Stem cells are those cells that are capable of self-renewal by cell division to differentiate into other cell types. Thus, a stem cell could create new skin cells, blood cells, neural cells, etc...
Very early in development, all cells in the embryo are stem cells (they can become any cell). But at some point, the embryonic cells are directed to develop or differentiate in a certain direct, some cells differentiating into gut cells, some into skin cells, some into nerve cells and some into heart cells. At this point, they are no longer stem cells and they can only produce similar cells via cell division.
Stem cells however are present in adults. They are found in bone marrow, the skin and in the liver. Such cells allow these organs considerable ability to regenerate and repair damage.
Stem cells are sought as potential cures for Parkinson's Disease, strokes and multiple sclerosis. These are diseases where nerve cells are damaged or destroyed. Nerve cells have very limited ability to regenerate so stem cells would be used to replace the damaged and destroyed cells, hopefully returning full function to the affected individual. Stem cells might also be useful in repairing damage to the muscles of the heart, mitigating the damage of heart attacks or coronary disease.
a) Stem cells have been used as treatments in animals which are paraplegics (nerve impulses can't pass a break in the spinal chord). Early results show that there is some resumption of nerve transmission past the break, allowing limited mobility. Evidently the myelin sheath around the nerves has regenerated allowing some nerve transmittion. Negative side affects have included the sensation of pain due to stimuli that would normally not be painful.
b) Treatement of Juvenile-onset Diabetes: Transplants of pancreas tissues (from deceased donors) to persons with this disease allows production of insulin. There are insufficient donors for this process so the ability to stimulate embryonic stem cells to differentiate into insulin-secreting cells is being sought.
c) Bone marrow transplants: Hematopoietic stem cells (HS cells) are found in bone marrow. These stem cells normally divide in the bone marrow to create new red and white blood cells. They have remarkable powers of cell division. Just 100 HS cells can replace the blood system of a mouse whose entire bone marrow has been destroyed by radiation or chemotherapy. Diseases such as leukemia, multiple myeloma, SCID (severe combined immune deficiency) and lymphoma can be treated via this method. If the HS cells of the patient are still normal, some will be removed. The bone marrow is then destroyed, killing normal cells as well as any cancer cells. The HS cells are then transplanted back to the marrow to grow. In that way, only normal blood cells will be in the blood system, curing the patient. In some cases, HS cells from the bone marrow of suitable donors will be used if the HS cells of the patient are deficient.
| Embryonic Stem Cells | Adult Stem Cells |
|---|---|
| Currently much easier to obtain than adult stem cells. | No embryo needs to be destroyed (typically happens with embryonic stem cells). |
| Almost unlmited growth potential (much more so than adult stem cells) . | No rejection. Cells are fully compatible with tissues of the adult when their own adult stem cells are used. |
| Less chance of genetic damage than with adult stem cells. | Less chance of malignant (invasive & spreading) cancers forming. |
| Greater ability to differentiate into a wide variety of cell types than adult stem cells. |
| Embryonic Stem Cells | Adult Stem Cells |
|---|---|
| An embryo currently needs to be destroyed. (Ethics & Morality: Should embryos be afforded the same protections as adults?) | Less ability to differentiate into the needed cells. |
| Greater chance of malignant cancers. | Greater chance of genetic damage. |
| Chance of rejection. Cells are fully compatible with tissues of the individual receiving embryonic stem cells. | Currently much more difficult to obtain. |
| Limited growth potential. |
Human Skin Cells Reprogrammed into Embryonic Stem Cells (ScienceDaily: Feb. 12, 2008)
Embryonic stem cells (ScienceDaily)
Stem cells (Widipedia)