Memorandum 64
Supplementary submission from the Centre
for Regenerative Medicine, the Queen's Medical Research Institute,
University of Edinburgh
RE: SCIENCE AND TECHNOLOGY SELECT COMMITTEE
INQUIRY INTO THE APPROPRIATENESS OF CURRENT GOVERNMENT PROPOSALS
FOR REGULATION OF RESEARCH USING CHIMERA AND HYBRID EMBRYOS
I am writing to address specific questions that
you raised in regard to this area of research.
1. Do you envisage a requirement to take
studies using human-animal chimera or hybrid embryos past the
14th day of development as per current HFEA regulations which
prohibit the keeping or use of a human embryo which is more than
14 days old?
I do not envisage a benefit in keeping the embryos
beyond day 14. Indeed in the great majority of studies the period
of culture would be for six or seven days which is sufficient
time for the embryo to reach the stage from which stem cells may
be derived.
2. Assuming that it is possible to produce
cells eg embryonic stem cells created through somatic cell nuclear
transfer of human genetic material into enucleated animal ova,
do you envisage the need to establish totipotency or pluripotency
of these cell lines? For what reasons might such studies be required?
Strictly, a cell is said to be totipotent only
if it is able to form an offspring. That would mean transferring
the entire reconstructed embryo to a surrogate mother to give
it the chance to develop into a child. There is no interest in
this information and such a study has already been made illegal.
By contrast, it is important to understand and
define the extent to which a cell population is able to form different
tissues, its "developmental potential". This is a very
basic step if the cells are to be used. Are they able to form
all of the different types of cell of an adult (pluripotency)
or is their potential limited (perhaps to multipotentiality).
It is absolutely essential that groups working in different parts
of the world co-operate to establish and then use standard methods
of assessment so that work done in the different laboratories
can be compared directly. The Medical Research Council is one
organisation that is already supporting such an international
initiative with human embryo stem cell lines derived from fertilised
embryos (as distinct from those produced by somatic cell nuclear
replacement).
3. What mechanisms would be used to establish
totipotency or pluripotency of stem cell lines eg those produced
through somatic cell nuclear transfer of human genetic material
into enucleated animal ova? Is there a need for implantation of
such cells into animals eg animal blastocysts?
As noted already a test of totipotency is not
envisaged.
In total three tests have been used to assess
developmental potential and the methods used in the past to make
this assessment have varied with the species from which the cells
were obtained. I will return to tests with cells that have developed
from stem cells in answer to question 4 later in the letter.
The most stringent test involves mixing the
cells with an embryo. This may be at any early stage of development,
but has usually been at the 8-cell stage by aggregation or the
blastocyst stage by injecting a small number of cells into the
fluid filled cavity of the embryo. The embryo may then be cultured
briefly before being transferred to a surrogate female. This method
of assessment has only been used with laboratory and farm animals,
but not with non-human primate or human embryo stem cell lines.
In conversation with international colleagues who work with non-human
primate embryo stem cells two reasons are given for the decision
not to use this method of assessment. They judge that methods
that only use culture provide adequate information. Furthermore,
experiments involving chimera production after injecting cells
into blastocysts obtained from other primates would be very expensive.
In addition to these concerns, in the case of human embryo stem
cell lines there are very serious ethical issues. I do not know
of any laboratory that envisages inserting human embryo stem cells
into an animal blastocyst.
The second test involves placing the cells in
specific sites of immune-deficient mice which are not able to
reject the cells. Typically, the cells develop into tumours in
which it is possible to see cells of many different kinds, providing
evidence that the cell population has the potential to form those
cell types, probably all types. This test has been used in all
species from which embryo stem cells have been obtained, specifically
including human. As it raises different ethical issues and is
of considerable cost, this method is used frequently, but is not
the initial means of assessment.
In the least stringent test cells are cultured
in systems that promote the formation of many different tissues.
Typically, cells are lifted from their attachment to the culture
dish and allowed to aggregate in medium that promotes growth and
differentiation. Over a short period and in a rather haphazard
manner different types of cell are formed. This is the day to
day method for assessment of the ability of embryo stem cells
to form different types of tissue and would be used routinely
in any research to derive cells from human embryos by somatic
cell nuclear transfer.
In summary then, the most frequently used method
of assessment is to culture the cells. Greater confidence can
be gained by assessing tissue formation within tumours formed
in immune-deficient mice.
In the future it is likely that molecular tests
will become more effective means of characterising a cell population
than at present. This might involve monitoring the expression
of many genes. Alternatively, the quantity of specific proteins
on the cell surface might be measured as the cells are passed
through scanning equipment able to assess several proteins at
the same time, the process is known as FACs scanning or sorting.
However, studies in animals will always be required from time
to time.
4. Do you envisage additional requirement
for implantation of stem cell lines produced via somatic cell
nuclear transfer of human genetic material into enucleated animal
ova other than for establishment of pluripotency? For what reasons
might such studies need to be conducted?
Human cells are introduced into experimental
animals for different reasons. The most common reason is to discover
if healthy cells are able to treat a disease that closely resembles
a human disease, such as Parkinson's disease or spinal cord injury.
Such a study is an essential preliminary to trials with human
patients. At some time in the future this might be necessary if
cells from cloned human embryos were being assessed for their
therapeutic potential. This approach was that envisaged by Professor
Hwang in Korea with his proposed "Patient specific cells".
The initial research proposals, by contrast,
envisage producing cells with the inherited characteristics of
a disease so that the disease may be better studied in the laboratory.
Placing cells that have been derived from embryo stem cell lines
for this purpose into animals may provide important information
about the characteristics of the cells. In this case transplantation
would be carried out at later stages of development than the blastocyst,
perhaps in a fetus or even after birth.
This situation can be exemplified by a hypothetical
experiment to study inherited forms of Parkinson's or Motor Neuron
Disease. Cells with the potential to form the nerve cells of the
human brain might be introduced into the brains of a mouse fetus.
By transplanting into different mice either healthy cells or cells
known to be vulnerable to the human disease a comparison could
be made of healthy cells with those known to be vulnerable to
the disease. These "chimeras" would be made up almost
entirely of mouse cells, but with a proportion of human cells
in the brain. Once it had been confirmed that the cells showed
symptoms of the disease these chimeric animals might then provide
a means of assessing the efficacy of new drugs. Such a series
of experiments has been initiated in Stanford University and initial
findings suggest that the cells are able to integrate in the animal,
but that the behaviour of the animal is not changed.
It should be emphasised that no studies of this
kind are envisaged at present, but it would be helpful if the
law allowed the regulatory authority the opportunity to approve
such studies, should research in the meantime provide evidence
that they would be technically feasible and likely to provide
important information. Particularly strict requirements for the
supervision of the animals could be required.
I hope that this provides the information that
you require, but I would be glad to respond to further questions
if you wish. I apologise for the delay in writing.
February 2007
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