Natural residues versus antiretroviral drug-selected mutations in HIV type 1 group O reverse transcriptase and protease related to virological drug failure in vivo.

HIV-1 group O viruses were first recognized as a distinct subgroup of HIV-1 with the isolation and characterization in 1990 of a virus (ANT70) from a woman (individual A) and her spouse (individual B), both from Cameroon (De Leys R, et al.: J Virol 1990;64:1207-1216). During the 5-6 years before treatment, individual A remained asymptomatic, with viral RNA levels between 2.5 and 2.8 log10 copies/ml, as measured by a newly developed group O-specific quantitative NASBA-based RNA assay. Individual B developed mild clinical symptoms, with 3.1 to 3.6 log10 copies of viral RNA per milliliter. HIV-1 sequences obtained from both individuals showed pretreatment residues in protease that confer resistance to protease inhibitors in group M viruses (10I, 36I, and 71V). Individual A showed an initial response to AZT, but shortly after addition of ddC and saquinavir, the RNA levels returned to baseline, while subsequent treatment with d4T, 3TC, and indinavir reduced the RNA level to less than 50 copies/ml for the time of follow-up. Individual B showed no response to AZT or ddC monotherapy, and a change to d4T, 3TC, and indinavir had, in contrast to individual A, only a temporary effect. While a multitude of mutations in HIV-1 group O reverse transcriptase (RT) and protease appeared that are associated with drug resistance in group M viruses, the observed T215N mutation in RT and the V15I and V22A mutations in protease have not previously been described and may represent resistance-conferring mutations specific to group O viruses. These results indicate that treatment of HIV-1 group O-infected individuals with antiretroviral drug regimens that include protease inhibitors might lead to rapid selection for resistance-conferring mutations. This probably results from preexisting protease residues contributing to reduced sensitivity of group O viruses to protease inhibitors, as is observed in vitro.