An optimized intranasal LNP formulation for potent immune responses of mRNA-based RSV vaccines

Nasal immunoglobulin A (IgA) has been shown to be associated with the prevention of respiratory syncytial virus (RSV) infection and viral replication. However, generating strong mucosal IgA for mRNA vaccines administered <i>via</i> intramuscular injection has proven challenging so far. Herein, we describe mRNA-LNP-based intranasal vaccines that enable the induction of systemic immune responses and strong respiratory mucosal IgA antibodies. After exploring the impact of the types of ionizable lipids and helper lipids, as well as optimizing lipid types and molar ratios, two mRNA-loaded LNP formulations (F4 and F12) achieve significantly enhanced mRNA delivery to the nose and lungs <i>via</i> intranasal administration compared with our MC3-based LNPs (F_MC3 and F0). Our optimized intranasal mRNA vaccines encoding RSV antigenic proteins (F4-mRSV and F12-mRSV) exhibit high encapsulation efficiency (∼99%) and stability during storage. Compared with the intranasal F0-mRSV vaccine based on an intramuscular injection formulation, intranasal F4-mRSV and F12-mRSV vaccines induce potent serum RSV-specific IgG and IgA. The intranasal F4-mRSV vaccine induces higher serum-neutralizing antibodies and splenic cellular immunity. Compared with intramuscular vaccination, the intranasal F4-mRSV vaccine induces potent mucosal IgA in the nose and lungs without inducing significant systemic adverse effects. In conclusion, our results suggest that the intranasal F4 LNP formulation is a promising platform for mucosal mRNA vaccines against respiratory viruses.