Transplantation of organs from animals into humans has been tried in the past. Because of that, we know what full on rejection of non-human organs looks like.

Transplantation of organs from animals into humans has been tried in the past. Because of that, we know what full on rejection of non-human organs looks like. It sounds like this was actually quite successful in that the immune system didn’t immediately start attacking it, as would be the case with a normal pig heart.