Studies have shown that gut bacteria improve our immunity and may even help cancer immunotherapy. However, the precise mechanism of its working was not known. A recent study by the University of Calgary may have identified the intestinal bacteria that help our immune system to fight cancerous tumors and how they work. This can also explain why some cancer immunotherapy works and some don’t.
The animal study, which was published in the journal Science, also found that the immune system may work better if we combine very specific microbial therapy with immunotherapy. This may have better chances of identifying and fighting cancer cells in certain melanoma like colorectal and bladder cancer. 
The research team three bacterial species in the intestinal tract of the mouse models. These were found to increase the efficiency of the immune system, particularly the checkpoints. The team found that the bacteria produced a small molecule known as inosine. It is this molecule that could enhance the immunotherapy response in the body. When immunotherapy decreased the gut barrier function, inosine translocation was triggered, activating the anti-tumor cells. The study thus showed how immunotherapy along with gut bacteria could help in triggering the anti-tumor cells.
“Identifying how microbes improve immunotherapy is crucial to designing therapies with anti-cancer properties, which may include microbials,” Dr. Kathy McCoy, Director, International Microbiome Centre, University of Calgary and lead author of the study. “The microbiome is an amazing collection of billions of bacteria that live within and around us every day. We are in the early stage of fully understanding how we can use this new knowledge to improve efficacy and safety of anti-cancer therapy and improve cancer patient survival and well-being.