The postischemic environment differentially impacts teratoma or tumor formation after transplantation of human embryonic stem cell-derived neural progenitors.

BACKGROUND AND PURPOSE: Risk of tumorigenesis is a major obstacle to human embryonic and induced pluripotent stem cell therapy. Likely linked to the stage of differentiation of the cells at the time of implantation, formation of teratoma/tumors can also be influenced by factors released by the host tissue. We have analyzed the relative effects of the stage of differentiation and the postischemic environment on the formation of adverse structures by transplanted human embryonic stem cell-derived neural progenitors. METHODS: Four differentiation stages were identified on the basis of quantitative polymerase chain reaction expression of pluripotency, proliferation, and differentiation markers. Neural progenitors were transplanted at these 4 stages into rats with no, small, or large middle cerebral artery occlusion lesions. The fate of each transplant was compared with their pretransplantation status 1 to 4 months posttransplantation. RESULTS: The influence of the postischemic environment was limited to graft survival and occurrence of nonneuroectodermal structures after transplantation of very immature neural progenitors. Both effects were lost with differentiation. We identified a particular stage of differentiation characterized in vitro by a rebound of proliferative activity that produced highly proliferative grafts susceptible to threaten surrounding host tissues. CONCLUSIONS: The effects of the ischemic environment on the formation of teratoma by transplanted human embryonic stem cell-derived neural progenitors are limited to early differentiation stages that will likely not be used for stem cell therapy. In contrast, hyperproliferation observed at later stages of differentiation corresponds to an intrinsic activity that should be monitored to avoid tumorigenesis.

The use of superporous Ac-CGGASIKVAVS-OH-modified PHEMA scaffolds to promote cell adhesion and the differentiation of human fetal neural precursors.

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with laminin-derived Ac-CGGASIKVAVS-OH peptide sequences have been developed to construct scaffolds that promote cell adhesion and neural differentiation. Radical copolymerization of 2-hydroxyethyl methacrylate with 2-aminoethyl methacrylate (AEMA) and ethylene dimethacrylate in the presence of ammonium oxalate crystals resulted in the formation of superporous P(HEMA-AEMA) hydrogels. They were reacted with gamma-thiobutyrolactone to yield 2-(4-sulfanylbutanamido)ethyl methacrylate (P(HEMA-AEMA)-SH) unit. The Ac-CGGASIKVAVS-OH peptide was immobilized to the sulfhydryl groups of P(HEMA-AEMA)-SH by 2,2'-dithiodipyridine linking reagent via 2-[4-(2-pyridyldisulfanyl)butanamido]ethyl methacrylate (P(HEMA-AEMA)-TPy). The adhesion and morphology of rat mesenchymal stem cells were investigated on the Ac-CGGASIKVAVS-OH-modified P(HEMA-AEMA) as well as on PHEMA, P(HEMA-AEMA)-SH and P(HEMA-AEMA)-TPy hydrogels. Superporous Ac-CGGASIKVAVS-OH-modified PHEMA scaffolds significantly increased the number of attached cells and their growth area on the hydrogel surface in the absence and in the presence of serum in the culture medium. Additionally, the Ac-CGGASIKVAVS-OH peptide supported the attachment, proliferation, differentiation and process spreading of human fetal neural stem cells during the first two weeks of expansion and contributed to the formation of a high percentage of more mature neural cells after four weeks of expansion. The Ac-CGGASIKVAVS-OH modification of superporous P(HEMA-AEMA) hydrogels improves cell adhesive properties and promotes neural stem cell differentiation.

Analysis of in vitro and in vivo characteristics of human embryonic stem cell-derived neural precursors.

During the last decade, much progress has been made in developing protocols for the differentiation of human embryonic stem cells (hESCs) into a neural phenotype. The appropriate agent for cell therapy is neural precursors (NPs). Here, we demonstrate the derivation of highly enriched and expandable populations of proliferating NPs from the CCTL14 line of hESCs. These NPs could differentiate in vitro into functionally active neurons, as confirmed by immunohistochemical staining and electrophysiological analysis. Neural cells differentiated in vitro from hESCs exhibit broad cellular heterogeneity with respect to developmental stage and lineage specification. To analyze the population of the derived NPs, we used fluorescence-activated cell sorting (FACS) and characterized the expression of several pluripotent and neural markers, such as Nanog, SSEA-4, SSEA-1, TRA-1-60, CD24, CD133, CD56 (NCAM), beta-III-tubulin, NF70, nestin, CD271 (NGFR), CD29, CD73, and CD105 during long-term propagation. The analyzed cells were used for transplantation into the injured rodent brain; the tumorigenicity of the transplanted cells was apparently eliminated following long-term culture. These results complete the characterization of the CCTL14 line of hESCs and provide a framework for developing cell selection strategies for neural cell-based therapies.