A. Coreceptor usage of 42-month and 48-month variants of child 1690 was determined by entry inhibition into TZM-bl cells with 1 μM CXCR4 inhibitor (AMD 3100) or CCR5 inhibitor (TAK-779). Viruses SF128A, NL4-3 and 89.6 served as controls for CCR5, CXCR4 or CCR5/CXCR4 usage virus, respectively. B, C. Infection and blocking with cognate coreceptor inhibitor were performed in U373-MAGI-CCR5 (B) or U373-MAGI-CXCR4 (C) cells. Viruses SF128A, NL4-3 and 89.6 served as controls for CCR5, CXCR4 or CCR5/CXCR4 usage virus, respectively. The data are expressed as mean values from experiments performed in triplicate, and the error bars indicate standard deviations.