Controlling gene editing

The title does not mean societal or legal control of gene editing technology.  Rather, it speaks of controlling, or shutting off, a specific gene editing process.  In retrospect, it had to be the case that there is a resistance, or control, mechanism for the CRISPR system, the gene-editing machinery that functions as a way for bacteria to resist invasion by viruses.  An engaging essay in Nature this week discusses this on a level accessible to one who, like me, is not a technical specialist in the field.  Briefly, a few years ago a grad student at UC/San Francisco discovered cases in which the CRISPR system was ineffective in certain bacteria.  Following up led to the discovery of some 50 proteins that can act as “kill switches” for CRISPR.

On a surface level, the implications are clear—learn how to deploy these proteins and one can monitor one’s gene editing efforts for unwanted effects, or for spinning out of control, and if things haven’t gotten too far out of hand, one could turn things off—have an antidote, as it were.

Suppose at some future date that someone were being treated with a gene editing approach for a genetic disease, and things start happening suggesting that other genes than were intended to be the target were being altered.  Presumably one could intervene to treat or prevent the consequences.  Or suppose that genes were being edited to control a certain pest, like malaria-causing mosquitoes.  Presumably there could be an intervention to try to stop the process.

That’s a pretty superficial discussion, but technical experts in the field are trying to learn how to use these “kill switches” to control their gene-editing efforts. 

The also-superficial implication seems clear: these efforts should be understood, and applied in laboratory systems, then perhaps in “somatic” gene editing (treating an existing person for a genetic disease) BEFORE attempts are made to edit human embryos, whether the embryos are intended for gestation or birth or not.  Until things are MUCH more fully understood, there should be no direct work on heritable genome editing.

Chastening and enthusiasm about genome editing

A writer in Nature says that China sent a “strong signal” by punishing He Jiankui and two colleagues with fines, jail times, and bans against working again in human reproductive technology or applying for research funding.  (They lost their jobs as well and may not be able to do research work, presumably in any field, in a Chinese institution again.)  It is encouraging, this writer says, that China took this action demonstrating a commitment to human research ethics.  He and other researchers doing gene-editing work that is not ethically objectionable worry that there may be collateral damage, so to speak, against ANY gene-editing research in China.

Another writer in Nature says cites progress under “appropriate caution” for using gene editing techniques for so-called “somatic” gene editing; that is, editing disease genes in an existing person with that disease, to treat it.  This is, in essence, a form of gene therapy and is ethically permissible under proper research ethical guidelines.  Some clinical trials in progress involve injecting the gene-editing apparatus into a person, while most such trials remove the person’s blood cells, edit them in the laboratory, then re-introduce them into the bloodstream, after which the edited cells are left to mature normally.  The latter approach is particularly attractive to treat genetic blood diseases such as sickle cell anemia.

Both perspectives seem correct, as far as they go—never mind whether Dr. He’s jail sentence fits the crime, as Joy Riley asked on this blog last weekend.  Never mind also whether Dr. He’s research should be published; as Mark McQuain commented, it’s a bit incongruous to want to assess the technical merits of work that should not have been done in the first place.  He linked an opinion in Technology Review that argued, briefly, that because the ethics of editing genes in human embryos is under societal debate, people trying to decide on the ethical merits should be able to assess for themselves whether Dr. He succeeded, technically at what he set out to do.  (The consensus to date seems to be, no, he did not.)   But the role of technical success in assessing the ethical merits of a medical intervention—or, better, an intervention made in the name of medicine—depends on the degree to which the ethical judgment is a matter of making a reasonably reliable of risk and benefit, and the degree to which risk-benefit is a criterion for judging the ethical merits.  And therein, as they say, lies the rub—which I hope to revisit in coming posts.

Can we hop the gene-editing train?

As Joy Riley pointed out on this blog on December 7, the world and the scientific community recently marked, with almost no fanfare, the one-year birthday of “Lulu” and “Nana,” the first (we think) and still only (we think) humans to have had their genes edited heritably—in a way that will be passed on to future generations.  Joy commented these children are “experimental subjects for life,” or, to use the phrase I found and discussed some time ago on this blog, “the babies are the experiment.”  To wit: it is not possible fully to assess and limit the risks of heritable genome editing before actually editing humans.  One must forge ahead.  Even if one were to edit a series of embryos, and abort them at different times during gestation to get a full assessment of their prenatal development, the questions about lifelong effects and effects on future generations would persist. 

