Educational Resources

What are stem cells?



Stem cells are unspecialized cells that can renew themselves through cell division for long periods of time. Under specific conditions (physiological or experimental), stem cells can mature into specialized cell types such as muscle cells, nerve cells, bone cells etc. 

Where do they come from? 


We all have stem cells and they are necessary for our survival. For example, skin stem cells renew and repair our skin. Cells in our bone marrow generate the different cell types in our blood. The stem cells in our bodies are adult stem cells—unspecialized cells found in a tissue or organ that can yield all the specialized types of cells of that tissue or organ. The term “adult stem cells” is misleading because babies and children have them as well. 

Adult stem cells are also referred to as multipotent stem cells. Multipotent means that they can only generate the cell types in the particular organ in which they are found. However, some studies suggest that under certain conditions adult stem cells may be able to give rise to cell types of other tissues as well. Another source of multipotent stem cells is umbilical cord blood. Stem cells that have the potential to generate the cell types in any organ or tissue in the body are called pluripotent. 

Embryonic stem cells are pluripotent. Embryonic stem cells come from a blastocyst—a small sphere of cells that results from cell division in a fertilized egg. For research purposes, cells are harvested from the inner cell mass of the blastocyst when it is approximately six days old and consists of around 200 cells.

How can stem cells be used to treat disease?

Researchers are exploring two main avenues for using stem cells to treat disease.

  1. Stem cells as “replacement parts.” A wide range of diseases (heart disease, Parkinson’s, Alzheimer’s, diabetes, motor neuron disease, etc.) may be amenable to stem cell therapy if stem cells can be made to go to the appropriate place in the body and become the appropriate cell type. For example, if stem cells could be made to migrate to an injured spinal cord and become nerve cells, it might be possible to cure paralysis.
  2. Developing drug therapies. It is possible to make stem cells that are genetically identical to those of a patient with a disease such as amyotrophic lateral sclerosis. The stem cells can be made to generate the cell type that is defective in that disease (e.g. nerve cells). By studying these cells, researchers can gain insight into what goes wrong at the molecular level in the disease. They can also use these cells to test drugs that might block the progression of the disease

How are stem cells cultivated?

In the laboratory, stem cells are cultivated in dishes with a cocktail of nutrients and growth factors. Most stem cell lines have been cultivated on a “feeder layer” of animal cells. However, cells produced this way may not be safe for use in human therapies because of the possibility that viruses or other harmful agents might be transmitted to patients receiving the stem cells. Recently, researchers have produced the first embryonic stem cell lines grown on human feeder cells. Another group has reported cultivating stem cells without using any feeder cells. Cell lines grown using these new methods should be safer for use in therapies.

How are stem cells used in current therapy?

The most common stem cell therapy is the bone marrow transplant. It has been used for decades to treat patients whose bone marrow has been damaged by chemotherapy, or who have certain genetic diseases that lead to anemia or immune deficiency. Bone marrow contains stem cells that can give rise to all of the cell types in the blood, including red blood cells, white blood cells and platelets.

A number of other stem cell therapies have shown promise in animal studies or clinical trials with small numbers of humans. These include the use of stem cells to repair damaged heart muscle, to generate cells that produce insulin to treat diabetes and to repair damaged spinal nerves.

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UCSD Stem Cell Courses