What are stem cells?
Stem cells are the unspecialised cells of the body that have the capacity to self-renew through mitosis and differentiate into a diverse range of cell types.
How many potencies of stem cells are there? What are they?
Three - Totipotent, pluripotent and multipotent.
What are Totipotent stem cells?
Can give rise to all types of cells that make up the human body and also all of the cell types that make up the membranes that surround the foetus (including the placenta).
The master of human cells. Each cell can develop into a human.
What are Pluripotent stem cells?
Can give rise to all types of cells that make up the human body (over 200) but not the cells types that make up the embryonic membranes.
What are Multipotent stem cells?
Cells that have already differentiated but can still form a limited number of other tissues.
What is the source for Totipotent stem cells?
From the first few divisions of the fertilised egg only - early embryo (1-3 days)
What is the source for Pluripotent stem cells?
Cells from a blastocyst (embryo of 5-14 days)
What is the source of Multipotent stem cells?
Found in foetal tissue, blood of the umbilical cord (cord blood) and adult tissue.
What determines the potency of stem cells?
Their stage of development.
i.e. Stem cells of a 1-3 day old embryo are totipotent, whereas the stems cells of a blastocyst are pluripotent and the stem cells of a foetus and adult are multipotent.
What are the differences between embryonic and adult stem cells?
- Embryonic: Pluripotent
- Adult: Multipotent
- Embryonic: Able to differentiate into all cell types except for those that make up the embryonic membranes
- Adult: Thought to be limited to differentiating into the different cell types of their tissue of origin
- Embryonic: Can be grown relatively easily in cell culture
- Adult: Rare in mature cells, harder to isolate and harvest and methods of expanding their quantity in cell culture have not yet been established
Currently believed to be less likely
of initiating rejection
after transplantation as one’s own cells
can be expanded
and then reintroduced into the body
How are stem cells harvested?
A growth factor medicine is taken a few days beforehand
This forces stems cells from the bone marrow into general circulation (mobilisation)
A catheter is placed in each arm and blood is withdrawn
Stems cells are removed and the blood is returned in a process called apheresis
How are stem cells cultured in the lab?
The cells are transferred to a culture dish containing a nutrient solution.
Over a few days the cells divide, spread over the surface of the culture medium, and begin to fill the dish.
At this stage they are removed and placed in several fresh culture dishes.
This subculturing can be repeated many times over a number of months to ensure the cells have the capacity of long-term growth and self-renewal.
A stem cell line is developed and within six months, the 30 cells from the original inner cell mass can developed into cultures containing millions of embryonic stem cells.
The cultures cells can be frozen and made available for research in other laboratories.
Outline the governments response to stem cell research in Australia.
Research Involving Human Embryos Act 2002 permits research on surplus embryos from IVF programs. Researchers must be licensed and there are thorough regulations to ensure ethical standards are observed. Written permission is required of the female (and her partner, where appropriate) for whom the embryo was created.
Prohibition of Human Cloning Act 2002 put a comprehensive ban on human cloning, including for therapeutic purposes. The only legal purpose for human embryo creation in Australia at the time was to achieve pregnancy in a woman.
Both these acts were reviewed in 2005 – it recommended that the present regulatory frameworks be maintained and cloning for therapeutic purposes be allowed under strict ethical regulations.
In December of 2006, The Australian Parliament passed a bill that allows the cloning of human embryos for therapeutic purposes.
What are the potential uses of stem cells?
• Studies of human embryonic stem cells will yield information of the events that occur during human development
• Despite that scientists know that the turning on and off of genes is essential, a goal of this research is to identify the way in which an unspecialised cell begins to differentiate to form tissues and organs
• Some of the most serious diseases, such as cancer and birth defects, arise from abnormal cell division and differentiation. A more complete understanding of the genetic and molecular processes may yield further information as to the cause and potential therapies/cures of such diseases.
• Currently, the need for transplantable tissues and organs far outweighs the available supply. Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat diseases such as Alzheimer's disease, spinal cord injury, stroke, burns, heart disease, diabetes, arthritis etc.
• Tissues developed from a person’s own stem cells would not provoke an immune response when transplanted into the person’s body.
What are some ethical considerations of stem cell research and the uses of stem cells?
- The most promising lines of research involve the use of human embryos. Whilst the stem cells can be cultured in a lab and differentiated into any other cell type, research on human embryos raises many
- ethical questions.
that may result from embryonic stem cell research have the potential
of treating currently incurable diseases
much human suffering
. However, at the same time, we are destroying
human embryos. Thus, in embryonic stem cell research we have a conflict in values
Each of us must make up our own mind
as to which moral principle
is of greater importance: prevention of suffering
or respect for the value of human life