The announcement that South Korean scientists have successfully cloned human embryos and extracted stem cells from them represents a promising step forward, writes Richard Gardner.
Most research on embryonic stem cells at the moment is being done using spare embryos from in vitro fertilisation. If these stem cells were eventually used to treat patients, they would run the same risks of rejection that are such a big factor in organ and tissue transplants today.
The problem is that the stem cells would not be genetically compatible with those of the patient.
This is where cloning technology might hold a solution. If a cloned embryo was produced using the nucleus of a cell from a patient, the genetic make-up of the stem cells extracted from it would be almost identical to that of the cells in the patient's body.
Although some people have suggested that this might one day become a routine therapy, the process of cloning and cultivating stem cells to produce replacement tissues and organs would remain extremely difficult and time-consuming.
But therapeutic cloning may lead to even more useful advances. Ultimately, researchers would like to learn the secret of reprogramming the nucleus, since it is this that controls the cell.
We know that the process of cloning, in which a nucleus is transferred from an adult cell into an egg cell and an electrical current or chemical stimulation is applied, produces this reprogramming. The adult nucleus is reset and becomes the nucleus of a single-celled embryo.
If therapeutic cloning allows the secret of this reprogramming process to be unlocked, then potentially a whole range of medical leaps forward could be explored.
Could cells adjacent to the damaged part of an organ be reprogrammed to produce replacement cells, such as in spinal injuries? Could defective cells be reprogrammed to act normally, to tackle cancer for instance? The possibilities would be truly amazing.
Even if they can be realised, such possibilities are many years away.
More work, including further investigation of yesterday's results, is now needed. They may only have stimulated a process called parthenogenesis, in which an egg cell starts to undergo development, but without the involvement of the adult nucleus. In this case it would not be the adult nucleus in control, and the embryo would not be a true clone.
But we remain hopeful that they have truly taken the first steps towards successful therapeutic cloning. It is important that legislation and funding allows such research to continue, so that we might realise these possible great benefits to human health.
Prof Richard Gardner is chairman of the British Royal Society working group on stem cells and cloning.
- (Guardian Service)