ABSTRACT
The glycan shield of human immunodeficiency virus type 1 (HIV-1) gp120 contributes to viral evasion from humoral immune responses. However, the shield is recognized by the HIV-1 broadly neutralizing antibody (Ab), 2G12, at a relatively conserved cluster of oligomannose glycans. The discovery of 2G12 raises the possibility that a carbohydrate immunogen may be developed that could elicit 2G12-like neutralizing Abs and contribute to an AIDS vaccine. We have previously dissected the fine specificity of 2G12 and reported that the synthetic tetramannoside (Man4) that corresponds to the D1 arm of Man9GlcNAc2 inhibits 2G12 binding to gp120 as efficiently as Man9GlcNAc2 itself, indicating the potential use of Man4 as a building block for creating immunogens. Here, we describe the development of neoglycoconjugates displaying variable copy numbers of Man4 on bovine serum albumin (BSA) molecules by conjugation to Lys residues. The increased valency enhances the apparent affinity of 2G12 for Man4 up to a limit which is achieved at ∼10 copies per BSA molecule, beyond which no further enhancement is observed. Immunization of rabbits with BSA-(Man4)14 elicits significant serum Ab titers to Man4. However, these Abs are unable to bind gp120. Further analysis reveals that the elicited Abs bind a variety of unbranched and, to a lesser extent, branched Man9 derivatives but not natural N-linked oligomannose containing the chitobiose core. These results suggest that Abs can be readily elicited against the D1 arm; however, potential differences in the presentation of Man4 on neoglycoconjugates, compared to glycoproteins, poses challenges for eliciting anti-mannose Abs capable of cross-reacting with gp120 and HIV-1.
Detection and activation of HIV broadly neutralizing antibody precursor B cells using anti-idiotypes
