A Primer on Stem Cells
Stem Cells: What are They?

E. Christian Brugger
Reproduced with Permission
Catholic Culture

Stem Cells: What are They?

Human development begins when the head of a male gamete (sperm cell) penetrates the cell wall of a female gamete (ovum or egg), the nuclei of the two cells fuse together, and the genetic material (DNA) from both cells - 23 chromosomes each - combine. This process, which is called fertilization or conception, gives rise to an entirely new and genetically unique individual called a zygote. The zygotic individual contains all the genetic information and dynamism necessary to orchestrate its development from a zygote to an embryo, to a fetus, an infant, toddler, adolescent, and adult. The capacity of this single-celled human zygote to develop into an organically mature human person (i.e., the capacity for total human development) is termed totipotency.

The developmental process continues with the first cell division. In the hours after fertilization, the single-celled zygote divides into two identical cells, both of which are totipotent. The pair of cells divides again, producing four totipotent cells, and again, producing eight, and so on.

At approximately day five, the aggregate of totipotent cells begins to take the specialized form of a hollow sphere of cells, like a tiny basketball. The sphere has a layer of cells on the outside and a cluster of cells on the inside called the inner cell mass (picture a clump of attached marbles inside a basketball). The individual at this stage is called a blastocyst. The outer cell layer of the blastocyst will go on to form the placenta and other supporting tissues needed for fetal development in the uterus, while the cells of the inner cell mass - also called stem cells - will go on to form virtually all the organs and tissues of the human body. Although the inner cell mass cells have the capacity to form virtually every type of cell in the human body (e.g., cardiac, neural, muscular, skeletal), they can no longer form a total organism because they are unable to give rise to the placenta and supporting tissues necessary for development in the uterus. So although they are not totipotent, each inner cell mass cell (i.e., each stem cell) is still pluripotent (i.e., while unable to develop into a complete organism, each cell has the potential to develop into the different tissue types in the human body).

In time these stem cells will undergo further specialization into specialized stem cells committed to specific kinds of tissue production (e.g., blood stem cells, cardiac stem cells, neural stem cells). Once a stem cell's code is "turned on," it is no longer pluripotent, but rather multipotent (i.e., has the capacity to generate a particular type of tissue).

IVF, Cloning, and Embryonic Stem Cell Research

Because of their wide-ranging capacities to produce human tissue types, both pluripotent and multipotent stem cells are coveted by clinical scientists, who see in them great potential for generating healthy tissue for persons who require the repairing or replacing of diseased or damaged tissue. These stem cells are extracted from human embryos in the blastocyst stage. There are two ways by which embryos can be created in a laboratory: in vitro fertilization (IVF) and cloning. IVF entails harvesting a female egg from a donor and fertilizing it in a petri dish using donor sperm. The resulting embryo is grown in a nutrient rich medium for four to seven days, at which point its inner cell mass cells (i.e., stem cells) are mature enough for harvesting.

The other method, cloning - the most common type called somatic cell nuclear transfer - involves harvesting an unfertilized female egg and carefully extracting its nucleus. The nuclear contents are then discarded, leaving the egg "enucleated." A somatic cell (i.e., any cell from the human body other than an egg or sperm cell) is then harvested from another donor, its nucleus likewise extracted, but rather than discarding its contents, the nuclear contents are transferred into the enucleated egg. Since an individual's virtually entire genetic blueprint is contained, in the form of DNA, in the nucleus of each somatic cell, the donor egg, after receiving the somatic cell's nucleus, now has a complete 46-chromosome genetic complement, all it would have if the egg had been fertilized by a male sperm cell. It needs only to begin dividing for the process of human development to proceed. Stimulate it with an electrical impulse or chemicals and, if successful, you get an actively dividing human embryo who is almost genetically identical, not with the woman who donated the egg, but with the donor of the somatic cell (who may be male or female). As with the IVF-made embryo, the cloned embryo would be cultivated in a laboratory and its stem cells matured and extracted. Embryo cloning for purposes of stem cell extraction is commonly called therapeutic cloning, a misnomer indeed, since the technique is manifestly un-therapeutic to the embryo. (The technique can also be used for making babies, commonly called reproductive cloning. In this case, the cloned embryo would be implanted into a female uterus and carried to term.)

If experimentation of this sort is welcomed by the Western world, then a massive for-profit industry will develop around these techniques. Huge numbers of human embryos will be created, frozen in cryo-labs (freezing labs), stored in embryo freezers, thawed, cultivated, harvested for stem cells, and then, when their utility has ceased, their useless remains will be destroyed and dumped.

The Ethics of Embryo Research

The status of the embryo

The crucial ethical question is this: What is the status of the human embryo? Is it human life, as prolife advocates and the Catholic Church affirm (see "Declaration on Use of Human Embryonic Stem Cells," Pontifical Academy for Life, Aug. 2000)? Or is it merely pre- or potential human life, as proembryo research advocates claim? If it is merely prehuman, then when we are dealing with the human embryo we are not dealing with a unique human being. Hence, lethal experimentation, which for compelling reasons - such as the development of life-saving medical procedures - could be justified, would not be the killing of human beings. But if the human embryo is human life and hence a human being, then this kind of experimentation would entail the wide-scale creation of human beings in the laboratory, their exploitation for purposes unrelated to their own welfare, and their ultimate destruction. It would be the creation, use, and killing of human beings - lots and lots of human beings. Defenders of stem cell research doubt whether the embryo is human life. To them the scientific and clinical benefits of embryo experimentation outweigh the presumption in favor of preserving what they argue is merely potential human life. They frequently place the question of the status of the embryo outside the domain of science, relegating it to the domains of philosophy or religion. Now, no one is doubting that philosophy and religion have something to say to the question, and even that people's ethical judgments are often shaped exclusively by their religious or philosophical views. But the question of the status of the human embryo is not exclusively or even primarily a philosophical or theological one. The question is first and foremost a matter for empirical observation.

