[P006] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P03-432] Engineered probiotic bacteria producing an RNA-based TLR7/8 agonist for enhanced cancer immunotherapy

Hyungjin Sun¹, ○Jinyoung Kim², Pyunghwajun Lee¹, Sang Woo Seo^1,2,3,4,5, Junsang Doh^1,4,6,7 (1. Interdisciplinary Program in Bioengineering, Seoul National University (Korea), 2. Department of Chemical and Biological Engineering, Seoul National University (Korea), 3. Institute of Chemical Processes, Seoul National University (Korea), 4. Bio-MAX Institute, Seoul National University (Korea), 5. Institute of Bio Engineering, Seoul National University (Korea), 6. Department of Materials Science and Engineering, Seoul National University (Korea), 7. Research Institute of Advanced Materials, Seoul National University (Korea))

Keywords:

Cancer immunotherapy,Synthetic biology,TLR7/8 agonist,Engineered probiotic bacteria,Immune activation

Toll-like receptor 7/8 agonists (TLR7/8a) are promising immunotherapeutic agents for remodeling the tumor microenvironment (TME); however, their clinical application is limited by systemic toxicity and insufficient tumor-localized activity. Here, we present an engineered probiotic strategy to enable localized and sustained delivery of RNA-based TLR7/8 agonists. Escherichia coli Nissle 1917 (EcN) was genetically modified to produce a uridine-rich single-stranded RNA (ssRNA) harboring TLR7/8 agonistic activity. The synthetic transcriptional cassette, stabilized by a 5′ hairpin structure, was integrated into multiple genomic loci to achieve robust expression. The engineered strain, EcN-3rTLR7/8a, significantly enhanced dendritic cell activation in vitro, as evidenced by increased CD80/CD86 expression and elevated IFN-β secretion. In a B16F10 melanoma model, intratumoral administration of EcN-3rTLR7/8a led to marked tumor regression and prolonged survival, and induced systemic anti-tumor immunity, as demonstrated in a distal tumor model. Immune profiling revealed a reprogrammed TME with increased effector T cell activity and pro-inflammatory macrophage polarization. Importantly, the engineered bacteria remained confined to tumor tissues, indicating minimal systemic dissemination and reduced toxicity. Furthermore, combination therapy with anti–PD-L1 blockade resulted in enhanced therapeutic efficacy and durable immune memory, with complete tumor remission observed in a subset of treated animals. Collectively, this study demonstrates that engineered probiotics can serve as a programmable platform for localized RNA delivery, enabling effective TME reprogramming and improved cancer immunotherapy outcomes.