ScienceDaily (July 9, 2008) — For the first time in the world
scientists have succeeded in developing human embryonic stem cells
(hESCs) from a single cell, or blastomere, of a 4-cell stage embryo,
the 24th annual conference of the European Society of Human
Reproduction and Embryology heard on July 9. Dr. Hilde Van de Velde,
from the Vrije Universiteit Brussel (VUB), Brussels, Belgium, said
that their research meant that it might be possible in the future to
produce hESC lines at an earlier stage without destroying the embryo.
Blastomeres are formed in the very early stages of embryonic
development. About 24 hours after fertilisation the egg divides into
two cells. Division into four cells occurs after 48 hours. After 96
hours, at the morula stage, the fertilized egg has divided four to
five times. During this time the size of the embryo does not increase,
so the cells become smaller and smaller and they are strongly attached
to each other which makes them more difficult to manipulate. At this
early stage important decisions are taken: inner cells will become the
foetus (including germ cells) and outer cells will become trophoblast
(the outermost layer of the embryo that attaches to the wall of the
uterus and serves as a nutritive pathway). There was, until now,
uncertainty about which stage of early development the blastomeres
ceased to be totipotent, i.e. able to develop into all cell types of
the body.
Worldwide, the majority of established hESC lines have been derived
from the inner cells at the blastocyst stage; these are said to be
pluripotent. "Previously, scientists have been able to derive hESC
lines at the 8-cell stage," said Dr. Van de Velde, "but success rates
were variable and it was necessary to culture them by mixing with
established hESC lines. We have been able to derive hESCs at an
earlier stage of embryonic development, and without the need for
co-culture with established hESC lines. Now we have derived a second
hESC from one cell of a 4-cell stage embryo. Given the complex nature
of earlier attempts, we were pleased that we could develop a technique
that seemed simple and was also reproducible."
The scientists used mature eggs donated by couples being treated at
the University's IVF centre. Embryos were obtained after ICSI using
sperm from a consenting donor. Three, good quality 4-cell stage
embryos were split into 12 single blastomeres and allowed to grow in
vitro to produce twelve morulas that were cultured in the conventional
way for hESC derivation. From these twelve, one resulted in a stable
hESC line. The scientists concluded that at least one cell was
pluripotent.
These new data confirm their recent report that at the 4-cell stage
the cells are equal and totipotent. "Now we will try to derive four
hESC lines from the same embryo in order to compare the potency
capacity of all four cells," said Dr. Van de Velde.
The work could have major ramifications for preimplantation genetic
diagnosis (PGD), by enabling the biopsy of one cell from a 4-cell
stage embryo, allowing the remaining three cells to develop into a
blastocyst (five day embryo) which could be transferred into the
uterus and develop into a healthy baby. "Currently, PGD is performed
at the 8-cell stage, when one or two cells are removed; others have
derived stable hESC lines at this stage but with low efficiency. If
hESC derivation at the 4-cell stage turns out to be more efficient
then at the 8-cell stage, we might consider to change our PGD policy
in cases where we perform human leukocyte antigen (HLA) typing," said
Dr. Van de Velde.
HLA molecules play an important role in the immune system by ensuring
that our bodies recognise their own cells as their own. By being able
to select an HLA-identical embryo, the cord blood of the 'saviour
siblings' could help cure an older brother or sister suffering from a
genetic disease affecting the production and/or function of
hematopoietic (blood producing) stem cells. "We could also combine the
pregnancy of an HLA-matched healthy baby with the derivation of a
personal hESC line that could be used to generate in vitro
hematopoietic stem cells as an additional source of hematopietic stem
cells," she said.
"We need to determine whether the removal of one cell at the 4-cell
stage impairs the capacity of the embryo to develop into a healthy
child in comparison with the removal of one/two cells at the 8-cell
stage. We understand that some people may have ethical concerns about
the production of hESCs," said Dr. Van de Velde, "but we already know
from cryopreserved embryos that the loss of one cell from a 4-cell
stage embryo does not affect its capacity to implant in the womb. We
believe that by making it possible to intervene at an earlier stage,
and without destruction of the embryo, these ethical concerns will be
diminished."
In fact, opinion among the public is very much in favour of stem cell
research, another researcher told the conference. Ms Jaclyn Friedman,
a clinical embryologist at Reproductive Biology Associates, Atlanta,
Georgia, USA, undertook an on-line survey looking at attitudes towards
IVF around the world. Two questions related specifically to human
embryonic stem cell research and use in therapy.
"This is the first time an on-line questionnaire has been used to
establish a cross-sectional view of ethical opinion in the global
community," said Ms. Friedman. "Because stem cell research is
increasingly important, we felt that we needed to gauge opinion among
members of the public, as well as IVF patients, doctors and scientists
working in the field."
The researchers analysed the following two questions:
* "I believe that it is morally wrong to use embryonic stem cells
for research"
and
* "I believe that it is morally wrong to use embryonic stem cells
for medical treatment."
573 people responded to these questions. The researchers found that
47.1% strongly disagreed with the viewpoint posed in question 1,
whereas only 4.5% strongly agreed. 4.1% agreed, 10% were neutral, and
31.2% disagreed, meaning that in total 78.3% of respondents disagreed
with the view that it is wrong to use hESCs in research.
For the second question, the results were broadly similar, although
fewer people (3.1%) felt that it was morally wrong to use ESCs in
medical treatment than in research. "We found no difference between
male and female attitudes towards using hESCs for research, but when
it came to medical treatment, men showed significantly more support
than women. "We found no significant differences when we looked at
particular age groups, but a higher level education of respondents
correlated with greater support for the use of hESCs, both in research
and medical treatment. There were no important differences among
regions of the world.
"We hope that this questionnaire might act as a pilot study for
something much larger and more representative of the views of the
international community. But even with our existing numbers, we found
enough difference between the views of people working in the field,
the general public, and patients, to know that the results have
statistical significance. Our study shows that public, patient, and
scientific opinion is very much in favour of both stem cell research
and the therapeutic use of stem cells in medical treatment. This is
different from the perceived equal distribution for and against hESC
use reported in the news media," she said.
Adapted from materials provided by European Society for Human
Reproduction and Embryology, via EurekAlert!, a service of AAAS.
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