And, as mentioned in other posts on this blog earlier this year, there is the issue of “nonphysical” harms to how we understand ourselves and our human existence.

A number of world scientific bodies are assessing, independently of each other, what regulatory safeguards should be instituted, on the assumption that heritable genome editing is something that should be pursued.  Last month, the journal Nature editorialized that efforts by the World Health Organization, US and UK scientific bodies, and a third international commission should not proceed separately (they are all due to report their findings in 2020), but should work together.  The editors apparently think that it would be straightforward, obvious, and right to adopt a moratorium on clinical applications of heritable genome editing, establish an enforced registry for all experimentation in this area, and expand the conversations to include representatives of people with disabilities.  If I read that correctly, it’s hard to disagree.

In the laboratory, things are moving fast and it is well-nigh impossible to keep up with the science or the conversations about it without that work being one’s main occupation.  A recent contribution linked by the Nature editors is called “prime editing” that appears to increase substantially the efficiency of gene editing, raising the prospect of correcting abnormalities associated with the vast majority of genetic diseases.  The relatively naïve, like your present correspondent, might wonder whether this approach could be limited to already-born people with genetic diseases, as treatment, rather than engineer the genomes of the unborn in an apparent attempt to eliminate these abnormalities from the human prospect.

Even thinking about the general public trying to influence where this work leads feels like assuming the role of an old-style hobo, trying to hitch a free ride by jumping onto a moving freight train.  One is liable to fall under the wheels.  But in the case of heritable genome editing, you’re likely to get run over anyway.

More on Physicians’ Conscience Rights

Yesterday’s post to this blog addressed physicians’ conscience rights.  The standard shape of arguments about preserving individual physicians’ conscience rights goes, broadly, like this:  certain actions now sanctioned by society (e.g., abortion, assisted suicide) have been embraced by the medical profession as standard medical care which all physicians should be willing to perform, but this stance runs counter to the long tradition of medicine and to the proper ethical stances of some individual physicians.  Therefore, objecting physicians should be free to decline to perform them, without fear of professional or legal reprisal.  In this vein, the current U.S. Administration had promulgated a regulatory rule in May of this year attempting to ensure that, consistent with existing statute, such conscience rights are protected.  This week, a federal judge struck down the rule in its entirety, arguing that a) the propose rule, which, like all regulations, would have had the force of law, went beyond the statute behind it by making unwarranted interpretations and expansions of the statute’s wording; b) the government’s process of promulgating the rule violated other laws governing such rule-making; c) that it was unconstitutional, violating not only the separation of powers but also the Fifth Amendment because the rule was too vague, and the First Amendment because it would have “required employers to conform their business practices to the religious practices of their employees.” 

One might wonder whether at least some of the court’s reasoning—especially the separation of powers and Fifth Amendment arguments, and the concern (“a” above) about bureaucratic overreach—might not in fact apply to a wide range of government regulations.  That notwithstanding, the Christian Medical and Dental Associations, which has been particularly vigilant to protect conscience rights when it comes to abortion and assisted suicide, vowed to fight on.

The Journal of the American Medical Association (JAMA) cites a different case, involving assisted suicide in Colorado.  There, assisted suicide was made legal, with only limited restrictions, by a public referendum.  Notably for the present case, while health care organizations such as hospitals may opt out, and decline to provide assisted suicide, they may not enforce a blanket prohibition against their physician-employees doing so on their own initiative.  Such a prohibition could only be enforced on the organizations’ actual premises. 

So apparently a physician who worked for a Catholic hospital wrote (on her own time, outside hospital premises, and of her own volition) a prescription for a lethal prescription for a cancer patient.  The physician cited judgment of her own conscience.  The hospital cited its moral reasoning, its own freedom of religion, and, it appears, a claim that the physician was, or should have been, considered to be acting as an agent of the hospital.  The matter is the subject of a lawsuit.

The hospital fired the physician.  It is said she found another job.  But that of course is not the point, is it?  If a physician, who has a covenantal relationship with the patient, finds in her moral judgment that, in a given case, assisting suicide is ethically permissible, why does the hospital system have a right to override that judgment—especially if it was exercised, as it is argued here, in accordance with existing civil law?  One can certainly argue, as I would, that the physician has erred in her moral reasoning, and misapplied the physician-patient relationship. 

