Basic Questions
What are human embryonic stem cells?
What classes of stem cells are there?
Where do stem cells come from?
Why do scientists want to use stem cell lines?
Do embryonic stem cells come from an aborted human fetus?
Healthcare Questions
Why are doctors and scientists so excited about human embryonic stem cells?
What are the potential medical benefits of stem cell research?
Have human embryonic stem cells been used successfully to treat any human diseases yet?
What will be the best type of stem cell to use for therapy?
What is the relationship connecting embryonic stem cell research with in-vitro fertilization?
Why does in-vitro fertilization result in so many discarded embryos?
Research and Policy Questions
Which research is best to pursue?
Why not use adult stem cells instead of using human embryonic stem cells in research?
May individual states pass laws to permit human embryonic stem cell research?
Are the existing embryonic stem cell lines approved by President Bush sufficient to advance this research?
Basic Questions
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. A more detailed primer on stem cells can be found at /info/basics.
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.
Do embryonic stem cells come from an aborted human fetus?
No. There is no connection between abortion and human embryonic stem cells. Embryonic stem cells are derived from embryos created by in-vitro fertilization, within a few days of fertilization in a dish. Embryonic stem cells can only be derived from embryos at the very earliest stages of development, prior to implantation into the uterus, and prior to the formation of any organs. Embryos at this stage of development are microscopically small and contain no nervous system, no heart and no specialized human tissues. By the time a human embryo in the uterus has developed into a fetus (at the end of the eighth week after conception), all of its embryonic stem cells have been committed to becoming specific tissues. Human fetal tissue cannot be used to generate embryonic stem cells.
Healthcare Questions
Why are doctors and scientists so excited about human embryonic stem cells?
Stem cells have potential in many different areas of health and medical research. To start with, studying stem cells will help us to understand how they transform into the dazzling array of specialized cells that make us what we are. Some of the most serious medical conditions, such as cancer and birth defects, are due to problems that occur somewhere in this process. A better understanding of normal cell development will allow us to understand and perhaps correct the errors that cause these medical conditions. Another potential application of stem cells is making cells and tissues for medical therapies. Today, donated organs and tissues are often used to replace those that are diseased or destroyed. Unfortunately, the number of people needing a transplant far exceeds the number of organs available for transplantation. Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues to treat a myriad of diseases, conditions, and disabilities including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.
What are the potential medical benefits of stem cell research?
Studying stem cells will help us understand how they transform into the dazzling array of specialized cells that make us what we are. Some of the most serious medical conditions, such as cancer and birth defects, are due to problems that occur somewhere in this process. A better understanding of normal cell development will allow us to understand and perhaps correct the errors that cause these medical conditions. All types of stem cell research hold great promise for relieving human disease and suffering.
Another potential application of stem cells is making cells and tissues for medical therapies. Today, donated organs and tissues are often used to replace those that are diseased or destroyed. Unfortunately, the number of people needing a transplant far exceeds the number of organs available for transplantation. Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues to treat a myriad of diseases, conditions, and disabilities including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis.
Have human embryonic stem cells been used successfully to treat any human diseases yet?
Scientists have been able to do experiments with human embryonic stem cells (hESC) only since 1998, when a group led by Dr. James Thompson at the University of Wisconsin developed a technique to isolate and grow the cells. Moreover, Federal funds to support hESC research have been available since only August 9, 2001, when President Bush announced his decision on Federal funding for hESC research. Because many academic researchers rely on Federal funds to support their laboratories, they are just beginning to learn how to grow and use the cells. Thus, although hESC are thought to offer potential cures and therapies for many devastating diseases, research using them is still in its early stages.
Adult stem cells, such as blood-forming stem cells in bone marrow (called hematopoietic stem cells, or HSCs), are currently the only type of stem cell commonly used to treat human diseases. Doctors have been transferring HSCs in bone marrow transplants for over 40 years. More advanced techniques of collecting, or "harvesting," HSCs are now used in order to treat leukemia, lymphoma and several inherited blood disorders. The clinical potential of adult stem cells has also been demonstrated in the treatment of other human diseases that include diabetes and advanced kidney cancer. However, these newer uses have involved studies with a very limited number of patients.
