Growth and functional maturation of β-cells in implants of endocrine cells purified from prenatal porcine pancreas

The development of islet cell transplantation as a cure for diabetes is limited by the shortage of human donor organs. Moreover, currently used grafts exhibit a marginal beta-cell mass with an apparently low capacity for beta-cell renewal and growth. Although duct-associated nonendocrine cells have often been suggested as a potential source for beta-cell production, recent work in mice has demonstrated the role of beta-cells in postnatal growth of the pancreatic beta-cell mass. The present study investigated whether the beta-cell mass can grow in implants that are virtually devoid of nonendocrine cells. Endocrine islet cells were purified from prenatal porcine pancreases (gestation110 days) and implanted under the kidney capsule of nude mice. beta-Cells initially presented with signs of immaturity: small size, low insulin content, undetectable C-peptide release, and an inability to correct hyperglycemia. They exhibited a proliferative activity that was highest during posttransplant week 1 (2.6 and 5% bromodeoxyuridine [BrdU]-positive beta-cells 4 and 72 h posttransplant) and then decreased over 20 weeks to rates measured in the pancreas (0.2% BrdU-positive cells). beta-Cell proliferation in implants first compensated for beta-cell loss during posttransplant week 1 and then increased the beta-cell number fourfold between posttransplant weeks 1 and 20. Rates of alpha-cell proliferation were only shortly and moderately increased, which explained the shift in cellular composition of the implant (beta-cell 40 vs. 90% and alpha-cell 40 vs. 7% at the start and posttransplant week 20, respectively). beta-Cells progressively matured during the 20 weeks after transplantation, with a twofold increase in cell volume, a sixfold increase in cellular insulin content, plasma C-peptide levels of 1-2 ng/ml, and an ability to correct diabetes. They became structurally organized as homogenous clusters with their secretory vesicles polarized toward fenestrated capillaries. We concluded that the immature beta-cell phenotype provides grafts with a marked potential for beta-cell growth and differentiation and hence may have a potential role in curing diabetes. Cells with this phenotype can be isolated from prenatal organs; their presence in postnatal organs needs to be investigated.