Pumping iron: new way of tracking transplanted stem cells uses anemia drug

Stanford researcher,
Heike Dalrup-Link

Stanford scientists have made it easier to peer inside our bodies to see what transplanted stem cells are up to. In a study published online yesterday in the journal, Radiology, they describe how they enlisted a drug normally used to treat anemia, ferumoxytol, to tag stem cells inside a living body.

Ferumoxytol contains iron-oxide nanoparticles. The researchers injected it into rats, where it was aborbed by the rats’ cells. They then harvested the rats’ bone marrow and filtered it for mesenchymal stem cells, which can develop into bone, cartilage, muscle, tendon or fat cells.

They finally injected the filtered bone marrow into other rats’ knees. The iron-containing mesenchymal cells were captured visually with a magnetic resonance image (MRI) scanner over several weeks. The researchers are using ferumoxytol’s iron nanoparticles to tag stem cells the way biologists use radio beacons on whales and seals to see where they go after they are released back into the water.

The research team plans to use the technique this fall in a clinical trial, led by orthopaedic surgeon Jason Dragoo, of knee repair patients who will get transplants of mesenchymal stems from their own bone marrow.

So far, a small number of patients have had this kind of stem cell treatment, mostly for knee injuries, but it’s also a potential treatment for people with osteoarthritis, a breakdown of joint cartilage. Treating the condition early with mesenchymal stem cell transplants could help avoid knee replacement surgery later on.

My father had a knee replaced a few years ago and suffered complications that meant knee pain for a year and two additional surgeries to fix the problem. I’m drawn to the idea that he could have been spared a lot of that pain by simply transplanting his own stem cells when his knees first started bothering him, but widespread use of that kind of intervention is years away.

Part of the problem is that doctors are only beginning to understand what transplanted stem cells are doing in the body. In a press release, lead researcher Heike Dalrup-Link explained some of the possible problems this way:

“Here, too, things can go wrong. The newly transferred cells might fail to engraft, or die. They might migrate away. They could develop into tissues other than cartilage, most commonly fibrous scar tissue.”

Seeing what stem cells do once the surgeon closes the sutures is a big step toward understanding the risks and benefits of stem cell therapies. Before this, the only other way to tag stem cells required incubating them in a laboratory so they absorbed chemicals that could be seen with MRI scanners or X-rays. Injecting the chemical tag before extracting the bone marrow reduced the time the cells are outside the body and the risk of contamination.

So often, when scientists get a new ways of observing cells, it means a leap forward for research, so I’m curious to see how the technique fares in the clinical trial – and whether other stem cell researchers eventually adopt it.

Rina Shaikh-Lesko

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