Types of Stem Cells

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Stem cells are the most basic type of cell. They are ‘unspecialized’ cells that are the building blocks of other types of cells. They give rise to all cells with specialized functions, such as blood, bone, brain and heart cells. They are also capable of dividing and self-renewing for long periods of time. These features make them different from any other type of human cell.

The flexibility and endurance of stem cells makes them useful for medical treatments. Today, stem cell transplant is an option for people with bone marrow and blood-related diseases, such as leukemia. Stem cell research is actively exploring other potential uses of stem cells. In the future, stem cell therapy may be available for a variety of medical problems. The possibilities are theoretically limitless once scientists can reliably harness the power of these cells.

To understand stem cell therapy, it helps to start with understanding the types of stem cells. Scientists can use stem cells from the body to grow a stem cell line in a laboratory. A cell line is a uniform group, or population of cells. Once they establish a stem cell line, it will essentially last forever. The usefulness of the line in treating different medical conditions depends on the type of stem cell. Today worldwide, there are several hundred stem cell lines, predominantly derived from embryos.

Embryonic Stem Cells

Embryonic stem cells come from a human embryo that is 3 to 5 days old. This is the most versatile form of stem cell. They are pluripotent cells. This means they can divide into more stem cells or go on to become any and every type of cell in a developing fetus.

Most embryonic stem cells are from extra, unused embryos created in an IVF (in vitro fertilization) lab. They are donated for research purposes. However, this raises ethical questions and concerns about using this type of stem cell for medical treatments.

One challenge in using embryonic stem cells is controlling differentiation—the process of an unspecialized stem cell becoming a specialized cell, such as a heart muscle cell. Scientists have been studying this process for many years. They have had some success manipulating the process. They call this directed differentiation. For example, they have been able to direct the process to make insulin-secreting cells. Once they can reliably control the process, scientists may be able to develop treatments for an array of medical conditions.

Another challenge with embryonic stem cells is the body’s immune system. Transplanting cells that are not your own into your body can trigger an immune response. The immune system attacks these cells as foreign invaders and destroys them. Scientists must find a way around this problem before widespread use is possible.

Adult Stem Cells

Adult stem cells are present in your body today. However, they are multipotent, or tissue-specific cells. This means they have less flexibility for change than embryonic cells. They can only give rise to the different cells of a specific organ or tissue. The purpose of adult stem cells is for repair and regeneration. This is how your skin heals from a cut and how the liver can regrow.

At one time, scientists thought stem cells only existed in certain tissues, such as the bone marrow. Recent research has found stem cells in unexpected places, such as the brain and heart. This has exciting implications for future stem cell therapies. However, the ease of collecting adult stem cells depends on the type of tissue. For example, doctors can harvest stem cells for a bone marrow transplant from circulating blood. Stem cells from the bone marrow or from the circulating, or peripheral bloodstream are hematopoietic stem cells. They give rise to new blood and immune cells. Doctors use peripheral hematopoietic stem cells to perform most stem cell transplants today.

There are advantages and disadvantages with adult stem cells. They do not carry the same ethical issues as embryonic stem cells. And it is possible to use your own stem cells, which shouldn’t trigger the immune system. Researchers have even discovered that some adult stem cells are more flexible than they originally thought. However, it is difficult to get adult stem cells to grow in large quantities. Also, using donor cell lines in a recipient patient would have the same immune challenges as embryonic stem cells.

Induced Pluripotent Stem Cells

Induced pluripotent stem (iPS) cells are relatively new. They are ordinary adult cells that scientists alter to act like embryonic stem cells. Skin and blood cells are the most common source for iPS cells. Scientists reprogram the genes in these cells to make them pluripotent.

There are several potential advantages of iPS cells. They have the flexibility of embryonic stem cells without the ethical concerns. The technique may also prevent immune system activation. However, this research is in its infancy. Much more study is necessary to see if these cells are safe to use.

Perinatal Stem Cells

Perinatal stem cells are a form of adult stem cells. They are present in umbilical cord blood and amniotic fluid. Umbilical cord blood banking has been around for many years. A baby’s cord blood is a genetic match for the baby and possibly other family members. It can be a source of stem cells for bone marrow transplant to treat leukemia and other blood-related disorders.

Researchers are currently studying amniotic fluid stem cells. Many pregnant women have an amniocentesis test to check the amniotic fluid for genetic defects. Instead of discarding the fluid, scientists are studying the idea of using these stem cells to treat certain birth defects. Tissue they grow from these stem cells would match the baby. And it may be possible to treat the birth defect before birth. This area of stem cell research is in the very early stages. Scientists need more time to explore the potential of these stem cells.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2019 Feb 6
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