Cloning's ups and downs. (Biomedicine).

There's been good news and bad news about cloning of late. On the worrisome side, one of the creators of Dolly, the world's first cloned mammal, report that the nearly 6-year-old sheep has developed arthritis in her left hip and knees. That's early for a sheep to show such a malady, and the report renews concern that cloning may accelerate aging (SN: 4/29/00, p. 279).

There's no way to confirm that the arthritis is attributable to cloning, cautions Ian Wilmut, one of Dolly's cloners at the Roslin Institute in Edinburgh. Still, he calls upon other cloners to monitor the long-term health of their animals.

Now the good news: In an advance that one day may help people needing transplants, two biotech firms have turned to cloning in their attempt to create pigs with organs that human bodies won't reject. Using nonhuman organs such as pig hearts and kidneys in people is the basis of a controversial strategy known as xenotransplantation.

One barrier to this approach has been that pig cells sport a sugar molecule foreign to the human body, so a person's immune system would quickly reject the animal tissue. To overcome this, scientists have struggled to create pigs in which the gene for the enzyme that makes the sugar doesn't work.

In the Jan. 4 SCIENCE, investigators from Immerge BioTherapeutics in Charlestown, Mass., and the University of Missouri in Columbia report disabling one copy of the gene in pig cells and using the cells to clone a litter of piglets bearing the nonworking gene. Since pigs have two copies of the gene, the scientists now are interbreeding the litter to create swine with both genes deactivated. Meanwhile, PPL Therapeutics, the Scottish company that funded Dolly's creation, has announced that it also has cloned pigs with one disabled copy of the gene. --J.T.