Scientists have succeeded in generating new stem cells in living mice and say their success opens up possibilities for the regeneration of damaged tissue in people with conditions ranging from heart failure to spinal cord injury.
The researchers used the same "recipe" of growth-boosting ingredients normally used for making stem cells in a petri dish, but introduced them instead into living laboratory mice and found they were able to create so-called reprogrammed induced pluripotent stem cells (iPS cells).
"This opens up new possibilities in regenerative medicine," said Manuel Serrano, who led the study at the Spanish National Cancer Research Centre in Madrid.
Stem cell experts who were not directly involved in the study said its success was exciting, but noted that the technique as it stands could not be used in humans since the reprogrammed cells also lead to tumours forming in the mice.
"Clearly nobody wishes to do this for therapeutic purposes because this leads to the formation of tumours called teratomas," said Ilaria Bellantuono, a reader in Stem Cell and Skeletal Ageing at Britain's University of Sheffield.
But she added that Serrano's work was a "a proof of concept" that opened up the opportunity to investigate ways to partially reprogram cells in the body up to a certain stage.
"In principle, these partially dedifferentiated cells could then be induced to differentiate to the cell type of choice inducing regeneration in vivo without the need of transplantation," she said.
Stem cells are the body's master cells and are able to differentiate into all other types of cells. Scientists say that by helping to regenerate tissue, they could offer new ways of treating diseases for which there are currently no treatments - including heart disease, Parkinson's and stroke.
There are two main types of stem cells - embryonic stem cells, harvested from embryos, and adult or iPS cells, cells taken from skin or blood and reprogrammed back into stem cells.
Serrano, who spoke to reporters in a briefing ahead of his study's publication in the journal Nature on Wednesday, said one of his most striking findings was that the iPS cells generated in the living mice seem to be more similar to embryonic stem cells than to iPS cells created in petri dishes.
Specifically, he said, the iPS cells reprogrammed in living mice showed the potential to differentiate into more cell types than standard iPS cells or embryonic stem cells - suggesting that reprogramming cells in a living mammal produces cells with greater potential, or what scientists call more plasticity.
Chris Mason, a professor of regenerative medicine at University College London, said he had no doubt that being able to reprogram cells in the body to different cell types would be useful in producing future therapies capable of transforming patients' lives, but said there were many more years of research ahead before that would be possible.
"The cells that will be useful will not be the pluripotent stem cells (iPS cells), but their more specialised ('adult') offspring," he said.
"This.. is an interesting proof of concept of the first step in the process, but it still needs these iPS cells to be safely converted to useful 'adult' cell types in the body."
He said the major challenge in this potential approach to treating patients in the future would be tightly controlling every step of the process to make sure it delivered benefits while also avoiding complications.