Improved induction of antibodies against key neutralizing epitopes by human immunodeficiency virus type 1 gp120 DNA prime-protein boost vaccination compared to gp120 protein-only vaccination

A major challenge in human immunodeficiency virus type 1 (HIV-1) vaccine development is to elicit potent and broadly neutralizing antibodies that are effective against primary viral isolates. Previously, we showed that DNA prime-protein boost vaccination using HIV-1 gp120 antigens was more effective in eliciting neutralizing antibodies against primary HIV-1 isolates than was a recombinant gp120 protein-only vaccination approach. In the current study, we analyzed the difference in antibody specificities in rabbit sera elicited by these two immunization regimens using peptide enzyme-linked immunosorbent assay and a competitive virus capture assay. Our results indicate that a DNA prime-protein boost regimen is more effective than a protein-alone vaccination approach in inducing antibodies that target two key neutralizing domains: the V3 loop and the CD4 binding site. In particular, positive antibodies targeting several peptides that overlap with the known CD4 binding area were detected only in DNA-primed sera. Different profiles of antibody specificities provide insight into the mechanisms behind the elicitation of better neutralizing antibodies with the DNA prime-protein boost approach, and our results support the use of this approach to further optimize Env formulations for HIV vaccine development.