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How babies might be made:
Create eggs from stem cells // add sperm // place favorite embryo into uterus //
pass the next nine months debating ethical issues
Hard to Conceive
by anita slomski //
baby: hisayoshi osawa/getty images
O
n December 28, 1981, two days before his
71st birthday, gynecologic surgeon Howard Jones wrote a news release he hoped
he wouldn’t have to use. The first baby created by in vitro fertilization in the United
States was scheduled to be born by caesarean section that morning, and Jones and his wife, reproductive
endocrinologist Georgeanne Jones, feared that the small size
of the baby’s head meant a tragic defect had occurred, possibly as a result of the IVF procedure they had performed on
schoolteacher Judy Carr, whose three ectopic pregnancies had
destroyed her fallopian tubes. Jones left a blank space in the
release for whatever anomaly had doomed the child.
More than 15 years earlier, Jones had collaborated with British physiologist Robert Edwards from the University of Cambridge in England to fertilize a human egg in a cell culture dish.
Then, in 1980, Jones founded the first IVF clinic in the United
States at Eastern Virginia Medical School in Norfolk. But the
work was controversial, with Jones and his wife under constant
attack for what critics described as their unethical, morally indefensible medical experimentation. No less a luminary than
Nobel Prize winner James Watson, who with Francis Crick
had discovered the structure of DNA, told Edwards and Jones
in 1971 that infanticide was a likely outcome of IVF. “What are
we going to do with the mistakes?” Watson asked.
But Elizabeth Jordan Carr, born at 7:46 a.m. that December day, was perfectly healthy, and in 2010, Robert Edwards,
with whom Jones had collaborated, would be awarded the
Nobel Prize in Physiology or Medicine for developing IVF.
Jones, now 101, believes the recognition would have come
sooner save for religious opposition. Of Edwards, who died
in April, Jones notes that “the world has lost a true pioneer.”
And even though assisted reproductive technologies have resulted in more than five million births since 1978, challenges
to their legitimacy continue. In Personhood Revisited: Reproductive Technology, Bioethics, Religion and the Law, published
late last year, Jones takes on opponents who want to pass laws
asserting that personhood begins with fertilization—a major
threat to IVF, he says.
Yet ongoing debate about IVF and other assisted reproductive technologies hasn’t kept science from further expanding
the boundaries of human reproduction. Last year, two major
scientific studies raised the possibility that women whose egg
supply has dwindled because of age or exposure to agents that
damage egg cells may one day be able to use their own stem
cells to revitalize their ovaries with new eggs. That could reduce the need for IVF, and some researchers envision a time
in which a woman might freeze sufficient numbers of primitive egg cells to become pregnant whenever she wants. Meanwhile, scientists have for the first time sequenced the entire
genome of a fetus. The combination of having an unlimited
supply of eggs and the ability to manipulate genes in utero
could someday enable a couple to choose from among dozens
or even hundreds of their own embryos to create a healthy,
genetically desirable child.
The ethical issues that would pose are only beginning to be
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explored. Of more immediate concern is new research from
Australia that finds higher rates of birth defects in offspring
conceived by assisted reproductive methods. “These technologies have opened doors for countless people who would
never have had a chance at pregnancy,” says Thomas Toth, director of the Vincent In Vitro Fertilization Unit at Massachusetts General Hospital. “However, as the field evolves, we’re
realizing that we need to perturb nature as little as possible.”
W
omen, like other female mammals, are born with
all of the eggs they’ll ever have, as accepted scientific thinking goes. A fetus in the womb has seven
million immature egg cells called oocytes. A genetically controlled process of cell deletion winnows that to one million by
the time she’s born and to 200,000 at puberty. By menopause,
the supply is virtually exhausted. “We think oocyte death is
part of an audition process to ensure that only the best egg
ovulates during each cycle,” says Jonathan Tilly, investigator in
the Vincent Center for Reproductive Biology at MGH.
Typically, only one egg matures when a woman ovulates,
and that egg then allows only one sperm to fertilize it. But
if pregnancy doesn’t occur naturally, IVF may be called in to
help. With IVF, injected hormones spur the production of
multiple eggs. Using ultrasound to gauge when the ripening
eggs are about to emerge from the ovarian follicles that house
them, surgeons use a hollow needle to remove the eggs, which
are then combined with sperm in the lab. Usually after a few
days, the resulting embryo or embryos are transferred into the
uterus, and if all goes well, one (or sometimes more) attaches
itself to the uterine wall and a viable pregnancy results.
