In this video, we are going to take a look at what stem cells are and their use in medical
research as well as the ethical concerns for the different sources of stem cells for research
and therapeutic medicine.
Stem cells are undifferentiated cells, they have the ability to create more stem cells
as well as differentiate to become specialised cells.
Stem cells possess important properties that have made them important for active areas
of research in biology and medicine especially in the treatment of disease.
The first property is self-renewal, stem cells can divide over and over again, they can produce
large numbers of identical cells.
The second property is potency, stem cells are undifferentiated, which means they can
still produce different specialised cells and tissues.
When a cell differentiates into a specialised cell it loses its ability to form other cell
types.
There are several types of stem cells.
Totipotent stem cells have the ability to form into any cell type as well as being able
to become placental tissue in mammals.
A zygote is a diploid cell that is formed from the fusion of a sperm and an egg.
A zygote is totipotent, it consists of a single totipotent cell that has the ability to form
into any cell type and the placenta.
Pluripotent stem cells can also form into any cell type but not into placental tissue.
In the early stage of embryo development, a blastocyst is formed, which has an inner
mass of cells that are pluripotent, which means they can form into any cell type.
Multipotent stem cells are already partially differentiated, but still have the ability
to become many closely related cell types.
An example of multipotent stem cells are those found in the umbilical cord as well as stem
cells found in the bone marrow.
Stem cells found in the bone marrow are able to differentiate into all forms of blood cells,
but they are unable to form into any other cell types.
Unipotent stem cells cannot differentiate into new cells but do have the ability to
self-renew.
For example, liver stem cells can generate new liver cells.
Stem cells are most common in early embryonic development (in the blastocyst stage) in multicellular
organisms because at this stage most of the cells have yet to differentiate, as an organism
continues through embryogenesis more and more of these cells differentiate and become specialised
for the specific functions of the growing embryo and fewer stem cells are present.
Stem cells are used in medical research and treatment because of their ability to divide
and differentiate into different cell types.
They allow researchers to be able to watch the stem cells mature into other cell types,
which helps increase understanding of how diseases occur.
They also allow for regenerative medicine, as they generate new healthy cells that can
be used to replace diseased cells.
They are also used to test new drugs, testing whether they are safe and/or effective on
desired cells, by testing them on specific cells generated from stem cells.
Stargardt’s disease is an example of a disease where stem cell therapy is being researched
to treat the disease.
Stargardt’s disease is a form of juvenile macular degeneration.
It is caused by a mutation in the ABCA4 gene and is recessive.
The mutation impairs energy transport within the retinal photoreceptor cell, which results
in the photoreceptors dying in the center of the retina.
This results in progressive vision loss that begins in childhood or adolescence.
Stem cells could be used to treat Stargardt’s disease by replacing the dead cells in the
retina with new ones derived from stem cells.
Leukemia is an example of a disease where stem cell therapy is used to treat.
Leukemia is a form of cancer affecting the blood-forming tissues such as the bone marrow
and the lymphatic system.
It is caused by the overproduction of abnormal white blood cells (called leukocytes), these
abnormal cells cannot fight off infection.
Stem cells are used in the treatment of leukemia.
First, all the abnormal leukocytes need to be removed, such as through chemotherapy,
once they are removed a bone marrow transplant can occur.
The bone marrow transplant replaces the diseased stem cells producing the abnormal white blood
cells with new multipotent cells that form healthy blood cells.
Parkinson’s Disease is an example of a disease where stem cell therapy is being researched.
Parkinson’s disease is a degenerative disorder of the central nervous system.
It is caused by the death of dopamine-secreting cells in the midbrain, affecting those afflicted’s
ability for smooth and purposeful movement, leading to tremors, rigidity and postural
instability.
Stem cells could be used in the treatment of Parkinson’s by replacing the dead nerve
cells, with new dopamine-producing cells.
There are ethical considerations associated with using stem cells, and these ethical considerations
vary depending on the source of the stem cell.
Stem cells can be derived from specific adult tissues (such as from the bone marrow), from
umbilical cord blood of a newborn baby, and from embryos.
Multipotent adult stem cells are effective for certain conditions, but because they can
only differentiate into limited types of cells, they are then limited in what they can be
used to treat.
They are also limited because they are not common and hard to obtain from adult tissue.
A benefit of using adult stem cells from the same person being treated is that they will
be 100% compatible with the stem cells, there is no risk of rejection by the immune system.
Adult stem cells do not raise as much of an ethical concern as the other sources of stem
cells, as they are derived from the adult themselves, and are becoming used more in
research and therapeutic treatment.
Umbilical cord stem cells are derived from the umbilical cord itself.
The first drawback of this source of stem cell is that they are multipotent, which limits
the cell types that can be formed from them.
The second drawback is that they need to be frozen and stored to be preserved, and this
costs, which causes issues in terms of availability and access to this source of stem cells.
The benefits of using this source of stem cells are that they are easy to obtain, they
will be compatible with the donor baby, so there is no risk of rejection by the immune
system.
They also do not raise much ethical concern.
Embryonic stem cells can come from early-stage embryos (from blastocysts).
The drawback is that there is the potential for embryonic stem cells to develop into cancerous
or diseased cells.
There are also ethical considerations with this source of stem cells, as it requires
the destruction of the embryo, and every embryo is a potential human which to some is considered
unethical to cause harm or kill this potential life.
The main benefit of using embryonic stem cells is that they are the largest source of pluripotent
stem cells and because the stem cells are pluripotent, they can also form into any cell
type.
The cells can be removed from embryos that are left over from IVF, from embryos that
would have stopped developing and died regardless.
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