Aside from its function as a digestive organ, the human intestinal tract is also an immune organ consisting of groupings of immune cells known as gut associated lymphoid tissue (GALT) . These cells act as the intestinal frontier of the immune system, warding off potentially harmful infections. The human microbiome, all microscopic organisms in and on our body, works synergistically with GALT. One role of the microbiome is to teach the immune system to recognize and attack harmful invaders.
A study released in the November 2015 issue of Science found that intestinal bacteria like Bacteriodes fragilis and Bacteriodes thetaiotaomicron play a key role in the effect of certain chemotherapeutics. CTLA-4 blockade chemo drugs depend on white blood cell responses specific to healthy bacteria found in the digestive tract. Melanoma tumours in antibiotic-treated mice (mice lacking healthy bacteria) did not respond to pharmaceutical CTLA-4 blockade, whereas mice with B. fragilis and B. thetaiotaomicron did respond to treatment. This defect was overcome when the antibiotic treated mice were inoculated with the two bacterial types. This study reveals the antitumour effects of this particular type of chemotherapeutic depend on distinct bacterial species found in the digestive tract. Cancer patients frequently treated with antibiotics or currently on antibiotics may not respond as favorably to CTLA-4 blockade chemo drugs.
The longest longitudinal study of the microbiome in acute myelogenous leukemia (AML) patients during chemotherapy found that during the course of chemotherapy, there was a decrease in the oral and intestinal microbial diversity of patients. Those patients with lower diversity were more likely to develop a clinically defined infection with fever during chemotherapy. Of those patients who maintained or increased their microbial diversity, none became infected within 90 days of starting chemotherapy. Infections during chemotherapy may prevent a patient from receiving subsequent rounds of treatment.
These studies clearly indicate that the human biome may used as a treatment tool, either prophylactically or adjuvantly in cancer patients.
How can we optimize our intestinal biome? A diet low in processed sugars and fats, high in fibre and oral probiotic supplementation are simple ways to reduce risk of infection during chemotherapy and improve effectiveness of certain chemo drugs. A study published in the January 2014 edition of Nature found that a beneficial adaptation in microbiome can occur within 24hours of making these dietary changes.