Scientists have broken through a technical barrier in human embryo research and now face an ethical one.
Two separate studies published in Nature and Nature Cell Biology today report on new methods allowing human embryos to cultured and studied in Petri dishes for as long as 13 days. Previous studies have struggled to keep embryos alive outside of the womb for more than seven days.
The new methods allow unprecedented insight into the critical stages of human development during early stages and will offer new avenues for fertility research.
In accordance with internationally recognised ethical guidelines, the experiments were concluded before 14 days into development. An accompanying commentary article in Nature explains that this ‘two week’ rule was largely symbolic as it was considered impossible to keep human embryos alive this long outside the body. However the new research will force a rethink on these rules, say the authors.
“Now that it has become possible to culture human embryos to the 14-day limit and perhaps beyond, the time is right for the scientific community to educate the public about the potential benefits and to work with regulators on ethical consensus to guide this important research,” says Amy Wilkerson, associate vice president of research support at Rockefeller University and an author on the commentary article.
Read more about the research on Scimex.org.
The Science Media centre collected the following commentary:
Assoc Prof Michael Legge, Department of Biochemistry University of Otago, comments:
“Whilst animal models (primarily the mouse) have been valuable in understanding pre-implantation and post-implantation embryo development, they are limited to the embryological time frame of embryogenesis (20 days in mice). To fully understand the developmental programme of human embryos it is necessary to transfer the techniques and knowledge from animal embryos to human embryos.
“Taking in‐vitro embryo development up to 14 days will significantly enhance the understanding of cellular decision making and programming for specific cell lineages, understanding cell migration and the role of embryonic stem cell biology in making those decisions.
“When this approach is combined with the newer ‘gene-editing’ techniques it will provide a powerful developmental biology analytical system to understand how early gene signaling influences normal development, and will provide a greater insight in understanding how abnormalities develop during embryogenesis.”
New Zealand’s stance on embryo research
“Human embryo research is governed by the Human Assisted Reproductive Technology Act (2004), which allows, in principle, research on human embryos up to 14 days with appropriate ethical approval. Two committees resulted from the Act, the Advisory Committee on Assisted Reproductive Technology (ACART) primarily responsible for setting policy, guidelines and advice to government ministers and the Ethics Committee on Assisted Reproductive Technology (ECART) with the overarching responsibility of ethical approval of reproductive technology procedures that are not an established procedure, which includes any embryo research.
“Currently in New Zealand suitable guidelines for human embryo research have not been formulated although research is clearly stated in the Act and decisions relating to establishing guidelines are awaiting ministerial direction.“
Declaration: Michael Legge is currently a member of the Advisory Committee on Reproductive Technology.
Our colleagues at the UK Science Media Centre collected the following commentary:
Johnathon Montgomery, Chair of Nuffield Council on Bioethics, comments:
“At our annual ‘Forward Look’ planning meeting in February, the Nuffield Council on Bioethics learned of potentially important scientific research that could be achieved by maintaining embryos in the laboratory for longer than 14 days, which is the current UK legal limit for research using human embryos. As a result of that discussion the Council agreed to explore whether arguments for reviewing the 14-day limit are gaining force, in the expectation that any move to review this limit will be likely to generate significant moral controversy and would require careful analysis.
“Later this year, the Council intends to bring together invited participants with a range of perspectives on embryo research in order to evaluate whether, after 25 years, there may be persuasive reasons to review this legal limit, or whether the reasons for its introduction remain sound. It will publish a note of that meeting and then consider whether to undertake further work.”
Professor Azim Surani, Director of Germline and Epigenomics Research, The Gurdon Institute, said:
“The two studies are important and show that it is possible to culture human embryos through to early postimplantation period. These will be useful for studies on early stages of extra embryonic development, including aspects of human embryo implantation. They reach maximum development that is equivalent to Carnegie Stage 5c (~day 11-12 post fertilisation). According to the Brivanlou paper, the embryos collapsed at this point and became disorganised and could not be interpreted with respect to in vivo embryos. This however also marks the currently allowed limit for in vitro culture of human embryos; 14 days.
“There are two challenges looking ahead. First, the regulatory framework would need to be looked at so that the embryos can be cultured beyond the 14 day limit. Second, there might be technical challenges to getting the embryos go through gastrulation, that is when single layered epiblast develops into trilaminar structure consisting of ectoderm, mesoderm and endoderm; Carnegie stage 7 (~15-17), when primordial germ cells, precursors of sperm and eggs are also established (my own particular interest). To my knowledge, the equivalent stages of mouse development from blastocysts in vitro have not so far been reported.
