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)
1. Isolation and characterization of human embryonic stem cells and future applications in tissue engineering therapies
1.1. Derivation of human embryonic stem cells from the ICM
The destruction of the preimplantation human embryo in order to derive hESC lines has prompted fierce ethical debate in many countries, especially on religious grounds, which to some extent remains unresolved and irresolvable. The result is the implementation of policies of ethical oversight, regulation and permission for hESC research, which vary from country to country, and even within a country (the United States). In the United Kingdom, early introduction of laws related to human embryo research and the formation of a regulatory body (Human Fertilisation of Embryology Authority, HFEA) provided a framework (and important public confidence) for continuation of hESC research. Clinical-grade hESCs must meet compliance with conditions set by the EMA and overseen in the United Kingdom by the Human Tissue Authority. In the United States, the FDA and National Institutes of Health (NIH) undertake this responsibility. Since the development of cell therapies using pluripotent stem cells is novel, it remains to be determined exactly how regulatory authorities will implement conditions of compliance.
The induction of pluripotency in mouse and human somatic cells in 2006 – 07 using retroviral vectors to introduce four genes to reprogramme the genome (Oct4, Sox2, Klf4, and c-Myc) and enable the derivation of induced pluripotent stem cells (iPSCs) (Takahashi et al., 2007) radically changed the landscape of human pluripotent stem cell (hPSC) research (Yamanaka, 2012). This technology not only provides a potential route for the creation of patient-specific stem cell lines for use in cell therapies but also makes pluripotent cell lines available to many more laboratories, with seemingly fewer ethical bottlenecks. However, hESCs remain the current gold standard as their cellular reprogramming events are those that are normally evoked in the early embryo, rather than artificially induced, and they are therefore less likely to be subject to aberrant epigenetic effects on their gene function. Moreover, ethical issues related to obtaining informed consent from donors to use tissue samples to derive iPSCs still persist. Progress in the use of hESCs (or iPSCs) for therapy will depend on whether robust protocols for their expansion and differentiation to a precise and economic manufacturing level can be devised, and a key aspect in meeting this objective is the implementation of reliable and accurate assays of cell type and quality.