Molecular analysis of antigenicity and immunogenicity of a vaccine-induced escape mutant of hepatitis B virus

To analyze the mechanisms of mutant escape, we established a murine model of hepatitis B virus (HBV) infection and studied the interaction of the envelope protein of the virion with various kinds of anti-hepatitis B antibody. Mutation from glycine to arginine at aa145 was introduced into replication-competent DNA of HBV. The resulting mutant HBV DNA was transfected into cultured hepatoma cells and livers of mice using liposome-mediated gene transfer. Then, interactions between the antigenic envelope protein (in culture or in circulation) and anti-hepatitis B antibody were examined. Mutant envelope protein escaped human hepatitis B immunoglobulin, rabbit polyclonal anti-hepatitis B surface antigen (HBsAg) antibody, and monoclonal anti-a antibody in vitro and in vivo. There was a difference in the degree of inhibition between hepatitis B immunoglobulin and the other two antibody types in vitro. Transfection with an HBV construct containing a mutation in the a-loop resulted in levels of HBsAg in circulation and seroconversion to anti-HBs antibody that were similar to those produced by a wild-type construct. The degree of escape by the mutant envelope protein differed according to antibody type. Of the three types of antibody used in this study, HBV immunoglobulin was least affected by mutation in the a-loop. There appears to be no correlation between antigenicity and immunogenicity of the escape mutant, and the a-loop mutant may cause hepatitis with the usual serum viral markers.