Broad Humoral Immunity Generated in Mice by a Formulation Composed by Two Antigens From Delta Variant of SARS-CoV-2 (preprint)

Due to the rapid development of new variants of SARS-CoV-2 virus, as well as the real threat of new coronavirus zoonosis events, the development of a preventive vaccine with a broader scope of functionality is highly desirable. Previously, we reported the functionality of a nasal formulation based on the preparation of the nucleocapsid protein with the ODN-39M and combined with RBD, both antigens from Delta variant of SARSCoV-2. This combination induces a cross-reactive immunity in mucosal and systemic compartments until sarbecovirus level. In the present study, we explored the magnitude of the immunity generated in Balb/C mice by the same formulation, but adding alum as adjuvant, so as to enhance the humoral immunity against the two antigens. Animals were immunized with three doses of the bivalent formulation, administered by subcutaneous route. The humoral immunity was tested by ELISA and by a Surrogate of Viral Neutralization test. The cell-mediated immunity was also explored. High levels of antibodies against both antigens (N and RBD) were obtained upon immunization. Additionally, the anti-RBD Abs with neutralizing capacity reacted against the three SARS-CoV-2 variants of RBD assayed, including Omicron. At the same time, the Abs also recognized the nucleocapsid proteins from: SARS-CoV-1 and SARS-CoV-2 Delta and Omicron. Taken together, these results make the bivalent formulation tested, an attractive component of a pancorona vaccine able to broaden the scope of humoral immunity against both antigens. This will be particularly important in the reinforcement of immunity from previously vaccinated and/or infected populations.

The Nucleocapsid Protein Of SARS-CoV-2, Combined With ODN-39M, Is A Potential Component For An Intranasal Bivalent Pancorona Vaccine (preprint)

Despite the rapid development of vaccines and their reported efficacy for controlling the COVID-19 waves, two key challenges remain: the scope of the immunity against upcoming variants and zoonosis events, and the induction of mucosal immunity able to clear the virus in the upper respiratory tract for halting the transmission. The present study is aiming at assessing a potential component for a new generation of vaccines so as to overcome such limitations. The recombinant nucleocapsid (N) protein from SARS-CoV-2 Delta variant was combined with a phosphodiester backbone CpG ODN (ODN-39M), forming high molecular weight aggregates. 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 lungs, which along with the specific IgG in sera and CMI in spleen, resulted cross-reactive against the nucleocapsid protein of SARS-CoV-1. Furthermore, the nasal administration of the N+ODN-39M preparation combined with the RBD Delta protein, as inductor of neutralizing Abs, enhanced the local and systemic immune response against RBD with a modulation toward a Th1 pattern. Taken together, these results make the N+ODN-39M preparation a suitable component for a future intranasal pancorona vaccine against Sarbecoviruses. Particularly, the bivalent vaccine formulation N+ODN-39M+RBD could be used as an effective nasal booster in previously vaccinated population.