[Transgenic pigs for xenotransplantation for humans]

Transgenic livestock have been generated via microinjection of DNA-constructs into pronuclei of zygotes. However, efficiency is low and only 1-3% transgenic offspring are to be obtained. Integration of the transgene occurs at random and expression is independent from the number of integrated copies but can be affected by the integration site. To overcome the shortage of human organs, transgenic pigs have been generated that express human complement regulatory genes. This approach enables to overcome the hyperacute rejection response as shown by an average survival rate (40-90 days) of the immunosuppressed primate recipients receiving a heart from a transgenic pig. It is expected that transgenic pigs would be available as organ donors in the next 5-10 years. A major prerequisite, however, is the prevention of the potential transfer of pathogenic microorganisms, in particular porcine endogenous retroviruses (PERV). Improvements of the efficiency in the generation of transgenic pigs will be achieved by the use of genetically modified donor cells in nuclear transfer technology (cloning).