Amplifying immunogenicity of prospective Covid-19 vaccines by glycoengin- eering the coronavirus glycan-shield to present α-gal epitopes

Abstract

The many carbohydrate chains on Covid-19 coronavirus SARS-CoV-2 and its S-protein form a glycanshield that masks antigenic peptides and decreases uptake of inactivated virus or S-protein vaccines by APC. Studies on inactivated influenza virus and recombinant gp120 of HIV vaccines indicate that glycoengineering of glycan-shields to present -gal epitopes (Gal1-3Gal1-4GlcNAc-R) enables harnessing of the natural anti-Gal antibody for amplifying vaccine efficacy, as evaluated in mice producing anti-Gal. The -gal epitope is the ligand for the natural anti-Gal antibody which constitutes ~1% of immunoglobulins in humans. Upon administration of vaccines presenting -gal epitopes, anti-Gal binds to these epitopes at the vaccination site and forms immune complexes with the vaccines. These immune complexes are targeted for extensive uptake by APC as a result of binding of the Fc portion of immunocomplexed anti-Gal to Fc receptors on APC. This anti-Gal mediated effective uptake of vaccines by APC results in 10-200-fold higher anti-viral immune response and in 8-fold higher survival rate following challenge with a lethal dose of live influenza virus, than same vaccines lacking -gal epitopes. It is suggested that glycoengineering of carbohydrate chains on the glycan-shield of inactivated SARS-CoV-2 or on S-protein vaccines, for presenting -gal epitopes, will have similar amplifying effects on vaccine efficacy. -Gal epitope synthesis on coronavirus vaccines can be achieved with recombinant 1,3galactosyltransferase, replication of the virus in cells with high 1,3galactosyltransferase activity as a result of stable transfection of cells with several copies of the 1,3galactosyltransferase gene (GGTA1), or by transduction of host cells with replication defective adenovirus containing this gene. In addition, recombinant S-protein presenting multiple -gal epitopes on the glycan-shield may be produced in glycoengineered yeast or bacteria expression systems containing the corresponding glycosyltransferases. Prospective Covid-19 vaccines presenting -gal epitopes may provide better protection than vaccines lacking this epitope because of increased uptake by APC.