By Charles S. Yanofsky, M.D.
Biological replication is inexact. Offspring are not copies of their parents. Even mitoses don't generate identical daughter cells. Replicative infidelity accounts for the biological phenomena of diversity, evolution, sexual reproduction and death. Cloning violates this First Principle of biology.
Index:
Therapeutic Vs. Reproductive Clones
Applied Embryology – An Attack
Sources of Further Insight
Neurologists would love to be able to replace neurons, myelin producing cells, muscle cells, or to repair injured spinal cords in paraplegics. What about founding an immortal cell line, to be able to bring back a part of ourselves after we leave this earth? Contrary to popular misconception, a human clone is a mere genetic copy, not a personal reproduction. Animal clones, as popularized in Jurassic Park, are more faithful copies of the original than humans could possibly be. The reason is that genetics does not make the person. Identity is determined by the combined effects of experience and memory on the host of that experience. Knowing about my interest in looking at some of the larger questions, I’ve been asked by some of my non-physician acquaintances about my opinion of cloning. Also I’ve had so many expectant hopeful questions from patients and families, cloning has been so much in the news, it was time to look at it in depth.
Science fiction and religion, which drive popular thought about clones, are more myth than reality. They veer toward hyperbole and extreme overestimation of technological capabilities. We are not ready to churn out cadres of identical marine privates to send into battle on faraway planets, or to harvest whole organs from zombies fashioned for this purpose. I have no idea about if or when an embryo is imbued with a soul or should be considered a human person. I would not confuse an embryo, blastocyst or zygote with a formed child or person, even if a zygote may have the potential to become a person after some years, eventually, under certain limited circumstances, as indeed does any collection of genetic material, including the nucleus of every somatic cell. My discussion of the ethics of cloning is from a Benthamite utilitarian perspective. I shall consider cloning “good” if it results in a net gain for mankind, “bad” if it causes net harm. There may be certain overwhelming harmful effects, deal breakers, which while not outweighing bad effects, may be of themselves too much to accept. Sitting through a basketball game of identical Michael Jordan clones might be one of those.
A small company, Advanced Cell Technology, succeeded in making a single human clone comprised of just 6 cells, rekindling the debate on clones. Some monkey ova produced parthenogenetically have also been stimulated to divide. What does this mean and what is the projected utility? What about future implications?
Cloning happens when you make a perfect genetic copy of a cell or whole organism. It is the deliberate production of genetically identical individuals. When your body is invaded by a virus or even a foreign protein, your immune system springs into action, stimulating genetically identical clones of antibody-producing plasma cells to reproduce. You can take a mature somatic cell from an adult animal or plant, extract the genetic material to produce a perfect genetic copy. Cloning is not the same as genetic engineering of which cloning is a small part. Why would anyone want to do such a thing?
For quite a few reasons. Once you have developed a high yielding disease and weather resistant crop, you wouldn’t want to take your chances with genetic diversity. You’d keep using whatever works. The same goes for milk producing cattle, for chickens and for fish and that championship horse. No need to pay premium prices for a stud horse then take chances that the offspring will also win races. Use cloning technology and bet on a sure thing. The stud is donating just half of his genetic material to the offspring. You’ve got a champion. Why not go for the full monty? And the same goes for winning breeds of dogs and sheep etc. For some purposes you’ll want the best milk cow. For beef you’d want different characteristics and all of this would be done by design. Cloning is where biology and mass production meet.
Those amber waves of grain, horse races too, might get more than a little monotonous when you eliminate diversity. To reproduce exact copies you may have to go to great pains. You could try the natural route through sexual reproduction amongst males and females in otherwise genetically identical cloned organisms which would work in some species, especially plants. A few cloned cows have already calved. I’d imagine some more intelligent animals might die of boredom seeing only identical specimens of the opposite sex. Technically you run into some problems where there is a detrimental or lethal recessive trait which turn out to be quite common. Where clones reproduce, an excess of detrimental recessive traits might be expressed, but with a little bit of work, you could eliminate recessive traits to form that “perfect” for your own private purposes, animal or plant. Whenever you cross close relatives such as siblings who share approximately half their genes, there’s a very good chance the offspring will carry two copies of a lethal recessive trait. That is one reason for incest taboos in most societies. Crossing clones is extreme incest in a way. So cloning is somewhat more complicated than other means of making designer organisms, especially breeding. Breeding animals and plants, fostering certain genetic crossings and abandoning others, led to domestication (civilization).. It is why we’re not still hunter gatherers and is behind much of the success of our own species. Human and non-human genetic crossing and design is mentioned in Genesis when Jacob waxed rich by specially crossing multicolored animals.
Consequences non-human cloning are complicated enough, but the real ethical conundrum arises with human clones. Dolly the sheep is bad enough but just imagine when we start mass producing identical humans.
Therapeutic
vs. Reproductive Cloning:
What advantage accrues in cloning humans? Lots of us would like to have copies of ourselves in our children or even found immortal cell lines. Until now, it hasn’t been possible to make exact copy of oneself. We’ve had to be content to contribute approximately half of the genetic material to our children and marveling at similarities and differences among them. Alas, our kids turn out to be some hybrid of mother and father. But imagine being able to make an identical twin growing up in the next generation. It may seem some of us are more “successful” than others and we may naturally want a clone of a successful businessman, scientist, basketball player or movie star more than that of a homeless person or drug addict.
