Mutations in Human Embryonic Stem Cell Lines
In 2001, President Bush approved a limited number of existing human embryonic stem cell lines (hESC) for federally funded research. From over 60 genetically distinct stem cell lines, only 22 are available today. Using DNA microarray, scientists at Johns Hopkins School of Medicine and the NIH report in Nature Genetics that eight of the stem cell lines approved have mutated.
Mutations occur all the time as cells grow, but inside the body, mutated cells with harmful effects are often cleared out by the immune system, whereas in the laboratory culture dish — where there is no immune system — mutated cells can grow uncontrolled like a cancer. Over time, any cell line grown in the laboratory — including stem cells — can develop mutations that are compounded over many generations. The danger is that scientists may think they are studying stem cells identical to those present in the human body, but in reality the laboratory-grown cells have mutated, and any discoveries may not accurately reflect what is happening in people.
Three different methods were used to detect the mutations in the genomes of early generation and late generation cells.
- Five of the nine embryonic stem cell lines they studied were missing genes or had too many copies of certain genes. These mutations are called “copy number changes.”
- Two of the nine cell lines had developed mutations in their mitochondrial DNA.
- An examination of 14 specific genes found that all nine stem cell lines had developed chemical modifications of their DNA — called methylation — in at least one of three genes.
This is bad news for U.S. scientists who are trying to compete against countries which have no restrictions on stem cell research.
Genetic Engineering News, September 4, 2005
