Stem cells can be categorized based on their potential to differentiate into other types of cells.
Embryonic stem cells are the most potent, as they can differentiate into every type of cell in the body.
The different types of stem cells based on their ability to differentiate are:
Totipotent: These stem cells can differentiate into all possible cell types. The first few cells that appear as the zygote starts to divide are totipotent.
Pluripotent: These cells can turn into almost any cell. Cells from the early embryo are pluripotent.
Multipotent: These cells can differentiate into a closely related family of cells. Adult hematopoietic stem cells, for example, can become red and white blood cells or platelets.
Oligopotent: These can differentiate into a few different cell types. Adult lymphoid or myeloid stem cells can do this.
Unipotent: These can only produce cells of one kind, which is their own type. However, they are still stem cells because they can renew themselves. Examples include adult muscle stem cells.
Embryonic stem cells are considered pluripotent instead of totipotent because they cannot become part of the extra-embryonic membranes or the placenta.
Uses
Stem cells themselves do not serve any single purpose but are important for several reasons.
First, with the right stimulation, many stem cells can take on the role of any type of cell, and they can regenerate damaged tissue, under the right conditions.
This potential could save lives or repair wounds and tissue damage in people after an illness or injury. Scientists see many possible uses for stem cells.
Tissue regeneration
Tissue regeneration is probably the most important use of stem cells. Classically, for a kidney transplant, one had to wait for a donor. Since there is a shortage of donor organs, stem cells can be directed to differentiate in a certain way to grow a specific tissue type or organ.
For example, doctors have already used stem cells from just beneath the skin’s surface to make new skin tissue and repair a severe burn or another injury by grafting this tissue onto the damaged skin to grow new skin.
Cardiovascular disease treatment
In 2013, a team of researchers from Massachusetts General Hospital had created blood vessels in laboratory mice using human stem cells1. Within 2 weeks of implanting the stem cells, networks of blood-perfused vessels had formed. The quality of these new blood vessels was as good as the nearby natural ones. This technique could eventually help to treat people with cardiovascular and vascular diseases.
Brain disease treatment
Stem cells may replace damaged cells and tissues in brain diseases, such as Parkinson’s and Alzheimer’s. In Parkinson’s, damage to brain cells leads to uncontrolled muscle movements that could be replenished by healthy stem cells and lead to the arrest of uncontrolled muscle movements.
Cell deficiency therapy
Scientists hope one day to be able to develop healthy heart cells in a laboratory that they can transplant into people with heart disease.
These new cells could repair heart damage by repopulating the heart with healthy tissue.
Similarly, people with type I diabetes could receive pancreatic cells to replace the insulin-producing cells that their own immune systems have lost or destroyed.
The only current therapy is a pancreatic transplant, and very few pancreases are available for transplant.
Blood disease treatments
Adult hematopoietic stem cells are being used to treat diseases, such as leukemia, sickle cell anemia, and other immunodeficiency problems.
Hematopoietic stem cells occur in blood and bone marrow and can produce all blood cell types, including red blood cells that carry oxygen and white blood cells that fight disease.
Donating or harvesting stem cells
Stem cells can be donated to help a loved one, or possibly for one’s own use in the future.
Donations can come from the following sources:
Bone marrow: These cells are harvested under a general anesthetic, usually from the hip or pelvic bone. Technicians then isolate the stem cells from the bone marrow for storage or donation.
Peripheral stem cells: Several injections are given that cause the bone marrow to release stem cells into the blood. Next, blood is removed from the body, a machine separates out the stem cells, and the blood can be returned to the body.
Umbilical cord blood: Stem cells can be harvested from the umbilical cord after delivery, with no harm to the baby. Some people donate the cord blood, and others store it. This harvesting of stem cells can be expensive, but the advantages for future needs include:
the stem cells are readily accessible
less chance of transplanted tissue being rejected if it comes from the recipient’s own body.
Research and scientific discovery
Stem cells are useful not only as potential therapies but also for research purposes.
For example, scientists have found that switching a particular gene on or off can cause it to differentiate. Knowing this is helping them to investigate which genes and mutations cause which effects. This will help in discovering what causes a wide range of illnesses and conditions, some of which do not yet have a cure.
Abnormal cell division and differentiation are responsible for conditions that include cancer and congenital disabilities that stem from birth. Understanding the mechanisms for the loss of controlled division could lead to a cure.
Stem cells can also help in the development of new drugs. Instead of testing drugs on human volunteers, tissue grown from stem cells may provide the model for testing.
1Kusuma S, Shen YI, Hanjaya-Putra D, Mali P, Cheng L, Gerecht S. Self-organized vascular networks from human pluripotent stem cells in a synthetic matrix. Proceedings of the National Academy of Sciences. 2013 Jul 30;110(31):12601-6.
