Multicenter evaluation of the NucliSens EasyQ HIV-1 v1.1 assay for the quantitative detection of HIV-1 RNA in plasma

The Nuclisens EasyQ HIV-1 v1.1 assay (Biomerieux) is a real-time detection method combined with NASBA technology designed to measure plasma HIV-RNA. Its performance was assessed in 1008 clinical specimens collected from individuals infected with clade B (774) and non-B (234) HIV-1 variants at four European laboratories. The results were compared with those obtained using three other commercial viral load assays: Cobas Amplicor Monitor HIV-1 v1.5 (Roche), Versant HIV-1 RNA assay (Bayer) and Nuclisens HIV-1 QT (Biomerieux). Overall, the linearity, specificity and reproducibility of the EasyQ assay was comparable with that from the other tests. The correlation coefficient (R) between methodologies was 0.85 for Amplicor; 0.87 for Versant; and 0.91 for Nuclisens. The specificity of the assay was 99.4%. Of note, Versant missed 17% of specimens with non-B subtypes which could be detected by EasyQ, while Amplicor provided similar results than EasyQ. HIV-1 group O specimens were only detected by the EasyQ assay. In conclusion, the performance of the EasyQ assay seems to be similar to that of other HIV-1 viral load tests currently on the market, but it is more sensitive than Versant for HIV-1 non-B subtypes and shows a wider dynamic range than Amplicor. Moreover, as it incorporates the advantage of real-time detection procedures, it facilitates high throughput and short turnaround time.

Reactivity and amplification efficiency of the NASBA HIV-1 RNA amplification system with regard to different HIV-1 subtypes

In view of the genetic diversity of the human immunodeficiency virus Type 1, we assessed the sensitivity and quantification efficiency of the HIV-1 RNA NASBA amplification system with respect to different HIV-1 subtypes and recombinants. Twenty cell culture supernatants representing 17 HIV-1 group M and 3 group O strains were tested, and NASBA RNA loads were compared with results obtained with a RT-PCR based HIV-1 RNA quantitation method, with p24-antigen concentrations and with the infective dose. The current HIV-1 RNA NASBA seemed suitable to quantitate representatives of different HIV-1 M subtypes. Differences between NASBA and RT-PCR loads were observed for certain HIV-1 M strains. Significantly lower RT-PCR loads were measured for most gag A, gag B and gag F strains, whereas NASBA detected lower copy numbers in 1 gag H strain and 1 gag H/env G recombinant. NASBA was not able to quantify 1 HIV-1 group M recombinant. Some of these differences could be explained by the presence and position of mismatches with primers. HIV-1 group O strains were not detectable by both RNA amplification methods. A firm correlation was not observed between the measured RNA loads and either the p24-antigen concentration or the infective dose.

Discrimination of determinant specificity of two encephalomyocarditis virus neutralizing monoclonal antibodies by competition, mixed neutralization and anti-idiotypic antibodies

To investigate the epitope(s) on encephalomyocarditis virus (EMCV) involved in neutralization, two neutralizing monoclonal antibodies (MAs) (MA UM 21.1 and MA UM 21.2) were tested in a competition binding assay (CBA), a mixed neutralization test and an enzyme immunoassay (EIA) with specificity for the detection of idiotypes on MAs. With a CBA in cell culture, using EMCV infected L cell monolayers as binding antigen, strong homologous competition was observed between unlabelled MAs and horse radish peroxidase (HRPO-) labelled MAs but considerable heterologous competition did also occur, especially between the unlabelled MA UM 21.1 and HRPO-labelled MA UM 21.2. In the mixed neutralization test (50% plaque reduction) preincubation with slightly neutralizing or nonneutralizing doses of MA UM 21.2 had no diminishing effect on the neutralizing capacity of MA UM 21.1, the PRT50 value remains in all cases -10log titre of 5.8. Furthermore rabbit polyclonal antibodies against the idiotypes of MAs UM 21.1 and UM 21.2 did not cross react in the EIA. In conclusion both MAs recognize different viral determinants as indicated by the results obtained with a CBA, a mixed neutralization test and an EIA for detection of idiotypes on MAs.