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Even after successful isolation and expansion, the major obstacle of differentia-
tion into the specifi c cell type remains, and once transplanted these cells must effec-
tively integrate with the patient’s body systems and function together with other
cells. Following transplantation cell survival and the correct desired function must
be ensured (Buxton 2009 ). Most importantly, serious side effects such as cancer or
infection must be prevented. Since ES cells can proliferate indefi nitely, they could
result in both quantity and compatibility issues (Brunt et al. 2012 ). The challenge is
to strike a balance between directing cell growth and differentiation into specialised
tissues that can replace damaged ones and ensuring that cells do not excessively
grow becoming cancerous. Following transplantation, the issue of tissue compati-
bility still remains one of the biggest challenges, and recipients usually have to take
strong immunosuppressive drugs to minimise the risk of rejection; however, these
drugs make the patient vulnerable to any other infections.
Another issue with ES cell-based therapies is timing: when to transplant these
cells into the patient? Stem cells go through many intermediate stages before they
become fully specialised; deciding when to transplant these cells remains an open
question, and the answer is different for different diseases (Bor 2004 ).
Good Manufacturing Practice (GMP) guidelines are set up to ensure that the
manufacturing of medicinal products is under quality standards; these must be
employed in order to produce clinical grade cells with defi ned quality and safe
usability in patients. Unlike a conventional pill, ES cell-based therapies involve
living cells and so cannot be standardised easily. Before ES cells can be used in
patients, fi rstly several components of the culture need to be developed according
to GMP standards. As explained by Unger et al. ( 2008 ), ‘the feeder cells or the
culture matrix, all the components of the culture and cryopreservation media, and
all the processes involved’ have to be described, validated and standardised
according to the GMP quality system. GMP adaptation for differentiation to other
different cell types might prove to be even more diffi cult. Re-evaluation of GMP-
verifi ed human ES cell culture conditions must be carried out as these ES cell-
derived cells are used to treat humans, so all safety precautions must be taken
(Unger et al. 2008 ). As shown in Fig. 9.5 , controlling, monitoring and achieving
these vital standards is a complex and expensive process and remains a major
constraint.
Human ES cell research should be conducted in accordance with all applicable
laws and guidelines relating to recombinant DNA research and animal care. The
federal government sets up protocols regarding the management of laboratories
where products that might ultimately be used in humans (as in a clinical trial) are
being developed. FDA’s Good Laboratory Practice (GLP) regulations establish
principles for nonclinical laboratory studies which include in vitro or in vivo exper-
iments, determining the test articles, an activity that would be necessary in the
preclinical phase of human ES cell research. Failure to abide by GLP regulations
would leave human ES cells less useful in the future if they were considered for
clinical trials of tissue transplantation or other cell-based therapies (Medicine and
Council 2005 ).
D.M. Kalaskar and S.M. Shahid