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Is it acceptable from an ethical point of view to use stem cells from human embryos for scientific research and clinical therapy? And what are the weaknesses.
Table of contents
- An intercultural perspective on human embryonic stem cell research
- Issues and ethics of human embryos generated from reprogrammed cells
- Should the 14‐day rule for embryo research become the 28‐day rule?
- STEM CELLS, HUMAN EMBRYOS AND ETHICS: INTERDISCIPLINARY PERSPECTIVES
This week, teams led by researchers at the Rockefeller University and the University of Cambridge, UK, report 1 , 2 that they cultured intact human embryos in vitro and obtained interpretable images up to day 12— Each team stopped its studies by day 14 in accordance with UK law and international guidelines. The latest work provides compelling insight into how the early human embryo transitions from a floating hollow ball of cells to a three-layered gastrula attached to the uterus.
Studies on human embryos sustained in culture could help to clarify whether self-organizing structures truly mimic early human development. Tracking, in real time, the morphological and molecular changes in embryonic cells and the interactions between them during these later days of development, could elucidate the cell-signalling pathways that guide embryo organization and tissue formation.
These techniques could shed light on the disorders that result in early pregnancy losses and birth defects, and facilitate clinical applications of stem-cell research. In conjunction with gene-editing tools, they could even help to determine the role of specific genes in human development. In principle, these two lines of research could lead to scientists being able to study all aspects of early human development with unprecedented precision. Yet these advances also put human developmental biology on a collision course with the 'day rule' — a legal and regulatory line in the sand that has for decades limited in vitro human-embryo research to the period before the 'primitive streak' appears.
This is a faint band of cells marking the beginning of an embryo's head-to-tail axis. The day rule has been effective for permitting embryo research within strict constraints — partly because it has been technologically challenging for scientists to break it.
Now that the culturing of human embryos beyond 14 days seems feasible, more clarity as to how the rule applies to different types of embryo research in different jurisdictions is crucial. Moreover, in light of the evolving science and its potential benefits, it is important that regulators and concerned citizens reflect on the nature of the restriction and re-evaluate its pros and cons. In at least 12 countries, this limit is encoded in laws governing assisted reproduction and embryo research see 'International agreement'. The rule is also embodied in numerous reports commissioned by governments, and in scientific guidelines for embryo and assisted-reproduction research.
Some versions of the rule cover embryos created by any means; others apply only to products of fertilization. Some explicitly refer to gastrulation when three different cell layers appear or the formation of the primitive streak; others mention only the 14 consecutive days of development. In most cases, however, what seems to be crucial is the stage of development that the 14th day typically represents, not the consecutive number of days in culture. The formation of the primitive streak is significant because it represents the earliest point at which an embryo's biological individuation is assured.
Before this point, embryos can split in two or fuse together. So some people reason that at this stage a morally significant individual comes into being. Yet views differ on the moment in development at which a human embryo obtains sufficient moral status that research on it should be prohibited. Some, for instance, believe that the cut-off is the point of fertilization; others argue that it comes much later, when the embryo develops into a fetus that can experience pain, exhibit brain activity or survive outside the womb.
Revisiting the day rule might tempt people to try to rationalize or attack the philosophical coherence of the limit as an ethical tenet grounded in biological facts.
An intercultural perspective on human embryonic stem cell research
This misconstrues the restriction. The day rule was never intended to be a bright line denoting the onset of moral status in human embryos. Rather, it is a public-policy tool designed to carve out a space for scientific inquiry and simultaneously show respect for the diverse views on human-embryo research. In fact, as a public-policy instrument, the day rule has been tremendously successful.
It has offered a clear and legally enforceable stopping point for research, because the primitive streak can be visibly identified and it is possible to count the number of days that an embryo has been cultured in a dish. The alternatives at each extreme — banning embryo research altogether or imposing no restrictions on embryo use — would not have made for good public policy in a pluralistic society.
