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The newspaper of The Johns Hopkins University September 12, 2005 | Vol. 35 No. 2
Researchers Develop New Ways to Track Migration of Stem Cells

A team of scientists from the Johns Hopkins Department of Radiology and Institute of Cell Engineering has used a noninvasive imaging technique called SPECT/CT to successfully trace stem cells' destinations after being injected into the body to treat animal hearts damaged by myocardial infarction, or heart attack.

In the study, researchers surgically induced acute myocardial infarctions in seven dogs, six of which later received canine mesenchymal stem cells, or MSCs, labeled with a radioactive tracer and magnetic resonance imaging contrast agent to enhance image quality. Both the tracer and contrast agent are widely used in research and routine clinical practice.

The internal distribution of the injected stem cells was tracked with SPECT/CT and MRI scanners immediately after injection as well as at multiple time points over seven days to assess whether the MSCs preferentially migrated or "homed" in on damaged cardiac tissue. Previous studies in animals were only able to demonstrate homing by examining the tissue microscopically after death.

The team's results, reported in the Sept. 6 issue of Circulation, revealed redistribution of the radiolabeled MSCs from the initial localization in the lungs to the target organ, the heart, at 24 hours post-injection. Moreover, the cells remained visible in SPECT/CT images until seven days after the injection.

SPECT/CT also found redistribution of the MSCs to nontarget organs, such as the liver, kidney and spleen. Measuring the radiation levels in tissues obtained from the animals after their death validated these findings.

MRI, because of its lower sensitivity, was unable to demonstrate targeted cardiac localization of MSCs.

"Our study demonstrates that SPECT/CT imaging is well-suited to dynamically track the biodistribution and movement of stem cells to both target and nontarget organs," said lead investigator Dara L. Kraitchman, an associate professor of radiology in the Russell H. Morgan Department of Radiology and Radiological Science. "Such a noninvasive means of studying stem cell movement could be very helpful in monitoring therapeutic safety and efficacy in clinical trials." Kraitchman said that she and her co-workers, Jeff W.M. Bulte, Mark F. Pittenger, Benjamin M.W. Tsui, Randell G. Young and Richard L. Wahl, anticipate that this technique will be useful in developing customized therapies for future patient trials.

SPECT, or single photon emission computed tomography, is a special type of emission computed tomography, or ECT, scan in which a small amount of a radioactive tracer is injected into a vein and a scanner is used to make detailed images that are highly sensitive to the location of the radioactive materials inside the body. CT, or computed tomography, uses X-rays to produce high-resolution images of the anatomical structure of the body's interior. Combining the two techniques greatly enhances anatomical mapping and localization, permitting researchers to know more precisely what cells or organs are taking up the radiolabeled tracer.
—Gary Stephenson


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