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in vitro and in vivo (Chiu and Rao 2003 ), they cannot give rise to extraembryonic
tissues such as the placenta and membranes necessary for complete development
and so cannot form a whole new individual (Wert and Mummery 2003 ).
In most cases to date, spare IVF embryos have been used for ES cell isolation,
although in some occasions IVF embryos were specially created for this purpose
(Lanzendorf et al. 2001 ). Embryo quality is a major factor considered in the deriva-
tion of human ES cell lines (Turksen 2012 ). The best source would be from embryos
created via nuclear transfer, also known as therapeutic cloning (see Sect. 9.4.1 ),
especially to obtain ES cells. As summarised in Fig. 9.2 , a strict regime is followed
when selecting human ES cell lines for clinical application. Failure to apply the
appropriate selection procedure could have many consequences, some of which
include negative publicity of stem cell research, contamination of human ES cells,
considerable waste of time and resources, loss of rights on discoveries and with-
drawal of publications.
9.2.2 Isolation
Initially, most of the ES cells in humans were obtained by the isolation of the ICM
from the trophectodermal (TE) cells of the blastocyst using immunosurgery, a two-
step cytotoxicity procedure for selective killing of TE cells by pre-incubation with
Fig. 9.2 Selection criteria followed when obtaining human ES cell lines
D.M. Kalaskar and S.M. Shahid