Dolly clouds cloning hopes

The push to develop commercially viable cloned animals as a source of organs for human transplants ratcheted up another success last month, but veteran Dolly, the cloned sheep has raised some doubts about the wider issues of cloning. Two teams produced piglets cloned from adult cells in which a copy of a gene controlling production of a particular cellsurface sugar had been knocked out. Shortly before publication in Science of details about one group of piglets produced in the autumn by a team at the University of Missouri in collaboration with scientists at Immerge BioTherapeutics in Charlestown, Massachusetts, PPL Therapeutics, based near Edinburgh, announced to the media the birth of its knock-out piglets on Christmas Day. Humans do not produce this sugar which leads to rapid rejection if organs containing it are transplanted into humans. Pigs are the most promising species for organ transplants because they are physiologically quite similar to humans. But progress has been slow because of fears new viruses may be transmitted from pigs to humans in a transplanted organ, and the rapid rejection of any pig organ. Earlier work has produced transgenic pigs that produce proteins that can protect the organs from some immune attack. But the latest work involved knocking out the gene for galactosyl-transferase needed to make the sugar. The new cloned piglets have one copy of the gene disrupted but can still make the sugar with the other copy of the gene. Conventional breeding is likely to used to create a double knock-out that should not produce any of the sugar and so News focus