Pig cloning breakthrough but virus fears may delay organ transplants

Two independent groups of scientists announced new techniques that enabled them to create the first cloned pigs. They hope their work will lead to the use of pig organs in human transplant operations.

Two independent groups of scientists announced new techniques that enabled them to create the first cloned pigs. They hope their work will lead to the use of pig organs in human transplant operations.

But a third team said that it had found more evidence of pig viruses being able to infect human cells, which could sabotage attempts at pig-human transplants.

British scientists led by Alan Colman of PPL Therapeutics, the company spun out of research at the Roslin Institute, Edinburgh, where Dolly the sheep was cloned, used a "double nuclear transfer" to produce a litter of five pigs from the skin cells of an adult animal.

The research, to have been published in Nature magazine but released early in the light of a rival study due to appear in the journal Science, increases the possibility of being able to produce genetically engineered pig organs that would not be rejected in a human transplant.

But Daniel Salomon, of the Scripps Institute, in California, found more evidence that porcine endogenous retroviruses, which lurk in the genetic material of pigs, can pass into human cells. The discovery raises further concern that transplanting pig organs into people might introduce infectious agents from animals into the human population.

The PPL team transferred a cell nucleus into an unfertilised egg cell and allowed it to "incubate" before transplanting it again into a fertilised egg with its genetic material removed.

A rival approach by Japanese and United States researchers involves cutting out the nucleus of a skin cell of an adult pig and microinjecting it into an unfertilised egg with its own nucleus removed. Microinjection avoids having to fuse the entire donor cell with the empty unfertilised egg, as used to create Dolly, which is thought to be partly responsible for the failure until now to clone pigs.

Anthony Perry, of the Rockefeller University and a co-author of the study, said: "With microinjection you... can separate the chromosomes out and avoid contaminating the egg with the rest of the material from the donor-cell nucleus."

One piglet, named Xena after the process of animal transplants called xenotransplantation, was produced by the Japanese team after 110 attempts. PPL's litter of five was born on 4 March and Xena was born on 2 July. Both teams of researchers hope to alter the genetic make-up of pigs to trick the human immune system into accepting the animal organs without rejection.