An engineered mutant of HIV-1 gp120 formulated with adjuvant Quil A promotes elicitation of antibody responses overlapping the CD4-binding site.

A major priority in HIV vaccine research is the development of an immunogen to elicit broadly neutralizing antibodies (NAbs). Monoclonal antibody (mAb) b12 is one of now several broadly neutralizing mAbs that bind epitopes overlapping the CD4-binding site (CD4bs) on HIV-1 gp120 and that serve as templates to engineer effective immunogens. We are exploring a strategy whereby extra glycans are incorporated onto gp120 to occlude the epitopes of non-neutralizing mAbs while maintaining exposure of the b12 site. Immunizing with these so-called hyperglycosylated gp120s is hypothesized to preferentially elicit b12-like NAbs. Here, the effects of two adjuvants, monophosphoryl lipid A (MPL) and Quil A, on eliciting b12-like responses when formulated with a new hyperglycosylated mutant, ΔN2mCHO(Q105N), is presented. Sera from ΔN2mCHO(Q105N)_MPL immunized animals bound the homologous antigen ΔN2mCHO(Q105N) with greater preference than sera from ΔN2mCHO(Q105N)_QuilA immunized animals, demonstrating the modulation of antibody fine specificity by these two adjuvants. We also found that sera from ΔN2mCHO(Q105N)_QuilA immunized animals bound best to a resurfaced HIV gp120 core protein on which non-CD4bs epitopes are substituted with non-HIV residues, suggesting that these sera contain a relatively larger fraction of CD4bs-specific antibodies. Consistent with these data, inhibition assays revealed epitope overlap with the binding sites of the CD4bs-specific antibodies b12, b13 and VRC03. Unexpectedly, these sera did not exhibit significant neutralizing activity against a set of HIV-1 primary strains. Our results show that although formulating mutant ΔN2mCHO(Q105N) with Quil A promotes the elicitation of CD4bs-directed antibodies relative to wild-type gp120, tweaking of the immunization regimen is needed to yield robust, CD4bs-focused NAbs.