Biotech Hobbyist Magazine.

Scientists Cultivate Cells at Root of Human Life.

Pushing the frontiers of biology closer to the central mystery of
life, scientists have for the first time picked out and
cultivated the primordial human cells from which an entire
individual is created.
The cells, derived from fertilized human eggs just before they
would have been implanted in the uterus, have the power to
develop into many of the 210 different types of cell in the body
-- and probably all of them. Because they can divide indefinitely
when grown outside the body without signs of age that afflict
other cells, biologists refer to them as immortal.
Eventually, researchers hope to use the cells to grow tissue for
human transplants and introduce genes into the body to remedy
inherited disease.
But there is a thicket of ethical and legal issues, as well as
technical problems, to be tackled. The cells are obtained from
embryos created at in-vitro fertilization clinics and so far do
not seem definably different from the handful of primordial cells
from which an entire individual is created.
Though the scientists involved in the work consider use of the
cells justified because they come from embryos that would
otherwise have been discarded, other believe the cells have a
special status in that they retain the potential to develop into
an individual, and that the use of the cells may draw criticism
if this status is not taken into account.
The new cells, known as human embryonic stem cells, have eluded
capture until now because they exist in this state only
fleetingly before turning into more specialized cells, and need
special ingredients to be kept alive outside the body.
The cells have many possible uses, of which the most promising is
to grow new tissue, of any kind, for transplant into a patient's
body. The cells may also offer effective routes to human cloning,
although both the researchers and their sponsor deny any interest
in this application. Another likely use is in gene therapy, the
insertion of new or modified genes into body tissue.
Two forms of human embryonic cells have been developed, one by a
team under Dr. James A. Thomson of the University of Wisconsin in
Madison, the other by Dr. John Gearhart and colleagues at the
Johns Hopkins University School of Medicine in Baltimore, Md. Dr.
Thomson's work is reported in this week's issue of Science, Dr.
Gearhart's in the Proceedings of the National Academy of
Congress in 1995 banned Federal financing of research on fetal
cells, including those derived from embryos, and the university
researchers whose work was announced today were funded by the
Geron Corporation of Menlo Park, Calif., a biotechnology company
that specializes in anti-aging research.
The research "has potential health benefits which I think are
extremely promising, and I am sorry that the law prevented us
from supporting it," said Dr. Harold Varmus, director of the
National Institutes of Health.
Cells Are Specialized as They Develop
After an egg is fertilized, it divides several times and forms a
blastocyst, a hollow sphere with a blob of 15 to 20 cells, known
as the inner cell mass, piled up against one wall. It is from
these cells that the embryo develops. Dr. Thomson grew his
embryonic stem cells from the inner cell mass of blastocysts that
had been left over from fertility treatments and were due to be
discarded. The donors of the blastocysts granted permission for
them to be used in research.
As an embryo grows and develops, its cells become irreversibly
committed to their fates as specialized components of the body's
organs. A pocket of cells, known as embryonic germ cells, is
protected from the commitment process so as to create the next
generation of eggs and sperm. Dr. Gearhart's group has developed
embryonic stem cells from the germ cells of aborted fetuses. The
cells developed by the two groups may well be equivalent but this
has yet to be proved.
If researchers are able to use the cells to grow new tissues, the
work could alleviate the shortage of livers and other organs for
transplant. Cultures of the cells in the laboratory could be
nudged down different developmental pathways to become heart or
bone marrow or pancreatic cells. Before reaching their final
stages, the about-to-become heart cells, for example, could be
injected into a patient's ailing heart. Guided then by the body's
own internal regulatory signals, the cells would develop into
new, young heart tissue, supplementing or replacing the heart
cells already there.
The same approach should in principle work with any tissue of the
body. Human embryonic stem cells would thus serve as a universal
spare parts system. Because the cells grow and divide
indefinitely in the laboratory, very few blastocysts would be
Many technical problems remain to be resolved. The art of
directing embryonic stem cells down specific pathways is in its
infancy. But heart muscle cells have been grown from mouse
embryonic stem cells and successfully integrated with the heart
tissue of a living mouse.
