Recent scientific advances in human stem cell research have brought into fresh focus the dignity and status of the human embryo. These developments require.
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- Examining the ethics of embryonic stem cell research | Harvard Stem Cell Institute (HSCI)
There is wide agreement that embryonic stem cell research holds unique promise for developing therapies for currently incurable diseases and conditions, and for important biomedical research. However, as it is currently done, the isolation of embryonic stem cells involves a process in which an early embryo is destroyed, which many find highly problematic.
This has resulted in what I refer to in my book as. The Problem. Either one supports embryonic stem cell research and accepts resulting embryo destruction, or one opposes embryonic stem cell research and accepts that the potential benefits of this research will be foregone. The first type of response has been to adopt a middle ground position—a position between the dominant opposing views on the permissibility of embryonic stem cell research.
The two dominant opposing views hold respectively that all embryonic stem cell research is morally unacceptable and that embryonic stem cell research is no more problematic than other kinds of research in cell biology. By contrast, middle ground positions—positions between these two views—distinguish between different types or aspects of embryonic stem cell research, accepting some but not others. The second type of response to the Problem has been the development of technical solutions.
Several techniques have been proposed to enable researchers to obtain embryonic stem cells, or their functional equivalents, without harming or destroying embryos. I aim to show that they all fail for similar reasons: they depend on inconsistent argumentation. In each case, either i the argument that the supposedly permissible kind of research is permissible also shows that the supposedly impermissible kind of research is permissible, or ii the argument that the supposedly impermissible kind of research is impermissible also shows that the supposedly permissible kind is impermissible.
The arguments for these positions only appear to succeed if we apply those arguments selectively to certain types of pluripotent stem cell research, without drawing out their implications for others. Even if they are not the correct ethical positions, we might still have strong reasons to publicly defend or accept them, for example, because this will have the best consequences, or because this expresses respect for a variety of reasonable views in a democratic society.
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I conclude that the central tension in the embryonic stem cell debate remains unresolved. This conclusion has important implications for the stem cell debate, as well as for policies inspired by this debate. Please, see here for further information. Lanza of Ocata Therapeutics has perfected a procedure that does not kill the ball of cells called the Blastomere at the pre -embryonic stage before the morula is formed …. The processes causing this transition to tumorigenicity are not well understood.
But safe therapies involving ES cells will be difficult to develop unless a way is found to restrain this aspect of their power. The second hurdle to ES cell therapies concerns the problem of immune rejection. By contrast, many adult stem cell therapies can avoid the problem of immune rejection by using stem cells that actually come from the recipient, which allows for the transplantation of stem cells that are genetically identical to the patient. The problem with immune rejection has led to increasing interest in SCNT cloning as a method of obtaining embryonic stem cells.
A third major challenge facing embryonic stem cell therapy involves generating the right kinds of differentiated cells using pluripotent stem cells. While ES cells have the theoretical ability to differentiate into any type of cell in the body, coaxing ES cells to develop into specific, functional cell types in the laboratory will require a thorough understanding of the factors that control stem cell differentiation. Beyond the possibilities of ES cell-derived regenerative therapies, which are still largely speculative, there lie a number of more immediate scientific and medical benefits to be gained from the study of ES cells.
At the most basic level, ES cells give scientists the opportunity to learn more about cell differentiation and about the factors implicated in gene expression. Such knowledge is additionally helpful in our understanding of the development of the human organism from its zygotic stages on, and will come to be integrated into the broader understanding of genetics and epigenetics. A second expected benefit comes from the use of ES cells to learn more about the workings and natural histories of genetic diseases.
By studying ES cells taken from embryos with particular genetic conditions — often identified through preimplantation genetic diagnosis — scientists can learn more about how deficiencies in gene expression arise, and thus how they might be prevented or cured. Finally, stem cell cultures that have been differentiated into particular tissue types may be used to study the effects of certain drugs, or to test for the toxicity of various chemicals. For all these reasons, embryonic stem cells are considered by many researchers to be of critical scientific value and medical importance.
However, in order to avoid the ethical worries that arise from destroying or harming embryos, researchers have proposed a number of alternative techniques for procuring pluripotent stem cells that are the functional equivalent of embryonic stem cells — techniques not dependent upon human embryos. In the following section we turn to some of the key attempts to find alternatives to embryonic stem cell research.
I n this section we look at two of the most prominent methods suggested for obtaining pluripotent stem cells without extracting them from embryos.
