Richard Slayman was a pioneer. He made an amazing decision, to see if it could be done. This was hard work done through eGenesis, and the steps to get to this point is quite interesting.
>> First, the donors were often created on a commercial pig breed whose heart and kidney sizes are too large for human application. Although elimination of growth hormone receptor gene expression could reduce organ sizes, it comes with other undesired biological consequences. Second, the donors were designed for testing in OWMs. They lacked the α-Gal (galactose-α-1,3-galactose) or the α-Gal and Sd(a) (Sia-α2.3-[GalNAc-β1.4]Gal-β1.4-GlcNAc) glycans but expressed the Neu5Gc (N-glycolylneuraminic acid) glycan to match with Neu5Gc expression in OWMs. However, in vitro analysis suggests that a human-compatible porcine donor should ideally have all three glycans eliminated to match with the absence of the three glycans in humans. Although renal grafts derived from the porcine donors lacking these three glycans and carrying various human transgenes have been tested in OWMs, graft survival was short8 or not all human transgenes were expressed. Third, the donors carried porcine endogenous retrovirus (PERV) sequences in their genome, which present a zoonotic risk, as PERV transmission to human cells in culture and their integration into the human genome have been demonstrated.
OWM is old-world monkey, for those who don't bio.