Systemic delivery of messenger RNA (mRNA) to non-hepatocytes using lipid nanoparticles (LNPs) remains challenging. Inspired by anion coordination chemistry, here we report the rational chemical design of thiourea-functionalized ionizable lipids (TUILs) for delivering mRNA potently and specifically to the secondary lymphoid organs (SLOs). The leading TUIL, namely 4A3-LNSC8, features an impressive thiourea-based linker capable of binding with various halide anions (F, Cl, I) through hydrogen-bonding interaction, enabling precise regulation of LNP organotropism in vivo. When administered systemically, the representative Cl-4A3-LNSC8 LNPs exclusively redirected mRNA delivery from the liver to SLOs, yielding a 65-fold and 29-fold increase in splenic mRNA expression compared to DLin-MC3-DMA and SM102 LNPs with the addition of anionic lipid (18PA). Notably, upon intravenous injection of 0.2 mg kgCre mRNA, Cl-4A3-LNSC8 LNPs demonstrated strong tropism for splenic macrophages with high gene editing efficiency up to 65.7%, outperforming the current state-of-the-art spleen-targeted LNPs. Moreover, by leveraging iodine's CT contrast properties, I-4A3-LNSC8 LNPs mediated efficient theranostic mRNA delivery to lymph nodes, allowing early detection of lymphatic metastasis via dual-modal CT and bioluminescence imaging. This work provides new insights into the development of cell-specific ionizable lipids, advancing future applications of macrophage-targeted therapies. ----1