But I wonder whether, as the saying goes, “what is sauce for the goose is sauce for the gander,” in this case.  We might consider: the hospital could employ the physician based on an upfront, written agreement that the latter would act in accordance with certain moral stances of the former.  Absent such an upfront agreement, it’s hard to agree with disciplining the physician as was done in this case.  But even then, such insistence on upfront agreements seems to run counter to much of the spirit of much discussion about conscience rights, setting up a regime in which the relative power of available employers of physicians determines the constraints on medical practice.  Even then, if medicine remains a learned profession at all, perhaps insistence on conscience rights should be understood to cut both ways.

Drs. Stephanie Harman and Abraham Verghese seem to lean in this direction in an accompanying editorial in JAMA—but by emphasizing physician autonomy.  Their examples betray their preferred value judgments, but the overarching concern still seems relevant and valid.

Skepticism about polygene scores to select for IQ and height

One caution when objecting to the prospect of heritable human gene editing is to take care not to overestimate what it technically possible.  That is, an all-too-easy argument is that attempts to edit a disease gene will lead, by momentum if nothing else, to “designer babies,” with children not just being genetically selected but in fact engineered in great detail for traits like attractiveness, athletic prowess, height, and intelligence.  This contributor to this blog has repeatedly taken the position that heritable human gene editing is a project that fundamentally alters the way we see ourselves and each other; that divides the human race into “actors” and “acted upons;” that has no prospect of prospectively assessing long-term, unintended consequences, to an individual subject, subsequent generations, or society at large; and that fortifies a perspective of admitting to the human race only those members we want to admit.

Along the way, we must keep in mind that “designer babies” are not likely to be feasible in the foreseeable future.  One recently-reported case in point is a study by scientists at the Hebrew University of Jerusalem.  A preprint (in advance of publication in a peer-reviewed journal, it is said) is publicly available here.  I daresay the details will be inaccessible to all but specialists in genetics, but a summary of key points is provided by a technical writer at a website called GenomeWeb.  In brief, some of those points:

  • A score based on assessment of multiple genes has previously been suggested to explain only about 5% of the difference between individuals in IQ (300,000 people genetically tested) or 25% in height (700,000 people tested).
  • These researchers tested about 1000 people, and considered about 15,000 genetic variations.
  • They looked at offspring of actual couples and also “simulated” matches for about 500 would-be couples made from individuals for whom they had genomic data.
  • Of note, they appear to have looked at “SNPs,” or “single nucleotide polymorphisms,” which are relatively easy to catalog across the 30,000 or so human genes, and which themselves run into the hundreds of thousands across those genes, but SNPs are far from the whole genetic story.  Larger differences in genes, or how those genes are translated into biological traits, is much more complex to assess.
  • They surmised that, if their score were used to try to predict height, the average gain would be about 2.5 cm (about one inch), with a range of 1-6 cm.  If used to predict IQ, the average gain would be about 2.5 points, with a range of 1-7 points.
  • Then they also looked at 28 actual families with lots of kids, from 3 to 20 (!).
  • For the actual families, the score predicted to cause the tallest child did so for only 7 of the 28 families, and the highest scoring child was actually shorter than average in the family in 5 of the 28 families.  No attempt to assess IQ for these real families, apparently.
  • They point out other reasons why trying to select for IQ might be problematic—potential association with autism and anorexia, for example, as well as just general complexity.
  • They suggest that for most people undergoing IVF, and creating fewer than 10 embryos in the process with less than 100% success after implantation in the womb, the odds are not good for making a reliable forecast of an offspring’s height or IQ.
  • They make these points without commenting more broadly on the ethics or policy wisdom of allowing or encouraging heritable genome editing to proceed.

A complex story, and a developing one, to be sure, but one should not be too quick to accept grandiose promises for predicting complex traits based on genetics.  At least for now, those appear to be rather “ahead of the puck,” shall we say.

Future new CRISPR baby in Russia?

Nature reports that Russian scientist Denis Rebrikov has started experiments intended to lead to editing a gene, in human oocytes (egg cells) associated with human deafness.  Prior reports had claimed that he was working on eggs from deaf women in an attempt to repair the defect and, presumably, provide a normal egg for IVF.  This apparently is not the case—yet.  At the moment, he is using eggs donated by women who can hear, to do experiments on editing the gene in question and ferret out what might go wrong in the process—that is, is the right gene edited, is only the right gene edited, and related questions.   