But IVF could be more effective—or might not even be
needed—if women could produce new oocytes, and controversial research by Tilly suggests that it might be possible. In
2004, he published a paper asserting that he’d found oocyte
precursor cells—stem cells—in mouse ovaries that could
change into oocytes. He had suspected that might be the case,
he says, because when he counted the number of follicles—
the ovarian structures that house oocytes—in mice at various
stages during their lives, he realized they were losing far too
many follicles too fast to sustain reproduction. That, along
with several other experimental observations, convinced
him the mice must be making new oocytes. But the scientific
community was skeptical. “At least 30 editorials claimed that
our interpretations were wrong,” says Tilly. Since that initial
paper, however, several other labs around the world have confirmed and extended Tilly’s observations.
Last year, Tilly stirred new controversy when he announced
in a paper published in Nature Medicine that he had isolated
oocyte stem cells in women using the same procedure that
helped him discover egg precursor cells in mice. Using fragments of frozen human ovaries from women in Japan who
had undergone gender reassignment surgery, Tilly separated
the stem cells from the immature oocytes in the ovaries, and
when he examined the isolated cells under a microscope, the
hair on his arms stood up. “These stem cells have a size and
shape like no other,” he says. “They are very small—about 6
to 8 microns in diameter—and they’re perfectly round. These
cells also had the specific gene pattern we expected to see. I
The Trouble With Older Fathers //
As men age, genetic mutations in their sperm multiply, raising risks for their offspring.
As science has attempted to accommodate
women’s desire to prolong their childbearing
years, men have tended to worry much less
about the ticking of their biological clocks. But
new research from Iceland suggests older men
don’t get a free pass. In the largest study to
date, whole genome sequencing was performed
on 78 nuclear families—father, mother and
child—to find genetic mutations that appear
only in the child. Spontaneous mutations that
occur at the time of conception—known as
de novo mutations—are important in natural
selection, helping delete the function of genes
that may be disadvantageous to the species. But
about 10% of de novo mutations are considered
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harmful, giving offspring a higher risk of autism,
schizophrenia and other disorders and diseases.
Fathers pass on nearly four times as many de
novo mutations as do mothers, and the older the
father is, the more mutations the child receives.
Because men make approximately 200 million
sperm a day, the precursor stem cells that
turn into sperm are continually dividing—and
creating opportunities for mutations to arise.
According to the Icelandic study, the mutation
rate doubles with every 16.5 years of age and
increases eightfold in 50 years.
“One out of 30 people is born with a de novo
mutation that results in the loss of the function
of a gene,” which is bound to have some impact
on that person’s traits, says neurologist Kari
Stefansson, chief executive of deCODE Genetics
in Reykjavik and an author of the study. Given
that half of all human genes affect the brain,
coding errors in DNA are particularly likely
to contribute to neuropsychiatric disorders
such as autism and schizophrenia. Stefansson
notes that people with those largely inherited
disorders tend to have few children, so logically
the diseases should become less and less
common. “Yet autism is on the rise today, and
the prevalence of schizophrenia has remained
the same for the past 100 years,” he says.
“There must be a very significant contribution
by de novo mutations.”
knew right then what I was looking at.”
Tilly marked the cells with a fluorescent green protein so he
could track them. Then he injected them back into the human
ovarian tissue and grafted that tissue into immunocompromised female mice. Within two weeks, he found glowing green
oocytes in the grafted tissue—proof, he says, that the human
stem cells had differentiated themselves into human oocytes.
Tilly’s critics say he has simply found immature egg cells,
not stem cells. But Tilly says you only have to watch the cells
proliferate in culture dishes to know that they are egg precursor cells, which can make more of themselves, rather than immature egg cells or oocytes that are unable to proliferate. This
is because oocytes and sperm undergo a unique process called
meiosis, losing half their DNA as they divide. That happens so
that when sperm and egg are joined as an embryo, there won’t
be twice the normal number of chromosomes. “Not only can
you make more of these cells outside the body; if you put them
back in the body, at least in mouse studies, they will commit to
meiosis and make eggs that fertilize and develop into healthy
embryos and offspring,” says Tilly.
vladimir godnik/getty images
M
itinori Saitou, professor of anatomy and cell biology at Kyoto University in Japan, has used a different type of stem cell to create mouse eggs that
have produced two generations of mouse pups. Saitou found a
new source for eggs in stem cells he obtained from fetal mice
and from pluripotent stem cells (primordial cells that can be
coaxed to differentiate into specialized cells, such as eggs),
also from fetal mice. Using cytokines and growth factors,
Saitou programmed the fetal cells to become primordial germ
cells that started to differentiate into oocytes in a lab dish. To
get the cells to mature and function as oocytes, Saitou mixed
them with other fetal ovarian cells to make “reconstituted
ovaries,” which he transplanted into immune-deficient adult
female mice. After four weeks, Saitou removed the ovaries,
isolated the oocytes, fertilized them with mouse sperm and
transferred the embryos to surrogate mice, which gave birth
to seemingly healthy pups that were also fertile.
