Stem Cell Processing (Stem Cells in Clinical Applications)

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they have increased expression of a gene called telomerase. High levels of telomer-
ase maintain the telomere ends of the chromosomes after every cell division giving
these cells the ability to divide indefi nitely (Thomson et al. 1998 ). Even though ES
cells possess the proven ability to form derivatives of all three germ layers, both

Fig. 9.1 Generating ES
cell lines from human
blastocysts

9 Human Embryonic Stem Cells and Associated Clinical Concerns