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
GO TO