WASHINGTON, Nov. 2 (Xinhua) -- Bacteria that live in the human digestive tract can influence how cancer responds to immunotherapy, opening a new avenue for research to improve treatment, according to two new studies published Thursday in the journal Science.
One study led by researchers at the University of Texas MD Anderson Cancer Center showed that "good bacteria" are more abundant in patients who respond well to immunotherapy.
For the study, the team collected and analyzed microbiome samples from 112 patients with metastatic melanoma who were also taking PD-1 inhibitors, a type of therapy that activates the immune system to attack tumors.
Patients who had a high abundance of the bacteria Faecalibacterium and Clostridiales were more likely to respond to treatment and to experience longer, progression-free survival, while the opposite was found for patients who had a high abundance of the Bacteroidales bacteria.
Analysis of patients' immune responses revealed that those with the beneficial microbes tended to have more immune cells, which may be more likely to infiltrate and kill tumors.
Transplanting the microbes from responding patients into germ-free mice and monitoring their response to PD-1 inhibitors yielded similar results to what was observed in humans, the researchers reported.
In the second study, French, Swedish and U.S. researchers explored how antibiotics might influence the outcomes of patients with lung or kidney cancer undergoing immunotherapy when treated with the same PD-1 inhibitors.
Patients who had previously taken antibiotics, for urinary or dental infections, for example, had reduced survival compared to those who were not on antibiotics.
Analysis of patients' gut microbes revealed that an abundance of the bacteria Akkermansia muciniphila was associated with the best clinical outcome.
The species was detectable in 69 percent and 58 percent of patients exhibiting a partial response or stable disease respectively, but only detectable in 34 percent of patients who did not respond to therapy.
In mice treated with antibiotics, oral supplementation of the bacteria increased the efficacy of the mice's immune cells, boosting their response to therapy.
"You can change your microbiome, it's really not that difficult, so we think these findings open up huge new opportunities," said Jennifer Wargo, associate professor of the University of Texas MD Anderson Cancer, who led the first study.
