An Oral Nanovaccine Secreted by Genetically Engineered and Ultrasound-Responsive Bacteria for Colon Cancer Immunotherapy

Colorectal cancers represent a major global morbidity and mortality burden, neccessitating improved treatment paradigms. In this work, an ingestible, genetically engineered Escherichia coli (E. coli) 1917 termed "E. coli (AH1-CDA-Co1)" is designed that upon ultrasound exposure secretes bacterial outer membrane vesicles (OMV) incorporating the AH1 tumor rejection epitope, an enzyme producing the stimulator of interferon genes (STING) agonist CDA, and the microfold cell-targeting peptide Co1. For oral administration, a polydopamine system (iPDA) coating on bacteria is exploited to resist the acidic condition in stomach, increase the bacterial survival, and prolong the intestinal transit time. Upon harmless ultrasound exposure, sustained secretion of engineered OMV vaccines is triggered that efficiently cross the intestinal epithelium. Both cyclic GMP-AMP synthase (cGAS)-STING and TLR4 innate immune signaling pathways are activated, triggering long-term antigen-specific immune responses that overcome the immunosuppressive tumor microenvironment. In subcutaneous and orthotopic murine colorectal tumor models, the E. coli (AH1-CDA-Co1)@iPDA system inhibits tumor growth and prolongs survival without recurrence. E. coli (AH1-CDA-Co1)@iPDA also inhibits tumor growth and recurrence in a postoperative orthotopic colonrectal tumor model of lymph node metastases. Taken together, E. coli (AH1-CDA-Co1)@iPDA demonstrates a potent oral vaccine system for improved colon cancer immunotherapy.