Some religions regard pigs as unclean on the grounds that pig flesh is closest in composition to human flesh. I don't believe this for one instant, but it got me thinking, just how close is pig and human on the evolutionary tree?
Last common ancestor is about 97.5 Million Years Ago.
That being said, they are close enough to us that they are a vector for influenza viruses that are able to make the jump to human pretty easily.
Also we use their tissue as a homologue for human in forensic research. We also use valves from pig hearts to replace defective human valves.
This Nature News Article reviews some of the work being done with Pig to Human Tissue Transplantation. Though granted the methods they are looking at rely heavily on targeted gene editing.