Salk Institute scientist Joseph Ecker holds a flow cell slide used in a genome sequencing machine. Ecker and colleagues compared the genomes of two kinds of artificial embryonic stem cells for a study comparing their quality.

In a setback for hopes of therapy with a promising kind of artificial embryonic stem cells, a study published in the journal Nature has found that these "induced pluripotent stem cells" have serious quality issues.

However, scientists who performed the study, including researchers from the Salk Institute and UC San Diego, say it should be possible to improve the quality of these IPS cells. They say lessons can be learned from studying a newer technique of making human embryonic stem cells through nuclear transfer, the same technology used to create Dolly the cloned sheep.

In addition, the study does not prove that the quality problems will affect therapy with the cells, said scientists who examined the study. That remains to be tested.

The IPS cells are made from skin cells treated with "reprogramming" factors that turn back the clock, so they very closely resemble embryonic stem cells. The hope is that these IPS cells could be differentiated into cells that can repair injuries or relieve diseases. Because they can be made from a patient's own cells, the cells are genetically matched, reducing worries of immune rejection.

In San Diego, scientists led by Jeanne Loring at The Scripps Research Institute have created IPS cells from the skin cells of Parkinson's disease patients, and turned the IPS cells into neurons that produce dopamine. They hope to get approval next year to implant these cells into the patients, relieving symptoms for many years. The project is online under the name Summit4StemCell.org.

A major concern is that IPS cells display abnormal patterns of gene activation and repression. This is controlled by a process called methylation. This process adds chemicals called methyl groups to DNA, but these "epigenetic" changes do not change the underlying DNA sequence. Methylation represses gene function; removing the methyl groups, or demethylation, activates them.

The Nature study was led by Shoukhrat Mitalipov of Oregon Health & Scence University. Mitalipov made headlines last year for applying nuclear transfer to derive human embryonic stem cells, the first time this has been achieved in human cells. These cells can be made to be a near-perfect genetic match to the patient, and their quality closely resembles those of true embryonic stem cells.

"We know that the embryonic stem cells are the gold standard, and we've been always trying to make patient-matched cells that would match the gold standard," Mitalipov said. "And at this point it looks like the NT (nuclear transfer) cells produce exactly those cells that would be best."

Nuclear transfer involves placing a nucleus from a skin cell into an egg cell that has had its nucleus removed. The cell is then stimulated, and starts dividing in the same way a fertilized egg cell divides to form an embryo.

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Artificial embryonic stem cells have quality problems: study