The prospect of a manned mission to Mars raises all kinds of uncertainties, including how the explorers will feed themselves and find shelter, assuming that they make it there in the first place. But one of the real reservations scientists currently hold about travel to the Red Planet is what kind of impact deep-space radiation might have on the human body. In a new NASA-funded study, researchers have found that it may heighten the risk of leukemia in humans, brought on by changes to the health and function of vital stem cells.

The question of how radiation affects humans in space is being addressed from a number of angles, with NASA conducting studies into its impacts on spacewalking astronauts, how it might affect cognition and behavior and how it might switch genes on and off. One source of radiation is galactic cosmic rays (GCRs), which predominantly travel from outside our solar system, while a closer source is our own Sun, which shoots off solar flares and energy in the form of electromagnetic waves and particles.

Here on Earth we are guarded from these dangers by our planet's magnetic field, but in space and on Mars – whose magnetic field disappeared billions of years ago – we'll receive no such protections. This week, NASA even floated the idea of one day creating an artificial magnetic field around Mars to protect crewed missions there in the future.

Research into the effects of deep-space radiation will help scientists determine how necessary such extreme measures might be. In the latest example of this, a team from Wake Forest Baptist Medical Center carried out a study looking to assess its impacts specifically on human hematopoietic stem cells (HSCs). These immature cells can develop into all types of blood cells, including those that fight infections and malignant cells, and have shown promise as tools in the fight against HIV and leukemia.

The team did this by taking HSCs from healthy donors aged between 30 and 55 (to represent typical astronauts) and exposed them to simulated solar energetic particles and GCRs at the same levels one is expected to experience during a Mars mission. Analysis of the cells in the lab afterwards revealed that the radiation affected the cells at the stem cell level, causing mutations in genes that affected their ability to develop into mature blood cells.

"Radiation exposure at these levels was highly deleterious to HSC function, reducing their ability to produce almost all types of blood cells, often by 60 to 80 percent," says Christopher Porada, senior researcher on the project. "This could translate into a severely weakened immune system and anemia during prolonged missions in deep space."

Humanizing mice

Studying the radiation-treated cells in the lab is one thing, studying them in the body is another. To get an insight into what that might look like, the team then transplanted the GCR-irradiated HSCs into mice – in effect, "humanizing" them. The mice went on to develop T-cell acute lymphoblastic leukemia. The team describe this as the first demonstration that deep space radiation may increase the leukemia risk in humans.

"Our results show radiation exposure could potentially increase the risk of leukemia in two ways," says Porada. "We found that genetic damage to HSCs directly led to leukemia. Secondly, radiation also altered the ability of HSCs to generate T and B cells, types of white blood cells involved in fighting foreign 'invaders' like infections or tumor cells. This may reduce the ability of the astronaut's immune system to eliminate malignant cells that arise as a result of radiation-induced mutations."

The research was published in the journal Leukemia.

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