Controlled genetic modification of stem cells for developing drug discovery tools and novel therapeutic applications.

Unlike most adult stem cell populations, embryonic stem cells (ESCs) can replicate indefinitely in culture while preserving genetic, epigenetic, mitochondrial and functional profiles. In addition, ESCs and some adult stem cell populations are pluripotent or multipotent, so are excellent candidates for introducing targeted genetic modifications in a single population and investigating its effect in different cellular contexts. The ability of human ESCs (hESCs) to self-renew in prolonged culture and the unique advantages that this ability offers for gene therapy or drug discovery, have not attracted as much attention as cell replacement strategies, personalized medicine or other more direct clinical applications. In this review, advances made in vector design and gene insertion in human cells are assessed and novel strategies that might be used to achieve controlled genetic modifications in the setting of hESCs, with a focus on site-specific integration, homologous recombination, transposons and zinc finger nuclease systems, are discussed.