ENHANCED REPLICATION OF A HEPATITIS-B VIRUS MUTANT ASSOCIATED WITH ANEPIDEMIC OF FULMINANT-HEPATITIS

Hepatitis B virus (HBV) mutants unable to synthesize HBV e antigen hav e been described in association with fulminant hepatitis. We have clon ed and sequenced the entire viral genome of an HBV strain associated w ith an epidemic of fulminant hepatitis. This strain contained, in addi tion to two G-to-A mutations in the precore region (nucleotides 1898 a nd 1901), numerous other mutations in conserved nucleotide positions r esulting in significant amino acid substitutions in HBV gene products. We introduced either or both of the two G-to-A mutations into wild-ty pe HBV by oligonucleotide-directed mutagenesis and generated replicati on-competent constructs of these mutants as well as the fulminant stra in. Viral antigen synthesis, transcription, and replication were analy zed after transfection into human hepatoma cells. All viral constructs produced and secreted similar levels of envelope proteins (HBV surfac e antigen). Analysis of cellular lysate for core-specific immunoreacti vity demonstrated a much higher level of core-associated antigens in c ells transfected with the fulminant strain. While cells transfected wi th mutant and wild-type HBV DNAs synthesized similar levels of viral R NAs, the fulminant strain directed the synthesis of a much higher leve l of core-associated replicative intermediates (as well as virion part icles) than the wild type and mutants with either or both of the preco re mutations. Increase in the encapsidation of pregenomic RNA into cor e particles is likely the basis for the enhanced replication associate d with the fulminant strain. Our study suggests that an HBV mutant wit h enhanced viral replication may be important in the pathogenesis of f ulminant hepatic failure, and mutations other than the precore mutatio ns may be responsible for this variant behavior.