U.S. researchers announced Thursday they have developed a method for generating "induced pluripotent stem cells" (iPS cells) without the side effects.

The new finding, appearing in the Sept. 26 issue of Science, demonstrates that iPS cells can be grown using viruses that do not integrate themselves into the hosts' genome, bypassing a problem that has undermined the success of previous iPS cells.

In the past, scientists have grown iPS cells that resemble embryonic stem cells, but the process, which involves introduction of particular DNA-binding proteins to cells via potentially harmful viruses, often altered the cells' genomes and caused tumors in animals.

The new method can generate iPs cells without the permanent genetic damage previously associated with their design, and it represents a major step forward in the future application of iPS cells in a clinical setting, said Science.

Matthias Stadtfeld from Massachusetts General Hospital and colleagues grew their iPS cells, which show potential for growing into a variety of other specialized cells including lung, brain, and heart cells, and they say that they have not observed any unwanted side effects yet.

In the past, similar reprogrammed cells have been shown to alleviate the symptoms of Parkinson's disease and sickle cell anemia in mouse models, so this new discovery could lead to advances in cell therapy and treatments of human disease as well, Science commented.

However, the researchers say that it will be important to determine if human iPS cells generated in the future by this method are as potent as human embryonic stem cells for potential clinical applications.