"I want things to happen quickly. I certainly want to benefit in my lifetime. I don't want to wait to get out of this wheelchair at age 75. I am 51, and am now very healthy, and would like to be out of the chair very soon. I'm not willing to resign myself to being an advocate for research that will benefit people only after I'm gone. I'm not that noble." - Christopher Reeve (1952-2004) in a 2003 interview¹

Disability activist Christopher Reeve's sentiments echo those of many people with disabling and life-threatening conditions who anticipate the day when stem cells can reverse the effects of disease. Embryonic stem cells were first isolated in mice more than 20 years ago,² but it wasn't until 1998 that scientists demonstrated for the first time that human stem cells - produced at the blastocyst or earliest stage of development - could be isolated, cultured, and grown in apparently limitless quantities.² This remarkable discovery has raised expectations about the potential of stem cells to prevent or cure a number of serious diseases.

As the public becomes more informed about regenerative medicine - the use of stem cell technology to replace diseased organs - nurses will be expected to have a basic and accurate understanding of what stem cells are, their potential benefit to humanity, and issues associated with stem cell research.³

Properties of stem cells

Stem cells have certain properties that distinguish them from other cells. They can divide and renew themselves for long periods of time, they are unspecified, and under certain physiologic or laboratory conditions they can become the source of one of the 220 types of cells and tissues in the body.^2,4 Scientists work with two kinds of stem cells from animals and humans: embryonic stem cells and adult stem cells.^2,4 Embryonic and adult stem cells have different functions and characteristics. Embryonic stem cells are the earliest form of human cellular life.⁵ In humans, the term embryo refers to the developing organism from the time of fertilization to the eighth week of gestation. After this time, the organism is known as a fetus. When an embryo is less than 4 days old, its cells are called totipotent stem cells, so named because they have total potential and could form a human being if they were separated and implanted individually into a woman's uterus.^3,5 About four days after conception, stem cells begin to become specialized.

This process, known as differentiation, allows some cells to become neurons, epidermal cells, myocardial cells, and other types of specialized cells. At this stage the stem cells are referred to as pluripotent. Pluripotent stem cells have the potential to form every cell in the body but no longer can form an entire human being. As the stem cells continue to become more differentiated, they are known as multipotent. Multipotent stem cells have the potential to form several but not all types of cells.^3-5 Pluripotent stem cells are isolated from human embryos that are a few days old and are used to create stem cell lines, cell cultures that can be grown indefinitely in the laboratory.^2,4 Pluripotent stem cell lines also have been developed from fetuses. Once established, a stem cell line can be grown in the laboratory for an indefinite period. A stem cell line may be frozen for storage or distributed to other researchers.² Most of the existing human embryonic stem cell lines in the world were obtained from unused embryos created for couples seeking in vitro fertilization, a procedure in which an ovum is fertilized outside the body.³

Adult, or nonembryonic, stem cells are found in both adults and children. The primary purpose of adult stem cells in living organisms is to maintain and repair the tissues in which they are found.² Scientists believe that adult stem cells function as a kind of backup system. If a particular type of cell needs to be replaced, adult stem cells can differentiate and form new cells. Adult stem cells are more differentiated than embryonic stem cells. Adult stem cells typically generate the cell types of the tissue in which they reside. For example, a hematopoietic adult stem cell in the bone marrow normally differentiates into erythrocytes, leukocytes, and platelets based on changing physiological needs.²

Embryonic stem cells and adult stem cells have both advantages and disadvantages. Because they are pluripotent, embryonic stem cells are extremely versatile and have the potential advantage of developing into any cell type.³ Moreover, large numbers of embryonic stem cells can easily be grown in culture and stimulated to replicate quickly and indefinitely, so a virtually limitless supply of cells can be created and stored. This is an important advantage, as large numbers of cells are needed for stem cell replacement therapies. Use of embryonic stem cells also has some disadvantages. The potential for immune system rejection exists when embryonic stem cells are used, as they have the same likelihood of immune system rejection as do other transplanted cells.^3,5 Another major barrier to using embryonic stem cells is an ethical one. In the process of harvesting stem cells, the embryo is destroyed. In contrast, an advantage of using adult stem cells is that the ethical concern about destruction of potential human life is eliminated. Another advantage of using adult stem cells is that the patient's own cells could be replicated in the laboratory. Using the patient's own stem cells would eliminate the possibility that the stem cells would be destroyed by the person's immune system.² However, adult stem cells also have specific disadvantages. As multipotent stem cells, they lack the ability to differentiate into all types of human cells. As a result, adult stem cells may be able to cure a limited number of diseases.^4,5 Adult stem cells also are difficult to locate and, when found, are present in small amounts.

In addition, methods for growing adult stem cells have not yet been completely developed. Adult stem cells take some time to grow and thus may not grow fast enough to help a person who is seriously ill.² Until recently, scientists believed that an adult stem cell in one tissue, such as the bone marrow, could not differentiate into other types of cells. However, a number of experiments conducted during the past several years have raised the possibility that adult stem cells from one tissue, through a process known as plasticity, may be able to give rise to cell types of a completely different tissue.² Scientists have also found adult stem cells in many more tissues than once thought possible.² These findings have prompted additional research using adult stem cells.

