X‐Ray‐Responsive Engineered Bacteria for Synergistic Radioimmunotherapy and Photoacoustic Immunomonitoring of Triple‐Negative Breast Cancer

Engineered bacteria offer promising opportunities for cancer immunotherapy, yet precise in vivo activation and real‐time tracking of immune responses remain formidable challenges. Here, we present an x‐ray‐sensitive engineered bacterium, composed of Escherichia coli ( E. coli ) and gold‐silver nanorods (Ec‐GS NRs), for synergistic radioimmunotherapy and photoacoustic (PA) immunomonitoring of triple‐negative breast cancer (TNBC). Upon x‐ray irradiation, Ag + release induces bacterial damage, stimulating the host immune system and triggering immunogenic tumor cell death. Moreover, radiation‐induced etching alters nanorod optoacoustic properties, enabling noninvasive PA monitoring of immunotherapy initiation. In TNBC models, Ec‐GS NRs combined with x‐ray irradiation achieved near‐complete tumor regression through enhanced radioimmunotherapy. Concurrently, PA signal ratio (PA 808 /PA 1064 ) increased 127‐fold, allowing in situ monitoring of immune activation. Notably, Ec‐GS NRs elicited a strong abscopal effect, suppressing distant metastases and extending overall survival. This study thus establishes a bacteria‐enabled radioimmunotheranostic strategy integrating x‐ray‐controllable immune activation, radiosensitization, and PA‐immunomonitoring to address limitations in precision cancer therapy.