Investigation of the immunogenicity of Zika glycan loop

Authors: HENDERSON, ELIZABETH - Keck Graduate Institute; Tam, Christina; Cheng, Luisa; NGONO, ANNIE - La Jolla Institute For Allergy And Immunology; NGUYEN, ANH-VIET - La Jolla Institute For Allergy And Immunology; SHRESTA, SUJAN - La Jolla Institute For Allergy And Immunology; MCGEE, MATT - Novici Biotech Llc; PADGETT, HAL - Novici Biotech Llc; GILL, LARRY - Keck Graduate Institute; MARTCHENKO, MIKHAIL - Keck Graduate Institute

Submitted to: Virology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 3/31/2020
Citation: Henderson, E., Tam, C.C., Cheng, L.W., Ngono, A.E., Nguyen, A., Shresta, S., McGee, M., Padgett, H., Gill, L., Martchenko, M. 2020. Investigation of the immunogenicity of Zika glycan loop. Virology Journal. 17:43. https://doi.org/10.1186/s12985-020-01313-1.
DOI: https://doi.org/10.1186/s12985-020-01313-1

Interpretive Summary: Zika virus belongs to the Flavivirus genus of the Flaviviridae family, which is composed of viruses such as yellow fever virus, dengue virus, Japanese encephalitis virus, Tick-borne encephalitis virus, West Nile virus and the hepatitis C virus. Recent outbreaks have shown that Zika virus infections are associated with a variety of severe outcomes, such as Guillain–Barré syndrome and congenital Zika syndrome. The Zika virus contains three structural proteins: the capsid protein, the envelope protein and the membrane protein. The envelope (E) protein is antigenically important and has been shown to induce protective immunity. Humans previously infected with ZIKV possess low but detectable levels of antibodies that recognize a glycan loop of the envelope protein. In this study, we developed antibodies to different envelop protein glycan loops and identified neutralizing antibodies that bind to different forms of the E monomer. This discovery may have significant implications for the development of ZIKV vaccines, therapeutics, and diagnostics with analogous significance to other flaviviruses.

Technical Abstract: Zika virus (ZIKV) is a major human pathogen and member of the Flavivirus genus. Previous studies have identified neutralizing antibodies from Zika patients that bind to quaternary epitopes across neighboring envelope (E) proteins, called E dimer epitopes (EDE). An asparagine-linked glycan on the “glycan loop” of the ZIKV envelope protein protects the functionally important “fusion loop” on the opposite E subunit in the dimer, and EDE antibodies have been shown to bind to both loops. Human EDE antibodies have been divided into two subclasses based on how they bind to the glycan loop region: EDE1 antibodies do not require glycosylation for binding, while EDE2 antibodies strongly rely on the glycan for binding. We report here the existence of ZIKV neutralizing antibodies that bind to E monomers through epitopes that include the glycan loop. We show that sera from human Zika patients contain antibodies capable of binding to the unglycosylated glycan loop in the absence of the rest of the envelope protein. Furthermore, mice were inoculated with recombinant E monomers and produced neutralizing antibodies that either recognize unglycosylated glycan loop or require glycan for their binding to monomeric E. We demonstrate that both types of antibodies neutralize ZIKV in a cellular virus neutralization assay. Analogous to the existing EDE antibody nomenclature, we propose a new classification for antibodies that bind to E monomer epitopes (EME): EME1 and EME2 for those that do not require and those that do require glycan for binding to E, respectively.