Scientific advances are now prompting re-evaluations of other long-established research policies. For instance, it has proved difficult to maintain a previous consensus among funders, regulators and researchers that genetic engineering of human cells is permissible as long as those cells are not sperm, eggs or embryos. The clinical use of mitochondrial-replacement therapies — which cause heritable changes to future generations — was approved last year by the UK government , and deemed 'ethically permissible' earlier this year by a committee of the US Institute of Medicine.
Some might conclude from such developments that policymakers redefine boundaries expediently when the limits become inconvenient for science. If restrictions such as the day rule are viewed as moral truths, such cynicism would be warranted.
But when they are understood to be tools designed to strike a balance between enabling research and maintaining public trust, it becomes clear that, as circumstances and attitudes evolve, limits can be legitimately recalibrated. Any decision to revise the day rule must depend, however, on how well any proposed changes can uphold the rule's two chief goals: supporting research and accommodating diverse moral concerns. The rule became a standard part of embryo-research oversight through the convergence of deliberations of various national committees over decades.
Hundreds of medical and scientific associations submitted recommendations, and dozens of public forums were held. Any formal changes to this rule should occur through similar processes of consensus-building involving experts, policymakers, patients and concerned citizens. Ideally, discussion should begin at an international level given the global nature of this research — although taking local cultural and religious differences into account properly would also require national-level debates. A complication is that in many countries, a revision to the day rule would involve a legislative change.
Yet the kind of international discourse that we envision could facilitate and inform local decisions to amend law or research policy. There are precedents for this type of international discourse. The second component of this initiative — a science and policy review and report on human gene editing — is ongoing. The ethical ramifications associated with human PG and ES cells research are not taken lightly by Varmus. He said that NIH respects and recognises the many ethical and legal concerns people have about the use of human pluripotent stem cells and the way they are procured.
Snyder and his co-workers removed cells from deep within the forebrain of an aborted fetus and cloned the ENS cells. They grafted the immature stem cells into different areas of the developing mouse brain, and the ENS cells migrated along existing developmental pathways, maturing into location-specific neural and glial cells. The in-culture-enzyme-producing ENS cells appear to correct the underlying Tay-Sachs deficiency, offering hope that single-gene or multi-gene inherited cerebral disorders might be corrected in this fashion. The work of Snyder's group falls outside the current debate on fetal tissue research, as they were able to perpetuate a single sample of fetal tissue into constantly renewing stable cell lines.
A technician must isolate and incubate an embryo prior to removing the pluripotent ES cells from the inner cell mass of the blastocyst. Arguing that ES cells are not human beings because they cannot develop into adult human beings is probably a correct inference, but is a blastocyst a human being?
I contend that it is. After all, it contains a complete genome and all that is needed to develop into an adult human being.
Issues and ethics of human embryos generated from reprogrammed cells
The only alternative is to term it cadaveric tissue, 7 which it certainly is not! Hence, our ethical dilemma is one step removed from the problem of procurement ie, elective abortions or in vitro fertilisation. What is the ethical justification for sustaining the life of human embryos in vitro for the express purpose of harvesting PG and ES cells? In the opinion of Arthur Caplan and others who are reasoning in an exclusively utilitarian way , we have a duty to consider the promise future stem cell therapies offer for those who are paralysed, burned, or dying of liver or pancreatic failure, brain injuries, and other debilitating conditions.
In effect, the moral status of embryos must be balanced with the needs of those who are sick, injured or dying. I submit that we need a clear definition of the moral and legal status of human embryos and that we should call for a moratorium on human blastocyst research in vitro.
This will not be easy to achieve unless we reach a consensus on biological criteria indicative of the sanctity of human life. The most significant issue to address in discussions of genetic science is a proper understanding of human nature.
One of the more common meanings of this biblical image is intelligence and will. Obviously, an embryo or fetus cannot manifest knowledge or love, and presumably has no innate experience of either.
