Where are the sources of stem cells?
Do adult stem cells have the same capability as embryonic stem cells?
How are cell therapies being used today?
What are some of the challenges?
What is the future of cell therapy?
How can I donate umbilical cord stem cells for research?
What do the terms totipotent, pluripotent and multipotent mean?
Stem cells are unspecialized cells that have two important characteristics that distinguish them from other cells in the body. First, they can replenish their numbers for long periods through cell division. Second, after receiving certain chemical signals, they can differentiate, or transform into specialized cells with specific functions, such as a heart cell or nerve cell.
Stem cells can be classified by the extent to which they can differentiate into different cell types:
At the end of the long chain of cell divisions are "terminally differentiated" cells, such as a liver cell or lung cell, which are permanently committed to specific functions. These cells stay committed to their functions for the life of the organism or until a tumor develops. In the case of a tumor, the cells dedifferentiate, or return to a less mature state.
Research is now being conducted on both adult and embryonic stem cells to determine the characteristics and potential of both to cure disease.
What are the sources of stem cells?
There are three sources of stem cells:
Cell therapy can be defined as a group of new techniques, or technologies, that rely on replacing diseased or dysfunctional cells with healthy, functioning ones. These new techniques are being applied to a wide range of human diseases, including many types of cancer, neurological diseases such as Parkinson's and Lou Gehrig's Disease, spinal cord injuries, and diabetes. Replacing dead cells in the retina with new ones may someday cure even presently incurable eye diseases such as glaucoma and macular degeneration. To understand how cell therapy works, it helps to understand the role of cells in the body.
The Function of Cells
Cells are the basic building blocks of the human body. These tiny structures compose the skin, muscles, bones and all of the internal organs. They also hold many of the keys to how our bodies function. Cells serve both a structural and a functional role in the body, performing an almost endless variety of actions to sustain the body's tissues and organs.
There are hundreds, perhaps thousands, of different specialized cell types in the adult body. All of these cells perform very specific functions for the tissue or organ they compose. For example, specialized cells in the heart muscle "beat" rhythmically through the conduction of electrical signals, while the cells of the pancreas produce insulin to help the body convert food to energy. These mature cells have been differentiated, or dedicated, to performing their special tasks. Conventional wisdom has long maintained that under normal conditions, once a cell has become specialized, it cannot be changed into a different type of cell.
Like the body itself, cells have a finite life span; they eventually die. Most of the body's cells divide and duplicate throughout life, but some cells either don't replenish themselves or do so in such small numbers that they cannot replace themselves fast enough to combat disease.
While cells are indispensable in performing vital functions for the body, they can also exist outside the body. They can live and divide in "cultures," special solutions in test tubes or Petrie dishes. This ability of certain cell types to live isolated from other cells under controlled conditions has allowed scientists to study them independently of the organ or system they are normally a part of. Through the isolation and targeted manipulation of cells, scientists are finding ways to identify young, regenerating ones that can be used to replace damaged or dead ones in diseased organs. This therapy is similar to the process of organ transplant, only the treatment consists of the transplantation of cells rather than organs. The cells that have shown by far the most promise of supplying diseased organs with healthy new ones are called stem cells.
Do adult stem cells have the same capability as embryonic stem cells?
For many years, scientists have conducted studies to determine whether the stem cells in adult tissue have the same developmental capability as embryonic stem cells. The general consensus is that adult stem cells seem to be less versatile. Scientists think that embryonic stem cells have a much greater utility and potential than the adult stem cells, because embryonic stem cells may develop into virtually every type of cell in the human body. Adult stem cells, on the other hand, may only be able to develop into a limited number of cell types. Embryonic stem cells also continue to divide indefinitely when placed in culture, while this may not be the case for adult stem cells and this would reduce their capacity to form new cell types. Both adult and embryonic stem cell research should continue simultaneously as they are both critical to our understanding of the etiology, progression and treatment of disease.
How are cell therapies being used today?
