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Cellular replacement therapy holds promise for the treatment of diabetes mellitus but donor tissue is severely limited. Therefore, we investigated whether insulin-secreting cells could be differentiated in vitro from a monolayer of cells expanded from human donor pancreatic islets. We describe a three-step culture protocol that allows for the efficient generation of insulin-producing cell clusters from in vitro expanded, hormone-negative cells. These clusters express insulin at levels of up to 34% that of average freshly isolated human islets and secrete C-peptide upon membrane depolarization. They also contain cells expressing the other major islet hormones (glucagon, somatostatin, and pancreatic polypeptide). The source of the newly differentiated endocrine cells could either be indigenous stem/progenitor cells or the proliferation-associated dedifferentiation and subsequent redifferentiation of mature endocrine cells. The in vitro generated cell clusters may be efficacious in providing islet-like tissue for transplantation into diabetic recipients.

Several recent studies have suggested that the adult bone marrow harbors cells that can differentiate into tissues from all three germ layers. Other reports have contradicted these findings or attributed them to cell fusion. In this study, we investigated whether bone marrow−derived cells contribute to the renewal of adult pancreatic endocrine cells, in particular insulin-producing β-cells, in vivo. To address this issue, we studied mice transplanted with green fluorescent protein (GFP)−positive, sex-mismatched bone marrow. We also extended our studies to pancreatic injury models (partial pancreatectomy and streptozotocin administration). All animals showed stable full donor chimerism in the peripheral blood and microscopic analysis at 4–6 weeks and 3 months after transplantation, indicating that the GFP+ and Y chromosome−positive donor bone marrow contributed substantially to blood, lymphatic, and interstitial cells in the pancreas. However, after examining >100,000 β-cells, we found only 2 β-cells positive for GFP, both of which were in control animals without pancreatic injury. Thus our study results did not support the concept that bone marrow contributes significantly to adult pancreatic β-cell renewal.