So, recently, a group of scientists from the Karolinska Institute in Stockholm and other institutions began to wonder about white blood cells. Part of the immune system, white blood cells play a key role in our defense against cancer by noting, navigating to and often annihilating malignant cells. Researchers have known for some time that different types of immune cells tend to target different types of cancer. But little has been known about if and how exercise affects any of these immune cells and if those changes might somehow be contributing to exercise’s cancer-blunting effects.
Now, for the new study, which was published in October in eLife, the scientists in Sweden decided to learn more by inoculating mice with different types of cancer cells and letting some of the rodents run, while others remained sedentary. After several weeks, the researchers saw that some of the runners showed little evidence of tumor growth. More intriguing, most of these active mice had been inoculated with cancer cells that are known to be particularly vulnerable to a specific type of immune cell, known as CD8+ T cells, which tend, primarily, to fight certain forms of breast cancer and other solid tumors.
Perhaps, the researchers speculated, exercise was having particular impacts on those immune cells.
To find out, they then chemically blocked the action of these T cells in animals carrying tumor cells and let them run. After several weeks and despite being active, the animals without functioning CD8+ T cells showed significant tumor growth, suggesting that the CD8+ cells, when working, must be a key part of how exercise helps to stave off some cancers.
For further confirmation, the scientists then isolated CD8+ T cells from animals that had run and those that had not. They then injected one or the other type of T cells into sedentary, cancer-prone animals. Animals that received immune cells from the runners subsequently fought off tumors noticeably better than animals that had received immune cells from inactive mice.
These results surprised and excited the researchers, says Randall Johnson, a professor of molecular physiology with dual appointments at the University of Cambridge in England and the Karolinska Institute, who oversaw the new study. They seemed to demonstrate “that the effect of exercise on the T cells is intrinsic to the cells themselves and is persistent,” he says.