Development of xenotransplantation is in large part driven by the fact that the demand for human organs for transplantation far exceeds the supply. According to the FDA's Center for Biologics Evaluation and Research (CBER), 10 patients die every day in the U.S. while on the waiting list to receive transplants. According to the United Network for Organ Sharing (UNOS), the supply of organs remained flat throughout the 1990s at about 5,000 donors, while demand rose from about 20,000 in 1990 to more than 60,000 patients