A Bioactive Lipid Nanoparticle Integrating Arachidonic Acid Enables High-Efficiency mRNA Delivery and Potent CAR-Macrophage Engineering

Genetic engineering of macrophages, particularly for chimeric antigen receptor macrophage (CAR-M) therapy, holds great promise for immunotherapy, yet is constrained by the challenge of efficient gene delivery into primary macrophages, which are notoriously resistant to transfection. While conventional strategies focus on optimizing the physicochemical properties of lipid nanoparticles (LNP), they often fail to overcome the intrinsic biological barriers of these cells. Here, we introduced a "bioactive nanocarrier" paradigm, hypothesizing that incorporating a cellular modulator directly into LNP structure can synergistically overcome these barriers. We designed and synthesized a novel LNP by integrating the pro-inflammatory fatty acid, arachidonic acid (ARA), as a functional structural component (ARA-LNP). Systematic optimization of the ARA content and mRNA payload revealed a formulation that achieves high transfection efficiency (83.76%) in primary M2-polarized bone marrow-derived macrophages (BMDMs), a cell type that recapitulates pro-tumoral phenotype in the tumor microenvironment. Leveraging this advanced delivery platform, we successfully generated HER2-targeting CAR-M that demonstrated potent and specific phagocytic activity against HER2-expressing tumor cells in vitro. This work presents a powerful strategy where the nanocarrier itself transiently modulates the target cell state to enhance gene delivery, providing a new design principle for engineering macrophages and other hard-to-transfect immune cells for therapeutic applications.