Characterizing Lipid Nanoparticle mRNA Delivery to the Central Nervous System

Lipid nanoparticles (LNPs) have demonstrated safety, versatility, and clinical relevance as vehicles for RNA delivery. Currently, there are three FDA-approved LNP-RNA drugs: ONPATTRO®, the systemically administrated siRNA treatment for hereditary liver disease from Alnylam; and two intramuscular mRNA vaccines against COVID-19: SPIKEVAX® produced by Moderna and by Pfizer-BioNTech’s COMIRNATY®. However, beyond vaccination and liver targeting, LNP-RNA drugs are far from reaching their full potential. Research has shown that LNPs can deliver RNA effectively to non-liver tissues, such as lung, spleen, solid tumors, and bone marrow. For the treatment and management of nervous system disorders, gene therapies hold great promise but require safe and effective delivery vehicles. Therefore, a need exists to design LNPs that transfect cells in the central nervous system (CNS). Presently, LNPs with CNS tropism either i) carry ligands, ii) rely on blood-brain barrier disruption, or iii) are administrated locally. In this work, we have investigated mRNA delivery to the CNS upon systemic administration without targeting ligands. Firstly, we optimized the isolation of various cell types from the brain. Secondly, we have studied mRNA delivery readouts for liver de-targeted LNPs, and identified nanoparticle characteristics for subsequent high-throughput LNP screening. Thirdly, we formulated and screened LNPs with these chosen characteristics that we administrated intravenously, and characterized the in vivo tropism of brain-delivering LNPs at the cellular level. Lastly, we used spatial transcriptomics to understand where in the brain the best-performing LNP achieved functional delivery and how mRNA was distributed within the tissue. Through this work, we have shown CNS delivery by liver de-targeted LNPs, and demonstrated the feasibility of systemic delivery of therapeutic mRNA to the cells of the blood-brain barrier without the use of targeting ligands.