Diabetes is a syndrome characterised by disordered metabolism and inappropriately high blood sugar resulting from either low levels of the hormone insulin or from abnormal resistance to insulin's effects coupled with inadequate levels of insulin secretion to compensate. The symptoms usually are excessive urine production, excessive thirst and increased fluid intake, and blurred vision; these symptoms are likely absent if the blood sugar is only mildly elevated.

The current best medical practice for those with type 1 diabetes includes insulin by multiple daily injections or continuous pump infusion. Recently developed insulin analogues have helped to more closely approximate normal glucose homeostasis and have been especially beneficial in reducing hypoglycaemia while tightly controlling blood glucose. Glargine insulin provides nearly 24 hours of low level basal insulin activity, while meal-time peaks in activity can be mimicked by administration of rapid acting insulin analogues such as lispro and aspart insulins. Delivery of insulin by continuous infusion pump allows even finer tuning of insulin activity.

Although current insulin delivery modalities are quite good and improving, limitations still exist. Frequent self-monitoring of blood glucose is still required, as is estimation of insulin doses based on multiple factors that might affect future glycaemic changes.

Stem cells offer a potential solution to the opposed requirements of cell proliferation and function. In theory, these cells can proliferate in an undifferentiated state and then be converted to take on required metabolic functions through genetic and epigenetic manipulations. Stem cells have been isolated from embryonic tissues as well as a variety of fetal and adult sources, including umbilical cord blood, bone marrow, central nervous system, liver and pancreas. One potential advantage of adult stem cells is that they could be used for autologous transplantation. This might preclude the use of immunosuppressive medications to prevent allorejection. However, recurrent autoimmune-mediated destruction targeting cell proteins would remain problematic.

Xenogeneic cells are a potential source of cells for transplantation therapy. Because pigs regulate glucose in a similar physiological range to that of humans, and because porcine insulin has been used as an exogenous source of insulin, pigs are generally considered the most promising donor animal. However, islets from xenogeneic pancreata are more immunogenic than allogeneic islets.