Background: This study was aim to explore the characteristics of phenotypic resistance of resistant strains of HIV type-1 (HIV-1) subtype B and to compare the concordance between the phenotypic resistance and genotypic resistance.
Methods: The genotypic resistance assay for the HIV-1 clinical isolates was performed. One isolate without resistance mutation was chosen as a drug-sensitive reference strain and seven subtype B isolates with resistance mutations were phenotypically tested. Fifty percent inhibitory concentrations (IC50) between resistant and sensitive viruses were compared. The resistance extent was determined by the folds of the increased IC50. The concordance between the phenotypic resistance and genotypic resistance was also analyzed.
Results: IC50 of resistant isolates were 0.0006 - 0.1300 micromol/L for zidovudine (AZT), 0.0016 - 0.0390 micromol/L for lamivudine (3TC), 0.0104 - 0.4234 micromol/L for nevirapine (NVP), and 0.0163 - 0.1142 micromol/L for indinavir (IDV), respectively. Genotypic and phenotypic resistance assays indicated that the resistant strains were intermediately and highly resistant to nucleotide analog reverse transcriptase inhibitors and non-nucleotide analog reverse transcriptase inhibitors. The phenotypic assay was consistent with the genotypic assay. For measuring the potential resistance, the genotypic assay was more sensitive than the phenotypic. In evaluating the resistance to protease inhibitors, these two assays were discrepant.
Conclusions: Both the phenotypic and genotypic assays indicate that the resistant viruses exist in HIV-infected patients in China who have received treatment. Phenotypic and genotypic assays have high concordance, and the genotypic assay could replace the phenotypic assay to predict the HIV-1 resistance.