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To clone or not to clone
Whether or not embryos should be cloned and then destroyed for their stem cells has been one of the hottest issues in science this year. James Sherley, a professor at MIT, says that the use of cells from cloned embryos is scientifically and ethically dubious.
MercatorNet: Professor Sherley, you have been outspoken in your opposition to therapeutic cloning. What’s wrong with destroying a human embryo, especially if this research might benefit people with terrible diseases?
James Sherley: Despite the confusion that some like to create on the questions of “are embryos human beings?” and “when does a human life begin?”, both scientists and physicians know very well that human embryos are alive and human. A human life begins when a diploid complement of human DNA is initiated to begin human development. Therefore, a life can be initiated by the fusion of sperm and egg or by the introduction of a diploid nucleus into an enucleated egg (ie, “cloning”).
Given that embryos are human beings, they have a right to self and a right to life. Exploiting their parts (ie, cells) or killing them for research is moral trespass that society should not allow. Even if the research might, and let’s be clear, might benefit others, this trespass is not justified.
MercatorNet: But can you distinguish between a human life and a human being?
Sherley: A human life is the experience of a human being until its death. It begins with a single cell that has a diploid complement of human DNA, programmed for human development.
MercatorNet: What are the scientific drawbacks of using human embryonic stem cells in clinical applications and in research?
Sherley: The most profound drawback, which has not been adequately disclosed, is that they cannot be used directly to treat mature tissues and organs. The tissues and organs of the body undergo constant cell turnover. Cells are born by cell division, they turn into functional cells (ie, “differentiate”), they function, they get old, they die, and finally they are lost or removed from their tissue or organ. So, to treat mature tissues and organs by giving mature cells produced from embryonic stem cells is not enough. The cells that normally sustain cell turnover are adult stem cells that reside in every tissue and organ which has this cell turnover process, and that is nearly all tissues. This means that, in order to use embryonic stem cells for diseases in mature tissues, they must be turned into adult stem cells.
Another reason that embryonic stem cells cannot be used directly is that they form tumours when transplanted into mature tissues. Knowing these facts, it is pure scientific folly to place such emphasis on embryonic stem cells research to the exclusion of support for adult stem cell research. No matter what the hurdles are for success with adult stem cell-based therapy development, embryonic stem cell research faces the same hurdles and more.
MercatorNet: Many supporters of embryo research are aware of possible drawbacks to using HESCs, but say that it would be wrong to ignore an avenue that might lead to cures. What is your opinion of two-track research?
Sherley: I would agree, if it did not require that human beings be exploited and killed.
MercatorNet: Nearly every researcher advocating therapeutic cloning also decries reproductive cloning because it is unsafe. Does that seem contradictory to you?
Sherley: Yes, amazingly so! See my October 2004 Boston Globe op-ed. But as I like to say, “If a position seems illogical or contradictory, look for a hidden agenda.” Proponents of therapeutic cloning have set up reproductive cloning as the greater of two evils and then insisted that the public must choose one. This leaves the public with therapeutic cloning as the lesser evil. In fact, we can decide to reject them both as evils, but I see reproductive cloning as the lesser of the two presented evils. Instead of promoting deaths, it promotes life; although, of course, the nature of cloned lives raise many deep concerns and fears.
MercatorNet: Your rejection of therapeutic cloning must be a lonely stand, especially in Cambridge, where therapeutic cloning is championed by several eminent researchers at MIT and Harvard. Why do you think most scientists back it?
Sherley: I don’t know that they are doing anything more than protecting their own turf and promoting their own goals with a variety of motivations, including, in some cases, the best intentions of doing public good. However, they can often turn an amazingly blind eye to the contradictions in their position on therapeutic cloning. For example, the same scientists who argue that reproductive cloning would produce disease-ridden individuals insist that tissues created from therapeutic cloning will function normally! Illogical position, hidden agenda.
MercatorNet: Do you think that most stem cell scientists have an open mind towards adult stem cell research?
Sherley: It’s rather hard to know what most stem cell scientists or cell biologists in general, for that matter, think about these issues. I have asked the leaderships of both the American Society for Cell Biology and the International Society for Stem Cell Research to conduct anonymous on-line polls of their membership regarding their views on human embryo research. Neither has been willing to do so. Many scientists who do not support human embryo research are afraid to speak out because of possible reprisals from powerful scientists who can affect grant success, publication acceptances, tenure promotion, and employment.
MercatorNet: Do adult stem cells have advantages over HESCs?
Sherley: Yes. The main advantage is that adult stem cells are already programmed for function in adult tissues and organs. In addition, they do not form tumours when transplanted from one person to another.
MercatorNet: Is it true that it is impossible to propagate and grow adult stem cells in quantities sufficient for clinical applications?
Sherley: Impossible is not true. Challenging is true. We have recently published a report of a successful approach to multiplying adult stem cells from rat liver and we have a patent application pending for the adaptation of the method to human adult liver stem cells. Each adult stem cell is unique, and this requires development of somewhat unique methods for the growth of each type. Every adult stem cell has an intrinsic property to multiply itself, but this process is highly restricted in some tissues. As research elucidates the basis for these restrictions, more adult stem cells will become available for therapeutic development.
MercatorNet: What about tissues like the heart, pancreas and the brain which apparently do not have adult stem cells? Will embryonic stem cells be needed to provide transplant therapies?
Sherley: Yes, the heart is tough one. It’s on my list of organs with little evidence of cell turnover, and therefore unlikely to have stem cells, though this is not certain yet. This being said, embryonic stem cells are not likely to be able to impact heart muscle significantly either and their tumour risk in the heart and after migration to other sites is likely to be prohibitive. We need to stay sober. The belief that stem cell therapy will be a panacea is naïve and greatly misguided. There is still a lot of other disease research that we should continue to support, as the cures for heart disease may lie in a non-stem cell domain.
There is good evidence for adult stem cells in the brain. However, it is unclear how these cells normally function in the brain and what are all of the regions of the brain that they might supply with young cells. For brain diseases that primarily affect motor or sensory function, these cells may have applications down the road.
The recent report concluding that there were no adult stem cells in the pancreas from the Melton lab at Harvard had several shortcomings in logic and experimental analysis and did not evaluate the human pancreas. This conclusion has been used as a basis of persuasion that we must conduct human embryo research in order to cure diabetes. Illogical position, hidden agenda.
MercatorNet: How long do you think it will be before adult stem cells are used as medicines in American hospitals?
Sherley: First it should be noted that preparations of adult stem cells are already used as medicines in hospitals worldwide. Bone marrow transplantation, immobilized peripheral blood stem cell transfusions, and cord blood cell transplants in children are all examples of standard medical therapy with hematopoietic stem cells, which are the adult stem cells responsible for blood cell formation. There is still much work to be done to improve the effectiveness of these treatments by developing methods that increase the number of stem cells in the donor cell preparations.
Forecasting the future is always difficult to do when a field is still in primarily a research phase. By the very nature of the research it is difficult to predict when discoveries that will lead practical applications will occur, even though there is a high probability of success. If we can breach the adult stem cell multiplication barrier in liver, skin, hair follicle, pancreas, and skeletal muscle-derived cells, we will move these adult stem cell types into a phase of development that may allow more faithful prediction of the beginning of the era of adult stem cell-based medicine.
Michael Cook is editor of MercatorNet and also of the free international bioethics newsletter BioEdge. He writes from Melbourne.
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