Glycan masking in vaccine design: Targets, immunogens and applications

Inducing enhanced neutralizing antibodies against broad SARS-CoV-2 variants through glycan-shielding multiple non-neutralizing epitopes of RBD

Introduction

Since the outbreak of SARS-CoV-2, vaccines have demonstrated their effectiveness in resisting virus infection, reducing severity, and lowering the mortality rate in infected individuals. However, due to the rapid and ongoing mutations of SARS-CoV-2, the protective ability of many available vaccines has been challenged. Therefore, there is an urgent need for vaccines capable of eliciting potent broadly neutralizing antibodies against various SARS-CoV-2 variants.

Methods

In this study, we developed a novel subunit vaccine candidate for SARS-CoV-2 by introducing a series of shielding glycans to the Fc-fused receptor-binding domain (RBD) of the prototypic spike protein. This approach aims to mask non-neutralizing epitopes and focus the immune response on crucial neutralizing epitopes.

Results

All modified sites were confirmed to be highly glycosylated through mass spectrometry analysis. The binding affinity of the glycan-shielded RBD (gsRBD) to the human ACE2 receptor was comparable to that of the wildtype RBD (wtRBD). Immunizing mice with gsRBD when combined with either Freund's adjuvant or aluminum adjuvant demonstrated that the introduction of the glycan shield did not compromise the antibody-inducing ability of RBD. Importantly, the gsRBD significantly enhanced the generation of neutralizing antibodies against SARS-CoV-2 pseudoviruses compared to the wtRBD. Notably, it exhibited remarkable protective activity against Beta (B.1.351), Delta (B.1.617.2), and Omicron (B.1.1.529), approximately 3-fold, 7- fold, and 17-fold higher than wtRBD, respectively.

Discussion

Our data proved this multiple-epitope masking strategy as an effective approach for highly active vaccine production.

Contemporaneous SARS-CoV-2-Neutralizing Antibodies Mediated by N-glycan Shields

Mutations and the glycosylation of epitopes can convert immunogenic epitopes into non-immunogenic ones via natural selection or evolutionary pressure, thereby decreasing their sensitivity to neutralizing antibodies. Based on Thomas Francis's theory, memory B and T cells induced during primary infections or vaccination will freeze the new mutated epitopes specific to naïve B and T cells from the repertoire. On this basis, some researchers argue that the current vaccines derived from the previous strains of the SARS-CoV-2 virus do not increase immunity and may also prevent the immune response against new epitopes. However, evidence shows that even if the binding affinity is reduced, the previous antibodies or T cell receptors (TCRs) can still bind to this new epitope of the Beta, Gamma, and Delta variant if their concentration is high enough (from a booster injection) and neutralize the virus. This paper presents some convincing immunological reasons that may challenge this theory and argue for the continuation of universal vaccination to prevent further mutations of the SARS-CoV-2 virus. Simultaneously, the information presented can be used to develop vaccines that target novel epitopes or create new recombinant drugs that do not lose their effectiveness when the virus mutates.