A Russian scientist, Alexander Maximov, found out in 1908 that blood cells could originate from only one cell type which he named stem cells. He suggested that some triggers were responsible for making these cells differentiate into different types of cells which were found in blood. It was however in the 1960’s, that scientists were really able to prove, using mice; that some cells were self renewing. Since then; several milestones have been reached in this revolutionary branch of science.
The raging debate and legal battles over “stem cell research” have led to many people wondering what exactly these are; and what they can be used for. Simply put; stem cells are cells which are capable of regenerating themselves and can differentiate into specialized cells like for example blood cells. Stem cells are grouped into three different types.
Adult stem cells
Adult stem cells are undifferentiated (unspecialized) cells found in the tissues and organs of both young and adult animals. These cells can be called “maintenance cells”; and are triggered to differ into specialized cell types within that tissue or organ. This is particularly useful for repair of damaged cells or replacement of worn out cells in tissues and organs. A good example of this is epidermal skin cells, which are self-renewing. Adult stem cells in the blood also produce new blood cells, and bone marrow cells have been used to help treat leukaemia. Adult stem cells are also found in the heart, blood, intestines, bone marrow among others. More emphasis is laid on mammals and other animals kept for research purposes.
Adult stem cells are found among specialized cells of a tissue or organ; in an area known as “niches”. They are surrounded by “niche cells” which transmit signals for the adult stem cells to differentiate when needed.
Click here for a video on stem cell niches from the Genetic Science Learning Center at the University of Utah.
Cord blood stem cells
Cord blood stem cells are unique because they are found in the umbilical cord of newborn babies. The umbilical and placental blood of newborns has been found to contain stem cells which are haematopoetic (capable of producing new blood cells). These stem cells are similar to the ones found in the bone marrow and give rise to red and white blood cells, as well as platelets. Cord blood stem cells have become very popular and are being used to treat blood diseases and disorders, as well as genetic and nervous system disorders. Techniques are currently being developed in order to treat diabetes, brain injury among others. As a result, cord blood stem cells are being banked. They are collected after a child is born, isolated from the blood, frozen in liquid nitrogen and kept until needed. This enables parents to “bank” stem cells to treat genetic and other diseases as they arise in their children and close relatives. This is helpful because it reduces the risk of rejection of the stem cells by the body of the recipient since it is likely to be a close match. Cord blood stem cells cannot however be used to treat genetic disorders in the same person (autologous) as these cells will still carry the same genetic defect.
Embryonic stem cells
Embryonic stem cells, as their name suggests, are obtained from embryos which are ultimately sacrificed since it is the cells in the developing embryo that are used. However, they are derived form fertlised eggs from in-vitro fertilization treatments. Most of these are actually “excess cells” which would have been disposed of. They are isolated from the inner cell mass of the blastocyst or fertilized egg which is about 5 days after it has been fertilized, but isolating the inner cell mass destroys the embryo. This has caused a lot of controversy over whether it is right to “harvest” cells from something that could become a full adult human being.
Embryonic stem cells are in very high demand because they can differentiate into virtually every kind of cell found in the body and they are capable of regenerating indefinitely making them easy to culture in the laboratory for future use. They can be used to treat a variety of diseases; including genetic diseases, neurological disorders, cancers, tissue replacements, grafts among others.
Genetic Science Learning Center (2011). Go Go Stem Cells.Learn.Genetics. Retrieved February 22, 2011, from http://learn.genetics.utah.edu/content/tech/stemcells/sctypes/
Michelle Kerns ( ) (The history of stem cell discovery) Retrieved February 22, 2011 from: http://www.ehow.com/about_5606644_history-stem-cell-discovery.htm
Rippon, H.J., Bishop A.E. (2004). Embryonic stem cells in: Cell Proliferation. 37, 1
U.S. Department of Health and Human Services (2010). Stem Cell Basics: What are adult stem cells? In Stem Cell Information. Retrieved February 22, 2011 from: http://stemcells.nih.gov/info/basics/defaultpage.asp