In situ CAR-M engineered by liposomal mRNA nanomedicine remodels fibrotic microenvironment for ameliorating liver fibrosis.

Liver fibrosis is a severe complication of diverse chronic liver diseases characterized by a dysregulated hepatic microenvironment, and effective clinical therapeutic strategies for this condition remain lacking to date. Chimeric antigen receptor macrophages (CAR-Ms) hold considerable therapeutic potential for liver fibrosis via antigen-specific recognition and efferocytotic activity, yet their clinical translation is largely hindered by the sophisticated ex vivo preparation procedures. Herein, we report an in situ CAR-M engineering strategy that uses a phosphatidylserine (PS)-incorporated, macrophage-targeted lipid nanoparticle (LNP) for the codelivery of CAR messenger RNA (mRNA) and Cas9 mRNA in vivo. Our findings demonstrate that this engineered LNP achieves efficient targeting of liver-resident macrophages. Transfection with fibroblast activation protein α (FAPα)-CAR mRNA equips macrophages with the capacity to specifically target activated hepatic stellate cells (aHSCs), whereas Cas9-mediated follistatin-like protein 1 (FSTL-1) gene editing enhances the efferocytotic function of macrophages in liver tissues. Consequently, functional CAR-Ms are generated in situ, which elicits robust antifibrotic effects, including reduced collagen deposition, restored sinusoidal architecture and enhanced immune-mediated antifibrotic activity. Collectively, our customized LNP-mediated in situ engineering of liver macrophages into CAR-Ms enables precise antifibrotic intervention for liver fibrosis and circumvents the cumbersome ex vivo CAR-M preparation process.