Covalently photosensitized probiotic bacteria for light-triggered tumor clearance and self-limiting immunotherapy.

Live bacterial therapy holds great promise in tumor treatment due to its inherent ability to target tumors and activate the immune system. However, its clinical translation faces significant challenges, including limited antitumor efficacy and safety risks posed by bacterial residue. To address these challenges, we developed a self-limiting, light-activatable biohybrid system named OTTQ-Cl@HEcN. It consists of the probiotic Escherichia coli Nissle 1917 (EcN) covalently conjugated with a hypoxia-tolerant Type I photosensitizer (PS) OTTQ-Cl via a genetically engineered HaloTag conjugation strategy. Upon light irradiation, OTTQ-Cl@HEcN generates localized reactive oxygen species (ROS), simultaneously killing tumor cells and bacteria. This built-in bacterial self-elimination ensures effective tumor clearance and minimizes systemic exposure. In multiple tumor models, OTTQ-Cl@HEcN elicited potent local and systemic antitumor immunity, characterized by robust dendritic cells (DCs) maturation, enhanced T cells activation, and the establishment of long-term immune memory that prevented tumor recurrence and metastasis. The key features of OTTQ-Cl@HEcN include its precise tumor targeting, hypoxia compatibility, potent immune activation, and intrinsic biosafety, collectively enabling a controlled and effective antitumor response.