Encapsulated pancreatic progenitors derived from human embryonic stem cells as a therapy for insulin-dependent diabetes.

Background: Cellular-based therapies for insulin-dependent diabetes are potential means of achieving and maintaining normal blood glucose levels (BGL) without the need for insulin administration. Islets isolated from donor pancreases have been the most common tissue used to date, but supply is a limiting factor. The use of human embryonic stem cells (hESC) as a therapy became a possibility with the report that these cells could be differentiated to pancreatic progenitors (PP) over 12 days in vitro. Conversion of PP to glucose-responsive insulin-secreting cells can be achieved by transplanting the progenitors in vivo where cell maturation occurs. To date this step has not been shown under in vitro conditions.

Methods: Prior to transplanting, cells are encapsulated in alginate to prevent the immune cells of recipient attacking the graft. The alginate capsules have pores with a molecular weight cut-off of 250 kDa. These are too small to allow entry of immune cells, but large enough for passage of nutrients and insulin.

Results: Encapsulated insulin-producing cells survive and function when transplanted, and have been shown to normalize BGL when allografted into diabetic mice. As few as 750 encapsulated human islets are sufficient to normalize BGL of diabetic non-obese diabetic severe combined immunodeficient (NOD/SCID) recipient mice for at least 2 months. The safety of transplanting encapsulated human islets as demonstrated by the lack of major adverse events and infection was recently shown in a first-in-human clinical trial. Finally, fetal porcine islet-like cell clusters, which are akin to PP derived from ESC, mature and normalize BGL of diabetic recipient mice with the same efficiency as non-encapsulated clusters placed under the kidney capsule.

Conclusion: Transplanting encapsulated PP, derived from hESCs, into diabetic recipients is the strategy that is now being explored in the Australia Diabetes Therapy Project.