High‐Throughput In Vivo Screening Using Barcoded mRNA Identifies Lipid Nanoparticles With Extrahepatic Tropism for In Situ Immunoengineering

Interest continues to grow in the use of mRNA vaccines and therapeutics. While effective for immunization against infectious diseases, lipid nanoparticle (LNP) formulations used for other mRNA delivery applications suffer from off-target accumulation, poor immune transfection, and reactogenicity, limiting their application to immunoengineering. Development of new mRNA LNPs is severely bottlenecked by the LNP discovery process, which is historically low-throughput due to reliance on low-plex measurements. Here, we develop a high-throughput in vivo mRNA LNP screening platform based on barcoded mRNA (b-mRNA). Using this b-mRNA screening platform to simultaneously evaluate 122 LNPs, we identify novel LNP formulations capable of potent hepatic and extrahepatic transfection. We evaluate a lead LNP candidate for in situ immune modulation in a syngeneic mouse model of melanoma and demonstrate a significant reduction in tumor burden and extended survival compared to mice treated with a gold standard mRNA LNP formulation. We employ novel biochemical characterization techniques to analyze nanoparticle protein corona formation with single-particle resolution and gain insight into the influence of protein adsorption on hepatic and splenic transfection. Together, our results demonstrate the value of advanced LNP screening and characterization techniques for the development of next-generation mRNA LNPs for immunoengineering.