Normalization of blood glucose after islet cografting with placental tissues in diabetic mice

A fetus in the uterus is not rejected at any time during the entire gestational period, even without the administration of immunosuppressive agents, though fetus is a kind of allograft. This prevention of rejection is considered to be associated with the presence of placental tissues. This hypothesis was tested by the allografting of islets together with placental tissues (trophoblasts) in streptozotocin (STZ)-induced diabetic mice. Placentae were harvested from the mice at the 14th postgestation day by being peeled off carefully and with the maternal decidua left behind, and cut into small pieces. Five hundred freshly isolated islets together with placental tissues obtained from ICR mice were placed under the left kidney capsule of STZ-induced diabetic C57BL/6J mice. The nonfasting blood glucose level was reduced from 477 +/- 41 mg/dl at the time of pretransplant to that of the intact normal mice (161 +/- 18 mg/dl) soon after the cografting, and did not return to the pretransplant level before the 14th posttransplant day. The grafting of the same number of islets alone and/or liver tissues dropped the blood glucose level, but not to that of the intact normal mice. It returned to the pretransplant level within 1 week. This is the first successful prolongation of survival of allografted islets without immunosuppressive agents through cotransplantation of allogenic placental tissues. The underlying mechanism remains to be clarified.