Researchers are beginning to understand the behavior of transplanted or implanted stem cells that may one day be used to develop new treatments for disease by combining PET imaging with bioluminescence, according to a study in the December online issue of the Journal of Nuclear Medicine.
The unique combination of noninvasive PET imaging and optical (bioluminescent) imaging is "an ideal method for tracking stem cell transplantation in small animal models," said Zhenghong Lee, an associate professor of nuclear medicine/radiology and biomedical engineering departments at Case Western Reserve University in Cleveland, Ohio. Researchers were able to use these two imaging techniques to "follow" stem cells for a longer time than previously had been achieved to determine their "fate," said Lee.
Human mesenchymal stems cells or multipotent marrow stromal cells (hMSCs), which are self-renewing adult stem cells found in adult donor bone marrow, may change into bone, fat tissue and cartilage, said Lee. "The promise of MSC therapies—derived from adult bone marrow and used as a viable and renewable source of stem cells—mandates research leading to a better understanding of the long-term fate and trafficking of transplanted MSCs in animal and human subjects," Lee said. “These progenitor cells may have great potential in providing future treatments for heart diseases, brain disorders and cancer and greatly reduce the need to use embryonic stem cells or other fetal tissues.”
For this study, researchers used a fusion protein combining firefly luciferase (a light-emitting substance) for optical imaging, a red fluorescent protein for cell separation and a virus enzyme thymidine kinase for PET imaging in mice to visualize biological processes at the molecular level.
"The triple-fusion reporter approach resulted in a reliable method of labeling stem cells for investigation by use of both small-animal PET imaging and bioluminescent imaging," said Lee. PET scans use very small amounts of radioactive pharmaceuticals that are detected or "traced" by a special type of camera that works with computers to provide quantitative pictures of the area of the body being imaged. To image dim light from bioluminescence, researchers use an ultra-sensitive camera from an external vantage point.