Clinical isolates of HIV-1 contain few pre-existing proteinase inhibitor resistance-conferring mutations.

Proteinase inhibitors are an important new class of antiviral agents for AIDS, however, in vitro experiments have identified proteinase mutations that confer resistance to several different families of the inhibitors. This study was undertaken to determine if these resistance-conferring amino-acid substitutions occur in HIV strains before the application of selective pressure. We determined the nucleic acid sequence of the proteinase gene from the 23 clinical isolates of HIV-1 and three laboratory-adapted strains using a method that detects the majority species present in viral populations. Analysis of minor subpopulations will require alternative strategies. The clinical isolates studied contained an average of 3 (range 1-8) amino-acid substitutions as compared to the prototypical BH10 sequence. We did not detect substitutions characteristic of reported highly proteinase-resistant strains. These results suggest significant variation occurs in the HIV-1 proteinase gene but pre-existing highly proteinase-resistant strains are uncommon.