Hepatitis B virus (HBV) mutants resistant to treatment with nucleoside or nucleotide analogs and those with the ability to escape from HBV-neutralizing antibody have the potential to infect HBV-vaccinated individuals. To address this potential serious public health challenge, we tested the efficacy of immunity induced by a commercial hepatitis B vaccine against a tissue culturederived, clonal HBV polymerase mutant in HBV seronegative chimpanzees. The polymerase gene mutant contained a combination of three mutations (rtV173L, rtL180M, rtM204V), two of which resulted in changes to the overlapping viral envelope of the hepatitis B surface antigen (sE164D, sI195M). Prior to the HBV mutant challenge of vaccinated chimpanzees, we established virologic, serologic, and pathologic characteristics of infections resulting from intravenous inoculation of the HBV polymerase gene mutant and the sG145R vaccine-escape surface gene mutant. Cloning and sequencing experiments determined that the three mutations in the polymerase gene mutant remained stable and that the single mutation in the surface gene mutant reverted to the wild-type sequence. Immunological evidence of HBV replication was observed in the vaccinated chimpanzees after challenge with the polymerase gene mutant as well as after rechallenge with serum-derived wild-type HBV (5,000 chimpanzee infectious doses administered intravenously), despite robust humoral and cellular anti-HBV immune responses after hepatitis B vaccination. Conclusion: Our data showing successful experimental infection by HBV mutants despite the presence of high anti-HBs levels considered protective in the vaccinated host are consistent with clinical reports on breakthrough infection in anti-HBs-positive patients infected with HBV mutants. In the absence of a protective humoral immunity, adaptive cellular immune responses elicited by infection may limit HBV replication and persistence. (HEPATOLOGY 2009;49:1483-1491.)
H epatitis B is a global health problem; an estimated 350 million people worldwide are chronically infected with hepatitis B virus (HBV) and are at risk of developing chronic active hepatitis, liver cirrhosis, and primary liver cancer. 1 Vaccination against HBV prevents new infections and efforts toward the control of chronic disease have involved the therapeutic inhibition of viral replication using analogs of nucleotides or nucleosides. 2 Lamivudine was the first drug in this class to be licensed for the treatment of chronic hepatitis B and remains in widespread use. Antiviral drug-resistant mutations selected during treatment with lamivudine in the HBV polymerase gene (Pol) clustered within its B domain (rtV173L, rtL180M) and in the C domain in the conserved YMDD motif (rtM204V). 3,4 It has been reported that these mutant viruses are transmissible 5 and may have the potential to cause breakthrough infections among recipients of hepatitis B vaccine. 6,7 The development of