Fitness of human immunodeficiency virus type 1 protease inhibitor-selected single mutants

Human immunodeficiency virus type 1 (HIV-1) evolution under chemotherapeutic selection pressure in vivo involves a complex interplay between an increasing magnitude of drug resistance and changes in viral replicative capacity. To examine the replicative fitness of HIV-1 mutants with single, drug-selected substitutions in protease (PR), we constructed virus that contained the most common mutations in indinavir-selected clinical isolates, PR M461 and V82T, and the most common polymorphic change in drug-naive patients, PR L63P. These mutants were competed in vitro in the absence of drug against the otherwise isogenic WT virus (NL4-3). Phenotypic drug susceptibility was determined with a recombinant virus assay using a single cycle of virus growth. PR M461 and L63P were as fit as WT. However, PR V82T was out-competed by WT. None of these mutants had appreciable phenotypic resistance to any of the protease inhibitors, including indinavir. The PRV82T mutant was hypersusceptible to saquinavir. Thus, the impaired fitness of the V82T single mutant is consistent with its low frequency in protease inhibitor-naive patients. The similar fitness of WT (NL4-3), L63P, and M46I is consistent with the common occurrence of L63P in the absence of protease inhibitor-selection pressure, but not with the rare detection of M46I in drug-naive patients.