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

## TL;DR

A new hybrid polymer system improves mRNA vaccine delivery to the lungs by overcoming mucus barriers and enhancing immune activation.

## Contribution

A hybrid PLGA/PBAE system coordinates endosomal escape and mRNA release for efficient pulmonary mRNA delivery.

## Key findings

- The PLGA/PBAE system enables mucus penetration and effective mRNA transfection in airway models.
- The system retains transfection efficiency after nebulization and promotes immune activation in dendritic cells.

## Abstract

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 ex vivo 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.

•PLGA/PBAE coordinates endosomal escape and timely mRNA release in APCs•PLGA/PBAE enhances mRNA transfection in APCs and promotes immune activation•PLGA/PBAE enables mucus penetration and effective mRNA transfection in airway models•PLGA/PBAE retains transfection efficiency after nebulization

PLGA/PBAE coordinates endosomal escape and timely mRNA release in APCs

PLGA/PBAE enhances mRNA transfection in APCs and promotes immune activation

PLGA/PBAE enables mucus penetration and effective mRNA transfection in airway models

PLGA/PBAE retains transfection efficiency after nebulization

Respiratory viruses, such as coronaviruses, influenza, and respiratory syncytial virus (RSV), continue to challenge global health, highlighting the need for vaccines that can elicit mucosal immunity directly in the airways. Pulmonary mRNA vaccination offers this promise, yet its development has been constrained by the difficulty of transporting mRNA across airway mucus and enabling efficient transfection in lung antigen-presenting cells through clinically relevant aerosol delivery.

In this study, we present a hybrid polymeric delivery system that leverages the complementary properties of poly(lactic-co-glycolic) acid (PLGA) and poly(β-amino esters) (PBAEs) to address these challenges. Designed to act through a coordinated sequence of mRNA protection, intracellular transport, and timely cytosolic release, the hybrid nanoparticles enable efficient mRNA transfection in antigen-presenting cells and support productive immune activation. Importantly, the hybrid nanoparticles can penetrate airway mucus, function in physiologically relevant human lung models, and withstand the mechanical stresses of vibrating-mesh nebulization, features essential for translating pulmonary mRNA delivery toward practical use. Such hybrid systems may help accelerate the development of next-generation inhalable vaccines and broaden the therapeutic reach of mRNA technologies.

Development of inhaled mRNA vaccines is challenging due to airway biological barriers and the need for efficient transfection of pulmonary antigen-presenting cells. This study introduces a hybrid PLGA/PBAE system that coordinates endosomal escape with timely mRNA release, enabling effective transfection in dendritic cells and downstream immune activation. By enhancing delivery across the mucus barrier and retaining activity after nebulization, this platform provides a conceptual advance toward inhalable mRNA vaccines.