Microbiome bacteria help cancer cells evade the immune system

Optical microscope image of bacteria from the genus Fusobacteria.

Optical microscope image of bacteria from the genus Fusobacteria.

A few weeks ago Kris Campbell wrote about the microbiome’s association with colorectal cancer.  This association is complex, but perhaps critically important, and last week a new study reinforced this connection.  Researchers, primarily from Israel, published results in Cell Immunity that showed common microbiome bacteria are protecting cancer cells by helping the cancer cells evade the immune system.

The researchers noticed that a type of bacteria, Fusobacterium nucleatum, which is normally found in the oral microbiome and is a cause of periodontal disease, can be found in high concentrations around colorectal tumors.  In addition, these same bacteria had been linked to various microbiome associated diseases, such as preterm birth and rheumatoid arthritis.  They suspected that these bacteria may somehow be protecting the cancer cells from the immune system, so they performed a series of experiments to find out.

The scientists grew cancer cells in the presence and absence of the F. nucleatum and then exposed these cancers to immune system cells that are designed to attack cancers.  They noticed that those cancer cells that had been grown with the bacteria were naturally protected from these immune cells.  Through a series of tests they discovered that the bacteria produce a protein called Fap2 that naturally bound with the immune cells and essentially deactivated them (technically speaking, Fap2 bound to the Natural Killer cells’ TIGIT inhibitory receptors).  Interestingly, this TIGIT receptor is nearly ubiquitous across many types of immune system cells, which means that this bacteria, and others like it, may be especially good at protecting themselves and other cancer cells from our bodies’ natural defenses.

It may be surprising for our readers to hear that bacteria are sometimes used to destroy cancer cells, like in the case of bladder cancer, but this paper shows a more dichotomous relationship between the microbiome and cancer.  While some bacteria may be helpful in killing cancers others may be helping them grow.  Either way, one thing is clear, the microbiome and cancers are intimately related, and learning about the microbiome should lead to advanced therapies for treating cancers.

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