Looking to the future

Stem cell research is rapidly increasing knowledge about how human organisms develop and how healthy cells replace damaged cells.² Although stem cells are not yet used to cure any specific condition, bone marrow transplants using adult hematopoietic stem cells have been used for more than several decades to treat diseases such as leukemia and lymphoma, as well as nonmalignant conditions such as aplastic anemia.³ In the future, stem cells may be used to replace diseased cells, form new tissues, develop new drugs, and increase our knowledge of how cellular abnormalities such as gene alterations and malignancies occur. (See sidebar: Examples of Stem Cell Research in Regenerative Medicine.)

If scientists can prompt stem cells to become specialized into any type of cell, physicians may be able to use them to treat a variety of diseases. Parkinson's disease, a condition that affects more than 2% of those older than 65, may be one of the first conditions to be treated with stem cell technology.² Parkinson's disease is caused by a progressive degeneration of dopamine-producing neurons that results in muscle tremors, rigidity, and decreased mobility. Researchers are developing a number of techniques for producing dopamine from stem cells in the laboratory that may be transplanted into patients with Parkinson's. Researchers also are developing ways to prompt stem cells to differentiate into pancreatic beta cells that could be implanted into the body of a person with diabetes.⁴ Stem cells also could be used to grow new myocardial cells to treat heart disease. Cancer treatment is another promising area for the use of stem cell technology. Chemotherapy and radiation therapy can seriously damage or destroy hematopoietic stem cells. Bone marrow depression is a major limiting factor in cancer therapy. By using stem cells to reproduce healthy bone marrow, physicians could use more potent cancer treatments. Stem cells also could be used to create specific cancer-fighting cells or to regenerate tissues that have been removed or destroyed during cancer treatment.^4,5 The effects of progressive neurological conditions such as Alzheimer's disease and amyotrophic lateral sclerosis could be reversed using stem cell technology.²

Stem cells potentially could also be used to form new tissues and organs. For example, stem cells injected into a diseased organ, such as a failing liver or heart, may be able to keep the organ functioning. Stem cell technology could also grow a new organ, giving a second chance to patients on waiting lists for transplants. The first potential application of human embryonic stem cell technology may occur in the area of new-drug discovery.² Today, chemicals that show promise as drugs are evaluated by time-consuming processes before they can be tested on human subjects. Safety testing for new drugs could be done using cells from pluripotent stem cell lines.² Embryonic stem cell research also may enhance the study of human development. Learning more about how human embryonic stem cells function can offer insight into early human development that cannot be studied directly in humans in utero or fully understood through the use of animal models.⁵ Understanding the events that occur at the first stages of human development may help physicians prevent or treat birth defects, infertility, and pregnancy loss.⁵

Legal and ethical issues

Embryonic stem cell research already has enabled scientists to learn more about human growth and development, but legal and ethical issues, including concerns about safety, efficacy, resource allocation, and methods of harvesting stem cells, accompany these developments. In August 2001, President George Bush announced that for the first time federal funding would be available for human embryonic stem cell research if the stem cell line meets the following criteria.^2,5 First, the cells must have been removed from an embryo before August 9, 2001. Second, the embryo from which the stem cell line was derived must no longer have the possibility of developing further as a human being. Third, the embryo must have been created for a reproductive purpose, but no longer be needed for that purpose. Last, the person donating the embryo must do so voluntarily without financial inducement.^2,5

In additional to federal funding allocated based on the criteria outlined above, individual states have the authority to pass laws to permit human embryonic stem cell research using state funds.⁴ In 2004, California voters approved a measure to fund $3 billion over the next 10 years for embryonic stem cell research. Although there is widespread agreement about the goals of stem cell research and its potential benefit for humanity, several ethical issues are to be considered. Some people argue that an embryo has a similar value to other human beings and that the potential benefit of embryonic stem cell research does not justify the destruction of unborn individuals. Others argue that excess embryos produced as a result of in vitro fertilization will be discarded anyway. People holding this view also point out that these embryos are donated with consent and it is immoral to waste the potential they have to cure human disease.⁴ The potential for reproductive human cloning compounds the ethics debate. Another ethical dilemma involves the issue of whether everyone will have access to regenerative medicine, regardless of ability to pay. Also, with any new discovery, how can individuals distinguish between genuine promise and unsubstantiated claims?

Helping patients through the information maze

The public is often inundated with news reports highlighting the promise of stem cell applications to cure disease. Despite the possibility to reverse the effects of some devastating conditions, the consensus among scientists is that there is much work to be done to understand the potential of stem cells.⁴ It is important to help those who are interested in stem cell research to realize that even if legal and funding restrictions in the United States and other countries were lifted immediately, many technical obstacles still must be overcome before stem cells could safely be used to treat patients. Experts emphasize that stem cell science still is in its infancy and predict that it may be years before clinical applications become a reality.² Also to be considered are premature, scientifically unsubstantiated claims of stem cells' usefulness in treating diseases and the danger of exploiting people who are ill or disabled.

Nurses can help patients and families find objective information about stem cell research. Reliable sources include government agencies such as the National Institutes of Health and the President's Council on Bioethics, as well as patient advocacy groups and organizations that fund and support research.² These groups generally have a broad understanding of research developments and may be the first to learn of opportunities for clinical trials and experimental treatments.² Examples of patient advocacy groups that provide information about stem cell research include the Juvenile Diabetes Research Foundation International, the Amyotrophic Lateral Sclerosis Association, the American Parkinson Disease Association, the Michael J. Fox Foundation for Parkinson's Research, the American Heart Association, and the National Spinal Cord Injury Association.

Nurses and other health care professionals have an ethical duty to offer accurate information and encouragement about progress in stem cell research without misleading or exploiting the fears of those who may be desperate to find a cure or more effective treatment.