Preliminary evaluation of a DDA cationic liposome-based pulmonary mucosal immunization platform carrying a SARS-CoV-2 spike-derived branched peptide.

Introduction: Current injectable vaccines targeting respiratory viruses are highly effective in inducing systemic immunity, yet they fall short in establishing effective defenses at mucosal sites, ultimately failing to completely block viral infection and transmission. Developing novel immune strategies that can simultaneously activate mucosal and systemic immunity is vitally important. Methods: In this study, we created a pulmonary mucosal immune nanovaccine platform based on dimethyldioctadecyl ammonium (DDA) cationic liposomes. The immune effect was systematically evaluated using Results: The results showed that the prepared formulation had a uniform particle size (approximately 101 nm), positive zeta potential (+42.67 mV), and high encapsulation efficiency (over 80%). The formulation effectively stimulated the maturation of dendritic cells, induced high levels of antigen-specific IgG antibodies in serum and IgA antibodies in bronchoalveolar lavage fluid. It also significantly promoted the proliferation of activated T/B cells and the formation of tissue-resident memory T cells in lung tissues. Mechanistic studies revealed that the vaccine was retained in the lung for a long time and was subsequently detected in mediastinal lymph nodes, accompanied by increased activation-associated dendritic-cell phenotypes, thereby synergistically activating mucosal and systemic immune responses. Discussion: Overall, this study provides preliminary proof-of-concept evidence that the DDA liposome-based formulation has immunogenic potential following pulmonary mucosal administration. However, additional