Liposomal sprays for nasal vaccination: a comparative study of cationic and anionic formulations involving stability upon nebulization, sprayability, and in vitro immune activation

Nasal immunization is a promising non-invasive route, enabling needle-free self-administration and activating immune cells in the mucosal tissue of the upper airways. This vaccination method is particularly appealing when paired with biocompatible and biodegradable nanocarriers like liposomes, which serve as an effective tool for the nasal delivery of antigenic molecules. In the present study, the model antigen ovalbumin was encapsulated in liposomes using an eco-friendly method. Negative and positive liposomes were formulated with Phospholipon® 90 G alone (anionic liposomes) or combined with 1,2-dioleoyl-3-trimethylammonium-propane (cationic DOTAP-liposomes). These liposomes were smaller than 130 nm and remained stable for up to 3 months. Their sprayability was assessed based on criteria established by the European Medicines Agency and the Food and Drug Administration for nasal products. Both formulations were easily sprayable, generating droplets larger than 5 μm, which are expected to deposit in the nose while avoiding the lungs. Furthermore, after nebulization, they retained their dimensions, structures, and high encapsulation efficiencies ('70 %). In a co-culture system of dendritic cells and B3Z OT-I hybridoma cells, it was shown that they enhanced antigen delivery and presentation, producing approximately 6–9 times more interleukin-2 compared to the ovalbumin solution. Lastly, when tested on macrophages, they did not induce any proinflammatory effect. However, due to their higher muco-adhesiveness (∼88 % vs ∼8 %) and better deposition in the posterior nasal cavity (∼52 % vs ∼43 %) compared to anionic liposomes, cationic DOTAP-liposomes appeared more suitable for nasal administration.