An empirical consideration

Before fertilization the egg and sperm cells are clearly not unique human individuals. Both are body cells of other human individuals, extensions we might say of those individuals, as an epithelial or epidermal cell is part of someone's body. After fertilization we are no longer dealing with a part of another's body, but an entirely new, genetically unique and organized individual. Unless seriously defective or prevented from the outside, this organism will develop into a completely differentiated fetus, which in due course will eventually be born, in the majority of instances alive and healthy. This organism is manifestly alive, that is, it has its own principle of unity and dynamism (though still in need of placental nurture) and it is manifestly human, that is, it is not the embryo of a frog, a mosquito, or a bat. Should we not therefore conclude it is human life? And doesn't conventional language as found among family and friends, ob-gyns, What to Expect When You Are Expecting, and dealers in baby apparel commonly refer to this human organism as a "baby," even as "he" or "she"? "Son, I'm worried that Carrie is having another baby; are you sure you can support another child?" "Congratulations, Sherry, have you found out yet whether it's a girl like granny hopes?" "Dr. Hortence, can you see from the ultrasound yet whether it's a boy or a girl?" Might not common parlance be telling us something?

But there is an even better reason for concluding that the human embryo is more than a blob of protoplasm, for there is no discreet point after the moment this new organism comes to be at which we can say, "now human life is present while then it was not," neither at the onset of differentiation, nor at the point of viability, nor at birth, toddlerhood, childhood, adolescence, or adulthood. Any attempt to draw a line after fertilization is arbitrary. Development from 40 minutes to 40 days to 40 years is a steady, organized continuum which will cease only if the organism itself ceases (i.e., dies). Everything the fetus has at 40 days or the man at 40 years is coded for and anticipated by the zygote in its first moments of existence. Therefore, drawing the line at the blastocyst stage is as arbitrary as drawing it at the first recognizable sign of neural tissue development, the beginning of a heartbeat, or at viability (which becomes earlier with better technology). Indeed, the only point at which something radically and entirely new begins or occurs is the point at which the organism becomes what it is, and that point is at fertilization. Compared to that, everything else is incidental development in size and form.

Like an oak tree is an acorn writ large, so a fully grown man or woman is an embryo writ large. One thing everyone reading this article can say with scientific certitude is, "I was an embryo." Had someone destroyed the embryonic life that you and I once were, is there any doubt he would have destroyed you and me? There was no point after you and I were conceived when you and I were not in a real substantive sense you and me. If, therefore, we look strictly at the empirical evidence, it is reasonable to conclude that when we are dealing with a human embryo, we are dealing with a tiny human being, and that destroying that embryo is destroying a human life.

A thought experiment

Let's approach the ethical question from another angle. If you were hunting in a forest and saw at a distance something stirring in the bushes but were uncertain whether the stirring was that of a deer or another hunter, would you be morally justified in shooting to kill based simply on the premise that the figure you see stirring in the distance "might not" be another human? If it turned out to be another hunter and you shot and killed him, would the dead man's wife and fatherless children, or a jury of your peers, or Dan Rather and the CBS news team, or any reasonable person say that your decision to shoot was ethically warranted based simply on the fact that you were unsure of the status of the object moving in the distance? So even if we begin from the doubtful premise that the status of the embryo is uncertain (something empirical evidence, as I have shown, argues against), should we be willing to proceed with experimentation that results in the destruction of organisms which in the absence of better empirical evidence present themselves to us as living human beings? Unless we are certain that what we are dealing with is not a human being (and who could truly be certain?), then to proceed with experimentation of this kind says we are willing, even if wrong, to experiment on and kill innocent human beings. A will willing to kill the innocent is a bad will.

The question of utility

But what about the great good that could result? Doesn't helping other people, perhaps large numbers of other people, overcome disease and suffering justify the destruction of embryos? Let's answer with another question. In attempting to balance out economic inequalities, were the Bolshevik revolutionaries justified in killing off the aristocracy and real or suspected political opponents? Because a goal is good, it doesn't mean all ways of pursuing that goal are good. A good end does not justify an evil means (see Rom. 3:8). Sound moral reasoning confirms that any deliberate action that destroys innocent human life at any stage from conception to natural death is wrong. The fact that an embryo is small and we are large is insufficient ground for concluding that the former can be destroyed. In fact, the opposite is the case; precisely because the human embryo is voiceless and defenseless, and can't fight back, all good people, especially Christians, must speak out and fight on behalf of innocent and helpless human life.

Just say "no!"

The humanity of the human embryo is not a religious question, but a matter of empirical fact. What is at stake at present is the production of tiny human lives for reasons entirely unrelated to the good of those lives. A new watershed is about to be crossed in our nation no less momentous than the one crossed in 1973 when the Supreme Court invented the constitutional right of abortion. And given the fact that there are morally acceptable alternative sources for stem cells - for example, stem cells found in adult bone marrow, adipose tissue, fetal umbilical cords and placenta, which, according to the latest research, promise equal if not greater results than embryonic stem cells - the question of proceeding with the making and destroying of human embryos should not even be an issue. After the grave mistakes and horrors of the past century, shouldn't we resist the temptation to watch silently while an entire class of human beings, in this case embryonic human life, is resigned to a moral status no higher than a laboratory rat?