Bacterially derived synthetic mimetics of mammalian oligomannose prime antibody responses that neutralize HIV infectivity

Abstract

Oligomannose-type glycans are among the major targets on the gp120 component of the HIV envelope protein (Env) for broadly neutralizing antibodies (bnAbs). However, attempts to elicit oligomannose-specific nAbs by immunizing with natural or synthetic oligomannose have so far not been successful, possibly due to B cell tolerance checkpoints. Here we design and synthesize oligomannose mimetics, based on the unique chemical structure of a recently identified bacterial lipooligosaccharide, to appear foreign to the immune system. One of these mimetics is bound avidly by members of a family of oligomannose-specific bnAbs and their putative common germline precursor when presented as a glycoconjugate. The crystal structure of one of the mimetics bound to a member of this bnAb family confirms the antigenic resemblance. Lastly, immunization of human-antibody transgenic animals with a lead mimetic evokes nAbs with specificities approaching those of existing bnAbs. These results provide evidence for utilizing antigenic mimicry to elicit oligomannose-specific bnAbs to HIV-1.

Serum alpha-mannosidase as an additional barrier to eliciting oligomannose-specific HIV-1-neutralizing antibodies

“…Antibody binding is restored when kifunensine, a highly specific alpha-mannosidase inhibitor 29,30 , or EDTA is added to the serum, demonstrating that the loss of antibody binding is due to Ca 2+ -dependent alpha-1,2-specific mannosidase activity. Secondly, and perhaps more significantly, we show that early antibodies produced in animals immunized with a CRM 197 -conjugated glycomimetic of oligomannose 31 bind better to serum-treated glycoconjugate (i.e., enzyme-trimmed) than to buffer-treated glycoconjugate, suggesting that glycoside trimming indeed occurs in vivo. In addition to having obvious implications for the design of glycoconjugates for eliciting oligomannose-specific bnAbs, we show that our findings are also of relevance to efforts employing recombinant envelope glycoproteins.…”

“…Bacterially derived glycomimetic of mammalian oligomannose conjugated to protein carrier CRM 197 retains favorable antigenicity. We have reported previously on a synthetic antigenic mimic of mammalian oligomannose 31 , which was designed based on the lipooligosaccharide backbone of an Rhizobium radiobacter strain that closely resembles the D1 arm of oligomannose 32,33 and then synthetically extended to create an analog of the D3 arm of mammalian oligomannose. For practical purposes, the mimetic was conjugated initially to BSA 31 .…”

“…We have reported previously on a synthetic antigenic mimic of mammalian oligomannose 31 , which was designed based on the lipooligosaccharide backbone of an Rhizobium radiobacter strain that closely resembles the D1 arm of oligomannose 32,33 and then synthetically extended to create an analog of the D3 arm of mammalian oligomannose. For practical purposes, the mimetic was conjugated initially to BSA 31 . We subsequently conjugated it to CRM 197 , a more clinically apt carrier protein 34 that stimulates robust T-follicular helper (Tfh) responses [35][36][37][38] .…”

Comparisons of the antibody repertoires of a humanized rodent and humans by high throughput sequencing

“…Today, many new transgenic animal models have been developed including rodents, chickens, rabbits and cows 8 . These animal models have been used extensively for the discovery of monoclonal antibodies (mAbs) 9 , tolerance studies 10 and more recently for modelling human antibody responses to vaccine candidates 3,4 .…”

“…One limitation is their use of non-human immunoglobulin (V, D, J) genes in antibodies which can be restricted in their specificity 1 , and/or lack residues needed for priming by a germline targeting immunogen 2 . One approach to solving this problem of wild-type animal models is to use humanized immunoglobulin loci-transgenic rodents 3,4 . The first demonstration of a transgenic rodent with the ability to express human IgM was 30 years ago 5 .…”