Once the technology develops you could consider that it might be a novelty for childless couples or the wealthy or nobility who would want to pass down their assets to children. How better to accomplish this than with exact clones? This is the issue of reproductive cloning, something likely to be useful for barren couples, older persons who wish to have offspring, homosexual couples, rich single persons, parents grieving over the loss of one child but who might have some preserved genetic material from the departed, and the like. Perhaps if you have some terrible disease or have a child with failed kidneys, diabetes or a tumor, you might think of creating a genetic identical twin to provide bone marrow or an organ transplant. We’ve already seen instances of families having children solely for the purpose of providing organs or bone marrow for another sick child. There is so much hype in the media on this subject and rational consideration isn’t aided by the characters who appear on TV, so-called “Raelians” who maintain that mankind was created by space aliens with DNA technology and their" bishop"Dr Brigitte Boisselier, physicist Richard Seed and reproductive specialists waiting in the wings to create human clones even before it can be determined that this would not increase disease, accelerate aging, before anyone can determine such activity is safe and salubrious. The Raelians claim to have made human clones already has fallen off of our radar screen because they haven't been able to support their claims. That didn't stop them from being interviewed by all the media.
Are clones, identical twins in other words, truly identical? The answer is no, as every mother of identical twins can tell you. Experience tells us that identical twins, and cloned animals who have exactly the same genes, may be physically and temperamentally different. Cohorts of genetically identical cloned animals will establish a dominance hierarchy. Different members of the caste may not react the same to the same stimulus. Some are cuddly, some aloof, some go out of their way to explore their environment while others prefer relative safety. How is this possible? Biological diversity is not dictated only by genotype. For one thing we all have two copies of all of our genes, one from mom, the other from dad. On the X-chromosome of which every lady has two copies only one copy typically is expressed. The gene that derives from one's father (termed an allele) is always expressed, transcribed to a greater or lesser extent than its fellow allele on the second copy of the chromosome. Genetic expression of each of our two gene copies varies from animal to animal. We have little knowledge about the determinants of gene expression, so that in genetically identical individuals it is possible to express mother's or father's individual gene to a greater or lesser extent if at all. Other physical characters are determined after genetic expression such as the marbling of a tabby cat's coat. Tabby twins lack identical markings because marbling happens randomly after genetic translation much as it occurs in a cake. There are countless explanations for non-identical clones. We know little of the effect of uterine environment, placentation, exposure to hormones and other chemicals in the uterus to say nothing of experience after birth.
Anyone who's had exposure to lots of identical twins will tell you that identical twins are far from identical in appearance or behavioral characteristics. I've seen instances where one twin had a beautiful complexion, the other a huge port-wine purple facial nevus (so-called Sturge-Weber syndrome), one 70 year old with Alzheimer disease, the other without though both lived in almost identical environments. Identical twins are frequently discordant for various diseases thought to have a strong genetic predisposition, MS, Schizophrenia, bipolar disease and so forth. So identical genes don't produce identical offspring, not by a longshot.
Reproductive cloning is different from therapeutic cloning, the use of this technology not for people to make identical replicas, but to raise cells for some purpose to make stem cells or for other forms of transplantation. Cloning would allow the production of spare parts and cells of all description. Have diabetes? Wouldn’t it be wonderful to be able to implant pancreatic islet cells that are a perfect genetic match? Suddenly the issue of rejection is eliminated. And for Parkinson disease cells could be implanted in the brain again without worry about rejection. Some day it might be possible to replace lost cortical neurons in persons who’ve had a stroke, or to replace spinal cord neurons in persons with a spinal trans-section, to replace myelin in multiple sclerosis. Blood diseases ranging from malignancies to aplastic anemias could be handled with bone marrow products. Graft versus host reactions and rejection would be a thing of the past. Some time in the distant future the technology for forming whole organs first livers, or bones then highly evolved structures kidneys, and even hearts perhaps would develop. Imagine being able to order up a living heart for transplant for the 5 million or so Americans who have heart failure. That is a dream for the distant future but implanting myocytes heart or peripheral muscle cells for cardiac or neuromuscular disease is a reasonable prospect.
The most promising means of doing so would be cloning. It is not necessary to create a whole new organism. A child with severe juvenile diabetes could benefit greatly from a transplant of pancreatic islet cells that produce insulin. The problem is that islet cells from a non-identical donor are often rejected. You take a sample of the diabetic child’s cells, say a scraping from the mouth. Under a microscope you remove the nucleus, or, if the cell is small enough, take the whole cell itself and implant that into an egg cell (ovum) from which the genetic material has been extracted, also under the microscope, with a tiny pipette. In an ovum the DNA conveniently congregates close to the edge in a “polar body” and so is easily removed and discarded. This method is known as somatic cell nuclear transfer (SCNT)
Technically not all of the DNA resides in the cell nucleus. Some of it is in the energy handling organelles called mitochondria. When you exchange the ovum’s DNA for that of a new cell nucleus you still leave the mitochondrial DNA of the ovum, in other words the original maker of the egg cell. Mitochondrial DNA could conceivably turn out to affect something important, be an antigenic determinant in a transplant or disproportionately affect energy intensive tissues, namely muscle and brain.
All that is left is to stimulate the ovum, now in essence a diploid zygote, to divide using certain chemical or electric signals. The dividing “zygote” will turn into a ball of cells, a blastocyst in a few days. At this stage it is not a formed embryo with recognizable body parts but there are cells inside this ball, the inner cell mass, that have the capability of growing into stem cells of various types. Exposed to other sets of chemical signals, these are made to differentiate into mesodermal, blood forming hematopoetic cells, or muscle cells, ectodermal cells such as skin and neurons and neuroglial cells, etc. What these pluripotent cells eventually differentiate into has been found to be determined strictly by the kinds of chemical environment the cells are in. Embryos progress from undifferentiated pluripotent cell lines to more differentiated, committed specialized cells, from a ball of cells that are capable of giving rise to any cell type, a neuron, myocyte, white blood cell, hepatocyte, anything to, over the generations of cell reproduction, one cell type from which point it is very difficult to turn back. Over hundreds of reproductions, the progeny of different groups of cells become more committed. This occurs because of the cell’s chemical environment.
