Transient selection of a hepatitis B virus polymerase gene mutant associated with a decreased replication capacity and famciclovir resistance

Prolonged therapy for chronic hepatitis B (HBV) with nucleoside analogs may result in the emergence of HBV mutants resistant to antivirals. Here, we d escribe the transient selection of an HBV polymerase gene mutant that was a ssociated with viral persistence in an immune competent patient treated wit h famciclovir. Viral polymerase gene sequence was analyzed directly on poly merase chain reaction (PCR) products and also after cloning. The results sh owed the transient selection of a V542I mutant in the C domain of the viral polymerase, This mutation was associated with a stop codon at amino acid p osition 199 in the overlapping S gene. The mutated sequence was subcloned i n a vector expressing the entire HBV pregenome to study its replication cap acity after transient transfection in cultured hepatoma cells. The results showed that the V542I mutant has a decreased replication capacity compared with wild type virus and does not produce HBsAg. The sensitivity of the V54 2I mutant to penciclovir, the active metabolite of famciclovir, was further studied in tissue culture. This mutant was shown to be resistant to pencic lovir, but remained sensitive to lamivudine, as was subsequently observed i n vivo. These findings indicate that a prolonged administration of famciclo vir may allow for the selection of HBV polymerase gene mutants in immune co mpetent patients. The impaired replication capacity of this V542I mutant ma y have contributed to the absence of outgrowth of this viral strain in vivo . The study of the in vitro sensitivity of HBV polymerase mutants to nucleo side analogs will be important to design new anti-HBV strategies.