Cardiac fibrosis (CF) is a common pathophysiological process in the development of various cardiovascular diseases, during which many cardiac fibroblasts undergo myofibroblast transdifferentiation. Fibroblast activation protein (FAP) can serve as a specific target for myofibroblasts, and chimeric antigen receptor (CAR)-based therapy is a promising immunotherapy strategy. In this study, we attempted to construct CAR natural killer (NK) cells that target FAP and explored their potential therapeutic role in CF. Our results suggested FAP CAR-NK-92 cells can specifically recognize and kill FAP+ cells in vitro. In addition, compared with parental NK-92 cells, FAP CAR-NK cells cocultured with FAP HEK-293 T cells presented increased cytotoxicity, cytokine secretion, and degranulation, indicating an effect-to-target ratio dependence. Coculturing FAP CAR-NK cells with mouse cardiac fibroblast lines (MCFs) eliminated the activated fibroblasts, reduced fibrosis-related protein secretion, and significantly reversed the contractile phenotype of myofibroblasts, which is characterized by alpha-smooth muscle actin (α-SMA) and stress fiber formation. Intravenous injection of FAP CAR-NK cells in mice 7 days after Ang II/PE-induced injury significantly improved cardiac function and reduced fibrosis. In terms of the killing mechanism, the early apoptosis rate of target cells was significantly increased, the antiapoptotic protein Bcl-2 was significantly decreased, and the proapoptotic proteins Bax and Caspase 3 were markedly increased. Our findings demonstrate that FAP CAR-NK-92 cells can specifically recognize FAP+ target cells and exert potent anti-fibrotic effects both in vitro and in vivo. Therefore, FAP CAR-NK-92 cells could be considered an effective therapeutic option for CF patients.
