Journal of Virology, July 2001, p. 6729-6736, Vol. 75, No. 14
Blood Centers of the Pacific, San Francisco,
California 94118, and Department of Medicine, University of
California, San Francisco, California 94143
Received 29 January 2001/Accepted 15 April 2001
Monitoring the evolution of human immunodeficiency virus type 1 (HIV-1) drug resistance requires measuring the frequency of closely
related genetic variants making up the complex viral quasispecies found
in vivo. In order to resolve both major and minor (
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.14.6729-6736.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Population Genetic Analysis of the Protease Locus of Human
Immunodeficiency Virus Type 1 Quasispecies Undergoing Drug
Selection, Using a Denaturing Gradient-Heteroduplex Tracking
Assay
2%) protease gene
variants differing by one or more nucleotide substitutions, we analyzed
PCR products derived from plasma viral quasispecies by using a
combination of denaturing gradient gel electrophoresis and DNA
heteroduplex tracking assays. Correct population sampling of the high
level of genetic diversity present within viral quasispecies could be
documented by parallel analysis of duplicate, independently generated
PCR products. The composition of genetically complex protease gene
quasispecies remained constant over short periods of time in the
absence of treatment and while plasma viremia fell >100-fold following
the initiation of protease inhibitor ritonavir monotherapy. Within a
month of initiating therapy, a strong reduction in the genetic
diversity of plasma viral populations at the selected protease locus
was associated with rising plasma viremia and the emergence of drug
resistance. The high levels of protease genetic diversity seen before
treatment reemerged only months later. In one patient, reduction in
genetic diversity at the protease gene was observed concomitantly with
an increase in diversity at the envelope gene (E. L. Delwart, P. Heng, A. Neumann, and M. Markowitz, J. Virol.
72:2416-2421, 1998), indicating that opposite population genetic changes can take place in different HIV-1 loci. The rapid emergence of drug-resistant HIV-1 was therefore associated with a
strong, although only transient, reduction in genetic diversity at the
selected locus. The denaturing gradient-heteroduplex tracking assay is
a simple method for the separation and quantitation of very closely
related, low-frequency, genetic variants within complex viral populations.
*
Corresponding author. Mailing address: BCP, 270 Masonic
Ave., San Francisco, CA 94118. Phone: (415) 923-5763. Fax: (419)
791-4220. E-mail: delwarte{at}medicine.ucsf.edu.
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