Background: Naturally-occurring polymorphisms at the human immunodeficiency virus type 1 (HIV-1) protease which have been associated to resistance to protease inhibitors (PIs) in clade B viruses are frequently found in non-B subtypes, with unknown clinical significance.

Objective: To assess the susceptibility of non-B viruses to different PIs.

Study design: Plasma samples from 58 drug-naive individuals infected with HIV-1 non-B subtypes (2A, 22C, 2D, 1F, 29G and 2J) defined by phylogenetic analyses of the protease gene were tested using a phenotypic assay (PhenoSense, ViroLogic, South San Francisco, CA, USA). Twenty of them were further analyzed with another assay (Antivirogram, Virco, Mechelen, Belgium). All 58 non-B viruses harbored amino acid substitutions associated with reduced PI susceptibility in clade B (positions 10, 20, 36, 63, 70, 77 and 82).

Results: Using PhenoSense-HIV assay, all but two individuals harbored viruses completely susceptible to all six PIs tested (indinavir (IDV), ritonavir (RTV), saquinavir (SQV), nelfinavir (NFV), amprenavir (APV), lopinavir (LPV)). The two viruses with reduced susceptibility belonged to clade G. The first virus, which had K20I, M36I and V82I, showed 2.9-fold decreased susceptibility to APV, while the second virus showed 3.9-fold decreased susceptibility to both NFV and RTV, with amino acid substitutions K20I, M36I, L63P and V82I. Of note, several other viruses displayed the same constellation of mutations but without showing any reduced susceptibility, suggesting that these polymorphisms per se do not affect PI susceptibility.

Conclusion: PI susceptibility in HIV-1 non-B viruses seems to be preserved despite the presence of polymorphic changes which have been associated to PI resistance in clade B viruses.