Dr. Thomson in 1995 isolated the embryonic stem cells of a
monkey, and Geron intends to do pilot experiments in these cells.
Another problem lies in making grafted cells compatible with the
patient's immune system.
Dr. Thomas B. Okarma, Geron's vice president for research, said
Geron would explore several ways of doing this. One, the least
preferred, would be to set up a bank with enough different human
embryonic cells that most patients could be matched. Another
would be to suppress the self-recognition genes that make the
stem cells appear foreign to the patient's immune system or, more
elegantly, to replace them with copies of the patient's own
self-recognition genes.
A third approach would be to convert one of the patient's own
body cells back to embryonic form by fusing it with a human
embryonic stem cell whose own nucleus had been removed. Embryonic
cells may have the power, not yet understood, to rescue an adult
cell's nucleus from its specialized state by flicking all the
switches on its DNA back to default mode. This reprogramming of
DNA is presumably what happened when mice were cloned in July
from adult cells.
Ethical Concerns Prevent Some Tests
The ethical status of the cells is also likely to be a matter of
discussion. They cannot become a fetus, as their blastocyst no
longer exists, yet they are very similar, if not identical, to
the 20 or so primordial cells from which the embryo develops.
Both research groups refer to their cells as "pluripotent"
because, when injected into a mouse with no immune system, the
cells develop into many of the major tissues of the body. The
tissues are disorganized and do not develop into a normal embryo.
The cells may also be "totipotent," meaning they can form every
one of the body's cell types. The test for totipotency, developed
with mouse embryonic stem cells, is to inject stem cells into
another blastocyst. A normal mouse will usually develop, but it
is composed of a patchwork of cells, some from the blastocyst and
some from the injected embryonic stem cells, proving the stem
cells retain all their powers.
It would be unethical to perform such an experiment on people,
but if it could be done, it seems likely that the human embryonic
cells cultured by the researchers would also prove to be
totipotent. If so, they may be capable in principle of
contributing to the generation of a new individual.
But ethicists say great care must be taken in work involving
human embryonic cells.
"Any time you take a cell off a blastocyst, that cell could be
used itself to create a human being, so some groups in our
society believe in making it transplantable you have derailed it
into becoming a kidney or some other tissue," Dr. Lori Andrews,
an expert on the laws governing reproductive technology at the
Chicago Kent College of Law, said.
"Some researchers say, 'It's just a bunch of cells, why should
people care?' But that totally avoids the fact that some people
do care, and I'm concerned that if the researchers don't take
into consideration the variety of viewpoints about embryos, they
might ultimately end up with more restrictive regulations."
Geron, which has exclusive licenses to use the cells, under
patents held by the researchers' universities, says it regards
them as qualitatively different from other cells used in
"Because these cells are derived from human blastocysts there is
a moral authority here, so we take these cells seriously," Dr.
Okarma, of Geron, said.
Dr. Okarma said he believes that use of the cells is justified
because they are something less than a living embryo, and
life-saving treatments may be derived from them. "We are not
saying the ends justify the means, but that given that the moral
authority of these cells is subordinate to that of the embryo,
the work we contemplate with them is appropriate," he said.
But Dr. Gearhart said he did not consider the cells that he and
Dr. Thomson have isolated to have a special moral status because
"they cannot form a fetus -- you cannot take one of these cells
and form a being out of it."
Still, Dr. Gearhart said he would not argue with the view of Dr.
Okarma at Geron that the cells had a different standing from
ordinary cells. Dr. Johnson, too, said that they were "special
Dr. Kevin T. Fitzgerald, a geneticist and Jesuit priest at Loyola
University Medical School, said that if the human embryonic stem
cells are totipotent, "then you are disrupting the viability of
life and we are back to the question of how to justify destroying
life for the purposes of scientific advancement."
The new cells may well reawaken fears of human cloning, although
many ethicists have now come around to believing that the
public's fears, despite science fiction writers' portrayal of
clonal armies of frenzied despots, are largely beside the point.
