Characterization of Systemic and Mucosal Humoral Immune Responses to an Adjuvanted Intranasal SARS-CoV-2 Protein Subunit Vaccine Candidate in Mice

Abstract

Continuous viral evolution of SARS-CoV-2 has resulted in variants capable of immune evasion, vaccine breakthrough infections and increased transmissibility. New vaccines that invoke mucosal immunity may provide a solution to reducing virus transmission. Here, we evaluated the immunogenicity of intranasally administered subunit protein vaccines composed of a stabilized SARS-CoV-2 spike trimer or the receptor binding domain (RBD) adjuvanted with either cholera toxin (CT) or an archaeal lipid mucosal adjuvant (AMVAD). We show robust induction of immunoglobulin (Ig) G and IgA responses in plasma, nasal wash and bronchoalveolar lavage in mice only when adjuvant is used in the vaccine formulation. While the AMVAD adjuvant was more effective at inducing systemic antibodies against the RBD antigen than CT, CT was generally more effective at inducing overall higher IgA and IgG titers against the spike antigen in both systemic and mucosal compartments. Furthermore, vaccination with adjuvanted spike led to superior mucosal IgA responses than with the RBD antigen and produced broadly targeting neutralizing plasma antibodies against ancestral, Delta and Omicron variants in vitro; whereas adjuvanted RBD elicited a narrower antibody response with neutralizing activity only against ancestral and Delta variants. Our study demonstrates that intranasal administration of an adjuvanted protein subunit vaccine in immunologically naïve mice induced both systemic and mucosal neutralizing antibody responses that were most effective at neutralizing SARS-CoV-2 variants when the trimeric spike was used as an antigen compared to RBD.

Comprehensive analysis of nasal IgA antibodies induced by intranasal administration of the SARS-CoV-2 spike protein

“…Elevated levels of antigen-specific IgA and IgG responses were found in serum taken from the immunized mice, which is consistent with a previous study showing that intranasal vaccinations induce both nasal and serum IgA levels ( Sterlin et al, 2021 ) ( Maltseva et al, 2022 ). We selected three immunized mice with high nasal IgA titers and isolated antigen-specific plasma cells from the nasal mucosa, spleen, lung and blood.…”

“…To date, some intranasal vaccines are under development and have shown a robust mucosal and humoral immune responses in human and animal models ( Houston, 2023 ) ( Chavda et al, 2021 ) ( Alu et al, 2022 ) ( Barrett et al, 2021, Bricker et al, 2021, D’Arco et al, 2021, Kim et al, 2021 ) ( Vabret et al, 2020 ) ( Ohtsuka et al, 2021 ). Considerable efforts have been made to develop mucosal vaccines against pathogens, and nasal lavage fluids containing polyclonal S-IgAs have been used to evaluate the response to these vaccinations ( Maltseva et al, 2022 ) ( Gianchecchi et al, 2019 ) ( Wong et al, 2022 ) ( Afkhami et al, 2022 ) ( Sui et al, 2021 ) ( Azzi et al, 2022 ). However, it is difficult to obtain information regarding the functions of individual antibodies that comprise the polyclonal anti-viral mucosal repertoire from such broad assays.…”

Comprehensive analysis of nasal IgA antibodies induced by intranasal administration of the SARS-CoV-2 spike protein

“…1A ). Elevated levels of antigenspecific IgA and IgG responses were found in serum taken from the immunized mice, which is consistent with a previous study showing that intranasal vaccinations induce both nasal and serum IgA levels (Sterlin et al, 2021) (Maltseva et al, 2022 ). We selected three immunized mice with high nasal IgA titers and isolated antigen-specific plasma cells from the nasal mucosa, spleen, lung and blood.…”

“…To date, some internasal vaccines are under development and have shown a robust mucosal and humoral immune responses in human and animal models (Houston, 2023 ) (Chavda et al, 2021 ) (Alu et al, 2022 ) (Barrett et al, 2021, Bricker et al, 2021, D'Arco et al, 2021, Kim et al, 2021 (Vabret et al, 2020 ) (Ohtsuka et al, 2021 ). Considerable efforts have been made to develop mucosal vaccines against pathogens, and nasal lavage fluids containing polyclonal S-IgAs have been used to evaluate the response to these vaccinations (Maltseva et al, 2022 ) (Gianchecchi et al, 2019 ) (Wong et al, 2022 ) (Afkhami et al, 2022 ) (Sui et al, 2021 ) (Azzi et al, 2022 ). However, it is difficult to obtain information regarding the functions of individual antibodies that comprise the polyclonal anti-viral mucosal repertoire from such broad assays.…”

Antibody Response Following the Intranasal Administration of SARS-CoV-2 Spike Protein-CpG Oligonucleotide Vaccine

“…Thus, the superior immunogenicity of the spike protein may also be attributed to its trimeric structure, which is considerably more stable than the monomeric form of RBD. Repeated trimeric antigen presentation of the spike protein may increase cross-linking to B cell receptors and induce greater B cell activation and IgA responses [ 41 ].…”