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be used to carry out more accurate drug discovery and toxicity studies on human
models (Rubin 2008 ). Stem cells help to overcome the limited availability of
patients and diseased tissues for study. Researchers and doctors are also using stem
cells as human models to augment their understanding of how the body works and
further why diseases and conditions develop.
Embryonic stem (ES) cells are one of the most discussed biomedical issues of
the day. These pluripotent cells have tremendous clinical potential in tissue repair
and represent potential to cure many common diseases; transplantation of human
ES cell-derived equivalents to damaged tissues in patients can restore normal func-
tion. However, the use of human ES cells raises many ethical concerns as they are
derived from human preimplantation embryos which are then destroyed (see
Sect. 9.3.1 ). Further, understanding the diversity amongst human ES cell lines and
overcoming associated technical constraints, such as successfully isolating lines
with robust differentiation potential, stand in the way of their full potential being
realised.

9.2 Human ES Cells

9.2.1 Sources

ES cells are cells derived from the inner cell mass (ICM) of the blastocyst (see
Fig. 9.1 ) which develops within 5 days of fertilisation of the oocyte (Thomson et al.
1998 ). They are capable of unlimited and undifferentiated proliferation in vitro as

Table 9.1 Different types of stem cells. Summary of different types of stem cells found in the
body and their potential use

Type of stem cells

Where do they come

from? What can they do?

Embryonic stem cells

(ES cells)

Inner cell mass of a

blastocyst (early-stage

embryo)

Differentiate to form all the different cell

types found in the body

Tissue stem cells (TS

cells)

Adult body tissues (e.g.

skin, blood)

Form only the cells found in their tissue

type, e.g. skin stem cells will only

differentiate to form types of skin cells

and not blood cells

Mesenchymal stem

cells (MS cells)

Bone marrow Form cells of the skeletal tissues (bone,

cartilage and fat)

Assist blood stem cells to make new

blood cells

Umbilical cord blood

stem cells

Umbilical cord after

childbirth

Form different cell types found in the

blood

Induced pluripotent

stem cells (iPS cells)

Made in the lab from

differentiated adult cells,

e.g. skin cells

Differentiate to form all the different cell

types found in the body (similar to ESCs)

D.M. Kalaskar and S.M. Shahid