|Although a tropism
switch whereby CXCR4-using virus emerged on MVC resulting from these 7-17
amino acid substitutions in the CCR5 precursor cannot be ruled out from the
review of the data submitted,
|From the amino
acid sequence differences and phylogenetic tree data, the most likely
explanation is the CXCR4-using clones in these 6 subjects emerged from a
pre-existing CXCR4-using virus not detected by the assay at BL.