Stem Cells and Parthenogenesis

Author: E. Christian Brugger


Stem Cells and Parthenogenesis

Are Parthenotes Human Embryos?

Here is a question on bioethics asked by a ZENIT reader and answered by the fellows of the Culture of Life Foundation.

Q: What is the Catholic perspective on the ethics of parthenogenesis to produce stem cells from an ovum without fertilization by sperm? Thank you for your insights. Sincerely, R.P. Panama City Beach, Florida, USA

E. Christian Brugger offers the following response:

The term "parthenogenesis" (from the Greek words parthenos, "virgin" + genesis, "birth") refers to a form of asexual reproduction, naturally occurring among some insects, birds and lizards, in which an unfertilized egg develops without being fertilized by a male gamete.

In mammals — and so humans — parthenogenesis refers to a process in which an egg (oocyte) begins to divide without being fertilized by a male sperm. Since mamalian reproduction is sexual, parthenogenesis in humans is a profoundly abnormal process. Although we use the same term as we do with insects and lizards, we don’t know if true reproduction ever takes place in human parthenogenesis. By "reproduction" I mean embryogenesis, the coming into existence of an embryo, not full-term fetal development, which, because the developmental potential of an unfertilized human oocyte is very minimal, is probably not possible.

Human parthenogenesis is interesting to scientists because in recent years studies suggest that pluripotent (embryonic-like) stem cells can be derived from parthenogenically activated human eggs. This seems to promise a way around the ethical controversy found in embryonic stem cell research by providing a supply of pluripotent stem cells without needing to create or destroy human embryos.

In the studies, female oocytes were activated with electrical and chemical stimulations and some began to parthenogenically divide. Among those that did, some developed into structures that looked like blastocysts with a visible inner cell mass. "Blastocyst" is the term used to refer to an embryo at approximately day five after fertilization when its body shape is spherical, with a fluid-filled cavity, and with a clump of cells on the inside called the inner cell mass (ICM), which will go on to form all the structures of the human body. In embryonic stem cell research, ICM cells are harvested by tearing open the embryo’s body, which is lethal to the embryo.

In the studies mentioned above, the activated eggs formed blastocyst-like structures with a visible ICM. When the ICM cells were extracted and analyzed, they were found to possess a similar type of pluripotency to embryonic stem cells.

The real thing?

The big question bearing upon ethical analysis is, of course, whether the "blastocyst-like" structures were in fact blastocyts, that is, living human embryos at day five of development, or were they simply biological tissue-structures that mimic the appearance of embryos and give rise to pluripotent stem cells?

It is reasonable to conclude that an oocyte (an egg) as such is not an embryo. But parthenogenic activation induces the oocyte to divide, at least for a few days, in a way that appears characteristically human. Is it possible that in the process of activation the oocyte can transform into an embryo? The question presently is unsettled.

Although the empirical question of the status of a human parthenote is unsettled, the underlying moral principle is straightforward. Unless we have moral certainty that a dividing parthenogenetically activated human oocyte is not an embryo, we have an obligation to avoid research with human parthenotes.

This is what is taught in the Instruction on Certain Bioethical Questions, "Dignitas Personae," published in 2008 by the Congregation for the Doctrine of the Faith. The text says that certain "scientific and ethical" questions have been raised concerning the "ontological status" of the product of some "new techniques" claiming to be able to produce pluripotent stem cells without bringing into existence human embryos. Footnote 49, introduced at this precise point in the text, mentions three examples, one of which is "human parthenogenesis." The text goes on to say that until these questions are adequately resolved, if there is a "mere probability" that a human embryo is involved, this would "suffice to justify an absolutely clear prohibition" (no. 30).

Does there then exist a "mere probability" that a parthenogenically activated egg is or ever becomes an embryo? This is a point of debate among scientists and ethicists faithful to the magisterium.

Some Catholic thinkers, including Nicanor Austriaco, O.P., Joachim Huarte and Antoine Suarez, have argued that since human oocytes are not embryos, and that since the parthenogenic activation of oocytes does not seem capable of inducing the complex transition from a single cell gamete (an egg) to a whole human organism (an embryo), parthenotes should not be considered human embryos.

Other ethicists, such as Mark Latkovic, have argued that because parthenogenically activated eggs develop in a characteristically human way, at least for several days, we should presume they are human embryos and act accordingly.

Their arguments are complex and I do not mean to reproduce them here. But I would like to say three things and then give my own opinion.

A question for science

First, the magisterium does not teach authoritatively on scientific questions. But it does teach on moral questions, some of which rely for their accuracy on scientific premises. So it is not for the pope or bishops to judge whether or not the sufficient biological conditions are present in a developing parthenote to constitute a human organism. But the magisterium can teach, and in fact, as I have shown, has taught that reasonable doubt must be ruled out before research on parthenotes can be legitimate. The question then of the status of parthenotes is only rightly answered by attending to the best scientific evidence.

Second, simply because parthenogenesis in humans is an anomalous process and cannot result in a healthy gestated baby, does not settle the question of the status of parthenotes, although it does give evidence as to whether or not nature might permit human organismic development to take place in the context of such an anolmaly.

Third, simply because the behavior of an artificially activated parthenote mimics the behavior of an embryo at its very earliest stages also does not settle the question of identity. We know, for example, that an egg whose nucleus has been removed (so it’s no longer even a cell), when stimulated can begin to divide and proceed through several divisions. Or again, many cell clusters in a Petri dish will form blastocyst-like structures in vitro, but are not embryos.

Having said this, the present evidence on whether parthenotes are ever embryos seems to me inconclusive. Some mammalian parthenotes in controlled studies (e.g., mice) have been found to form a fairly well developed nervous system, including considerable brain and organ formation. Analogous studies in humans have not been done, and indeed would be immoral to do in the absence of the moral certitude that the studies themselves would be seeking to obtain.

Observations of naturally occurring human parthenotes would seem to me to be the only legitimate way to gain the requisite knowledge necessary to settle the empirical question. In a recent essay treating such observation I wrote:

"Scientists believe that mature teratomas of the ovary result from parthenogenetically activated eggs. Some of these tumors form rudimentary neural tissue. Some even organize into a basic human body plan (the so-called "fetiform" tumors) with a recognizably differentiated brain and spinal nerve, with blood vessels, skin, hair, teeth, trachea, thyroid gland, bone, cartilage, bone marrow, and other differentiated features. But rigorous genetic analysis on these specimen has not been done, so we cannot be certain that the tumors really were parthenotes (they could be ectopic pregnancies or fetus-in fetu—a reabsorbed twin)."[1]

Given the evidence to date, at least with which I am familiar, I do not think it can be established with moral certitude that parthenotes are never human embryos.


[1] E. Christian Brugger, "Parthenotes, iPS Cells, and the Product of Ant-Oar: A Moral Assessment Using the Principles of Hylomorphism," National Catholic Bioethics Quarterly, vol. 10, no. 1 (Spring 2010), 123-142

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E. Christian Brugger is a Senior Fellow of Ethics at the Culture of Life Foundation and the J. Francis Cardinal Stafford Chair of Moral Theology at St. John Vianney Theological Seminary in Denver, Colorado.

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