Commitment is the outcome of signals, in some cases there is a gradient of chemical concentrations that determines what a tissue will be. It is a gradient of chemical concentrations that differentiates the entire head to tail axis of an animal. Finding the precise chemical combination that determines embryonic differentiation and using this information is no small task. Eventually, it should be possible to make pancreatic islet cells which are genetically identical with the needy diabetic recipient, heart muscle cells to help the patient with heart failure which occurs after a heart attack, neurons and neuron supporting cells (glia) for patient with all manner of neurological diseases ranging from Parkinson’s disease to stroke and multiple sclerosis. In other words the therapeutic possibilities are enormous.
A much simpler approach is to let the cloned embryo develop to the stage of fairly advanced differentiation and then to harvest certain cell types once this specialization is declared. This would present less technical difficulty because research as to the precise nature of chemical differentiation determining signals and the application of this information would be unnecessary. For instance at the four to five weeks the embryo could be far enough along to harvest nascent cardiac cells. One would have to create an environment nurturing embryonic growth whether that would be a human womb or a simulated environment. Whole cell lines have been extracted in this way as stem cells of various types, neurons and blood tissue cells for instance. The problem is that these pre-existing stem cell lines are not genetically identical to any prospective recipient and so stand the chance of being rejected.
Disorders that involve loss of simple cells rather than whole organs would be prime candidates for the product of therapeutic cloning. I mention diabetes since all that would be needed would be an amorphous viable pocket of pancreatic islet cells. Even so, curing juvenile diabetes, a disorder resulting from the destruction of islet cells, would not be trivial. One would need a mechanism to control reproduction among transplanted pancreatic islet cells. Also you need to be able to implant just the right amount, not too few or too many. Some negative feedback mechanism that controls the output of pancreatic islet cells in all of us would give a lot of leeway in errors in quantity of cells needed for transplantation. For Parkinson’s disease, there is similarly some room for error. Parkinson’s results from a deficit in dopamine producing neurons in the midbrain. Transplantation of even genetically identical cells into a situation ensuring the survival of the transplant is not a trivial matter and we still have the problem of determining the precise “dosage” of transplanted cells, since presumably the feedback mechanisms aren’t nearly so precise in this instance. Where there is serious heart disease it would be wonderful to be able to implant heart muscle cells to help with the work of muscle contraction. That could be helpful in other conditions involving muscle cells, certain injuries or neuromuscular diseases. Disorders of all kinds that result in the destruction of certain types of cells for example liver cells in hepatitis might be treated. Cloned cells could be life-saving in certain malignancies and autoimmune disorders where treatment is often aimed at wiping out the bone marrow that produces blood cells and in any of a slew of disorders that affect the blood cell production, aplastic anemias, cytopenias and so forth. If we had some reliable means of wiping out then replacing bone marrow or some of the more specialized elements within bone marrow with a genetically identical transplant, that could lead to a cure for some diseases such as psoriasis, rheumatoid arthritis, multiple sclerosis and so forth and hematological malignancies such as leukemias. All of this is very exciting; the applicability is much more complicated and expensive than it appears on the basis of armchair speculation yet almost limitless. The Geron Corporation generously made a deal with the University of Wisconsin in which this small biotechnology company retains rights to develop embryonic stem cells from nerve, muscle and pancreatic stem cells. This is far too much for this small company to handle!
On the other hand the most obvious method for having available whole organ transplants is making an identical whole clone or virtual whole human whose organs can be harvested. This could be done without fully activating the brain perhaps taking advantage of some lower brain or brainstem function but avoiding cortical activation and experience that defines a full human. At some time in the very distant future, it may well become possible to serve up single organs on an as needed basis with just in time delivery for the purposes of transplantation. This is the kind of vision that brings to mind armies of cloned zombies waiting to have their organs harvested. A study recently published in the New England Journal of Medicine found that transplanted heart found a surprising degree of infiltration of the heart cells of the recipient. It may turn out that transplanted organs have many recipient cells in any case even without having to clone the organ.
I’m sure in reading all of this all kinds of ethical considerations have entered your mind. The topic of cloning is best analyzed and objections raised one step at a time. Each specific use of clones raises ethical concerns. The easiest application to accept is the idea of producing genetically identical or nearly identical crops and animals. Successful breeds can be more successful, as we take advantage of increased growth rates, disease resistance and other characteristics such as improved yield, for example milk or meat production. On the other side of this is human cloning, conveniently broken into reproductive cloning and therapeutic cloning.
Esthetically the whole idea of mass production of identical biological products rubs me the wrong way. This isn’t just a feeling. There’s a logical explanation which I’ll try to convey here. You may well come up with the perfect cow for a Pennsylvania town, which produces the most milk in a particular environment. I’d suppose this cow to be more disease resistant. Obviously there would be a total absence of variation. What if the environment shifts a little? Suppose the weather is drier or a colder or there’s a new disease. Then all our cows would be identically vulnerable. A single disease of environmental change could wipe out the entire herd. Genetic variation is an asset where a group of organisms is exposed to an environmental shift or a disease. With genetic variation the herd might be exposed to a disease and some of the animals would die, but others, usually the majority, would survive. Moreover offspring of the survivors would then be much less vulnerable to the perturbation. Here we’ve hit upon something very basic.
