🦠 Scientists engineered a probiotic bacterium to manufacture chemotherapy and immune-boosting drugs directly inside tumors — completely eliminating 43% of colorectal tumors in mice.
Researchers at Columbia University used Escherichia coli Nissle 1917, a non-disease-causing probiotic strain that can preferentially accumulate inside tumors.
Within five days, the bacteria reached more than a billion cells per gram of tumor tissue while largely disappearing from major organs.
The team then turned the bacteria into tiny drug factories.
They engineered them to produce cytosine deaminase, an enzyme that converts the relatively non-toxic compound 5-fluorocytosine, or 5-FC, into the chemotherapy drug 5-fluorouracil, or 5-FU, directly inside the tumor.
Researchers also deleted bacterial genes that normally break down 5-FU, allowing more chemotherapy to remain active.
But chemotherapy alone triggered tumor defenses.
So the bacteria were further engineered to release an IL-15 superagonist, which stimulates cancer-fighting immune cells, and a nanobody that blocks PD-L1, a protein tumors use to suppress immune attacks.
With this three-part strategy, a single bacterial injection followed by 5-FC completely eliminated three of seven colorectal tumors — about 43%.
Even untreated tumors elsewhere in the body grew more slowly, suggesting the therapy triggered a broader immune response.
The treatment also produced immune memory in mice, helping protect them when tumor cells were introduced again later.
But this is still early preclinical research.
The experiments involved small numbers of mice with implanted tumors, and much of the treatment was delivered directly into tumors.
Still, the study shows how engineered probiotics could one day concentrate cancer treatment inside tumors while reducing exposure elsewhere in the body.
📃 RESEARCH PAPER
📌 Yang et al., “Engineered probiotics for tumor-targeted combination chemoimmunotherapy”, Science Translational Medicine (2026)