Scientists fear that security-driven switch to X-ray irradiators will harm their research.
Anybody who wants to conduct experiments on mice in Margaret Goodell’s immunology lab must submit to a host of security measures, starting with a background check by the FBI. That’s because Goodell, a researcher at Baylor College of Medicine in Houston, Texas, uses a caesium-based irradiator to destroy bone marrow in mice that are set to receive stem-cell transplants. The US government fears that the radioactive caesium could be stolen to make a ‘dirty’ bomb.
Now the US National Nuclear Security Administration (NNSA) is working with scientists to investigate how — or whether — to replace caesium irradiators with less dangerous X-ray technology. Researchers have used the caesium devices for decades, to study everything from immunotherapy to cancer treatment, and some fear that switching to X-ray irradiators will affect their results.
Goodell, who has found subtle differences in how the mouse immune system responds to the two types of device, prefers Baylor’s caesium irradiator. Her research has revealed that immune cells called B lymphocytes recovered more slowly in mice treated with an X-ray irradiator than in those exposed to caesium. But other immune cells, known as myeloid cells, rebounded faster after the X-ray treatment (B. W. Gibson et al. Comp. Med. 65, 165–172; 2015). Because of this, she says, “it would be difficult to compare studies using X-rays to the research that was done ten years ago”.
For nuclear regulators, the risk posed by caesium is clear. The element’s highly radioactive isotope caesium-137 comes in a powdered form that can be dispersed in air or water; exposure to the substance can cause burns, radiation sickness or death, depending on the dose. Caesium irradiators, which have long been used to eliminate pathogens in supplies of blood as well as for research applications, rely on small capsules of radioactive caesium chloride encased in a lead-covered box. There are more than 800 such devices in US medical and research facilities.
Several countries — including France, Norway and Japan — are shifting away from using caesium irradiators in blood banks because of security fears, and last year the NNSA began working with hospitals in the United States to do the same. But finding alternative ways to treat blood is relatively simple. The NNSA is working with researchers to pin down the more complicated issue of how X-ray irradiators might differ from conventional caesium instruments for other applications.
“You talk to the doctors, and they are afraid that we are going to be taking away their devices,” says Maegon Barlow, director of radiological security at the NNSA. “But it’s really trying to facilitate, not force.”
The agency is negotiating with the Mount Sinai Health System in New York City to support a new round of studies that will compare X-ray and caesium irradiators. Jacob Kamen, Mount Sinai’s chief radiation-safety officer, notes that some researchers there have already conducted similar experiments.
Peter Heeger, head of organ-transplant research at Mount Sinai’s Icahn School of Medicine, and his colleagues use caesium irradiators when testing immune responses in people who are going to receive organs. To predict whether a recipient’s body will reject a new organ, the researchers culture B lymphocytes from the organ donor and test them against immune cells from the recipient. But B lymphocytes will not divide unless they are activated — here, by the presence of connective-tissue cells called fibroblasts. Heeger’s team irradiates the fibroblasts to prevent them from replicating during this process. The scientists have run a series of unpublished experiments to determine how much X-ray radiation is necessary to suppress fibroblast growth.
“Now we know, and we are now comfortable switching for this particular procedure,” says Heeger.
But Goodell says that many researchers would have to conduct lengthy experiments to ensure that they can make the transition without losing confidence in their results. Nor is she convinced that a switch to X-rays is necessary, given the security safeguards that are already in place. Anybody who needs to use the caesium irradiator at Baylor must present a security badge, enter a personal identification number and then submit to an iris scan. And if a person inside the secure room that contains the irradiator breaches any security protocols, an alarm automatically goes off in the university’s security office.
“As a biologist, it’s not clear to me what case has been made for [caesium irradiators] being an enormous security risk,” she says.
Advocates of ending use of the devices say that the goal is to eliminate the risk of nuclear material falling into the wrong hands wherever possible. The security measures in place to protect caesium irradiators would not necessarily prevent the theft of nuclear material by somebody with permission to access these instruments, says Charles Ferguson, president of the Federation of American Scientists in Washington DC. Efforts to secure nuclear materials are often focused on this ‘insider threat’, as well as the disposal and recycling of irradiators, which can contain enough caesium to pose a hazard for centuries.
“I would not want humanity to lose the benefits of science,” says Ferguson. “But if we can develop alternative technologies that prove comparable and can reduce the security threat to zero, I think that’s a good thing.”
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Tollefson, J. Biologists struggle with push to eliminate radioactive caesium in labs. Nature 533, 156–157 (2016). https://doi.org/10.1038/533156a