Practically the most universal fact in biology is the absence of exact reproduction! Even cells that simply split via mitosis, don’t produce exact copies of themselves. The best example is in the embryo whose cells reproduce via fission yet over many generations, differentiate into all the tissues necessary to comprise a whole organism. A bacterium that splits into two when it reproduces obviously makes non-identical offspring. Some bacterial DNA mutates, in other instances there is an exchange of DNA using plasmids or other methods of exchange, so much that in a single infection with say tuberculosis, or Pneumococcus there sufficient variation some of the offending bacteria will be more or less resistant to antibiotic. It’s because of that variation even among bacteria depending upon fission for reproduction, that some of them survive doctor’s best efforts to use a lethal combination of antibiotics. The AIDS virus like other viruses, depends on the cellular machinery of its host to reproduce, but still in all does not reproduce itself with exact fidelity. It is just this discrepancy in exact reproduction, that allows the virus to survive the immune surveillance systems of the host. So it is with the influenza virus which alters itself so frequently a new vaccine in necessary every year.
Single and multi-celled plants and animals have devised a nearly universal system, sexual reproduction, whose main purpose seems to be fostering diversity. Sexual reproduction is complex. It is necessary to have two copies of most genes and to have evolved a second type of cell division, meiosis, then a mechanism for mixing genetic qualities of each parent during meiosis, crossing over, which is used to randomly shuffle genes so as to make the products of such mating as diverse as possible. Why go to all that trouble? Because diversity of product allows nearly continuous variation and adaptation. Virtually every species, plant or animal on this planet reproduces sexually to remain diverse.
This is a commentary on cloning. Obviously there were many species who made identical copies of themselves. They did not survive. Now there are some “flukes” a few species of plants or animals that have haploid gene counts or reproduce via parthenogenesis. What we find even in those few instances is that their method or reproduction either alternates with more conventional sexual reproduction in other forms during a life cycle, or still provides some intrinsic method for gene shuffling so as to avoid putting out identical gene products. Some of those species are insects which reproduce only a certain subform of the species parthenogenetically or only under very limited circumstances. There are some animal groups that create whole new colonies by budding.
Non-exact reproduction is so universal in biology that we may safely conclude cloning or the faithful reproduction of exact copies of any organism is maladaptive. Cloning is Anti-Biological. Just in case any of your kids wants to know why we have sex, that is why - to promote variation, the raw material for adaptation. And if your children ask why we die, the answer is the same. (We die to promote diversity. Long life is maladaptive for a species or type because long livers consume resources, the carrying capacity of the environment. Long livers can be helpful to subsequent generations if they help train, pass down wisdom and thus promote survival of younger generations - hence grandparents.) I assume that there were many organisms of the past who “experimented” with either long life or eternal life. None of these species survived either, just as the ones who made exact copies of themselves are no longer around. As you increase generation time of an organism, your bet that that individual will be able to handle the vicissitudes of his environment increases. If he dies before reproducing and he is one of only a handful (because of excessively long life) of nearly identical genetic products who also die of the same cause, your species is history. Increased longevity decreases possible variation and adaptation to environmental change and resistance to disease. If one male or female produces too many offspring that will decrease variation that is the raw material for adaptation. Those organisms with the shortest generation time, adapt to change that much faster. That’s why bacteria and insects adapt so quickly to the “challenges” that humans lay before them in the form of antibiotics and insecticides. They can adapt faster than our pharmaceutical houses and chemical companies can think! What does this mean? The big picture is that each and every one of us is a unique experiment in nature. We are more or less successful (“fit”) not just in a number of offspring but in founding a resistant genetic line that will compete over more generations. Some of us may not actually reproduce but devote our talents to helping close relatives who share many of our genes. (Humans live far beyond reproductive age for two reasons, artificial effects of advanced society and medical knowledge, and survival advantages of being able to hand down learned cultural as well as a genetic endowment.)
There is no such thing
as an organism, plant, animal, protozoan, bacterial, viral etc that replicates
exactly in nature. Apparently none has ever survived! Thus every single “type”
or species, makes a pact with the devil. It can reproduce itself, but never
with exact fidelity, nor can any one specimen live too long, else it will
surely die.
When it came to some of the worst scourges in history, like bubonic plague, one third of a city’s populace could easily be lost in a single epidemic attack. Part of the remainder was conferred immunity, and their offspring, children of survivors, inherited genetic characteristics that gave them increased resistance to the disease. A relationship between plagues and people is now very well described but only recently appreciated. Repeated attacks on a populace by the same organism over time, decreases lethality. It’s why bubonic plague is really not much of a problem anymore and the reason humankind has such a close relationship with Herpes viruses. The beauty of sexual reproduction (besides the fact that it is fun) is that it provides some means of shuffling genotypes enhancing variation, ensuring that some members of a species will resist environmental change and disease. Not only that, it allows other members of a cohort to pre-adapt to different environments, for example hairier, fatter members of a species might radiate into colder climates increasing the adaptability (success) of a species. Their less hairy cousins are confined to warm surroundings and consume all of their food sources. Cloning does the opposite of sexual reproduction. It amputates variation. So you think you have a perfect product and you want to reproduce this product by design ad infinitum. Think again. Your product isn’t the best under even slightly different circumstances. Agro-industrial cloning of animals and plants isn’t going to be a panacea. Predictably it will have negative effects, not the least of which is increasing crop and animal vulnerabilities, diminishing variety, the spice of life.
