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Stem cell method finds cure

In another advance, scientists heal mice of sickle cell anemia.

December 07, 2007|Karen Kaplan | Times Staff Writer

But before scientists were able to do that, the first paper on reprogrammed iPS cells appeared.

Townes teamed up with Rudolf Jaenisch, a stem cell researcher at Whitehead and MIT, to see if iPS cells would work in place of embryonic stem cells.

They took cells from the tail of a 12-week-old mouse with sickle cell anemia and used viruses to turn on four dormant genes that are active in days-old embryos. One of those genes, c-Myc, has a tendency to cause tumors, so after the cells had completed their transition back to an embryonic state, the researchers deleted it.

Then they corrected the genetic flaw that causes sickle cell anemia by engineering a string of DNA that had an A in place of a T but was otherwise identical to the original. It was swapped into place with the help of an electric shock.

The researchers grew the iPS cells into bone marrow stem cells by exposing them to special growth factors and culture conditions. When the cells were ready, they were transplanted into three sick mice that were genetic twins of the donor mouse.

Twelve weeks later, the mice were producing the normal version of hemoglobin beta protein, and virtually all of their red blood cells were round. Their body weight and respiratory capacity improved. Their urine, previously watery due to the disease, had normal levels of electrolytes.

None of the mice developed tumors, a sign that the threat from c-Myc had been eliminated.

Plath said it was encouraging that the skin cells could be reprogrammed, genetically altered and able to yield their therapeutic benefits in a relatively short period of time.

"If this is ever applied to the human system, you need this to work fairly fast," she said. "You can't waste three years waiting for the cells."

Jaenisch is now using the same approach to treat other diseases, though he declined to say which ones.

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