Many-armed magnets reveal stem cells

In the next few years, doctors may start injecting people with human embryonic stem cells to treat maladies such as multiple sclerosis and diabetes. However, tracking those cells, which can differentiate into any cell type in the body, is a challenge. In animal studies (SN: 9/1/01, p. 143: Stem cell research marches on), researchers dissect their subjects to find out where such cells go and how they develop.

Fortunately, stem cells readily absorb composite magnetic particles called magnetodendrimers. These “sticky” specks could open the way to monitoring stem cell therapy without invading the body, says Jeff W. M. Bulte of Johns Hopkins University School of Medicine in Baltimore.

He and his colleagues have created the particles by marrying magnetic iron oxide crystals to intricately branched polymers called dendrimers (SN: 6/21/97, p. 384). Because of their electrical charges and bristly structure, the new particles stick to and penetrate stem cells in a test tube.

In the December Nature Biotechnology, Bulte and his coworkers report that stem cells took up sufficient numbers of magnetodendrimers to become visible in standard magnetic resonance imaging (MRI) scans. Although there are other ways to noninvasively track cells, such as by slipping radioactive labels into target cells, those methods aren’t as precise at locating the cells as MRI is, Bulte says.

The researchers injected cells harboring magnetodendrimers into the brains of newborn rats that had been genetically engineered to lack a critical nerve cell coating called myelin. This coating degrades in people with multiple sclerosis. Using MRI repeatedly over several weeks, the team watched the injected cells migrate within the brain and become cells capable of manufacturing the needed coating.