Branched‐Tail Lipid Nanoparticles for Intravenous mRNA Delivery to Lung Immune, Endothelial, and Alveolar Cells in Mice

Lipid nanoparticles (LNPs) are proven safe and effective delivery systems on a global scale. However, their efficacy has been limited primarily to liver and immune cell targets. To extend the applicability of mRNA drugs, 580 ionizable lipidoids are synthesized and tested for delivery to extrahepatocellular targets. Of these, over 40 enabled protein expression in mice, with the majority transfecting the liver. Beyond the liver, several LNPs containing new, branched‐tail ionizable lipidoids potently delivered mRNA to the lungs, with cell‐level specificity depending on helper lipid chemistry. Incorporation of the neutral helper lipid 1,2‐dioleoyl‐sn‐glycero‐3‐phosphoethanolamine (DOPE) at 16 mol% enabled highly specific delivery to natural killer and dendritic cells within the lung. Although inclusion of the cationic lipid 1,2‐di‐(9Z‐octadecenoyl)‐3‐trimethylammonium‐propane (DOTAP) improved lung tropism, it decreased cell specificity, resulting in equal transfection of endothelial and lymphoid cells. DOTAP formulations are also less favorable than DOPE formulations because they elevated liver enzyme and cytokine levels. Together, these data identify a new branched‐tailed LNP with a unique ability to selectively transfect lung immune cell populations without the use of toxicity‐prone cationic helper lipids. This novel vehicle may unlock RNA therapies for lung diseases associated with immune cell dysregulation, including cancer, viral infections, and autoimmune disorders. This paper describes several new and efficacious ionizable lipids for mRNA delivery to the liver, spleen, and/or lungs in mice when administered by intravenous injection. The most potent lipid nanoparticles contain branched tails and preferentially targeted natural killer and dendritic cells in the lungs without the use of toxicity‐prone cationic lipids such as DOTAP.