Many experts now predict human cloning is more likely to end up
as a rare treatment offered in fertility clinics, no different
from others like in-vitro fertilization and egg donation in that
they were first bitterly denounced and are now regarded as
"Human cloning will likely also be accepted once it becomes a
reality. Most of today's ethical arguments against it were
previously used against in-vitro fertilization and turned out to
be false," writes Dorothy C. Wertz, a bioethicist at the Shriver
Center, in the current issue of Gene Letter.
The availability of human embryonic stem cells suggests a quite
different possibility to biologists, who are well aware of how
mouse embryonic stem cells have long been used to generate
genetically altered mice.
The belief that humans can now be modified like the mouse "will
be the kneejerk reaction of the academic community," Dr. Thomson
He said human embryonic stem cells were unlikely to be used in
this way because there were more promising approaches for gene
therapy in people. For one thing, the mouse method requires the
creation of many embryos in order to obtain the few in which new
genes integrate in exactly the correct position, as well as the
breeding of a male and female mouse that have been genetically
altered. In its present form, the technique is evidently
inapplicable to humans.
Federal Law Shifts Research to Industry
The National Institutes of Health and the university scientists
it funds often play a leading role in reviewing new biomedical
But because of the Federal funding ban, university scientists
cannot get Government support to study human embryonic stem
cells. But industry can do whatever research it pleases, without
necessarily obtaining government approval. Academic biologists
believe this asymmetry is unfortunate and that the new technique
would receive better and more detached review if the agency and
its scientists could take part in the discussion.
Dr. Varmus said that an expert panel on human embryo research had
recommended to the health institutes that attempts to derive stem
cells from human embryos should be permitted, but Federal efforts
along this line were thwarted in 1995, with the Congressional
funding ban. Dr. Varmus said he believed the public "will see how
important the benefits of this research might be."
A Senate bill to ban human cloning was defeated in February this
year, the principal argument of its opponents being that its
overly broad language would prohibit promising research on human
embryonic stem cells.
In any event, any ultimate use of human embryonic stem cells may
face legal hurdles in the nine states that have outright bans on
research on human fetal tissues, Dr. Andrews said.
Some laws also prohibit payment for embryos, a restriction that
might extend to cells and tissues derived from embryos.
A Possibility of Eternal Cells
The technique reported today reaches to the central mysteries of
life and death. As biologists have recently begun to understand,
the body's cells are not inherently mortal. They become mortal
only when committed to developing into one or another of the
body's mature cell types. These specialized cells have mostly
lost the ability to grow and divide, but a few, typically those
of the skin and intestinal lining, can divide in culture about 50
times and then die.
In January this year, biologists at Geron learned how to
manipulate the section of DNA that marks off the 50 or so
permissible divisions. By reversing the changes in this section
of DNA, called the telomere, they created lines of cells that
divided well beyond the usual limit and are still going strong,
while retaining their youthful vigor and appearance. Biologists
refer to these cultured cells as immortal because they are
expected to grow and divide indefinitely.
Embyronic stem cells are also immortal because, until they become
committed to specialized fates, their telomeres are renewed each
time they divide. Unlike ordinary cells, they grow indefinitely
in culture.
In the lineage of living organisms, they cycle indefinitely from
the embryo to the germ line to a new embryo, forever avoiding
specialization into the mortal cell types that comprise the body.
Geron biologists believe they can manipulate the telomeres of the
human embryonic stem cells so that the cells stay immortal even
as they turn into specialized tissues. Can the mortal body
therefore be repaired with new, tissues that remain youthful
indefinitely? "Exactly," Dr. Okarma said.
Critics have said it would be folly to tamper with the telomere
division-counting system because it probably arose in evolution
as the body's last-ditch defense against any runaway cell likely
to become a cancer. Dr. Okarma said that new experiments had
largely laid this concern to rest by showing that telomerised
cells are no more likely to become malignant than are normal
These grand schemes may or may not come to pass, but the
techniques now at hand for manipulating human embryonic stem
cells will at least allow them to be seriously attempted. 
November 6, 1998