The Nucleocapsid Protein of SARS-CoV-2, Combined with ODN-39M, Is a Potential Component for an Intranasal Bivalent Vaccine with Broader Functionality

Abstract

Despite the rapid development of vaccines against COVID-19, they have important limitations, such as safety issues, the scope of their efficacy, and the induction of mucosal immunity. The present study proposes a potential component for a new generation of vaccines. The recombinant nucleocapsid (N) protein from the SARS-CoV-2 Delta variant was combined with the ODN-39M, a synthetic 39 mer unmethylated cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN), used as an adjuvant. The evaluation of its immunogenicity in Balb/C mice revealed that only administration by intranasal route induced a systemic cross-reactive, cell-mediated immunity (CMI). In turn, this combination was able to induce anti-N IgA in the lungs, which, along with the specific IgG in sera and CMI in the spleen, was cross-reactive against the nucleocapsid protein of SARS-CoV-1. Furthermore, the nasal administration of the N + ODN-39M preparation, combined with RBD Delta protein, enhanced the local and systemic immune response against RBD, with a neutralizing capacity. Results make the N + ODN-39M preparation a suitable component for a future intranasal vaccine with broader functionality against Sarbecoviruses.

A Nasal Vaccine Candidate, Containing Three Antigenic Regions from SARS-CoV-2, to Induce a Broader Response

“…In the first mouse experiment, the immunogenicity of the chimeric protein measured by anti-N and anti-S2NDH IgG in sera, regardless of the adjuvant and route employed, was clearly evidenced. Such results are in contrast to those previously obtained by our group, in which mice immunized with the non-adjuvanted SARS-CoV-2 Nucleocapsid protein by the intranasal route did not elicit response in either sera or BALF [ 34 ]. In addition, 40% of animals receiving non-adjuvanted S2NDH intranasally were positive for CMI.…”

“…In the present study, the ODN-39M was selected based on its proven adjuvant capacity over viral proteins by parenteral routes [ 31 , 32 , 33 ]. Moreover, for nasal immunity enhancement, we previously demonstrated its capacity using the whole nucleocapsid protein as an antigen [ 34 ].…”

The Key to Increase Immunogenicity of Next-Generation COVID-19 Vaccines Lies in the Inclusion of the SARS-CoV-2 Nucleocapsid Protein

“…Moreover, sera from the immunized mice showed cross-reactivity with RBD from Alpha and Beta VOCs [ 84 ]. A combination of spike and nucleocapsid proteins using a conventional formulation with aluminum hydroxide, lipids, or other adjuvants has shown induction of humoral and cellular response [ 85 , 86 , 87 , 88 , 89 ]. Moreover, formulation of spike + nucleocapsid with cationic or anionic lipids showed that this combination of antigens induced IgG and IgA antibodies and production of IL-5 and IFN- γ [ 86 ].…”