SARS-CoV-2 RBD-Tetanus toxoid conjugate vaccine induces a strong neutralizing immunity in preclinical studies

Abstract

The development of prophylactic vaccines at unprecedented speed is necessary to control the global pandemic due to SARS CoV 2 infection. Vaccines approved for use and those under development intend to block viral sites binding to the hosts cellular receptors by means of neutralizing antibodies. Virus infection is mediated by the spike glycoprotein trimer on the virion surface via its receptor binding domain (RBD). Antibody response against this domain is an important outcome of the immunization and correlates well with viral neutralization. Here we show that macromolecular constructs with recombinant RBD conjugated to tetanus toxoid induce a potent immune response in laboratory animals. Some advantages of the immunization with the viral antigen coupled to tetanus toxoid have become evident such as predominantly IgG immune response due to affinity maturation and long term specific B memory cells. This work demonstrates that subunit conjugate vaccines can be an alternative for COVID19 paving the way for other viral conjugate vaccines based on the use of small viral proteins involved in the infection process.

Safety and efficacy of the two doses conjugated protein-based SOBERANA-02 COVID-19 vaccine and of a heterologous three-dose combination with SOBERANA-PLUS: double-blind, randomised, placebo-controlled phase 3 clinical trial

“…SOBERANA 02 antigen is the recombinant RBD from SARS-CoV-2 (25 g) chemically conjugated to TT in a molar ratio ~6/1 and adsorbed on 500 g alumina [2]. SOBERANA Plus was develop as a universal booster; the antigen is dimeric RBD (50 g) adsorbed on 1250 g alumina [11].…”

“…The antigen is the recombinant receptor binding domain (RBD) protein conjugated chemically to tetanus toxoid (TT) in a molar ratio 6/1. [2] The development of protein-polysaccharide conjugation technology in the 1980s furnished safe, highly immunogenic novel pediatric vaccines against Haemophilus influenzae type b [3]. Other conjugate vaccines based on carbohydrate antigens are in use in pediatric population for Neisseria meningitidis and Streptococcus pneumoniae [4,5,6,7].…”

Chemical Conjugation Strategies for the Development of Protein-Based Subunit Nanovaccines

“…Valdes-Balbin et al conjugated fused SARS-CoV-2 RBD with an additional Cys538 to highly immunogenic carrier protein tetanus toxoid through maleimide-thiol chemistry [148]. A higher level of virus neutralization was achieved by the antibody elicited by the conjugates absorbed on alum, compared to RBD/alum.…”

A COVID-19 vaccine candidate composed of the SARS-CoV-2 RBD dimer and Neisseria meningitidis outer membrane vesicles

“…5,16,18 Different strategies have been implemented to increase the immunogenicity of RBD-based immunogens, including the use of potent adjuvants and multivalent antigen display in larger macromolecular constructs. 13 The recombinant RBD has been conjugated to large protein carriers as tetanus toxoid 19 and incorporated into self-assembled nanoparticles, 13,20 leading to highly immunogenic multivalent constructs. Another approach has been the use of dimeric RBD immunogens, which have been produced in the form of fusion RBD-Fc chimeras 21,22 or as an RBD dimer with a tandem-repeat single chain (sc-dimer) connecting the two RBD units.…”

“…Our endeavor on the use of the recombinant RBD as an antigen focuses on exploring different alternatives to improve its immunogenicity. RBD(Arg319-Phe541-(His) 6 ), which intentionally includes unpaired Cys538, 19 was expressed in CHO cells as a mixture of the RBD monomer and dimer. The RBD monomer (RBD-m) was site-selectively conjugated to tetanus toxoid (TT) for producing an RBD-TT conjugate vaccine candidate, 19 which recently completed phase III clinical evaluation under the name SOBERANA02 and received emergency approval in Cuba.…”