Researchers at the Max Planck Institute for Molecular Biomedicine in Münster, Germany, have broken new ground by reprogramming skin cells from mice into neurons without regressing the cells through a pluripotent stage. The skin cells were reprogrammed directly into multipotent neuronal stem cells - that is, into cells which could only turn into new neurons. This procedure avoids the significant risk that pluripotent stem cells, which can grow into any type of tissue, may accidentally form tumors rather than the desired replacement tissue.

One major theme of stem cell research has been the reprogramming of ordinary cells in the body into pluripotent stem cells. These are cells that, given the right environmental clues, can differentiate into any tissue within the body. This flexibility limits the application of pluripotent stem cells for many potential therapeutic uses, as some portion may grow into undesired tissue types.

Hans Schöler and his research team have succeeded in reprogramming skin cells into stem cells which are multipotent, rather than pluripotent. Such stem cells cannot give rise to all cell types, but only to a select subset, which usually share a common role within the body. In the study reported here, the multipotent stem cells can only grow into various types of neuronal tissue.

A growth factor was found that very effectively guided skin cells toward conversion into neuronal somatic stem cells. As the reprogrammed cells divide, they gradually lose their molecular memory (residual structures) and forget that they were once skin cells. After a few cycles of cell division (stimulated by growth factors and media), the new stem cells are practically indistinguishable from normal stem cells.

The ability to use multipotent stem cells for regeneration or replacement of damaged or diseased tissues dramatically reduces the risk of cancer, which is a significant risk when using pluripotent stem cells. The new therapeutic approach still must be reproduced using human cells, and questions remain about the long-term stability of the identity of the newly reprogrammed tissues, but Schöler feels the approach offers substantial potential for new and highly effective medical treatments, given the appropriate political climate.

"The blueprints for this framework are all prepped and ready to go - all we need now are for the right political measures to be ratified to pave the way towards medical applicability," he said.