E. coli in uncooked meat can cause diarrhea and food poisoning. Scientists, however, have found a way to turn the bacterium into a delivery agent that takes drugs straight to a tumor and transforms it into a tiny cancer drug dispensary.

E. coli has a natural tendency to travel through the body and specifically colonize and grow inside tumor cores. A recent study by researchers from Columbia University harnessed this trait and genetically engineered a probiotic strain of the bacterium to produce an enzyme called cytosine deaminase (CD) that anchors to tumor tissue. This allows it to convert 5-FC, a nontoxic prodrug that remains harmless in the body until activated, into 5-FU, a powerful cancer-killing chemotherapy drug, directly inside the tumor.

The cancer-fighting abilities of the engineered bacteria didn’t end there. The researchers also got the bacteria to co-produce two additional immune-modulating molecules directly inside the tumor microenvironment: an IL-15 superagonist and a PD-L1-blocking nanobody. One activates antitumor immune cells inside the tumor, while the other blocks PD-L1 signals that cancer cells use to hide from immune attack.