A new ally against cancer: the bacteria in our intestines

Céline Giustranti
Increasingly in the spotlight, the bacteria in our intestines - the famous microbiota - appear to influence the growth of a tumor, but also the response to treatment, in particular immunotherapy. This observation led to the launch of a PIC3i dedicated to studying the intestinal flora during cancer treatments, a project self-financed in large part through public generosity. 
Eliane Piaggio

There are approximately 100,000 billion bacteria living in our intestines. They are essential for assimilating food, and they live in perfect harmony with their host. This symbiosis goes even further. “We already knew that the microbiota played a critical role in how the immune system functions. There is increasing evidence to support a role of the microbiota in patients’ response to immunotherapy,” explains Eliane Piaggio, Inserm research director, director of the Translational Immunotherapy (TransIm) research team (SIRIC, Institut Curie) () and coordinator of the PIC3i on intestinal flora. “Furthermore, it has recently been shown that if there is no microbiota, certain immunotherapy treatments are no longer effective in mice with tumors.” These studies have been carried out with the latest immunotherapy treatments, namely immunomodulators. These are antibodies that target PD-1 or CTLA-4, which are molecules present on the surface of the T-cells.


Increasing the effectiveness of immunotherapy

At Institut Curie alone, close to 10 clinical immunotherapy trials are currently in progress with these immunomodulators. This new therapeutic class is very promising and has proven effective in 10% to 40% of patients suffering from certain types of cancer. Physicians and researchers therefore want to understand why certain patients do not respond. “Attention is turning increasingly to the microbiota to find explanations for this dilemma,” continues Eliane Piaggio. “Thanks to the preclinical investigation laboratory, led by Didier Decaudin, and to the collaboration with Romina Goldszmid from the NIH in the USA, we are going to develop animal models of breast tumors to study the contribution of the microbiota to the response to immunomodulators. Our goal is to identify families of bacteria that would stimulate or inhibit the effect of these immunotherapy treatments.” Indeed, hopes and expectations for immunotherapies are high. Of course, treatments have to be improved and biomarkers identified in order to anticipate responses to treatment. Their development requires better understanding of their method of action, but also of the cumulative effect with other therapies such as chemotherapy or targeted therapies. The future of oncology will no doubt lie in the combination of several approaches, including immunomodulators, targeted therapies, vaccine strategies, chemotherapy.