Differentiation of fetal pig endocrine cells after allografting into the thymus gland

Background. The thymus of large animals, such as the pig, is thought to be an appropriate site for transplanting adult islets, which contain numerous beta cells, for the purpose of reversing diabetes, Whether fetal islet-like cell clusters (ICCs), which contain few beta cells, will develop at this s ite, so that adequate amounts of insulin can be produced, is unknown, Methods, Between 15,000 and 40,000 ICCs were injected into the thymus gland of six juvenile immunosuppressed pigs, and the animals were killed up to 3 0 days later. The graft was then examined histologically and comparisons ma de with untransplanted ICCs and those grafted into the omentum of immunosup pressed pigs, Results. At transplantation, the percentage of cells in the ICCs containing insulin, glucagon, somatostatin, or pancreatic polypeptide was 9+/-1%, 13/-2%, 9+/-1%, and 3+/-1% respectively, Within 9-30 days of transplantation into the thymus, the percentage of all endocrine cells increased, insulin t o 41+/-3%, glucagon to 43+/-6%, somatostatin to 26+/-4%, and pancreatic pol ypeptide to 9+/-3%. There was co-localization of more than one hormone in s ome cells. Omental grafts contained a similar percentage of insulin and glu cagon-containing cells, but significantly fewer somatostatin and pancreatic polypeptide-containing cells. Conclusions. Endocrine cells from the fetal pig pancreas will differentiate when transplanted into the thymus gland of the pig, making this a suitable site for grafting ICCs to test their ability to normalize blood glucose le vels of diabetic recipients.