Cell success has huge potential

US scientists are claiming a major breakthrough that could lead to a limitless supply of human tissue for transplantation.

For the first time, they have managed to isolate and grow indefinitely in the laboratory human embryonic stem cells. These are the parent cells for all the tissues in the body.

The potential of these unique, versatile cells for human biologic studies and medicine is enormous

Prof John Gearhart

If the way these cells subsequently differentiate can be controlled and directed, it opens the door to growing from scratch everything from heart muscle to bone marrow and brain tissue. The scientists say their work, which has been in progress for more than 15 years, has profound implications for medicine.

They believe the cultured cells will give pharmaceutical companies new ways to test the effectiveness and safety of drugs. The cells should also tell us far more about how life develops in those crucial first few days and weeks after fertilisation, leading to new fertility treatments and giving us a greater understanding of birth defects.

Although embryonic stem cells have been derived from mice and other animals they have never been isolated and cultured from humans before.

Two separate American teams have announced the breakthrough. Dr James Thomson and colleagues at the University of Wisconsin-Madison have published their research in the journal Science.

Professor John Gearhart and his Johns Hopkins group have reported their findings in this month's Proceedings of the National Academy of Sciences.

Different techniques

The two teams have used slightly different techniques. Wisconsin took their cells from blastocysts - balls of about 140 cells that develop just a few days after fertilisation. The embryos from which the blastocysts developed were originally produced as part of an infertility treatment programme.

The Johns Hopkins group used what they call primordial germ cells taken from small samples of non-living, human foetal tissue - cells that eventually would have become eggs and sperm.

Human embryonic stem cells in different stages of development (Wisconsin-Madison)

The success of both teams depended on the methods used to culture the cells in the laboratory. Given the right conditions, the cells will proliferate indefinitely.

Both groups say they were able to watch the cells differentiate into the three primary germ lines that make up the body - endoderm, ectoderm and mesoderm - and from there to an array of different tissues.

"The gold standard," says Dr Michael Shambolt from the Johns Hopkins team, "was seeing if the cells have true potential - if they'd develop into the three basic layers of cells found in all mammalian embryos. And ours did."

The Geron Corporation, a biotechnology company that helped fund both sets of scientists, is now patenting the technologies.

"The potential of these unique, versatile cells for human biologic studies and medicine is enormous," says Professor John Gearhart.

"These cells will rapidly let us study human processes in a way we couldn't before. Instead of having to rely on mice or other substitutes for human tissues, we'll have a unique resource that we can start applying to medicine."

Further research

The scientists warn that many of the most exciting applications are still years, even decades, away. "Although a great deal of basic research needs to be done before these cells can lead to human therapies, I believe that in the long run they will revolutionise many aspects of transplantation medicine," says Dr James Thomson.

Confidence is high after animal work in which heart muscle cells derived from mouse embryonic stem cells were injected into - and successfully integrated with - the heart muscle of adult mice.

The stem cells differentiate into different cell types: (A) gut (B) neural (C) bone marrow (D) cartilage (E) muscle (F) kidney

This sort of research now needs to be developed and extended to human cells. It raises the prospect of transplantation being used to treat a wide range of cell-based diseases such as juvenile onset diabetes and Parkinson's disease which occur because of defects in one of just a few cell types.

Professor Gearhart said: "Not only should scientists be able to generate specific nerve, muscle, skin or other cells for transplantation, but we should also be able to alter these cells, as has been done in mouse studies, to reduce the likelihood of rejection.

"We could make universal donors. More specific cells could become transplant therapies for diabetes, spinal cord injury, neurodegenerative disorders like Parkinson's disease, muscular dystrophies, atherosclerosis and wound healing."