In vivo emergence of drug-resistant mutations at less than 50 HIV-1 RNA copies/mL that are maintained at viral rebound in longitudinal plasma samples from human immunodeficiency virus type-1-infected patients on highly active antiretroviral therapy.

Objective: Emergence of human immunodeficiency virus type-1 (HIV-1) genotypic drug resistance is generally attributed to noncompliance, poorly absorbed drugs, or drug-to-drug interaction. Attempts to determine emerging genotypic drug resistance from study subjects on highly active antiretroviral therapy (HAART) relied on insensitive polymerase chain reaction (PCR) techniques, revealing wild type HIV-1 or precursor resistant genotypes from few plasma samples successfully amplified with <50 copies/mL.

Study Design/methods: In this analysis, using Applied Biosystems' ViroSeq HIV-1 Genotyping Systems, Version 2.0 (Applied Biosystems, Foster City, CA, USA) and the supplemental, for research use only, nested PCR primers, genotypic drug resistance was determined in longitudinal plasma samples from 11 study subjects on HAART.

Results: In 4 of 11 study subjects, newly emerging genotypic primary resistant mutations were detected in plasma samples with <50 copies/mL. Most of these primary drug-resistant mutations were detected in subsequent longitudinal samples with detectable viral load (viral breakthrough).

Conclusions: This analysis suggests sufficient viral replication <50 copies/mL to generate genotypic drug resistance in study subjects on suppressive HAART.