Evolution of Multi-Drug Resistant HBV: Implications on Rescue Therapy. said:
Background: Multi-drug resistant HBV have been reported in patients who received sequential treatment with nucleoside monotherapy. In vitro studies showed that HBV constructs with mutations resistant to lamivudine (LAM) and adefovir (ADV) have marked reduction in sensitivity to combination of LAM+ADV, while constructs with mutations resistant to either drug remain sensitive to the other drug. Aims: To determine if mutations conferring resistance to multiple antiviral agents are present on the same HBV genome in vivo and to describe the evolution of these mutations. Methods: Sera from 6 patients found to have dual-resistant HBV mutations on direct sequencing were cloned after nested PCR, 18-20 clones from each sample were sequenced. Results: Mutations to both therapies were present on the same genome in 163/195 (84%) clones from 10 samples with dual-resistant mutations to LAM+ADV, LAM+HBIG, or LAM+entecavir (ETV) on direct sequencing, 32 (16%) clones had mutations to one drug. Evolution of mutations was examined in 3 patients. Patient 1 received LAM+ETV after LAM breakthrough, all 18 clones had L180M and M204V/I at month 0 (start of ETV), clonal analysis first detected ETV-resistant mutation (T184L) at month 20, 6 months earlier than direct sequencing. Both treatments were stopped at month 34 (T184L: 20/20 clones); 6 months later, T184L was detected in 12/20 clones while L180M and M204V/I remained detectable in 19/20 clones. Patient 2 was switched to ETV monotherapy after LAM breakthrough, all 20 clones had L180M+M204V at month 0. At month 36, ETV-resistant mutation I169T was detected in 15 and S202G in 4 clones. At month 41, S202G was present in 17 clones and I169T in 4 clones, LAM-resistant mutations remained detectable in all 20 clones. Patient 3 developed HBV recurrence after transplant despite receiving LAM+HBIG. All 18 clones had M204I and sG145R when HBV recurrence was diagnosed. ADV was added and LAM stopped 7 months later. ADV breakthrough occurred after 41 months of ADV when all 18 clones had ADV-resistant N236T. Four months after reintroduction of LAM, all 20 clones had L180M+M204V, 12 clones had additional V173L change. However, N236T was replaced by a different ADV-resistant mutation P237H. Conclusions: Our study showed that mutations conferring resistance to multiple antiviral agents are present on the same viral genome, suggesting that combination therapy directed against mutants resistant to each treatment may not be adequate in suppressing dual-resistant HBV. Sequential antiviral therapy leads to selection of multi-resistant HBV; mutations evolve during continued treatment resulting in mutants with increased replication fitness.