What will be the best type of stem cell to use for therapy?
Pluripotent stem cells, while having great therapeutic potential, face formidable technical challenges. First, scientists must learn how to control their development into all the different types of cells in the body. Second, the cells now available for research are likely to be rejected by a patient's immune system. Another serious consideration is that the idea of using stem cells from human embryos or human fetal tissue troubles many people on ethical grounds. Until recently, there was little evidence that multipotent adult stem cells could change course and provide the flexibility that researchers need in order to address all the medical diseases and disorders they would like to. New findings in animals, however, suggest that even after a stem cell has begun to specialize, it may be more flexible than previously thought.
There are currently several limitations to using adult stem cells. Although many different kinds of multipotent stem cells have been identified, adult stem cells that could give rise to all cell and tissue types have not yet been found. Adult stem cells are often present in only minute quantities and can therefore be difficult to isolate and purify. There is also evidence that they may not have the same capacity to multiply as embryonic stem cells do. Finally, adult stem cells may contain more DNA abnormalities—caused by sunlight, toxins, and errors in making more DNA copies during the course of a lifetime. These potential weaknesses might limit the usefulness of adult stem cells.
What is the relationship connecting embryonic stem cell research with in-vitro fertilization?
Initial embryonic stem-cell research centered on the use of embryos created by in-vitro fertilization (IVF), an assisted reproductive technology. Many persons experiencing difficulty conceiving a child go to fertility clinics for IVF. IVF is a process by which eggs are removed from a female’s body and fertilized with sperm in a culture dish. After some of the fertilized eggs develop into blastocysts, one or more of the highest quality blastocysts are placed in the woman's uterus. If a blastocyst implants in the wall of the uterus and continues to develop, it can result in a normal pregnancy. Additional blastocysts can be frozen for later use, or discarded because they are of unsuitable quality for implantation. Blastocysts that are of unsuitable quality or no longer needed for fertility treatment can be donated by the parents for research. If they are donated, scientists can remove the cells inside the blastocyst and use them to create new lines of human embryonic stem cells for research.
Many IVF users want the embryos they still have in storage to be used in stem cell research, as it would be more meaningful for them to be used for research than to have them defrost and die on a laboratory bench. In 1999, the president's National Bioethics Advisory Commission recommended that hESC harvested from embryos discarded after in vitro fertility treatments, but not from embryos created expressly for experimentation be eligible for federal funding.
How many frozen embryos are available in the United States for research and why is it that in-vitro fertilization results in so many discarded embryos?
RAND researchers together with the Society of Assisted Reproductive Technology (SART) Working Group completed a project designed to inform the policy debate by providing accurate data on the number of frozen embryos in the United States and how many of those embryos are available for research purposes. They found that as of April 2002 nearly 400,000 embryos had been frozen and stored since the late 1970s in fertility clinics nationwide - 84% of which regularly discard unwanted embryos. Patients have designated only 2.8 percent (about 11,000 embryos) for research.
Most clinics offering IVF create additional embryos that are not implanted but frozen for use in later pregnancy attempts. In order to increase the likelihood of a successful pregnancy, the IVF clinic harvests and fertilizes as many eggs as it can from the donor couple. But in the four to five days those fertilized eggs develop in the laboratory, some of them develop abnormally or are found to carry genetic defects that cause serious diseases. Embryos that cannot be implanted because of abnormal development or serious genetic defects, as well as frozen embryos that are no longer needed for fertility treatment, can be donated by parents and used by scientists to derive embryonic stem cell lines. Scientists may only use the blastocysts after they have already been slated for disposal, and only with the informed consent of the donors.
Research and Policy Questions
Which research is best to pursue?
The development of stem cell lines that can produce many tissues of the human body is an important scientific breakthrough. This research has the potential to revolutionize the practice of medicine and improve the quality and length of life. Given the enormous promise of stem cells therapies for so many devastating diseases, NIH believes that it is important to simultaneously pursue all lines of research and search for the very best sources of these cells.
