Résumé
The rapid rate of HIV-1 replication in vivo (10 super(9) virions per day), coupled with the poor fidelity of reverse transcription of the HIV-1 genome, results in the production of new virus variants. This makes it easy to understand how multiple clades of HIV-1 have emerged throughout the world and explains the development of genetic diversity even within clades. To assess the impact of genetic variability on HIV-1 RNA quantification, we evaluated these commercial kits by using a panel of HIV-1 isolates representing clades A to H. Group O HIV-1 strains were not tested, because the different assays are exclusively recommended for quantitation of RNA for group M HIV-1 strains. These isolates were expanded in culture. Virus was collected by ultracentrifugation and resuspended in HIV-seronegative plasma. To standardize the quantities of virus to similar levels in each preparation, the p24 antigen was determined (Coultronics, Margency, France) and the volume adjusted so that each specimen contained approximately 10 pg of p24 antigen per ml. These results demonstrate that quantification of HIV-1 RNA is highly influenced by the HIV-1 genome sequence. The level of detection of clade A strains by the Amplicor qualitative and quantitative assays has been previously reported (6,7). Our results confirm these findings and indicate that the NASBA procedure is also influenced by the HIV-1 genomic diversity. In contrast, HIV-1 RNA quantification with the Quantiplex bDNA assay demonstrated minor influence by genetic variability, presumably because of the large number of probe sequences designed into the assay (5). All three tests can be used for the quantification of RNA from clade B HIV-1 strains, which are predominant in European and American countries. However, in the case of an HIV-1 RNA level lower than the detection limit obtained with RT-PCR or NASBA in an untreated, HIV-1-infected patient, the clinician should consider verifying the RNA level by another procedure; this observation should also lead to the characterization of the HIV-1 clade.