Lung metastasis and recurrence is mitigated by CAR macrophages, in-situ-generated from mRNA delivered by small extracellular vesicles

Cancer metastasis and recurrence remain the leading causes of cancer-related mortality, and lung is a major metastatic anatomical location. Chimeric antigen receptor macrophages (CAR-M) represent promising candidates for cancer therapy owing to their superior tumour-infiltrating and antigen-specific phagocytotic abilities, and to being professional antigen presenting cells. However, broader applications of CAR-Ms face challenges such as complex manufacturing processes and predominant accumulation in the liver following intravenous administration. Here we present an inhalable engineered small extracellular vesicle (sEV), which contains mesothelin-specific CAR messenger RNA (CAR^mRNA@aCD206 sEVs) for in situ generation of CAR-Ms. The sEVs are surface-integrated with anti-CD206 single-chain variable fragments (scFv) to target CD206-expressing, immunosuppressive (M2 phenotype) macrophages. The results in mouse models suggest that inhaled CAR^mRNA@aCD206 sEVs could accumulate in lung tissue and deliver CAR mRNA specifically to macrophages, facilitating in situ CAR-M production. In a lung metastasis model, inhaled CAR^mRNA@aCD206 sEVs effectively inhibit tumor growth and prime long-term memory immunity to prevent tumour recurrence. Collectively, our engineered sEV delivery platform demonstrates capability to selectively deliver CAR mRNA to macrophages in lung tissue, providing a promising immunotherapy strategy to effectively combat lung metastasis and recurrence via generation of CAR-Ms in situ.