Boron Neutron Capture Therapy‐Derived Extracellular Vesicles via DNA Accumulation Boost Antitumor Dendritic Cell Vaccine Efficacy

Abstract Radiated tumor cell‐derived extracellular vesicles (RT‐EVs) encapsulate abundant DNA fragments from irradiated tumor cells, in addition to acting as integrators of multiple tumor antigens. Accumulating evidence indicates these DNA fragments from damaged cells are involved in downstream immune responses, but most of them are degraded in cells before incorporation into derived RT‐EVs, thus the low abundance of DNA fragments limits immune responses of RT‐EVs. Here, this study found that different radiations affected fates of DNA fragments in RT‐EVs. Boron neutron capture therapy (BNCT) induced DNA accumulation in RT‐EVs (BEVs) by causing more DNA breaks and DNA oxidation resisting nuclease degradation. This is attributed to the high‐linear energy transfer (LET) properties of alpha particles from the neutron capture reaction of 10 B. When being internalized by dendritic cells (DCs), BEVs activated the DNA sensing pathway, resulting in functional enhancements including antigen presentation, migration capacity, and cytokine secretion. After vaccination of the BEVs‐educated DCs (BEV@BMDCs), the effector T cells significantly expanded and infiltrated into tumors, suggesting robust anti‐tumor immune activation. BEV@BMDCs not only effectively inhibited the primary tumor growth and metastasis formation but also elicited long‐term immune memory. In conclusion, a successful DC vaccine is provided as a promising candidate for tumor vaccine.