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Date:   6/23/2006 10:07:59 AM ( 18 y ago)

While "stem cells" have become a commonplace term in the news today, many people only have a vague idea of what stem cells are, where they come from and what they do. Below we have put together a simple guide on stem cells.

We encourage those who wish to learn more to read the excellent information at the U.S. government's National Institutes of Health site.


Stem Cell Fact Sheet

What are stem cells?

Stem cells are special cells that can turn into many different cell types in the body such as heart muscle cells, brain cells, and skin cells.

Where do stem cells come from?

Stem cells for therapeutic use can be obtained from three potential sources:

Embryonic
Certain Adult Tissues
Umbilical Cord Blood
How many kinds of human stem cells are there?

There are two kinds of stem cells.[1]

Adult Stem Cells - a supply of stem cells that can multiply when needed to repair adult organs and tissue. Adult stem cells are found in the human body and in umbilical cord blood. The most well known source of adult stem cells in the body is bone marrow but they are also found in many organs and tissues; even in the blood
Embryonic Stem Cells - cells found early (less than 2 wks.) in the development of an embryo that can progenerate a developing fetus and ultimately a human baby


What are the differences between embryonic, fetal and adult stem cells?

All stem cells have the ability to divide into more cells that can either remain a stem cell or begin changing into another kind of cell such as a red blood cell or a nerve cell. The change from stem cell to another kind of cell happens in many steps. After each step, the stem cell's "assignment" [2] becomes more specialized.


Example of embryonic cell becoming a blood cell:



Step 1. Embryonic Stem Cell (Could become anything)
Step 2. Adult Stem Cell (Assigned to become a vascular system cell or a kind of nerve cell)
Step 3. Vascular Stem Cell (Assigned to become a blood cell or a blood vessel cell)
Step 4. Blood Cell



Normally, stem cells become more specialized. In humans and other mammals, these developmental events are irreversible, and in this sense, cell development resembles a family tree.

However, "reassignment" has been observed in embryonic cells. For example, an embryonic stem cell that has already been assigned to become a brain cell somehow becomes a blood cell instead. [3]

There is some evidence suggesting that adult stem cells also have this ability. An adult stem cell that has been assigned to become a vascular system cell may, in fact, reassign to become a kind of nerve cell under the right conditions. This has not yet been proven conclusively.

Embryonic stem cells are the most versatile because they can become any cell in the body including fetal stem cells and adult stem cells
Adult stem cells are more specialized since they are assigned to a specific cell family such as blood cells, nerve cells, etc.
Advantages, Disadvantages and Ethical Issues of Stem Cells

Embryonic Stem Cells

Advantages

Because they have the potential to become any cell in the human body, embryonic stem cells are commonly considered to hold the most promise for treating disease and replacing tissue and cells
Large numbers can be easily grown in the laboratory
Disadvantages

Safety and effectiveness in humans has not yet been determined
Because they have the potential to become any cell in the human body, they are difficult for scientists to control
They can grow out-of-control forming tumors.
They can change into unintended types of cells in the body. For example cells intended to become liver cells may become pancreatic cells
The Patient's immune system rejection of embryonic cells has yet to be overcome
Ethical Issues

Many people oppose embryonic stem cell research because they believe that once formed, the embryo is a human life that should not be destroyed. This is a very significant political, moral, and religious issue for many
Adult Stem Cells

Advantages

Have been safely used in humans for over 30 years
No danger of immune system rejection with cells from the patient's own body
Extremely low risk of tumor growth
Easier to control than embryonic cells
Disadvantages

Present in the body in very small numbers [4]
More limited in what they can become than fetal or embryonic cells
More difficult to grow in the laboratory
Ethical Issues

No significant ethical issues

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[1] For simplicity, this fact sheet treats umbilical cord blood stem cells and fetal stem cells as adult stem cells and embryonic stem cells respectively.

[2] The technical term for this progression is differentiation.

[3] The technical term for this transformation is plasticity .

[4] VesCell™ has overcome this obstacle



 

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