J Leukoc Biol. 2025 Jul 09. pii: qiaf086. [Epub ahead of print]117(7):
Neutrophils are innate immune cells that perpetually patrol the circulation and tissues. They sense and migrate toward invading microbes to initiate and orchestrate a robust immune response. Their highly reactive nature, driven by multiple and redundant receptor families recognizing bacterial components, makes them particularly sensitive to contaminants or nonsterile implants. This often leads to a neutrophil-driven foreign body reaction that shields the implant and triggers inflammation, collateral tissue damage, or even sepsis. This presents a significant challenge for living therapeutic materials, an innovative biomedical approach using genetically engineered bacteria encapsulated in natural or synthetic polymers. Since bacterial turnover inevitably releases pathogen-associated molecular patterns that activate neutrophils to mitigate or prevent a potent neutrophil response, living therapeutic material design strategies are required to protect the living therapeutic material from damage while maintaining its functionality. This review focuses on current strategies involving bacterial genetic engineering, immune-shielding materials and factors, and modified hydrogel-based systems to minimize immune recognition. Engineering the bacterial chassis to produce immune tolerance-inducing metabolites from commensals, modified pathogen-associated molecular patterns, and pathogen-associated molecular pattern-cleaving autolysins may enhance biocompatibility. A crucial aspect for clinical translation is robust biocontainment to prevent bacterial escape, ensuring living therapeutic material remains a safe and effective therapeutic platform. While the potential of the living therapeutic material concept lies in the development of tailored medicine specifically designed for a specific disease and enabling local, cost-effective, site- and stimulus-responsive treatment, balancing the neutrophil immune response remains an important milestone on the path to living therapeutic material for future biomedical applications.
Keywords: engineered bacteria; gene modification; hydrogel; immune tolerance; neutrophils