Embryoids: Explanations and Ethical Issues
February 26, 2018
Last spring, MIT Technology Review reported on a University of Michigan team’s discovery that they had made an embryo-like entity from human embryonic stem cells. The team was trying to make organoids—small three-dimensional clusters of cells grown in the lab that are similar to tiny organs. But they found that these clusters of cells started self-organizing and demonstrated many of the features of a developing embryo.
As it turned out, these embryoids lacked key cell types that would allow them to continue to develop beyond a certain point. However, because of their similarities to early embryos, the Michigan team destroyed them before the fourteen-day limit, a rule for embryo research.[1]
The product from the Michigan team’s research is just one example of a burgeoning field that delves into morally ambiguous territory regarding the beginning of human life. Ethicists and scientists are still unclear on where to draw the lines for what one eLife article calls “synthetic human entities with embryo-like features.”[2]
Legalities
In the United States, research on human embryos is limited to the first fourteen days of development, or the appearance of the primitive streak. The primitive streak was held to be indicative of the first stages of the embryo developing a body plan. While the fourteen day rule was set forth as ethical guidance, until recently,[3] embryos made in the laboratory could not survive in vitro for more than a week, preventing scientists from nearing the fourteen-day limit.
When the fourteen-day rule was first determined by the National Research Council, the reasoning was that they did not want the embryo to experience pain or sentience (i.e., at the point of neurulation), so they limited experimentation to a point that occurred before the formation of the nervous system or the brain.[4] The Council determined that the formation of the primitive streak was a clear demarcation that occurred before the formation of the nervous system.
John Aach, Jeantine Lunshof, Eswar Iyer, and George M. Church argue in a March 2017 paper entitled “Addressing the Ethical Issues Raised by Synthetic Human Entities with Embryo-Like Features” that the fourteen-day rule is no longer adequate to draw the appropriate ethical lines because it was based on a linear track of normal embryonic development. As these synthetic entities, or SHEEFS as they call them, have demonstrated, they can bypass normal embryonic stages. They argue, instead, that ethical lines should be based on the emergence of “morally concerning features.”[5]
Additionally in the U.S., the Dickey-Wicker Amendment—an appropriations bill rider first passed by the U.S. Congress in 1995 and renewed annually— prevents federal funds from being used for the creation of a human embryo for experimental purposes or for research with human embryos in which they are destroyed or discarded. The amendment defines an embryo as “any organism, not protected as a human subject under 45 CFR 46 [the Human Subject Protection regulations] . . . that is derived by fertilization, parthenogenesis, cloning, or any other means from one or more human gametes or human diploid cells.”[6] Violation of the Dickey-Wicker Amendment hinges upon whether or not an embryo-like entity is an organism.
Embryos, Almost Embryos, and Organoids
The products of IVF, cloning, and gametogenesis are considered embryos, partly because animal models show that they engage in a directional process that can lead to a live birth. However, live birth as a developmental endpoint is not adequate to define what an embryo is. Neither can an embryo be defined as the product of gametes, or egg and sperm.
Take cloning, for example. Cloning is done by a process called somatic cell nuclear transfer (SCNT), which involves combining an oocyte with the nucleus of a somatic cell. The oocyte with a somatic cell’s nucleus is chemically or electrically tricked into thinking it has been fertilized by a sperm cell. It begins growing and dividing in an orchestrated directional process that could potentially produce an individual.
Animal studies have shown that SCNT can produce a live birth. However, for every one individual successful birth, there are hundreds of failed attempts. Sometimes the SCNT process does not work, and no embryo was made. Sometimes an embryo is made in vitro but it does not survive due to defects. However, defective or not, these entities are still considered embryos.
Alternatively, gametogenesis involves the production of egg or sperm cells from induced pluripotent stem cells (iPSCs). In mouse studies, these synthetic gametes have been combined to form embryos that were able to grow into live mouse pups. This has not been done in human models, although there is some preliminary research on producing human gametes from iPSCs.[7] The products from gametogenesis would be embryos.
A key factor is that the products of IVF, cloning, and gametogenesis display overall organization in which they engage in a pattern of development that forms the parts that comprise the whole organism. Even defective embryos display this pattern of development.[8]
Are Embryoids Just Another Type of Organoid?
Organoids are made from existing tissue, induced pluripotent stem cells, or embryonic stem cells. They are three-dimensional spherical structures that are grown on a scaffold. This shape is important in that two-dimensional cell cultures do not display the same properties that three-dimensional ones do. If scientists want to accurately test whether a drug affects a certain organ in the body, they need to work with a three-dimensional structure of those cell types so they can model how an actual organ would respond to a drug or develops a disease.
Embryoids, on the other hand, are made from ESCs or iPSCs that are placed in a gel matrix. These embryoids are made in a kind of batch process where the cells and the materials are placed in a constrained area (e.g., a microwell array) and allowed to grow. When the cells are not spatially constrained, they do not form embryoids.
Eventually these embryoids will exhibit a line of cells called a primitive streak that indicates body formation and directionality. In normal embryonic development, the embryo first goes through a gastrulation stage when the three main cell layers are formed (i.e., ectoderm, mesoderm, and endoderm), which is then followed by the formation of the primitive streak. Embryoids can go through gastrulation, although some embryoids, such as the ones made in Shao’s group, do not make all of the cells types necessary to produce another organism but still indicate the presence of a primitive streak.
Ethical Questions
To evaluate these embryo-like products and the procedures to make them, it may be helpful to employ an enquiry-based approach to understand where the ethical questions lie. Below is a proposed set of questions to guide deliberation of these issues.
