What are embryonic stem cells?

They are cells found exclusively in early-stage embryos, from which all the body’s 200-plus types of tissue ultimately grow. They are the body’s master cells. They were first isolated from animal embryos by a British scientist, Sir Martin Evans, in 1981. The first human embryonic stem cells were derived in 1998 by an American team led by Jamie Thomson

Why do they excite scientists?

Their incredible versatility means they have the potential to provide replacement tissue to treat all manner of disorders, including Parkinson’s disease and diabetes

Why are they controversial?

The process of extracting embryonic stem cells generally requires embryos to be destroyed. This is opposed by those who believe embryos have the same right to life as people

Where do the embryos come from? How many are needed?

The embryos used by Geron were given by IVF patients who had some left over after treatment. Some embryos are also created especially for research and stem cells are generally extracted after five days’ growth. As embryonic stem cells divide indefinitely, a single embryo could provide the raw material for a colony or “line” of cells for use in treatment. Not every embryo produces a viable line so dozens are needed. Tissue from aborted foetuses is not used in embryonic stem-cell research, though it is used in other approaches to stem-cell medicine.

Are there any alternatives?

Many types of adult stem cell are being used in medical therapies: last year scientists reported the transplant of a whole organ, a section of windpipe, grown from these. Adult stem cells, however, are partially specialised, and so cannot provide every kind of tissue.

Another option is to reprogramme adult skin cells by manipulating genes, so they acquire the versatile properties of embryonic stem cells. These “induced pluripotent” stem cells have great potential, but many hurdles remain before they are ready for human trials

Isn’t embryonic stem-cell research banned in the US?

No: this is a common misconception. President Bush banned the use of federal funds for most embryonic stem-cell research in 2001, but private funding is not restricted. Federally funded scientists can also use lines of embryonic stem cells created before 2001

What does President Obama think?

He plans to lift the restrictions (so did John McCain). As the Bush policy was imposed by executive order, President Obama could end it immediately. If he were to wait for Congress formally to approve the work, that would also deal with the Dickey-Wicker Amendment, which bans public spending on research that destroys human embryos

What’s the position in Britain?

Embryonic stem-cell research is legal, provided experiments are licensed by the Human Fertilisation and Embryology Authority. Several academic and commercial groups are pursuing it, though none is anything like as close as Geron to clinical trials

What does the Geron therapy involve?

The company has used embryonic stem cells to produce large stocks of a specialised kind of cell called oligodendrocyte precursor cells, which stimulate the growth of nerve cells in the spine, and produce myelin, which protects the nerves and is critical to their activity. The OPCs are injected to the spine at the site of the injury, to promote nerve recovery

What happens now?

The Geron trial will start recruiting patients who have recently suffered spinal cord injuries. Between 7 and 14 days after their injuries, their spines will be injected with OPC cells. The main purpose of the trial is to monitor safety, but scientists will also start assessing its effectiveness

When might a therapy be available more widely?

If all goes well, clinical trials generally take four to five years from the start of safety tests on volunteers to the licensing of drugs for widespread use

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