational patterns in HBV/HDV-infected patients and novel functional interactions between HBV and HDV.

Comprehensive analysis of mutations in the hepatitis delta virus genome based on full-length sequencing in a nationwide cohort study and evolutionary pattern during disease progression.

Delta hepatitis, caused by co-infection or super-infection of hepatitis D virus (HDV) in hepatitis B virus (HBV) -infected patients, is the most severe form of chronic hepatitis, often progressing to liver cirrhosis and liver failure. Although 15 million individuals are affected worldwide, molecular data on the HDV genome and its proteins, small and large delta antigen (S-/L-HDAg), are limited. We therefore conducted a nationwide study in HBV-HDV-infected patients from Iran and successfully amplified 38 HDV full genomes and 44 L-HDAg sequences from 34 individuals. Phylogenetic analyses of full-length HDV and L-HDAg isolates revealed that all strains clustered with genotype 1 and showed high genotypic distances to HDV genotypes 2 to 8, with a maximal distance to genotype 3. Longitudinal analyses in individual patients indicated a reverse evolutionary trend, especially in L-HDAg amino acid composition, over time. Besides multiple sequence variations in the hypervariable region of HDV, nucleotide substitutions preferentially occurred in the stabilizing P4 domain of the HDV ribozyme. A high rate of single amino acid changes was detected in structural parts of L-HDAg, whereas its post-translational modification sites were highly conserved. Interestingly, several non-synonymous mutations were positively selected that affected immunogenic epitopes of L-HDAg towards CD8 T-cell- and B-cell-driven immune responses. Hence, our comprehensive molecular analysis comprising a nationwide cohort revealed phylogenetic relationships and provided insight into viral evolution within individual hosts. Moreover, preferential areas of frequent mutations in the HDV ribozyme and antigen protein were determined in this study.