Thousands of Americans die each year waiting for new organs. The tens of thousands lucky enough to receive transplants face years of immune suppressant drugs which compromise their health. In order to help alleviate the primary demand and solve the secondary problem of organ rejection, scientists are looking at ways to create specialized organs that can be used for transplant. The most promising of these efforts are xenotransplantation and stem cell regeneration. For xenotransplantation, biologists are working on designing special pigs that could produce organs for human use. The program reveals why pigs might be the perfect donors, and analyzes the problems scientists face in their efforts to genetically engineer swine so that the human immune system doesn't attack the transplanted pig organs. Scientists also must be careful that when they open the immune system's door for pig organs, they don't open the door to potentially deadly pig diseases, allowing them to jump species.