Stem cells have great therapeutic potential to replace diseased cells, because stem cells can now be isolated and differentiated into many different cell types. Tracking transplanted cells in vivo may provide information for the optimization of stem-cell therapies. To monitor their fate after transplantation, Jeff Bulte and colleagues have designed tiny magnetic tags that can be used for tracking labeled cells' movement in the body using a medical technique called magnetic resonance imaging (MRI) (Nature Biotechnology, Dec 01).
MRI is a noninvasive technique that uses a strong magnet and radiofrequency waves to produce "images" of tissues or structures deep inside the body. For stem cells to be visualized and tracked by MRI, they need to be tagged magnetically so that they stand out from other tissues. Bulte and colleagues have developed a new class of highly magnetic probes called magnetodendrimers or MD-100. These were developed by enveloping magnetic iron particles within established polymers, termed dendrimers, that can ferry drugs and DNA into a wide variety of cell types. As a result, labeling can be achieved simply by adding MD-100 to cells in the culture dish - an advantage over other approaches that require tags to be attached to proteins or peptides that then interact with cell-surface receptors in order to enter cells.
The researchers showed that human neural stem cells labeled with MD-100 were viable and able to differentiate normally into neurons, which retained the tags. Labeled cells transplanted into rat brain could be tracked using MRI for at least six weeks after transplantation. This technique could be used to trace a variety of other cells, such as those from a tumor, to evaluate cell migration events.
Jeff W.M. Bulte
Department of Radiology
Johns Hopkins University School of Medicine
Baltimore, MD 21205-2195
(C) Nature Biotechnology press release.
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