H uman immunodeficiency virus type 1 (HIV-1) protease is a highly mutable protein. More than one-half of the enzyme's 99 amino acids are subject to variation under protease inhibitor (PI) selection pressure (1, 2). In addition, viruses from patients treated unsuccessfully with multiple-PI-containing antiretroviral (ARV) treatment regimens often develop complex patterns of PI resistance amino acid substitutions (3, 4). The many genetic manifestations of PI resistance present challenges to researchers who require representative PI-resistant viruses for in vitro mechanistic studies and for testing of new inhibitors active against the most clinically relevant multi-PI-resistant variants.To address these challenges, we created a panel of recombinant infectious molecular virus clones containing clinically derived protease genes with amino acid substitution patterns similar to those in the most common multiple-PI-resistant viruses. The panel was drawn from a repository of cryopreserved plasma samples from patients who received multiple PIs and harbored viruses with multiple PI resistance amino acid substitutions. To assess the validity of this panel, we performed an independent correlation network analysis of PI resistance amino acid substitutions in publicly available sequences from more than 10,000 patients.
MATERIALS AND METHODS
PI resistance amino acid substitutions and phenotypic cutoffs.Amino acid substitutions were defined as differences from the consensus B protease sequence (http://hivdb.stanford.edu/DR/asi/releaseNotes/index .html#consensusbsequences). PI resistance amino acid substitutions were defined as (i) protease substitutions that give rise to HIV-1 variants with reduced susceptibility to one or more PIs in cell culture assays (5); (ii) nonpolymorphic substitutions, defined here as those occurring in Յ0.5% of pooled group M viruses from PI-naive persons; and (iii) substitutions occurring in Ն0.5% of virus isolates from PI-experienced patients. Fortyone substitutions at 23 positions met two or more of these criteria: L10F, V11I, L24I, D30N, V32I, L33F, K43T, M46IL, I47AV, G48MV, I50LV, F53L, I54ALMSTV, Q58E, G73ACST, T74P, L76V, V82ACFLST, N83D, I84V, N88DS, L89V, and L90M (see Table S1 in the supplemental material). Each amino acid substitution had a prevalence of Յ0.5% in pooled group M viruses from PI-naive individuals, and with the exception of the V82C substitution, each has been shown to significantly contribute to decreased in vitro PI susceptibility (5). In addition, each amino acid substitution except for I47A (0.3%), I50L (0.4%), and V82L (0.3%) had a prevalence of Ն0.5% in pooled group M viruses from PI-experienced patients.High-level resistance was defined according to the Monogram Biosciences (South San Francisco, CA) clinical cutoffs for the PhenoSense assay (6): atazanavir-ritonavir (ATV/r) at Ͼ6-fold, darunavir-ritonavir (DRV/r) at Ͼ90-fold, fosamprenavir-ritonavir (FPV/r) at Ͼ11-fold, indinavir-ritonavir (IDV/r) at Ͼ10-fold, lopinavir-ritonavir (LPV/r) at Ͼ56-fold, nelfinavir (NFV) at Ͼ...