Stem Cell Biology

- Types of Stem Cells

Stem cells come in two main forms. They are embryonic stem cells and adult stem cells.

• Embryonic stem cells. The embryonic stem cells used in research today come from unused embryos. These are the results of in vitro fertilization procedures. They are donated to science. These embryonic stem cells are pluripotent. This means they can become more than one type of cell.
• Adult stem cells. There are two types of adult stem cells. One from fully developed tissues, such as the brain, skin, and bone marrow. There are only a few stem cells in these tissues. They are more likely to produce only certain types of cells. For example, stem cells from the liver simply make more liver cells.

The second category is induced pluripotent stem cells. These are adult stem cells that have been changed in the lab to look more like embryonic stem cells. In 2006, scientists reported for the first time that human stem cells could be altered in this way. Induced pluripotent stem cells appear to be no different from embryonic stem cells, but scientists have yet to find one that can develop into a variety of cells and tissues.

- Stem Cell Therapy

Cells, tissues and organs are sometimes permanently damaged or lost due to disease, injury and genetic conditions. Stem cells may be a way to generate new cells that can then be transplanted into the body to replace damaged or lost cells. 

Adult stem cells are currently used to treat certain diseases, such as:

• Hematopoietic stem cells are used to provide a source of healthy blood cells for people with certain blood disorders such as thalassemia and for cancer patients who have lost their own blood stem cells during treatment.
• Skin stem cells could be used to generate new skin for people with severe burns.

Age-related macular degeneration (AMD) is an example of a disease for which stem cells could in the future be used as a new form of treatment: 

• Some people with age-related macular degeneration go blind because of cells in the retina. Cells in the eye called the retinal pigment epithelium (RPE) stop working. 
• Scientists are using induced pluripotent stem cells in the lab to generate new RPE cells, which are then placed in patients' eyes to replace damaged cells.

Stem cells can be used to generate new organs for transplantation:

• Currently, damaged organs can be replaced by obtaining healthy organs from donors, but donated organs can be "rejected" by the body because the immune system sees them as foreign objects.
• Induced pluripotent stem cells generated from the patient's own body can be used to grow new organs with a lower risk of rejection.

- Stem Cell Research Challenges

Stem cells need more research before expanding their use. Scientists must first learn more about how embryonic stem cells develop. This will help them understand how to control the type of cells they are created from. Another challenge is that the embryonic stem cells available today are likely to be rejected by the body. Some people find the use of stem cells derived from embryos ethically disturbing. 

Scientists also face challenges when working with adult pluripotent stem cells. These cells are difficult to grow in the lab, so researchers are looking for ways to improve the process. These cells are also found in small numbers in the body. They are more likely to contain DNA problems.

Clinical trials using stem cell therapy are currently underway in the United States. If you are interested in trying this therapy for a medical condition, ask your healthcare provider about available trials in your area.

[More to come ...]