Biosynthetic OMVs with endogenous GM-CSF loading for ultrasound-triggered in situ cancer vaccination

Impaired dendritic cell (DC) recruitment, maturation, and antigen presentation within the immunosuppressive tumor microenvironment (TME) critically limit the efficacy of cancer immunotherapies. Strategies attempt to restore DC function using systemically administered granulocyte-macrophage colony-stimulating factor (GM-CSF) are constrained by poor tumor accumulation and dose-limiting toxicity. Herein, we developed a biosynthetic, ultrasound-triggered in situ cancer vaccine based on a hybrid nanoplatform (OMVs^GM-Lip@Ce6) that integrates GM-CSF-expressing bacterial outer membrane vesicles (OMVs^GM) with pH/ultrasound-responsive liposomes encapsulating the sonosensitizer chlorin e6 (Ce6). In the acidic TME, the hybrid vesicles destabilize, enabling localized release of biosynthetically loaded GM-CSF. Subsequent local ultrasound irradiation activates Ce6 to generate reactive oxygen species (ROS), inducing immunogenic cell death (ICD) and thereby promoting the in situ release of tumor-associated antigens (TAAs) and damage-associated molecular patterns (DAMPs). These endogenous danger signals, together with pathogen-associated molecular patterns (PAMPs) intrinsically carried by OMVs, synergize with locally delivered GM-CSF to enhance DC recruitment, expansion, and maturation, ultimately facilitating efficient antigen presentation and priming of tumor-specific T-cell responses. This biosynthetic OMVs-based platform thus realizes spatially controlled GM-CSF delivery and self-adjuvanted in situ cancer vaccination, effectively remodeling the immunosuppressive TME and eliciting robust systemic antitumor immunity to overcome resistance to immunotherapy.