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Stem cells are biological cells found in all multicellular organisms
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Stem cells are biological cells found in all multicellular organisms


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  • 1. Stem cells are biological cells found in all multicellular organisms, that can divide (through mitosis) and differentiate into diverse specialized cell types and can self-renew to produce more stem cells. In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing adult tissues. In a developing embryo, stem cells can differentiate into all the specialized cells[ectoderm,endoderm and mesoderm-see induced pluripotent stem cells] (these are called pluripotent cells), but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues. There are three accessible sources of autologous adult stem cells in humans: 1. Bone marrow, which requires extraction by harvesting, that is, drilling into bone (typically the femur or iliac crest), 2. Adipose tissue (lipid cells), which requires extraction by liposuction, and 3. Blood, which requires extraction through pheresis, wherein blood is drawn from the donor (similar to a blood donation), passed through a machine that extracts the stem cells and returns other portions of the blood to the donor. Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk. By definition, autologous cells are obtained from one's own body, just as one may bank his or her own blood for elective surgical procedures. Highly plastic adult stem cells are routinely used in medical therapies, for example in bone marrow transplantation. Stem cells can now be artificially grown and transformed (differentiated) into specialized cell types with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture. Embryonic cell lines and autologous embryonic stem cells generated through therapeutic cloning have also been proposed as promising candidates for future therapies.[1] Research into stem cells grew out of findings by Ernest A. McCulloch and James E. Till at the University of Toronto in the 1960s.[2][3] Ethics of Stem Cell Research First published Fri Apr 25, 2008; substantive revision Mon Jan 28, 2013 Human embryonic stem cell (HESC) research offers much hope for
  • 2. alleviating the human suffering brought on by the ravages of disease and injury. HESCs are characterized by their capacity for self-renewal and their ability to differentiate into all types of cells of the body. The main goal of HESC research is to identify the mechanisms that govern cell differentiation and to turn HESCs into specific cell types that can be used for treating debilitating and life-threatening diseases and injuries. Despite the tremendous therapeutic promise of HESC research, the research has met with heated opposition because the harvesting of HESCs involves the destruction of the human embryo. HESCs are derived in vitro around the fifth day of the embryo's development (Thomson et al. 1998). A typical day- 5 human embryo consists of 200–250 cells, most of which comprise the trophoblast, which is the outermost layer of the blastocyst. HESCs are harvested from the inner cell mass of the blastocyst, which consists of 30–34 cells. The derivation of HESC cultures requires the removal of the trophoblast. This process of disaggregating the blastocyst's cells eliminates its potential for further development. Opponents of HESC research argue that the research is morally impermissible because it involves the unjust killing of innocent human beings. Scientists recently succeeded in converting adult human skin cells into cells that appear to have the properties of HESCs by activating four genes in the adult cells (Takahashi et al. 2007; Yu et al. 2007). The reprogrammed cells— ―induced pluripotent stem cells‖ (iPSCs)—could ultimately eliminate the need for HESCs. However, at present, the consensus in the scientific community is that both HESC and iPSC research should be pursued, as we do not yet know whether iPSCs have the same potential as HESCs or whether it is safe to transplant them into humans. Thus, the controversies around HESC research will continue, at least in the near-term. While the principal source of the controversy surrounding HESC research lies in competing views about the value of human embryonic life, the scope of ethical issues in HESC research is broader than the question of the ethics of destroying human embryos. It also encompasses questions about, among other things, whether researchers who use but do not derive HESCs are complicit in the destruction of embryos, whether there is a moral distinction between creating embryos for research purposes and creating them for reproductive ends, the permissibility of cloning human embryos to harvest HESCs, and the ethics of creating human/non- human chimeras. This entry provides an overview of all but the last two issues just listed; cloning and human-non-human chimeras are addressed in separate entries.
