Gut Flora May Inhibit the Immune Response Against Tumors

The human digestive system contains bacteria with complex and dynamic relationships. Studies increasingly suggest that gut bacteria influence the immune system's attack on cancer cells and the response to immunotherapy . According to a study published in May 2018 in Science, certain types of bacteria in the gut inhibit the development of an immune response against tumors in the liver.

Gut bacterial colonies play a very important role in human health. Our gut flora help develop immunity against harmful organisms and participate in digestion and metabolism. Disruption of the balance of gut flora causes numerous infections and inflammatory conditions affecting the liver to develop.

Previous studies reported important discoveries about how gut bacteria regulate the relationship between the immune system and cancer. However, how this happens in the liver had not yet been clarified. 70 percent of the blood reaching the liver comes from the gut. The liver is therefore continuously exposed to byproducts produced by bacteria. This study examined the relationship between gut bacteria and the immune system in liver cancer.

According to the Study Results:

• Primary and metastatic liver cancer mouse models treated with antibiotics showed both a reduction in the number of gut bacteria and smaller and fewer tumors.
• At the same time, an increase in the number of natural killer cells in the liver was observed. These cells showed increased activity of the CXCL16 protein. Natural killer cells are key cells that fight cancer cells. Bile acid was found to increase CXCL16 protein activity. Activation of this protein enhances the antitumor effect.

The Most Interesting Finding of the Study:

A type of gut bacterium, Clostridium scindens, was found to reduce the number of natural killer cells by controlling bile acid metabolism, facilitating cancer spread.

In other words, bile normally helps the digestive system digest fats. Secondary bile acids formed as a result of disruption of the gut flora affect immune system function, increasing liver cancer and metastasis.

What Does This Study Mean for Us?

•  This is an important study showing how basic science guides clinical practice and treatments. Clinical oncology can hardly advance without effective results from basic science. Cancer can therefore only be treated through a multidisciplinary perspective.
• The role of gut flora in the intestinal response against cancer has once again been demonstrated. Modifying gut flora using “modern medicine” methods may improve the effectiveness of immunotherapies.
• It must be emphasized that this study was carried out in mouse models in a laboratory. Further studies are needed to confirm these results.
• In the future, CRISPR could eliminate gut bacteria that help cancer cells, providing an effective treatment combination with CAR-T cell therapy.
• The Mediterranean Diet Increases Beneficial Gut Bacteria!
• What Is Gut Flora (Microbiota, Microbiome)? How Is It Related to Colorectal Cancer?