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Discovery – intestinal bacteria enhances cancer immunity


The term “intestinal bacteria” has been established worldwide, and everyone knows that “intestinal bacteria are important” and “intestines are important”.  

But, knowing that it is important, if you are asked if you know how much active intestinal bacteria are efficient, what comes to mind is a vague idea “enhancing your stomach’s condition”.

I saw some interesting news, saying,  “eleven kinds of intestinal bacteria that increase the ability to attack cancer cells were found”.  Professor Kenya Honda of Keio University and his research team from RIKEN found them.

Reducing amount of cancer with intestinal bacteria⁉ 

Cancer cells are known to be attacked by immune cells when it can be done day by day in healthy people. Also, among immune cells, we know that immune cells called “CD8 T-cells” play an important role in suppressing cancer and infectious diseases.

It turned out that eleven kinds of intestinal bacteria specified this time activated the function of this CD8 T-cell.

In experiments using mice with tumors, the mice subcutaneously received a mixture of eleven intestinal bacteria in “cancer check inhibitor”, a cancer therapy agent. In comparison to cases where only the drugs were administered, it appears that tumor size was reduced to less than half by the combination with intestinal bacteria.  

Many CD8 T-cells had gathered in the mouse tumors. Furthermore, evidently, when removing the CD8 T-cells and carrying out the same experiment, no tumor shrinkage effect was seen.

In other words, eleven kinds of intestinal bacteria exerted an anti-cancer effect by amassing and activating CD8 T-cells.

In addition, immunity checkpoint inhibitors were not used in combination, and it seems that a distinct anti-cancer effect was seen even in the experiment in which only the 11 types of intestinal bacteria were administered to mice.

Intestinal bacteria work as a team

In this study, we are investigating the effect on infectious diseases not just cancer.

After having been infected with bacteria causing food poisoning, etc., mice were administered a mixture of eleven kinds of intestinal bacteria. The result was that symptoms such as weight loss were reduced as compared to mice without the administered intestinal bacteria.

According to this study, it appears that these 11 types of intestinal bacteria are not acting directly, but by activating CD8 T-cells, an important immune cell, by working in tandem.

So, are these 11 kinds of intestinal bacteria sufficient for our intestines too?

The answer is, “highly unlikely”. 

Eleven types of intestinal bacteria are able to demonstrate preventive effects against cancer and infectious diseases in our own bodies; what standard of life can we sustain with them? There are still things we don’t understand.

But it seems certain that intestinal bacteria are important.


◎ Keio University Press Release

“Intestinal bacteria that isolate infection resistance and antitumor effect from healthy individuals”

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