Principles of stem cell biology and cancer: future applications and therapeutics. Edited by T. Regad, T. J. Sayers and R. C. Rees. John Wiley & Sons (2015)
220.127.116.11. In vitro: EBs
18.104.22.168. In vivo: teratoma formation
Immediately following their derivation, hESCs are identified fundamentally on the basis of their indefinite capacity for self-renewal, their ability to form derivatives of all three embryonic germ layers and, usually, their ability to maintain a euploid karyotype over extended periods in culture. However, not every derivation procedure results in an established hESC line, and a variety of other cell types may grow out from isolated embryo cultures. Furthermore, hESCs may be derived at different stages of embryo development (i.e. early or late blastocyst) while still retaining pluripotency, which can alter the subsequent features of their cell population. While cell lines may be superficially similar in these aspects, they often show significant differences in stem cell surface antigen expression, DNA methylation status, X-chromosome inactivation, variation in specific gene expression, cell doubling time, and capacity to differentiate. The cause of this variation between cell lines is largely unknown, but it is likely, in part at least, to be due to the wide genetic background of human donors (mESCs, by contrast, are produced from inbred mouse strains); it also depends on environmental conditions and stresses, which can impart phenotypic changes on cells during derivation and culture. It is therefore essential that hESCs are characterized under a set of criteria which allows for accurate, valid and robust comparisons to be made both within and between laboratories. In this section, we look more closely at the characteristics that currently define hESCs.