GENETIC-ENGINEERING OF PIGS FOR XENOGENEI C HEART-TRANSPLANTATION

Given the worldwide shortage of organs for human allotransplantation, the pig is considered a potential candidate as a source of organs for donation because of similarities in size, anatomy and organ physiology between pigs and humans. However, hyperacute rejection as a result of activation of human complement has prevented the use of pigs as organ donors. The action of endogenous complement in humans is usually bloc ked by cell surface proteins which are regulators of complement activa tion (RCA). The aim of this research programme was to produce pigs tra nsgenic for human decay accelerating factor (DAF), one of these human RCAs. A 6.8kb DNA construct was prepared; it included the 4kb genomic DNA fragment incorporating the 5' untranslated and signal peptide sequ ence of the human DAF gene. The first exon and intron of the gene are linked to the main cDNA for hDAF by use of this hDAF minigene. This co nstruct was then microinjected into the pronucleus of fertilised ova c ollected from mature Large White gilts. 49 transgenic pigs incorporati ng between 1 and 30 copies of the DAF minigene in the genome were prod uced. It was found that hDAF could be expressed in all the different t issues and organs of the pigs without causing any harmful effect to th e animal in terms of well-being, growth, sexual maturity and reproduct ion. In some pigs, hDAF levels expressed were higher than those found in the equivalent human tissue. Subsequently, hearts from hDAF transge nic pigs were transplanted both with and without immunosuppression int o non-human primates. These studies show the following: (i) hearts fro m transgenic pigs are not hyperacutely rejected by cynomolgus monkeys; and (ii) survival of such hearts over 2 months can be achieved by imm unosuppressive treatment of the recipient.