Our immune systems help us fight off diseases and invasions of our bodies by foreign organisms. How surprising might it be to learn that our immune systems actually help tumors spread through our bodies?
Dr. Karin de Visser and her team at the Netherlands Cancer Institute have discovered that breast tumors cells induce certain immune cells to enable the spread of cancer cells. They published their findings online on March 30 in the journal Nature.
About one in eight women will develop breast cancer in Western countries. Of those women who die of this disease, 90 percent of them die because the cancer has spread to other parts of their body and formed metastases. Given these grim facts, cancer researchers are spending a good deal of time, treasure and energy to understand how metastasis occurs. A few years ago, several cancer biologists reported that breast cancer patients who showed high numbers of immune cells called neutrophils in their blood show an increased risk of developing metastatic breast cancers. Immune cells like neutrophils are supposed to protect our body. Why then are high neutrophil levels linked to worse outcome in women with breast cancer?
Dr. Karin de Visser, group leader at the Netherlands Cancer Institute, and her team discovered that certain types of breast tumors use a signaling molecule called Interleukin-17 to initiate a domino effect of reactions within the immune system. The tumor cells stimulate the body to produce lots of neutrophils, which typically occurs during an inflammatory reaction. However, these tumor-induced neutrophils behave differently from normal neutrophils. These tumor-induced neutrophils block the actions of other immune cells, known as T cells. T cells are the cells that can (sometimes) recognize and kill cancer cells.
De Visser and her team went on to define the role of the signaling protein called interleukin-17 (or IL-17) in this process. “We saw in our experiments that IL-17 is crucial for the increased production of neutrophils”, says De Visser. “And not only that, it turns out that this is also the molecule that changes the behavior of the neutrophils, causing them to become T cell inhibitory.”
The first author of the Nature paper, postdoctoral researcher Seth Coffelt, showed the importance of the IL-17-neutrophil pathway when he inhibited the IL-17 pathway in a mouse model that mimics human breast cancer metastasis. When these neutrophils were inhibited, the animals developed much less metastases than animals from the control group, in which the IL-17-neutrophil route was not inhibited. “What’s notable is that blocking the IL-17-neutrophil route prevented the development of metastases, but did not affect the primary tumor,” De Visser comments. “So this could be a promising strategy to prevent the tumor from spreading.”
Inhibiting neutrophils would not be a prudent clinical strategy, since drugs that inhibit neutrophils would make patients susceptible to all kinds of infections. However, Inhibition of IL-17 might be a safer strategy. Fortunately, drugs that inhibit IL-17 already exist. Presently, anti-IL-17 drugs are being tested in clinical trials as a treatment for inflammatory diseases, like psoriasis and rheumatism. Last month, the first anti-IL-17 based therapy for psoriasis patients was approved by the U.S. Federal Drug Administration (FDA). “It would be very interesting to investigate whether these already existing drugs are beneficial for breast cancer patients. It may be possible to turn these traitors of the immune system back towards the good side and prevent their ability to promote breast cancer metastasis,” De Visser says.