Diminished replicative fitness of primary human immunodeficiency virus type 1 isolates harboring the K65R mutation

Abstract

The human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) resistance mutation K65R confers intermediate levels of resistance to several RT inhibitors, including a three- to fourfold reduction of tenofovir susceptibility. Here, we have used for the first time primary HIV-1 isolates from individuals who developed the K65R mutation while enrolled in a clinical trial of tenofovir to analyze the impact of this mutation on HIV-1 replicative fitness. A marked impairment in replicative fitness was observed in association with the selection of viruses carrying the K65R mutation in all patients. The mean replicative fitness among these viruses was 20% relative to the corresponding baseline wild-type virus, ranging from 10 to 32% depending on the accompanying RT mutations. These results support a reduction in in vivo replication for K65R mutant viruses.

FIG. 1.

Replication kinetics of viruses obtained from four patients enrolled in the GS-99-903 study. PBMC were infected with each viral stock calibrated to infect cells at an MOI of 0.02 IU/cell. Virus production was monitored over time by measuring the RT activity in the cell-free supernatant. Values are representative of two independent infections. Drug resistance-associated mutations in each particular time point (week) are indicated. Mutations associated with resistance to protease inhibitors are depicted in italics, while primary mutations are indicated in boldface.

FIG. 2.

Analysis of HIV-1 replicative fitness in four HIV-1-infected patients from the GS-99-903 study. A viral replicative fitness value was calculated for each HIV-1 isolate and pol recombinant virus with growth competition experiments and TaqMan real-time PCR as described in Table 1. Drug resistance-associated mutations are indicated (see Fig. 1 legend for details).