Gut bacteria may affect the success of cancer treatments

Health 5 November 2015
Gut bacteria may affect the success of cancer treatments

How well a cancer treatment works might depend on what’s living in your gut. Two studies in mice have shown that gut bacteria can influence the effectiveness of treatments for cancer.

Drugs such as ipilimumab, which is given to people with advanced melanoma, work by activating the immune system to help it fight cancer.

Some people who take the drug experience inflammation in the gut. This led Mathias Chamaillard at the University of Lille, France, to wonder whether gut bacteria might be interacting with the drug.


To investigate, Chamaillard and his colleagues gave ipilimumab to mice that lack bacteria in their gut. The drug wasn’t as effective at treating cancer in these mice compared with mice with normal gut bacteria. The effectiveness of the drug also decreased when the normal mice were given antibiotics to wipe out their gut bacteria.

Faecal samples revealed that ipilimumab caused a decrease in two types of bacteria, Bacteroidales and Burkholderiales, in the gut. Replenishing these microbes in both sets of mice restored the efficacy of the drug.

What’s in your gut?

The team then took faecal samples from 25 people with melanoma and tested them for levels of Bacteroidales. When they transplanted the samples into mice without gut bacteria and gave them ipilimumab, they found that those that received transplants containing more Bacteroidales responded better to the treatment.

Chamaillard thinks these bacteria prime the immune system in a way that facilitates the effects of the drug. He now plans to test whether the profiles of bacteria living in someone’s gut can predict how well they will respond to treatment.

In the second study, Thomas Gajewski at the University of Chicago and colleagues noticed differences in how quickly tumours grew in two groups of mice with different sets of gut microbes. The team found that a type of bacteria called Bifidobacteria appeared to be related to a stronger immune response and slower tumour growth. When gut microbes were transplanted from this group to the other group it slowed tumour growth by almost the same extent as treatment with an anti-cancer drug currently being trialled in humans.

How exactly gut bacteria influence immune responses and cancer therapies is still unclear. Gajewski says doctors need to start analysing people’s gut flora and working out if certain types of bacteria affect the clinical benefit or toxicity of treatments. “As we identify which bacteria have a similar effect in humans, it should be possible to develop probiotic supplements that specifically improve efficacy of immunotherapies,” he says.

Alternatively, Chamaillard suggests that altering people’s diets could encourage the growth of the most helpful bacteria.

“This fascinating research adds a new dimension to our understanding of how the latest cancer immunotherapies work,” says Graham Taylor, an immunologist at the University of Birmingham, UK. “They have remarkable potential, but at the moment only some patients benefit from them. The idea of using bacteria to help convince the immune system that there is an invader present and that it needs to kick into gear may offer a simple way to increase their effectiveness. So far this work has only been done using mice and we now need to see how it works in people.”

Journal references, in order: Science, DOI: 10.1126/science.aad1329; Science, DOI: 10.1126/science.aac4255

Image credit: SCIMAT/SPL

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