Why not use adult stem cells instead of using human embryonic stem cells in research?
Human embryonic stem cells are thought to have much greater developmental potential than adult stem cells. This means that embryonic stem cells may be pluripotent—that is, able to give rise to cells found in all tissues of the embryo except for germ cells rather than being merely multipotent—restricted to specific subpopulations of cell types, as adult stem cells are thought to be.
May individual states pass laws to permit human embryonic stem cell research?
Individual states have the authority to pass laws to permit human embryonic stem cell research using state funds. Unless Congress passes a law that bans it, states may pay for research using human embryonic stem cell lines that are not eligible for federal funding.
Are the existing embryonic stem cell lines approved by President Bush sufficient to advance this research?
No. Most of these lines turned out not to be viable embryonic stem cells, and all are contaminated with animal proteins and can never be used in a patient. None of these lines model human diseases. We need many more stem cell lines in order to conduct research that may lead to better medical treatments and drug discoveries.
Much of the informational content used above was compiled from the
National Institutes of Health and is meant for educational purposes only.
Please visit http://stemcells.nih.gov/
for more information regarding stem cell research.
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Autoimmune Diseases/ Musculoskeletal/ Connective Tissue Disorders:
Arthritis, Crohn's Disease, Devic's Syndrome, Juvenile Rheumatoid Arthritis, Multiple Sclerosis, Osteoporosis, Systemic Lupus Erythematosus (Lupus), Systemic Sclerosis, Type 1 Diabetes
Cancers
Bladder/Kidney, Brain/Central Nervous System, Breast, Colon/Lower Bowel, Endometrium/Cervix/Ovary, Esophagus, Leukemia, Liver, Lungs/Respiratory System, Lymphoma, Myeloma, Pancreas, Prostate, Skin, Stomach
Cardiovascular Diseases
Acute Ischemic Heart Disease (angina), Myocardial Infarction (heart attack), Chronic Ischemic Heart Disease (athersclerotic heart disease), Cardiomyopathy Cerebrovascular Disease (stroke)
Circulatory/Respiratory Diseases
Chronic Obstructive Pulmonary Disease, Pulmonary Fibrosis
Injuries
Severe Burns, Shaken Baby Syndrome, Spinal Cord Injury
Eye Disorders
Macular Degeneration, Retinitis Pigmentosa
Infectious Diseases
HIV/AIDS
Metabolic Diseases Adrenoleukodystrophy, Aspartylglycosaminuria, Canavan's Disease, Cystic Fibrosis, Fabry Disease, Fucosidosis, Gaucher Disease, Leukodystrophy, Mucopolysaccharidoses, Niemann-Pick Disease, Pompe Disease, Porphyria, Sickle Cell Disease, Tay-Sachs Disease, Type 2 Diabetes
Muscular Dystrophies
Becker, Duchenne, Emery Dreifuss, Facioscapulohumeral, Fukuyama, Limb Girdle, Myasthenia Gravis, Myotonic Dystrophy
Neurological Diseases of Adulthood
Alzheimer's Disease, Huntington's Disease, Lou Gehrig's Disease (ALS), Parkinson's Disease
Neurological Diseases of Childhood
Asperger Syndrome, Autism, Cerebral Palsy, Childhood Disintegrative Disorder, Down Syndrome, Epilepsy, Hydrocephalus, Rett Syndrome
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Potential U.S. Patient Populations for Stem Cell-Based Therapies
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MEDICAL CONDITION | NUMBER OF PATIENTS | Cardiovascular Disease | 58 million | Autoimmune Disease | 30 million | Diabetes | 16 million | Osteoporosis | 10 million | Cancer | 8.2 million | Alzheimer's Disease | 5.5 million | Parkinson's Disease | 5.5 million | Burns (severe) | 0.3 million | Spinal-Cord Injuries | 0.25 million | Birth Defects | 0.15 million per year |
Source: Derived from the National Academy of Sciences |
