Regenerative medicine spoilt for choice

Only ten years ago, 'stem cells' was a buzz word for all kinds of anticipated miracle cures, following the first production of human embryonic stem (ES) cell lines from blastocysts (early stage embryos) in 1998. As embryonic stem cells are pluripotent, they can generate the specialised cells for any kind of organ or tissue that one may want to create or repair, given the right enticement. While some countries, such as Germany, had qualms about the use of blastocysts discarded after IVF, others, including the UK, took the pragmatic view that these would have been destroyed anyway and took the lead in a rapidly growing and promising field. Then, in 2006, Shinya Yamanaka showed that a cocktail of only four factors suffices to turn back the clock of embryonic development and turn a differentiated somatic cell into a pluripotent one, which came to be known as an induced pluripotent stem (iPS) cell. Earlier on, the cloning of Dolly the sheep had demonstrated that the clock can be turned back in a cellular environment, but the finding that researchers can achieve this in vitro with a relatively simple protocol came as a surprise. The bad news was that one of the factors was a known oncogene. While this factor could be eliminated eventually, it drew attention to the more fundamental problem that pluripotency includes the potential for the cells to become malignant. Recently, a third option came onto the scene, when direct conversion of one cell type into another was demonstrated first for mouse and then for human cells. Although the rules are still being established, this so called transdifferentiation appears to be possible even between completely unrelated cell types, without having to go via pluripotent cells. The magic of transdifferentiation In February 2010, the group of Marius Wernig at Stanford reported the rapid and efficient conversion of mouse fibroblasts (a cell type found in connective tissue, which is also used for the production of iPS cells) into functional neurons They achieved the conversion by inducing only three transcription factors specific for the targeted cell type. This was the first conversion between unrelated cell lineages — previous efforts had shown that one type of blood cell Feature can be converted into another, and different types of neurons, as well as pancreatic cell types, can be interconverted. a similar transdifferentiation success with human cells. This group had managed to convert human fibroblasts …