Even though most of the work done in this field has been experimental, most scientists find cell therapy so promising that they believe it is only a matter of time before its use becomes routine. And while many of the hoped-for uses of cell therapy sound futuristic, there are a few forms of this technique that have already been in use for years. Bone marrow transplants are an example of cell therapy in which the stem cells in a donor's marrow are used to replace the blood cells of the victims of leukemia and other cancers. Cell therapy is also being used in experiments to graft new skin cells to treat serious burn victims, and to grow new corneas for the sight-impaired. In all of these uses, the goal is for the healthy cells to become integrated into the body and begin to function like the patient's own cells.
So far, the results of such experiments have exceeded expectations. In a recent advance, pancreatic cells grown from stem cells were implanted into the body of a diabetic and began to produce insulin. Even though cell therapy is a new science, early results like the above have caused great optimism in the scientific community. However, there are several scientific challenges that must be overcome before we can truly harness the power of stem cells.
What are some of the challenges?
One of the first challenges that must be overcome for stem cell therapies to become more commonplace is the difficulty of identifying stem cells in tissue cultures, which contain numerous types of cells. While scientists are discovering new cell types almost every day, they estimate that there could literally be thousands of human cell types. The process of identifying any desired type of stem cell will involve painstaking research. Second, once stem cells are identified and isolated, the right biochemical solution must be developed to cause these progenitor cells to differentiate into the desired cell type. This too will require a great deal of experimentation.
Assuming that the above obstacles have been overcome, new issues arise when the cells are implanted into a person. The cells must be integrated into the patient's own tissues and organs and "learn" to function in concert with the body's natural cells. Cardiac cells that beat in a cell culture, for example, may not beat in rhythm with a patient's own heart cells. And neurons injected into a damaged brain must become "wired into" the brain's intricate network of cells and their connections in order to work properly.
Yet another challenge is the phenomenon of tissue rejection. Just as in organ transplants, the body's immune cells will recognize transplanted cells as "foreign," setting off an immune reaction that could cause the transplant to fail and possibly endanger the patient. Cell recipients would have to take drugs to temporarily suppress their immune systems, which in itself could be dangerous.
Yet another concern is the possible risk of cancer. Cancer results when cells lose their internal "brakes" and keep dividing when further proliferation is no longer desirable. Researchers must find a delicate balance between fostering the growth of new cells to replenish damaged tissues and making sure that cells don't overgrow and become cancerous. However, most scientists believe that, with the appropriate research, these obstacles can be overcome and the power of stem cells can be harnessed.
What is the future of cell therapy?
Despite the many challenges before us, most scientists believe that cell therapy will revolutionize medicine. With the use of cell therapies, we may soon have dramatic cures for cancer, Parkinson's, diabetes, kidney disease, multiple sclerosis, macular degeneration and a host of other diseases. Cell therapies have also shown great promise in helping to repair catastrophic spinal injuries, and helping victims of paralysis regain movement. It is even possible that the human life span could be greatly extended due to the replenishment of tissues in aging organs. We may even have the ability one day to grow our own organs for transplantation from our own stem cells, eliminating the danger of organ rejection. While we will undoubtedly encounter the limits of cell therapy one day, there is every reason to hope that this revolutionary new approach will result in radically improved ways to treat disease.
The following organizations can provide detailed information:
Can excess frozen embryos that were created during fertility treatments be donated for medical research?
Frozen embryos that were created by fertility clinics and are no longer needed by the couple can be used to produce embryonic stem cells for research funded by private organizations.
Therapeutic cloning has recently been the subject of intense debate. Therapeutic cloning is not the same as reproductive cloning, which is intended to genetically duplicate a person.