When it comes to reproductive cloning of humans we run into many more practical problems than are dreamed of in our philosophy. One of the biggest difficulties is that we don’t appear to know nearly as much about genes as we recently thought we did. In recent years with the Genome Project and through other research it’s become apparent that there are many details about genetic reproduction and DNA that may affect the process and which we did not dream of before. For example we now know there is a host of human diseases caused by simple repeats of three nucleotides, (trinucleotide repeats). Recall that it takes three DNA nucleotides to specify a single amino acid. So you have a disease such as Huntington’s chorea which looks like a dominant genetic trait but it really isn’t one thing. The more of these repeats you have, essentially the more serious is the disease. Each trinucleotide repeat makes another copy in the chain of amino acid constituting the initial protein, glutamate, so you have a polyglutamate residue in the protein. It turns out there are many genetic diseases that have the same mechanism. We don’t know enough about proteins and other factors controlling gene expression. This is the hallmark of cell differentiation the signature that determines whether a certain cell will be a hepatocyte, a glial cell, a myocyte and so on, despite the fact that all the cells in our body have identical genes. We don’t know enough about the factors controlling DNA replication and cell division, what turns cell reproduction on and off. Most importantly, our knowledge about aging cell divisions, what determines when a cell will stop dividing, is limited. Recent research as far as aging clones of cells has focused on the telomere which is a repeating code of DNA at the end of chromosomes. As the chromosome replicates itself, the telomere on its end is shortened unless exposed to telomerase enzyme which maintains its length. This is one mechanism behind aging of cell lines. After a given number of replications, a cell line will cease to divide. They can replicate, but only for so many generations. Some animals like rotifers always make an exact number of cells. Neurons had always been considered the paragon of finite cell division. Most simply stop mitosing. But no one knows exactly why. Were these cells to divide endlessly, they would constitute an immortal line of reproduction and might form a group of cancer cells ceaselessly dividing. But given the wisdom of biology and the reproductive process, there are telomeres and other constraints on cell division that scientists have yet to elucidate. Now suppose you take the DNA from a mature animal cell and insert that DNA into an ovum, you have no idea of how many divisions that DNA will be permitted to have. Perhaps there are chromosomes within that nucleus which have varying lengths of Telomeres. Perhaps there is more or less telomerase in the cell. Will there be cell lines say in skin, that will prematurely stop dividing thus accelerating the aging in that animal (progeria)? Or in other cases will other tissues continue to replace their cells interminably causing cancers?
There are other problems that we cannot even conjecture about given out level of ignorance. There is the danger of taking ordinary somatic cells and trying to convert the chromosomes in that nucleus to make a model of an entire person. Something may well have happened to the chromosomes in that all important nucleus to be implanted in the egg, such as sun or radioactivity exposure causing mutation. Even more important, scientists have only recently described two processes, reprogramming and imprinting. Reprogramming describes the process that must occur before the DNA in transplanted nuclei can be utilized to make a totally new embryo. Mostly genetic material, previously repressed, needs to be freed to express itself, the products of genes will now need to be translated into proteins. The mature nuclear genetic material will need to be rejuvenated in order to bring about normal development. There is some concern that simply transplanting the nucleus of a mature cell will not bring this process to life.
A second concern is the newly elucidated process of genomic imprinting. Little did we know that amongst the two copies of each gene were in some cases versions of genes encoded to be expressed which come from the mother while there are others encoded to be expressed from the father’s genome. Some of this is communicated via special chemical changes along the DNA code, mostly via methylation. Under certain conditions some chromosomal material is aberrantly expressed from the wrong parent resulting in rare disorders so called Angelman’s and Prader-Willi syndromes involving chromosome 15. The mechanism of imprinting has survived because under certain circumstances the “interests” of the female and male parent are not the same. For example, from the male’s standpoint, the offspring ought to be as large as possible so as to maximize the investment of the mother to the detriment of the offspring of other males who might impregnate her over which the larger offspring might dominate. In other words in a situation where women aren’t monogamous the offspring of the different males who impregnate her compete, are more or less fit. On the other hand the mother’s interests are to produce a smaller child as long as there is no disadvantage to survival, then perhaps be impregnated later by another male. These genetic mechanisms, just beginning to be appreciated and not controlled via current methodologies, could affect the human offspring in cloning experiments. Extensive work in animals and later in primates is necessary to measure the effects of these as well as what is likely to be a large number of unknown genetic novel mechanisms.
Having mapped the genome of several different organisms it is newly apparent that just as the genotype does not determine the cell type in an individual organism- the neuron is different from the hepatocyte and so on even though they have exactly the same genes-identical genes also fail to produce identical offspring. You can have identical genes but not all of them are expressed. Identical twin humans may have a set of genes that increases the risk for schizophrenia or bipolar disease but a good portion of the time only one of them has the disease. The gene for this disorder and other characteristics may not be expressed. Factors controlling the expression of genes are termed epigenetic. Epigenetics is at this time a hotbed of research. Just one fertile area of epigenetics has to do with transposons or jumping genes, bits of DNA that flit about the genome being ligated at various loci. Transposons partially control gene expression. One piece of recent research has related maternal diet with elemental genetic risks for obesity and cancer in offspring with identical genes. Genetics has entered a golden age now precisely because we are far more ignorant of genetic processes. We have RNA molecules acting as enzymes and undoubtedly there are problems that scientists haven't yet dreamt of. Genetics is a prime example of the adage that the truly wise appreciate their own ignorance.
Think about how irresponsible it would be to create humans with these and other grave problems. It’s precisely because of our ignorance of the perhaps the majority of these regulatory processes that it is very premature to contemplate any kind of human cloning.
We know so little, that only a very small proportion of embryos survive any attempt at cloning. It is extremely rare that an animal is born of one of these mammalian clones. There is a high rate of disease in the offspring. No one is sure about why this is. The answer may have a profound effect on the offspring, perhaps causing premature aging. For the sheep that would not be a disaster but for a human clone we may have what I call an ethical deal breaker- a disaster. Trying to produce human clones is premature until we have reasonable knowledge of the process, and as with everything, we ought not to let our natural hubris get in the way. We know far less than we think we do. For this reason the National Academy of Sciences has recommended a moratorium on human reproductive cloning with the further recommendation that this subject be revisited in five years. Personally, I have grave reservations about animal and plant clones as well. But I don’t think there ought to be a ban. Negative consequences will have to be experienced for themselves.
