Inability of fetal skin to induce allograft tolerance in fetal lambs.

Fetal lambs of 53-55 days gestation invariably failed to accept skin allografts from fetal donors of similar age but retained allografts from adult donors. Autografts of skin were accepted by 53-55-day fetuses. When the survival of allografts transplanted from fetal donors of a range of gestational ages was examined, skin from fetuses of up to 85 days was rejected but that from a 95-day donor was retained. Histological examination of fetal skin allografts revealed that these were subject to lymphocytic invasion, evident as the entry of lymphatic vessels and extravasation of lymphocytes within the first week after placement. These manifestations of an allograft reaction became more prominent during the following 2 weeks, with graft rejection being evident by the end of a month. Allografts of adult skin were subject to occasional focal lymphocytic infiltration but otherwise healed in uneventfully.