Changes in Human Immunodeficiency Virus Type 1 Populations after Treatment Interruption in Patients Failing Antiretroviral Therapy

Abstract

Mutations in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and protease that confer resistance to antiretroviral agents are usually accompanied by a reduction in the viral replicative capacity under drug-free conditions. Consequently, when antiretroviral treatment is interrupted in HIV-1-infected patients harboring drug-resistant virus, resistant quasi-species appear to be most often replaced within several weeks by wild-type virus. Using a real-time PCR-based technique for the selective quantification of resistant viral sequences in plasma, we have studied the kinetics of the switch from mutant to wild-type virus and evaluated the extent to which minority populations of resistant viruses not detected by genotyping persist in these individuals. Among 12 patients with viruses expressing the V82A or L90M resistance mutation who had undergone a 3-month interruption of therapy and for whom conventional genotyping had revealed an apparent total reconversion to wild-type virus, minority populations expressing these mutations, representing 0.1 to 21% of total virus, were still detectable in 9 cases. Kinetic studies demonstrated that viruses expressing resistance mutations could be detected for >5 months after the discontinuation of treatment in some patients. Most of the minority resistant genomes detected more than 3 months after the interruption of therapy carried only part of the mutations present in the resistant viruses prior to treatment interruption and appeared to result from the emergence of existing strains selected at earlier stages in the development of drug resistance. Thus, following the interruption of treatment, viral populations containing resistance mutations can persist for several months after the time when conventional genotyping techniques detect only wild-type virus. These populations include viral strains with only some of the resistance mutations initially present, strains that presumably express better fitness under drug-free conditions.

Evolution of Human Immunodeficiency Virus Type 1 Protease Genotypes and Phenotypes In Vivo under Selective Pressure of the Protease Inhibitor Ritonavir

“…Even after up to 12 months of RTV treatment and in the presence of several pro mutations that could be considered compensatory in nature, none of the resistant variants recovered pretreatment-specific infectivity levels, consistent with observations made by others (2). The reversion of resistant virus populations to drug-susceptible populations even after prolonged treatment failure (Ն12 months) also suggests that compensation is indeed incomplete (15,18,24,30). The infectivity measurements presented here are consistent with the infectivity of single-, double-, and triple-mutant strains described by Mammano et al (37) but lower than the fitness of clones harboring multiple resistance mutations measured by coculture experiments (40,44).…”

Role of Minority Populations of Human Immunodeficiency Virus Type 1 in the Evolution of Viral Resistance to Protease Inhibitors

“…All plasma samples with a detectable viral load obtained during the interval between the initiation of treatment with protease inhibitors and the detection of L90M resistance mutation on standard genotyping were evaluated. The techniques used to quantify viral populations expressing the V82A and L90M mutations have previously been described (21). Briefly, 1 ml of plasma was centrifuged (23,500 ϫ g, 1 h, 4°C), and RNA was extracted from the pellet (QIAamp Viral RNA Mini Kit; Qiagen, Valencia, Calif.).…”

“…Although resistance mutations confer a decisive advantage to these variants over their parental wild-type counterparts for replication in the presence of antiretroviral drugs, there is accumulating evidence that resistant HIV strains are less fit than wild-type virus for replication in the absence of drug and that, overall, the replicative capacity of many drug-resistant HIV variants is reduced (1,2,4,7,13,19,21,22,37,39). Resistance mutations in the protease are thought to modify the size and shape of the substrate-binding domain of the enzyme, thereby reducing the affinity of inhibitors for the enzyme (30,39,44,47).…”

“…It is now recognized that plasma virus is composed of a mixture of numerous quasispecies (8). In patients undergoing treatment and harboring resistant viral strains, the dominant quasispecies is accompanied by minority populations expressing distinct resistance genotypes (8,14,21,34,46). Because these viral species can evolve independently, an initially minority population, having followed a distinct evolutionary pathway, could emerge as the dominant population, either because it had evolved higher resistance or because a change in drug pressure gave that population a growth advantage over the prior majority population.…”

Issues in resistance, adherence, and comparative efficacy of the single-tablet regimen combination of tenofovir, emtricitabine, and efavirenz in the management of HIV-1 infection

“…[116][117][118][119][120] Unequal exposure to antiretrovirals and treatment interruptions are thought to underlie the development of resistance in some patients. [121][122][123][124][125] Different rates of adherence to medications within a regimen (discordant adherence) combined with varied pharmacokinetics of the agents can lead to viral replication, and subsequent exposure to sub-optimal treatment regimens. 77,98,126,127 Fixed-dose regimens such as Atripla may promote more complete adherence in a "take one, take all" fashion which would limit unequal viral exposure to cART components.…”