REUTERS/NIH

A cancer cell (white) being attacked by two cytotoxic T cells (red), part of a natural immune response triggered by immunotherapy.

A pair of new studies revealed that the chances of cancer treatment working may rely on bacteria inside the gut. This veers away from the popular belief that it is the immune system that is largely responsible for attacking cancerous tumors, giving drugs a sharp stick in every patient.

Some intestinal-dwelling bacteria were observed to corral and train immune cells to fight off cancer cells. In both studies published by Science Magazine, researchers found that certain patients who lacked the gut bacteria saw no benefit from drugs after taking antibiotics, while patients who had considerable amount of the bacteria responded to the drugs prompting the immune system to release cancer-killing T-cells.

The results were also mirrored in germ-free mice with cancer when the gut microbes were transferred into their bodies. This means that mice who got gut bacteria from non-responding patients also did not respond to immunotherapies, while mice who got the gut microbes from responding patients also responded to the drugs. When the researches switched responder gut bacteria into mice that did not respond prior to the swap, the mice converted and fought back cancer.

The type of immunotherapy used in the study is known as a P1-D inhibitor, and assess how microbes influence therapeutic outcome. P1-inhibitors fight cancer by blocking a molecule called "checkpoint" on T-cells which tumors use to shut down immune cells.

Surgical Oncologist and Geneticist at the University of Texas MD Anderson Cancer Center Dr. Jennifer Wargo and her colleagues of the study conclude that their findings showed the potential of receiving checkpoint blockade immunotherapy and modulating gut bacteria.

Wargo advised that the data gathered from the study should be approached with care as any given bacteria may aid one cancer and the immunotherapy associated with it, but could have an adverse effect on a different patient dealing with a different disease and different drugs. She added that they also warrant the start of cancer patient evaluation through clinical trials.