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Trofile Assay Usually Matches Cell Test in Figuring Coreceptor Use
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6th European HIV Drug Resistance Workshop
March 26-28, 2008
Budapest, Hungary
Mark Mascolini
HIV coreceptor results with Monogram's plasma-based standard Trofile assay closely matched results with cell-based MT-2 cultures in three separate experiments [1]. The enhanced Trofile assay did even better. Determining CD4-cell coreceptor use--CXCR4 versus CCR5--is essential before prescribing CCR5 antagonists, which do not control CXCR4-using virus.
MT-2 cell cultures have long served as a research tool to distinguish syncytium-inducing (SI) HIV from non-SI (NSI) HIV. SI virus corresponds to CXCR4-using HIV, and NSI virus corresponds to CCR5-using HIV. Although researchers agree on the MT-2 assay's reliability, it requires too much lab effort for clinical use. This analysis scrutinized cell and plasma samples from members of the Amsterdam Cohort Studies on HIV/AIDS who had MT-2 assay results at intervals of about 3 months.
Testing 21 HIV clones derived from virus of 2 people, standard Trofile and MT-2 agreed on 20 coreceptor calls (95%). The one discordant call involved a clone that the MT-2 assay called NSI and Trofile called dual/mixed (D/M), meaning the virus can use either CCR5 or CXCR4.
Analyzing 42 MT-2 culture-derived supernatants (the liquid left lying above spun cells) derived from cells of 4 patients, the investigators found concordant MT-2 and Trofile results in 39 samples (93%). Of the 3 discordant samples, 2 were NSI on MT-2 and D/M on Trofile and 1 was SI on MT-2 and CCR5 on Trofile. The MT-2 assay and Trofile agreed on coreceptor use in 19 of 20 cell samples (95%); the one disagreement again involved an NSI virus called D/M by Trofile.
Turning their attention to 67 plasma samples from 10 people in whom the MT-2 test spotted a switch from NSI to SI, the Amsterdam-Monogram team found that Trofile rated virus D/M at or before first SI detection in 5 people. In the other 5 Trofile called HIV D/M 3, 3, 6, 6, and 15 months after MT-2 cultures showed a shift from NSI to SI. The enhanced Trofile assays detected CXCR4-using HIV at or before SI detection in 9 of these 10 samples. Analysis of SI versus NSI calls in 4 people with repeat MT-2 testing showed that the MT-2 assay can yield variable results.
The investigators suggested that "assay detection limit (standard versus enhanced Trofile) rather than tissue compartment (plasma versus peripheral blood mononuclear cells) determines most differences in assay results."
Reference
1. Coakley E, Reeves J, Huang W, et al. Detection of CXCR4-using HIV by the Trofile and MT2 assays in clinical samples. 6th European HIV Drug Resistance Workshop. March 26-28, 2008. Budapest. Abstract 81.
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