Questions About Embryonic Stem Cells

What are human embryonic stem cells?

Stem cells are cells that have the remarkable potential to develop into many different cell types in the body.

Serving as a sort of repair system for the body, they can theoretically divide without limit to replenish other cells for as long as the person or animal is still alive.

When a stem cell divides, each "daughter" cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.

What classes of stem cells are there?

There are three classes of stem cells: totipotent, multipotent, and pluripotent.

A fertilized egg is considered totipotent, meaning that its potential is total; it gives rise to all the different types of cells in the body.

Stem cells that can give rise to a small number of different cell types are generally called multipotent.

Pluripotent stem cells can give rise to any type of cell in the body except those needed to develop a fetus.

Where do stem cells come from?

Pluripotent stem cells are isolated from human embryos that are a few days old. Cells from these embryos can be used to create pluripotent stem cell "lines" —cell cultures that can be grown indefinitely in the laboratory.

Pluripotent stem cell lines have also been developed from fetal tissue obtained from fetal tissue (older than 8 weeks of development).

Why do scientists want to use stem cell lines?

Once a stem cell line is established from a cell in the body, it is essentially immortal, no matter how it was derived. That is, the researcher using the line will not have to go through the rigorous procedure necessary to isolate stem cells again.

Once established, a cell line can be grown in the laboratory indefinitely and cells may be frozen for storage or distribution to other researchers.

Stem cell lines grown in the lab provide scientists with the opportunity to "engineer" them for use in transplantation or treatment of diseases.

For example, before scientists can use any type of tissue, organ, or cell for transplantation, they must overcome attempts by a patient's immune system to reject the transplant.

In the future, scientists may be able to modify human stem cell lines in the laboratory by using gene therapy or other techniques to overcome this immune rejection.

Scientists might also be able to replace damaged genes or add new genes to stem cells in order to give them characteristics that can ultimately treat diseases.

Reference for Stem Cells Article

National Institutes of Health

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