In 2008, a modified version of the test known as the enhanced sensitivity Trofile assay

(ESTA) superseded the original Trofile as a screening tool [24]. ESTA has a nominal lower limit of sensitivity of 0.3% for detecting CXCR4-using virus within clonal mixtures, but sensitivity with clinical samples appears to vary [25]. ESTA was found to more accurately identify patients likely to show a virological response to maraviroc in a post hoc re-analysis of the MERIT trial of maraviroc versus efavirenz (in combination with zidovudine/lamivudine) in treatment-naïve patients, which used the original Trofile assay to screen patients for inclusion [17, 23, 26]. ESTA also showed a marginal benefit over Trofile in a post hoc re-analysis of the AIDS Clinical Trials Group (ACTG) 5211 trial of vicriviroc in treatment-experienced patients Ivacaftor clinical trial [23, 27]. There are a number of factors limiting the use of ESTA in routine patient care: testing is only performed in a central laboratory in California, and is expensive and labour-intensive, with a turn-around time of about 4 weeks and a relatively high failure rate (reflecting the assay complexity

and stringent sample collection, storage and transport requirements) [28]. A minimal volume of 3 mL selleckchem of plasma is recommended, which often poses a problem for testing of stored samples and in children. In addition, there is a minimum viral load requirement of 1000 copies/mL for reliable amplification [1], thus excluding this approach in patients with low or undetectable viral load. To circumvent this limitation, use of proviral DNA recovered from peripheral blood mononuclear

cells (PBMC) is being explored but the data remain preliminary [29]. Other phenotypic assays have been developed in some laboratories that show generally good but not complete concordance mafosfamide with Trofile [30]. Genotypic systems use bioinformatic tools to predict tropism from gp120 V3 sequences and offer the advantage of platform portability, low cost and rapid turn-around. Examples of the interpretative systems include position-specific scoring matrices (PSSMs) and Geno2Phenocoreceptor. The latter can also incorporate clinical parameters (most importantly the nadir CD4 T-cell count, but also the CD8 T-cell count and viral load), to improve predictive power for CXCR4-using virus. Genotypic tropism testing (GTT) is easy to implement in laboratories routinely performing genotypic drug-resistance testing, although commercial assays are not yet widely available. GTT is performed by bulk sequencing and typically shows a lower limit of sensitivity for detection of CXCR4-using virus of approximately 10–20%.