Transplantation of neonatal islets from LEA29Y‐transgenic pigs restores normoglycemia in streptozotocin‐diabetic NSG‐mice

Abstract

Beta cell replacement therapy represents the only way towards complete restoration of the physiological glucose homeostasis in patients with Type 1 diabetes. Xenotransplantation of transgenic pig islets expressing immunomodulatory molecules might represent a promising approach to overcome the problems of lacking organ donors, adverse effects of the required systemic immunosuppression, and disappointing transplantation outcomes. LEA29Y, a second generation CTLA‐4‐Ig fusion protein exerts potent immunosuppressive effects by selective blockade of the B7 costimulatory pathway. To assess the impact of high local LEA29Y concentrations on xenogeneic islet graft rejection, a transgenic pig model with islet‐specific LEA29Y transgene expression was generated. Islet‐like clusters from neonatal pigs expressing LEA29Y under the control of the porcine insulin promoter and from wild‐type pigs were isolated by collagenase digestion and subsequent in vitro culture. After 6 days 2500 clusters/mouse were transplanted under the kidney capsule of streptozotocin‐diabetic NOD‐scidIL2Rgamma null (NSG) mice. After an initial period of insulin dependency, mice developed stable normoglycemia within 8 weeks after transplantation. Transplanted mice of both groups (Tx, wt; Tx, LEA29Y) exhibited normal and as compared to non‐transplanted normoglycemic NSG mice even improved fasting glucose and glucose tolerance resulting from glucose‐responsive graft‐derived porcine insulin secretion. Beta cell‐specific expression of LEA29Y was detectable in neonatal porcine pancreas, in the grafts of transplanted mice, and was also measurable in the plasma of normoglycemic mice. Furthermore, mice with LEA29Y transgenic grafts exhibited a glucose‐dependent LEA29Y release during glucose tolerance testing. The present study demonstrates that LEA29Y transgenic islet‐like clusters display normal beta cell function and have the same potential as wild‐type islet clusters to restore normoglycemia in streptozotocin‐diabetic NSG mice after an in vivo maturation period towards a functional endocrine tissue. NSG mice with LEA29Y islet grafts may therefore represent a promising model to study the modulation of human‐anti‐pig xenograft rejection in detail. In ongoing experiments xenograft rejection is analyzed in “humanized” mice after the transfer of human PBMCs or isolated CD34 + stem cells.