Transient Macrophage Depletion Circumvents Scavenging and Redirects Biodistribution of mRNA-Lipid Nanoparticles

The mononuclear phagocytic system is recognized as a major scavenger of mRNA-lipid nanoparticles (LNPs), clearing and redirecting these particles away from their intended targets and thus diminishing their delivery efficacy. Understanding the mechanism by which mRNA-LNPs interact with phagocytes and how this interaction affects the mRNA transfection is critical to enhancing the delivery of mRNA. In this study, we temporarily depleted both circulating and resident macrophages (MF) and evaluated the transfection efficiency and biodistribution of mRNA-LNPs. We first demonstrated the enhanced liver expression using two liver-tropic formulations and the significant improvement of the <i>in vivo</i> gene editing efficiency of CRISPR-Cas9 in the Ai14 mouse model after MF depletion, providing a versatile strategy for enhanced mRNA delivery to the liver regardless of the formulation employed. We then extended our investigations to lung-tropic and lymphoid-tropic LNP formulations and discovered that MF depletion abolishes the targeting capacities of these non-liver-tropic formulations, providing insights into the organ targeting of LNPs. Finally, we screened and compared various clinically relevant MF depletion methods, providing the translation potential of this method on enhanced hepatic delivery of mRNA.