An Evaluation of the Cellular and Humoral Response of a Multi-Epitope Vaccine Candidate Against COVID-19 with Different Alum Adjuvants.

Abstract

SARS-CoV-2 (Betacoronavirus pandemicum) is responsible for the disease identified by the World Health Organization (WHO) as COVID-19. We designed "CHIVAX 2.1", a multi-epitope vaccine, containing ten immunogenic peptides with conserved B-cell and T-cell epitopes in the receceptor binding domain (RBD) sequences of different SARS-CoV-2 variants of concern (VoCs). We evaluated the immune response of mice immunized with 20 or 60 µg of the chimeric protein with two different alum adjuvants (Alhydrogel^® and Adju-Phos^®), plus PHAD^®, in a two-immunization regimen (0 and 21 days). Serum samples were collected on days 0, 21, 31, and 72 post first immunization, with antibody titers determined by indirect ELISA, while lymphoproliferation assays and cytokine production were evaluated by flow cytometry. The presence of neutralizing antibodies was assessed by surrogate neutralization assays. Higher titers of total IgG, IgG₁, and IgG_2a antibodies, as well as increased proliferation rates of specific CD4⁺ and CD8⁺ T cells, were observed in mice immunized with 60 μg of protein plus Adju-Phos^®/PHAD^®. This formulation also generated the highest levels of TNF-α and IFN-γ, in addition to the presence of neutralizing antibodies against Delta and Omicron VoC. These findings indicate the potential of this chimeric multi-epitope vaccine with combined adjuvants as a promising platform against viral infections, eliciting a T_H1 or T_H1:T_H2 balanced cell response.