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 (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:
Bone marrow, which requires extraction by harvesting, that
is, drilling into bone (typically the femur or iliac crest),
Adipose tissue (lipid cells), which requires extraction by
liposuction, and
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. Research into stem cells
grew out of findings by Ernest A. McCulloch and James E. Till at the University
of Toronto in the 1960s.
Recently John B. Gurdon of the University of Cambridge in
England and Shinya Yamanaka of Kyoto University in Japan shared the Nobel prize
for medicine or physiology. They were
awarded the prize for changing adult cells into stem cells, which can become
any other type of cell in the body.
Prof Gurdon used a gut sample to clone frogs and Prof
Yamanaka altered genes to reprogramme cells
Stem Cell Research: 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 can believe that embryonic stem cell research
instrumentalizes and violates the sanctity of life and some also view it as
tantamount to murder. The fundamental assertion of those who oppose embryonic
stem cell research is the belief that human life is inviolable, combined with
the belief that human life begins when a sperm cell fertilizes an egg cell to
form a single cell.
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.
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."
In 2006, researchers at Advanced Cell Technology of
Worcester, Massachusetts, succeeded in obtaining stem cells from mouse embryos
without destroying the embryos. 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.
Update article to include 2009/2010 current stem cell usages
in clinical trials. The planned treatment trials will focus on the effects of
oral lithium on neurological function in people with chronic spinal cord injury
and those that have received umbilical cord blood mononuclear cell transplants
to the spinal cord. The interest in these two treatments derives from recent
reports indicating that umbilical cord blood stem cells may be beneficial for
spinal cord injury and that lithium may promote regeneration and recovery of
function after spinal cord injury. Both lithium and umbilical cord blood are
widely available therapies that have long been used to treat diseases in
humans.
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.
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. 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.
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, or when the brain begins developing activity,
which has been detected at 54 days after conception.
Efficiency
In vitro fertilization (IVF) generates large numbers of
unused embryos (e.g. 70,000 in Australia alone). Many of these thousands of IVF
embryos are slated for destruction. Using them for scientific research uses a
resource that would otherwise be wasted.
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.
Abortions are legal in many countries and jurisdictions. The
argument then follows that if these embryos are being destroyed anyway, why not
use them for stem cell research or treatments?
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.
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.
Embryonic stem cells have greater plasticity, potentially
allowing them to treat a wider range of diseases.
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.
DNA abnormalities found in adult stem cells that are caused
by toxins and sunlight may make them poorly suited for treatment.
Embryonic stem cells have been shown to be effective in
treating heart damage in mice.
Embryonic stem cells have the potential to cure chronic and
degenerative diseases which current medicine has been unable to effectively
treat.
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.
Viability
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." 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. Embryos used in medical research for stem cells are well below
development that would enable viability.
Moral and ethical concerns
It is liable to abuse. It violates a person's right to
individuality, autonomy, self-hood. It allows eugenic selection.
His journal goes into details of the advantages of using
stem cell lines mainly for therapeutic reasons with great emphasis on control.
The main reason is that if this regeneration practice goes un-checked, there
will be someone out there that will be "playing God."
Objection
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.Furthermore, adult stem
cell research may be able to make greater advances if less money and resources
were channeled into embryonic stem cell research.
Embryonic stem cells have never produced therapies (to date,
adult stem cells have been used in treatment). 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. 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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