V3 loop alterations contribute to MVC resistance in subjects 17 and 24. Luciferase reporter viruses pseudotyped with unmodified Envs from subject 17 or subject 24, or resistant Envs carrying the V3 loop region of the respective sensitive Envs, were used to infect NP2-CD4/CCR5 cells in the presence of increasing concentrations of MVC (A). A similar experiment with unmodified and mutant Envs from subject 17 was conducted in 293-Affinofile cells that were induced to express maximal levels of CD4 and CCR5 as described previously [51, 58] (B). Virus inhibition curves were constructed as described in the Methods. The data points represent the mean and standard error of the mean from quadruplicate wells, and are the results from 4 independent experiments. Inhibition curves were constructed using Prism, version 4.0c (GraphPad).