Preparation and Immunological Activity Evaluation of an Intranasal Protein Subunit Vaccine Against Ancestral and Mutant SARS-CoV-2 with Curdlan Sulfate/O-Linked Quaternized Chitosan Nanoparticles as Carrier and Adjuvant

Background: COVID-19, a widely spread infectious disease, has lasted for more than three years, which threatens human health and lives worldwide. Vaccines are effective means for preventing infectious diseases such as COVID-19. Nasal mucosal vaccine can develop barriers in upper respiratory tract which is promising to stop SARS-CoV-2 transmission.Methods: We used two polysaccharide derivatives, O-(2-Hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (O-HTCC) and curdlan sulfate (CS), as the carrier and mucosal adjuvant, and SARS-CoV-2 spike receptor binding domain (S-RBD) as the antigen, to develop a nasal mucosal protein subunit vaccine CS/S-RBD/O-HTCC though ionic crosslinking (prepared at the ratio of 2:1:5). The vaccine candidate was tested in BALB/c mice (5μg antigen per mouse) as a primary or booster immunization vaccine with single or bivalent antigen though nasal inoculation.Findings: CS/S-RBD/O-HTCC could induce strong systemic and localized immune response in BALB/c mice using ancestral S-RBD. What is more, after giving one booster vaccination with mutated S-RBD (beta), a broadly protective effect against ancestral and different mutated S-RBD was found. In addition, vaccination of the BALB/c mice with CS/S-RBD/O-HTCC containing S-RBD mix antigens (ancestral and omicron) could induce protective effect against both of the two antigens.Interpretation: CS/O-HTCC is a promising carrier and nasal mucosal adjuvant to prepare protein subunit vaccine for both primary and booster immunization, and the adjuvant is suitable for loading more than one antigen for preparing multivalent vaccines against mutated viruses.Funding: This work was supported by the grants from the Key Project of Science and Technology Boosting Economy 2020 of China (SQ2020YFFO426291).Declaration of Interest: We declare no competing interests. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Ethical Approval: The experimental protocols were approved by the Experimental Animal Welfare and Ethics Committee of Shandong University (No. 18001) and performed in accordance with the U.K. Animals (Scientific Procedures) Act 1986 and its associated guidelines, Directive 2010/63/EU for animal experiments. We have complied with ARRIVE guidelines.