Steinberg said that the iron particles, called superparamagnetic iron oxide or SPIO, have been used for more than a decade to track cells in living animals, including in rat neural stem cells. If the point is to use the technique in humans, he and postdoctoral scholar Raphael Guzman, MD, wanted to make sure that the particles worked in human cells as well.
"I think it's critical that we are applying this technique in human stem cells that can be used in human clinical trials," said Guzman, who is lead author of the paper. He said that because they chose to work with those cells, their results can be directly translated to human trials.
They were reassured that putting the iron particles in the cells didn't change the stem cells' biological properties. Also, when the group placed those iron-filled human neural stem cells into the brains of rats--either healthy fetal and adult rats or those that had experienced a stroke--the cells behaved as expected in each case.
In fetal mice with brains still developing, the group injected stem cells into the fluid-filled brain regions called ventricles. From there, the iron-filled cells migrated along the path that stem cells normally take to populate the developing brain. Those stem cells also matured into the proper types of brain cells.
In adult rats that had a simulated stroke, the human stem cells migrated into the damaged region, matured into the appropriate type of neuron and support cells and appeared to integrate into the surrounding tissue. The research group is currently testing whether those transplanted cells repaired stroke-induced damage to the rats' ability to move or learn.
The only situation that rendered the neural stem cells immobile
was the healthy adult rat brain. As with Steinberg's previous work,
the group found that in the absence of any signals to beckon the
stem cells, they stayed close to where the researchers implanted