While the potential of stem cells to become and replace almost any of the body's cells holds the promise of a cure for numerous serious injuries and degenerative diseases, developing therapies using stem cells has been slower than many hoped.
Current Approved Treatments
Currently, the only approved therapies that use stem cells are hematopoietic stem cell transplants and reconstituted skin for burns. Actually, though, both of these therapies predate the recent focused research efforts to develop stem cell technology.
Hematopoietic Stem Cell Transplants
Primarily used to treat leukemia and lymphoma, hematopoietic stem cell transplants (HTSC) are really an extension of bone marrow transplants started 60 years ago. Scientists realized then that bone marrow, the liquid center of the bones, produced the billions of new blood cells required daily to replenish the circulatory system. The new blood cells are formed from hematopoietic cells—blood-forming stem cells that can become red blood cells, platelets, or one of the several white blood cells cells.
Bone marrow can be harvested from the sternum and processed to remove blood and bone fragments then stored for later injection into the patient. Nowadays, though, rather than harvesting bone marrow, typically hematopoeitic cells are filtered directly from the donor's circulating blood in a procedure known as apheresis. Hematopoietic cells can come from a closely matched donor or the patient themselves before their cancer is treated. Also, cells can be isolated from a patient's umbilical cord blood if it was stored when they were born. However it is done, the harvested hematopoietic cells are then injected into the patient's blood after radiation treatment, and they make their way back to the bone to grow and produce new blood cells.
Laboratory Grown Skin Grafts
Growing laboratory cultivated skin grafts occurred in 1983 at Boston Shriners Burn Hospital for Children when two young brothers with burns covering over 90% of their bodies were treated using them. Growing skin grafts starts with some of the main type of skin cells, keratinocytes, from the patient, then uses specialized cell culture techniques in the lab to grow layers of new skin. Genzyme now provides skin tissue grown using this technique as EPICEL cultured epidermal autografts.
It wasn't until several years later that researchers understood the skin could be grown because some of the keratinocytes are actually adult skin stem cells. This realization initiated research on improving the method, and have opened the door to innovative approaches such as the skin stem-cell gun.
Bogus Claims and Unproven Stem Cell Treatments
While routine clinical use of stem cells has only been approved for the two treatments mentioned above, there are a number of companies that have started removing adult stem cells, concentrating them, and reinjecting them into a patient and calling it "stem cell therapy." These are not FDA approved treatments but, since they are done with the patient's own cells, it is not clear they need to be regulated by the FDA—at least that is what the clinics argue.
There is no published scientific evidence these procedures have any benefit. It remains to be seen if they will be able to continue this practice without regulation—at least to the degree of providing proof of some benefit for the risk they encourage patients to take. In the meantime, they contribute little to advancing stem cell technologies since they work outside generally accepted scientific procedures for developing and evaluating new treatments.
Reliable Stem Cell Treatments in Development
While there is no proven therapeutic value to support the clinics that remove and reinject adult stem cells, there are a number of bona fide adult stem-cell trials that are in fact showing promising results. Companies such as Aastrom and Mesoblast, developing treatments to treat cardiovascular disease, BrainStorm developing treatments for neurologically diseases, and Histogenics developing treatments for cartilage and ligament repair are all working with adult stem cells.
Adult Stem Cell Limitations
Adult stem cell treatments appear to be making significant headway but the ability of these cells is limited. They can only develop into a limited number of cells. They may be the basis for excellent tissue repair therapies but, for example, may not be able to regrow functional organ parts, such as elements in the eye, or repair complex tissues for which adult stem cells don't exist, such as neural pathways. For these treatments, researchers continue to work with more pluipotent cells, such as embryonic stem cells and induced stem cells. Progress with these cells has been slower because the science is more challenging.
Embryonic and iPS Stem Cells Treatments
Only two trial therapies using embryonic stem cells have been approved by the FDA. The first, started by Geron in July 2010, involved using embryonic stem cells to repair spinal injury. However, after injecting 4 patients with cells for phase I trials, Geron decided to cease the trial and focus on its four cancer drugs. The decision seems to be have been made mainly for financial reason but it was blow to embryonic stem cell research.
The second approved trial with embryonic stem cells, the only currently active one, involves using retinal pigment epithelial cells produced by Advanced Cell Technologies from embryonic stem cells to correct macular degeneration of the eye. In July of 2012, the company received notice that it could double the number of cells used per patient. These cells are being tested on three different patient profiles and the status of the trial can be found at clinicaltrials.gov.
An alternative to embryonic stem cells are induced pluripotent stem cells (iPS cells), which are made in the lab by genetically reprogramming normal body cells from skin, blood, or other tissue. Currently, these are primarily used for basic research but, since they could be made from a patient's own cells in essentially unlimited amounts, they may be uniquely suited for some therapies. For example, there are focused efforts looking at these cells for neurological disorders, and immune diseases.