Engineered probiotics for tumor-targeted combination chemoimmunotherapy

Achieving tumor-specific delivery and sustained activation of both cytotoxic and immune-modulating agents remains a critical challenge in chemoimmunotherapy. Here, a bacterial platform was engineered to combine enzyme/prodrug chemotherapy with immunotherapy, in which tumor-homing Escherichia coli Nissle 1917 expressed cytosine deaminase to convert the prodrug 5-fluorocytosine into the cytotoxic drug 5-fluorouracil and concurrently produced an IL-15 superagonist and a PD-L1 blocking nanobody in tumors. This platform demonstrated potent antitumor effects in murine MC38 and B16-F10 solid tumor models. Mechanistic analyses showed that bacterial enzyme/prodrug therapy alone elicited both immune activation and compensatory immunosuppressive responses, whereas inclusion of IL-15 superagonist and PD-L1 blockade enhanced activation of antigen-presenting cells, T cells, and natural killer cells and attenuated immunosuppressive pathways. Abscopal and rechallenge experiments indicated that this bacterial chemoimmunotherapy strategy induces systemic antitumor immunity and durable immune memory. In summary, our approach integrates enzyme/prodrug therapy and immunotherapy into a single bacterial delivery system, overcoming key limitations of conventional therapies by providing a rationally designed framework for spatially controlled chemoimmunotherapy.