Advances in Biotechnology and Molecular Genetics

5. The major advances in biotechnology that might favour further development of xenotransplantation relate to producing transgenic pigs that express human genes which inhibit rejection. Two break-throughs are especially important. First, recent studies have led to the cloning of pigs,(⁴³) allowing for simple genetic manipulation compared with the methods currently available. With this procedure, at least in principle, new genes can easily be introduced into the DNA of the pig genome during the cloning process, and other genes "knocked out" so that they would no longer be functional. For instance, the gene that leads to expression of the "a-gal" antigen on porcine endothelial cells could be knocked out so that at least one of the causes of rejection would presumably be reduced.

Second, although still at the experimental level, methods to regulate the expression of transgenes have been devised.(⁴⁴) It may well be that a certain transgene would be highly desirable at a given moment after transplantation while it would be undesirable at a different moment. Therefore, being able to regulate the expression of a transgene would represent a great advance in the development of xenotransplantation.