A gut bacterial enzyme helped immunotherapy fight colorectal cancer in mice

An enzyme produced by a gut bacterium improved tumor control when combined with immunotherapy in mice. The findings, published in Nature Microbiology on April 17, 2026, suggest a possible route to making colorectal cancer more responsive to treatment. Original study

Immunotherapy helps the immune system attack cancer. But tumors can interfere with that response. Some cancer cells display a protein called PD-L1, which connects with another protein on immune cells and sends a signal telling them to hold back.

These signals normally help protect healthy tissue from excessive immune attacks. Cancer can exploit the same system to protect itself. Drugs called checkpoint inhibitors block this interaction, allowing immune cells called T cells to attack the tumor. How checkpoint inhibitors work

The new study investigated Faecalibacterium prausnitzii, a gut bacterium linked in patient data to better cancer outcomes and immunotherapy responses. Researchers identified an enzyme it produces, called fpPRPS, that showed anti-tumor activity in experiments. Original study

The enzyme lowered levels of ATP, a molecule cells use for energy, inside colorectal cancer cells. This disrupted the machinery that transports PD-L1 to the cell surface, weakening its ability to suppress an immune response.

When combined with an anti-PD-1 immunotherapy, the enzyme strengthened cancer-fighting T-cell responses and improved tumor control in mice. Study findings

The distinction matters: this was an experimental enzyme treatment, not evidence that taking probiotics treats cancer. Patient associations do not establish treatment benefits, and whether the approach is safe and effective in people remains unproven. Original research