Stem cells: Q & A

President Bush has announced that he will allow federal funds to be used for limited research into stem cells. What are the implications of this decision?

What are stem cells?

Stem cells are master cells that have the ability to develop into any of the body's tissue types, such as blood, liver, muscle and other cells.

Scientists hope that by growing such cells in the laboratory they can programme them to form specific tissue such as kidney, heart or even brain tissue.

This tissue could then be used to treat diseases such as Parkinson's, diabetes and Alzheimer's or perhaps provide an alternative to organ transplants.

Where do stem cells come from?

Stem cells can be extracted from human embryos obtained from fertility treatments or abortions.

Once isolated, the cells can be grown up in the laboratory and stored for future use. Each reservoir of cells, derived from a single embryo, is known as a cell line.

A more reliable supply, however, would be obtained by copying or cloning embryos specifically for their stem cells.

One embryo could, therefore, be a source for many thousands of cells.

This process, known as therapeutic cloning, is permitted in the UK but in many other countries, the rules are unclear.

In the United States, new legislation, which has yet to become law, will ban all human cloning including cloning for stem cell research.

What are the implications of President Bush's decision?

President Bush has decided to allow federal funds to be used for embryonic stem cell research, under strict limits.

Taxpayers' money can only be used for work on 60 stem cell lines that already exist - those that are stored in different laboratories around the world.

Federal funds cannot be used to pay for creating new stem cell lines because US law bars funding research that harms a human embryo.

However, some researchers have questioned whether 60 stem cell lines actually exist. Furthermore, since many of these cell lines are owned by private companies, federally funded scientists may not be able to use them.

What happens elsewhere?

Most countries do not have any laws on human embryo research or cloning but in Britain limited cloning for therapeutic purposes is allowed.

Japan has taken a step towards authorising research on stem cells taken from human embryos.

The decision by a bioethics panel is likely to be approved by the government later this month.

Strict guidelines would control researchers' work. They would not, for example, be allowed to use cloning techniques to create the stem cells.

The guidelines set out how embryonic cells can be used in scientific study. Only those cells retrieved from the discarded embryos made in fertility research will be deemed acceptable.

Japanese scientists would not be allowed to use cells that were "harvested" from embryos that had been made using cloning technology.

If final approval is given for the guidelines, scientists could probably start stem cell research by the end of the year.