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We know that stem cells from adult mice, when grown in mouse or chick embryos, revert to an unspecialised state and become identical to the surrounding tissue, depending on which cell layer they are injected into.
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The extent to which stem cells transdifferentiate is uncertain; some of them also seem to fuse with host cells, forming pluripotent cells, and recent debate and experiment has aimed at finding out the extent of these two factors. In October a third quality of stem cells was discovered.
Scientists at the University of California in San Diego found, amazingly, that when embryonic stem cells — just 15 cells, taken from normal mice — are injected into the abdomen of mice pregnant with fetuses carrying a genetic heart defect, the pups are born with normal hearts. The stem cells do not cross the placenta into the fetuses, but secrete hormone-like chemicals that play an essential role of normal growth and development. A further development, pioneered in animals and now entering clinical practice, is to use donor stem cells to treat certain serious and often fatal inherited blood disorders such as Fanconi anaemia, severe combined immune deficiency, and, potentially, sickle cell disease and thalassaemia.
Research has aimed to replace various missing tissues using bone marrow stem cells, and there seems to be evidence that this happens at least some of the time. The problem researchers have faced is knowing whether, some months later, any of the cells in the tissue being studied usually heart or brain is derived from the injected stem cells.
Even learning and exercise can stimulate new nerve cell production. One way round this problem is to inject male cells into female bodies, wait a few months, and see if the brain or other organ contains Y-chromosomes, which are only normally found in males. It is also essential to check whether the Y-chromosomes are in new nerve cells and are not —as sometimes happens—merely the product of fusion of the injected stem cells with existing cells. Scientists have developed techniques to do this.
A further problem is that a wait of six months between giving the transplant and killing a rodent for study represents a quarter of its lifespan. In April , two papers in the prestigious science journal Nature challenged these observations and the science underpinning them. Using state-of-the-art genetic tools, they discovered that bone marrow stem cells showed little or no capacity to turn into heart muscle.
Instead, they turned into blood cells.
Any functional improvement, they said, seems to have been caused by growth of new blood vessels, which has proved an unexpected side effect of treatment. In view of the potential hazards of mistaken cellular identity, reports of bone marrow stem cell versatility are now undergoing rigorous scrutiny. Better, but mixed, results came from research using muscle stem cells. The best animal results yet May came when embryonic stem cells were transplanted within a man-made 3D structure into damaged hearts of rodents which had suffered heart attacks. In the same month there were reports of successful human grafts, where it was shown that new heart cells were derived from injected umbilical cord stem cells.
In animals, fetal heart cells graft easily into the heart, adopt the identity of adult heart cells, and become electrically coupled. However, their use in humans is ethically problematic. The search is now on for heart precursor cells and to discover the signals that guide the way they migrate, renew themselves, and become adult heart cells.
New muscle cells have been formed in mouse muscle in the test-tube, and in living mice. In both cases the cells were reprogrammed by signals from surrounding cells, suggesting that adult tissues may be able to instruct transplanted cells to adopt the fates appropriate to their new location.
Stem cell research: Trends in and perspectives on the evolving international landscape
Muscle regeneration has also resulted from injecting several types of stem cells — from bone marrow, from human knee joints, and from newborn mouse muscles — repairing damage similar to muscular dystrophy. No funding was to be granted for "the use of stem cell lines derived from newly destroyed embryos, the creation of any human embryos for research purposes, or cloning of human embryos for any purposes" The debate over funding for embryonic stem cell research depends heavily on the ethical status of the research. There are two main arguments surrounding the ethics of embryonic stem cell research: the research is ethical because of the unique potential that embryonic stem cells have to cure currently untreatable diseases; and the research is unethical because it requires the destruction of life in the form of an embryo or fetus.
Ultimately, the possible benefits and controversial status of life that an embryo embodies qualify embryonic stem cell research as ethical, as long as the stem cells are obtained in an ethical manner. In the realm of stem cell research, embryonic and adult stem cells are often compared. The controversial use of embryonic stem cells is supported on the basis of the many advantages that they have over adult stem cells. Embryonic stem cells are easier to obtain; they have a greater cell growth, otherwise known as proliferation, capacity; and they are more versatile. Embryonic stem cells are isolated from embryos in the blastocyst stage and the process damages the structure of the embryo to a point from which the embryo can no longer develop.
