Characterization of immune responses induced in rabbits immunized with 887-SOS-T and 936-SOS-T VLPs and the corresponding SOSIPs. (A) Immunization protocol. Animals were immunized with two DNA primes and 3 VLP or SOSIP boosts at 3-week intervals. Two weeks after the last boost, rabbits were exsanguinated. (B) ELISA sera endpoint titers against Bal rgp120 during the immunization process (*, P < 0.05; **, P < 0.01; ***, P < 0.001; two-way ANOVA Bonferroni posttest compared to the VLP Gag immunized group). VLPs or SOSIPs boosts are indicated. (C) ELISA sera endpoint titers against Bal rgp120 at exsanguination, week 17 (n.s., not significant; *, P < 0.05; Mann-Whitney U test). (D) IFN-γ sera levels at exsanguination, week 17.