The research shows that it is possible to create functional
eggs using stem cells, but Saitou cautions that we are a long
way from producing eggs from an adult woman’s skin cells (a
potential source of induced pluripotent stem cells). The stem
cells Saitou used were embryonic, and the signaling they required to turn into functional oocytes came from the fetal
ovarian tissue into which they were transplanted. That process isn’t possible for human reproduction because it would
mean destroying human embryos. “We have to understand
what these embryonic stem cells are doing to create germ cells
before we can develop a strategy to induce human primordial
germ cells,” says Saitou.
Tilly, however, says his stem cells are ready for in-depth testing. One of Tilly’s fiercest initial critics—Evelyn Telfer, a reproductive biologist at the University of Edinburgh—is now collaborating with Tilly to coax oocyte stem cells obtained from
women undergoing cesarean sections into mature eggs outside
the body. If this is possible, the team plans to fertilize them and
see whether they’re functional. (Generating human embryos
for experimental purposes is illegal in the United States, but
it’s permitted in the United Kingdom under tight regulation.)
If the research is successful, there could be many applications, Tilly says. Because these oocyte stem cells can proliferate, a snip of ovarian tissue might yield hundreds of cells that
could be frozen for later use. A woman whose ovaries have been
damaged by chemotherapy, for example, might get an infusion
of her own stem cells to restore her egg pool. The stem cells
could also make IVF more efficient by generating many more
than the six to eight eggs that can usually be retrieved today.
With an endless supply of cells to work with, researchers might
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protomag.com
”It’s unthinkable that there should be any area of
scientific investigation set off limits,” said IVF pioneer
Howard Jones in 1971.
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also add hormones or drugs to discover the right environment
for inducing cells to make more eggs in the ovaries.
Perhaps the earliest clinical application of this research
would be to use stem cells to re-energize old eggs and improve
the odds of successful IVF. Older eggs often lack the energy
to divide to make a good quality embryo, causing a higher rate
of miscarriage and chromosomal abnormalities. In the 1990s,
Dutch embryologist Jacques Cohen attempted to rejuvenate
old eggs by transferring mitochondria—a cell’s energy source—
from the cytoplasm of the egg cells of younger women. That
procedure, known as cytoplasmic transfer, led to higher fertilization rates and the birth of 30 children before the Food and
Drug Administration banned it in 2001, citing potential danger
to offspring that received DNA from two women as well as the
father. (Jones says he saw no reason why the procedure should
not have been tried.)
OvaScience, a public company co-founded by Tilly, has
started a clinical trial with women ages 38 to 42 who have
failed to conceive after two to five tries with conventional
IVF. Their eggs will be injected with mitochondria obtained
from their own egg cells, thereby avoiding the problem of
foreign DNA from donor eggs. “If you start with better embryos,” says Tilly, “then you may only need to transfer a single
embryo back into the patient’s uterus, which would eliminate
the risk of multi-gestational births in a single pregnancy.”
A
lmost a third of pregnancies through assisted reproduction in the United States do indeed result in
twins or triplets, and in part because those children
are likely to be born prematurely, they have an elevated risk
of developmental disorders and other problems. And those
aren’t the only potential perils of assisted conception. Last
year, an Australian study that analyzed more than 300,000
births from 1986 through 2002 found that the rate of birth
defects was higher when conception was achieved with IVF
and intracytoplasmic sperm injection (ICSI) than for naturally occurring pregnancies. Compared with a 5.8% rate of birth
protomag.com // Spring 13
defects in the general population, women who used assisted
reproductive technologies to get pregnant had an 8.3% risk
of delivering a baby with problems ranging from holes in the
heart to bowel malformation.
But how much of that increased risk is attributable to reproductive technologies and how much relates to the characteristics of the women who turn to assisted reproductive techniques?
Women seeking fertility assistance tend to be older, heavier and
more likely to have hypertension and metabolic disorders such
as diabetes and polycystic ovary syndrome, all of which are risk
factors for birth defects. Indeed, when researchers for the Australian study factored in such characteristics, they found that
IVF added little to the risk of birth defects.
