A hybrid polymeric system for pulmonary mRNA delivery: Advancing mucosal vaccine development

Effective pulmonary messenger RNA (mRNA) vaccination requires delivery systems capable of overcoming the airway barrier and efficiently transfecting pulmonary antigen-presenting cells. Here, we developed a hybrid polymeric system incorporating poly(lactic-co-glycolic) acid (PLGA) and poly(β-amino esters) (PBAEs) to enhance pulmonary mRNA delivery. The components acted through a spatiotemporally coordinated cascade: early PLGA hydrolysis acidified endosomes, boosting PBAE protonation and tightening mRNA condensation for protection; increased buffering, driven by accelerated protonation, strengthened proton-sponge-mediated escape; and weakened electrostatic interactions in the cytosol enabled rapid mRNA release and translation in dendritic cells, supporting immune activation. These findings highlight the need to balance endosomal escape with timely mRNA release for functional expression. The system also overcame the mucus barrier and enabled mRNA transfection in <i>ex vivo</i> human lung tissue samples. After vibrating-mesh nebulization, it retained superior activity compared with lipid nanoparticles. These results support the PLGA/PBAE system as a viable platform for pulmonary mRNA vaccine delivery.