Research on stem cells is leading scientists to investigate the possibility of cell-based therapies to treat disease, which is often referred to as regenerative medicine.
Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods of time through cell division. The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions.
There are two different sources of stem cells. Embryonic cells are derived from fetal tissue and are a source of great controversy. Adult stem cells (ASC), on the other hand, are found in normal people.
ASC can renew themselves, and can differentiate to yield the major specialized cell types of the tissue or organ. Their primary role in a living organism is to maintain and repair the tissue in which they are found.
Research on adult stem cells has recently generated a great deal of excitement. Scientists have found adult stem cells in many more tissues than they once thought possible. This finding has led scientists to ask whether adult stem cells could be used for transplants. In fact, adult blood forming stem cells from bone marrow have been used in transplants for 30 years. Certain kinds of adult stem cells seem to have the ability to differentiate into a number of different cell types, given the proper conditions.
Bone marrow derived stem cells give rise to a variety of cell types: bone cells (osteocytes), cartilage cells (chondrocytes), fat cells (adipocytes), and other kinds of connective tissue cells such as those in tendons.
According to information from the National Institutes of Health, “One of the fundamental properties of a stem cell is that it does not have any tissue-specific structures that allow it to perform specialized functions. Unlike muscle cells, blood cells, or nerve cells-which do not normally replicate themselves-stem cells may replicate many times.
When cells replicate themselves many times over it is called proliferation. A starting population of stem cells that proliferates for many months in the laboratory can yield millions of cells.”
The process by which unspecialized stem cells become specialized cells is called differentiation. Adult stem cells typically generate the cell types of the tissue in which they reside. A blood-forming adult stem cell in the bone marrow, for example, normally gives rise to the various types of blood cells such as red blood cells, white blood cells and platelets. Until recently, it had been thought that a blood-forming cell in the bone marrow could not give rise to the cells of a very different tissue.
However, a number of experiments over the last several years have raised the possibility that stem cells from one tissue may be able to give rise to cell types of a completely different tissue. This phenomenon is referred to as “plasticity.”
Two research presentations this past year shore up the promise of stem cells in arthritis. First, research presented in April 2008 at the UK National Stem Cell Network Annual Science Meeting in Edinburgh offered hope that stem cells may be harnessed to repair the damaged cartilage that is one of the main symptoms of osteoarthritis.
On a related note, scientists at Cardiff University in the United Kingdom have successfully identified stem cells within articular cartilage of adults, which have the ability to become chondrocytes, cells that make up cartilage. The team has even been able to identify the cells in people over 75 years of age.
Lead researcher Professor Charlie Archer from the Cardiff School of Biosciences said:
“This research could have real benefits for arthritis sufferers and especially younger active patients with cartilage lesions that can progress to whole scale osteoarthritis.”
According to Dr. Nathan Wei, a rheumatologist and clinical investigator in Frederick, Maryland, “We are focusing our efforts on adult autologous stem cells (“autologous” meaning derived from the patient himself). These cells are present within a patient’s bone marrow. Once we obtain the stem cells, they need to be concentrated using special techniques in order to secure the number of stem cells per unit volume needed. We have been using this treatment, combined with growth factors obtained from other cells, for both osteoarthritis of the knee as well as the hip. Preliminary results using both subjective as well as objective measures show much promise. If these results are validated, the springtime of your life when it comes to weight-bearing joints may actually be 55-75.”