Does the procedure make an embryo? In the case of SCNT (i.e., cloning) the answer is yes. Because of the rules for research on embryos as well as moral objections to experimenting on nascent human life, the fact that a procedure makes an embryonic product is a cause for concern. Other procedures, such as parthenogenesis and gametogenesis, may make an embryo in which case, the ethical issue centers around experimentation on embryos.
If it is unclear whether a procedure makes an embryo or not, then the next question is, does the procedure make an entity that self-assembles, has global organization, and engages in a directional process that produces a new organism? Global organization that then undergoes a directional process indicates a unique organism. Even if certain factors are removed such that the developmental process stops at a particular point, is it still fair to say that this is an organism? For many ethicists, such an occurrence would still mean that this organism must be considered an embryo, even if it would be deemed a severely damaged or disabled embryo.
Does the process involve the use of stem cells whose procurement requires the destruction of an embryo? Many of these embryo-like products, whether gastruloids or embryoids, are made from ESCs. Because the procurement of embryonic stem cells involves the destruction of an embryo, even if the product is not an embryo, the fact that an embryo was destroyed in the process poses an ethical concern. Embryoids can be formed from iPSPCs, which come from adult cells, such as skin. Unlike ESCs, the source of these stem cells is not ethically problematic, assuming appropriate consent.
What is the intended purpose of the process? Laws forbid the intentional creation of embryos for research purposes. Some researchers, such as Ali Brivanlou’s group at Rockefeller University,[9] want to make these embryo-like entities in an effort to eventually create synthetic embryos. They reason that synthetic embryos would not have the same restrictions as “normal” embryos. However, this treads on shaky ethical ground because in other cases, such as in vitro fertilization and cloning, the process used to create an entity does not change the nature of what that entity is. Others, such as Shao’s group, intentionally create entities that lack certain cells that would allow the developmental process to continue. Their goal is to understand human development for reproductive purposes as well as to use these embryoids to test how certain pharmaceuticals affect development without making a synthetic embryo.
Animal studies are helpful in understanding the potential benefits and risks of these procedures. Conducting a new procedure with mouse cells and determining if the product is a clump of disorganized pluripotent stem cells or an embryo is less ethically problematic than doing so using human cells. However, human development is different from animal development, as exemplified in gametogenesis. While researchers have been able to create mouse gametes from induced pluripotent stem cells, they have not had success with humans. Primates might be a better model than mice, but there are differences between humans and primates, particularly in certain genetic signals that are specific to one species and not the other.
Some of the differences in human development compared to other animals are still unknown. Scientists do not always know why a drug, for example, is safe in primates, but causes developmental problems in humans. Some people consider this an adequate reason to either extend the fourteen-day rule or to create embryoids as models of actual embryos.
Shao said he decided that the purpose for developing embryoids is worthy, but he does not want to generate a complete human embryo. His embryoids, which he initially called “asymmetric cysts” to avoid confusion with synthetic embryos, do not have the cells necessary to make a placenta and only have one of the three cell types required to produce a human body. He said that in talking to others about the ethics of his research, some suggested only focusing on re-constructing the parts necessary to answer research questions, and not to re-construct all of the necessary components of an embryo.
Shao includes in his presentations an ethics statement noting that his embryoids “do not have human organismal form or potential.” However, part of the impetus behind this research is the self-organizing abilities of these embryoids, and there is no guarantee that others will heed this caution.[10]
Human embryoids pose a conundrum for ethicists. For example, many of the current procedures involve the destruction of an embryo to obtain an embryonic stem cell that is then used to make embryoids. However, even when embryoids are made from induced pluripotent stem cells, the nature of these products still poses an ethical issue because it is unclear whether or not they are embryos. Embryoids are sufficiently embryo-like to serve as models for early development, but for now, lack the ability to develop into their assumed end. They exhibit morally relevant and therefore morally concerning features, but bypass typical steps in embryonic development. Their existence raises questions over the minimal features required for something to be considered a human embryo.
References
[1] Antonio Regalado, “Artificial Human Embryos Are Coming, and No One Knows How to Handle Them,” MIT Technology Review, September 19, 2017, https://www.technologyreview.com/s/608173/artificial-human-embryos-are-coming-and-no-one-knows-how-to-handle-them/.
[2] John Aach et al. “Addressing Ethical Issues Raised by Synthetic Human Entities with Embryo-like Features” eLife 6:e20674 (2017), doi: 10.7557/eLife.20374
[3] Patrick Monahan “Why This Lab-Grown Human Embryo Has Reignited an Old Ethical Debate,” Science, May 4, 2016, http://www.sciencemag.org/news/2016/05/why-lab-grown-human-embryo-has-reignited-old-ethical-debate.
[4] Aach et al. “Addressing Ethical Issues Raised by Synthetic Human Entities with Embryo-Like Features.”
[5] Aach et al., “Addressing Ethical Issues Raised by Synthetic Human Entities with Embryo-Like Features.”
[6] H.R. 1105 Omnibus Appropriations Act 2009 (See section 509): https://www.congress.gov/bill/111th-congress/house-bill/1105/text.
[7] Antonio Regalado “A New Way to Reproduce,” MIT Technology Review, August 7, 2017, https://www.technologyreview.com/s/608452/a-new-way-to-reproduce/.
[8] Maureen Condic “Alternative sources of pluripotent stem cells: altered nuclear transfer,” Cell Proliferation 41, no. s1 (February 2008): 7–9.
[9] Regalado, “Artificial Human Embryos Are Coming, and No One Knows How to Handle Them.”
[10] Yue Shao, et al. “A Pluripotent Stem Cell-Based Model for Post-Implantation Human Amniotic Sac Development,” Nature Communications 8, no. 208 (2017), https://www.nature.com/articles/s41467-017-00236-w.