The Parthenon on the Acropolis is a great temple built by the Athenians in honor of their sponsor Athena. Zeus had impregnated Metis, goddess of wisdom and fearful she would give birth to a son who would later challenge him, Zeus ate her whole. Athena budded or was hacked (depending on which version you read) from the forehead of Zeus, a maiden fully formed in the raiment of war. Athena was goddess of wisdom, weaving and war, supporter of Odysseus and a lifelong virgin hence Parthenon from parthenos for virgin. Certain female animals reproduce without male fertilization, via parthenogenesis. Bees and ants give birth to haploid infertile female workers, while the queen reproduces sexually, mixing gametes. Some vertebrates, fish and reptiles, may reproduce parthenogenetically and other animals may do so over part of their lifecycle. Typically they may resort to sexual reproduction under more adverse challenging circumstances or seasonally. Parthenogenesis works under certain conditions where genetically identical offspring suffice such as in the case of specialist workers or where there is little environmental challenge but again, for the most part, sexual reproduction, which maximizes variation, has for the most part, proven to be the most adaptive form of animal and plant reproduction.
As it turns out, parthenogenesis has played a pivotal role in the fast moving world of cloning experiments. Research entrepreneurs are in a race to produce “parthenotes”, the products of usually female immaculate conception. They figure they can sideswipe arguments of the anti-abortionists because human parthenotes aren’t likely to be able to mature into whole persons. That being the case one can’t make the argument that doing away with them or harvesting tissues is immoral, because parthenotes don’t have the potential to become whole human beings, so you really can’t call a parthenote embryo a child. The jury is still very much out as to whether the Catholic Church or other groups will buy this.
In parthenogenesis you can have either a haploid or a diploid product and may even make two copies of a male sperm start to form an embryo. Sometimes this latter process happens naturally. Some hydatidiform moles seem to be diploid products of male sperm. Two sperms may fertilize an egg then kick out the maternal DNA! They act like placentas (trophoblasts) and don’t mature into embryos, but can even become malignant and spread about the body of a pregnant woman. Humans have 46 chromosomes, twenty two pairs of autosomes plus a pair of sex chromosomes. A haploid cell would contain just 23 chromosomes. The only haploid cells in humans are eggs and sperm, the product of meiosis. You could take an ordinary egg and if by some means either with currents of electricity by means of a special chemical bath, if you could get the egg to divide, it might start to produce an embryo or the earliest stage of division, a multi-celled blastocyst. The more likely scenario which has been used, is to take an egg from a slightly earlier stage of cell division while it is still in the diploid state (46 choromosomes), before the final stage of meiosis that produces a haploid egg and get that egg to divide. This has been done with some monkey ova. Perhaps you could coax this ball of cells with further cell divisions to keep dividing long enough to turn out stem cells of various types, suitable for further growth to eventually transplant. In an ideal scenario you could take a woman with a bad heart, still of childbearing age, producing eggs and clone heart cells from a parthenogenetic embryo to transplant.
Of course the most efficient natural means of making an egg cell start to divide is to make it into a diploid zygote by having the egg fertilized by a sperm. The other thing you could do is introduce the genetic material from another haploid cell into the egg and that would be tantamount to fertilization. The product would be diploid but the source of the genetic material would again be the mother. Then the resulting diploid parthenogenetic zygote could be made to divide. The interesting thing with this method is that if you figure it out, though both sources of the 23 chromosome haploid genetic material come from the mother, the diploid parthenote would not quite be identical with its “mother”. Some pieces of her chromosomes would be left out while others would be reduplicated.
Or, you could take two copies of the haploid genetic material from sperm implant them in the egg and produce a similar diploid parthenote. This is like the hydatidiform mole scenario above. Since you still need the egg which can only come from a woman, even though you use none of her genetic material, this can’t strictly be considered parthenogenesis but is close enough for our purposes here. Actually, some DNA would still come from the maker of the egg because a tiny amount of DNA is outside the nucleus in the mitochondria which are part of the egg.
Why won’t diploid parthenotes which come from a male only or from a female only not ever be able to embryologically mature to a fetus or baby? Actually we don’t know that parthogenesis is incapable of producing a viable embryo but one theory holds that some genes are “imprinted” with markers of their male or female parent by methods described above. And again, there may well be other mechanisms that induce properly united gametes in zygotes produced by natural means (sex) to begin to divide and form natural embryos then fetuses.
Cloning is applied embryology. There is the dichotomy of cloning for therapeutic purposes and reproductive cloning. The Therapeutic cloners are trying to apply techniques from early embryology. They determine the genetic makeup of an ovum usually in a diploid state, then get it to divide at least into the blastocyst stage, later try to harvest immature stem cells from an inner cell mass. At some time in the distant future it may be possible to create whole organs from stem cells but that is not the goal for the immediate foreseeable future. In reproductive cloning the goal is again to determine the genetic makeup of an embryo but ultimately experimenters want to create a whole organism or even a person of a predetermined genotype.
