Enhanced cancer immunotherapy using engineered tumor-colonizing Salmonella typhimurium
Jin Hai Zheng1, Wenzhi Tan2, Yeongjin Hong2, Shee Eun Lee3, Joon Haeng Rhee2, and Jung-Joon Min1*
Department of Nuclear Medicine, 2Department of Microbiology, Chonnam National University Medical School, 3Department of Pharmacology, Chonnam National University School of Dentistry, Gwangju, Republic of Korea.
Attenuated Salmonella typhimurium show tumor-targeting capacities and significantly suppress tumor growth in mice. The levels of IL-1β and TNF-α were markedly increased in tumors colonized by ΔppGpp Salmonellae. The transcript levels of the core molecules of inflammasome signaling, IPAF, NLRP3 and P2X7, were significantly elevated only in Salmonellae-treated tumors. ATP released from damaged cancer cells was also identified as a mechanism of NLRP3 activation. Inhibiting IL-1β production in Salmonellae-treated mice restored tumor growth, whereas tumor growth was suppressed for longer by local administration of recombinant IL-1β or TNF-α in conjunction with Salmonella therapy.
Based on this finding, we developed a novel strategy of enhanced cancer immunotherapy using an engineered strain of attenuated S. typhimurium secreting Vibrio vulnificus flagellin B (FlaB) in tumor tissues. Engineered FlaB-secreting Salmonellae significantly suppressed tumor growth and metastasis in mouse models and prolonged survival. These therapeutic effects were completely abrogated in TLR4 and MyD88 knockout mice, and partly in TLR5 knockout mice. Tumor microenvironment colonization by engineered Salmonellae appeared to induce the infiltration of abundant immune cells such as monocytes/macrophages and neutrophils via the TLR4 signaling. Subsequent secretion of FlaB from colonizing Salmonellae resulted in phenotypic and functional activation of intratumoral macrophages with M1 phenotypes and a reciprocal reduction in M2-like suppressive activities. These findings provide evidence that non-virulent tumor targeting bacteria liberating multiple TLR ligands can be used as novel cancer immunotherapeutics.
This work was supported by the Pioneer Research Center Program (2015M3C1A3056410).