3rd Conference on Retroviruses and Opportunistic Infections Washington, DC - January 28-February 1, 1996

Conf Retroviruses Opportunistic Infect 1996 Jan 28-Feb 1; 3rd:54 (abstract no. 7)

Nijhuis M, De Jong D, Van Leeuwen R, De Groot T, Keulen W, Schuurman R, Boucher C
Antiviral Therapy Laboratory, NATEC, University of Amsterdam, The Netherlands.

INTRODUCTION: 3TC monotherapy results in the selection of 3TC resistant HIV-1 variants containing a mutation at amino acid 184 (M184V) of RT. In vitro studies showed that the introduction of the Ml84V mutation into an AZT resistant HIV-1 variant (M41L, T215Y) resulted in a virus which was highly resistant to 3TC but sensitive to AZT.

OBJECTIVE: To study the effect of the addition of AZT to symptomatic HIV-1 infected patients treated with 3TC monotherapy.

METHODS: At regular intervals during 3TC monotherapy and subsequent 3TC/AZT combination therapy, HIV- 1 RNA was isolated from plasma and quantified using a PCR assay. For further analyses we selected patients who were AZT-naïve before start of the study, and showed a rebound in HIV-1 RNA load during 3TC/AZT combination therapy. Sequence analyses of the RT gene from amino acid 1-262 were performed on clones obtained from HIV-1 RNA isolated at start of 3TC monotherapy, at the addition of AZT and after about 1 year of 3TC/AZT combination therapy. The sequenced RT clones were subsequently cotransfected with an RT deleted HXB2 molecular clone (small HXB2RT), and the recombinant viruses were tested for 3TC and AZT susceptibility using the HeLa CD4 + plaque reduction assay.

RESULTS: Upon addition of AZT to patients treated with 3TC monotherapy a decline in HIV-1 RNA load was observed, followed by an increase back to the baseline concentration, Sequencing analyses revealed sustained presence of the M184V mutation and the presence of known AZT resistance mutations (M41L, D67N, K70R, L21OW, T215Y), Moreover additional mutations were detected, in particular at codon 135. All the recombinant viruses obtained after one year of combination therapy were 3TC resistant (greater than 1000 fold) and, depending on the pattern of AZT resistance conferring mutations present, also showed dscreased AZT susceptibility (up to 16 fold).

CONCLUSION: We demonstrated the sustained presence of 3TC resistant HIV-1 variants (Ml84V) after the addition of AZT. Moreover AZT/3TC double resistant viruses were selected. The observed outgrowth of these double resistant variants are likely to be responsible for the rise in HIV-1 RNA load back to the baseline concentration during 3TC/AZT combination therapy.

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Copyright © 1996 - Foundation for Retrovirology and Human Health . Reproduction of this abstract (other than one copy for personal reference) must be cleared through the Foundation for Retrovirology and Human Health.