Antibody responses to Env after SIV infection in macaques immunized against Gag. ADCVI activity (A) and antibody titers to Env (C) at 2 and 4 weeks after SIVmac251 infection in control monkeys (sham, n = 6) and monkeys vaccinated against Gag by different prime boost regimens with vectors based on adenovirus types 5, 26, or 35 (Ad-Gag, n = 16). Mean titers with SEM are shown. B) Correlation analysis of ADCVI activity and viral load at week 2. D) Correlation analysis of Env antibody titers at week 4 with the viral load during the first 4 weeks after challenge. AUC: area under the viral load curve. Groups were compared by the Mann–Whitney test (A, C) and data were evaluated by the Spearman rank correlation test (B, D). All data are derived from .