In a previous article I discussed what stem cells (SCs) are… they are blank slate cells. And I discussed the various properties they have. They can divide and renew themselves; they are unspecialized, meaning they have not yet become a specific tissue type; and they are capable of becoming specialized cell types.
Also, when placed in certain environments with special stimuli, they can be induced to become specific organs.
I also discussed the various types of SCs used such as embryonic stem cells, donor (allogeneic SCs), and finally autologous SCs, also known as “repair” SCs.
Autologous SCs are often referred to as adult SCs because they have fully differentiated into a particular type of tissue.
These cells have been found in a number of locations including bone marrow, central nervous system, blood, muscle, baby teeth, periosteum of bone, skin, and intestine.
In the adult, they function as tissue repair and maintenance cells traveling to areas of injury to help with the healing process. The process that makes this possible is the proliferation effect. SCs can multiply and renew themselves almost indefinitely.
There a number of different sources of SCs in the adult. Usually, adult SCs tend to differentiate into the tissue of origin. These include:
• Hematopoietic cells which become different types of blood cells.
• Mesenchymal cells which lead to connective tissue. These are the ones that have found the most utility so far in conditions such as osteoarthritis.
• Neural SCs that become cell types found in the central and peripheral nervous system.
• Digestive system cells that form various cells in the gut.
• Skin SCs that lead to various parts of the skin and subcutaneous tissue.
Some recent experiments suggest that adult SCs can be programmed to become cells of a different organ system. This process is called “transdifferentiation.” What causes this to occur and the exact limitations invoked on the adult stem cell as far as how much they can differentiate is still open to conjecture.
What is clearly understood so far is that adult SCs do not have the pluripotent capabilities of embryonic SCs.
As mentioned in a previous article, one type of cell that seems to fall midway between the embryonic SC and the autologous adult SC is the induced pluripotent SC.
These are adult cells that have been genetically altered so that they are to possess many of the properties of embryonic SCs.
Clearly much work remains to try and figure out the best way to use SCs in clinical medicine as well as in research.
One big question: are these cells transplantable… in other words, can they be used as donor tissues, like donated organs?
How much repair are they capable of? What is the length of time they will be functional?
The application of autologous SCs to arthritis will be the topic of future articles.
A much more in depth discussion of the emerging science of stem cells can be found at stemcells.nih.gov