LOSS OF VIRAL FITNESS ASSOCIATED WITH MULTIPLE GAG AND GAG-POL PROCESSING DEFECTS IN HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 VARIANTS SELECTED FOR RESISTANCE TO PROTEASE INHIBITORS IN-VIVO

We examined the viral replicative capacity and protease-mediated proce ssing of Gag and Gag-Pol precursors of human immunodeficiency virus (H IV) variants selected for resistance to protease inhibitors. We compar ed recombinant viruses carrying plasma HIV RNA protease sequences obta ined from five patients before protease inhibitor therapy and after vi rus escape from the treatment. Paired pretherapy-postresistance recons tructed viruses were evaluated for HIV infectivity in a quantitative s ingle-cycle titration assay and in a lymphoid cell propagation assay. We found that all reconstructed resistant, viruses had a reproducible decrease in their replicative capacity relative to their parental pret herapy counterparts. The extent of this loss of infectivity was pronou nced for some viruses and more limited for others, irrespective of the inhibitor used and of the level of resistance. In resistant viruses, the efficiency of Gag and Gag-Pol precursor cleavage by the protease w as impaired to different extents, as shown by the accumulation of seve ral cleavage intermediates in purified particle preparations. We concl ude that protease inhibitor-resistant HIV variants selected during the rapy have an impaired replicative capacity related to multiple defects in the processing of Gag and Gag-Pol polyprotein precursors by the pr otease.