Amplifying immune responses via a parenteral prime-intranasal boost strategy using a lipidated chitosan...

As COVID-19 continues to spread and new SARS-CoV-2 variants emerge, the immunity provided by first-generation vaccines has been waning, highlighting the need for new strategies to enhance antigen-specific immune responses and overall vaccine efficacy. Nasal vaccination is a promising approach for inducing mucosal immune responses, offering protection at the primary sites of SARS-CoV-2 infection. In this study, we report the development of a novel vaccine formulation, CSOA-LipoCov, consisting of oleic acid-functionalized chitosan nanoparticles loaded with a lipidated multi-epitope peptide-conjugated receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. The CSOA-based nanoparticles platform demonstrated enhanced uptake by antigen-presenting cells, thereby improving the vaccine's immunogenicity. In vivo studies demonstrated that the parenteral prime followed by intranasal boosting immunization strategy of CSOA-LipoCov induced superior systemic and mucosal immune responses compared to homologous vaccination regimens; either intranasal or parenteral administration. Serum cytokine analysis of the prime-pull regimen indicated a balanced Th1/Th2 milieu and the presence of IL-17 A. These findings represent a systemic snapshot of the immune environment rather than definitive cellular activation and, given the low cytokine concentrations, support the overall safety and lack of pathological inflammation of the vaccine candidate. Our findings underscore the potential of CSOA nanoparticles as an effective intranasal vaccine delivery system, particularly for use as a booster dose, based on the enhanced immunogenicity observed with the prime-intranasal boosting strategy.