The answers to the following questions were written and reviewed by a panel of scientists who specialize in Stem Cell Research. (www.isscr.org)
1. What are stem cells?
Stem cells are the foundation cells for every organ, tissue and cell in the body. They are like a blank microchip that can ultimately be programmed to perform particular tasks. Stem cells are undifferentiated or “blank” cells that have not yet fully specialized. Under proper conditions, stem cells begin to develop into specialized tissues and organs. Additionally, stem cells can self-renew, that is they can divide and give rise to more stem cells.
There are many different types of stem cells. These include embryonic stem cells that exist only at the earliest stages of embryonic development; as embryonic stem cells can form all cell types of the body, they are referred to as ‘pluripotent’ stem cells. There are various types of ‘adult’ or ‘tissue-specific’ stem cells that exist in a number of different fetal and adult tissues. These stem cells generally can only form a limited number of cell types corresponding with their tissues of origin; they are called ‘multipotent’ stem cells.
2. Where do stem cells come from?
Embryonic stem cells are derived from the inner cell mass of a blastocyst: the fertilized egg, called the zygote, divides and forms two cells; each of these cells divides again, and so on. Soon there is a hollow ball of about 150 cells called the blastocyst that contains two types of cells, the trophoblast and the inner cell mass. Embryonic stem cells are obtained from the inner cell mass.
Stem cells can also be found in small numbers in various
tissues in the fetal and adult body. For example, blood stem
cells are found in the bone marrow that give rise to all
specialized blood cell types. Such tissue-specific stem cells
have not yet been identified in all vital organs, and in some
tissues like the brain, although stem cells exist, they are not
very active, and thus do not readily respond to cell injury or
Stem cells can also be obtained from other sources, for
example, the umbilical cord of a newborn baby is a source of
blood stem cells. Recently, scientists have also discovered the
existence of cells in baby teeth and in amniotic fluid that may
also have the potential to form multiple cell types. Research on
these cells is at a very early stage.
Recently, cells with properties similar to embryonic stem
cells, referred to as induced pluripotent stem cells (iPS cells)
have been engineered from somatic cells (see ‘What is are
induced pluripotent stem cells?’).
3. What is a stem cell line?
A stem cell line is a population of cells that can replicate themselves for long periods of time in vitro, meaning outside of the body. These cell lines are grown in incubators with specialized growth factor-containing media (liquid food source), at a temperature and oxygen/carbon dioxide mixture resembling that found in the mammalian body.
4. What is an embryonic stem cell?
Embryonic stem cells are those grown from the cells that make up the inner cell mass of the blastocyst. Embryonic stem cells have been derived from a variety of animals, including human, and are described as ‘pluripotent’- that is, they are capable of generating any and all cells in the body under the right conditions.
Embryonic stem cell lines can be grown indefinitely in vitro
if the correct conditions are met. Importantly, these cells
continue to retain their ability to form different, specialized
cell types once they are removed from the conditions that keep
them in an undifferentiated, or unspecialized, state.
The most widely studied are mouse embryonic stem cells. Mouse embryonic stem cells have taught us a lot about how pluripotent cells grow and specialize, and how embryonic development works. Indeed, mouse embryonic stem cells are a critical research tool for studying the function of individual genes and modeling human diseases. Mouse embryonic stem cells can be manipulated to contain specific genetic changes then used to generate mice which contain this change. Capecchi, Evans and Smithies were awarded the Nobel Prize in Physiology or Medicine, 2007 for developing this process. Read more.
Human embryonic stem cells were isolated relatively recently, in 1998. They are more difficult to work with than their mouse counterparts and currently less is known about them. However, scientists are making remarkable progress, learning about human developmental processes, modeling disease and establishing strategies that could ultimately lead to therapies to replace or restore damaged tissues using these human cells.
5. What is an adult stem cell?
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 30 years. More advanced techniques of collecting, or “harvesting,” HSCs are now used in order to treat leukemia, lymphoma and several inherited blood disorders.
Adult Stem Cells Advantages:
Have been used safely in humans for over 40 years in the United States for the treatment of bone marrow cancer and leukemia.
