Culture and Characterization of hESC

were generated in Madison, Wisconsin, by Thompson’s group in 1998 (99). In contrast, murine ESC were isolated and initially described in the 1980s (27, 83) and have been used in many different models ever since, paving the way for current studies on hESC. The promise generated by the possible application of hESC to disease treatment has led to a tremendous interest in stem cell research overall. However, success in the cloning of large animals has raised concerns that stem cell research could eventually result in human cloning (19, 106). Current methods for ESC derivation are still very elaborate and require specialized labs for the successful derivation of ESC. Two such approaches for the derivation of hESC have been described. A number of hESC lines have been derived by immunosurgery from the inner cell mass of the blastocyst-stage preimplantation embryos produced by in vitro fertilization (99). An alternative to the use of embryos derived after egg fertilization is nuclear transfer (NT), a technique whereby the nucleus of a somatic cell is transferred into an enucleated oocyte. This procedure has already been successfully performed in sheep and bovine cells (19, 106). These results demonstrate a potentially less controversial and ethically more acceptable method of ESC derivation in humans. It appears therefore that NT would be the preferred method over the classical ESC derivation via the generation of an embryo. If further developed, NT would allow the generation of many more cell lines without the need for in vitro fertilization or the destruction of an already existing embryo. However, we need to learn more about the potential differences between hESC lines generated by NT vs. those generated via an embryo after oocyte fertilization by a sperm. Although the focus of this review is on hESC, the data in the literature is limited. Here we will discuss hESC in the light of available human and mouse ESC data.