Partial restoration of the fitness loss of the T242N mutant by compensatory mutations.

<p>The relative fitness was determined between the T242N mutant and the NI (A and B) and NA (C and D) mutant as well as between the T/F virus and NI (E and F) or NA (G and H) mutant in the single-passage assay (left panels) and the multiple-passage assay (right panels). Same amount (5 ng p24) of each compared virus was mixed to infect 10⁶ of purified CD4⁺ T cells in triplicates. In the single-passage assay, the viruses were cultured for three days and the culture supernatant were harvested daily by completely replacing the medium. In the multiple-passage assay, 200 µl of cell-free virus harvested at day 3 at each passage was used to infect 10⁶ of fresh CD4⁺ T cells. The viruses were subsequently passaged three additional times. The percentage of each virus in the inoculum stock and the culture supernatant was determined by PASS. Mean ± standard deviations are shown. The relative fitness was determined by modeling the replication slope of each virus in the single- and multiple-passage assays as previously described <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102734#pone.0102734-Song1" target="_blank">[25]</a>.