Correction of diabetes in primates by macroencapsulated pig islets

Abstract

Although islet allotransplantation represents a useful therapeutic tool for patients with Type 1 diabetes mellitus (T1DM), the discrepancy between the number of potential recipients and the number of donors remains a major hurdle to its widespread use [1]. The use of pig islets to correct T1DM could solve the shortage of insulin-producing cells. In that sense, recent reports clearly demonstrate that a multiple-drug immunosuppressive regimen allows pig islets to correct diabetes in non-human primates for months [2, 3]. To completely eliminate the use of immunosuppressive drugs, we studied the potential of encapsulating pig islets in microbeads or in a macrodevice composed of extra-pure alginate. We first demonstrated the full biocompatibility of alginate in non-human primates for 6 months [4], and here we show that complete control of diabetes was possible for up to 6 months without immunosuppression when pig islets were implanted in the subcutaneous space. Adult pig islets were transplanted in 12 streptozotocin-diabetic cynomolgus macaques. When empty alginate microbeads were implanted (n = 2), there was no correction of diabetes. Similarly, when non-encapsulated pig islets were transplanted (n = 2), the xenograft was rapidly rejected due to both humoral and cellular processes and no significant correction of glycemia was observed. Microencapsulated pig islets (15 000 to 30 000 islet equivalent [IEQ]/kg) were then implanted under the renal capsula in four diabetic monkeys. Complete control of diabetic clinical and biological signs was obtained for a maximum of 20 days; however, no signs of immune rejection or fibrosis were evident to explain the return of high glycemia. The probable reason for implant failure in these animals was the lack of appropriate oxygenation due to a multilayer deposition of the pig islets in the subcapsular space. We therefore designed a monolayer device composed of a human collagen acellular matrix covered by a monolayer of pig islets (30 000 IEQ/kg) embedded in pure alginate. This device was placed in the subcutaneous abdominal space in four primates. All recipients had prolonged xenograft function until 17, 25, 25, and 26 weeks post-transplantation with a complete correction of diabetes signs: fasting blood glucose (FBG) ranging between 52 and 107 mg/dl, undetectable glycosuria, detectable porcine C-peptide, and a normalization of the glycosylated hemoglobin (HbA1C <8 ± 1.4%). Harvesting the device after diabetic signs returned allowed detecting scattered positive insulin immunochemistry as well as determining the absence of CD3 and CD68 cell infiltration. All animals that received micro- or macroencapsulated pig islets developed anti-pig IgG antibodies, but no signs of humoral rejection could be found in encapsulated pig islets after harvesting. In order to emphasize the absence of xenogeneic humoral immune response against these encapsulated pig islets, we retransplanted two primates that had previously received a subcutaneous monolayer device and clearly became diabetic again. In these two primates, the replacement by a new subcutaneous monolayer device allowed a second period of up to 20 weeks of diabetic control without immunosuppression (HbA1C normalization between 7.4% and 9.7%).