Jin Hai Zheng1,2, Vu H. Nguyen1,3, Sheng-Nan Jiang4,5, Seung-Hwan Park6, Wenzhi Tan7, Seol Hee Hong8, Myung Geun Shin9, Ik-Joo Chung10, Yeongjin Hong7, Hee-Seung Bom4, Hyon E. Choy2,7, Shee Eun Lee8, Joon Haeng Rhee2,7,* and Jung-Joon Min1,2,4,7,*
1Laboratory of In Vivo Molecular Imaging, Institute for Molecular Imaging and Theranostics, Chonnam National University Hwasun Hospital, Jeonnam 58128, Republic of Korea.
2Department of Molecular Medicine (BrainKorea21 Plus), Chonnam National University Graduate School, Gwangju 61469, Republic of Korea.
3Department of Experimental Therapeutics, Beckman Research Institute of City of Hope, Duarte, CA 91010, USA.
4Department of Nuclear Medicine, Chonnam National University Medical School, Gwangju 61469, Republic of Korea.
5Department of Nuclear Medicine, Affiliated Haikou Hospital, Xiangya School of Medicine, Central South University, Hainan 570-208, China.
6Biological Resource Center, Korea Research Institute of Bioscience and Biotechnology, Jeongeup 56212, Republic of Korea.
7Department of Microbiology and Clinical Vaccine R&D Center, Chonnam National University Medical School, Gwangju 61469, Republic of Korea.
8Department of Pharmacology and Dental Therapeutics, School of Dentistry, Chonnam National University, Gwangju 61186, Republic of Korea.
9Department of Laboratory Medicine, Chonnam National University Medical School, Gwangju 61469, Republic of Korea.
10Department of Hemato-Oncology, Chonnam National University Medical School, Jeonnam 58128, Republic of Korea.
We report a method of cancer immunotherapy using an attenuated Salmonella typhimurium strain engineered to secrete Vibrio vulnificus flagellin B (FlaB) in tumor tissues. Engineered FlaB-secreting bacteria effectively suppressed tumor growth and metastasis in mouse models and prolonged survival. By using Toll-like receptor 5 (TLR5)–negative colon cancer cell lines, we provided evidence that the FlaB-mediated tumor suppression upon bacterial colonization is associated with TLR5-mediated host reactions in the tumor microenvironment. These therapeutic effects were completely abrogated in TLR4 and MyD88 knockout mice, and partly in TLR5 knockout mice, indicating that TLR4 signaling is a requisite for tumor suppression mediated by FlaB-secreting bacteria, whereas TLR5 signaling augmented tumor-suppressive host reactions. Tumor microenvironment colonization by engineered Salmonella appeared to induce the infiltration of abundant immune cells such as monocytes/macrophages and neutrophils via TLR4 signaling. Subsequent secretion of FlaB from colonizing Salmonella resulted in phenotypic and functional activation of intratumoral macrophages with M1 phenotypes and a reciprocal reduction in M2-like suppressive activities. Together, these findings provide evidence that nonvirulent tumor-targeting bacteria releasing multiple TLR ligands can be used as cancer immunotherapeutics.