Molecular Dynamics‐Guided Sterol Engineering of mRNA‐Lipid Nanoparticles Reprograms Biodistribution and Enhances Spleen‐Selective Immunity

Multicomponent membrane organization of mRNA-lipid nanoparticles (LNPs) critically determines their formulation behavior, organ selectivity, and immunological outcomes. However, compared to ionizable lipids, sterols remain a relatively underexplored design axis. This study discusses the engineering of a library of nine bile acid-derived sterols with different hydroxylation patterns and alkyl tail lengths, and systematically maps how sterol structure governs formulation-level properties and organ-level expression profiles. After integrating physicochemical characterization with all-atom molecular dynamics (MD) simulations, the experimentally observed formulation behaviors correlate with MD-derived membrane structural descriptors. These descriptors provide a quantitative evaluation framework for prioritizing sterol chemotypes based on their predicted encapsulation performance and membrane organization, supporting the notion that sterol-dependent membrane organization provides a structural basis for formulation properties, including mRNA encapsulation. Moreover, substituting cholesterol with bile acid-derived sterols consistently attenuated hepatic expression and shifted organ-level expression toward spleen-dominant profiles, which is central to immune priming and adaptive immune activation. Among bile acid-derived sterols, CA-20 LNPs functionally enhance antigen-specific humoral immunity and elicit antigen-specific cellular immune responses, including improved memory-associated immune features, while maintaining an acute safety profile. Collectively, these results establish sterol engineering as a powerful design strategy for modulating LNP formulation properties, in vivo fate, and immunological function.