Pig‐to‐human transplantation (xenotransplantation) is currently the most advanced approach to solving the increasing demand for human organs and tissues. However, two critical requirements must be addressed before xenotransplantation can be considered for clinical application. First, the level of immunosuppression required to maintain xenografts must be equivalent to (or less than) that used in allotransplantation. It is now evident that multiple genetic modifications of the donor pig will be needed to achieve this goal (d’Apice et al. 2002 Transplant Proceedings. 33: 3053‐3054). These include gene knockouts (e.g. of the GalT gene, responsible for synthesis of the major porcine xenoantigen) and gene addition by transgenesis. Progress has been hindered by the current technology, which allows only a single cycle of genetic modification per generation and therefore necessitates large and complex breeding programs. Second, donor pigs should have defined, relatively homogeneous genotypes including the inability to produce endogenous retroviruses (PERV) that may infect human recipients. Inbred miniature swine are best suited in this regard but are difficult to genetically manipulate due to poor reproductive capacity. What is critically needed to advance xenotransplantation to the clinic is the ability to perform multiple cycles of genetic modifications per generation on the background of choice. We have recently made an important step towards this goal by developing a novel method for the isolation of porcine embryonic stem cells (ESC) (Vassiliev et al. 2010 Cellular Reprogramming 12: 223‐230). These cells can be stably grown for at least 150 population doublings, dramatically increasing the window for introducing multiple genetic modifications before the cells are used to clone pigs by somatic cell nuclear transfer (SCNT). Furthermore we have used this method to isolate ESCs from cloned embryos (Vassiliev et al 2011 Cellular Reprogramming 13: 205‐213) which allows us to isolate ESCs directly from breeds of pigs specifically bred for xenotransplantation. Together these advances will accelerate xenotransplantation research to the clinic.

• Mark Nottle(Robinson Institute, University of Adelaide, Adelaide, Australia)
• Ivan M Vassiliev(Robinson Institute, University of Adelaide, Adelaide, Australia)
• Sharon Harrison(Robinson Institute, University of Adelaide, Adelaide, Australia)
• Stephen McIlfatrick(Robinson Institute, University of Adelaide, Adelaide, Australia)
• Wayne Hawthorne(Westmead Millennium Institute, Sydney, Australia)
• Philip O’Connell(Westmead Millennium Institute, Sydney, Australia)
• Peter Cowan(St Vincent’s Hospital, Melbourne, Australia)
• Anthony d’Apice(St Vincent’s Hospital, Melbourne, Australia)