Few recent developments have created more excitement in the world of cancer research than the rise of immunotherapy. After decades of frustration, scientists have finally found effective ways of turning the immune system against tumors, with spectacular results. Patients with kidney cancers and melanomas that had spread all over their bodies—diseases that would typically carry dire prognoses—have been cured. Immunotherapy, once a poster
child for neglect and failure, has finally come of age.
The same could be said for the human microbiome. The trillions of bacteria and other microbes that share our bodies were ignored for centuries. But recent studies have shined a spotlight onto these multitudes, by showing how important they are, not least in their ability to train and calibrate our immune systems.
Today, these two trendy fields are colliding head-on. Working independently, two teams of scientists have shown that gut microbes—at least in mice—can dramatically affect the immune system’s ability to deal with cancer. These microbes affect an individual’s natural immunity to cancer, and how well they respond to immunotherapy drugs. And certain species of bacteria
are especially potent at driving anti-tumor immunity, suggesting new ways of making new cancer drugs that much more potent.
There were signs of this already. In 2013, two groups of scientists showed that three cancer drugs can mobilize the immune system to kill tumors, but only in the presence of the right gut microbes. Laurence Zitvogel at the Gustave-Roussy Cancer Campus, who led one of the two teams, wanted to see if the same was true for a new wave of promising immunotherapy drugs called checkpoint inhibitors.