[Molecular biological focus on stem cell research]

Stem cells are defined by their capacity to reproduce themselves and to differentiate into many other cell types. Differentiation requires external signals and involves activation of a small number of genes. Which source of stems cell will eventually be used in the clinic has not yet been determined. Embryonic stem cells have unlimited in vitro division capacity and can differentiate to all cell types, but there may be a problem with genomic instability. Stem cells from cord blood and adult tissue seem to have limited in vitro division and differentiation potential, but stable genomes.