Sensitive assay for quantification of hepatitis B virus mutants by use of a minor groove binder probe and peptide nucleic acids.

Lamivudine is the first nucleoside analogue that was shown to have a potent effect on hepatitis B virus (HBV). However, the emergence of mutants resistant or cross-resistant to nucleoside/nucleotide analogues remains a serious problem. Several assays for the detection and quantification of antiviral-resistant mutants have been reported, but it has been difficult to measure the amounts of mutants accurately, especially when the target strain is a minor component of the mixed population. It has been shown that accurate measurement of a minor strain is difficult as long as a matching reaction with a single probe is included in the assay. We developed a new method for the quantification of lamivudine-resistant strains in a mixed-virus population by real-time PCR using minor groove binder probes and peptide nucleic acids, and we achieved a wide and measurable range, from 3 to 10 log10 copies/ml, and high sensitivity, with a discriminative limit of 0.01% of the predominant strain. The clinical significance of measuring substitutions not only of M204 but also of L180 residues of HBV polymerase was demonstrated by this method. This assay increases the versatility of a sensitive method for the quantification of a single-nucleotide mutation in a heterogeneous population.