Growth and Functional Maturation of β-Cells in Implants of Endocrine Cells Purified From Prenatal Porcine Pancreas

Abstract

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 β-cell mass with an apparently low capacity for β-cell renewal and growth. Although duct-associated nonendocrine cells have often been suggested as a potential source for β-cell production, recent work in mice has demonstrated the role of β-cells in postnatal growth of the pancreatic β-cell mass. The present study investigated whether the β-cell mass can grow in implants that are virtually devoid of nonendocrine cells. Endocrine islet cells were purified from prenatal porcine pancreases (gestation >110 days) and implanted under the kidney capsule of nude mice. β-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 β-cells 4 and 72 h posttransplant) and then decreased over 20 weeks to rates measured in the pancreas (0.2% BrdU-positive cells). β-Cell proliferation in implants first compensated for β-cell loss during posttransplant week 1 and then increased the β-cell number fourfold between posttransplant weeks 1 and 20. Rates of α-cell proliferation were only shortly and moderately increased, which explained the shift in cellular composition of the implant (β-cell 40 vs. 90% and α-cell 40 vs. 7% at the start and posttransplant week 20, respectively). β-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 β-cell phenotype provides grafts with a marked potential for β-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.