Antibodies against Manα1,2-Manα1,2-Man oligosaccharide structures recognize envelope glycoproteins from HIV-1 and SIV strains

Design of an envelope glycoprotein (Env)-based vaccine against human immunodeficiency virus type-1 (HIV-1) is complicated by the large number of N-linked glycans that coat the protein and serve as a barrier to antibody-mediated neutralization. Compared to normal mammalian glycoproteins, high-mannose-type glycans are disproportionately represented on the gp120 subunit of Env. These N-glycans serve as a target for a number of anti-HIV molecules that bind terminal alpha 1,2-linked mannose residues, including lectins and the monoclonal antibody 2G12. We created a Saccharomyces cerevisiae glycosylationmutant, Delta mnn1 Delta mnn4, to expose numerous terminal Man alpha 1,2-Man residues on endogenous hypermannosylated glycoproteins in the yeast cell wall. Immunization of rabbits with whole cells from this mutant induced antibodies that bound to a broad range of Env proteins, including clade A, B, and C of HIV and simian immunodeficiency virus (SIV). The gp120 binding activity of these immune sera was due to mannose-specific immunoglobulin, as removal of high-mannose glycans and alpha 1,2-linked mannoses from gp120 abrogated serum binding. Glycan array analysis with purified IgG demonstrated binding mainly to glycans with Man alpha 1,2-Man alpha 1,2-Man trisaccharides. Altogether, these data demonstrate the immunogenicity of exposed polyvalent Man alpha 1,2-Man alpha 1,2Man structures on the yeast cell wall mannan and their ability to induce antibodies that bind to the HIV Env protein. The yeast strain and sera from this study will be useful tools for determining the type of mannose-specific response that is needed to develop neutralizing antibodies to the glycan shield of HIV.