No danger of immune system rejection with cells from the patient’s own body.
Unlike embryonic stem cells there is an extremely low risk of tumor growth.
Easier to control than embryonic stem cells.
There are no ethical issues in the use of adult stem cells and their use is endorsed by the Catholic Church Medical Association.
6. What are ‘induced pluripotent cells’ or iPS cells?
Induced pluripotent cells (iPS cells) are non-pluripotent cells that were engineered (‘induced’) to become pluripotent, that is, able to form all cell types of the body. In other words, a cell with a specialized function (for example a skin cell) was ‘reprogrammed’ to an unspecialized state similar to that of an embryonic stem cell. While iPS cells and embryonic stem cells share many characteristics they are not identical.
The generation of mouse iPS cells was reported in 2006 (read
the ‘Briefing’), and the generation of human iPS cells at the
end of 2007 (read the ‘Briefing’).
Currently, iPS cells are produced by inserting copies of
three-four genes into specialized cells known to be important in
embryonic stem cells using viruses. Different groups have used
slightly different combinations of genes. It is not completely
understood how each of these genes functions to confer
pluripotency and ongoing research is addressing this question.
The technology used to generate iPS cells holds great promise
for creating patient- and disease-specific cell lines for
research purposes. However, a great deal of work remains before
these methods can be used to generate stem cells suitable for
safe and effective therapies.
7. What are the potential uses of human stem cells?
Stem cell research contributes to a fundamental understanding of how organisms develop and grow, and how tissues are maintained throughout adult life. This is knowledge that is required to work out what goes wrong during disease and injury and ultimately how these conditions might be treated. The development of a range of human tissue-specific and embryonic stem cell lines will provide researchers with the tools to model disease, test drugs and develop increasingly effective therapies.
Replacing diseased cells with healthy cells, a process called
cell therapy, is a promising use of stem cells in the treatment
of disease; this is similar to organ transplantation only the
treatment consists of transplanting cells instead of organs.
Currently, researchers are investigating the use of adult, fetal
and embryonic stem cells as a resource for various, specialized
cell types, such as nerve cells, muscle cells, blood cells and
skin cells that can be used to treat various diseases.
In theory, any condition in which there is tissue
degeneration can be a potential candidate for stem cell
therapies, including Parkinson’s disease, spinal cord injury,
stroke, burns, heart disease, Type 1 diabetes, osteoarthritis,
rheumatoid arthritis, muscular dystrophies and liver diseases.
In addition, retinal regeneration with stem cells isolated
from the eyes can lead to a possible cure for damaged or
diseased eyes and may one day help reverse blindness. Bone
marrow transplantation (transfers blood stem cells) is a
well-established treatment for blood cancers and other blood
8. What are the obstacles that must be overcome before the
potential uses of stem cells in cell therapy will be realized?
Here are just a few of the challenges that lie ahead. Firstly, a source of stem cells must be found. The process of identifying, isolating and growing the right kind of stem cell, for example a rare cell in the adult tissue, is painstaking. In general, embryonic and fetal stem cells are believed to be more versatile than tissue-specific stem cells. Secondly, once stem cells are identified and isolated, the right conditions must be developed so that the cells differentiate into the specialized cells required for a particular therapy. This too will require a great deal of experimentation. Thirdly, a system that delivers the cells to the right part of the body must be developed and the cells once there must be encouraged to integrate and function in concert with the body’s natural cells.
Furthermore, just as in organ transplants, the body’s immune
system must be suppressed to minimize the immune reaction set
off by the transplanted cells.
9. Are stem cells currently used in therapies today?
Hematopoietic stem cells (HSCs) or blood stem cells, present in the bone marrow are the precursors to all blood cells. Blood stem cells are currently the only type of stem cells commonly used for therapy. Doctors have been transferring blood stem cells by bone marrow transplant for more than 40 years. Advanced techniques for collecting or “harvesting” HSCs are now used to treat leukemia, lymphoma and several inherited blood disorders. Cord blood, like bone marrow, is stored as a source of HSCs and is being used experimentally as an alternative to bone marrow in transplantation.
