FIG 4.

Vaccine-induced Env-specific humoral immune responses in group 2. (A) Env-binding antibodies (Abs) were measured by ELISA using plate-bound gp140 at multiple time points during the vaccine phase. Straight 1:200 dilutions of plasma from each RM in group 2 were used for this analysis. (B) Log-transformed endpoint titers of vaccine-induced gp140-binding Abs in sera from the group 2 vaccinees collected at the time of the first SIV challenge. As a reference, these values were plotted alongside the endpoint titers of gp140-binding Abs in four RMs that had been infected with SIVmac239Δnef for 28 weeks as part of a previous experiment (70). The endpoint titers of gp140-binding Abs in macaques vaccinated with an EP rDNA/rAd5/rVSV/rRRV regimen encoding env, gag, vif, tat, rev, and nef are also shown (27). (C) Ab-dependent cellular cytotoxicity (ADCC) activity was screened against SIVmac239-infected target cells using plasma collected from the group 2 vaccinees at the time of the first i.r. SIV challenge (black lines). SHIV_AD8-EO-infected target cells were used as internal controls (green lines) for nonspecific killing. The decrease in relative light units (RLU) indicates the loss of virus-infected cells in the presence of an NK cell line during the duration of the assay. Dotted lines indicate 50% activity. Plasma from an SIV-infected RM (382-03) with a defined ADCC titer against SIVmac239-infected cells was used as a positive control for these measurements.