Intraperitoneal transplantation of pancreatic anlagen.

To determine whether embryonic pancreatic anlagen transplanted to an intraperitoneal site in adult hosts grow, differentiate, and function, we implanted pancreas from embryonic day (E) 12.5 Lewis rat embryos into the omentum of adult Lewis rats or C57Bl/6J mice. E12.5 pancreatic anlagen were relatively undifferentiated except for the presence of condensing tubuloacinar cords. By 2 weeks after implantation, pancreatic anlagen transplanted into rats had enlarged and differentiated such that islets of Langerhans that stained positive for insulin could be delineated. Continued differentiation, as reflected by the presence of "ductal" islets connected to the duct epithelium, was observed at 6 weeks after implantation. At 15 weeks after implantation, "mature" islets had separated from the ducts. Electron microscopy showed eccentric dense bodies within clear vacuoles consistent with insulin granules. Little or no acinar tissue was present in developed anlagen. Within 5 weeks of pancreatic anlagen transplantation, levels of glucose in rats rendered diabetic by an injection of streptozotocin were normalized compared with levels in nontransplanted diabetic controls. Rat pancreatic anlagen underwent growth and development in the peritoneum of C57Bl/61 mice that received costimulatory blocking agents but not in the absence of costimulatory blockade. We concluded that whole E12.5 pancreatic anlagen undergo growth, differentiation, and function after intraperitoneal placement. Implantation of the embryonic pancreas, a "cellular" transplant, is followed by selective differentiation of islet compared with acinar components.