The prospective egg donor must be subjected to hormones that foster the maturation of multiple ova to a certain stage for harvesting, then a laparoscopic surgical procedure for the removal of eggs. Hormone use probably carries the greatest risk as there may be unknown long term effects and pro-coagulant effects with rare complications even stroke, thrombophlebitis or pulmonary emboli. However, there is some clinical experience harvesting human ova for previous research endeavors. These are procedures with certain known risks about which she would have to be made fully aware. The egg donor would have to give informed consent and be duly compensated for her services. In most cases her genetic material would not be used but as with all medical procedures maintenance of privacy would be expected. These issues would be considered similar to other routine medical and surgical procedures. Surgical procedures for obtaining genetic material are by comparison rather trivial but privacy would have to be maintained. These matters are rather routine in the clinical practice of medicine.
Other researchers, some in working in China and Korea for example, have figured out ways to bypass obtaining human ova. Ova can be harvested from rabbits or other mammals then a chimera formed by removing the rabbit ova genetic material and replacing that with a diploid set of human genes. The ovum will then have rabbit mitochondria and protoplasm and a human cell nucleus. Will the embryo thus formed be fully human? Just suppose all of the egg cytoplasm could be removed and replaced with human cell cytoplasm. Then we would have the rabbit cell membrane and its human contents. Multiply all of these considerations by all possible animal and plant permutations and you could "conceive" monster chimeras of all descriptions as in HG Wells' Island of Dr. Moreau. Such nightmarish visions drive popular misapprehensions of cloning.
Cloning is bound to be very expensive and complex. In the scenario presented above we are likely to see transplanted cells first probably insulin producing cells for juvenile diabetes, Dopamine secreting neurons for Parkinson disease, myocytes for heart and muscle disease and neuron transplants for strokes and spinal cord disease, perhaps in that order. Let’s take the simplest scenario first, insulin producing islet cells. Raising human clones of more than about 6 or so cells has proven difficult at this particular stage. For one reason or other very few diploid ova cells survive in specially devised growth media through even a few cell divisions. But it’s going to take a long time first to separate pluripotential cells out of an inner cell mass of other part of a growing clone, then to create just the proper chemical environment to signal these cells to differentiate in exactly the direction desired. Once such islet or muscle or other cells are produced, they would be good only for the specific individual requiring the transplant. This process, no matter how routine, is akin to custom fitting and is likely to be prohibitively expensive for the vast majority of diabetics or Parkinsonians or heart patients. However this process may not be as prohibitive as it now seems. By some estimates it may be sufficient to develop some 200-300 clones. This small number of clones might provide a close enough genetic match for most recipients.
One may extend the same technology to organ production. Perhaps hepatocytes or liver cells might be the most self organizing. Here we run into different problems. No longer is it adequate to grow small colonies of cells in a growth medium. In order to create organs an infrastructure of blood vessels, and scaffolding has to be developed. It may be possible in many instances merely to replace clusters of cells in a failing organ, counting on retained organization within the organ to aid in regeneration using fresh cells. That would probably be the initial strategy.
But other simpler strategies are likely to make an end run out of cloning and cure the disease. For juvenile diabetes scientists are likely to devise some membrane to isolate bags of transplanted cells from the immune system and which would provide some growth of blood vessels or at least a chemical environment for their sustenance. Or the specific membrane factors leading to early rejection may be better defined so as to eliminate the need for identical gene cloning. As for neurons in stroke, simpler preventive strategies are much more likely to prove useful, such as controlling blood pressure and cholesterol levels, smoking cessation anti-platelet and anti-clotting drugs and neuro-protection. For Parkinson’s disease, ALS, Multiple sclerosis it seems smarter to pursue the classical medical approach, trying to define the process by which neurons, axons, and myelin are lost and then attempting to manipulate and slow this process. Research into chemical factors that repair damaged cells and tissues is likely to be much more productive. Investing in therapeutic cloning is a bet that something more efficient won’t come along. Intrinsically from the ethical perspective, other strategies might be more promising but there is very little down side to pursuing such research as long as entrepreneurs and universities and government agencies are favorably inclined.
Probably the most important criticism is that there are far simpler means for creating replacement cells! In persons with heart failure why not remove a few functioning heart cells and find a way to make a few cells reproduce and then harvest a whole lot of them for transplant. That would avoid cloning altogether. Also if successful human transplants would involve between 200 to 300 genetic types, why not maintain a library of 200-300 different human myocytes perhaps derived originally from cadavers to later transplant? And the same goes for hematopoetic or bone marrow cells for cancer and autoimmune disease, islet cells for diabetes etc. Why bother with clones at all? In other words there seems not to be a need to go back anywhere near the level of the embryo in order to produce large numbers of any given cell type. Thus we see that although cloning is very sexy, there are all kinds of other possibilities for making an end run around therapeutic cloning especially involving embryos. To me it appears embryonic cloning makes relatively simple problems much more complex.
Still the prospect of therapeutic cloning is interesting because it is applied embryology. Should research continue, and I hope it does, we are likely to learn a great deal more about genetics and the mechanisms of embryologic maturation and production of specialized cells and organs in humans and animals. Some of the questions this research might answer: What stimulates a cell to divide, to commit or transform into a certain type, to organize into tissues, how does development translate into anatomy? What triggers a cell to start or to stop dividing? What are the concomitants of aging and cell division, what controls the expression of genes and hosts of other questions basic to our understanding of life.
My biggest point in all these ruminations is trying to stick with the basics. Cloning is anti-biological because organisms do not replicate exactly and cloning violates this basic principle. Now we have politicians trying to limit scientific research. Science is knowledge. When President Bush bowing to his constituency and popular opinion purportedly showing a 4/5 bias against cloning research proposes legislation to outlaw the advance of scientific knowledge that gets my back up. You can't limit scientific exploration. If Americans fail to do research someone else will. Politicians should never be allowed to limit the efflorescence of knowledge. Let scientists do their research. It's just that knowledge needs to be applied to beneficial ends. A lot of embryonic stem cell research is destined to die in the marketplace of ideas, as much of it appears to be an inefficient means to reach therapeutic goals.
