The ability to genetically modify human embryonic stem cells (HESCs) will be critical for their widespread use as a tool for understanding fundamental aspects of human biology and pathology and for their development as a platform for pharmaceutical discovery. Here, we describe a method for the genetic modification of HESCs using electroporation, the preferred method for introduction of DNA into cells in which the desired outcome is gene targeting. This report provides methods for cell amplification, electroporation, colony selection and screening. The protocol we describe has been tested on four different HESC lines, and takes approximately 4 weeks from electroporation to PCR screening of G418-resistant clones.

The application of human embryonic stem (hES) cells in regenerative medicine will require rigorous quality control measures to ensure the safety of hES cell-derived grafts. During propagation in vitro, hES cells can acquire cytogenetic abnormalities as well as submicroscopic genetic lesions, such as small amplifications or deletions. Many of the genetic abnormalities that arise in hES cell cultures are also implicated in human cancer development. The causes of genetic instability of hES cells in culture are poorly understood, and commonly used cytogenetic methods for detection of abnormal cells are capable only of low-throughput analysis on small numbers of cells. The identification of biomarkers of genetic instability in hES cells would greatly facilitate the development of culture methods that preserve genomic integrity. Here we show that CD30, a member of the tumor necrosis factor receptor superfamily, is expressed on transformed but not normal hES cells, and that CD30 expression protects hES cells against apoptosis.

Human embryonic stem cells (hESCs) have been advanced as a potential source of cells for use in cell replacement therapies. The ability to identify hESCs and their differentiated progeny readily in transplantation experiments will facilitate the analysis of hESC potential and function in vivo. We have generated a hESC line designated 'Envy', in which robust levels of green fluorescent protein (GFP) are expressed in stem cells and all differentiated progeny.

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