Loss of lamivudine resistance in a zidovudine and lamivudine dual-resistant HIV-1 isolate after discontinuation of in vitro lamivudine drug pressure

We examined the in vitro phenotypic and genotypic profiles of an extensivel y passaged human immunodeficiency virus type 1 clinical isolate which has b een selected for lamivudine resistance, with an M184V mutation in a zidovud ine-resistant genetic background, and then cultured with zidovudine alone. Our passaging strategy led to a decrease in lamivudine IC50 values, which w ere comparable to those prior to lamivudine exposure, and the genotypic res toration of the wild-type sequence at codon 184 of reverse transcriptase.