Are located in a homopolymeric region. We evaluated the sensitivity of the NGS for quantifying CXCR4-using variants with artificial mixtures of pure X4 (CHS02) and R5 (CHS11) virus clones. The MiSeq NGS detected 0.5 of X4 viruses in 2/3 mixtures and 1 in 3/3 mixtures. The 454 GS-Junior NGS detected 1 of X4 viruses in 2/3 mixtures and 5 of X4 viruses in 3/3 mixtures (Table 1). Linear regression