Secondary lymphoid organs (SLOs) are an important target for mRNA delivery in various applications. While the current delivery method relies on the drainage of nanoparticles to lymph nodes by intramuscular (IM) or subcutaneous (SC) injections, an efficient mRNA delivery carrier for SLOs-targeting delivery by systemic administration (IV) is highly desirable but yet to be available. In this study, we developed an efficient SLOs-targeting carrier using phosphatidylserine (PS), a well-known signaling molecule that promotes the endocytic activity of phagocytes and cellular entry of enveloped viruses. We adopted these biomimetic strategies and added PS into the standard four-component MC3based LNP formulation (PS-LNP) to facilitate the cellular uptake of immune cells beyond the charge-driven targeting principle commonly used today. As a result, PS-LNP performed efficient protein expression in both lymph nodes and the spleen after IV administration. In vitro and in vivo characterizations on PS-LNP demonstrated a monocyte/macrophage-mediated SLOs-targeting delivery mechanism.

Systemic delivery of mRNAs into neurons is limited by the blood-brain-barrier (BBB) preventing the entry of carriers into the brain. Leukocyte-derived extracellular vesicles (EVs) can cross the BBB, emerging as promising carriers to target the brain. However, efficient mRNA encapsulation into EVs and their neuronal uptake remain challenges. We incorporated inside EVs the endogenous retrovirus-like Arc protein capsids, stabilized by RNA elements, Arc 5’UTRs, enabling effective cargo loading and delivery. Equipped with adhesion molecules from donor leukocytes, EVs extravasate BBB at inflammatory sites. Arc components promote endocytosis and cargo release, due to their native roles in transferring mRNAs inter-neuronally. Produced from self-derived leukocytes, engineered retrotransposon Arc EVs (eraEVs) are immunologically inert with minimal clearance. Possessing high effectiveness like viral vectors and biocompatibility as naturally occurring vesicles, eraEVs can be produced from virtually all donor cell types, potentially leading to the development of future clinical therapies for a range of diseases.Abstract Figure