to be the best candidates for organ donation. The risk of cross-species disease transmission is decreased because of their increased phylogenetic distance from humans. Pigs have relatively short gestation periods, large litters, and are easy to breed, making them readily available. They are inexpensive and easy to maintain in pathogen-free facilities, and current gene editing tools are adapted to pigs to combat rejection and potential zoonoses. Pig organs are anatomically comparable in size, and new infectious agents are less likely since they have been in close contact with humans through domestication for many generations. Treatments sourced from pigs have proven to be successful such as porcine-derived insulin for patients with diabetes mellitus. Increasingly, genetically engineered pigs are becoming the norm, which raises moral qualms, but also increases the success rate of the transplant. Current experiments in xenotransplantation most often use pigs as the donor, and baboons as human models. In 2020 the U.S. Food and Drug Administration approved a genetic modification of pigs so they do not produce alpha-gal sugars. Pig organs have been used for kidney and heart transplants into humans. In the field of regenerative medicine, pancreatogenesis- or nephrogenesis-disabled pig embryos, unable to form a specific organ, allow experimentation toward the in vivo generation of functional organs from xenogenic pluripotent stem cells in large animals via compensation for an empty developmental niche (blastocyst complementation). Such experiments provide the basis for potential future application of blastocyst complementation to generate transplantable human organs from the patient's own cells, using livestock animals, to increase quality of life for those with end-stage organ failure. Barriers and issues Immunologic barriers To date, no xenotransplantation trials have been entirely successful due to the many obstacles arising from the response of the recipient's immune system. "Xenozoonoses" are one of the biggest threats to rejections, as they are xenogenetic infections. The introduction of these microorganisms are a big issue that lead to the fatal infections and then rejection of the organs. This response, which is generally more extreme than in allotransplantations, ultimately results in rejection of the xenograft, and can in some cases result in the immediate death of the recipient. There are several types of rejection organ xenografts are faced with, these include hyperacute rejection, acute vascular rejection, cellular rejection, and chronic rejection. A rapid, violent, and hyperacute response comes as a result of antibodies present in the host organism. These antibodies are known as