FIG. 3.

Anti-gp120 binding Ab elicited by SOSIP.R6 immunization. (A) The schematic for the second-stage study highlights the DNA construct [empty vector, SOSIP.R6, or SOS.R6(T)] used for priming (open arrows) the protein construct (SOSIP.R6 trimer, SOSIP.R6 trimer coupled to paramagnetic beads, or empty beads) used for each of the protein boosts (filled arrows), and the serum collection times (grey arrows). The designation numbers for the individual animals in each arm (A to E) are also listed. (B) Rabbits were primed with 1 mg pPPI4 expressing soluble gp140 SOSIP.R6 Env (▴, □, ▵; arms B, C, and D) or membrane-bound SOS.R6 Env (•; arm E) or primed with the empty-vector control (▪; arm A). The animals were then boosted with 30 μg of SOSIP.R6 trimer (▪, ▴, •; arms A, B, and E), 30 μg of SOSIP.R6 trimer coupled to beads (▵; arm D), or empty beads as a control (□; arm C) at the times indicated. The anti-gp120 Ab responses were measured by ELISA. Each datum point represents the mean (n = 4 animals) midpoint anti-gp120 binding titer for each arm. The mean (± standard deviation) anti-gp120 titer in the gp140 Wt DNA-primed and gp120-boosted animals (5695-1 to 5695-6) at week 20 of the pilot study is indicated by the dotted lines for comparison.