Five cloned pigs born

Five pigs cloned using nuclear transfer technology - the 'Dolly technique' - were born on 5 March, announced UK firm PPL Therapeutics last week. Genetic tests have proved that the pigs, called Millie, Christa, Alexis, Carrel and Dotcom - are all genetically identical to an adult female pig.

The scientists say they now hope to use genetic modification (GM) to develop pig organs for human transplants. 'An end to the chronic organ shortage is in sight' said Ron James, managing director of PPL. But the UK Xenotransplantation Interim Regulatory Authority (UKXIRA) is still considering the safety of the technique, including the possibility that pig viruses may be transferred to humans.

PPL has already produced GM sheep that have human genes added. The proteins produced by this type of sheep 'pharming' will eventually be used for treating human illnesses. 'What cloning allows us to do for the first time is switch genes off as well', said Ron James, head of PPL. The next step in developing genetically altered pigs that have 'humanised' organs is to switch off a gene called alpha 1-3 gal transferase, which is involved in the rejection of pig tissue by the human body. Cloning will also give the PPL scientists a 'flying start' in their attempts to create a colony of genetically altered pigs.

Cloning pigs has proved a technical challenge, partly because pigs need more than one healthy fetus to sustain a healthy pregnancy. Ultrasound scans originally led PPL scientists to expect a litter of three or four cloned piglets - the fifth was a 'bit of a surprise'.

Pigs now join cattle, sheep and mice on the list of successfully cloned adult mammals. However, Dr. James stresses that the breakthrough does not bring human cloning any closer. 'We should take comfort from the fact that nobody has even tried' he said.