Benefit analysis and risk-benefit ratio Ethical issues also play a role in the selection of solutions. Most patients perceive xenotransplantation as an acceptable alternative to human organ transplantation in life-threatening situations, provided that the potential benefits outweigh any likely adverse effects on animals. Xenotransplantation of chimpanzee and baboon organs has been avoided, due to ethical concerns as chimpanzees are listed as an endangered species and for fear of transmission of deadly viruses. Pigs are numerous, mature quickly, breed well in captivity, have large litters, and have vital organs roughly comparable in size to those of humans. Furthermore, there are physiological similarities between their antibodies and human antibodies, and since they are already used in the consumer market, the organs were mainly taken from pigs. Humans have had prolonged and close contact with pigs, their use for xenotransplantation purposes is thought to be less likely to introduce new infectious agents. Porcine islet cells of Langerhans were injected into patients with type 1 diabetes mellitus. Porcine skin was grafted onto burn patients, and porcine neuronal cells were transplanted into patients with Parkinson's disease and Huntington's disease. However, the use of porcine xenografts is associated with major immunological barriers, resulting in hyper acute rejection (HAR) or acute vascular rejection (AVR) when transplanted into a human recipient since humans have natural antibodies against porcine cells. To solve this problem, genetically modified pigs have been engineered to reduce the expression of various immunogenic substances. Additionally the graft is given a break from the attack when there...... middle of the paper...... date. In contrast, transplantation of baboon livers and chimpanzee kidneys into humans has resulted in deaths due to diseases unrelated to organ failure. But at the same time it is not possible to apply this result/estimate to all procedures as the precise risk will vary. from one procedure to another, depending on a number of factors that must be observed in the long term. The U.S. Public Health Service agencies (i.e., FDA, Centers for Disease Control and Prevention, National Institutes of Health, and Healthcare Resource Services Administration) and the Department of Health's Office of the Associate Secretary for Planning and Evaluation of human services are collaborating to develop an integrated approach to be applied at the social, institutional and individual (patient-physician) levels to address infectious disease problems in xenotransplantation.