Scientists have been able to turn back the clock in human adult cells and cause them to revert almost to the state in which they are found in embryos, called stem cells. If the technique is perfected, it may someday mean that stem cells are available for medical therapy without the need for cloning or the destruction of embryos to get them.
Harvard University scientists have created human embryonic stem cells from adult cells by using a technique that had been shown before only with mouse tissue. Researcher Kevin Eggan and colleagues fused individual adult skin and bone cells to embryonic stem cells, genetically reprogramming the adult cells so that they developed the characteristics of the stem cells. "We have carried this out with human cells for the first time, set back the clock on an adult cell to an embryonic state. In the cell hybrids that we make, the embryonic state completely dominates the adult state," he said.
Embryonic stem cells are immature ones that can become any kind of tissue in a developing fetus. They are important to medicine because researchers are learning if injecting these cells into sick people will allow them to take over from diseased cells in a variety of conditions and restore the functions of ailing systems.
Kevin Eggan says the researchers knew their cell fusion technique worked when they saw that the hybrids had characteristics of stem cells. "We saw little colonies of cells that were growing that looked a lot like embryonic stem cells. We then went on to do experiments and showed that their state had really been transformed to an embryonic state," he said.
As the researchers explain in the journal "Science," some of the tests demonstrated that the reprogrammed cells could actually be induced to mature into nerve cells, hair follicles, and muscle and gut cells.
The new technique could eventually permit scientists to create new stem cell lines without using human eggs or destroying human embryos as a source, a controversial issue in the United States and elsewhere. U.S. law bans the use of government money for this kind of research, although legislation is pending in Congress to overturn this ban. President Bush threatens to veto such a law, but it is gaining support among many of his partisans because they consider the research a way toward promising new treatments.
The Harvard scientists emphasize that the cell fusion method is far from developed enough to replace the use of embryos and that obstacles remain before it can be used. Most importantly, the fused cells remain hybrids with two sets of genes, those of the adult and the embryo. Some method has to be developed to remove the embryonic DNA so that the remaining genes will match the adult donor for whom the stem cell therapy is being tailored to prevent his immune system from rejecting it.
The researchers say they hope to learn how an adult cell switches to an embryonic state so that it can be induced to do so without fusion to a stem cell taken from an embryo.