Engineered Bacillus Calmette-Guérin Mediated Immunotherapy of Triple-Negative Breast Cancer

Live bacterial therapy has shown promise in inducing antitumor immunity, but its efficacy is often limited by the immunosuppressive tumor microenvironment (TME) and insufficient tumor-specific T cell activation. In this study, core-shell Au@ZnxMn1-xS nanoparticles (AZMS) were synthesized and covalently conjugated to Bacillus Calmette-Guérin (BCG) to generate the engineered bacterium AZMB, which was subsequently encapsulated within a hyaluronic acid-based matrix to fabricate the functional implant AZMB-IM. Upon percutaneous administration via a puncture needle, BCG acts as a potent immune initiator, significantly enhancing the recruitment of M1-type macrophages and natural killer cells to the tumor site, and also induced the maturation of dendritic cells. Concurrently, AZMB dissociates in the TME, releasing Zn²⁺ and Mn²⁺ ions. Zn²⁺ disrupts the mitochondrial membrane potential, triggering a reactive oxygen species (ROS) storm and inducing immunogenic cell death (ICD). Meanwhile, Mn²⁺ amplifies the ROS effect via a Fenton-like reaction and activates the cGAS-STING signaling pathway, which in turn drives robust T cell-mediated antitumor immunity. Collectively, through synergistic activation of innate immunity and ICD-driven adaptive immune responses, AZMB-IM remodels the TME and enhances antitumor immunity, highlighting its significant potential for clinical translation in the treatment of advanced and metastatic solid tumors.