A region of DNA that can boost the growth of stem cells has been found in the largest ever study of human embryonic stem cells. The discovery could lead to safer cell therapies, says study co-author Dr Andrew Laslett from CSIRO Materials Science and Engineering. The research by the International Stem Cell Initiative involved 38 laboratories across the globe studying 125 ethnically diverse cell lines in parallel experiments.

Study findings, reported in today's issue of Nature Biotechnology , uncover changes that arise from how cells are grown. Embryonic stem cells are powerful for their ability to become any other cell in the body. Stem cell therapy, which is entering early-stage human trials, turns stem cells into other cell types, like healthy nerve cells, to treat spinal cord injury, blindness and other ailments.

The cells need to be grown in nutritious culture to produce enough cells for therapy. Many stem cells die when they are first moved to a new culture, leading to natural selection and adaptation. Cells with a growth advantage expand faster and dominate. However, this can come at the price of genetic mutation, so growing fast is not always desirable. "It's the small fraction of cells that become abnormal that can be dangerous in a clinical situation," says Laslett. "If they find growth situations that suit them, they could grow into cancers."