Reproductive cloning is another matter. As far as agricultural cloning of animals and plants, I would guess that we are bound to run into a lot of trouble connected with the elimination of diversity as I have described above. Still cloning is likely to yield some commercial successes along with a lot of headaches in the foreseeable future.
My main objection to reproductive cloning of humans is humility. It’s clear to me that although we think we know a lot about genetics and reproduction, there is a lot we don’t know, there are a lot of principles discovered only in the last few years and some mechanisms that apply that we know very little about. This lack of knowledge translates into research that may be dangerous to humans. In all other fields of scientific research we assiduously avoid research dangerous to humans. Reproductive cloning should not be attempted at this time. This is in accordance with a recent opinion of experts from the National Academy of Sciences.
We are still uncertain about whether human reproductive cloning may someday be permissible under certain limited circumstances. Taking a logical point of view we should someday, as data accumulates, first decide whether it is safe to pursue cloning research in humans at all. We have not reached that stage yet. At that point, we will have to decide as a society whether cloning would be permissible under certain limited circumstances. What about in the case of a childless couple? Is creating a clone of one party a reasonable solution or could some other solution be found such as in vitro fertilization? What about an elderly, remarried, homosexual couples, rich folks who want a genetically identical heir, then how about making Pamela Anderson or Magic Johnson or Richard Feynman clones, cadres of space marines, or football players or physics geniuses. Not any of this sounds palatable to me at all but I have no doubt that one day we will easily be able to do it all. As a society we’ll have to decide whether any of it is worthwhile endeavor.
Should be pass laws now that have to do either with therapeutic or reproductive cloning? On the therapeutic side I can’t think of a scenario in this research that would be dangerous to our society. We are likely to learn a great deal from this research. As a neurologist I harbor high hopes for cloning of certain cells, Dopamine producing cells, myelin making cells, cells to replace neurons etc but it seems there will be other more efficient means or replacing damaged tissue or preventing its destruction. So if cloning proves to be useless or non-profitable a research dead end, then it will stop on its own. I’ve little use for zealots who seek to curtail the advance of scientific knowledge merely to make a point about abortion. The kind of therapeutic cloning research described here has nothing at all to do with the issue of abortion.
In most cases it's best to let market forces determine the direction of future research, not the opinion of some governmental or other agency. Certain avenues of research may seem to have more utility. Money and talent is likely to go toward these efforts. At a certain point some areas of research may prove to be fruitless, and efforts will shift in another direction. Occasionally it may be apparent that people are giving up prematurely in possibly fertile areas of research because of perceived lack of short term gain. At that point, government agencies such as the NIH might intervene. Entrepreneurial efforts prove inadequate in certain limited situations because of emphasis on short term profit, but in general, government should not get into the business if it can be avoided at all, of regulating or limiting private research, only harmful application of such knowledge.
On the other side are the reproductive cloning extremists especially such groups as the Raelians and plain old reproductive clinics who want to be the first kids on the block producing human clones. It may be necessary to pass certain laws to curtail the reproductive cloning of humans. Thinking about some of the basic applications of human reproductive cloning it might be reasonable to ban all types or reproductive cloning totally. Reproductive human cloning will inevitably be done somewhere anyway. Even so we haven’t lost much.
Making clones is not immoral, but it is anti-biological in the deepest sense. Biological entities reproduce, but never replicate exactly. Identical twins are far from identical so some variation will remain despite anyone's best efforts. Each miniscule difference between every organism, every individual cell and their offspring is tremendously important. Cloning is a paradox. Struggling for immortality, we figure as long as we must die why not reproduce after our own kind - forever. But genetic replication is far different from copying the whole person. Besides no cell line is immortal. Exact genetic replication not only is unnatural, it is a path to certain death. Our intellect is dwarfed by the wisdom in the natural world. We’re not as smart as we think.
I’ve had so many questions from patients, particularly people with MS, about the prospect of replacing myelin or neurons with cloned cells. People get the impression from the media that this therapy is right around the corner. I’ve had to tell them that I thought it might be something for the distant future and that anyway, it seemed to me, there were more promising avenues of research. Very recently cloning has been a lot in the news. One of the reasons is because at Advanced Cell Technologies.
See Cibelli, JB, Lanza RP, West MD, “The First Human Cloned Embryo” Scientific American January 2002 pp 44-51. Scientific American has updates at www.sciam.com
For the National Academy of Sciences Position on Cloning, especially reproductive cloning, they are the best source. This piece I think echoes their opinions on reproductive cloning see www.nap.edu/books/0309076374/html/.
In order to better understand cloning including some related topics especially parthenogenesis I had to open up again some basic biology texts. One of the most insightful and justly famous biologists is E.O. Wilson. I learned a lot about the biological effects of mating close relatives especially incest from his 1999 book, Consilience and also his tour de force, Sociobiology. Consilience explains the effect of lethal recessive genes which is magnified when you mate close relatives.
Ideas about resistance to infectious diseases and antibiotics come from clinical practice. Still there are some interesting insights on how biology affects history in The Third Chimpanzee by Jared Diamond and the earlier Plagues and Peoples by William H. McNeill, both modern classics.
Cloning bears on even more far flung notions of Immortality with the prospect of creating immortal cell lines. That’s one angle I might have missed if I hadn’t been reading a novel by that name of Milan Kundera, author of The Unbearable Lightness of Being.
I believe everyone who thinks has tried to come up with an
explanation of why we have sex and why we die. Some of my overly simplistic notions are found
in Beyond Biology which is partly
broadcast on this website www.pneuro.com
Charles S. Yanofsky, M.D.