“In my opinion, there has been a case to allow culture beyond 14 days even before these papers appeared. ”
Professor Harry Moore, Professor of Reproductive Biology, University of Sheffield, said:
“These two papers are important milestones as the investigators have found a way of consistently culturing human embryos further than previously reached in the lab.
“Both studies clearly demonstrate the incredible intrinsic ability of the embryo to organize itself as it starts to create the body plan (even in the absence of the mother). The results also point to some important differences between human embryos and those of the main model species, the mouse. This shows how important it is to study human embryos directly.
“Up to now, this stage of human embryo development has been very much a ‘black box’ and we have had to rely mainly on histological samples obtained in the 1930 and 40s when cell preservation techniques were much more rudimentary. Having these early stages of embryo development in the lab where we can start to use all the latest technology of genetic analysis is a major step forward. I would anticipate that over the next few years, further improvements in 3-dimensional culture techniques will mimic the embryo implantation process ever more accurately.
“Being able to carry out this sort of research is crucial for understanding how the early stem cells of the embryo develop.
“This research provides the detailed information we need to derive effective stem cell therapies to treat degenerative diseases, as well as improving the treatment of conditions of pregnancy such as recurrent miscarriage and pre-eclampsia.”
Professor Daniel Brison, Honorary Professor of Clinical Embryology and Stem Cell Biology and Scientific Director of the Department of Reproductive Medicine, University of Manchester, said:
“These two papers are highly significant as the culture system developed by the Cambridge group has allowed the study of early human embryo development in the laboratory much later than previously, to stages beyond the time of implantation into the womb. This has shown that the early human embryo is remarkably capable of self organising, even in an artificial laboratory system with no input from the mother. Some of the details appear to be different to animal models such as mouse, further strengthening the case for doing this research with human embryos. The culture system used may be capable of sustaining human embryo development in the laboratory beyond the current legal limit of 14 days after fertilisation. This limit was chosen more than 20 years ago as it was thought to represent the first point when individuality is assigned and twinning no longer possible, and carries strong support in the UK from patients and researchers. However, given the potential benefits of new research in infertility, improving assisted conception methods, and in early miscarriage and disorders of pregnancy, there may be a case in the future to reconsider this.”
Allan Pacey, Professor of Andrology, University of Sheffield, said:
“These are two very elegant papers which have the potential to revolutionise our understanding of the early events of human embryo development and, in time, some of the reasons behind aspects of human disease and disability. The papers are also an example of what can be achieved in a country with strong primary legislation designed to regulate such research in a well thought out ethical framework.
“The framework in which this work has been carried out was first set out in the Warnock report published in 1984, which concluded that it was ethical to conduct research on human embryos until day 14 of their development (when the rudimentary nervous system begins to be developed). Parliament agreed with this recommendation when the 1991 Human Fertilisation and Embryology Act was passed. But, until now, this has been a theoretical legal restriction as no one, until today, had the technical means to keep embryos alive in the laboratory much beyond day 7.
“What the scientists have done in these work is use a very clever system to keep human embryos alive in the laboratory beyond day 7 by utilising methods of culture first tested with mouse embryos. This has allowed them to undertake an almost hour by hour series of observations of human embryo development to see how key parts of them are developed and organised within the first two weeks. This has already provided new information in these papers, but in my opinion it is the potential that the approach offers to future researchers which is the most exciting.
“There will no doubt be people who will be opposed to this kind of research and may disagree fundamentally with the idea that legitimate and ethical research on human embryos can take place for up to 14 days in the laboratory. Whilst I respect the strength of their views and their conviction, this is a framework which was agreed over 30 years ago and I see no reason to change or revisit that decision. It will not open the door to couples being able to grow babies in the laboratory; this is not the dawn of a Brave New World scenario. But it does open up exciting opportunities to understand the nature of human disease and disability and for that reason the scientists involved should be congratulated.”
“Martin Johnson, Professor Of Reproductive Sciences, University of Cambridge, said:
“These highly significant papers both extend, and are based on, earlier work from the laboratory of Magda Zernicke-Goetz culturing mouse conceptuses over a more extended equivalent period in vitro. This development has enabled the researchers to demonstrate that the human conceptus can develop autonomously outside the uterine environment and that it does so in ways that differ structurally, functionally and temporally from the mouse conceptus. Perhaps the most intriguing, and unexpected, findings were (i) the deleterious effects of culturing in 5% oxygen – given that in vivo this is the oxygen level experienced by the early conceptus, and (ii) the unique molecular expression patterns shown by the emergent cell populations.
