Favorable outcome of experimental islet xenotransplantation without immunosuppression in a nonhuman primate model of diabetes

Abstract

Transplantation of pancreatic islets for treating type 1 diabetes is restricted to patients with critical metabolic lability resulting from the need for immunosuppression and the shortage of donor organs. To overcome these barriers, we developed a strategy to macroencapsulate islets from different sources that allow their survival and function without immunosuppression. Here we report successful and safe transplantation of porcine islets with a bioartificial pancreas device in diabetic primates without any immune suppression. This strategy should lead to pioneering clinical trials with xenotransplantation for treatment of diabetes and, thereby, represents a previously unidentified approach to efficient cell replacement for a broad spectrum of endocrine disorders and other organ dysfunctions.

Keywords: beta-cell replacement; diabetes; immune barrier; porcine islets.

Fig. 1.

Schematic view of the chamber system for islet macroencapsulation and encapsulated porcine islets. (A) The system is built from two islet compartments containing the islets immobilized in alginate and an oxygen module in center, connected to access ports for exogenous oxygen refilling. These ports allow direct injection of oxygen-enriched gas mixture (95% oxygen at 1.4 ATM; 1,011 Torr) into the central cavity. Oxygen is diffusing via the gas permeable membranes into two external chambers and via additional two gas permeable membranes into the cell chambers, where it is dissolved and consumed by the islets. According to mathematical models, refueling of oxygen every 24 h ensures minimal pO₂ within the islet module at above critical value of 60 Torr at all islets, (29). The plastic housing of the chamber is covered by porous membranes of hydrophylized polytetrafluoroethylene impregnated with alginate. Drawing is not to scale. (B) Microscopic image (brightfield) of porcine islets immobilized in alginate ready for integration into the chamber system.

Fig. 2.

Efficacy study of macroencapsulated porcine islets transplanted into diabetic nonhuman primates (n = 3). (A) The levels of fasting BG showed persistent stable glycemic control over time, despite a stepwise reduction in daily exogenous insulin dose (B). On explantation, the insulin demand immediately increased to prevent hyperglycemia. Values are shown as mean (solid line) ± SD (dashed line) for all three animals. Total insulin was composed of long-acting insulin (glargine; Lantus, Sanofi-Aventis) and short-acting insulin (glulisine; Apidra, Sanofi-Aventis). All animals were challenged by ivGTT before intervention and 1 wk, 4 wk, 3 mo, and 6 mo after transplantation, as well as after explantation of the islet graft. (C) During glucose challenge, there was adequate BG lowering comparable to healthy control, accompanied by porcine-specific C-peptide secretion (D). (Insets) AUC for BG (mmol × min × L⁻¹) and porcine C-peptide (ng × min × mL⁻¹) during the glucose challenge for each time.

Fig. 3.

Implantable device containing porcine islets. (A) Intraoperative situs with the device, embedded in a bluntly dissected pocket between the parietal peritoneum and the fascia of the abdominal muscles and s.c. fixed port connections for oxygen refueling. (B and C) Smooth explantation of device and port system without relevant fibrous adhesions. (D) Retrieved bioartificial pancreas device with intact and clean membrane surfaces.

Fig. 4.

Immunohistochemical analysis of islets after explantation and device surrounding tissue. (A and B) Representative images of tissue surrounding the device on the peritoneal site, stained for CD31 to visualize strong vascularization as crucial for exchange of glucose/hormones. (Red) CD31, (blue) DAPI. (C and D) Representative images of porcine islets immobilized in alginate analyzed after explantation of the device at 6 mo. (Green) insulin, (red) Glucagon, (blue) DAPI. The architecture and cell composition of explanted islet grafts were not different to the structure at the time of implantation. Although beta cells are often found as single cells or grouped together to form the core of islets at younger age, the retired breeder animals as used in this study typically show a rather compact structure with beta cells scattered throughout the islet and alpha cells predominantly in the periphery. For analysis of local immune reactions at the transplantation site, the surrounding tissue was stained for CD8⁺ T-cells (E), CD3⁺ activated cytotoxic T-cells (F), and CD68⁺ macrophages (G); (red) respective CD-molecules, (blue) DAPI. Arrows indicate the relevant structures in the respective images (exemplary).