Key information contained on this page covers the following areas:

• Summary
• Stem Cells: A definition
• Sources of stem cells
• What are the differences betwen human embryonic stemcells (hESC) and adult stem cells?

 

By clicking on the subheadings above you can jump to the relevant section of the page.

 

 

Summary

The main forms of stem cells

 

The above table has been created with reference to the BBSRC funded publication “Stem Cells: Science & Ethics”.

 

Scientists use three main types of stem cells:

• Pluripotent stem cells – These are stem cells which can generate all of the different cell types found in the body. Human embryonic stem cells (hESC) are perhaps the most well known and discussed type of pluripotent stem cell. hESC cells are obtained from early-stage embryos.
• Tissue stem cells – These stem cells are often termed adult stem cells but amongst the scientific community it is often felt that this is a less accurate term to use. These stem cells are found in many organs and tissues in the body, including bone marrow, blood, cornea, retina, intestine, muscle, nervous system, brain, and skin. They are also found in developing organs in the fetus, umbilical cord and placenta.
• Induced pluripotent stem cells – Reprogrammed specialised cells so that they become pluripotent, thereby losing their specialist functioning and start to behave in the same way as embryonic stem cells.

 

Stem cells: A definition

Many different definitions have been offered with regard to what stem cells are. However, perhaps one of the most helpful and precise definitions is one proposed by David A. Prentice, Professor of Medical and Molecular Genetics at Indiana State University. He defines stem cells as:

“cells that can proliferate with almost unlimited potential, maintaining a pool of growing and dividing cells, with the added ability that some of the daughter cells can differentiate into specific cell types.”

The usefulness of this definition in comparison to others is that it draws attention to the significance to the unique capacity of stem cells to constantly renew themselves at the same time as being able to adapt to the specific cell types needed by the human body.

It is these key properties that distinguish stem cells from other cell types.

The great attraction of stem cells is that genetically matched stem cells offer the exciting possibilities of discovering remarkable medical treatments for various diseases. Blood, skin, muscle and brain cells could be grown in the laboratory and implanted into the human body without any risk of them being rejected by the body given the fact that they are genetically matched to the patient. Anti-rejection treatment would also be no longer required.

 

Sources of stem cells

The human body offers a multitude of sources from which to obtain stem cells, therefore the key problem is not so much where to obtain stem cells but rather in isolating them from their source.

Scientists have identified several key “ready made” sources of stem cells which are often referred to as “reservoirs”. These include the following:

• Blastocysts – embryos after six days of growth.
• Early embryos created by human cloning
• Fetal tissue
• Adult of child tissue
• Adult or child cells that can be grown into stem cells

 

What are the differences between human embryonic stem cells (hESC) and adult stem cells?

It is generally perceived that adult stem cells and human embryonic stem cells can be differentiated between on the basis of their potential.

The key advantage with embryonic stem cells is their pluripotency. They have the ability to differentiate into all the cells present in the human body.

On the other hand, adult stem cells are multipotency, meaning that they can only differentiate into a limited number of cells.

However, research published in an edition of the Journal of Neuroscience Research and the American Journal Science in April 2000, revealed that adult stem cells could be grown into liver or nerve tissue and that human adult stem cells are of “generalised potential”.

Moreover, there has been further breakthrough research in the field of “induced pluripotent” stem cells (IPS). These IPS cells are adult stem cells that have been reprogrammed to act like hESCs (BBC News report 2007- “Skin transformed into stem cells”).

Consequently, adult stem cells are now considered by the majority of scientists to be pluripotent in the same way that hESC have been.