Xenotransplantation Without Immunosupression
Cross species organ transplantation has previously not been possible due to the large differences in blood group and tissue between humans and other animals. Human animal chimeras may make cross species organ transplantation possible, but only for future generations.
Organs must be carefully matched to donors to prevent antibody mediated transplant rejection. Even with transplants from close relatives, organ recipients must have indefinite immunosuppression treatment to prevent transplant rejection. The non specificity of immunosupression treatments increases susceptibility to infections limiting long term viability.
Only a complete genetic match, an identical twin or clone, does not require immunosupression treatment because the immune system recognize the transplant as self. The grafting of stem cells from an animal in a preimmune fetus results in chimerism in which foreign cells are identified as self. Transplanted cells or organs genetically identical to the existing transplanted stem cells are also recognized as self. In chimeric humans, organs from the donor animal could be grafted without immunosuppression treatment improving health and longterm viability.
Prenatal grafting of animal stem cells into human fetuses may become common practice for families genetically predisposed to organ failure, but careful implantation of animal cells is necessary to ensure completely human appearance. The establishment of clonal populations of pigs or dogs would ensure genetically compatible organ availability for all chimeric humans.