Submission from Professor Hui Z. Sheng
SCNT OR "THERAPEUTIC
(i) To avoid the problem of immune rejection
when transplanting cells of therapeutic value that have been derived
from hES cells. hES cells from conventional, IVF-derived embryos
can not provide a sufficiently good match for many types of transplant,
but an ES cell line derived using a somatic cell from the patient
will be genetically identical and therefore seen as "self"
by the patient's immune system.
(ii) Certain types of genetic disease are
very hard to study in the patients themselves, especially if the
effects of the mutation begin during embryonic development. The
ability to derive hES cells corresponding to the patient, from
which the appropriate tissue type could be obtained in cell culture,
would allow not only the study of the disease in vitro, but also
to screen potential therapies.
(iii) To explore basic mechanisms of nuclear
reprogramming. This knowledge might help to derive methods of
changing one type of adult cell to another.
There are several reasons for carrying out SCNT
experiments using animal oocytes, rather than human oocytes. These
would lead to the formation of cybrids (each of which has a human
nucleus and animal cytoplasm), which can develop to blastocyst
stages from which ES cells can be derived. My own work together
with that of others has shown this is feasible. There are interesting
scientific questions that can be addressed using human somatic
cells and animal oocytes, such as the species-specific nature
of nuclear reprogramming and mitochondrial biology. However, the
main reason is to overcome the shortage of human oocytes that
are available for research.
(i) Practice with animal oocytes, which
are readily available (eg, bovine ooctyes from slaughter houses),
can be used to help train the team of scientists in the methods
that could eventually be used with human oocytes. The methods
require many separate steps to all work in concert, so training
and experience are crucial to success.
(ii) It is unlikely that ES cell lines derived
in this way would be used directly for therapy in human patients,
but they could be used to test methods in animal models of the
(iii) Using the system we can learn about
the molecular mechanisms that are involved in efficiently reprogramming
the somatic cell. This will allow us to improve the methods, so
that fewer human oocytes would be required if SCNT was to be applied
Cybrid embryos are unlikely to be viable as
embryos much beyond the blastocyst stages due to inefficiencies
in reprogramming all genes required for postimplantation development
in all cells. However, ES cells derived from the blastocysts will
have undergone another selection process where only relatively
normal cells will survive in culture. These cells are therefore
very likely to be useful for research.
Simply banning this type of experiment will
impede progress towards finding cures for many types of genetic
and degenerative disease. It will also prevent the accumulation
of knowledge about early human embryonic development and about
reprogramming. Such knowledge is likely to be critical to allow
us to find ways to directly reprogram adult somatic cells into
therapeutically useful cell types, using defined factors, and
thus avoiding the use of oocytes and early embryos.
UK is currently a world leader not only in embryological
research and cloning, but also in policy making in this field.
The government in UK has established an image to be able to balance
scientific development and ethical issues with confidence and
vision. Its regulatory policy in embryological research has provided
a permissive but strictly regulated environment. Moreover, several
UK organisations, such as the Wellcome Trust, the Nuffield Bioethics
Council, the HFEA itself, have all put out reports and discussion
papers that have been very useful in the debate worldwide. The
UK policy has positively influenced the policy making in other
countries, including China, Japan, USA et al. Banning these types
of experiment in the UK would send a confusing and discouraging
message to the rest of the world.