Phenotypic assays for the determination of coreceptor tropism in HIV-1 infected individuals
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Updated: Jul 10, 2026
Prediction of HIV-1 Coreceptor Usage (Tropism) by Sequence Analysis using a Genotypic Approach
Published on: December 1, 2011
Patrick Braun1, Frank Wiesmann
1Praxenzentrum Blondelstrasse, Blondelstr. 9, 52062 Aachen, Germany. pab@pzb.de
Abstract:
Coreceptor tropism antagonists represent a new class of antiretrovirals for the treatment of HIV infection. The knowledge of patients' viral population tropism before the initiation of and during therapy with such compounds may be critical in order to optimize treatment strategies. In this review we focus on the characteristics of phenotypic assays for the determination of HIV coreceptor tropism. Beside traditional phenotypic assays, there are at least four phenotypic recombinant virus assays (RVA) available to predict coreceptor usage: Trofile (Monogram Biosciences), Phenoscript (VIRalliance), XtrackC/ PhenX-R (inPheno) and a platform developed by Virco. Trofile and Phenoscript represent single-cycle assays and are able to determine coreceptor tropism without cocultivation of HIV particles in cell culture. Trofile offers the most clinically validated data with currently about 25,000 analysed samples. The detection of minority variants is a limitation of all population-based assays and varies between 1 and 10%, depending on the assay used. XtrackC/PhenX-R and Virco's platform combine genotypic and phenotypic assays to analyze a patient's sample for tropism. Although all assays are validated for the assessment of coreceptor tropism in different HIV-1 subtypes, there is still a need for further evaluations. Furthermore, the establishment of cut-offs for X4 minority species will be difficult, and is affected by many factors like patient sample quality, the input volume, viral load, the detection limits and PCR variations. Overall, RVAs confirm efficiency and accuracy thus making them suitable for the clinical management of HIV infected individuals treated with coreceptor antagonists.
Insights
Phenotypic assays are crucial for determining HIV coreceptor tropism in patients receiving antiretroviral therapy. Recombinant virus assays (RVAs) offer efficient and accurate methods for guiding treatment strategies in HIV management.
Area of Science:
- Virology
- Immunology
- Pharmacology
Background:
- Coreceptor tropism antagonists are a novel class of antiretrovirals for HIV treatment.
- Understanding viral tropism is critical for optimizing HIV therapy, especially with new drug classes.
Purpose of the Study:
- To review the characteristics of phenotypic assays used for determining HIV coreceptor tropism.
- To evaluate available phenotypic recombinant virus assays (RVAs) for predicting coreceptor usage in HIV-1.
Main Methods:
- Review of existing phenotypic assays, including traditional and recombinant virus assays (RVAs).
- Focus on four specific RVAs: Trofile, Phenoscript, XtrackC/PhenX-R, and Virco's platform.
- Comparison of single-cycle assays (Trofile, Phenoscript) versus combined genotypic/phenotypic platforms.
Main Results:
- Trofile and Phenoscript are single-cycle assays that determine tropism without cocultivation.
- Trofile has extensive clinical validation with approximately 25,000 analyzed samples.
- Detection of minority variants remains a limitation across population-based assays (1-10% detection).
Conclusions:
- Phenotypic RVAs are efficient and accurate, making them suitable for clinical management of HIV.
- Further evaluations are needed for all assays across different HIV-1 subtypes.
- Establishing cut-offs for minority species detection presents challenges due to various factors.