“This is a unique achievement, that potentially challenges the 14 day rule, because to stop the culture at 14 days arbitrarily prevents study of the primitive streak development which stops us asking questions about the basis of twinning, the origins of spina bifida, and how the germ cells are set aside.
“The study design is essentially robust and the results do appear to support the bold claims made, but with one caveat: what is missing from both papers are the numbers of conceptuses that were started in culture and the proportion that were successfully cultured through to each stage?”
Peter Braude, Emeritus Professor of Obstetrics and Gynaecology, King’s College London, said:
“I am delighted that my colleagues King’s College at Guy’s Hospital have been able to facilitate in the collection of very beautiful and important data presented in the Nature Cell Biology paper. These two unique concurring papers demonstrate that good science still can be achieved within the limits set by the UK parliament of not keeping an embryo in vitro beyond 14 days.
“As far as I am aware, there has been no push from any scientists in this country to have extended, the 14 day limit as advised by the Warnock Enquiry, and set in legislation by the UK parliament. The limit was a negotiated decision based on factors that seemed acceptable to those who wished to continue with the embryo research already being conducted before the Act was considered, in order to further our understanding of reproduction and our early development, and those who were concerned about the morality of creating human embryos in vitro for research alone. The limit takes into account the fact that twinning does not occur after this point and the implications of that for individuality and the soul; and that the primitive streak stage is the first formation of the three primary germ layers that will give rise to tissues, and hence prior to this time there is no question of any form of sentience.
” Yes, it is possible that additional useful information about development might be gathered from examining later stages, but much of this can, and has already been gathered using stem cells, or from tissues grown from embryos disaggregated (separated into cells) at earlier stages than 14 days.”
Robin Lovell-Badge, Group Leader, The Francis Crick Institute, said:
“These two papers provide a first glimpse of how the early human embryo develops around and just after the point when it would usually implant in the lining of the womb and become invisible to observation and impossible to study experimentally. This is a period where many essential events occur that distinguish the region of the embryo that will go on to form the fetus in contrast to others that will contribute to the placenta and yolk sac. These latter structures not only help the fetus obtain nourishment from the mother, but they help direct how it is organized and patterned.
“The work confirms that aspects of early development in humans and mice are distinct, with respect to timing of events, of gene activity, cell types and their organization. But is also reveals that some mechanisms are similar, such as the way early cavities are formed by reorganization of cell-cell contacts rather than cell death, and that these stages are independent of the presence of maternal tissues.
“The methods reported here, in combination with genetic approaches, could yield many important details about this period of human embryo development, such as the nature of the genes required and whether and how these differ from the mouse, and what specifies uniquely human cell types. This in turn may help us understand the causes of embryo failure and to develop treatments for this.
“In both papers the human embryo cultures were stopped at 13 days after fertilization, respecting the widely accepted 14-day limit to experiments on intact human embryos. The process of gastrulation, where the embryo becomes organized into a basic body plan, begins shortly after this. We know little about this critical phase in human development. So it is pertinent to ask if the 14-day limit should be extended? This question does not come from these new experiments, nor does it come from several other relevant pieces of work carried out over the last few years. Indeed scientists and ethicists have debated the limit since it was first proposed. However, this debate has taken place in the absence of methods to allow extended periods of culture and there is little point arguing strongly for something that is not possible. The new methods are not perfect and they would probably not support the embryos for much longer. But with parallel advances in tissue engineering it is possible to envisage how they could be modified to extend the period of development. Proposing to extend the 14-day limit might be opening a can of worms, but would it lead to Pandora’s box, or a treasure chest of valuable information ? This is not a question to be left to scientists alone.”
Commentary collected by the US-based Genetic Expert News Service (abridged):
Dr. Vittorio Sebastiano, Assistant Professor, Department of Obstetrics and Gynecology, Stanford School of Medicine, comments:
“In these studies the researchers have shown for the first time that human embryos can be successfully cultured for approximately 12-14 days, way beyond previous attempts.
“This apparently trivial achievement is a rather remarkable milestone in the field.
“While studying rodent embryos can approximate some of these events, many features are human specific and necessitate a model that is based on human embryos.”
Henry (Hank) Greely, Director, Center for Law and the Biosciences; Professor (by courtesy) of Genetics, Stanford School of Medicine:
“In the past few decades, bioscience has made several promises it couldn’t be called on. ‘No human germline engineering,’ ‘no human reproductive cloning,’ ‘no embryo research more than 14 day after fertilization.’ None were possible at the time of the promises; all have started looking plausible in the last few years.
