Completely fresh supplies of human embryonic stem cells have been created for the first time without having to grow them on potentially contaminating mouse "feeder" cells. Nor do they need to be nourished with serum derived from animals.
The breakthrough boosts the prospects of growing safe tissues for transplant from embryonic stem cells - the unspecialised, primitive cells in the embryo from which all tissues originate.
"The ability to generate new stem cell lines in completely [mouse-]cell-free and serum-free conditions solves a major problem associated with the use of stem cells in the treatment of human medical conditions," says Bob Lanza of Advanced Cell Technology (ACT), the company in Worcester, Massachusetts, US, which pioneered the new production system.
Recent experiments showed that all lines of human embryonic stem cells grown on a scaffolding of mouse feeder cells may be potentially contaminated with animal substances and therefore unsafe for treatment. This includes the cell lines approved by President George W Bush in 2001, which federally-funded US scientists are restricted to use.
Now, the option of dispensing with mouse feeder cells and animal serum could at last generate stem cells safe enough for therapy.
However, although the fresh stem cells were not grown on feeder cells, there is still a risk of contamination because they were raised on coatings of animal origin. But ACT says that making the same coatings entirely from the corresponding human ingredients is now a formality.
"We're now working on lines which will be completely human," says Bob Lanza, ACT's president of scientific development. "There's nothing in the animal layer that can't be replaced with a human equivalent."
He says that although several groups of researchers now grow their human embryonic stem cells on human instead of mouse feeder cells, there is still the possibility that harmful viruses can lurk in the human feeder cells and pass into the stem cells.
By dispensing completely with feeder cells - whether human or animal - ACT's system gets round this once and for all, he says.
Firstly, he and his colleagues created the coating on which the stem cells would grow. To do this, they grew mouse feeder cells, then washed them away to leave an "extracellular matrix" - a natural coating of material which had accumulated around the growing cells. The matrix contains substances such as growth factors and nutrients which support the growth of any living cells deposited on the coating. Once sterilised of any living matter, the coating was ready to support the growth of stem cells.
To obtain human stem cells, Lanza first procured donated human embryos left over from infertility treatments. By "feeding" the embryo with specific ingredients usually found in animal serum, Lanza produced a blastocyst, a ball of cells containing a precious "inner cell mass" of stem cells.
After physically extracting the stem cells, Lanza's team transferred them into a dish containing the extracellular matrix, and they started multiplying indefinitely.
"This is a terrific breakthrough in the development of defined cultures for stem cell isolation, which is of critical importance to the safety and efficacy of embryo stem cell technology," says Paul De Sousa, a stem cell researcher at the Roslin Institute in Edinburgh, UK.
Journal reference: The Lancet (early online publication)
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