That question has now been at least partially answered by this latest report.

"This study is important as a proof of principle that these iPS cells can be used to correct mutations," said Dr. Jacob Hanna, lead author of the study, which is published in the Dec. 6 online issue of Science Express.

Hanna is a postdoctoral fellow in Rudolf Jaenisch's laboratory at The Whitehead Institute in Boston.

"It's very fascinating that they're using these reprogrammed cells to make hematopoietic cells [which can produce different blood and immune cells] to then treat the genetic defect in these mice," said Paul Sanberg, director of the University of South Florida Center for Aging and Brain Repair in Tampa.

Embryonic stem cells are pluripotent, meaning they have the capacity to develop into virtually any cell type in the body. The hope is that such cells may one day yield treatments or cures for diseases such as diabetes, liver failure, spinal injury, stroke, Alzheimer's disease and heart disease.

However, harvesting embryonic stem cells involves destroying a viable embryo, stirring much political debate. In the United States, embryonic stem cell research has been severely limited since August 2001, when President George W. Bush placed limits on federal funding of the field and restricted the number of embryonic stem cell lines that could be used.

Since that time, researchers have been racing to find other sources of viable stem cells -- iPS cells are one outcome of that race.

For this study, Hanna and his colleagues used a process similar to the one revealed two weeks ago, taking skin cells from the tails of mice with sickle cell anemia and using them to produce iPS cells. The researchers then replaced the mutated gene with a healthy gene in the new cells. Once the iPS cells had differentiated into hematopoietic stem cells, they were reintroduced into the mice, where they began to produce healthy blood cells.

Some 10 percent of the human population, mostly blacks, carry the mutation for sickle cell anemia. The exact mutation is well known, as is the protocol for differentiating embryonic stem cells into precursors of bone marrow adult stem cells, making the condition well-suited to study.

In sickle cell anemia, red blood cells become sickle-shaped and can't move easily through the blood vessels.

Although exciting, the process is still fraught with potential danger.

The procedure to turn skin cells into iPS cells could lead to cancer (although none of the mice in this study showed any evidence of tumors). Also, the healthy genes were introduced into the mice via retroviruses, which can introduce other problems.

"Now the major question in the field is can you make iPSs with a safer method, that don't use retroviruses, because viruses can integrate into the DNA and activate dangerous genes or silence necessary genes," Hanna explained.

"I like the fact that they're saying this is a first step, because they're using retroviruses, and they have to show that this is a safe approach," added Sanberg.

More information

Learn more about stem cells at the International Society for Stem Cell Research.