Stable rearrangements of the beta3-beta4 hairpin loop of HIV-1 reverse transcriptase in plasma viruses from patients receiving combination therapy.

OBJECTIVES: To study the genetic rearrangements of HIV-1 reverse transcriptase (RT) in circulating viruses from patients under combination therapy, and to determine the impact of these changes on the virological response to treatment. METHODS: Blood samples were extracted from total RNA and amplified by RT-PCR. The HIV-1 RT and protease genes were sequenced by fluorescent dye terminator cycle sequencing. RESULTS: Specific rearrangements in the RT coding region (between amino acids 66 and 71) were documented in nine patients. This region, which corresponds to a loop between the beta3 and beta4 strands of the fingers subdomain of RT, is involved in the interaction between the enzyme and the template primer. In vitro data with recombinant enzymes have shown the importance of this domain in the processive polymerization of HIV-1 RT. The rearrangements (eight deletions/insertions and one deletion with conservation of the reading frame) did not affect the overall secondary structure of the fingers subdomain, as assessed by the Garnier Osguthorpe Robson prediction method. The changes were generally stable over a follow-up of 10-12 months. With the exception of two cases, most of the patients of this study did not respond efficiently to antiretroviral therapy as assessed by measurements of plasma viraemia. Correspondingly, the RT and protease genes sequenced from these patients displayed numerous resistance-associated mutations. CONCLUSION: Functional and stable rearrangements in the beta3-beta4 hairpin of HIV-1 RT can be found in circulating viruses from patients under combination therapy. These rearrangements may affect the virological response to antiretroviral therapy by increasing the processivity of RT, an enzymatic parameter that reflects the fidelity of the polymerization process.