Human blastocyst, Getty Images

For more than 30years, scientists have followed a rule they imposed on themselves to avoid growing a human embryo in a lab dish for more than 14 days.

Until recently, the "14-day rule" was largely academic. Scientists couldn't grow themfor that long if they wanted to.

But in 2016, two teams of researchers reached 12days, and in 2019, another group grew monkey embryos for 19 days.

These advances have spurredsome scientists to argue in two recent papersthat the 14-day rule should bemodified or dropped. There's a lot to be learned by pushing embryos out to 28 days, they say.

The regulatory committee of theInternational Society for Stem Cell Research, which lays down guidelines for the scientificfield,has been debating the issuefor months and is expected to issue its final decision this month.

Some ethicists and scientistsare concerned that revising the rule just asit becomes technologically feasible to break it is ridiculous and morally repugnant.

"If you abandoned every rule or law that inhibits you as soon as it inhibits you, we'd live in a lawless world," said Ben Hurlbut, a historian of science at Arizona State University.

And somepeople consider human embryo researchto be unethical at any stage.

"Whether 14 days, 14 months, or anywhere in between, such 'rules'remain contrivances to justify the most unethical kinds of science and to allow for the exploitation of our own vulnerable human offspring," said Tadeusz Pacholczyk, a neuroscientist and director of education at the National Catholic Bioethics Center in Philadelphia.

A single cell is removed from a human embryo to be used in generating embryonic stem cells for scientific research.Advanced Cell Technology via AP

Countries are free to ignore rules set by the society, but scientists for decades have generally abided by them. (In the U.S., there's no national law about the 14-day rule, though some states have their own regulations.)

Some cultures and religions believe that human life begins at conception, or that the human embryo carries a special status from conception onward. Other cultures believe that life starts later in fetal development, or even at birth.

Biologists routinely grow amphibian and mammal embryos in petri dishes, but human embryos are different.

Until about 14 days after conception, the human embryo looks likean undifferentiated blob of cells, which is one of the reasons the two week timeframemade sense, several scientists said.

Robin Lovell-Badge, who sits on the International Stem Cell Society committee that's considering overturning the rule, said scientists will take any changes seriously.

"We've stuck with that rule for over 30 years," he said.

Lovell-Badgefavors extending the limit, as long as the research is scientifically justified and has public support.

Not everyone in the scientific community shares this position.

"It's been a difficult part of the guidelines to get agreement on," Lovell-Badge said. "You have very wide-ranging views."

Some scientists argue there's a lot to be learned by pushing the 14-day rule out another two weeks.

Right now the second two weeks after fertilization is considered a "black box" because so little is known about it, said Insoo Hyun, a professor of bioethics atCase Western and Harvard universities. Heco-wrote a March 5 opinion piece arguing for a careful, stepwiseextension of the 14-day rule.

"You have to really make your case for it,"Hyun said."You have to explain what you want to do and why, have a very clear picture of where the next stopping point is."

Women generally don't know they're pregnant before 28 days, so historically, there has not been tissue from aborted or miscarried fetuses available for research.

The central nervous system, heart and other organs begin to develop during this crucial two-week period. The body plan is established. Cells that will become eggs and sperm start to form. Aspects of theplacenta are set up.

In many ways,days 14 through28 are the most interesting period of human development, Lovell-Badge said. "You can do a whole lot of incredibly valuable research," in that timeframe, he said.

And it's in that window that many things can go wrong in a pregnancy, such as miscarriage or abnormalities.

Perhaps there are treatments that could be developed to fix these problems, if they are better understood,Hyunsaid, just as pregnant women now take vitamin supplements to prevent spina bifida, in which the spine doesn't developproperly.

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Developing embryos for another week "will thus illuminate this poorly understood period of our development and bring greater understanding of pregnancy loss and developmental disease,"saidMagdalenaZernicka-Goetz,theBritish scientist who developed the technique for growing human embryos for nearly two weeks.Zernicka-Goetz,author of a 2020 book on human development called "The Dance of Life,"would like to extend the 14-day rule out one week to 21 days.

"This will enable thescientiststo study a period of development that are highly susceptible to developmental failure, something that happens quite frequently in human pregnancy," she wrote in an email, stressing work should be closely regulated"to achieve these potential biomedical advances within an appropriate bi-ethical framework."

Despite their differences, most scientists seem to agreethere's no reason to push development past 28 days.

By onemonth after conception, embryonic tissue is easier to obtain and study and theorgans have formed, leaving fewer questions to answer.

"You wouldn't need to take them much beyond that point anyway," Lovell-Badgesaid.

Pacholczyk, of the Catholic Bioethics Center, said there's simply no justification for 14 days or any other time limit.

"Researchers have been feigning for a long time that the 14-day rule was somehow an ethical tenet grounded in biological facts while in reality it has been little more than a ceremonial 'line in the sand' and it should come as little surprise that they are now seeking to move that line beyond 14 days," he wrote in an email.

Even some who strongly supportscientific research are uncomfortable extending the 14-day rule.

HenryGreely, who directs the Stanford Center for Law and the Biosciences at Stanford University in California, saidthere should be a hard-stop endpointfor embryo research.

"Even though I do not personally give strong moral status to embryos, the idea of doing research on 18-day-oldhuman embryos is disturbing," said Greely, author of the new book "CRISPR People: The Science and Ethics of Editing Humans."

This sequence of images shows the development of embryos after correcting for a genetic error that would otherwise cause a type of inherited heart disease.OHSU

"I'd like to see an endpoint that had some rationale that would make it likely to stick," he said.

Growing an embryo in a lab dish instead of a woman's womb is necessarily different, Greely said, and may not represent a "real" embryo anyway.

"Does a 14-day embryo that is not implanted deep in a woman's uterus tell us anything meaningful about a 14-day embryo that is?" he asked.

Marcy Darnovsky, executive director of the Center for Genetics and Society, a nonprofit advocacy group,said efforts to overturn the 14-day rule are another example of scientific over-reach.

"There's a real problem with scientists who are jumping ahead of the public," she said.

Scientists should not be the ones who get to decide where society's moral boundaries lie,she and Hurlbut said.

"If moves are made to usurp these questions from wider society," Hurlbut said, "it's to the detriment of democracy and to the detriment of sciencecertainly in the long run, and probably in the short run."

Contact Karen Weintraub at kweintraub@usatoday.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

Published 10:13 am UTC May. 2, 2021 Updated 10:13 am UTC May. 2, 2021

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Should scientists be allowed to grow human embryos in a dish beyond 14 days? Is it scientifically important or morally wrong? - USA TODAY