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Both approaches rely upon what we know about the factors affecting gene expression in order to create pluripotent stem cells without ever creating embryos. Recall that in the successful cloning attempt that produced Dolly the sheep, the nucleus of a somatic cell was inserted into an enucleated oocyte, and the resulting new cell was dedifferentiated back to a totipotent, not a pluripotent, state. Likewise, a human stem cell in any state other than totipotency is not and cannot become a complete human organism. In the ANT procedure, unlike in the SCNT cloning procedure, the nucleus of the cell transferred to the oocyte, or the cytoplasm of the oocyte into which it is transferred, is altered in order to prevent the cell from going through the stage of totipotency that is characteristic of a true embryo.
These alterations change the patterns of gene expression to cause the cell to express genes characteristic of pluripotent stem cells, rather than the totipotent cells of the early embryo. Proponents of the procedure argue that none of the three cells involved in the process of ANT — the somatic cell with the altered nucleus, the oocyte, and the new cell — is at any point a zygotic, totipotent cell.
Thus, ANT appears to provide pluripotent but non-embryonic stem cells. Yamanaka and Thomson determined that by inserting genes for transcription factors associated with pluripotency into somatic cells by means of retroviruses, they were able to induce dedifferentiation in those cells, bringing them back to a stage of pluripotency. Induced pluripotent stem cells seem to solve two problems that have bedeviled researchers — one moral and one technical. Thus, no human embryos are created or destroyed in the formation and use of iPS cells, so that that moral controversy is sidestepped.
Additionally, like the embryos produced by SCNT and cells produced by ANT, iPS cell technology seems to offer a solution to the threat of immune rejection, because, in the event that regenerative therapies prove feasible, iPS cells could be dedifferentiated from the somatic cells of the diseased patient himself, and would thus have the same genome as the patient. Moreover, because of the relative ease and non-intrusiveness with which iPS cells can be generated, some of the research possibilities proposed using ES cells might be more readily achieved using iPS cells.
Induced pluripotent stem cells thus seem to offer many practical advantages sought by scientific and biomedical researchers.
Nevertheless, there are some concerns about the iPS approach. One involves the use of retroviruses to introduce the transcription factors into the somatic cells.
Some of these initial worries about iPS cells seem surmountable. Research conducted since the creation of the original iPS cells has shown that the process need not use some of the genes known to cause tumors. Another concern about iPS cells is that early attempts to generate them have not been very efficient: only a small proportion of the cells successfully dedifferentiate, with most studies reporting reprogramming between 0.
Additionally, there are some safety concerns related to the tendency of iPS cells to form dangerous tumors. The genetic and epigenetic changes necessary for inducing pluripotency share many features of the genetic and epigenetic changes associated with cancer; more research is needed to determine how to induce pluripotency without modifying cells in such a way that will increase the likelihood of cancer. A final difficulty related to the use of iPS cells is that it may not obviate the need for ES cells; as noted above, some researchers argue that ES cells are still necessary at least to provide a standard against which the success of iPS cells can be measured.
Recent work by scientists at the Sanger Institute in the United Kingdom has resulted in a new technique for creating iPS cells that appears to be safer and more efficient, and to produce cells even more useful for research and therapy than human ES cells. In sum, induced pluripotent stem cells are a very promising avenue for procuring pluripotent stem cells without the destruction of human embryos, but a number of difficulties with the procedure still need to be addressed.
I n this appendix we have given an account of stem cells, and more particularly, of embryonic stem cells and some techniques for producing cells with similar powers. Stem cells clearly hold great potential for scientific research and, hopefully, for new and improved therapies. In the next appendix , we offer a sketch of the state of the art in therapeutic uses of stem cells.
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Examining the ethics of embryonic stem cell research | Harvard Stem Cell Institute (HSCI)
Becker et al. Robert Lanza et al. Burlington, Mass. Xu et al.
Beyer Nardi and L. Anna M. Bunnell et al. Thomson et al. For the first successful derivation of embryonic stem cells in the mouse, see Martin J. Evans and Matthew H. Brivanlou et al. Teresa de la Morena and Richard A. Hoffman et al. Takeda et al.
An alternative version of the SCNT procedure, in which the egg nucleus was not removed prior to the fusion of the egg with the nucleus of the somatic cell, created human embryos that contained three sets of chromosomes rather than the typical two. While this procedure did successfully create human ES cell lines, such embryos would be highly unlikely to develop beyond an early stage, and the ES cells that were derived are likewise too abnormal to be useful in research or therapy.
Scott Noggle et al. Verpoest et al. The consequences of PGD on the health of children born from embryos on which the procedure was performed are described in I. Liebars et al. Landry and Howard A.