Since the first reports of the development of human embryonic stem cells (hESC), there have been several advances in the ability to grow these cells in vitro, but not all of these goals have been achieved to date. This chapter reviews the current status of development of culture systems for hESC. The development of human embryonic stem cells (hESC), presaged by work on stem cell lines from human embryonal carcinoma (EC) and monkey ES cells, led to a great surge of interest in potential therapeutic applications of pluripotent stem cells. The early reports of derivation of both monkey and hESC used serum-containing medium in combination with mouse embryo feeder cell support to maintain stem cell renewal, methodology that did not differ very much from those used previously to establish and propagate mouse ES cells or human EC cells. Several critical differences in growth properties of mouse and hESC soon emerged. The human cells display very low cloning efficiency when dissociated to single cells, and the addition of leukemia inhibitory factor (LIF) is without effect on the growth of human stem cells in the absence of a feeder cell layer. The original methods for cultivation of hESC had several drawbacks. The major challenges to the development of hESC culture systems are: to eliminate the use of serum in the medium, to eliminate the use of feeder cells, to improve the cloning efficiency, and to enable scale-up of the cultures.
