Stem cells are undifferentiated, or “blank,” cells that have the potential to develop into cells that serve many different functions in many parts of the body, such as the heart, lungs, and brain. Most cells in the body are differentiated cells. This means that they can only serve a specific function in a particular organ. For example, red blood cells are cells designed specifically to carry oxygen through the blood.
All human beings start out as only one cell. This cell is called a zygote, or a fertilized egg. The zygote divides into two cells, then four cells, and so on. Eventually, the cells begin to specialize and take on the function of a particular part of the body. This process is called differentiation.
Stem cells are cells that have not yet differentiated. They have the ability to divide and make an indefinite number of copies of themselves. Other cells in the body can only replicate a limited number of times before they begin to break down. When a stem cell divides, it can either remain a stem cell, or it can turn into a differentiated cell, such as a muscle cell or a red blood cell.
Since stem cells have the potential to turn into many other types of cells, scientists believe that they can be useful for treating and understanding diseases. Researchers at the Academic Health Center at the University of Minnesota (UMN) believe these cells can be used to:
- grow new cells in a laboratory to replace damaged organs or tissue
- fix or reprogram parts of organs that do not work properly
- make human cell models of diseases like cancer to learn why some cells develop into cancer cells
- research genetic defects in cells
- test new drugs in human cells instead of testing the drugs on animals (UMN)
Embryonic Stem Cells
Embryonic stem cells are stem cells that come from a human embryo. These cells are harvested during a process called in-vitro fertilization, in which an embryo is fertilized in a laboratory instead of inside the female body. These cells can give rise to virtually any other type of cell.
Nonembryonic (Adult) Stem Cells
Adult stem cells have a misleading name, because they are also found in infants and children. These stem cells come from already developed organs and tissues in the human body. They are used by the body to repair and replace damaged tissue in the same area in which they are found. For example, hematopoietic stem cells are found in bone marrow and make new red blood cells, white blood cells, and other types of blood cells. Adult stem cells cannot differentiate into as many other types of cells as embryonic stem cells can.
Adult stem cells do not present any ethical problems. However, in recent years there has been controversy about the way human embryonic stem cells are obtained. These cells are harvested through in-vitro fertilization, meaning that the egg is artificially fertilized in a laboratory.
The cells are harvested between five and 14 days after fertilization, when they undergo various testing for research purposes. In the process, the embryo (a fertilized egg that has begun cell division) is destroyed, and this raises ethical concerns for people who believe that destruction of a fertilized embryo is morally wrong.
Opponents believe that an embryo is a living human being, and do not want the fertilized eggs used for research. They believe that the embryo should have the same rights as every other human being and that these rights should be protected.
Supporters of stem cell research believe that the embryos are not yet humans, and note that they receive consent from the donor couple whose eggs and sperm were used to create the embryo. Additionally, supporters argue that the extra fertilized eggs created during IVF would be discarded anyway and might be put to better use for scientific research.
According to the National Institutes of Health, in August 2001, former President George W. Bush approved a law that would provide federal funding for limited research on embryonic stem cells, so long as research fit the following criteria (NIH, 2009):
- The harvesting process (which includes the destruction of the embryo) was initiated prior to 9 p.m. on August 9, 2001.
- The stem cells were derived from an embryo that was created for reproductive purposes and was no longer needed.
- Informed consent was obtained for the donation of the embryo and the donation did not involve financial inducements.
In March 2009, President Barack Obama revoked President Bush’s statement and released Executive Order 13505 entitled “Removing Barriers to Responsible Scientific Research Involving Human Stem Cells.” The order removed the restrictions on federal funding for stem cell research to allow the NIH to fund research that uses embryonic stem cells.
The NIH then published guidelines to establish the policy under which it would fund research. The guidelines were written to help make sure that all NIH-funded research on human stem cells is morally responsible and scientifically worthy. (NIH, 2009)
Executive Order 13505 can be found here: http://www.gpo.gov/fdsys/pkg/FR-2009-03-11/pdf/E9-5441.pdf
Stem cell research is ongoing at universities, research institutions, government laboratories, and hospitals around the world. Examples of stem cell projects include:
- injecting modified stem cells directly into the brain after a stroke, or into the eyes to restore vision after an injury
- using stem cells to “reprogram” cells of the pancreas to help a person with diabetes produce insulin
- altering the genes of stem cells to make them resistant to diseases, such as HIV/AIDS, and then inserting them into a person with the disease
- cultivating stem cells to repair broken bones