X-ray system for tracking stem cells in development

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Researchers at Johns Hopkins Medicine have developed a technique that transports therapeutic stem cells in a multilayer microcapsule that both protects the cells from immune system attack and enables them to be seen in x-ray images. Study results were presented yesterday at a Late-Breaking Emerging Technologies and Innovations session at the American College of Cardiology annual meeting in New Orleans.

The stem cell activity is visible through the use of microcapsules called XCaps. This technique has thus far only been performed in rabbits.

"In acute ischemia, you don't have the luxury of taking stem cells from the body and waiting two to three weeks to culture and expand them in the laboratory," said Dara L. Kraitchman, VMD, PhD, an associate professor of radiology at The Johns Hopkins University School of Medicine in Baltimore. "Ideally, we'd like to be able to take donor cells off the shelf, make them x-ray visible, protect them from the immune system, and deliver them precisely where we want them to be."

The XCaps are coated with alginate, a compound that provokes little immune response; barium a contrast agent; and poly-L-lysine, which holds the microcapsule together.

The researchers replicated the effects of severe peripheral arterial disease in 13 female rabbits by inserting a platinum coil in the artery supplying blood to the hind limbs of the animals.  The rabbits were then injected with the caps in various scenarios. XCaps were visible on X-ray both immediately after injection and at two weeks, allowing the researchers to monitor the delivery and disposition of the XCaps.

"The nice thing about XCaps is that you can see each individual capsule very clearly on x-ray," said Dr. Kenyatta Cosby, a postdoctoral fellow at Johns Hopkins. "We also observed no accumulation of fibrous material around the capsules, which suggests a minimal immune response."

“Since XCaps can be made using FDA-approved clinical-grade compounds, they represent the first potentially biocompatible therapy that will enable X-ray visualization of stem cells to assist in targeting cellular therapeutics,” Kraitchman said.