The intricate interplay between tumor cells, neighboring immune cells, and various immune cell types involves complex competitive-cooperative patterns rewired through metabolic and immune signals, which are essential for shaping the immunosuppressive tumor microenvironment (TME). This metabolic imbalance-immunosuppressive microenvironment plays a crucial role in treatment-resistant triple-negative breast cancer (TNBC) by influencing the disease and adverse prognoses. Malignant proliferating tumor cells strategically reprogram their metabolism to sequester essential nutrients from the TME and release various metabolites, thereby influencing TME status. This imposition of metabolic stress on infiltrating immune cells leads to alterations in metabolism-based functions. Recent evidence has revealed that tumor-associated macrophages (TAMs), which constitute 50% of the infiltrating immune cells in TNBC, are induced to upregulate arginase-1 (Arg-1) under metabolic stress and polarize toward the immunosuppressive M2 phenotype. Adding to the complexity, the tumor cells also overexpress the antiphagocytic signal CD24, establishing a “don’t eat me” cooperation with M2-TAMs to evade the immune-killing effect. Moreover, considering the crucial role of arginine in immune cell functions, competitive dynamics have emerged among various immune cell types for this essential nutrient. M2 TAMs, characterized by elevated Arg-1 expression, significantly deplete arginine, thereby hindering the arginine-dependent activation of T cells and suppressing their antitumor functions. The aforementioned interaction patterns of cooperation and competition often contribute to the overall tumor-promoting TME state. Consequently, targeting this interaction based on metabolism-immune crosstalk provides a promising therapeutic intervention for inhibiting tumor development. Nevertheless, the complex cellular interaction network involving tumor and immune cells demonstrates high flexibility and plasticity, necessitating coordinated modulation across multiple cell types to reshape competitive-cooperative patterns. Building on these concepts, we aimed to develop a delivery system that integrates diverse regulatory modules while maintaining functional separation, enabling precise modulation of distinct cellular states.
Outer membrane vesicles (OMVs) derived from bacterial outer membranes represent potent immune response enhancers, harboring antigens and pathogen-associated molecular patterns from bacteria. As intact nanoscaled lipid bilayer vesicles, OMVs have been applied in various combined immunotherapies. Fragmented OMVs have been reported to activate the immune system via pathogen-associated molecular patterns. Drawing inspiration from this, we proposed an OMV-based concept whereby internal cargo physicochemical changes would induce OMV fragmentation and separation. This concept aimed to utilize OMV fragments and their internal cargo to specifically target different cell types in the TME, maximizing the harmonization of interactions among immune cells and triggering antitumor immune responses.
Therefore, we designed charge-reversal nanocomplexes that are responsive to acidic environments induced by abnormal tumor metabolism and encapsulated them within engineered OMVs to form multifunctional multimodule intelligent vesicles (charge-reversal polymer/siRNA@CD24 scFv-OMV/PTX nanocomplexes, CR/si@ab-OMV/PTX nanoparticles (NPs)). Triggered by the reduced pH, the surface of the inside nanocomplexes becomes positive, disrupting the outside vesicle structure. The engineered OMVs were enriched with CD24 antibodies on the surface, which could navigate membrane fragments and hydrophobic chemotherapeutic drugs inserted in them to tumor cells. Consequently, tumor cells are killed, relieving metabolic stress in the TME and affecting Arg-1 expression in TAMs. The exposed positive nanocomplexes specifically target M2 macrophages via modified mannose and deliver siRNAs to silence Arg-1. TAMs repolarized to the M1 type, and the "don't eat me" signal was blocked by the antibodies, thereby enhancing macrophage phagocytosis of tumors. In addition, due to the increase in L-arginine in the TME, the function of effective T cells would be restored, forming an antitumor cooperative relationshipwith the repolarized TAMs in antitumor immunity. The activated immune system engages in a survival competition with tumor cells, hereby suppressing tumor proliferation. Collectively, the CR/si@ab-OMV/PTX NPs could achieve simultaneous and specific delivery of multitarget and multifunctional modules under simple conditions of reduced pH, demonstrating tremendous promise for reconciling the competitive-cooperative patterns among malignant and immune cells and activating antitumor immune response in the TNBC models.
Scheme 1. Schematic illustration of reconciling the cooperative-competitive patterns among tumor and immune cells of multi-module nanocomplexes (CR/si@ab-OMV/PTX NPs.)
Acknowledgements
Xuwen Li and Qin Guocontributed equally to this work. We also acknowledge the support from the National Natural Science Foundation of China (82361148716, 82121002), Shanghai Municipal Science and Technology Major Project (Grant 2018SHZDZX01), ZJLab and the Open Grant from the Pingyuan Laboratory（2023PY-OP-0106）.
