Human Cloning: What’s it all about? by Carlene Elsner, M.D.
Human Cloning: What’s it all about?
by Carlene Elsner, M.D.
The recent report from Seoul Korea on the production of a stem cell line from a cloned human blastocyst has reignited both interest and anxiety regarding the development of this technology. Images appear of “Mini-Me” from the Austin Powers’ movies or the creatures in “The Attack of the Clones”. The very suggestion of such human experimentation strikes fear in the hearts of all who remember the atrocities of the Nazi regime’s “scientific experimentation” on human subjects and desire to create the Aryan super race. Medical researchers agree that there is the potential for great benefit to humanity from the development of human cloning technology; so, what is this technology all about and what is the potential for abuse? The purpose of this article is to explore the technology and address some of these issues.
WHAT IS A CLONE?
What then is cloning? Cloning is defined as a form of asexual reproduction in which an exact genetic copy of an adult organism is reproduced. Asexual reproduction is the norm for certain simple life forms, like bacteria, yeasts, certain plants, and some snails and shrimp. More complex organisms reproduce sexually, which allows for reshuffling of the genetic material of two individuals to produce a third unique individual who is different from both parents, but who has some traits from each one. This process leads to diversity within a population. Each offspring is then different from its siblings and also from its parents.
When a complex organism receives all of its genetic material from a single parent and is genetically identical to that parent, it is called a clone. Dolly, the sheep, is the most famous example of a clone. The process by which she was produced is called reproductive cloning. She was produced by researchers in Britain and has since died prematurely. Clones have been produced in several other species like mice and calves, but in every species in which cloning has been successful in producing live offspring, there has been a high incidence of abnormalities in the offspring. These abnormalities include premature aging, “large offspring syndrome”, obesity in adult clones, and gross malformations with high fetal and neonatal death rates. Clearly, we are far from having the technology to produce a cloned human baby.
WHAT DID THE KOREANS DO?
So what did the Korean researchers do and why is it important? Young women underwent controlled ovarian hyperstimulation and egg retrieval. The researchers removed the nucleus from mature (MII) oocytes obtained at egg retrieval. (The oocyte nucleus contains half the genetic material of other body cells and is referred to as haploid.) The nucleus removed from a cumulus cell (the nutrient cells that surround the egg) was then placed within the zona pellucida of the enucleated egg and an electrical current was used to fuse the bare nucleus from the cumulus cell with the enucleated oocyte. Cumulus cells are diploid which means that they contain a complete (double) set of genetic information, so the resulting newly created zygotecontains all the genes and chromosomes necessary to form a new individual. However, all the genetic material in these embryos came from the woman stimulated rather than having half come from the female and half from the male partner as is usually the case. Therefore, these embryos produced were clones of the woman who produced the eggs. 176 mature oocytes were used to produce 30 cloned blastocysts. The blastocysts were cultured in the laboratory. From these cultured blastocysts the researchers were able to produce 1 stem cell line. These researchers did not intend to make a human being. This type of cloning is an example of therapeutic cloning.
ARE THERE DIFFERENT TYPES OF CLONING?
There are two types of cloning, reproductive and therapeutic. Both types of cloning begin in the same way, with the fusion of an adult somatic cell nucleus with the cytoplasm of an enucleated egg just as the Korean researchers did. In reproductive cloning, the cloned embryo is replaced into the uterus of a mature female of the species where it may implant and grow. There is a low success rate with this procedure, but if a liveborn offspring is produced, it is a reproductive clone, like Dolly the sheep. At present, most researchers worldwide consider this type of cloning to be unethical in the human because too little is understood about the process to make this technology safe for the intended offspring. The Ethics Committee of the American Society of Reproductive Medicine issued a report on cloning in 2000 in which it said that the “use of reproductive SCNT (cloning) by medical professionals does not meet the standards of ethical acceptability.” In therapeutic cloning, the cloned embryo is grown in the laboratory. The cells from the inner cell mass of the blastocyst when grown in tissue culture can sometimes produce a stem cell line. As with reproductive cloning, the success rate is low for the production of stem cell lines. However, if a stem cell line is produced, these cells are very primitive and totipotent which means that they have the potential to develop into any and all of the different cell types in the body. Also, the stem cell line is a perfect genetic match to the parent.
WHY ARE STEM CELLS IMPORTANT?
These two properties of stem cells, the ability to form any cell type and the fact that these cells would be a perfect genetic match to the parent, suggest huge potential for the use of stem cell therapy for the treatment or even cure of many serious medical diseases for which current treatment options are inadequate. Consider for a moment the case of a brittle juvenile diabetic who is not well controlled on insulin. This is a devastating disease that requires frequent hospitalizations and is associated with a short life expectancy. Stem cells genetically matched to this individual could be reprogrammed to make islet cells which are the cells in the pancreas that produce insulin. These islet cells could then be transferred to the sick individual where they could grow and replace the patient’s own defective islet cells. The new islet cells would then produce insulin, remove the need for external therapy, and the patient would be cured. The best part about such treatment is that the new islet cells would be an exact genetic match for the affected individual, so there would be no fear of possible rejection of the new cells as sometimes occurs in other nonautologous transplant procedures. There are a whole host of diseases that theoretically may be treatable using stem cell therapy. This is why the work of researchers like the Korean scientists is so important.
There is still a great deal of research that must be done before either reproductive or therapeutic cloning could possibly become practical for clinical use. Years of basic scientific research in multiple species will be needed to understand the complex process of reprogramming and the potential risks involved in cloning, so one should not expect to see the clinical application of any of these technologies for some time. Ongoing research will allow scientists to evaluate these technologies to determine what their real value may be, what refinements are necessary for safety and efficacy, and who may benefit from them most. Only then will it be appropriate to consider the clinical application of cloning.
The ethical debate concerning cloning continues to rage out of control. The issues being raised are mostly theoretical and far ahead of where the current technology stands. Debate is healthy and, over time, as scientific understanding of the processes involved in cloning increases and as the hysteria that arises from fear of the unknown subsides, a consensus of opinion will emerge among scientists, theologians and ethicists regarding the appropriate use of cloning technology. Then physicians will be able to decide what the role of cloning is in clinical practice. At the moment, many of those who say they oppose cloning do not fully understand what it is they say they are against.
Even some supporters of reproductive cloning may be misinformed. For instance, the Raelians, a religious sect, believe that reproductive cloning is the way to achieve immortality. This group has made unsubstantiated claims that they have already produced a human clone through their corporation, Clonaid. Most scientists believe these claims are false. But even if the claims were true, the clone would be a different individual from the parent. The genetic code is only one part of what makes us who we are. Environment plays at least as big a role in making an individual unique as does the genetic code. Those who think they can order a copy of themselves are mistaken.
On balance, the potential benefits of cloning may far outweigh the risks inherent in the technology. If a ban is placed on all scientific investigation in the field, we will never know what these benefits may be and we risk closing the door on technology that may be more important than invitro fertilization. Remember, 25 years ago when Louise Brown, the world’s first IVF baby, was born, many considered IVF to be unethical. For a time all research in human IVF was halted. If that ban had not been lifted, 1 million IVF babies born since that time would never have existed and many couples would have remained childless. We would not have available to us the most effective treatment for infertility ever devised.
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The Ethics Committee of the American Society for Reproductive Medicine. Human somatic cell nuclear transfer (cloning). Fertil. Steril., 74, 873 (2000).