Xenotransplantation Transgenesis. Are we there yet?

The xenotransplantation of pig organs and tissues aimed at overcoming the world-wide shortage that exists for these in humans will require multiple genetic modifications to be incorporated to overcome rejection and associated problems. We have recently produced α1,3 galactosyltransferase knockout (GTKO) pigs expressing human (h) CD55&59, fucosyltransferase (HTF), hCD39 and hTBM This was done by breeding GTKO pigs to animals expressing human hCD55 and hCD59 plus HTF and then transfecting adult fibroblasts obtained from their progeny with a hCD39 plus hTBM construct. Transfected cells were then selected based on hCD39 expression and used for animal cloning to produce these (Figure 1). The generation of these animals represents almost two decades of research focussed on developing the necessary molecular, cellular and reproductive technologies. Having produced GT KO pigs expressing five transgenes, it is an appropriate juncture to reflect on how this was achieved and what progress still needs to be made in terms of transgenesis technology to advance xenotransplantation to the clinic.