Should the 14‐day rule for embryo research become the 28‐day rule?
Thus Ronald Dworkin argues that while a fetus should be valued as intrinsically sacred, it does not possess the right to life because the rule of law does not touch upon intrinsic values; these are detached personal beliefs of conscience. Paul Ramsey warned that in failing to recognise the limits and constraints we must place on scientific inquiry we run the risk of re-enacting Promethean pride and hubris.
Moral knowledge, like all knowledge, is a discovery and not an invention. Far from censuring the efforts of science and technology in the service of humanity, Donum Vitae discusses biomedical research in light of our God-given dominion over creation. The fundamental criteria for making moral judgments about technical questions in bioethics are the inviolable integrity of each individual human life and the special nature of the transmission of life. If we are going to espouse a sanctity of life standard, how do we balance the promised benefit for the sick and disabled with an absolute prohibition against abortion?
Don't we compromise this standard by failing to condemn killing in a just war, in self-defence, and in allowing capital punishment? I leave aside the question of the philosophical validity of proportionalism 17 except to mention that the medical benefits which might accrue for some patients do not outweigh the grave consequences for the embryo that is killed in order to procure ES cells for medical therapy.
STEM CELLS, HUMAN EMBRYOS AND ETHICS: INTERDISCIPLINARY PERSPECTIVES
While the fifth commandment forbids killing a human being, the state has the right to entrust a soldier with the mission of killing a foreign combatant when just social order is gravely challenged. Similarly, the state can execute a convicted murderer if he or she continues to pose a serious threat to the common good. And if an assaulted party ends the conflict by killing the aggressor in self-defence, that person is not a murderer assuming he does not directly intend to kill the aggressor but to disable him. Only those who are free of grave injustices against the life of others retain the right to life in the strictest sense, because a defining circumstance of the right to life is innocence.
A conceptus is always innocent of wrongdoing, while a person who threatens the life of another ceases to be innocent. While current debates on life issues focus on the origin of life, we might also consider our ultimate destiny. Brian V Johnstone for one argues that the resurrection should have a central place in Christian ethics. Abortion is a challenging issue for Christians because there are no explicit New Testament texts concerning it, and in vitro fertilisation is even more difficult to address from a scriptural point of view. One of the biblical passages commonly cited in favour of protecting life in the womb is Psalm — None the less, the larger context of the symbolic world of Scripture does offer implicit paradigms for elucidating a proper evaluation of the ethical status of a fetus.
The most compelling metaphorical correlation is Jesus' parable of the Good Samaritan. Given the paucity of scriptural evidence directly addressing abortion, other forms of argument are usually adduced such as reason and experience. Although there are problems discussing this issue in terms of rights, the sacredness of life, or quality of life, clarifying our concept of rights can advance discussion of this issue as well as others.
Evan Snyder's research group has demonstrated that degenerating adult murine neocortical cells induce transplanted multipotent neural precursor cells to differentiate into neurons and glial tissue. The adult human brain has a very limited ability for self-repair, and that is especially true of neurons; nevertheless, neural stem cells can serve as self-renewing precursors of neurons and glia. Interestingly, these cells have been isolated from both the embryonic and adult mammalian CNS; and there may be latent CNS neuroepithelial stem cells in the adult brain for example, in the basal ganglia.
Several years ago I discussed the theoretical possibility of using autografts of progenitor cells to induce the regeneration of damaged tissue. Of equal importance to successful transplantation is the supporting connective tissue matrix. Even adult cells retain responsiveness to their surrounding connective tissue environment. Obtaining human PG and ES cells from aborted fetuses or surplus embryos of in vitro fertilisation are unacceptable from an ethical standpoint. Another possible source is spontaneous, non-elective abortions, but that solution does not address the question of embryo manipulation.
I discuss the possibility of using adult autologous PG and ES cells to avoid the destruction of human embryos.