Thomas Starzl and colleagues give a man a baboon liver.

1992: Xenotransplantation grabs headlines again when Starzl and his colleagues, now at the University of Pittsburgh Medical Center, perform a pair of baboon-liver transplants. One patient survives more than two months; the other, 26 days. Both die from postoperative infections that prove deadly because their immune systems are shut down by antirejection drugs. Starzl puts his xenotransplantation program on hold until the problems are better understood. Around the same time, researchers at Duke University receive permission to use a pig liver as a "bridge" to keep a critically ill woman alive as she waits for a human liver transplant. She survives only 32 hours.

Back in the lab, researchers at Massachusetts General Hospital discover that it’s a particular sugar on the surface of pig cells that provokes the attack of the natural antibodies. If scientists can use genetic engineering to create pigs that no longer put this sugar on their cell surfaces, the animals’ organs should be less irksome to the human immune system. Other researchers generate pigs that make proteins that can preemptively disable the very part of the immune system that would otherwise lay waste to the xenotransplant. Several biotechnology companies set out to make these "humanized" pigs and win approval for using the pig organs in humans.