Research reported this week by three different groups shows that normal skin cells can be reprogrammed to an embryonic state in mice. In theory, embryonic stem cells can propagate themselves indefinitely and are able to become any type of cell in the body. But so far, the only way to obtain embryonic stem cells involves destroying an embryo, and to get a genetic match for a patient would mean, in effect, cloning that person — all of which raise difficult ethical questions. As well as having potential ethical difficulties, the ‘cloning’ procedure is technically difficult. It involves obtaining unfertilized eggs, replacing their genetic material with that from an adult cell and then forcing the cell to divide to create an early-stage embryo, from which the stem cells can be harvested. Those barriers may have now been broken down.
Last year, Yamanaka introduced a system that uses mouse fibroblasts, a common cell type that can easily be harvested from skin, instead of eggs. Four genes, which code for four specific proteins known as transcription factors, are transferred into the cells using retroviruses. The proteins trigger the expression of other genes that lead the cells to become pluripotent, meaning that they could potentially become any of the body’s cells. Yamanaka calls them induced pluripotent stem cells (iPS cells). “It’s easy. There’s no trick, no magic,” says Yamanaka.