Scientists at Yale University have developed a breakthrough delivery system for mRNA therapeutics that could transform treatments for lung diseases and respiratory infections. The research team, led by Dr. W. Mark Saltzman, created biodegradable polymer nanoparticles that can effectively deliver mRNA molecules to the lungs when administered through the nose or airways.
The study, published in Science Translational Medicine, demonstrates that these specially designed poly(amine-co-ester) (PACE) polymers can protect fragile mRNA molecules and facilitate their entry into lung cells, particularly epithelial cells and antigen-presenting cells that are critical targets for respiratory therapies.
Engineering Polymer Nanoparticles for Lung Delivery
The researchers optimized their delivery system by screening various polymer formulations with different chemical end groups and polyethylene glycol (PEG) content. They found that a blend containing 90% end group-modified PACE (specifically with a modification called E14) and 10% PACE-PEG created small, stable nanoparticles that effectively protected mRNA from enzymatic degradation.
"The mucus is a barrier," explained Dr. Saltzman. "The trick is to make the nanoparticles resistant to adhesion to the mucus."
This careful engineering of the nanoparticle surface properties was crucial for enabling the particles to penetrate the protective mucus layer in the respiratory tract. The researchers demonstrated that their optimized formulation achieved significantly higher transfection efficiency in the lungs compared to commercially available delivery agents.
When delivered to mice, the PACE nanoparticles successfully transfected approximately 21.5% of lung epithelial cells and 19.6% of lung leukocytes. Particularly impressive was the high transfection rate (nearly 60%) in CD11c+CD11b+ antigen-presenting cells, which are crucial for initiating immune responses.
Demonstrating Therapeutic Potential with a COVID-19 Vaccine
To demonstrate the translational potential of their delivery system, the researchers developed an intranasal vaccine against SARS-CoV-2. They encapsulated mRNA encoding the SARS-CoV-2 spike protein in their optimized PACE nanoparticles and administered it to mice through the nose.
The vaccine induced robust immune responses in the lung-draining lymph nodes, including the activation of spike protein-specific CD8+ T cells and the expansion of receptor binding domain (RBD)-specific B cells. Importantly, the vaccination generated both systemic immunity (antibodies in the bloodstream) and local immunity in the lungs, including tissue-resident memory T cells that can provide rapid protection against infection.
When challenged with a lethal dose of SARS-CoV-2, vaccinated mice showed significantly reduced viral loads in their lungs and improved survival rates compared to unvaccinated controls. This demonstrated that the PACE-mRNA vaccine could provide effective protection against respiratory infection.
Advantages Over Current Delivery Methods
The PACE nanoparticles showed several advantages over existing mRNA delivery methods. Unlike lipid nanoparticles used in current mRNA vaccines, which can cause inflammation when administered to the lungs at high doses, the PACE formulation demonstrated good biocompatibility with minimal inflammatory response.
Dr. Akiko Iwasaki, a co-author of the study, noted: "By recruiting adaptive immune responses to the respiratory tract, mucosal vaccines could improve protective immunity and reduce viral transmission, potentially stopping infection earlier in its course."
The researchers also found that their delivery system could accommodate mRNAs of various sizes, from 1,000 to 4,000 nucleotides in length, without significant changes in nanoparticle properties. This versatility suggests that the platform could be used to deliver a wide range of therapeutic mRNAs.
Future Applications
The technology has broad potential applications beyond vaccines. For protein replacement therapy, the high epithelial cell transfection rate achieved by PACE nanoparticles could be particularly valuable for treating conditions like cystic fibrosis, where only a fraction of cells need to express the corrected protein to achieve therapeutic benefit.
"For disease mitigation, only a fraction of lung cells in cystic fibrosis need to express CFTR. For example, 17 to 28% of cells expressing CFTR in a porcine lung model restored 50% of normal CFTR function, an amount consistent with amelioration of symptoms," the researchers noted in their paper.
A company called Xanadu Bio has been established to develop vaccines based on this technology for respiratory conditions, including influenza and respiratory syncytial virus (RSV). The research team is also exploring applications for treating cystic fibrosis and other lung disorders.
While the current study was conducted in mice, the researchers are planning to test the delivery system in larger animal models and to explore alternative delivery mechanisms such as nebulization devices that could be more suitable for human use.
This innovative approach to mRNA delivery represents a significant advancement in the field of respiratory therapeutics and could lead to more effective treatments for a range of lung conditions as well as improved vaccines against respiratory pathogens.
