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When Korean stem cell researcher Woo-suk Hwang announced in 2005 that he had cloned 11 lines of patient-specific stem cells, the research community cheered. Media reports proclaimed that the feat would open up the world of stem cell transplants. But many scientists were excited for another reason: it meant they had a whole new toolbox to study human disease. Researchers could now search for new drug targets or test new therapies in a cell model that was potentially much more accurate than the standard tools.

No one has yet achieved this feat – Hwang’s stem cell lines turned out to be a fraud (see “Stem Cell Uncertainty”). But in the wake of that scandal, other researchers are revving up their efforts to create cloned stem cells. They say that, although cell transplants are an exciting possibility, a more immediate use for these cells will be as models to study human disease.

“You could make a stem cell line that has ALS or Parkinson’s, using DNA from a patient that really has the symptoms,” says Evan Snyder, director of the stem cells and regeneration program at the Burnham Institute in La Jolla, CA.

All existing stem cell lines were created from human embryos. Scientists can study how these cells develop into different cell types; but because researchers don’t know anything about the people who donated the eggs and sperm, they can’t link the behavior of the cells to a particular disease.

To create a cloned stem cell, scientists take the DNA from a human skin cell and insert it into an egg that has had its own DNA removed. The egg then starts dividing, and scientists can harvest stem cells a few days later. Because the cells would be genetically identical to the patient whose DNA was used to create the cell, they will undergo some of the same molecular changes that underlie that patient’s disease.

Scientists can coax the cells to develop into the cell type damaged in a disease, such as dopamine neurons in Parkinson’s or insulin-producing cells in diabetes, and study the progression of the disease and the best ways to treat it.

“Very often the animal models that exist for a particular disease really don’t authentically replicate what’s going on in a human,” says Snyder. “So if we have a treatment for mice, we don’t know if that will translate to treatment for humans.”

Unlike in most animal models, one of the major advantages of cloned stem cells is that scientists don’t need to know the exact genetic changes that underlie a particular disease, says Kevin Eggan, assistant professor of molecular and cellular biology at Harvard University, who plans to start human therapeutic cloning experiments as soon as he gets regulatory approval to study neurodegenerative diseases. These cells could be used to look for compounds and other factors that slow down or speed up the progression of the disease, he says. “You can replay development in the dish over and over under different environmental conditions.”

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