A Prospective Comparison of Discontinuous Euroficoll and Eurodextran Gradients for Islet Purification

Simplified method to isolate highly pure canine pancreatic islets

OBJECTIVES

The canine model has been used extensively to improve the human pancreatic islet isolation technique. At the functional level, dog islets show high similarity to human islets and thus can be a helpful tool for islet research. We describe and compare 2 manual isolation methods, M1 (initial) and M2 (modified), and analyze the variables associated with the outcomes, including islet yield, purity, and glucose-stimulated insulin secretion (GSIS).

METHODS

Male mongrel dogs were used in the study. M2 (n = 7) included higher collagenase concentration, shorter digestion time, faster shaking speed, colder purification temperature, and higher differential density gradient than M1 (n = 7).

RESULTS

Islet yield was similar between methods (3111.0 ± 309.1 and 3155.8 ± 644.5 islets/g, M1 and M2, respectively; P = 0.951). Pancreas weight and purity together were directly associated with the yield (adjusted R(2) = 0.61; P = 0.002). Purity was considerably improved with M2 (96.7% ± 1.2% vs 75.0% ± 6.3%; P = 0.006). M2 improved GSIS (P = 0.021). Independently, digestion time was inversely associated with GSIS.

CONCLUSIONS

We describe an isolation method (M2) to obtain a highly pure yield of dog islets with adequate β-cell glucose responsiveness. The isolation variables associated with the outcomes in our canine model confirm previous reports in other species, including humans.

Prospective and challenges of islet transplantation for the therapy of autoimmune diabetes

Pancreatic islet cell transplantation is an attractive treatment of type 1 diabetes (T1D). The success enhanced by the Edmonton protocol has fostered phenomenal progress in the field of clinical islet transplantation in the past 5 years, with 1-year rates of insulin independence after transplantation near 80%. Long-term function of the transplanted islets, however, even under the Edmonton protocol, seems difficult to accomplish, with only 10% of patients maintaining insulin independence 5 years after transplantation. These results differ from the higher metabolic performance achieved by whole pancreas allotransplantation, and autologous islet cell transplantation, and form the basis for a limited applicability of islet allografts to selected adult patients. Candidate problems in islet allotransplantation deal with alloimmunity, autoimmunity, and the need for larger islet cell masses. Employment of animal islets and stem cells, as alternative sources of insulin production, will be considered to face the problem of human tissue shortage. Emerging evidence of the ability to reestablish endogenous insulin production in the pancreas even after the diabetic damage occurs envisions the exogenous supplementation of islets to patients also as a temporary therapeutic aid, useful to buy time toward a possible self-healing process of the pancreatic islets. All together, islet cell transplantation is moving forward.

Effect of core pancreas temperature during cadaveric procurement on human islet isolation and functional viability

BACKGROUND

Success of human pancreatic islet isolation depends largely on the techniques used during pancreas procurement and the quality of the gland. Warm ischemia of the pancreas of any duration during organ procurement may be detrimental to subsequent islet yield and functional viability of the islets. The aim of this study was to correlate pancreas procurement technique with the core temperature within the pancreas during in situ procurement to the recovery and in vitro function of isolated human islets.

METHODS

Alternative pancreata were recovered from human cadaveric organ donors with needle-point myocardial temperature probes placed within the body of the pancreas. After vascular flushing with University of Wisconsin organ preservation solution, the first group of human pancreata were removed after standard liver and kidney procurement followed by in situ dissection of the pancreas. The second group of pancreata were removed using a similar protocol, except that the lesser sac was opened (and the spleen was mobilized to the midline) rapidly at the time of aortic cross-clamp. An additional 3-4 L of ice slush solution was placed behind and in front of the pancreas and replenished throughout the procurement process for the liver and kidneys. Immediately after recovery, in both groups, the pancreas was placed in cold University of Wisconsin solution and transported to the islet isolation laboratory for processing. Islets were isolated using a standard protocol of Liberase perfusion via the duct, gentle mechanical dissociation, and Ficoll purification.

RESULTS

The absence of in situ ice-chilling of the entire pancreas during liver and kidney procurement caused the core pancreas temperature to rise to a peak of 18.2 degrees C; but when the pancreas was surrounded and replenished with iced saline slush, the core pancreas temperature was maintained at approximately 4 degrees C. The lower pancreas temperature correlated with a significantly higher recovery of islets in the group of pancreata surrounded with iced saline (223+/-35x10(3) IE vs. 103+/-26x10(3) IE; mean +/- SEM). Functional ability of the islets was also significantly improved in glucose static incubation, with a stimulation index of 4.4+/-0.3 in the iced-saline pancreas group versus 3.0+/-0.4 in the standard procurement group (P<0.05, paired t test).

CONCLUSIONS

Procurement technique and the maintenance of a low temperature of the pancreas are critical to subsequent islet recovery and function. Maintaining a low pancreas temperature during procurement through the addition and replenishment of iced saline slush surrounding the anterior and posterior aspects of the pancreas greatly improves islet yield and functional viability of the isolated islets and is essential for success in clinical islet transplantation.

Beta cell replacement for the treatment of diabetes

The replacement of insulin-producing beta cells by islet transplantation can efficiently reverse diabetes. The recent improvements in clinical results were made possible by transplanting higher islet masses and through the introduction of new immunosuppressive protocols that avoid diabetogenicity. The need for alternatives to continuous immunosuppression, and an unlimited source of glucose-sensitive, insulin-secreting tissue, is emerging. In this review we discuss the various key steps in islet transplantation and offer perspectives for future developments in the replacement of insulin-producing beta cells for the treatment of type I diabetes.

Induction of allogeneic islet tolerance in a large-animal model

For islet allotransplantation to become a therapy widely applicable to patients with insulin-dependent diabetes, it will be important to avoid conventional immunosuppression and yet maintain long-term rejection-free islet survival. This possibility was tested in a large-animal model using mixed allogeneic chimeras established using total lymphoid irradiation (TLI) and donor-specific bone marrow transplantation (BMTX). Four recipient sex-mismatched and DLA class II-matched English springer spaniels became chimeric after TLI and donor-specific BMTX. Subsequent donor-specific renal allografts survived for more than a year. Acceptance of a donor-specific skin graft and rejection of a third-party graft demonstrated tolerance with maintenance of immunocompetence. Pancreatic microfragments containing islets were refluxed into the splenic vein of the recipient. Purified islets were placed under the capsule of spleen and liver. After 75 days, recipients underwent total native pancreatectomy. All four chimeric pancreatectomized dogs had functioning islet grafts 75 days after transplantation, evidenced by a prompt rise in serum insulin levels following an IVGTT and histological demonstration of islet tissue at the site of transplantation. After removal of the transplanted islet tissue, no insulin was released after IVGTT. In summary, intrasplenic allogeneic canine islets transplanted into chimeric dogs rendered tolerant to donor MHC survive and function for greater than 75 days in the absence of immunosuppression. This study represents proof of the concept that allogeneic islet transplants have the potential to reverse diabetes without the use of conventional immunosuppression.