Background. The acceptance of skin allografts has historically been among the most challenging problems in the field of transplantation, attributed, at least in part, to the existence of antigens expressed by skin but not by other tissues. Many studies have suggested the existence of skin-specific antigens in rodents, but data in large-animal models are more limited. Methods. We have recently developed protocols for attaining stable mixed hematopoietic chimerism in miniature swine, using MHC-matched donors and recipients. We have now assessed tolerance to donor-derived skin and cardiac allografts in these chimeric animals. Results. Skin-graft rejection was seen in four of six animals receiving skin grafts taken from the respective hematopoietic donors. In the other two animals, donor-derived skin grafts survived indefinitely. No cardiac-allograft rejection was observed in mixed-chimeric animals that received heart transplants from their hematopoietic donors, even in animals that had already rejected skin allografts from the same donors. In all animals assessed, in vitro hyporesponsiveness to donor hematopoietic cells persisted. Conclusion. These findings support the concept that skin expresses immunogenic alloantigens that either are not expressed or are not immunogenic in cardiac or hematopoietic tissue.
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