There are hundreds of trillions of microscopic, single-celled microbes in your gut, approximately 10 times the number of cells in your entire body.
Most of them benefit us in some way. Entire scientific endeavors are now devoted to trying to figure what these so-called microbiota do.
The latest study, reported in the journal Science, strongly suggests that some of them can help fight cancer.
In studies of mice, oncologist Tom Gajewsky and colleagues at the University of Chicago found that microbiota in the guts of certain mice produced a strong immune response against melanoma, a lethal skin cancer.
When the mice were given the chemotherapy drug PD-L1, their tumors shrank significantly and almost completely went away.
“We now have patients who have complete elimination of their tumor and, you know, are quite stable now for years," Gajewsky said. "That’s a small minority of patients. Now, if we could figure out all of the tricks to improve that immune response, maybe we can expand the number of patients who get this good immune response against their tumor.”
Researchers first noticed that mice obtained from one lab had a strong immune response against small melanoma tumors. Mice from another laboratory had a weaker anti-tumor response.
But when the mice were put together, researchers saw tumor reduction in both groups.
The researchers believed that living together transferred some beneficial gut microbiota to the rodents that didn’t do well when given PD-L1.
Investigators transferred fecal samples from the mice that had strong immune responses to the poor responders. A short time later, they saw significantly slower tumor growth in both groups of mice.
One family of gut bacterium, called Bifidobacterium, appeared to be especially beneficial.
Bifidobacterium worked as well as PD-L1, and when used together, Gajewski said, they could potentially produce a cure for certain cancers, including lung and head and neck cancers.
The antibody drugs are extremely expensive, but given with a dose of gut microbiota, Gajewski said, the treatment antibodies could become more widely accessible.
“And maybe more exportable to developing countries, as you think forward," he said. "Some of these expensive therapies, you might imagine, are not going to be available for a while in more developing countries, and something like a probiotic could be cheap and easy.”
Some microbiota, also called probiotics, are already available on the market. But Gajewsky cautioned against taking them at this point because some might weaken the immune system, promoting cancer or causing anti-tumor drugs to be less effective.