Expert opinion: Gut bacteria and the success of anticancer treatments
The results of a recent study at the University of Texas has suggested that the contents of our own guts might increase the effectiveness of some types of anticancer drugs.
The study looked at how effective immunotherapy – the stimulation of the immune system to fight cancer – was in different patients and found that the type of the bacteria in the gut was closely related to the outcome of treatment. This particular type of immunotherapy involves 'check point inhibitor' antibodies that take the natural 'break' of immune cells to encourage them to attack cancer cells. The patients who responded best to the treatment had a quite distinct population of gut bacteria, and in particular harboured a group of bacteria known as Ruminococcus.
It isn’t clear whether the different types of gut bacteria are actually responsible for the improved immune response against tumours. It is possible that there is a direct effect though, as some types of bacteria can metabolize an amino acid, tryptophan, to give a chemical called indole-3-aldehyde, which in turn stimulates human immune cells to secrete a protein called Interleukin 22 (IL22). IL22 is a potent activator of the immune system and turns on precisely those components that are needed to destroy cancer cells.
It is also possible that the gut bacteria have no direct effect on the immune response, but may instead be a reflection of the patient’s general health and nutritional state. For example, it is known that individuals who have a diet rich in fruit and vegetables have a distinct population of gut bacteria to those who don’t. Good nutrition is an important supportive treatment in cancer care, and the University of Texas study findings might indicate that it is particularly important in patients receiving immunotherapy. Further research is certainly justified to understand more about this phenomenon and to understand whether it can help to shape the treatment regimen. If the actual gut bacteria are of direct importance, it might be possible to replace “bad” bacteria for “good” bacteria in a so called trans-poo-sion, known less poetically as a faecal transplant, where the existing gut bacteria are removed and then replaced by the patient swallowing a capsule containing someone else’s faeces. This has already been tried clinically in treating otherwise intractable gut infections, although a healthy diet must surely be a preferable option.