Evolutionary trends of resistance mutational patterns of HBV reverse transcriptase over years (2002-2012) of different treatment regimens: The legacy of lamivudine/adefovir combination treatment

- HBV resistance to antivirals has evolved according to their historical use and was modeled by viral genotype.
- Combined/consecutive use of lamivudine and adefovir has selected peculiar variants, potentially involved in MDR.
- No common mutational pattern has emerged from adefovir and tenofovir treatment failures.

Antiviral therapy has revolutionized treatment of chronic HBV infections. First generation compounds, lamivudine and adefovir, displayed a high rate of treatment failures, and have been replaced by more potent compounds with high genetic barrier to resistance. However, the evolution of the virus towards resistance due the use of first generation compounds may still provide useful information for a better management of current antivirals. A single center sequence database including 705 HBV reverse transcriptase sequences from patients failing antiviral treatments (2002-2012) has been statistically analyzed to highlight viral evolution in relationship to the use of antiviral compounds and to their associations/sequencing in those years. The influence of viral genotypes and polymorphisms on resistance-related mutational patterns was also investigated. This study documents how, after the first years of antiviral therapy, the use of adefovir as an add-on strategy allowed a consistent reduction treatment failures. It also documents the effects of the initial misuse of entecavir in lamivudine experienced patients. In the latest years, the correct use of entecavir and the introduction of tenofovir allowed further curbing of resistance-related treatment failures, which virtually disappeared. Furthermore, the study allows a better understanding of how viral genotype (A vs D) conditions specific mutational pathways to resistance against lamivudine and entecavir, and demonstrates that the use of adefovir in lamivudine experienced patients is associated to peculiar mutational patterns, in particular A181V + F/Y221L. Despite some concern may arise for patients previously treated with lamivudine/adefovir, in sequence or combination, where the virus may have developed a lower genetic barrier against resistance to tenofovir, the outlook of antiviral treatment of HBV infection should be quite optimistic.