Towards site-directed covalent vaccination: HIV neutralization by antibodies to an electrophilic gp120 V3 peptide (47.38)

Abstract

Abstract We observed recently that antibodies (Abs) to an analog of full-length HIV gp120 analog containing electrophilic phosphonate groups located at Lys (E-gp120) form stable immune complexes characterized by very slow dissociation and resistance to denaturants. We hypothesize that the unusual stability is due to the partial covalent character of the complexes, mediated by enhanced Ab nucleophilic reactivity developing in response to electrophilic immunization. Here we tested the feasibility of inducing an epitope-specific nucleophilic Ab response on-demand using as immunogen the electrophilic analog of the principal neutralizing determinant of HIV gp120 (E-PND). Murine IgG Abs raised to E-PND and non-electrophilic PND displayed binding to intact HIV particles. Complexes of HIV with anti-E-PND IgG dissociated ~25-times slower than the complexes with anti-PND IgG. Anti-E-PND IgG neutralized HIV more potently than anti-PND IgG, determined using a T cell line assay (difference in IC50, ~50-fold). The slower dissociation kinetics can be expected to maintain long-lasting blockade of gp120 recognition by host receptors, resulting in superior HIV neutralization. These results suggest the utility of electrophilic immunization to enhance the protective efficacy of site-specific humoral immunity against peptide antigens.