Primer on stem cell research
The promise and potential of stem cell therapy
In 1998, scientists isolated pluripotent stem cells from early human embryos and grew them in culture. In the few years since this discovery, evidence has emerged that these stem cells can become almost any of the 350 known specialized cells of the body. This unprecedented discovery led to the notion that stem cells can repair or replace cells or tissues that are damaged or destroyed by disease and injuries.
There is tremendous expectation for stem cell therapy. However, it is too soon to say just how or when stem cells will be recognized as standard treatment for disease or trauma, but research and some clinical trials are beginning to show promise.
Below is a primer on stem cells terminology to provide a brief outline on the different stem cell types and properties that are being studied by researchers.
A stem cell from the embryo, fetus, or adult that, under certain conditions, has the ability to reproduce itself for long periods or, in the case of adult stem cells, throughout the life of the organism. A stem cell can give rise to specialized cells that make up the tissues and organs of the body.Essentially, a stem cell can develop or be coaxed into becoming a different cell type in which it assumes the role of those respective cells (i.e. red blood cell, nerve cell, brain cell, muscle cell, etc.).
Pluripotent stem cell
A pluripotent stem cell can develop and self-replicate, from the embryonic germ layers in which all cells of the body arise.
Induced Pluripotent Stem Cells (iPSCs)
Until recently the only known sources of human pluripotent stem cells were human embryos or certain kinds of fetal tissue. In 2006, scientists in Japan discovered a way to genetically reprogram skin cells to become very similar to embryonic stem cells. Since these cells are specific to the donor, this increases compatibility for a variety of uses with therapies, thus forming the basis for personalized medicine.
However, as with embryonic stem cells, researchers do not fully understand how iPSCs are locked into their cell lineages.
The good news is that research is moving quickly. iPSCs are being tested experimentally in numerous disease models, including SCI. Moreover, iPSCs are also being used widely as tools to model disease states in a culture dish, providing a unique way to screen therapeutic agents and understand the impact of specific interventions.
Embryonic stem cell
Embryonic stem cells, as their name suggests, are derived from embryos that develop from eggs which have been fertilized in vitro in a fertilization clinic and then donated for research purposes with informed consent of the donors. They are not derived from eggs fertilized in a woman's body.The current challenges include direct differentiation of embryonic stem cells into specialized cell populations and developing approaches to control replication or growth once placed in people. Uncontrolled, these cells can form teratomas, a benign form of cancer.
It’s important to remember that stem cells are unspecialized, meaning they are not structured to carry out specialized functions like red blood cells (carry oxygen). What stem cells can do, however, is give rise to specialized cells (i.e. muscle or nerve cells).
Differentiation is the process by which an unspecialized cell (such as a stem cell) specializes into one of the many cells that make up the body. During differentiation, certain genes become activated and others are inactivated in an intricately regulated fashion.
Adult stem cell
An adult stem cell is an undifferentiated (unspecialized) cell that is found in differentiated (specialized) tissues or organ and can renew itself. When an adult stem cell renews itself, it becomes specialized to maintain and repair the tissue in which it is found.Adult stem cells are capable of making identical copies of themselves for the lifetime of the organism. These cells have been identified in brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian epithelium, fat and testis.
Progenitor or precursor cell
This type of cell can occur in fetal or adult tissues and is partially specialized. When a progenitor/precursor cell divides, it can form similar cells or it can form two specialized cells, neither of which is capable of replicating itself.
Somatic cell nuclear transfer
Somatic cell nuclear transfer (also known as therapeutic cloning) involves removing the nucleus of an unfertilized egg cell, replacing it with the material from the nucleus of a "somatic cell" (i.e. skin, heart, or nerve cell), and stimulating this cell to begin dividing. Stem cells can be extracted five to six days later.
National Institutes of Health: Stem Cell Basics
Intended for anyone who wishes to learn more about the biological properties of stem cells, the important questions about stem cells that are the focus of scientific research, and the potential use of stem cells in research and in treating disease.
International Society for Stem Cell Research (ISSCR)
An independent nonprofit organization and the voice of the stem cell research community. The ISSCR was founded in 2002 to foster the exchange of information on stem cell research and now claims more than 4,100 members worldwide.