title: Generation of definitive endoderm from human embryonic stem cells cultured in feeder layer-free conditions.
abstract: OBJECTIVE
  The purpose of these studies was twofold: to reduce the level of nonhuman, potentially immunogenic sialic acid N-glycolylneuraminic acid (Neu5Gc) in human embryonic stem cells (hESCs) through culture of the cells in the absence of feeder layers; and to determine whether directed differentiation was preserved under these conditions, that is, using exclusively human-derived products.
  
  
  METHODS
  Using a technique developed in our laboratory to culture hESCs in the absence of feeder layers, all nonhuman cell culture reagents were replaced with recombinant or human-derived reagents. The level of the nonhuman sialic acid (Neu5Gc) was measured by high-performance liquid chromatography and monitored over many passages. Subsequently, the cells were subjected to in vitro differentiation into definitive endoderm by lowering the serum concentrations and elevating the amount of activin A.
  
  
  RESULTS
  Under standard tissue culture conditions using mouse and other animal products, the basal levels of Neu5Gc were measured between 7 and 10%. After the cell culture reagents were changed to all human products, Neu5Gc levels decreased steadily before leveling below 2%. Upon initiation of the differentiation protocol under these cell culture conditions, we observed robust endoderm formation, as measured by fluorescence-activated cell sorting analysis and the appearance of mRNA for markers of definitive endoderm (Sox17, CXCR4, Goosecoid and FoxA2).
  
  
  CONCLUSIONS
  Consistent with other findings, elimination of nonhuman products in cell culture of hESCs decreases the levels of nonhuman and potentially immunogenic sialic acid levels. Furthermore, our studies demonstrate that in this feeder layer-free system, hESCs undergo directed differentiation into definitive endoderm.
authors.affiliation: University of California, Whittier Institute, Department of Pediatrics, San Diego, 9500 Gilman Drive, Center for Molecular Genetics, Room 131, La Jolla, CA 92037-0634, USA. chking@ucsd.edu
authors.forename: Charles C
authors.initials: CC
authors.lastname: King
authors.forename: Gillian M
authors.initials: GM
authors.lastname: Beattie
authors.forename: Ana D
authors.initials: AD
authors.lastname: Lopez
authors.forename: Alberto
authors.initials: A
authors.lastname: Hayek
mesh_terms: D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D002469:Cell Separation; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D053595:Embryonic Stem Cells / Q000166:cytology*; D004707:Endoderm / Q000166:cytology*; D006801:Humans; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers