A Dual‐Adjuvanted Parenteral‐Intranasal Subunit Nanovaccine generates Robust Systemic and Mucosal Immunity Against SARS‐CoV‐2 in Mice

Abstract Existing parenteral SARS‐CoV‐2 vaccines produce only limited mucosal responses, essential for reducing transmission and achieving sterilizing immunity. Appropriately designed mucosal boosters can overcome the shortcomings of parenteral vaccines and enhance pre‐existing systemic immunity. Here, a new protein subunit nanovaccine is developed by utilizing dual‐adjuvanted (RIG‐I: PUUC RNA and TLR‐9: CpG DNA) polysaccharide‐amino acid‐lipid nanoparticles (PAL‐NPs) along with SARS‐CoV‐2 S1 trimer protein, that can be delivered both intramuscularly (IM) and intranasally (IN) to generate balanced mucosal‐systemic SARS‐CoV‐2 immunity. Mice receiving IM‐Prime PUUC+CpG PAL subunit nanovaccine, followed by an IN‐Boost, developed high levels of IgA, IgG, and cellular immunity in the lungs and showed robust systemic humoral immunity. Interestingly, as a purely intranasal subunit vaccine (IN‐Prime/IN‐Boost), PUUC+CpG PAL‐NPs induced stronger lung‐specific T cell immunity than IM‐Prime/IN‐Boost, and a comparable IgA and neutralizing antibodies, although with a lower systemic antibody response, indicating that a fully mucosal delivery route for SARS‐CoV‐2 vaccination may also be feasible. The data suggest that PUUC+CpG PAL subunit nanovaccine is a promising candidate for generating SARS‐CoV‐2 specific mucosal immunity.