Moreover, embryos that were first frozen and then thawed
before being inserted into the uterus actually had a belownormal rate of defects. “Developmentally compromised embryos don’t survive the frozen-thawed cycle,” says Michael
Davies, associate professor at the University of Adelaide’s
School of Paediatrics and Reproductive Health. Freezing embryos also allows IVF to be done after a woman’s body has had
time to recover from the drugs she must take to spur ovulation.
“After ovulation has been induced, the endometrium is more
compromised, so it’s not the ideal circumstance for an embryo
to implant and grow properly,” says Davies. “The frozen cycles
of IVF seem to produce remarkably healthy embryos.”
But the story is different for ICSI, which involves injecting
sperm directly into the egg. Davies found that almost 1 in 10
children born using ICSI and nonfrozen embryos had birth
defects. That statistic is particularly troubling to Davies because of the technology’s rising popularity. In the past, ICSI
was used only when there were problems with sperm that
made them unable to penetrate an egg on their own. Now,
however, many couples elect to have ICSI instead of IVF because ICSI’s pregnancy rate is a third higher than the rate for
IVF, according to Davies. ICSI accounts for 70% of assisted
reproduction in Australia.
ICSI’s higher risk of birth defects may happen because the
procedure bypasses natural selection by fertilizing an egg with
a sperm that might not have otherwise had a chance to fertilize
an egg in a woman’s body. The DNA damage causing the male
infertility that led to the treatment may also be a contributing
factor. But Davies acknowledges that the risks associated with
assisted conception may have declined since the study’s end in
2002, thanks in part to advances in embryology.
erproductions ltd/getty images
W
hether or not today’s assisted reproductive technologies increase the risk that a child will have
problems, there’s a growing perception that, soon
enough, parents will be able to create super-healthy kids by
genetically screening embryos. The news last year that scientists at the University of Washington and Stanford University
School of Medicine sequenced the entire genome of a fetus
for the first time only added to such expectations.
Yet that vision of the future may not be realistic. “The genetics field is not on a trajectory where you’ll be able to customize
your children any way you want,” says Mark Daly, chief of the
Analytic and Translational Genetics Unit at MGH. “We cannot
prenatally predict diabetes, schizophrenia or autism, which involve hundreds of genes—most of which haven’t been discovered—as well as environmental factors and chance.”
And if those problems were solved, there would still be
many ethical questions to answer. Suppose that, many decades in the future, a reproductive geneticist could scan computer readouts of the genomes of, say, 100 embryos a couple
has produced. The prospective patients might then select
one with the smallest susceptibility to a familial disease such
as Alzheimer’s or depression, says Ronald Green, director
emeritus of the Office of Genome Ethics at the National Human Genome Research Institute. But they might also make
choices not just to avoid disease but to make better babies by
“improving their genetic endowment,” says Green. Helped
by prenatal genetic engineering, children might be born with
greater resistance to disease, physical traits parents deem
desirable and perhaps even enhanced intelligence.
If such genetic tools become available and safe, some parents
may be unable to resist the promise of creating disease-free and
problem-free offspring. “As long as the demand is there, this
technology will be difficult to regulate,” says Green.
As assisted reproductive technologies expand around the
world at a pace far beyond what Jones envisioned in 1981, the
field will continue to inspire ethical and scientific debate. Yet
he argues against putting any predetermined constraints on
those explorations. “It’s unthinkable that there should be any
area of scientific investigation set off limits,” he said in 1971,
chiding medical peers for their hostility toward a technology
that would give hope to desperate couples wanting a child.
That bold approach may continue to shape a young field that
has already changed the world.
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Dossier
1. Pandora’s Baby: How the First Test Tube Babies Sparked the
Reproductive Revolution, by Robin Marantz Henig (Houghton Mifflin
Co., 2004). Henig tells the story of the physicians who pioneered
IVF and how they endured the contempt of scientists who claimed
that test-tube babies would launch science down the slippery slope
toward genetic engineering and human cloning.
2. “The Next (Re)Generation of Ovarian Biology and Fertility in Women: Is
Current Science Tomorrow’s Practice?” by Dori C. Woods and Jonathan
L. Tilly, Fertility and Sterility, June 2012. A case for the existence of
stem cells in the ovaries of reproductive-age women, a discovery that
will bring stem cell–based approaches for treating infertility “one
significant step closer to reality,” according to the authors.
3. Babies by Design: The Ethics of Genetic Choice, by Ronald M. Green
(Yale University Press, 2007). Green lays out the future capabilities
of genomic science in allowing parents to genetically modify their
offspring to free them of disease and enhance them with desirable
traits—raising ethical questions that should be asked now, he urges.
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