Reports that scientists in South Korea have succeeded in cloning a human embryo using human cells have been challenged by British cloning experts. A team of researchers at an infertility clinic in Kyunghee University Hospital, Seoul, claimed they had cultivated a human embryo in its early stages using an unfertilised egg and a somatic cell - those which make up most of the body - donated by a woman in her 30s.
They had destroyed the cloned embryo, developed using a technique devised by the University of Hawaii which earlier this year successfully cloned several generations of mice from a single adult female. They aborted the experiment within days, after last seeing the human embryo divide into four cells.
Experts from the Roslin Institute in Scotland, where Dolly the sheep was cloned, insisted however that the South Korean work failed to show that the embryo was genuine and viable. "We do not believe the Korean group has sufficient scientific evidence to back its claim," Dr Harry Griffin told the London Independent.
A fertilised human egg in its earliest form goes through its first three cell divisions on "autopilot". It is only after the eight-cell point, i.e. after the embryo has divided three times, that the nucleus of the cells takes control of further embryo development. Therefore, the key factor in showing the experiment had produced a genuine viable clone was to determine whether the egg cell's new nucleus really was in control of the cell. By stopping when they did, there was no evidence that the transferred nucleus had been successfully reprogrammed.
The challenge to the breakthrough comes as one of Germany's leading research institutes suggested that a significant development on the related technique of transplanting organs from animals to humans, known as xenotransplantation, might take a lot longer than many had predicted.
THE lives of some 40,000 people are saved every year by organ transplant procedures. There are three times as many on waiting lists because of the scarcity of donor organs. Xenotransplantation promises a solution.
Most work needs to be concentrated on solving organ rejection problems; overcoming physiological differences between parts generated in the "animal spare parts depot" and their human equivalent, and in reducing the risk of infection, according to the FraunhoferGesellschaft. In a study commissioned by the Swiss Science Council, it found a greater risk of organ rejection between animals and humans.
Attempts to solve this problem by means of genetic modification of the animals have raised further problems, according to Dr Barbel Husing. "In our view, xenotransplantation is an extremely complex procedure with uncertain chances of success. It will take another 15 to 20 years before widespread application is viable."
