Researchers from Revivcor, a division of United Therapeutics, are tweaking the pigs' biology so that they grow human organs. "We want to make organs come off the assembly line, a dozen per day," United Therapeutics founder and co-CEO Martine Rothblatt told MIT Tech Review. In the early 2000s, one researcher, who later co-founded Revivcor, figured out a way to suppress a type of sugar in the pigs that was triggering an immediate rejection response in human recipients. But in recent years, Revivcor researchers have been finding ways to put human genes in pigs and get them to work. In theory, this should be possible because pigs' bodies have a lot of the same functions as ours—for example they have their own version of thrombomodulin, a protein that prevents blood from clogging—but it has proven to be very difficult.