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Session 76 Poster Session HIV Resistance and Fitness Session Time: 4:30-6:30 pm Room 4E-F

577-T. Impaired in Vitro Fitness of Nevirapine Resistant HIV-1 Mutants K. Soderberg*, M. Thompson, and L. Alexander Yale Univ. Sch. of Med., New Haven, CT Background: Following cessation of antiretroviral (ARV) therapy, drug resistant virus in HIV-infected patients is progressively replaced by sensitive virus, suggesting diminished replicative fitness in ARV-resistant strains. This hypothesis has been supported by in vitro studies of either clinical isolates or engineered mutants resistant to several classes of ARVs. Methods: We have undertaken a systematic examination of the effects on replicative fitness of 5 common nevirapine-resistance mutants, alone and in combination (totaling 32 permutations), in the context of a defined genetic background. Nevirapine was selected because of its relatively long history of use, propensity to rapidly induce drug resistance, and its use as monotherapy for prevention of vertical transmission of HIV in developing countries. Acting on the hypothesis that accumulation of multiple nevirapine-resistance mutations will result in a cumulative decrease in replicative fitness, we selected 5 common reverse transcriptase mutations (K103N, V106A, Y181L, Y188L, and G190A) conferring nevirapine resistance, and using site-directed mutagenesis, created clones containing these mutations, alone and in combination, within an NL4-3 background. We then infected cell cultures with each of the mutant clones in combination with wild type virus, passed the cultures weekly, and determined relative concentrations of each clone at the time of by sequence analysis. Results: We found significant variability in fitness in relation to NL4-3, and a general decrease in fitness with the accumulation of more mutations. Most notably all clones containing K103N, Y181L, and Y188L in combination were defective for replication in culture. Conclusions: We conclude that in the absence of therapy, nevirapine resistant mutations compromise fitness of HIV-1. Therefore intermittent administration of this drug could inhibit replication of HIV-1 in infected humans.

©2002 9th Conference on Retroviruses and Opportunistic Infections