Since stem cells have the ability to differentiate into any type of cell, they offer something in the development of medical treatments for a wide range of conditions. Treatments that have been proposed include treatment for physical trauma, degenerative conditions, and genetic diseases (in combination with gene therapy). Yet further treatments using stem cells could potentially be developed thanks to their ability to repair extensive tissue damage.[2]
Great levels of success and potential have been shown from research using adult stem cells. In early 2009, the FDA approved the first human clinical trials using embryonic stem cells. Some researchers are of the opinion that the differentiation potential of embryonic stem cells is broader than most adult stem cells. Embryonic stem cells can become all cell types of the body because they are Pluripotent. Adult stem cells are generally limited to differentiating into different cell types of their tissue of origin. However, some evidence suggests that adult stem cell plasticity may exist, increasing the number of cell types a given adult stem cell can become. In addition, embryonic stem cells are considered more useful for nervous system therapies, because researchers have struggled to identify and isolate neural progenitors from adult tissues. Embryonic stem cells, however, might be rejected by the immune system - a problem which wouldn't occur if the patient received his or her own stem cells.
Some stem cell researchers are working to develop techniques of isolating stem cells that are as potent as embryonic stem cells, but do not require a human embryo.
Some believe that human skin cells can be coaxed to "de-differentiate" and revert to an embryonic state. Researchers at Harvard University, led by Kevin Eggan, have attempted to transfer the nucleus of a somatic cell into an existing embryonic stem cell, thus creating a new stem cell line.[3] Another study published in August 2006 also indicates that differentiated cells can be reprogrammed to an embryonic-like state by introducing four specific factors, resulting in induced pluripotent stem cells.[4]
Researchers at Advanced Cell Technology, led by Robert Lanza, reported the successful derivation of a stem cell line using a process similar to preimplantation genetic diagnosis, in which a single blastomere is extracted from a blastocyst.[5] At the 2007 meeting of the International Society for Stem Cell Research (ISSCR) [6], Lanza announced that his team had succeeded in producing three new stem cell lines without destroying the parent embryos. "These are the first human embryonic cell lines in existence that didn't result from the destruction of an embryo." Lanza is currently in discussions with the National Institutes of Health (NIH) to determine whether the new technique sidesteps U.S. restrictions on federal funding for ES cell research.[7]
According to a January 9, 2007 Daily Telegraph (London) article reporting on a statement by Dr. Anthony Atala of Wake Forest University, the fluid surrounding the fetus has been found to contain stem cells, that, when utilized correctly, "can be differentiated towards cell types such as fat, bone, muscle, blood vessel, nerve and liver cells", according to the article. The extraction of this fluid is not thought to harm the fetus in any way. "Our hope is that these cells will provide a valuable resource for tissue repair and for engineered organs as well," said Dr Atala.[8]
[edit] Viewpoints
The status of the human embryo and human embryonic stem cell research is a controversial issue as, with the present state of technology, the creation of a human embryonic stem cell line requires the destruction of a human embryo. Stem cell debates have motivated and reinvigorated the pro-life movement, whose members are concerned with the rights and status of the embryo as an early-aged human life. They believe that embryonic stem cell research instrumentalizes and violates the sanctity of life and is tantamount to murder.[9] The fundamental assertion of those who oppose embryonic stem cell research is the belief that human life is inviolable, combined with the fact that human life begins when a sperm cell fertilizes an egg cell to form a single cell. (see Sexual reproduction)
A portion of stem cell researchers use embryos that were created but not used in in vitro fertility treatments to derive new stem cell lines. Most of these embryos are to be destroyed, or stored for long periods of time, long past their viable storage life. In the United States alone, there have been estimates of at least 400,000 such embryos.[10] This has led some opponents of abortion, such as Senator Orrin Hatch, to support human embryonic stem cell research.[11] See Also Embryo donation.
Medical researchers widely submit that stem cell research has the potential to dramatically alter approaches to understanding and treating diseases, and to alleviate suffering. In the future, most medical researchers anticipate being able to use technologies derived from stem cell research to treat a variety of diseases and impairments. Spinal cord injuries and Parkinson's disease are two examples that have been championed by high-profile media personalities (for instance, Christopher Reeve and Michael J. Fox, who have lived with these conditions, respectively). The anticipated medical benefits of stem cell research add urgency to the debates, which has been appealed to by proponents of embryonic stem cell research.
In August, 2000, The U.S. National Institutes of Health's Guidelines stated:
"...research involving human pluripotent stem cells...promises new treatments and possible cures for many debilitating diseases and injuries, including Parkinson's disease, diabetes, heart disease, multiple sclerosis, burns and spinal cord injuries. The NIH believes the potential medical benefits of human pluripotent stem cell technology are compelling and worthy of pursuit in accordance with appropriate ethical standards." [12]
In 2006, researchers at Advanced Cell Technology of Worcester, Mass., succeeded in obtaining stem cells from mouse embryos without destroying the embryos.[13] If this technique and its reliability are improved, it would alleviate some of the ethical concerns related to embryonic stem cell research.
