Fap-directed CAR macrophage therapy improves cardiac function and reduces fibrosis in Dsg2-mutant arrhythmogenic cardiomyopathy mice

Background/Introduction Arrhythmogenic right ventricular cardiomyopathy (ARVC) features progressive myocardial remodeling with fibro-fatty replacement and malignant ventricular arrhythmias, yet disease-modifying therapies remain limited. Fibroblast activation protein (FAP) is enriched in activated cardiac fibroblasts, and FAP-directed CAR macrophages (FAP CAR-Ms) represent a promising anti-fibrotic immunotherapy strategy. Purpose To determine whether FAP CAR-M therapy improves cardiac function and attenuates myocardial fibrosis in a Dsg2mt/mt ARVC mouse model. Methods FAP CAR bone marrow–derived macrophages (FAP CAR-BMDMs) were generated and administered intravenously to Dsg2mt/mt ARVC mice using two regimens: early treatment initiated at 6 weeks of age and delayed treatment initiated at 8 weeks. Comparator groups included truncated CAR-Ms, control macrophages, PBS, and wild-type controls. Cardiac function was assessed longitudinally by echocardiography. Electrical phenotype, structural remodeling, fibrosis burden, target engagement, and systemic safety were evaluated at study end. Result FAP CAR-M treatment significantly improved cardiac function during the rapid disease-progression window (6–8 weeks). Notably, delayed initiation at 8 weeks also yielded meaningful functional improvement, supporting therapeutic benefit even after disease progression has begun. At 12 weeks, improved cardiac performance was maintained in both early- and delayed-treatment groups. ECG and gross assessment further indicated phenotypic improvement, including better QRS morphology with restoration of sinus rhythm features compared with untreated ARVC mice exhibiting ventricular arrhythmias and right bundle branch block. Consistent with these findings, myocardial fibrosis area was reduced in FAP CAR-M–treated hearts. Treatment was associated with selective targeting of FAP-positive activated fibroblasts and attenuation of pathological remodeling. Endpoint transcriptomics further supported therapeutic remodeling, showing downregulation of fibrotic/injury-associated pathways without activation of cardiac toxicity gene programs. Conclusion(s) FAP CAR-M therapy improves cardiac function, mitigates electrical abnormalities, and reduces fibrotic remodeling in a Dsg2mt/mt ARVC mouse model. These results support FAP CAR-Ms as a potential disease-modifying, anti-fibrotic approach for ARVC and other fibrotic cardiomyopathies.