Neutralization of the 205F chimera panel by each Mab localized differences in sensitivity to the V1V2 domain (data not shown). Examination of the V1V2 sequences of 0-to 26-month 205F Nab resistant Envs revealed that each one differed in length, pattern of predicted glycosylation sites, and sequence (Fig. S2) . However, all of the Nab resistant Envs from 8-months and beyond had acquired a mutation that created a potential glycosylation site in V2 at position 197 (highlighted in yellow in Fig. S2 ). Furthermore, 0-month EnvPL6.3 was the only 0-month Env that was resistant to 13.6A, and it lacked a potential N-gly site in V1 relative to the other Envs (highlighted in yellow in Fig. S2 ). Thus, Figure 2 . Moderate neutralization breadth of plasma from 185F and 205F against heterologous 0-month Envs. A single plasma sample from 185F (23-months) and 205F (20-months) was evaluated for neutralizing activity against heterologous Envs acquired during acute/early subtype C infection of six subjects. The Nab IC50 titer for each plasma-Env combination is shown on the vertical axis on a log10 scale. Each data point represents a single plasma-Env combination. Arrows indicate the Nab IC50 titer for the autologous plasma-Env combination; all other data points represent heterologous Envs. The plasma sample is indicated below each point plot. doi:10.1371/journal.ppat.1000594.g002 A and B) , and 205F 2-month PB2.3 (D) and chimeras or mutants from each of these Envs in the corresponding 0-month Env was evaluated using contemporaneous plasma. Pseudoviruses were created by expressing each Env with an HIV-1 env-deficient backbone, and their infectivity for JC53-BL13 (Tzm-bl) cells was evaluated in the absence or presence of serially-diluted patient plasma with luciferase as a quantitative measure. Percent virus infectivity relative to no test plasma is plotted on the vertical axis; the reciprocal of the plasma dilution is plotted along the horizontal axis on a log10 scale. Each curve represents one Env against serial plasma dilutions, and error bars represent the standard deviation of at least two independent experiments using duplicate wells. The legends list the parental Nab resistant Env followed by the chimeric and mutant Envs created in the 0-month Env background. Amino acid alignments are shown to indicate the sequence differences between the different Envs for 185F (C) and 205F (E). The color of the text corresponds to the curves on the graph. Only regions that contained differences are shown. doi:10.1371/journal.ppat.1000594.g003 . 185F Nab resistant variants at 28-months utilize distinct escape pathways. Neutralization of 28-month EnvPL5.1 (A) and 28month EnvPL3.1 (B) and the chimeric Env pseudoviruses generated from each of these Envs in the 0-month Env background was evaluated using the 28-month plasma sample in JC53-BL13 cells with luciferase as a quantitative measure. Percent virus infectivity is plotted against the reciprocal of the log10 plasma dilution. Error bars represent the standard deviation of at least two independent experiments using duplicate wells. The panels below each graph indicate the region that was transferred from the 28-month Nab resistant Env (PL5.1 in A and PL3.1 in B; gray boxes) into 0-month EnvPL3.1 (white boxes). (C) Amino acid alignment of the V5 region for the 0-month and 28-month Envs. doi:10.1371/journal.ppat.1000594.g004