He says he has had discussions with deaf women, but has not yet sought approval from the Russian regulators to try IVF with a gene-edited egg.  The regulators appear reluctant, and Rebrikov says he will not proceed without prior approval.  He had previously said he wants to edit the same HIV-susceptibility gene that was edited in twin babies born in China last year, but it looks like there aren’t too many candidates for that approaching him, and that attempt has not gone forward—yet.

He’s clearly impatient.  Other scientists working in the gene editing field—which has broad applications short of making “gene-edited babies”—are urging patience, and saying that it is at a minimum rashly irresponsible to rush ahead with the effort, particularly for non-fatal conditions like deafness.  And they are right—too little is known to justify the effort—yet—even if one thinks there are conditions for which it ethically could or even should be attempted.

But “the field” is working hard to define a path forward.  The second meeting of an international panel discussing how to move ahead meets in London November 14-15.

Nature includes a brief Q+A with Dr. Rebrikov.  Forgive me, but some of it is chilling, reflecting blindness to the deeper issues.  Paraphrasing selected questions, quoting the answers, offering italicized commentary:

  • Question:  don’t the risks of trying this outweigh the benefits, for a non-life-threatening condition like deafness?  Answer: “Any new drug carries certain risks. The deafness model is the most appropriate for applying genomic editing at the zygote [newly fertilized egg] stage. And it is only for deaf parents to decide whether … deafness is enough to not expect the same for their child.”  Beg pardon:  heritable gene editing is NOT A DRUG, and the risk-benefit decision is NOT solely the province of private decisions about reproductive-related risks.
  • Question:  the regulators point out that editing people is currently not permitted.  Answer: “Laws are written to change them. As soon as we demonstrate the safety of technology, the rule will change.”  Ahem: some laws are enduring, even eternal—cf. divine law. Recognizing that the regulators’ judgment is not divine, eternal law, reverent attention to the latter should be a paramount concern.  And ‘safety’ appears to be narrowly defined here, blissfully ignoring the deeper human questions posed by modifying people’s genes permanently.
  • Question: people trying to build a regulatory framework for human genome editing think researchers should slow down until the framework is agreed upon. What do you say?  Answer: “Are you serious? Where did you see the researcher willing to slow down?”  Hello!  McFly!  We are not ASKING you to slow down.
  • Question: Russian regulators and the World Health Organization say it is too soon to create edited children.  What do you say?  Answer:  “What does it mean, too soon? Lenin said ‘yesterday was too early, tomorrow it will be too late.”.

Lenin?? LENIN?!  For real??

Addressing gene editing with “thin” bioethics

Yesterday’s post on this blog, by Steve Phillips, warned that a narrow, “rules limited” approach to bioethics reduces ethics in science and medicine to matters of regulatory compliance and risks making thoroughly logical conclusions based on faulty premises that are adopted without regarding “deeper ethical thinking” for which scientists’ thinking must be brought under the discipline of broader humanitarian reflection if correct basic notions of what it is to be human, and what humans should be up to, are to be arrived at.

A different but closely related way to look at this was suggested by John Evans of the University of California, San Diego in his contribution to Human Flourishing in an Age of Gene Editing, a new collection of essays, edited by Erik Parens and Josephine Johnson.  In brief, Prof. Evans commented that too much of bioethics is “thin,” reduced to the Belmont principalism (respect for persons/autonomy; beneficence/nonmalificence; justice) governs human subject research.  This “thin” bioethics is convenient for regulators to use to derive a manageable set of rules, and for scientists to, if you will, hide behind (my expression, not Prof. Evans’s).  Rather, he writes, we must be willing to criticize the assumption that all we need to ask about technology is how to use it, and seek a deeper wisdom about what is a good or worthy human life, for individuals or communities.  In making this argument, he appeals to “critics of technology,” both politically conservative (Leon Kass) and politically liberal (Jacques Ellul).  Jacques Ellul!  How often does anyone hear him mentioned anymore?  How many of us have read him?  (I venture fewer than should!) 

