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Clones in the Pig Pen

By Sean Henahan, Access Excellence

piggy cloneWashington, DC (8/18/00)- Cloned pigs are the latest arrival in the biotech barnyard. This could be a step towards creating a ready supply of genetically engineered organs for rejection-free transplantation into humans. And, ethicists warn, it could be a another step towards the cloning of humans.

The scientists used a slightly different approach than that used to produce the famous Dolly sheep clone.Xena, a female piglet, was cloned by microinjecting genetic material from fetal pig skin cells into eggs lacking their own genetic material. A needle-like pipette used in the microinjection works like a tiny gun or drill, firing into the egg in a controlled and rapid motion.

Right: Xena, a healthy black piglet with her surrogate mother.

This method, sometimes known as the Honolulu technique is based on one reported two years ago by Teruhiko Wakayama and colleagues at the University of Honolulu to successfully clone mice. That experiment produced the first male mammal clone.

The researchers believe that the quick and clean insertion technique used in this case may be key to Xena's successful birth. The method transfers only the genetic material from the fetal donor cell. By comparison, the method used to clone Dolly fuses together the entire donor cell containing the genetic material and the empty egg.

"With microinjection, you can be quite selective about the genetic transfer," says Anthony C.F. Perry of the Rockefeller University. "You can separate the chromosomes out, and avoid contaminating the egg with the rest of the material from the donor cell nucleus."

Xena cloned from the genetic material of a black pig may have come as a surprise to he pink-white surrogate mother. Subsequent genetic testing confirmed what appeared to be obvious, that Xena was indeed a clone, with no genetic input from the host animal.

Organ Debate

Pigs have sometimes been considered the ideal animal for xenotransplnation because their organs are very similar in size and function to human organs. The cloning of Xena is being touted as a step towards producing organs for xenotransplantation, that is, from one species to another. Researchers believe it will be possible to modify the genome of cloned pigs so that they produce organs that would not be rejected by the human immune system.

By making these alterations at the genetic level in the cells used to create clones, "it may some day be possible to obtain a supply of pigs with organs suitable for human transplant," says Akira Onishi of the National Institute of Animal Industry in Japan.

However, the announcement of the new cloning achievement comes at a time when many scientists are backing away from the idea of xenotransplnation of any type, out of concern for the potential transmission of unknown viruses from pigs and other animals to humans. In fact, a recent study in the journal in Nature reported that mice receiving pig tissue transplants did become infected with a swine virus

More likely perhaps, the new cloning technique could prove a boon to the swine industry. The cloning approach would allow virtually unlimited production of favorite breeds for meat production and breeding stock.

Ethical watchdogs note that the new development also appears to be another step closer to human cloning, since the same technique may prove equally successful in humans. Indeed, a group calling itself Clonaid:announced it is ready to set up a laboratory and proceed toward the last steps to generate the first human embryonic clone. Also, the same week the current research appeared, the British government announced it was considering relaxing its strict prohibition against human embryo stem cell research.

Chief Medical Officer Professor Liam Donaldson said: "Stem cell research opens up a new medical frontier. It offers enormous potential for new treatments of chronic diseases and injuries, and the relief of human suffering. Our report offers a way to ensure that this potential can be fully explored, whilst ensuring full and rigorous safeguards. In particular reproductive cloning - the cloning of individuals - will remain banned in the UK."

Currently in the US, researchers can do human stem cell research, but only if no federal funding is involved.

The pig clone research appears in the 18 August '00 issue of Science.


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