This study provides a novel delivery paradigm for the combined application of tumor immunotherapy and chemotherapy, highlighting the need to prioritize the regulatory role of the host immune microenvironment on therapeutic efficacy when constructing genetically edited animal models.
Literature Overview
This article, "Engineered probiotics for tumor-targeted combination chemoimmunotherapy," published in Science Translational Medicine, systematically explores an innovative strategy utilizing engineered E. coli Nissle 1917 as a vector to integrate enzyme/prodrug chemotherapy with immune checkpoint blockade and cytokine therapy on a single platform. By leveraging the specific colonization of bacteria within tumors, the study achieved local prodrug activation and in situ release of immunomodulatory factors, significantly enhancing anti-tumor efficacy and inducing systemic immune memory.Background Knowledge
The core challenges in current tumor therapy lie in the systemic toxicity of chemotherapeutic agents and the difficulty of overcoming drug resistance and the immunosuppressive microenvironment with monotherapies. While traditional enzyme/prodrug therapies can achieve local activation, they are often limited by insufficient enzyme retention time at the tumor site and the detoxification of chemotherapy products by bacterial metabolism. Furthermore, the upregulation of immune checkpoints such as PD-L1 often suppresses chemotherapy-induced immune responses. This study addresses these issues by employing synthetic biology to knock out the bacterial preTA operon, blocking the metabolic detoxification of 5-FU, while co-expressing an IL-15 superagonist and a PD-L1 blocking nanobody. This approach constructs a synergistic therapeutic microenvironment within the tumor that efficiently kills tumor cells while reversing immunosuppression.
Research Methods and Experiments
The authors constructed an engineered strain, EcNx-pCD, expressing cytosine deaminase (CD) and introduced a heparin-binding peptide to enhance enzyme retention within the tumor stroma. Key experiments first validated the tumor-targeting colonization capability of this strain in MC38 colon cancer and B16-F10 melanoma models, finding that bacteria survived in large numbers only within tumors and were rapidly cleared from other organs. Subsequently, flow cytometry and immunohistochemistry analyses revealed that locally produced 5-FU activated CD8+ T cells and NK cells but also induced the recruitment of regulatory T cells (Tregs) and PD-L1 expression, forming an immunosuppressive feedback loop.
To overcome this bottleneck, the research team further knocked out the bacterial preTA operon (encoding dihydropyrimidine dehydrogenase), eliminating bacterial detoxification of 5-FU and significantly improving chemotherapy efficiency. Building on this, a triple-engineered strain, EcNxΔpreTA-pCD/PDL1nb/s15, was constructed to co-express the IL-15 superagonist (s15) and the PD-L1 blocking nanobody (PDL1nb). Bilateral tumor models and abscopal effect experiments confirmed that this combination therapy not only completely eradicated primary tumors but also activated systemic immune responses in lymph nodes and the spleen, generating durable immune memory.Key Conclusions and Perspectives
Research Significance and Prospects
This discovery has profound implications for drug development, indicating that using live bacteria as intelligent delivery systems can overcome the limitations of traditional chemotherapy and immunotherapy regarding pharmacokinetics and immune microenvironment regulation. For clinical monitoring, this strategy may reduce the risk of systemic immune-related adverse events while improving treatment response rates. In terms of disease modeling, the study emphasizes that when constructing tumor models, the interaction between host immune status and bacterial metabolism must be fully considered to accurately evaluate the efficacy of novel combination therapies.
Conclusion
Through clever synthetic biology design, this study successfully integrated enzyme/prodrug chemotherapy with immunotherapy on a single engineered probiotic platform, addressing the challenges of insufficient delivery precision and the difficulty of reversing the immunosuppressive microenvironment in traditional combination therapies. By knocking out the bacterial detoxification enzymes and co-expressing immunomodulatory molecules, this strategy achieved efficient in situ killing and durable systemic immune memory in various tumor models. This achievement not only provides new preclinical evidence for cancer treatment but also lays a solid foundation for developing intelligent, minimally invasive treatment protocols for refractory tumors in the future, marking a critical step forward for bacterial therapy in the field of precision oncology.
