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In December, the lab of George Daley, MD, PhD, associate director of the Children's Hospital Boston Stem Cell Program, became the first to report taking skin cells from a living person and genetically reprogramming them into cells that look and act like embryonic stem cells. This could provide a non-embryonic source for cells that can potentially create all the body's tissue types.
Before these induced pluripotent stem cells (iPS cells) can be used clinically, Daley's team must overcome some substantial hurdles. The genes that reprogram the skin cells and the retroviruses that deliver them pose a cancer risk, and the rate of conversion to iPS cells is low. But research applications are immediate. "Gene-based reprogramming will enable us to create cell lines from patients with specific diseases and study the disease process in the lab," says Daley.
Daley isn't abandoning work with human embryonic stem cells, however. His is one of the few labs in the world pursuing both gene-based reprogramming and nuclear transfer—transferring the nucleus of a patient's mature cell into an egg, inducing the egg to divide, and isolating embryonic stem cells that are exactly matched to the patient. These genetically pristine cells may provide a faster, safer route to the clinic.
The group is also exploring the use of unfertilized eggs alone to create embryonic stem cells that are genetically matched to the egg donor (and her close relatives) by tissue type. And recently, the group derived embryonic stem cells from flawed early-stage embryos discarded by an in vitro fertilization clinic.
"Each of these strategies has its own applications, and allows us to answer different research questions," says Daley. "We need to leave no stone unturned."
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