Stem cells: What they are and what they do
Stem cells: What they are and what they do
You've heard about stem cells in the news, and perhaps you've wondered if they might help you or a loved one with a serious disease. You may wonder what stem cells are, how they're being used to treat disease and injury, and why they're the subject of such vigorous debate.
Here are some answers to frequently asked questions about stem cells.
Why is there such an interest in stem cells?
Researchers and doctors hope stem cell studies can help to:
What are stem cells?
Stem cells are the body's raw materials — cells from which all other cells with specialized functions are generated. Under the right conditions in the body or a laboratory, stem cells divide to form more cells called daughter cells.
These daughter cells either become new stem cells (self-renewal) or become specialized cells (differentiation) with a more specific function, such as blood cells, brain cells, heart muscle or bone. No other cell in the body has the natural ability to generate new cell types.
Where do stem cells come from?
Researchers have discovered several sources of stem cells:
Why is there a controversy about using embryonic stem cells?
Embryonic stem cells are obtained from early-stage embryos — a group of cells that forms when a woman's egg is fertilized with a man's sperm in an in vitro fertilization clinic. Because human embryonic stem cells are extracted from human embryos, several questions and issues have been raised about the ethics of embryonic stem cell research.
The National Institutes of Health created guidelines for human stem cell research in 2009. Guidelines included defining embryonic stem cells and how they may be used in research and donation guidelines for embryonic stem cells. Also, guidelines stated embryonic stem cells may only be used from embryos created by in vitro fertilization when the embryo is no longer needed.
Where do these embryos come from?
The embryos being used in embryonic stem cell research come from eggs that were fertilized at in vitro fertilization clinics but never implanted in a woman's uterus. The stem cells are donated with informed consent from donors. The stem cells can live and grow in special solutions in test tubes or petri dishes in laboratories.
Why can't researchers use adult stem cells instead?
Although research into adult stem cells is promising, adult stem cells may not be as versatile and durable as are embryonic stem cells. Adult stem cells may not be able to be manipulated to produce all cell types, which limits how adult stem cells can be used to treat diseases.
Adult stem cells also are more likely to contain abnormalities due to environmental hazards, such as toxins, or from errors acquired by the cells during replication. However, researchers have found that adult stem cells are more adaptable than was initially suspected.
What are stem cell lines and why do researchers want to use them?
A stem cell line is a group of cells that all descend from a single original stem cell and is grown in a lab. Cells in a stem cell line keep growing but don't differentiate into specialized cells. Ideally, they remain free of genetic defects and continue to create more stem cells. Clusters of cells can be taken from a stem cell line and frozen for storage or shared with other researchers.
What is stem cell therapy (regenerative medicine), and how does it work?
Stem cell therapy, also known as regenerative medicine, promotes the reparative response of diseased, dysfunctional or injured tissue using stem cells or their derivatives. It is the next chapter of organ transplantation and uses cells instead of donor organs, which are limited in supply.
Researchers grow stem cells in a lab. These stem cells are manipulated to specialize into specific types of cells, such as heart muscle cells, blood cells or nerve cells.
The specialized cells can then be implanted into a person. For example, if the person has heart disease, the cells could be injected into the heart muscle. The healthy transplanted heart cells could then contribute to repairing defective heart muscle.
Researchers have already shown that adult bone marrow cells guided to become heart-like cells can repair heart tissue in people, and more research is ongoing.
Have stem cells already been used to treat diseases?
Yes, doctors have performed stem cell transplants, also known as bone marrow transplants. In stem cell transplants, stem cells replace cells damaged by chemotherapy or disease or as a way for the donor's immune system to fight some types of cancer and blood-related diseases, such as leukemia. These transplants use adult stem cells or umbilical cord blood.
Researchers are testing adult stem cells to treat other conditions, including a number of degenerative diseases such as heart failure.
What are the potential problems with using embryonic stem cells in humans?
To be useful in people, researchers must be certain that stem cells will differentiate into the specific cell types desired.
Researchers have discovered ways to direct stem cells to become specific types of cells, such as directing embryonic stem cells to become heart cells. Research is ongoing in this area.
Embryonic stem cells also could grow irregularly or specialize in different cell types spontaneously. Researchers study how to control the growth and differentiation of embryonic stem cells.
Embryonic stem cells also might trigger an immune response in which the recipient's body attacks the stem cells as foreign invaders, or simply fail to function normally, with unknown consequences. Researchers continue to study how to avoid these possible complications.
What is therapeutic cloning, and what benefits might it offer?
Therapeutic cloning, also called somatic cell nuclear transfer, is a technique to create versatile stem cells independent of fertilized eggs. In this technique, the nucleus, which contains the genetic material, is removed from an unfertilized egg. The nucleus is also removed from a somatic cell of a donor.
This donor nucleus is then injected into the egg, replacing the nucleus that was removed, a process called nuclear transfer. The egg is allowed to divide and soon forms a blastocyst. This process creates a line of stem cells that is genetically identical to the donor's — in essence, a clone.
Some researchers believe that stem cells derived from therapeutic cloning may offer benefits over those from fertilized eggs because cloned cells are less likely to be rejected once transplanted back into the donor and may allow researchers to see exactly how a disease develops.
Has therapeutic cloning in people been successful?
No. Researchers haven't been able to successfully perform therapeutic cloning with humans despite success in a number of other species.
However, in recent studies, researchers have created human pluripotent stem cells by modifying the therapeutic cloning process. Researchers continue to study the potential of therapeutic cloning in people.
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