Synthetic inducible bacteria normalize the microenvironment of refractory tumors, potentiating checkpoint inhibitor responses

Immunotherapy has transformed cancer treatment but remains ineffective in many solid tumors, largely due to the immunosuppressive tumor microenvironment (TME). A dense/stiff extracellular matrix (ECM) can hinder immune cell infiltration, limiting therapeutic success. To overcome this challenge, we developed a live biotherapeutic platform using engineered programmable bacteria that offer advantages for delivering enzymes that normalize the TME. These non-pathogenic, commensal-derived strains are equipped with tumor-inducible promoters to deliver hyaluronidase locally and safely within the TME. Our study demonstrates that bacterial-mediated hyaluronan degradation reduces tumor stiffness, restores vascular function, and enhances immune checkpoint inhibitor efficacy in breast cancer murine models by improving immune cell infiltration and activation. Using machine learning and feature importance analysis, we identified biomarkers predictive of therapeutic response. Notably, we found that the potency of antitumor responses depends highly on baseline stiffness levels and ECM composition in relatively stiff breast tumors. In contrast, responses in less stiff colorectal cancer models characterized by low hyaluronan deposition primarily associated with immune cell composition, particularly CD8+ and CD4+ T cells and M2 macrophages. Our study showcases the potential of programmable bacteria to reshape the TME and identifies distinct tumor-dependent mechanisms of response across different tumor types, paving the way for more effective cancer treatments.