Promiscuous Glycan Site Recognition by Antibodies to the High-Mannose Patch of gp120 Broadens Neutralization of HIV

HIV broadly neutralizing monoclonal antibodies targeting the high-mannose patch of Env can use alternate glycan sites for neutralization. Neutralizing Antibodies with a Sweet Tooth Sugar can be quite tempting—as anyone who’s seen a kid rip into birthday cake can attest. Yet, antibodies can also have a sweet tooth, targeting glycan modifications on the surface of proteins. Indeed, some antibodies that neutralize multiple HIV strains—broadly neutralizing monoclonal antibodies (bnmAbs)—target a high-mannose patch on the HIV protein Env. Although this high-mannose patch is centered around the glycan at position 332 (N332), it has remained unclear if the N332 glycan is absolutely required for neutralization and, if not, why not. Sok et al. found that these mannose patch–targeting antibodies can bind alternate glycans in the absence of N332, which helps to explain their ability to neutralize many strains of HIV. Specifically, some bnmAbs can bind to the N334 site when that replaces the N332 site and some can form more interactions with other glycans, particularly complex-type glycans on variable loops, if the N332 sugar is absent. These data also suggest that mannose patch–targeting bnmAbs can work in combination to neutralize a wider range of different strains than single bnmAbs. The promiscuity of glycan binding by these sugar-loving antibodies is important to consider for both vaccine and therapeutic antibody development. Broadly neutralizing monoclonal antibodies (bnmAbs) that target the high-mannose patch centered around the glycan at position 332 on HIV Env are promising vaccine leads and therapeutic candidates because they effectively protect against mucosal SHIV challenge and strongly suppress SHIV viremia in established infection in macaque models. However, these antibodies demonstrate varying degrees of dependency on the N332 glycan site, and the origins of their neutralization breadth are not always obvious. By measuring neutralization on an extended range of glycan site viral variants, we found that some bnmAbs can use alternate N-linked glycans in the absence of the N332 glycan site and therefore neutralize a substantial number of viruses lacking the site. Furthermore, many of the antibodies can neutralize viruses in which the N332 glycan site is shifted to the 334 position. Finally, we found that a combination of three antibody families that target the high-mannose patch can lead to 99% neutralization coverage of a large panel of viruses containing the N332/N334 glycan site and up to 66% coverage for viruses that lack the N332/N334 glycan site. The results indicate that a diverse response against the high-mannose patch may provide near-equivalent coverage as a combination of bnmAbs targeting multiple epitopes. Additionally, the ability of some bnmAbs to use other N-linked glycan sites can help counter neutralization escape mediated by shifting of glycosylation sites. Overall, this work highlights the importance of promiscuous glycan binding properties in bnmAbs to the high-mannose patch for optimal antiviral activity in either protective or therapeutic modalities.