Dirisala, A.; Chatterjee, B.; Nguyen, L. B. T.; Toh, K.; Masai, M. M.; Liu, X.; Tockary, T. A.; Qiao, N.; Ishikawa, J.; Norimatsu, J.; Mochida, Y.; Fukushima, S.; Oba, M.; Kataoka, K.; Uchida, S.

Ionizable lipid nanoparticles (iLNPs) are powerful platforms for mRNA based vaccines and immunotherapies; however, their intrinsic liver tropism compromises both safety and efficacy. Off-target hepatic protein expression from delivered mRNA raises safety concerns, and hepatic clearance limits efficient iLNP delivery to target organs. In this study, we address these challenges in mouse models by stealth-coating the liver sinusoidal endothelial (LSE) wall, the primary gateway for nanoparticle entry into the liver. Specifically, oligocations conjugated with two armed PEG (2 arm PEG oligocations), a clinically relevant material used in oligonucleotide delivery trials, were employed to transiently anchor PEG to the LSE wall with balanced affinity, ensuring robust coating followed by gradual biliary clearance. This approach reduced hepatic protein expression from iLNPs, subsequently administered either systemically or locally, by more than tenfold. Importantly, the strategy preserved iLNP accumulation in the spleen, a key target organ for vaccines, effectively redirecting iLNPs from the liver to the spleen. Consequently, in vaccine applications, pre-injection of the 2 arm PEG oligocation preserved or even enhanced vaccination efficacy while minimizing concerns associated with antigen expression in the liver. In applications involving cytokine mRNA therapy, specifically intratumoral interleukin 12 (IL 12) mRNA administration, systemic pre-injection of the 2 arm PEG oligocation successfully reduced off-target hepatic IL 12 expression and subsequent systemic IL 12 exposure, while maintaining antitumor efficacy. Collectively, these results demonstrate that LSE-wall stealth coating is a generalizable strategy to improve both the safety and efficacy of iLNP-based mRNA vaccines and immunotherapies.