|•In 14 subjects, CXCR4-tropic clones in the ‘on-treatment’
samples shared a common ancestor with a pre-treatment X4-tropic virus
indicating outgrowth of X4-tropic virus
|•In the remaining 6 subjects, CXCR4-using env clones
identified in the ‘on-treatment’ samples did not have a pretreatment X4
ancestor but they were also genetically distinct from both the
‘pre-treatment’ and ‘on-treatment’ R5 population.
|•The V3 loop sequences of the these on-treatment X4-tropic
clones differed by 7-17 amino acid residues from the V3 loop of the nearest
R5 sequence on the phylogenetic tree.
|ŘThe Monogram tropism assay has a sensitivity of 100% for
detecting CXCR4-tropic or dual/mixed HIV if present at 10% or more. If present at <10%, the sensitivity of
the assay goes down (83% at a 5% mixture).