proteins in the milk of sheep and other mammals by introducing one or two genes of human origin into the animal. This has since been developed into a wide set of potential medical applications. It is arguably the current leading example of genetic engineering in animals. The first protein to reach production by this means is alpha-1-anti-trypsin, which can counteract the lung damage found in emphysema and certain other diseases.The first stage of clinical trials began in 1996. Successful as this has been so far, the present methods of doing this genetic engineering are very inefficient, and by nature rather hit and miss. The manipulation takes place in the laboratory cell cultures, and the resulting modified embryos are put back in the recipient animal, but so far it has not been possible to know which ones have got the right modification until each lamb is born. It can take a lot of animals before you have got one with the right gene in the right place. You could modify many sets of cells, select the ones which had the right modification, but the problem has been, up till now that no one had a way of growing a live animal from those cells. Now Roslin and PPL have shown that you can grow a live sheep from cell cultures. This dramatic result opens the door to their next step - which will be to try it on genetically modified cells, to produce a genetically modified sheep, which has the modification in exactly the right place. If it works the method should allow a more precise manipulation with many less animals. Needless to say, careful scrutiny is needed, so that the only genetic manipulations this might be applied to would be ethically acceptable, but that is a question we already face. See our pages on The Ethics of Genetic Engineering? For more discussion of this issue. But the side effect of Roslin's growing a sheep from cells is that the resulting sheep is a clone ... and that could open the door to a lot of other uses, far beyond ...
