Messenger RNA Delivery with Lipid Nanoparticles to Non-Liver Targets

 Lipid nanoparticle vehicles are effective tools for delivering messenger RNA therapeutics. They have been successfully used in Moderna and Pfizer vaccines against COVID-19 and are in end stage clinical trials for several metabolic liver diseases. Despite their success, we do not have a complete understanding of how different lipid components affect particle tropism and efficacy in vivo. Currently, lipid nanoparticles are only efficient at targeting the liver, when administered systemically. This confines mRNA therapies to liver related diseases while the potential for messenger RNA application is much greater. Out of the four lipid components of the particle, chemistry of the ionizable lipid has the most influence on the lipid nanoparticle by impacting the particle’s protein corona and its endosomal escape facilitation. Understanding the exact structure function relationships between ionizable lipid chemistry and a nanoparticle’s behavior in vivo is crucial for rational and systematic design of lipids that are safe, efficient and endogenously target cells of interest.
Here, I focus on finding new materials capable of endogenous lung and hematopoetic stem cell delivery. I screened our 580 novel ionizable lipid library in mice to find materials and formulations capable of reaching non-liver targets. During my screen in mice, I found several new components capable of endogenous targeting of spleen and lungs, along with one lipid nanoparticle capable of transfecting natural killer, dendritic, epithelial, and endothelial cells in lungs in vivo. These cells are clinically relevant in treatment of various lung diseases, like cystic fibrosis or lung cancers. I also screened this library in ex vivo human hematopoetic stem cells in search of hematopetic stem cell transfecting materials. While I did see several potent materials, I found a significant variability in their efficacy between cell donors. During this work I also found that making lipid nanoparticles with microfluidic mixing can skew their organ tropism, and that our lipid nanoparticles can successfully deliver long messenger RNAs such as the CRISPRi system. I showed that this gene modulation tool has different protein silencing kinetics than what we see with siRNA. Together these findings advance the lipid nanoparticle capabilities to deliver mRNA therapeutics beyond the liver.