Immunotherapy is a promising area in cancer research and in emerging treatments. Several new studies highlight the role that gut microbes may play in the efficacy of immunotherapy treatments.

In a recent article in the Atlantic, author Ed Jong shares some of the recent discoveries in this innovative field of investigation.

One study, led by Laurence Zitvogel at the Gustave-Roussy Cancer Campus, just outside of Paris, France, discovered that three cancer drugs can stimulate the immune system to kill tumors, but only if the right gut microbes are present. The study involved testing immunotherapy drugs known as checkpoint inhibitors, which work by freeing T-cells, immune cells that seek and destroy potential threats such as cancer. Researchers discovered that this was dependent, however, on having the right gut microbes. When the test mice were treated with antibiotics which destroy native gut microbes, the immunotherapy drugs failed to stimulate the t-cells and failed to keep the tumors under control. The drugs also did not work on germ-free mice who had been raised in an environment free of microbes.

The article further explores the importance of several strains of bacteria, and discusses techniques used to re-sensitize mice to an immunotherapy agent, ipilimumab.

Additional studies have validated these findings, noting that mice from different lab sources sometimes demonstrated more active t-cell response. When different strains of mice were housed together, more efficient response was noted in the mice with lesser t-cell response. This was due to the fact that mice consume each others’ feces, thereby transferring the gut microbes to each other.

One strain of bacteria in particular, Bifidobacterium (Bifs for short), was consistently associated with anti-tumor t-cells. The number of these microbes increased when mice ate the stools of those who had higher levels of Bifs.

Although human studies have yet to be carried out, it holds promise for the future, for this may explain why some patients respond so well to immunotherapy drugs, while others do not. It may be possible in the future to profile the microbiome of a patient to assure that they have the right environment to respond to ipilmumab and other immunotherapies, and if not, to implement measures to correct this.