Another technique announced in 2007 may also defuse the longstanding debate and controversy. Research teams in the United States and Japan have developed a simple and cost effective method of reprogramming human skin cells to function much like embryonic stem cells by introducing artificial viruses. While extracting and cloning stem cells is complex and extremely expensive, the newly discovered method of reprogramming cells is much cheaper. However, the technique may disrupt the DNA in the new stem cells, resulting in damaged and cancerous tissue. More research will be required before non-cancerous stem cells can be created.[14][15][16][17]
[edit] Endorsement
- Embryonic stem cells have the potential to grow indefinitely in a laboratory environment and can differentiate into almost all types of bodily tissue. This makes embryonic stem cells a prospect for cellular therapies to treat a wide range of diseases.[18]
[edit] Human potential and humanity
This argument often goes hand-in-hand with the utilitarian argument, and can be presented in several forms:
- Embryos are not equivalent to human life while they are still incapable of surviving outside the womb (i.e. they only have the potential for life).
- More than a third of zygotes do not implant after conception.[19][20] Thus, far more embryos are lost due to chance than are proposed to be used for embryonic stem cell research or treatments.
- Blastocysts are a cluster of human cells that have not differentiated into distinct organ tissue; making cells of the inner cell mass no more "human" than a skin cell.[18]
- Some parties contend that embryos are not humans, believing that the life of Homo sapiens only begins when the heartbeat develops, which is during the 5th week of pregnancy,[21] or when the brain begins developing activity, which has been detected at 54 days after conception.[22]
[edit] Efficiency
- In vitro fertilization (IVF) generates large numbers of unused embryos (e.g. 70,000 in Australia alone).[18] Many of these thousands of IVF embryos are slated for destruction. Using them for scientific research utilizes a resource that would otherwise be wasted.[18]
- While the destruction of human embryos is required to establish a stem cell line, no new embryos have to be destroyed to work with existing stem cell lines. It would be wasteful not to continue to make use of these cell lines as a resource.[18]
- Abortions are legal in many countries and jurisdictions. The arguement then follows that if these embryos are being destroyed anyway, why not use them for stem cell research or treatments?
[edit] Superiority
This is usually presented as a counter-argument to using adult stem cells as an alternative that doesn't involve embryonic destruction.
- Embryonic stem cells make up a significant proportion of a developing embryo, while adult stem cells exist as minor populations within a mature individual (e.g. in every 1,000 cells of the bone marrow, only 1 will be a usable stem cell). Thus, embryonic stem cells are likely to be easier to isolate and grow ex vivo than adult stem cells.[18]
- Embryonic stem cells divide more rapidly than adult stem cells, potentially making it easier to generate large numbers of cells for therapeutic means. In contrast, adult stem cell might not divide fast enough to offer immediate treatment.[18]
- Embryonic stem cells have greater plasticity, potentially allowing them to treat a wider range of diseases.[18]
- Adult stem cells from the patient's own body might not be effective in treatment of genetic disorders. Allogeneic embryonic stem cell transplantation (i.e. from a healthy donor) may be more practical in these cases than gene therapy of a patient's own cell.[18]
- DNA abnormalities found in adult stem cells that are caused by toxins and sunlight may make them poorly suited for treatment.[18]
- Embryonic stem cells have been shown to be effective in treating heart damage in mice.[18]
- Embryonic stem cells have the potential to cure chronic and degenerative diseases which current medicine has been unable to effectively treat.
[edit] Individuality
- Before the primitive streak is formed when the embryo attaches to the uterus at approximately 14 days after fertilization, a single fertilized egg can split in two to form identical twins, or a pair of embryos that would have resulted in fraternal twins can fuse together and develop into one person (a tetragametic chimera). Since a fertilized egg has the potential to be two individuals or half of one, some believe it can only be considered a potential person, not an actual one. Those who subscribe to this belief then hold that destroying a blastocyst for embryonic stem cells is ethical.[23]
[edit] Objection
[edit] Value of life
The deliberate destruction of a human embryo is incompatible with Roman Catholic doctrine, according to which, Pontifical Academy for Life has stated that human blastocysts are inherently valuable and should not be voluntarily destroyed as they are "from the moment of the union of the gametes" human subjects with well defined identities.[24][25]
Viability is another standard under which embryos and fetuses have been regarded as human lives. In the United States, the 1973 Supreme Court case of Roe v. Wade concluded that viability determined the permissibility of abortions performed for reasons other than the protection of the woman's health, defining viability as the point at which a fetus is "potentially able to live outside the mother's womb, albeit with artificial aid."[26] The point of viability was 24 to 28 weeks when the case was decided and has since moved to about 22 weeks due to advancement in medical technology.
[edit] Better alternatives
This argument is used by opponents of embryonic destruction as well as researchers specializing in adult stem cell research.
Pro-life supporters often claim that the use of adult stem cells from sources such as umbilical cord blood has consistently produced more promising results than the use of embryonic stem cells.[27] Furthermore, adult stem cell research may be able to make greater advances if less money and resources were channeled into embryonic stem cell research.[28]
Adult stem cells have already produced therapies, while embryonic stem cells have not.[29][30] Moreover, there have been many advances in adult stem cell research, including a recent study where pluripotent adult stem cells were manufactured from differentiated fibroblast by the addition of specific transcription factors.[31] Newly created stem cells were developed into an embryo and were integrated into newborn mouse tissues, analogous to the properties of embryonic stem cells.
This argument remains hotly debated on both sides. Those critical of embryonic stem cell research point to a current lack of practical treatments, while supporters argue that advances will come with more time and that breakthroughs cannot be predicted.
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