Memorandum 66
Supplementary submission from Dr Stephen
Minger, Director, Stem Cell Biology Laboratory, Wolfson Centre
for Age-Related Disease, King's College London
In response to your letter of 7 February, 2007
regarding the generation of interspecies embryos using somatic
cell nuclear transfer.
1) I can see no reason for culturing the
embryo beyond the 14 day limit as set out in the HFE Act. In reality,
the embryo will only be cultured for five to seven days after
nuclear transfer and activation until the formation of inner cell
mass, at which the time the embryo is disaggregated and the inner
cell mass is placed into culture to form human embryonic stem
cells.
2 & 3) Like all embryonic stem cell
lines, it will be important to determine that interspecies cloned
stem cell lines are pluripotent, that is capable of differentiating
into cells of all three germ layers and thus into a wide range
of cell types. The general methods for determining pluripotency
are to a) allow embryonic stem cells to spontaneously differentiate
or to use differentiation protocols and then look for the generation
of a number of cell types across the three germ layers using markers
that recognise specific cell types; b) to inject undifferentiated
cells into mice lacking an immune system and then analysing the
resultant benign tumours (teratomas) that form for multilineage
differentiation; and c) introduction of labelled undifferentiated
stem cells into the inner cell mass of a developing blastocyst
which is then implanted into a surrogate uterus. Pluripotency
can thus be assessed by looking for the presence of marked cells
throughout the organs and tissues of the resultant embryo or adult
organism.
It is my belief that the first two tests of
pluripotency are sufficient to provide the necessary information,
though there may be instances where the third test might be valuable.
However, for our research projects we will rely solely on the
use of teratomas and in vitro differentiation to assess pluirpotency.
4) There are likely to be a number of instances
where implantation of human embryonic stem cell-derived populations
into experimental animals will be necessary. These include for
example, testing the neuronal differentiation pattern of cells
transplanted into lesioned brain, assessing the contribution of
stem cells to repair of the damaged spinal cord, and determining
the ability of stem cells to integrate into damaged myocardium.
These and other similar procedures all required Home Office approval
and do not differ in any significant way from traditional preclinical
testing of human cell populations in experimental animals.
Many thanks for allowing me to respond to your
queries.
February 2007
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