Validation of the HIV Tropism Test TROCAI Using the Virological Response to a Short-Term Maraviroc Monotherapy Exposure

Abstract

c TROCAI is a phenotypic tropism test developed using the virological response to a short-term exposure to maraviroc monotherapy (Maraviroc Clinical Test [MCT]). It was found that with TROCAI, a cutoff of <0.5% of dual/mixed viruses was needed to predict R5 HIV tropism. Here, we have validated TROCAI, using this cutoff, in a new cohort of 42 patients, finding a very high concordance between TROCAI and MCT (98%), and a good concordance (71 to 87%) with other genotypic/phenotypic methods. Determining HIV coreceptor usage is essential before prescribing the CCR5 antagonist maraviroc (MVC) (1, 2). The most widely used coreceptor tropism test is the recombinant enhancedsensitivity Trofile phenotypic assay (ESTA; Monogram Biosciences) (3). However, this phenotypic assay has some limitations, such as a significant rate of nonreportable results, and specimens must be shipped to the unique reference laboratory in the United States (4, 5). Consequently, other clinical (6), phenotypic (7), and genotypic (8) alternatives for determining viral tropism have been examined. We consider that the virological response to the drug, without the presence of other active drugs with a potential confounding effect that could affect the virological response, should be the most important criteria in order to decide on an MVC prescription. The Maraviroc Clinical Test (MCT) is an in vivo drug sensitivity test based on the virological response to a shortterm exposure to MVC monotherapy to be used prior to a recommendation of CCR5 antagonist therapy in both naive and treatment-experienced patients (9, 10). Using the MCT model, we developed a phenotypic tropism test (TROCAI) that overcomes some of the ESTA limitations and obtained a strong correlation between a cutoff of Ͻ0.5% dual/mixed viruses and sensitivity to MVC (11).Here, our aim was to validate TROCAI, using the above-mentioned cutoff, in a new cohort of patients, comparing the TROCAI results with those of the MCT, together with other genotypic/ phenotypic methods (see the supplemental material).Baseline characteristics (just before MVC administration) of the patients are shown in Table S1 in the supplemental material. TROCAI obtained an R5 result (X4 strains, Ͻ0.5%) in 35/42 (83%) patients, whereas dual/mixed (DM) results (Ն0.5% X4 strains) were obtained in 7/42 (17%) of them (Table 1). Virological response to MVC exposure was observed in 34 (81%) patients (MCTϩ), while 8 (19%) showed no virological response (MCTϪ). Interestingly, the number of HIV RNA copies in the cell line U87-CD4 ϩ CXCR4 ϩ (log viral load [VL] U87X4) was statistically different between the MCTϪ and MCTϩ groups (5.5 copies/ml [4.2 to 7.4 copies/ml] versus 2.8 copies/ml [2.3 to 3.3 copies/ml], respectively; P Ͻ 0.001) but not in the cell line U87-CD4 ϩ CCR5 ϩ (6.6 copies/ml [5.1 to 8.8 copies/ml] versus 6.3 copies/ml [5.7 to 7.1 copies/ml], respectively; P ϭ 0.848). In the multivariate logistic analysis including the variables associated in the unadjusted analysis, after controlling for potential confounders and avo...