Escape from cancer
Biologists explained how sports help in the fight against cancer
Maria Azarova, Naked Science
Doctors have long noticed that cancer patients who play sports usually have a more optimistic prognosis than patients who avoid physical activity. It is known that the activity has a beneficial effect on the immune system and increases the body's ability to suppress and prevent the growth of tumors. However, until now it was not clear why and by what mechanism exercises have such a protective effect.
The authors of the new study – scientists from the Karolinska Institute in Sweden – offered their explanation of why sports are necessary for cancer patients. Their work is published in the journal eLife (Rundqvist et al., Cytotoxic T-cells mediate exercise-induced reductions in tumor growth).
"Exercises have a wide range of effects. In animal models, repetitive physical activity reduces the progression of a malignant tumor, and from a clinical point of view, exercise can improve the prognosis for cancer patients. <...> One of the distinguishing features of cancer is the ability of cancer cells to evade detection by the immune system, which in some cases can prevent the body from destroying such cells," biologists write.
To understand how physical exercise helps the immune system to counteract the progression of tumors, scientists conducted experiments on mice. Rodents with cancer were divided into two groups: the first regularly trained on the wheel, and the second remained inactive. "When the mice trained, tumor growth slowed down, and this decrease depended on the levels of a certain type of immune cells – CD8+ (transmembrane glycoprotein, which serves as a coreceptor of T-cell receptors. – Ed.) and T-cells circulating in the blood (T-lymphocytes responsible for the destruction of specific foreign cells carrying markers (signals) for destruction by the immune system. – Editor's note)," the authors of the article explain.
Biologists have also found that CD8+ T cells become more efficient due to the molecules that muscles release into the blood during intense exercise: after exercise, white blood cells change how they use molecules to produce energy. In addition, scientists injected T-lymphocytes of "active" rodents to animals that were not subjected to training – this increased their survival rate and slowed down the progression of the tumor.
"To determine the role of an increase in the cytotoxic T cell population in slowing tumor growth during sports, we depleted CD8+ T cells with weekly injections of CD8 antibodies to mice from both groups. Exhaustion reduced the CD8 population in both the spleen and the tumor, and significantly reduced the positive effect of exercise on both tumor growth and long-term survival. Thus, we demonstrated the role of cytotoxic T cells in suppressing tumor growth using exercises on this model," the scientists added.
Taking samples of T-cells, blood and tissues of mice after training, biologists measured the levels of common metabolites that are produced in muscles and excreted into plasma in large quantities during exercise. Some of these metabolites, in particular lactate (a derivative of lactic acid), altered the metabolism of T cells and increased their activity.
The scientists partially tested their hypothesis on humans: they took blood samples from eight healthy men who had been riding a bicycle for half an hour before: so it turned out that the same metabolites produced after exercise are excreted in humans.
"Exercise affects the production of several molecules and metabolites that activate immune cells fighting cancer and thereby inhibit tumor growth. We hope that the results obtained will contribute to a deeper understanding of how our lifestyle affects the immune system and will help to obtain information about the development of new methods of immunotherapy against cancer," concluded Helen Rundqvist, senior researcher at the Department of Laboratory Medicine at the Karolinska Institute and lead author of the study.
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