This criticism of worshipping at the Belmont altar, if you will, is hardly new, but it’s critical, especially when something as profound as heritable human gene editing is being considered.  You see, Belmont principalism is quite robust when asking how to deal with clinical trials.  But it really most closely applies to things like regulated drug development, and germline gene editing goes far beyond drug development.  It isn’t drug development at all, and cramming it into the conceptual framework of drug development is fundamentally misguided.

Nonetheless, the International Commission on the Clinical Use of Human Germline Genome Editing appears to be proceeding merrily along the drug development path. The second meeting, in London, is next month; one can sign up for a webcast. Just check out the agenda, especially day 2’s planned sessions on risk-benefit analysis and defining “a translational pathway.”  That language applies to new therapy development, not fundamental alterations of human inheritance.

One should keep in mind also that the assumption one can assess risks and benefits is only as good as one’s data.  This week it is reported that scientists have retracted an analysis suggesting that babies edited for an HIV-susceptibility gene might be at risk of relatively short life spans, something this blog poster readily jumped on in his June 6, 2019 post.   But, then again, so did the prestigious journal Nature Medicine, so I guess I shouldn’t beat myself up too much.  Seems the researchers didn’t define matters carefully enough.  Even if this particular analysis, from a large database of human genetic data, was flawed, similar analyses in the future might be helpful, it is argued.  Until more is known, it is further argued, one should not seize on a retracted analysis to infer a full “green light” to edit unborn babies’ genes.  But that may take “thicker” bioethics than whatever risk-benefit analysis we think we can muster now.

Fewer U.S. Twins and the Development of IVF

Readers of this blog may have seen the report in the general press that, after three decades of increases, the rate of twin births in the U.S. has declined by 4% from 2014 to 2018.

Those three decades correspond to the era of IVF, since the birth of Louise Brown in England in 1978.  It seems likely that changes in IVF practice contributes at least in part, if not substantially, to the trend in twin births.

Specifically, doctors at IVF clinics are more commonly implanting only one, rather than more than one, embryo back into a prospective mother’s womb with each attempt at a live birth.  Multiple pregnancies—even twins, not just “Octomom” scenarios—carry increased risk for mother and babies.  Previously, two or more embryos were implanted in an effort to increase the chance that at least one would make it to live birth.  Sometimes, “selective abortion” was practiced to reduce the number of initially multiple pregnancies to one.  Now, it appears that gradually increasing success rates of IVF are supporting single-embryo transfer as a standard practice.

The Centers for Disease Control and Prevention (CDC), which provides a substantial amount of information on the current status of IVF on its website, summarizes the changes in the percentage of single-embryo transfers in recent years—increasing from 11.6% of non-donor-egg transfers in 2007 to 39.9% in 2016.

To the extent that this reduces the practice of selective abortion and, one hopes, decreases the number of embryos created but kept frozen, never to be born, at IVF clinics, this is a welcome development.  The Christian Medical Dental Association takes the position that, in IVF, the number of embryos should be kept to a minimum, and all embryos created should be so created with the intent of having the genetic mother carry all of them in pregnancy, to live birth one hopes.

IVF remains a transformative enabling technology that facilitates contractual arrangements for reproduction, profound changes in the structure of families, and the use of pre-implantation genetic diagnosis to control what sort of people are allowed to be born.  One might view these developments as non-physical harms, that alter our overall experience of being human in ways that may properly be subject to question.

And: the rate of twin birth is still twice what it was in 1980.  If one sees a mom or dad pushing a stroller with fraternal twins, chances are they are IVF kids.

“Velvet Eugenics”

Human Flourishing in an Age of Gene Editing is a new collection of essays, edited by Erik Parens and Josephine Johnson.  In the introduction, the editors explain they are concerned with “nonphysical harms” of human gene editing.  That is, these harms would not affect bodily systems, but harm “people’s psyches…[their] experiences of being persons,” and could impair human flourishing.  These harms could be incurred not only by gene editing but also by use of other “reprogenic” technologies such as preimplantation genetic diagnosis (PGD) and prenatal diagnosis.

