3rd International Workshop on HIV Drug Resistance 2-5 August 1994, Kauai, Hawaii, USA

RETROVIRAL RECOMBINATION CAN LEAD TO LINKAGE OF REVERSE TRANSCRIPTASE MUTATIONS THAT CONFER INCREASED ZIDOVUDINE RESISTANCE

Int Wkshop HIV Drug Res 1994 Aug 2-5;3:38 (abstract no. 37)

B.A. Larder and P. Kellam
Wellcome Research Labs., UK

Genetic recombination between viral genomes has been shown to contribute to the generation of genetic diversity during retrovirus infection. The role of recombination in the development of HIV-1 AZT resistance was investigated as a possible cause of the formation of the linked Leu 41+Tyr 215 resistance genotype. High level AZT resistance is conferred by the presence of subsets of four or five amino-acid substitutions in the HIV-1 reverse transcriptase. Therapy of asymptomatic HIV-1-infected individuals results in the selection of AZT resistant variants that possess defined combinations of the five resistance mutations. Of particular interest is the linked Leu 41+Tyr 215 genotype, since this appears central in the development of high-level AZT resistance. Using genetically tagged mutant viruses it has been possible to select recombinant viruses from mixed infections of Leu 41 and Tyr 215 single mutant viruses in the presence of AZT drug pressure. Initially, we determined the amount of background recombination that was created due to the analysis systems used. Thus, baseline levels of PCR-derived recombination were established as a function of the input HIV-1 DNA concentration. At 0.1 ng of input HIV-1 DNA, the level of background recombination was 5.5%. In the absence of AZT selection, little change in the mixed virus populations was noted. However, after 3 passages of a mixed population of Leu 41 and Tyr 215 viruses in the presence of AZT, 38% of clones screened by differential hybridization were recombinant double mutants. No evidence of de novo generation of mutations at codons 41 or 215 (or the other AZT resistance mutations) was seen. Sensitivity analysis of the passaged virus populations did not show large changes in AZT IC₅₀ values. However, the observed changes were consistent with susceptibility analysis of defined virus mixtures. This study provides an example of the role of retroviral recombination in the development of HIV-1 variants with increased drug resistance.

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1994-08-02
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