FIG. 5.

Prechallenge and early postchallenge levels of SIVsmE660-NAb in plasma of vaccinated macaques correlate with the degree of central memory CD4⁺ T-cell preservation in peripheral blood. (A) Titration curves of percent inhibition of virus infectivity by plasma samples of each macaque of the control group are shown for plasma samples collected prechallenge; at 4 days, 12 days, and 16 weeks postchallenge; and at necropsy. No neutralizing activity was detected until 16 weeks, with two animals (18655 and H426) showing very low titers of neutralizing activity consistent with rapid disease progression. (B) Bar graphs of reciprocal titers of NAb (log₁₀) to the challenge virus SIVsmE660 prechallenge; at day 4, day 12, and week 16 postchallenge; and at the time of necropsy in each vaccinated group. Titers of NAb are presented for each of the six monkeys per immunization group. Data are presented as the ID₅₀ neutralization titers determined by nonlinear regression of obtained virus infectivity inhibition curve as described in Materials and Methods. The assay limit of detection, which was the lowest reciprocal plasma dilution tested, was an ID₅₀ titer of >20. (C) Scatter plots of the correlations between percentage of central memory CD4⁺ T cells remaining in peripheral blood at week 4 post-SIVsmE660 infection and log of SIVsmE660-NAb titers in plasma from macaques immunized with MVA-SIV recombinants expressing SIV env (MVA-env or MVA-gag-pol-env). Data for prechallenge and day 12 postchallenge plasma samples are shown. P values for the Spearman rank correlation test are indicated.