Stem Cell classification
Because of stem cells' versatility and unlimited potential, they are future of regenerative medicine. The special cells are able to transform into different kinds of cells to renew and repair tissue. There are many different types of stem cells, and each one works in different ways to improve the health of an individual.
Stem cells are characterized by their two unique qualities: they are undifferentiated cells that can develop into a variety of specialized cells and they are "capable of dividing and renewing themselves for long periods."
POTENCY
Stem cells have different levels of potency, which is the ability to differentiate into other types of cells. The cells are classified into a continuum of potency based on the degree in which they can differentiate.
TOTIPOTENT - Totipotent stem cells can develop into any kind of specialized cell and can create a fully functional organism. They are the most versatile and are produced when a sperm and egg cell combine. The resulting zygote and its first few divisions are totipotent cells.
PLURIPOTENT - Pluripotent stem cells can develop into nearly any cell type, including all tissues. Unlike totipotent cells, they cannot create an entire organism. Pluripotent cells include embryonic stem cells from the three germ layers: endoderm (stomach lining, gastrointestinal tract, lungs), mesoderm (muscle, bone, blood, urogential) and ectoderm (epidermal, nervous system).
MULTIPOTENT - Multipotent stem cells can develop into a range of cells that are closely related to each other, like within a tissue type. For example, hematopoietic cells, multipotent blood stem cells, can differentiate into red/white blood cells or platelets, but not skin cells. Multipotent cells are found in adipose tissue, cardiac cells, bone marrow and wisdom teeth.
OLIGOPOTENT - Oligopotent stem cells can develop into only a few types of cells. They include lymphoid, myeloid and vasular stem cells. For example, lymphoid cells can become B and T cells, but not red blood cells.
UNIPOTENT - Unipotent stem cells can only produce one type of cell. They are able to make cells like their own, but are distinguished from other cells by their ability of self-renewal. Unipotent cells include muscle stem cells.
TYPES
The two major types of stem cells are embryonic and adult stem cells. Other types include induced pluripotent stem cells (IPSCs) and cord blood stem cells.
EMBRYONIC STEM CELLS
Embryonic stem cells are obtained from the inner cell mass of the blastocytes of early embryos. The embryos are from eggs donated in an in vitro fertilization clinic, not from eggs fertilized in a woman's body. They are pluripotent stem cells, so they can develop into nearly any cell type, but they require specific signals and conditions to differentiate into the desired type. If they are transplanted into a patient without these signals, they may uncontrollably develop into different cell types, creating a teratoma (a tumor) or the patient's immune system may reject the foreign stem cells.
To grow embryonic stem cells, scientists transfer the cells onto a dish with a culture medium. This process is called cell culture. The inner surface of the dish is coated with mouse embryonic skin cells, which are treated so they will not divide. These feeder cells release nutrients into the medium and provide an anchor for the stem cells. If the embryonic stem cells have successfully divided, they will be plated onto another dish and the process will be repeated. Embryonic stem cells can also be made through therapeutic cloning, where a patient's cells' nuclei are inserted into an egg cell with its nucleus removed. The nucleated egg cell then divides until it reaches the blastocyst stage, when the inner mass is removed and cultured just like normal embryonic stem cells.
Although embryonic stem cell therapy has potential, it is still in the early stages of research - no medical treatments have been accepted yet. Also, since it involves destroying an early embryo, there have been many ethical and moral issues surrounding embryonic stem cells.
 Embryonic Stem Cells |
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 Growing Embryonic Stem Cells |
 Therapeutic Cloning |
ADULT STEM CELLS
Adult stem cells, also known as somatic stem cells, are naturally found in human bodies. They are the most commonly used stem cell type in therapies and treatments and are found in organs and tissues all throughout the body, including the brain, blood, heart and skin.
The adult stem cells are multipotent, so they only can develop into the cells of the tissues from which they originated. They can be used to repair and renew organs and tissues and they are less likely to be rejected after transplanation, especially if the adult stem cells were from the patient's own body. Since the adult stem cells are found in small quantities, laboratories grow them using cell culture.
INDUCED PLURIPOTENT STEM CELLS
IPSCs are adult stem cells that have been converted into pluripotent stem cells. The technique of creating IPSCs by introducing new genes to reprogram the adult stem cells was developed in 2006. The IPSCs are able to develop into nearly any cell type in the body, just like embryonic stem cells, without most of the ethical and rejection concerns. However, the viruses that introduce the programming factors in the adult stem cells may cause cancer.
Scientists are currently researching new methods of reprogramming the stem cells and using IPSCs in humans. IPSCs have the potential to be used throughout the body in many different revolutionary medical treatments.
CORD BLOOD STEM CELLS
Cord blood stem cells are a type of adult stem cells. They are isolated from the umbilical cord blood of a newborn baby, since the blood is rich in multipotent hematopoietic stem cells. The hematoipoetic cells can develop into different types of blood cells, including red/white blood cells and platelets. Both public and private cord blood banks have been established to preserve the babies' umbilical cord blood for future use. Controversy concerning private cord blood banks has arisen because of the possiblity of using diseased or unsuccessful cord blood.
Learn about the challenges of stem cells research here
Learn about the history of stem cells here