Malik, S.; (2011) The role of the HIV-1 reverse transcriptase mutation H208Y to drug resistance and viral fitness. Doctoral thesis , UCL (University College London).

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Abstract

Accessory mutations are thought to arise alongside major or primary drug resistance mutations in order to augment resistance, restore viral fitness, or both. The H208Y mutation in the HIV-1 reverse transcriptase (RT) gene was hypothesised to be an accessory mutation. This thesis characterises the H208Y mutation in terms of linkage of H208Y to other major and accessory resistance mutations, and examines two phenotypic aspects, drug susceptibility and viral fitness. The HIV Resistance Database held at the Royal Free Hospital was searched for genotypes containing the H208Y mutation. The prevalence of H208Y in antiretroviral treatment naïve and treatment experienced patients was 5/3783 (0.1%) and 12/1304 (0.9%), respectively, indicating a high degree of conservation of position 208 in wild type virus and an increase in prevalence under selective drug pressure. Four patients were chosen to conduct further analysis of virus with H208Y, comprising a treatment naïve patient with subtype B virus, and three treatment experienced patients harbouring subtype A, subtype B and subtype C virus respectively. The RT gene from these patients was cloned and sequenced. H208Y was found to be associated with the thymidine analogue mutations (TAMs), particularly mutations at positions D67, T215 and K219. H208Y was always associated with accessory mutations at positions V35, K122 and T200. Recombinant viruses containing patient derived RT genes with and without H208Y were constructed to examine the impact of H208Y on drug susceptibility and viral fitness. A multiple cycle drug susceptibility assay showed that H208Y conferred a reduced susceptibility to the nucleotide RT inhibitor tenofovir in the context of subtype B wild type RT and subtype B RT containing TAMs. Growth competition assays were used to examine the fitness effects of H208Y using allele-specific PCR to differentiate between competing strains with and without H208Y. In the context of subtype B wild type RT, H208Y conferred a reduced viral fitness both in the presence and absence of drug. The effect may be proposed to contribute to the overall high degree of conservation of position 208. In contrast, H208Y did not appear to impact on viral fitness in the context of subtype B and subtype A RT containing TAMs.

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