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Title: Transmission of zidovudine resistant variants of HIV-1
Author: Quigg, Marlynne
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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To investigate the frequency of transmission of ZDV resistant strains of HIV-1, samples obtained from antiretroviral-naive HIV-1 positive individuals were chosen from the MRC Molecular Epidemiology Project, Edinburgh. From this collection of over 600 individuals, 35 patients that had never received any drug therapy were analysed genotypically for the presence of any variation at codon 215 of reverse transcriptase, a position strongly associated with ZDV resistance. Automated sequence analysis of proviral DNA obtained from peripheral blood mononuclear cells revealed variation at this position in two individuals. In these individuals the amino acid encoded at this position was aspartic acid, which has never been observed during ZDV therapy. Further analysis showed this to be linked with a known ZDV resistance-associated mutation methionine41→leucine. Estimated seroconversion dates were August 1992 and August 1993 for these two individuals. As samples obtained in both 1994 and 1996 contained variation at resistance-associated sites, they appeared to have survived within the drug free environment for a period of up to 4 years. To determine the phenotype of strains with variation at codon 215, recombinant virus was produced in a common genetic background (HXB2-D), with the RT sequence replaced by patient derived RT fragments. In addition to phenotypic assays these recombinants were used in competition experiments to determine the fitness of the virus in comparison to wild type variants in the absence of drug. The presence of the GAC codon at 215 conferred at most a 1.6 fold increase in resistance to ZDV, when linked to the 41L mutation. This variant was rapidly outgrown by the wild type RT in assays where the two variants were grown together in one continuous culture, indicating some loss of fitness conferred by these changes. The initiation of an HIV-1 infection with already resistant viral strains has serious clinical implications in patient management, and treatment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available