Reprogrammed stem cells show flaws

LOS ANGELES – Two studies released last week by the journal Nature show that work remains before so-called induced pluripotent stem cells are ready for use in laboratory studies or clinical therapies.

Induced pluripotent stem (iPS) cells are body cells that are programmed to unwind back into an embryonic state. Like embryonic stem cells, they have potential to develop into any other type of cell in the body.

But they don’t reprogram perfectly, researchers are finding. About a month ago, a team at the Salk Institute showed that iPS cells hold on to “memory” of their past identity.

The papers released last week show that the processes through which iPS cells are reprogrammed also can create significant abnormalities in the DNA itself – places where the cells’ basic genetic blueprint is altered.

Such reprogramming errors could affect the cells’ usefulness in the future, the authors wrote.

“These mutations could alter the properties of the stem cells, affecting their applications in studying degenerative conditions and screening for drugs to treat diseases,” said co-author Dr. Andras Nagy of the Samuel Lunenfeld Research Institute in Toronto.

Nagy said the discovery of the mutations also had “important implications” for the use of iPS cells in medical therapies.

Researcher Kun Zhang of the University of San Diego, a co-author on the other paper, referred to abnormalities as “permanent genome scars.”

The teams suggested that iPS cells should undergo careful genetic screening before they’re used.

Scientists have held out great hope for iPS cells. Because they aren’t generated from embryos, they don’t present the same ethical concerns as ES cells. Also, because they can be generated from a patient’s own cells, it is thought that iPS cells won’t pose the risk of rejection that tissues created out of embryonic stem cells do.