By integrating bacterial surface display, quorum-sensing regulation, and immune checkpoint blockade, this study provides a design paradigm for live bacterial therapies that enable precise targeting and controllable activation in cancer immunotherapy, offering direct guidance for the future development of safe and efficient microbial anti-cancer strategies.
Literature Overview
The study titled 'Octopus-inspired engineered bacteria with a plug-and-play surface display system achieves enhanced tumor-specific colonization and antitumor immunity,' published in the journal Military Medical Research, systematically investigates how biomimetic design can enhance bacterial-mediated tumor targeting and immune activation. The research team constructed a 'plug-and-play' surface display system based on attenuated Salmonella, utilizing SpyTag/SpyCatcherΔ covalent coupling technology to display poly-RGD peptides on the bacterial surface, significantly enhancing adhesion to tumor tissues expressing integrin αvβ3. Additionally, a quorum-sensing (QS)-regulated HtrA protein and anti-PD-1 nanobody expression system were introduced to achieve microenvironment-responsive activation and localized immune checkpoint blockade. This strategy not only addresses the limitations of poor targeting, high toxicity, and uncontrolled drug release in conventional bacterial therapies but also opens new avenues for the clinical translation of live bacterial vectors.Background Knowledge
Although tumor immunotherapy has achieved groundbreaking progress, the immunosuppressive microenvironment of solid tumors still limits T-cell infiltration and function, resulting in limited response rates. Tumor-colonizing bacteria such as Salmonella can naturally accumulate in tumor tissues, but their targeting efficiency is low and they often trigger systemic inflammation, restricting clinical application. Existing strategies, such as genetic engineering or chemical modification, frequently face challenges including protein misfolding, steric hindrance, or solvent toxicity, making efficient and stable functionalization difficult. Moreover, uncontrolled bacterial proliferation may lead to excessive immune stimulation or tissue damage. Therefore, there is an urgent need to develop intelligent bacterial systems capable of enhancing tumor-specific colonization while enabling on-demand immune activation. This study, inspired by the robust adhesion mechanism of octopus suckers and combined with synthetic biology-based QS circuits, precisely controls the spatiotemporal expression of therapeutic proteins, thereby improving targeting while reducing off-target toxicity, offering an innovative solution to these bottlenecks.
Research Methods and Experiments
The study used attenuated Salmonella ΔhtrA::luxI-VNP20009 as the chassis strain (AISI), into which SpyTag (ST) was inserted into the third loop region of the outer membrane protein A (OmpA) to construct the AISI-ST strain, enabling subsequent covalent coupling with SpyCatcherΔ (SC)-fused proteins. Through in vitro conjugation with SC-RGD×4 protein, the AISI-ST/SC-RGD×4 strain was formed, allowing stable multivalent RGD peptide display. Using BALB/c and C57BL/6 mouse models, different engineered bacterial strains were administered via tail vein injection, and their distribution in H22, B16-F10, and 4T1 tumor models was evaluated using bioluminescence imaging and CFU counting. Results showed that tetrameric RGD modification significantly enhanced tumor enrichment while reducing non-specific colonization in normal organs such as liver and spleen. Furthermore, a QS-responsive LuxI promoter-driven HtrA and anti-PD-1 nanobody (PD1nb) expression system was constructed to verify its ability to induce expression at high bacterial density. Flow cytometry and qPCR analysis revealed that HtrA re-expression promoted extracellular polysaccharide (EPS) secretion, activated the TLR4-NF-κB pathway, and induced M1 macrophage polarization. Upon co-expression of PD1nb, significant increases in intratumoral CD8+ T-cell infiltration and suppression of Treg cells were observed, enhancing antitumor immune responses.Key Conclusions and Perspectives
Research Significance and Prospects
This study provides a programmable and scalable engineered bacterial platform for the field of microbial therapy, whose 'plug-and-play' feature allows rapid adaptation to different targeting ligands and therapeutic proteins, greatly enhancing development flexibility. From a drug development perspective, this live bacterial vector can serve as a multifunctional immune modulator, particularly suitable for the transformative treatment of 'cold' tumors. In terms of clinical monitoring, bioluminescent signals allow real-time tracking of bacterial distribution, enabling visual monitoring of the treatment process. Moreover, the system has been validated effective in genetically well-defined mouse models, laying a solid foundation for future IND applications and clinical trials, potentially advancing bacteria-mediated precision immunotherapy into a new stage.
Conclusion
This study developed a novel engineered bacterial platform inspired by the octopus sucker mechanism, achieving dual control of tumor-specific colonization and on-demand immune activation. The system not only addresses the core challenges of insufficient targeting and excessive toxicity in conventional bacterial therapies but also precisely reshapes the tumor immune microenvironment through quorum sensing and localized antibody release. With a clear path from laboratory to clinical translation, this strategy offers a safe, controllable, and efficient live bacterial therapeutic candidate for immunotherapy of various solid tumors. Particularly in refractory cancers such as pancreatic cancer and melanoma, such engineered bacteria may overcome the current response limitations of existing immunotherapies. Future studies combining germ-free mouse models and humanized systems could further evaluate their stability and efficacy in complex microbiota environments, accelerating clinical advancement and establishing them as an indispensable component of cancer care systems.