  • 3. Stem cells hold great promise in helping us understand and treat many human diseases and conditions. That's because stem cells are quite unique compared to other types of cells. For one thing, unlike most normal types of cells, stem cells are capable of dividing and regenerating for long periods of time. Secondly, stem cells are unspecialized, which means they don't have a unique function, such as pumping blood to the heart or supporting muscles in the legs. These unspecialized cells can be trained, however, which means they could become specialized in whatever area of the body they're needed. Why do these properties portend medical breakthroughs? Many of the deadliest diseases, such as cancer, are the result of uncontrolled cellular division. By studying how stem cells are able to reproduce without causing damage, scientists may be able to better understand the disease and determine more effective treatments. And the ability to regenerate new, unspecialized cells could revolutionize treatment for conditions caused by cellular degeneration. For example, during a stroke, brain cells are irreparably damaged; stem cells could kick-start the regenerative process and undergo specialization to replace the lost cells. It's impossible to know every possible medical use of stem cells because scientists haven't been able to conduct extensive research with them, but researchers claim that they may be the key to treating a host of diseases and conditions, including Parkinson's disease, diabetes, heart disease, multiple sclerosis, baldness and spinal cord injuries. Research on possible treatments has been limited due to ethical concerns over where the stem cells came from. Until recently, scientists only knew of two ways to obtain stem cells -- from embryos and from adults. Adult stem cells are found in various parts of the body, such as the brain, bone marrow, blood, skin and heart, but they tend not to divide very often once they are removed from the body, and there has been some difficulty in re- specializing these cells. Embryonic stems cells are derived from a blastocyst, or an embryo that's between three and five days old. These embryos are usually furnished by clinics that perform in vitro fertility treatments; for one reason or another, they've been rejected for implantation into a womb. It is embryonic stem cells that cause controversy. Removing the stem cells requires the destruction of the embryo, which some people liken to destruction of a human being. The issue comes down to the question of when life begins: Those who believe that life starts at the moment of conception think that harvesting embryonic stem cells is akin to murder. Some critics of this viewpoint have argued that these
  • 4. embryos were marked for destruction and then donated by their owners, meaning that these embryos would never have come to term anyway, but others predict that this excuse might lead to more ethically questionable actions in the future, such as harvesting embryos specifically for research. In recent years, researchers have tried to find ways to obtain embryonic stem cells without destroying the embryos. One method of deriving stem cells from mice embryos has proven successful. Researchers are also experimenting with reprogramming adult stem cells to act more like embryonic stem cells. These cells, known as induced pluripotent stem cells, hold promise, but scientists would still like the opportunity to pursue work with the embryonic stem cells. The ethics of stem cells Ethical issues around stem cells focus almost entirely on embryonic stem cells. Stem cells have been used in medicine for many years - bone marrow transplantation is a form of stem cell therapy. Ethical concerns have focused mainly on the use of embryonic stem cells in research and their possible application in medicine. A core issue has been the source of embryonic stem cells. Until recently, these were obtained from embryos that were by-products of assisted fertilisation attempts; these could be voluntarily donated for use in research. More recently, UK law was changed to allow researchers to create human embryos for use in research, so that embryonic stem cells could be extracted. The key difference here was that new human embryos were being created specifically for research. Some commentators argued that this contravened the principle that human life should never be created as a means to an end. However, embryos created for research cannot by law be implanted in the womb, so never give rise to new individuals. A key ethical concept is the moral status of the embryo. The consensus, enshrined in the Human Fertilisation and Embryology Act in 1990, is that the embryo does have moral rights but not to the same extent as a living person. The interpretation is challenged by some groups, including the Catholic Church, which holds that new life begins at the point of conception and hence a fetus at any stage of development should hold full human rights. Others, including some other faiths, consider that the status of a
