The study was published in the Sept. 4 issue of Nature Genetics and reported in the press by CanWest. According to a team of scientists at John Hopkins University, led by Aravinda Chakravarti, the mutations are so serious that the cells will have to be carefully monitored and screened before being used to treat people.

The team compared the “genetic health” of different cell lines, which had been started at different times and which included some of the first cell lines created in 1998. They found that the more divisions the cells had undergone, the more mutations they had. The scientists described the mutations as those “commonly observed in human cancers.”

While previous studies suggested mutations were rare, CanWest reports that the new suggests claims that a steady supply of new cell lines will be needed to replace the old cell lines due to the mutations that occur when the cells divide.

This discovery may pose a dilemma for long-term embryonic stem-cell research and therapy in the United States, where President George W. Bush announced in 2001 that the government would only fund research on already existing stem-cell lines.