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A genetically modified bacterium destroys tumors by provoking an immune response, according to a study published Wednesday.

Using mice and cultures of human cancer cells, a South Korean-led scientific team demonstrated that Salmonella typhimurium engineered to make a foreign protein caused immune cells called macrophages and neutrophils to mobilize against the cancer.


The bacterium came from an attenuated strain that has little infectious potential. Such strains have been tested as vaccines. The protein, called FlaB, is made by a gene in the estuarine bacterium Vibrio vulnificus, a close relative of the cholera bacterium, Vibrio cholerae.

Tumors shrank below detectable levels in 11 out of 20 mice injected with the modified Salmonella, said the study, published in Science Translational Medicine.

Go to j.mp/salcancer for the study. The first author was Jin Hai Zheng of Chonnam National University Hwasun Hospital, in Jeonnam, South Korea.

The engineered Salmonella provoke a sustained immune response, in addition to preventing the spread of a human colon cancer implanted in a mouse. The bacterium also were found to be nontoxic, multiplying almost exclusively inside tumors.


Sandip Patel, MD, of UC San Diego Moores Cancer Center, praised the study’s “very novel strategy.”

“The importance of the host bacteria (the microbiome) on immune responses against tumor is increasingly appreciated and a very active area of research,” Patel said by email. “To utilize bacteria as a delivery system builds on this concept.”

“The immune effects induced by Salmonella here are an important first step in stimulating an immune environment that is primed to kill tumors. Further research looking into this therapeutic strategy, as well alternative means of modulating the tumor microenvironment (toll-like receptor agonists), will be needed to help our patients have the most effective options to fight their cancer.”

Researchers have explored the use of Salmonella against cancer for years, because it grows in the low-oxygen environment inside solid tumors. This environment is hard for the immune system to reach.


UC San Diego researcher Jeff Hasty has developed engineered Salmonella that deliver cancer-killing toxins inside the tumor. This bacterium periodically self-destructs when it reaches a certain population density, releasing the toxins. Some of the engineered Salmonella survive, rebuilding the population until it reaches the self-destruct density. So the tumor receives periodic doses of targeted chemotherapy.

Bacterial immunotherapy itself began more than 100 years ago, with experiments by bone surgeon and cancer researcher William Coley. But the results were inconsistent, and the method was abandoned in favor of advances in radiation, chemotherapy and surgery.


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