Mature Human Hepatocytes fromEx VivoDifferentiation of Alginate-Encapsulated Hepatoblasts

A localizable, biological-based system for the delivery of bioactive IGF-1 utilizing microencapsulated genetically modified human fibroblasts

Insulin-like growth factor 1 (IGF-1) is a potent mitogen and differentiation factor with particular relevance to orthopedic tissue engineering. A biologically based Ca2+-alginate microcapsule vehicle, utilizing genetically modified primary normal human fibroblasts (NHFs), was developed and characterized for localized synthesis and delivery of human IGF-1 (hIGF-1). Normal human fibroblasts were transfected to overexpress the hIGF-1 gene, leading to cells that expressed 4 ng of hIGF-1 per 10(6) cells per 24 hours. Encapsulation within alginate led to a six-fold enhancement in the generation and release of hIGF-1 to 22 ng of hIGF-1 per 10(6) cells per 24 hours. Release was constitutive, predictable, and exhibited highly repeatable first-order kinetics with no initial burst. Released growth factor was biologically active and exhibited a proliferative effect comparable to commercially available recombinant hIGF-1. The magnitude of hIGF-1 release met the requirements of orthopedic tissue generation, and this approach is considered an attractive alternative to other proposed methods of growth factor delivery.

The stem cell niche of human livers: symmetry between development and regeneration

Human livers contain two pluripotent progenitors: hepatic stem cells and hepatoblasts. The hepatic stem cells uniquely express the combination of epithelial cell adhesion molecule (EpCAM), neural cell adhesion molecule (NCAM), cytokeratin (CK) 19, albumin +/-, and are negative for alpha-fetoprotein (AFP). They are precursors to hepatoblasts, which differ from hepatic stem cells in size, morphology, and in expressing the combination of EpCAM, intercellular cell adhesion molecule (ICAM-1), CK19, albumin++, and AFP++. The hepatic stem cells are located in vivo in stem cell niches: the ductal plates in fetal and neonatal livers and canals of Hering in pediatric and adult livers. The hepatoblasts are contiguous to the niches, decline in numbers with age, wax and wane in numbers with injury responses, and are proposed to be the liver's transit-amplifying cells. In adult livers, intermediates between hepatic stem cells and hepatoblasts and between hepatoblasts and adult parenchyma are observed. Amplification of one or both pluripotent cell subpopulations can occur in diseases; for example, hepatic stem cell amplification occurs in mild forms of liver failure, and hepatoblast amplification occurs in forms of cirrhosis. Liver is, therefore, similar to other tissues in that regenerative processes in postnatal tissues parallel those occurring in development and involve populations of stem cells and progenitor cells that can be identified by anatomic, antigenic, and biochemical profiles.