Your correspondent has just begun to read this collection.  In the first entry, “Welcoming the Unexpected,” bioethicist Rosemarie Garland-Thomson of Emory University, takes the view that flourishing is not a matter of proximity to some ideal of health or human excellence, but is, for each person, a growing into expression of that person’s unique capabilities.  Accordingly, rather than embrace a project of eliminating disabilities, society should work to make the environment more welcoming to people with those conditions—many of which, after all, need not impair a person’s ability to live a life of happiness and contribution to others.  Communities have an obligation, she says, “to support the distinctiveness of its members according to the egalitarian principles of justice, liberty, and equality,” and “build environments that…support the widest spectrum of embodiments…in which human embodied existence can successfully thrive as it is.”  Put another way, we should not be building a regime in which we are deciding what sort of people we will allow to be born, but we should be ready to welcome and embrace the ones who are.  In this, Professor Garland-Thomson sounds a “caution against an aggressive normalization imperative…an outlook of humility about the human capacity to control future circumstances through present action…against the arrogance of [what one writer called] ‘the danger of a single story.'”

We should, she writes, adopt a stance of “growing” rather than “making” human beings, and “reconsider the logic of a velvet eugenics that would standardize human variation in the interest of individual, market-driven liberty and at the expense of social justice and the common good.”  In this, she embraces the argument of contemporary German philosopher Jurgen Habermas that rejects “a liberal eugenics regulated by supply and demand.”  One can be forgiven for hearing in this an echo of C.S. Lewis’s worries about “conditioners” in The Abolition of Man.

This is set in the author’s description of her ongoing friendship with three other women, all, like her, married PhD’s who like good wine, good food, and are amply supported by technology and community.  One of her friends is congenitally deaf, another has hereditary blindness, the third has a genetic muscular condition, and the author herself was born with what is now called “complicated ectodactyly,” with “asymmetric unusual hands and forearms.”  The sort of thing your correspondent understands the Chinese to be trying to eliminate through the use of PGD.

A remarkable essay to lead off a collection that appears worthy of careful consideration.

Two developments

A new effort at “somatic” gene editing in China is reported this week.  The key summary:

“As the researchers report in the New England Journal of Medicine,

[note to reader: subscription required]

they transplanted [blood stem] cells that had undergone CRISPR-based editing [of a gene that encodes for a receptor, or “docking station”] into a patient with HIV and acute lymphoblastic leukemia. While [the edited cells lasted for a long time in the bloodstream of the HIV-infected recipient], they only made up between 5 percent and 8 percent of blood cells. A higher percentage is needed for this to be an HIV cure…”

In “somatic” gene editing, mature cells, such as “adult stem cells” or diseased tissues, are gene edited for the purples of treating a fully-formed individual with a disease.  That is what appears to be in view here.  Similar efforts are in progress to treat sickle cell anemia and other genetic diseases.  The ethical issues are relatively well-understood, and fit within the regime of regulating cells-as-medicines in clinical trials of humans, under the ethical and regulatory regime that governs the latter.

That’s in contrast to “heritable” gene editing, which attempts to edit genes in embryos, fertilized eggs (zygotes), or gametes (sperm or eggs) with changes that would be passed on through the generations, as recent entries on this blog have been addressing.  The Chinese twin girls who were reported to have undergone gene editing late in 2018 are examples of an attempt at “heritable” gene editing.

A second report from Nature describes efforts to use human “reprogrammed” stem cells, aka pluripotent stem cells, to make human “embryo-like structures.”  This is distinct from making a human embryo, for example in IVF, then removing cells, likely destroying it, for use in research or to develop medical treatments.  In conservative commentaries in recent years, these “reprogrammed” stem cells are considered the “ethical embryonic stem cells,” because they can’t form a full individual and they don’t require creation and destruction of an embryo, that would under normal circumstances form a full individual.

Thing is, these “embryo-like structures” can still form something called a “primitive streak,” which, in normal embryos, is the first sign of formation of a nervous system.  The primitive streak usually forms 14 days after fertilization, so, to try to avoid concerns about research on embryos, scientists who think such research is ethical in limited circumstances have operated under a “14-day rule”–voluntary in the US, mandated by law in the UK–after which embryos would not be destroyed for research.  These “embryo-like structures” may form a primitive streak, it appears.  The situation is similar to “synthetic human entities with embryo-like features,” or “SHEEFs,” which may bypass the primitive streak but raise similar issues of whether something too like a natural human being is being engineered by this work for it to be ethical.

A developmental biologist at Caltech says, the California Institute of Technology in Pasadena. “We will have to confront ourselves with the question of what is a human embryo, and whether these models really have the potential to develop into one.”  The researchers making these synthetic embryos argue that they lack a placenta and other cells needed for development, so could not develop into a person.

At least for now.