  • 5. fetus changes as it develops, for example as its nervous system appears. The rights of a fetus at any a particular stage are balanced against the potentially large benefits that others may gain from research and, ultimately, stem cell-based treatments. This line of reasoning has led some to argue that use of embryonic stem cells is not justified, because alternatives are available, such as adult stem cells or, more recently, induced pluripotent stem cells. Most scientists counter that research on embryonic stem cells is still needed to clarify fundamental biological mechanisms and because it is not yet clear which types of stem cell will prove the best bet therapeutically. Use of pre-14-day embryos, still little more than a ball of cells, would therefore remain justified. Ethics of stem cell research The overwhelming objection to stem cell research is that it involves the destruction of an embryo or foetus. For many this constitutes destruction of a potential human, and conflicts with religious and moral views held in our society. For others, the potential for this research to provide treatments and possibly cures for debilitating illnesses that have no cure and significantly impact on our way of life overrides this concern. Central to any argument on this is what actually constitutes the beginning of life for a human. Opinions on this vary from the moment of conception, to a 14 day embryo, to a living baby at birth. This issue is highly emotive and it will always be necessary to consider all opinions and to balance the harm that might be done against the potential good this research may provide for those suffering from debilitating diseases. In Australia, legislation states that no embryo may be created for the purpose of this research or to generate stem cell lines. The embryonic stem and germ cells are obtained from either donated embryos not required for an IVF procedure that would otherwise be destroyed, or from pregnancies that were terminated for medical or social reasons. The other major ethical issue associated with stem cell research ties in with the combination of embryonic stem cell and cloning technologies, leading to generation of an embryo that is a genetic clone of the donor of the nucleus (see section on stem cells and cloning). What is critically different in this context as opposed to that above is that an embryo is actually created for research or therapeutic purposes, and this raises a wider range of objections, in that a potential life is created for a specific purpose. Also of issue here is the purpose of this cloning, which would be done purely for the purpose of generating tissue for transplantation. The
  • 6. embryo generated could be allowed to continue development and could potentially lead to the birth of a new human if implanted into a willing mother. There are serious ethical and medical concerns associated with the use of somatic cell nuclear transfer technologies to reproduce humans and it is illegal in Australia, UK and the USA to conduct any research into reproductive cloning of humans. The Prohibition of Human Cloning Act 2002 (Cth) prohibits all types of human cloning by any method. The Research Involving Human Embryos Act 2002 (Cth) allows for regulated use of an appropriate number of excess ART embryos in approved research programs. State and Territory governments are introducing complementary legislation to provide nationally consistent prohibition and regulation of use of excess ART embryos in research. Some people speculate that allowing any somatic cell nuclear transfer will be the start of a slippery slope into reproductive cloning. Given these concerns, which stem cell research should be permitted? There are pluses and minuses associated with the research and use of all types of stem cells. Which ones should research focus on? The ethical issues surrounding the origin of embryonic stem cells will always be a sensitive issue. There are strict guidelines and legislation regarding any research involving embryos, but for many, research on adult stem cells is the only acceptable alternative. Embryonic stem and germ cells can give rise to every cell type in the body. Adult stem cells, however, are multipotent, giving rise to a limited range of cell types. This may limit their use in cell-based therapies, and many researchers believe research using embryonic cells will be more fruitful. However, recent research has revealed that some adult stem cells may be able to generate different tissues under the right conditions and this may increase their therapeutic potential. Embryonic stem cells have a greater capacity for self-renewal and the cell lines that have been established will be useful for research into the effects of drugs and toxins, and also into early human development. Their uncontrolled growth also leads to the development of tumours called teratomas, which may restrict their use in cell-based therapies. Research is continuing into ways to control and regulate the growth of ES cells more effectively. Embryonic germ and adult stem cells do not form these tumours in culture, which may make them better alternatives for transplant tissue sources. Obviously there are pros and cons to the use of all three types of stem cells
  • 7. and most scientists agree that it is important to continue to pursue research into embryonic stem and germ cells and adult stem cells. All scientists are aware that they must undertake their work ethically and within the bounds of the law, and these can vary from country to country. In Australia, all research involving humans must be approved by Human Research Ethics Committees.