Genetically modified pigs as donors of cells, tissues, and organs for xenotransplantation

The number of donated human organs and tissues for patients with terminal organ failure falls far short of the need. According to the United Network for Organ Sharing (www.unos.org), more than 113,000 candidates for transplant are currently on the U.S. national waiting list, but only 36,527 organ transplants could be performed in 2018. Alternative sources, such as organs and tissues from animals, are therefore urgently needed. For a number or reasons, including size, anatomical, and physiological similarities with humans, the pig is the preferred donor species (reviewed in Cooper et al., 2016). Importantly, pigs can be optimized by genetic engineering as a source of cells, tissues, and organs for xenotransplantation. Recent advances in gen(om)e editing are speeding up progress in this field. Numerous genetically (multi-)modified pig lines have been generated to prevent immune rejection of xenotransplants, to overcome physiological incompatibilities, and to reduce the risk of transmitting zoonotic pathogens (Table 1; reviewed in Kemter et al., 2018). Table 1. Selection of genetic modifications of donor pigs for xenotransplantation