Replacing cholesterol and PEGylated lipids with zwitterionic ionizable lipids in LNPs for spleen-specific mRNA translation

The spleen is emerging as a key vaccination target. However, existing lipid nanoparticles (LNPs) primarily accumulate in the liver, limiting their efficacy in vaccine therapy. The cholesterol in current LNP formulations promotes their uptake by hepatocytes, while the polyethylene glycol-modified (PEGylated) lipids induce PEG immunogenicity, further reducing the efficacy in the setting of repeated administrations. We develop a three-component (ThrCo) LNP by replacing cholesterol and PEGylated lipids in Pfizer-BioNTech LNPs with zwitterionic pyridine carboxybetaine (PyCB) ionizable lipids (ILs), achieving ~70% lower liver accumulation and a 4.5-fold increase in spleen-specific mRNA translation. PyCB ILs enhance LNP hydrophilicity, stabilizing the outer membrane to compensate for cholesterol removal. PyCB groups also exhibit strong protonation at endosomal pH, facilitating mRNA translation. The zwitterionic surface of ThrCo LNP reduces protein adsorption, thereby preventing the accelerated blood clearance effect caused by PEGylated lipids following repeated administrations. Thus, ThrCo LNP–based vaccines efficiently deliver mRNA to splenic antigen-presenting cells, boosting immune responses and improving therapeutic outcomes.