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Journal of Virology, July 2001, p. 6729-6736, Vol. 75, No. 14
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

Laurence Doukhan and Eric Delwart*

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 (>= 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.


Journal of Virology, July 2001, p. 6729-6736, Vol. 75, No. 14
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.14.6729-6736.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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