Vaccination with SARS-CoV-2 spike protein lacking glycan shields elicits enhanced protective responses in animal models

Abstract

A major challenge to end the pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is to develop a broadly protective vaccine that elicits long-term immunity. As the key immunogen, the viral surface spike (S) protein is frequently mutated, and conserved epitopes are shielded by glycans. Here, we revealed that S protein glycosylation has site-differential effects on viral infectivity. We found that S protein generated by lung epithelial cells has glycoforms associated with increased infectivity. Compared to the fully glycosylated S protein, immunization of S protein with N-glycans trimmed to the mono-GlcNAc-decorated state (S MG ) elicited stronger immune responses and better protection for human angiotensin converting enzyme 2 (hACE2) transgenic mice against variants of concern (VOCs). In addition, a broadly neutralizing monoclonal antibody was identified from S MG immunized mice that could neutralize wild type (WT) SARS-CoV-2 and VOCs with sub-picomolar potency. Together, these results demonstrate that removal of glycan shields to better expose the conserved sequences has the potential to be an effective and simple approach for developing a broadly protective SARS-CoV-2 vaccine.

Principles of SARS-CoV-2 glycosylation

“…Previous studies in HIV-1 have shown differences in glycan composition at the basis of producer cells such as presence of lactosaminoglycans in macrophages whereas these glycan compositions are absent in peripheral blood mononuclear cells (PBMCs) [ 30 ]. Despite the apparent insensitivity of the immune response to glycan processing, terminal glycan structures could have implications for viral infectivity [ 31 ]. For example, S protein derived from pseudovirus expressed in lung epithelial cells have shown higher processing such as high sialylation content compared to protein expressed in HEK 293T cells and has shown to be associated with increased infectivity [ 31 ].…”

“…Despite the apparent insensitivity of the immune response to glycan processing, terminal glycan structures could have implications for viral infectivity [ 31 ]. For example, S protein derived from pseudovirus expressed in lung epithelial cells have shown higher processing such as high sialylation content compared to protein expressed in HEK 293T cells and has shown to be associated with increased infectivity [ 31 ]. However, the fine processing of glycans does not play critical role in influencing immunogenicity, in fact, truncation of S protein glycosylation enhances the immune response [ 31 ].…”

“…For example, S protein derived from pseudovirus expressed in lung epithelial cells have shown higher processing such as high sialylation content compared to protein expressed in HEK 293T cells and has shown to be associated with increased infectivity [ 31 ]. However, the fine processing of glycans does not play critical role in influencing immunogenicity, in fact, truncation of S protein glycosylation enhances the immune response [ 31 ]. Even the bulk change in glycosylation of S protein using chemical inhibitor, kifunensine, does not influence serological properties [ 32 ].…”

Insights into the structural peculiarities of the N-terminal and receptor binding domains of the spike protein from the SARS-CoV-2 Omicron variant

“…Another key structural feature of the NTD protein is its extensive glycosylation that plays a number of important biological roles by changing the physico-chemical nature of proteins after translation, thereby contributing to the life cycle of the virus and its escape from the immune system [ 16 ]. Owing to the importance of glycosylation in the camouflaging of immunogenic protein epitopes, no mutation in the glycosylation sites of SARS-CoV-2 VOCs have been observed during viral evolution [ 47 ]. In this study, analysis of the structural role of N -glycans showed an increase in the stability of glycosylated proteins compared to the non-glycosylated state.…”

K18- and CAG-hACE2 Transgenic Mouse Models and SARS-CoV-2: Implications for Neurodegeneration Research

“…SARS-CoV-2 S protein is known to be highly glycosylated, which is required for interaction with hACE2 and is believed to help mask the viral epitopes [78,79]. Based on this evidence, Huang et al immunized CAG-hACE2 transgenic mice using a modified S protein, N-glycans trimmed to the mono-GlcNAc-decorated state (S MG ), missing a glycan shield, to assess its efficacy as a vaccine candidate, and then challenged these animals with some variants of SARS-CoV-2 [80]. The results show that the S MG protein confers effective protection against both the Alpha and Gamma variants.…”