Science Snippet: Microbes May Play Role in Cancer Resistance

There are 500-1,000 species of bacteria in the human intestine and these tiny cells comprise a group collectively called the “microbiota” of the gut. Microbes in the gut make certain vitamins, send signals to the immune system, and release small molecules that enhance brain function. Now there is evidence that gut microbes may play a role in determining our resistance to cancer. When the immune system is not being challenged, the “find and kill” warrior cells (T-cells) of the immune system are resting. The relatively quiescent state of T-cells is caused by a molecule released by certain other cells of the immune system. The molecule is called CTLA-4, and its role is to help dampen the immune response when appropriate to keep warrior T-cells from getting out of control and attacking normal body cells. When T-cells successfully eliminate a threat, CTLA-4 binds to their surfaces and tells them to “take a break and rest.” There are times, however, when quiescent T-cells must be quickly activated so they can fight an invasive agent, such as a virus. A new immunotherapy treatment for cancer is to introduce a specific antibody to CTLA-4 that eliminates this protein’s ability to turn off T-cells. When this happens, the T-cells “wake up” and charge into battle, looking for foreign antigens or dying cells to eliminate. Recently it was demonstrated that, in mice at least, the degree of success using this kind of immunotherapy is dependent on the kind of microbiota in the patient’s intestine. Since the mix of microbiota can differ from person to person, the new immunotherapy treatment may work with some individuals and not with others, depending on the kinds of gut cells and the kind of cancer. In some cases the method has completely eliminated the cancer. (Science, Nov. 27, 2015 – three articles)