Induction of broadly neutralizing antibodies (bnAbs) that confer protection against diverse strains is a primary goal of HIV-1 vaccine design. In order accomplish this feat, antibodies must target conserved sites on the envelope (Env) surface. The V3-glycan epitope is a well-defined site of vulnerability targeted by a class of antibodies with extreme neutralization potency and breadth. We designed minimal nanoparticle-based immunogens that recapitulate this conserved site to focus the immune response on the V3-glycan epitope. We hypothesize vaccination with minimal immunogens will target and expand subdominant neutralizing antibodies (nAbs) without boosting dominant strain-specific non-nAbs.
V3-glycan epitope nanoparticles were produced in Freestyle293 cells and purified by 2G12 affinity chromatography. Formation of nanoparticles was determined by negative stain electron microscopy. Immunogen recognition by bnAbs was assessed by ELISA. Immunogenicity studies were performed using female New Zealand white rabbits. Rabbits (n=5 per group) were immunized intramuscularly with either SOSIP or adjuvant at week 0, 4 and 8. Animals received boosts with the V3-glycan epitope nanoparticle at weeks 12 and 22. Serum was collected 2 weeks after each immunization. Serum antibody binding titers were determined by ELISA. Epitope mapping of serum antibodies was assessed by decreases in binding to Env with mutated epitopes. Serum nAbs were determined by the TZM-bl assay using pseudoviruses.
We generated ferritin nanoparticles that each display 24 copies of a glycopeptide that mimics the V3-glycan epitope. These nanoparticles are antigenic for V3-glycan bnAbs but not linear V3 antibodies. Binding of the bnAbs was further enhanced by enriching for Man9GlcNAc2 protein glycosylation. Rabbits received three immunizations with a group M consensus stabilized Env SOSIP followed by two boosts with the glycan-V3 ferritin nanoparticles. A single boost elicited antibodies with preferential binding to the glycopeptide versus the aglycone peptide. A second boost increased glycopeptide binding, but also induced V3 peptide-specific antibodies. Boosting sustained titers of SOSIP-specific antibodies for 22 weeks–12 weeks after the final trimer immunization.
Glycan-V3 nanoparticle vaccination elicited V3-directed antibodies that were predominantly glycan-dependent. Our results establish a nanoparticle platform by which minimal immunogens can be used to target antibodies to a specific epitope.