Mannosylated Spleen-Targeted Lipid Nanoparticles Enable Enhanced mRNA Delivery to Antigen-Presenting Cells

Targeted delivery of lipid nanoparticles (LNP) to immune organs remains challenging, and here we introduce a mannosylated spleen-targeted LNP (LNP-PAM) that integrates active and endogenous targeting to enhance mRNA delivery to antigen-presenting cells. A mannose-conjugated fifth lipid (PA-Mannose, PAM) was incorporated into spleen-targeted LNPs at varying molar ratios, followed by a systematic evaluation of physicochemical properties, in vitro transfection, in vivo biodistribution, cellular uptake, and mRNA expression. All formulations exhibited uniform particle size and low polydispersity, and increasing PAM content from 5% to 10% shifted LNP accumulation from the liver to the spleen, ultimately achieving exclusive spleen localization. LNP-PAM showed superior in vitro transfection in macrophages relative to conventional LNPs and higher in vivo mRNA expression in the spleen, with flow cytometry confirming preferential uptake by macrophages and type-2 conventional dendritic cells (cDC2) populations consistent with CD206-mediated endocytosis. The system maintained physicochemical stability after freeze-thaw and demonstrated minimal cytotoxicity. Together, these findings indicate that mannosylation enhances spleen-targeted mRNA delivery through receptor-mediated uptake by macrophages and dendritic cells without compromising formulation robustness, positioning LNP-PAM as a practical platform for selective immune organ delivery and RNA-based immunomodulation.