“The latest is embryo research. It was easy to promise not to do research past 14 days because no one could keep ex vivo human embryos alive past at most nine days, usually seven.
“But now two groups have kept human embryos alive on ‘in vitro implantation platforms’ for 12 or 13 days. At least one of the groups destroyed its embryos to abide by the 14-day limit.
“At the same time as the scientific publication comes a call to ‘revisit’ or ‘reconsider’ this limit. Frankly, I am not convinced.
“What is the benefit from keeping human embryos alive in vitro for extra days? It is said it can ‘lead to scientists being able to study all aspects of early human development with unprecedented precision.’ Yet is an in vitro embryo attached to an ‘implantation platform’ really a model for ‘early human development’? Who knows – and, perhaps more importantly, who can know barring unavailable detailed information about early embryos inside women’s wombs?
“On the other side, if we do not use a 14 day rule, what limit will we use? Twelve weeks or so as in many European abortion laws? Viability (at around 23 weeks) as in U.S. abortion law? Human development is a seamless process, but ultimately lines need to be drawn even when – especially when – they do not naturally exist. I do not see a politically, or, for most people, morally acceptable line after 14 days. Given the questionable scientific value of the research, no case has been made for even revisiting the line, let alone changing it.”
Dr. Françoise Baylis, Professor and Canada Research Chair in Bioethics and Philosophy, Dalhousie University, comments:
“Scientific and political elites have long known the day would come when scientists would challenge the 14-day limit. Indeed, Sir Robert Edwards, one of the pioneers of IVF, suggested that the limit should be 21 days. More generally, as far back as the mid-90s there were those who insisted that the internationally accepted norm of 14 days ‘should be subject to modification should there be new and compelling ethical or scientific justification to do so.’
“So, a crucial question for us today is: do we have new and compelling ethical or scientific justification(s) to change the 14-day rule? What we certainly do have is technological prowess: scientists appear to have mastered keeping human embryos alive in vitro up to 14 days. But is this ‘scientific breakthrough’ enough to warrant a change in law or policy? Isn’t it somewhat ironic that when the agreed-upon limit might finally be practically relevant (meaning that it could function to stop scientists from doing something they might otherwise do), the suggestion is that now might be a good time to change the limit?
“In December 2015, the US National Academy of Sciences, the US National Academy of Medicine, the Chinese Academy of Sciences, and the UK’s Royal Society jointly hosted an international summit on human gene editing. At the close of that meeting, the organizing committee (of which I was a member) issued a final statement that endorsed basic and preclinical research in human embryos ‘subject to appropriate legal and ethical rules and oversight’. The statement also championed a commitment to international consensus-building. As such, I am very pleased to see Insoo Hyun, Amy Wilkerson, and Josephine Johnston encourage ‘processes aimed at consensus-building involving experts, policymakers, patients and concerned citizens.’ However, these authors may have reached the right conclusion, but for the wrong reason. Their primary concern seems to be with preventing ‘a public backlash and the implementation of reactive, or restrictive limits on research.’ This smacks of political expediency.”
Dr. Peter Donovan, Professor of Biological Chemistry and of Developmental and Cell Biology, University of California, Irvine, comments:
“Two important messages emerge from these studies. First, advances in technology have allowed the growth of embryos in a lab past the time which many scientists thought possible. Second, the studies demonstrate many of the events of embryo development (cell differentiation and shape changes) can be recapitulated in the lab, which indicates that these events are autonomous to the embryo. In other words, these events aren’t strongly influenced by being attached to the maternal tissue. So now science has a method to study a key period of human development that up until now has largely remained a black box.
“Of course, major advances like this often raise questions that go beyond the science. In many countries, growth of human embryos in the lab is prohibited past 14 days. In the past this has been of little issue because it was technically not feasible. Why is the 14 day limit important? At this time in development the embryo forms a structure called the primitive streak that marks the time at which the embryo has a definitive head and tail end. Before this time the embryo could split to form two individuals. So this marks the time at which an embryo could be considered an individual, as well as the time just before the embryonic brain begins to develop.
“What if scientists could culture the human embryo for longer than 14 days? Perhaps we could begin to understand the consequences of fetal alcohol syndrome, study the potential causes of autism and find out why some environmental chemicals can affect development. Perhaps we might, for examples, be able to more quickly understand what the Zika virus does to embryos to cause major problems with brain development. There could be major benefits for society, but if the 14-day line is crossed then society has to fully understand the science and come to an informed decision about the use of the technology.”