Pancreas and islet transplantation: an unfinished journey

Polymeric nano-shielded islets with heparin-polyethylene glycol in a non-human primate model

Intraportal pancreatic islet transplantation incurs huge cell losses during its early stages due to instant blood-mediated inflammatory reactions (IBMIRs), which may also drive regulation of the adaptive immune system. Therefore, a method that evades IBMIR will improve clinical islet transplantation. We used a layer-by-layer approach to shield non-human primate (NHP) islets with polyethylene glycol (nano-shielded islets, NSIs) and polyethylene glycol plus heparin (heparin nano-shielded islets; HNSIs). Islets ranging from 10,000 to 20,000 IEQ/kg body weight were transplanted into 19 cynomolgus monkeys (n = 4, control; n = 5, NSI; and n = 10, HNSI). The mean C-peptide positive graft survival times were 68.5, 64 and 108 days for the control, NSI and HNSI groups, respectively (P = 0.012). HNSI also reduced the factors responsible for IBMIR in vitro. Based on these data, HNSIs in conjunction with clinically established immunosuppressive drug regimens will result in superior outcomes compared to those achieved with the current protocol for clinical islet transplantation.

Pre-clinical model of composite foetal pig pancreas fragment/renal xenotransplantation to treat renal failure and diabetes

 

BACKGROUND

Development of a limitless source of β cells for xenotransplantation into patients suffering type 1 diabetes and renal failure that can control their diabetes and provide normal renal function in one procedure would be a major achievement. For the islet tissue to survive transplantation, as an islet-kidney composite graft this would have significant advantages. It would simplify the surgical procedure; remove the complications caused by the exocrine pancreas whilst reversing diabetes and uraemia. It was our hypothesis that a composite foetal porcine pancreas fragment (FPPF)/renal graft could achieve these objectives in a large pre-clinical animal model as a means to establish whether this would be feasible before moving to the clinic.

METHODS

Inbred 'Westran' pig FPPF were transplanted under the kidney capsule of syngeneic Westran pig recipients without immunosuppression. Following maturation of the FPPF under the renal subcapsular space of this recipient, this kidney bearing the composite FPPF piggyback graft was removed and transplanted into another nephrectomized and pancreatectomized recipient to demonstrate function.

RESULTS

Under the kidney capsule of the first transplant group (n = 6), the FPPF-transplanted tissue developed and matured to form islet cell nests. These composite FPPF/renal grafts were then successfully removed and transplanted into the second functional assessment recipient group. This second group of six composite FPPF/renal-grafted pigs had normal renal function for more than 44 days and normal glucose homoeostasis without exogenous insulin as assessed by normal glucose tolerance tests, K values and normal glucagon secretion. Histological analysis showed despite the ischaemic insult during the composite kidney transplant procedure, there was appropriate development of islet-like structures up to and beyond 224 days after the original transplantation under the kidney capsule.

CONCLUSIONS

This study shows that the use of composite FPPF/renal grafts can cure both diabetes and renal failure with a single-transplant procedure. Using such composite grafts for xenotransplantation would simplify the surgical procedure and protect the islet graft from the immediate innate immune response.

Evolution of pancreas transplant surgery

BACKGROUND

Type 1 diabetes mellitus is a chronic condition often leading to disabling complications including retinopathy, neuropathy and cardiovascular disease which can be modified by intensive treatment with insulin. Such treatment, however, is associated with a restrictive lifestyle and risk of hypoglycaemic morbidity and mortality.

METHODS

This review examines the role of pancreas transplantation in patients with Type 1 diabetes mellitus.

RESULTS

Pancreas transplantation is currently the only proven option to achieve long-term insulin independence, resulting in an improvement or stabilization of those diabetic related complications. The hazards of pancreas transplantation as a major operation are well known. Balancing the risks of a surgical procedure, with the benefits of restoring normoglycaemia remains an important task for the pancreas transplant surgeon. Pancreas transplantation is not an emergency operation to treat poorly managed and non-compliant patients with debilitating complications. It is a highly specialized procedure which has evolved both in terms of the surgical technique, patient selection and assessment.

CONCLUSION

Pancreas transplantation has emerged as the single most effective way to achieve normal glucose homeostasis in patients with Type 1 diabetes mellitus.

Subcutaneous transplantation of embryonic pancreas for correction of type 1 diabetes

Islet transplantation is a promising therapeutic approach for type 1 diabetes. However, current success rates are low due to progressive graft failure in the long term and inability to monitor graft development in vivo. Other limitations include the necessity of initial invasive surgery and continued immunosuppressive therapy. We report an alternative transplantation strategy with the potential to overcome these problems. This technique involves transplantation of embryonic pancreatic tissue into recipients' subcutaneous space, eliminating the need for invasive surgery and associated risks. Current results in mouse models of type 1 diabetes show that embryonic pancreatic transplants in the subcutaneous space can normalize blood glucose homeostasis and achieve extensive endocrine differentiation and vascularization. Furthermore, modern imaging techniques such as two-photon excitation microscopy (TPEM) can be employed to monitor transplants through the intact skin in a completely noninvasive manner. Thus, this strategy is a convenient alternative to islet transplantation in diabetic mice and has the potential to be translated to human clinical applications with appropriate modifications.