Human embryonic stem cells (hESC) were first described in 1998 and since then hESC research has become a field of constant progress and improvement. The specific characteristics of hESC make them a valuable tool not only for research in early human development, disease modelling, drug development and testing, but also a potential tool for future therapeutic indications. All this scientific and medical potential would not have been fulfilled without the progress made in the field of medically assisted reproduction, and especially in the in vitro culture of the human embryo to the blastocyst stage.
Research in the field of embryonic stem cells would also not have been possible without all those couples that have donated their embryos for research, and the legislators in many countries that have provided a legal framework for this type of research.
Human embryonic stem cells are derived from 4 to 7 days old human embryos. The inner cell mass cells are harvested and cultured to obtain pluripotent stem cells that can differentiate into any cell type of the human body, and that indefinitely self-renew in the laboratory.
Established hESC lines are the subject of different research activities, such as development of differentiation protocols that yield physiologically useful cells, or obtaining hESC that are proven safe for clinical use in cell-based therapies. One example relevant to the ESHRE membership are ongoing attempts to differentiate hESC into functional gametes – oocytes and sperm.
Somatic stem cells (SSC) are rare undifferentiated tissue-specific cells present in adult tissues and organs that are defined by the capacity to renew themselves and to differentiate into specialized cell types. They are usually in a quiescent state (G0 phase) and located in a protective environment named the niche. They proliferate through asymmetric cell division, giving rise to one replacement stem cell and one transit amplifying cell. The interactions with the stem cell niche are crucial to this process. SSC have been isolated from several tissue sources, including the central nervous system, bone marrow, retina and skeletal muscle, suggesting that most adult tissues potentially contain the SSC population. This specific cell cluster possesses a diverse differentiation repertoire ranging from unipotential adult stem cells capable of generating one specific cell type to oligopotent cells that produce a limited range of differentiated cell lineages according to their location. SSC are regulated by a specific physiological microenvironment within the niche, and they are different in their cellular composition, structure and location in different tissues. Niches have been identified and characterized in the hair follicle bulge and interfollicular regions of the epidermis, in the intestinal crypts, at the periosteum and blood vessels for HSC, neural stem cells in the subventricular and subgranular zone and in the mouse and human endometrium and myometrium.
Commonly abbreviated as iPS cells or iPSCs, these are pluripotent cells that are obtained by the overexpression of certain genes in adult somatic cells such as skin fibroblasts. This overexpression is typically achieved through insertion of viral vectors, such as retroviruses, which is a cause for concern if these cells were to be used in cell therapies. Research is actively ongoing to achieve protocols that obviate the use of viral transfection and genomic integration.
IPSCs were first produced in 2006 from mouse cells and in 2007 from human cells by Japanese researchers led by Shinyahynia Yamanaka. This important advancement in stem cell research may allow researchers to obtain pluripotent stem cells without the need for embryos and the recognition of this major breakthrough has led to the award of the Nobel Prize for Medicine for 2012 to Shinyynia Yamanaka. IPSC are believed to be very similar to hESC and thus equally constitute an important tool in research and regenerative medicine. However, the extent to which iPSC and hESC differ still needs to be fully explored.
Other cell types such as spermatogonial stem cells have proved to hold pluripotency characteristics and also constitute active fields of research related to human reproduction and embryology. Finally, adult stem cells also pervade some of the subspecialities in ART, such as the study of the endometrium or stem cells in the ovary.
Being aware of the importance of such a vigorous field of research directly related to our activity, the ESHRE has installed a Special Interest Group in Stem Cells in Madrid at the ESHRE 19th Annual Meeting, 2003. The SIG Stem Cells is of interest to ESHRE members who are involved in the present and future developments in hESC research. The aims of the SIG Stem cells are the promotion of the study and discussion of all aspects of hESC research as well as the provision of a forum for the exchange of information between scientists in this area. Of note is that quite a number of pioneers and leaders from such fields as clinical embryology and PGD are now actively involved in hESC research, making this field of particular interest for the ESHRE. We foresee that the interest will be growing in the next future.
Being aware of the importance of such an emerging field of research directly related to our activity, the ESHRE has settled a Special Interest Group in Stem Cells. The SIG started its activity in Madrid (ESHRE 19th Annual Meeting, 2003) and pre-congress courses have been organised in most annual meetings (Madrid, Prague, Lyon, Barcelona), in some cases in collaboration with other SIGs such as the Reproductive Genetics and the SIG in Ethics and Law. The SIG Stem Cells is of interest for ESHRE members who are involved in the present and future developments in hESC research. The aims of the SIG Stem cells are the promotion of the study and discussion of all aspects of hESC research as well as the provision of a forum for the exchange of information between scientists in this area. It has to be pointed out that a certain number of IVF laboratory pioneers and leaders are now actively involved in hESC research, making this field of particular interest for the ESHRE. We presume that the interest will be growing in the next future.