Bacteria don’t have the best reputation among humans, but they could be a cancer patient’s greatest ally: Researchers have just used a weakened Salmonella strain to deliver and release a protein within cancerous tissue that sets off the body’s alarm system and calls in its natural defenses to fight the tumor.

A study in Science Translational Medicine describes the process, saying it “effectively suppressed tumor growth and metastasis in mouse models and prolonged survival.”

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The protein that acted as a defensive signal in the mice was separated from Vibrio vulnificus, which is commonly known as flesh-eating bacteria. Although alone it does not cause the potentially lethal infection, it still “activates innate immune responses” in the body after it hitches a ride on the weakened Salmonella to the low-oxygen environment of a solid tumor, the study says. Immune cells flood the area to fight the invaders, catching the cancer bystander in its crosshairs.

Why use Salmonella, an already potentially harmful bacteria, to carry a simple protein and trick the body into fighting a growing tumor? The body’s defensive response is “far more potent” when the Salmonella releases the alarming protein than when Salmonella is introduced by itself into a cancer patient’s body, according to the study.

The American Association for the Advancement of Science said in a statement that the nontoxic bacteria “didn’t invade non-cancerous tissue in rodents,” only targeting the dangerous cells in the body. “Its good safety profile makes the engineered bacteria a promising potential anticancer strategy.”

Source: Min J, Zheng JH, Nguyen VH, et al. Two-step enhanced cancer immunotherapy with engineered Salmonella typhimurium secreting heterologous flagellin. Science Translational Medicine. 2017.

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