Therapeutic cloning is based on a technology called somatic cell nuclear transfer. Scientists first remove the nucleus, the part of the cell that contains the genetic material, from a normal egg cell of a woman or a female animal, such as a rabbit. They then extract a nucleus from a somatic cell—that is, any body cell other than an egg or sperm—from a patient who needs an infusion of stem cells to treat a disease or injury and insert the nucleus into the egg. The egg, which now contains the patient's genetic material, is allowed to divide and soon forms a hollow sphere of cells called a blastocyst. The blastocyst has an outer layer of cells and an inner cluster called the inner cell mass. Cells from the inner cell mass are isolated and used to develop new embryonic stem cell (ESC) lines.
These cells are pluripotent, meaning that they can give rise to all the cells in the body and therefore can be used to replace cells that have been damaged or destroyed. The advantage of therapeutic cloning is that the resulting ESCs have the patient’s proteins on their surfaces because the patient’s genes in the nucleus are controlling protein production. With the patient’s proteins on the ESC surfaces, the ESCs are unlikely to be rejected by the patient’s immune system when transplanted into the body. If ESCs from existing cell lines are used, the possibility exists that the ESCs will be rejected by the patient’s immune system because the surfaces of these cells contain foreign proteins.
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What do the terms totipotent, pluripotent and multipotent mean?
"Stem cells" is a term used to describe all cells that can give rise to cells of multiple tissue types. However, there are different types of stems cells. Totipotent cells, like the cells of a fertilized egg in the first few days after fertilization, can give rise to a fully functional organism. During normal development, the totipotent cells become more specialized and are considered pluripotent, meaning that they can give rise to every cell type in the body, but will not give rise to the placenta or supporting tissues necessary for fetal development. Because their potential is not total, they are not totipotent and they are not embryos. Pluripotent stem cells undergo further specialization into stem cells committed to giving rise to cells that are specialized for a particular function. Multipotent cells can give rise to the cell types found in the tissue from which they were derived, such as blood stem cells that give rise only to red blood cells, white blood cells and platelets, or skin stem cells that give rise only to the various types of skin cells.
Do you have a stem cell policy statement?
The Stem Cell Research Foundation (SCRF) is committed to supporting basic and clinical scientific research to alleviate the burden of human suffering caused by various illnesses and diseases including Parkinson’s disease, diabetes, spinal cord damage, stroke and birth defects. For many of these diseases or conditions, symptoms and suffering are directly caused by the destruction of cells and tissues that the adult human body cannot regenerate. In these situations, as well as in many others, future cures will almost certainly involve replacing the destroyed tissue or cells, and SCRF is committed to all avenues of research that lead to this goal. Any less effort would be a disservice to our many supporters, the millions of victims suffering from these conditions, and their families. Therefore, SCRF supports research to translate the promise of embryonic stem cell research into treatments and cures for millions of Americans suffering from devastating diseases. SCRF supports the ethical derivation and use of human pluripotent stem cells in research. SCRF believes it is our responsibility to make sure that the men, women, and children who are suffering from life-threatening diseases benefit as quickly as possible from the very best that science and technology has to offer.
SCRF understands that infertility treatments generate excess embryos that are discarded. SCRF supports obtaining human stem cells from discarded embryos, or from fetal tissue, and notes that it in no way alters their final disposition. Thus, stem cells destined for destruction can instead be saved to develop future medical benefits, provided that the donors of discarded embryos or fetal tissue are fully informed and give consent. In addition, SCRF supports research on somatic cell nuclear transfer (SCNT), or therapeutic cloning. This technology could allow a patient’s own genetic material to be used to develop stem cell therapies specifically tailored to that individual’s medical condition, thus not triggering an immune rejection response.
SCRF does not support reproductive cloning of human beings.
SCRF recognizes that these are complex issues that engender strong opinions. Indeed, it is impossible for any person or organization to adopt a policy on this subject that will not be in opposition to some opinions and feelings. However, the enormous potential benefit to be derived from this new area of research, and the clear relevance of these benefits to our mission, compel us to join with the broad scientific and patient advocacy communities in supporting the careful and ethical derivation and use of human pluripotent stem cells in scientific research.
