Improvement of RBD-FC Immunogenicity by Using Alum–Sodium Alginate Adjuvant Against SARS-COV-2

Abstract

Background: Adjuvants use several mechanisms to boost immunogenicity and to modulate immune response. The strength of adsorption of antigen by adjuvants can be a determinant factor for significant improvement of immunopotentiation. Methods: We expressed recombinant RBD-FC in PichiaPink Strain 4 and examined the vaccination of mice by vaccine formulation with different adjuvants (sodium alginate and aluminum hydroxide, alone and together). Results: Sodium alginate significantly increased the immunogenicity and stability of RBD-FC antigen, so RBD-FC formulated with combined alginate and alum (AlSa) and sodium alginate alone showed higher antibody titer and stability. Immunogenicity of RBD-FC:AlSa was determined by serological assays including direct enzyme-linked immunosorbent assay (ELISA) and surrogate virus neutralization test (sVNT). High levels of IgGs and neutralizing antibodies were measured in serum of mice immunized with the RBD-FC:AlSa formulation. On the other hand, cytokines IL-10 and INF-γ were severely accumulated in response to RBD-FC:AlSa, and after 10 days, their accumulation was significantly declined, whereas IL-4 showed the highest and the lowest accumulation in response to alum and alginate, respectively. Conclusions: Our data may suggest that combination of alum and sodium alginate has a better compatibility with RBD-FC in vaccine formulation.