Sloan, RD; (2008) Studies into the transmission of hepatitis B virus that mutate following therapy with nucleoside analogues and the potential for such transmission to be serologically undetectable. Doctoral thesis , UCL (University College London).

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Abstract

The hepatitis B virus (HBV) genome is organised so that the open reading frame encoding the polymerase overlaps that encoding hepatitis B virus surface antigen (HBsAg). Previous studies showed that acquisition of lamivudine resistance-associated mutations in pal result in a decreased affinity of HBsAg for its antibody (anti-HBs). It was sought to characterize epitope changes in the major immunogenic domain of HBsAg, the "a" determinant, that result from lamivudine, adefovir and entecavir resistance mutations. Recombinant (r) HBsAg was produced by transfecting Chinese Hamster Ovary cells (CHO) with a plasmid containing the surface open reading frame modified by site-directed mutagenesis to mimic mutations selected in the overlapping pol/S gene during antiviral therapy. Wild type and mutant rHBsAgs expressed from these constructs were assayed using a series of EIAs each employing a monoclonal antibody which binds distinct epitopes in the first and second loop of the "a" determinant. Specific combinations of mutations led to variable loss of immunoreactivity of the epitopes of the "a" domain, despite some mutations not being located in that domain. Some combinations of mutations led to restoration of reactivity of epitopes which were abrogated by single mutations. Thus mutations associated with antiviral resistance have the potential to affect serological reactivity through concomitant amino acid substitutions in HBsAg. These observations may have implications for the clinical treatment of chronic HBV, diagnostics and vaccine programmes. The molecular epidemiology of antiviral-associated mutants in England and Wales between 1997-2001 was also assessed. HBV DNA from the 1st 600 bases of the HBsAg-coding gene was amplified from 163 patients with acute hepatitis B and subjected to phylogenetic analysis. None of the patients were found infected with HBV mutants that would have arisen following the development of antiviral resistance or with vaccine-escape mutants. Transmission by pre-existing iatrogenic HBV mutants was therefore rare or did not occur.

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