8510). Discordances were mainly attributable to Dasatinib purchase X4 prediction from proviral DNA and R5 prediction from plasma RNA, thereby confirming earlier findings [12]. For four of six discordant samples, the presence of X4 strains, as detected in proviral DNA only, was supported by the results of PTT. While the increased detection of X4 virus in proviral DNA is of interest, it should be noted that GTT and PTT by OTA or

ESTA do not assess infectious virus and therefore cannot discriminate between replication-competent (and therefore clinically relevant) strains and defective strains that have no impact on virological responses to therapy. This is in contrast with the MT2 assay, which uses cultured virus. Remarkably, however, in this study the correlation between the Seliciclib ic50 results of the MT2 assay and GTT was higher for the proviral DNA samples (kappa coefficient 0.644 for an FPR of 5% and 0.631 for an FPR of 10%) than for the viral RNA samples (kappa coefficient 0.538 for an FPR of 5% and 0.474 for an FPR of 10%), arguing against a bias resulting from the presence of defective strains in the proviral DNA. In a comparison of the results for 126 longitudinal plasma RNA and proviral DNA samples, the concordance in predicted tropism was 87.3% at an FPR of 10% and increased to 90.5% at an FPR of 5%. Despite an interval of a mean of 55.6 months between the two sample times, the absolute FPR values were linearly correlated

(r=0.8297). Moreover, in patients with long-term suppression of viraemia, the size of the proviral DNA input may be rather small, which can introduce an element of variability in the results. However, based on the results presented, PtdIns(3,4)P2 the influence of this possible ‘selection’ bias appears to be limited. Discordant predictions

were observed for 15 patients at an FPR of 10% and for 12 patients at an FPR of 5%. In contrast to the observations for the simultaneous RNA/DNA samples, changes in tropism prediction from R5 to X4 and from X4 to R5 were seen at the same frequency. Many of the changes in prediction observed with the longitudinal samples appear to reflect interpretative fluctuations around the FPR cut-off. These findings argue against a selective pressure towards X4 evolution under suppressive therapy and confirm reports from previous studies showing that changes in tropism predictions occur with low frequency in treated patients experiencing virological failure [26,27] and with even lower frequency during fully suppressive treatment, although the actual rates vary considerably from study to study [11,28,29]. The concordance between GTT and PTT varied between 79.0 and 88.0%, with kappa values varying between 0.333 and 0.644, depending on the PTT method used and the FPR chosen for GTT. These figures are comparable with previous estimates [22,23,25,29]. Although the overall concordance with PTT was higher with an FPR of 5% than with an FPR of 10%, the difference was very small.