Cycling may boost stem cell donation with targeted cell release, pilot study suggests

A blood stem cell donation can save the lives of people with leukemia. To collect these cells from the bloodstream, donors are given medication that mobilizes blood stem cells from the bone marrow. A pilot study now suggests that physical exercise could specifically support stem cell donation.

Blood stem cells in the bone marrow continuously produce new blood and immune cells. When this system becomes diseased, as in leukemia, a transplant of healthy stem cells from a compatible donor can offer a chance of cure.

Before donating stem cells, donors receive the drug G-CSF, which mobilizes blood stem cells from the bone marrow so they can be collected from the blood. However, treatment with G-CSF is often associated with side effects such as bone pain. In some cases, the number of stem cells collected is also insufficient, requiring additional treatment cycles and medication.

Previous studies have shown that intense physical exercise can likewise release blood stem cells into the bloodstream. Unlike additional medication, physical exercise is considered very low risk. PD Dr. Julia Kröpfl together with a research team from the Department of Sport, Exercise and Health at the University of Basel, therefore investigated this effect in a pilot study. For the first time, the researchers directly compared in the same donors how physical exercise and G-CSF mobilize blood stem cells.

The findings are published in the European Journal of Applied Physiology.

Cycling for stem cell donation

In collaboration with Professor Andreas Holbro, senior physician at Blood Donation Northwest Switzerland and the Department of Hematology at the University Hospital Basel, the team recruited seven male and three female donors who were preparing to donate blood stem cells to family members. The participants first completed an intensive cycling session on an ergometer and provided blood samples before and after the exercise. A few days later, they underwent the conventional treatment with G-CSF.

The direct comparison revealed differences in both the quantity and composition of the mobilized blood stem cells. Previous studies have shown that, after an intense training session, the number of stem cells rises within minutes but then rapidly declines again. With G-CSF, by contrast, it takes several days for blood stem cell levels in the bloodstream to increase.

In terms of the number of blood stem cells in the blood, physical exercise had a significantly smaller effect than the medication. The acute exercise stimulus increased stem cell numbers only moderately—to around one-and-a-half to two times baseline levels. With G-CSF, however, stem cell levels increased 20- to 50-fold.

“The effect of acute physical exercise is small, but it is more targeted in terms of the composition of the mobilized cells,” explains Kröpfl.

G-CSF non-specifically releases all subtypes of blood stem cells. Intense physical exercise, by contrast, specifically dislodged cells considered beneficial for a successful transplant. These include, for example, platelet precursor cells and less mature—essentially “early”—blood stem cells, which are thought to have a particularly high capacity to establish themselves in the recipient’s body. What this means clinically for patients, however, remains unclear.

Not a replacement, but a promising adjuvant

Previous analyses suggest that acute physical exercise primarily mobilizes blood stem cells that adhere to blood vessel walls, due to increased blood flow. This could explain the faster effect of exercise compared with the medication.

“Physical exercise cannot replace G-CSF treatment for stem cell donation, but it could potentially complement it,” emphasizes Kröpfl. “The combination of both approaches would be promising.” While the drug releases stem cells from the bone marrow, physical exercise could additionally mobilize cells adhering to blood vessels, thereby complementing and potentially enhancing the effect of G-CSF.

Because of the small number of participants, the study provides only preliminary evidence that will need to be confirmed by further research. However, Kröpfl explains that a study combining G-CSF and cycling cannot currently be conducted in Switzerland for ethical reasons. There is too much uncertainty about whether physical exercise could worsen the side effects of G-CSF and potential complications during stem cell collection.

“However, it is entirely possible that exercise could actually alleviate these side effects, as has also been observed in patients undergoing chemotherapy,” says the molecular biologist. A study in England is already investigating the combination of G-CSF and cycling.

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Gaby Clark

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Andrew Zinin

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