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Because these stem cells are obtained at a point when the inner cell mass is concentrated in the embryo, they are more easily obtained than adult stem cells, which are limited in quantity. Another valuable benefit of embryonic stem cells is their ability to multiply readily and proliferate indefinitely when cultured in the proper conditions Devolder 9. Lastly, embryonic stem cells' pluripotent quality is the main factor that distinguishes them from adult stem cells The ability to differentiate into any cell type creates greater possibilities for the application of embryonic stem cells.
Supporters of embryonic stem cell research argue that the research is justified, though it requires the destruction of an embryo, because of the potential for developing cures and preventing unavoidable suffering. These backers often disagree with the belief that "a blastocyst — even one that is not implanted in a woman's uterus — has the same ethical status as a further-developed human" Clemmitt Arthur Caplan, professor of medical ethics at the University of Pennsylvania, asserts that "an embryo in a dish is more like a set of instructions or blueprint for a house.
It can't build the house. For the cells to develop into a human being requires an interactive process in the uterus between the embryo and the mother" Clemmitt Others in favor of the research, such as Heron, a biotechnology company, claim that "not to develop the technology would do great harm to over million patients in the United States alone who are affected by diseases potentially treatable by the many medical applications of hES [human Embryonic Stem] cells" Holland One example is the previously stated method of using embryonic stem cells to repair damaged tissue or organs.
The only way to restore cellular function in an organ is to literally replace the lost cells and embryonic stem cells provide the best option for producing these cells 3. Embryonic stem cells do also have some disadvantages that should be considered when making the argument for further support of embryonic stem cell research. Unlike adult stem cells, embryonic stem cells have a higher risk of causing tumor formation in the patient's body after the stem cells are implanted.
This is due to their higher capacities for proliferation and differentiation Devolder Embryonic stem cell-based therapies also possess the risk of immunorejection — rejection of the stem cells by the patient's immune system. Because embryonic stem cells are derived from embryos donated for research after in vitro fertilization treatment, the marker molecules on the surfaces of the cells may not be recognized by the patient's body, and therefore may be destroyed as the result of a defense mechanism by the body Holland This is a problem that will require a solution if embryonic stem cell research is to be the basis for future therapeutic medicine.
Currently, the isolation of embryonic stem cells requires the destruction of an early embryo. Many people hold the belief that a human embryo has significant moral status, and therefore should not be used merely as a means for research.
One position that opponents of embryonic stem cell research assert is what "The Ethics of Embryonic Stem Cell Research" calls the full moral status view This view holds that "the early embryo has the same moral status, that is, the same basic moral rights, claims, or interests as an ordinary adult human being. Therefore, with full moral status as a human being, an embryo should not be deliberately destroyed for research purposes simply because it is human Devolder The Roman Catholic Church is a strong supporter of this view, opposing stem cell research on the grounds that it is a form of abortion.
Several other groups, including American evangelicals and Orthodox ethicists, consider "blastocysts to have the same status as fully developed human beings" and therefore oppose embryonic stem cell research for this reason. Beliefs regarding the moral status of an embryo are subjective, and also their own controversial issue, which complicates the task of creating a universal law for the use of embryonic stem cells for research.
Others in opposition, such as Kevin T. Fitzgerald, a Jesuit priest who is a bioethicist and professor of oncology at Georgetown University Medical School, do not consider the moral status of an embryo, but rather assert that Embryos should be protected because they are "that which we all once were" Clemmitt This view is very similar to moral philosopher and professor of philosophy as the University of California at Irvine Philip Nickel's "Loss of Future Life Problem" in regards to embryonic stem cell research.
The Loss of Future Life Problem holds that it is unethical to take the lives of future humans by destroying embryos for research Tobis This stance stresses the potential of those future lives that will never have the chance to reach fulfillment if destroyed for research. In a retroactive sense, this can cause us to question "what if the embryo that developed into Albert Einstein was destroyed for embryonic stem cell research?
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