An article recently published in the journal Cell, raises the need to assign a legal status to new embryonic models – human embryos – obtained from pluripotent cells, coming from embryonic cells (human Embryonic Stem Cells (HESCs) or from reprogrammed somatic cells (Human Induced Pluripotent Stem Cells (hiPSCs)).

The authors propose a redefinition of the human embryo, which could be applied to these new biological realities, the “embryo models, embryoids or blastoids”, to enable their legal treatment and protection.

In their conclusions, they launch the proposal of a new definition of the embryo that is applicable to these new biological realities similar to human embryos but obtained by manipulation in the laboratory, different from the fertilization of gametes or somatic nuclear transfer (cloning). To do this, they define two characteristics on which the consideration of a human embryo would depend.

The first of them would be its potential capacity to develop and form a fetus, thus defined as of day 58 from fertilization. They call it the intrinsic capacity of cells to continue their development.

The second characteristic would consist of the existence of an external biological support, which the authors define as “elements fulfilling extraembryonic and uterine functions that, combined, have the potential to form a fetus.”

The evaluation of these two characteristics that would define the nature of the human embryo is, certainly, very complicated.

Firstly, evaluating the capacity of one of these embryonic models to continue its development beyond a certain maturation stage requires its transfer to a uterus, with the difficulties that this entails, both technical and legal, given that it is currently not permitted the transfer of these “embryo models” into human wombs to continue pregnancy.

On the other hand, the genetic manipulation to which they have been subjected to ensure that their cells proliferate as an embryo obtained after the fertilization of the male and female gametes would do, can induce changes in the genome that are not known and difficult to control. This would occur given the complexity of its functioning and how little is known about the interactions between its genes, with unpredictable consequences.

Secondly, establishing as an essential requirement for the consideration of a human embryo the existence of extra-embryonic structures that provide biological support to the progression of this embryo means removing the consideration of a human embryo from the zygote or preimplantation blastocyst. This would mean going back to the concept of pre-embryo, established in the 1980s following the appearance of in vitro fertilization, which allowed embryos to be obtained outside the womb. It is a concept that has already been surpassed and abandoned as obsolete and distant from the scientific evidence currently available.

The knowledge about the biological nature of the embryo that science provides today, and that we have previously analyzed, defines it as a “continuum” in terms of its evolution. This does not allow defining supposed evolutionary stages that imply substantial changes in its nature that justify modifying its biological status, which is why it is not considered as something different from a human embryo in any of its evolutionary stages, nor in the initial one.

The authors recognize this undeniable biological continuum, but at the same time they affirm that the legal protection of the embryo along this continuum must vary, since they focus on the characteristics of the embryo and not on its nature, ignoring at all times the concept of human dignity.

To overcome these difficulties, the authors of the aforementioned article propose that “human embryo models could be considered equivalent to embryos when:

(1) they have demonstrated the potential to be developed efficiently in vitro until a time to be decided based on local ethical and regulatory considerations; (2) when equivalent models of animal embryos are shown to have the potential to form live, fertile animals in multiple species, including those that are closest to humans (e.g., pigs, monkeys).”

Bioethical assessment

In our opinion, the authors’ approach is correct in that origin is not what should determine whether an entity is a human embryo or not, but rather what it really is, regardless of how it was generated. However, the model defended by the authors to try to grant a defined biological status to the new embryonic models that allows their consideration and legal treatment, contains, according to our criteria, the same difficulties that motivated the failed position of the “Warnock commission”. In its report issued in 1984 in the United Kingdom, it laid the foundations for the acceptability of research with embryos, establishing an arbitrary period of 14 days from conception – adopting the previous conclusions of the American EAB – in which the embryo would lack individual nature.

This means depriving the early embryo, specifically the preimplantation embryo, of the consideration of an individual of the human species, leaving it unprotected and being able to be manipulated and destroyed in research procedures that require it.

The attempt to establish criteria that can guide whether or not new embryonic structures obtained by procedures other than fertilization or somatic nuclear transfer (cloning) are considered human embryos means excluding the early embryo from its consideration as human. Either because its ability to evolve until reaching the characteristics of a fetus cannot be demonstrated, or because it lacks the extraembryonic structures on which its subsequent development will depend.

The fact that an embryo, which possesses a human genome, even if defective, cannot evolve beyond a certain point of complexity, does not seem to be a sufficient criterion to rule out its human nature. Many human embryos obtained by natural fertilization have genetic defects that prevent their evolution until birth and this does not deprive them of their human status.

Finally, the fact that the embryo must possess extra-embryonic structures to develop (such as the uterus) to be considered a human embryo does not constitute a solid argument. The existence or not of these extraembryonic support structures does not modify the intrinsic nature of the embryo, which has the potential for continuous development, without interruption, of increasing complexity and well structured, as long as it is provided with the biological support it needs to it. The fact that it does not have this support, as happens with embryos obtained in vitro or these new forms of embryonic models obtained in the laboratory, does not define its nature or its potential.

Thus, a neonate deprived of sustenance and condemned to die due to its total dependence on the environment is no less human than one that receives the necessary support and progresses to adulthood. Granting this support or not does not alter its nature or its potential and, therefore, the treatment that should be offered.

The position of the scientists who subscribe to the proposal we analyze seems to be aimed at granting the world of scientific research a margin of time to experiment with these embryos or embryoids, just as happened in the 80s. They try to redefine the status of the embryo , in order to avoid the ethical difficulties involved in manipulating and destroying an individual of the human species in an embryonic state, more or less mature, which is not transcendent in its consideration as human.

On the other hand, it is also true that the recognition of embryoids as embryos may limit certain uses of these embryonic models, since they would also have certain legal protection. However, it could also open it up for other purposes, such as reproductive ones, since after all they would be recognized as embryos. The authors warn of the need to discuss and regulate these possibilities.

The attempt to establish the similarity of these products obtained in the laboratory with the embryos that result from natural fertilization is extremely complex, and must be implanted in animal models first, in order to verify the degree of success or failure in their development. It cannot be ruled out that, if these procedures were successful, they would be tried on humans later, when permitted. This would put at risk not only the individual being evaluated, but also the pregnant woman, who may suffer the consequences of genetic alterations that are difficult to foresee.

The utilitarian criteria, on which the current proposed position is based, insist on justifying the means used, even if they are ethically unacceptable, depending on the goal pursued, the investigation and treatment of problems in embryogenesis and infertility.

It must be clarified that the ethical acceptability of every human act includes the legitimacy of the object, the means used and the end pursued. In this case, the destruction of human embryos, even of uncertain classification, is an illicit means that ethically disqualifies this type of research.

Julio Tudela and Lucía Gómez Tatay

Bioethics Observatory – Institute of Life Sciences

Catholic University of Valencia


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