Human embryos no longer required ?
(November 23rd 2007) Two research groups reported that they have reprogrammed human somatic cells to pluripotent stem cells showing almost all features of embryonic stem cells. The public press, scientists and many politicians are celebrating these new findings as a breakthrough in the long search for an answer to ethical problems posed by the use of human embryonic stem cells. Is this the first step in reprogramming the whole stem cell research?
Last year, Shinya Yamanaka and his team from the University of Kyoto (Japan) stunned the scientific community by showing how normal fibroblasts from adult mice could be reprogrammed to behave like pluripotent stem cells. They introduced the genes Oct3/4, Sox2, c-Myc and Klf4 into mice cells and, subsequently, selected for expression of the stem cell marker NANOG. Now, the Japanese scientists have translated their work successfully onto human cells (
Cell 2007, doi:10.1016/j.cell.2007.11.019).
Simultaneously, James Thomson and his group at the University of Wisconsin in Madison, who first coaxed stem cells from human embryos back in 1998, have reported the genetic reprogramming of human skin cells. He set the c-Myc gene used by the Japanese scientists aside because in their experiments with mice, 20 per cent of the transgenic animals developed tumours attributable to reactivation of the oncogene. Thomson and his colleagues obtained the so-called induced pluripotent stem (iPS) cells by retroviral mediated transduction of lung cells from aborted embryos and foreskin cells from a newborn boy (Science, 22 November 2007, doi: 10.1126/science.1151526). In both studies the iPS cells carried similar surface markers as embryonic stem cells and they show an almost identical behaviour in cell cultures.
What do these experiments tell us? If one could reprogram adult cells to a pluripotent status much of the research on human embryonic stem cells would become redundant. Are thousands of stem cell researchers going to become jobless?
Hans Schoeler from the Max Planck Institute for Molecular Biomedicine in Muenster (Germany) wrote in a commentary in Cell, “However, a big mistake now would be to consider human ES cells obsolete. There are still many hurdles to overcome before we fully understand pluripotency and before we have human iPS cells in hand that are suitable for therapeutic application.” (Do we already have embryonic stem cells suitable for therapies?)
Cloning pioneer Ian Wilmut already announced that he's about to stop all experiments on cloning human embryonic stem cells.
Anyway, the two reports are promising and perhaps really pave a way to introduce stem cells in science and therapy without using human embryos. The search is now on to find a way to reprogram somatic cells without retroviruses and to shed light on how iPS cells can be manipulated to either maintain them in their pluripotent state or to differentiate them into a cell lineage of interest. There is much work to be done and we're awaiting rapid progress in this fascinating field of science.
Karin Hollricher