New clinical applications for stem cells are currently being
tested therapeutically for the treatment of musculoskeletal
abnormalities, cardiac disease, liver disease, autoimmune and
metabolic disorders (amyloidosis), chronic inflammatory diseases
(lupus) and other advanced cancers. However, these new therapies
have been offered only to a very limited number of patients.
10. Why is cord blood a valuable resource?
Cord blood is rich in hematopoietic or blood stem cells and is currently being used as an alternative to bone marrow transplantation. The collection process is completely non-invasive; the host-donor match required for transplantation is less lower risk of graft vs. host disease.
11. Why are researchers interested in developing
disease-specific or patient-specific pluripotent stem cells?
The development of patient-specific or disease-specific pluripotent stem cells has great therapeutic promise for three reasons. Firstly, these cells could provide a powerful new tool for studying the basis of human disease and for discovering new drugs. Secondly, the resulting embryonic stem cells could be developed into a needed cell type, and if transplanted into the original donor, would be recognized as ’self’, thereby avoiding the problems of rejection and immunosuppression that occur with transplants from unrelated donors.
12. What is somatic cell nuclear transfer (SCNT)?
Somatic cell nuclear transfer (SCNT) is a technique in which the nucleus of a somatic cell, that is any cell of the body apart from the sperm or egg, is transferred into an egg that has had its original nucleus removed. The egg now has the same DNA, or genetic material, as the donor somatic cell. Given the right signals, the egg can be coaxed into developing as if it had been fertilized. The egg would divide to form 2 cells, then 4 cells, then 8 cells and so on until the blastocyst is formed. Embryonic stem cells can be derived from this blastocyst to create cell lines that are genetically identical to the donor somatic cell.
13. Why derive embryonic stem cell lines following somatic
cell nuclear transfer (SCNT)?
The derivation of patient-specific human embryonic stem cell lines using this technique (see ‘What is somatic cell nuclear transfer?’) Firstly, these cells could provide a powerful new tool for studying the basis of human disease and for discovering new drugs. Secondly, the resulting embryonic stem cells could be developed into a needed cell type, and if transplanted into the original donor, would be recognized as ’self’, thereby avoiding the problems of rejection and immunosuppression that occur with transplants from unrelated donors.
14. Can induced pluripotent cells replace research on embryonic stem cells or somatic cell nuclear transfer?
No. The derivation of human induced pluripotent stem cells opens up exciting new areas of stem cell research, however, this technology is at a very early stage and many fundamental questions remain. While iPS cells and embryonic stem cells share many characteristics they are not identical. The similarities and differences are still being explored.
Research on human embryonic stem cells, somatic cell nuclear
transfer and ‘adult’ or tissue-specific stem cells needs to
continue in parallel. All are part of a research effort that
seeks to expand our knowledge of how cells function, what fails
in the disease process, and how the first stages of human
development occur. It is this combined knowledge that will
ultimately generate safe and effective therapies.
15. What is reproductive cloning?
If an egg generated by somatic cell nuclear transfer (see ‘What is somatic cell nuclear transfer?’) was implanted into the womb of an animal, an individual would be born that has identical genetic material as the donor somatic cell and might be referred to as a ‘clone’. The procedure is referred to as ‘reproductive cloning’ and is fraught with profound technical and biological problems. The overwhelming consensus of the world’s scientific and medical communities is that at this time human reproductive cloning should be banned.
16. What is Regenerative Medicine?
The goal of regenerative medicine is to repair organs or tissues that are damaged by disease, aging or trauma, such that function is restored, or at least improved without the need for a transplant.
The term regenerative medicine is often used nowadays to
describe medical treatments and research that use stem cells
(either adult or embryonic) to restore the function of organs or
tissues. This can be achieved in different ways; first, by
administering stem cells, or specific cells that are derived
from stem cells in the laboratory; or second, by administering
drugs that coax stem cells that are already present in tissues
to more efficiently repair the involved tissue.
17. What is bioethics?
Bioethics is the study of the moral and ethical issues in the fields of scientific research, medical treatment and, more generally, in the life sciences. With advancing technology come new and exciting insights into scientific processes and diseases; at the same time, new ethical issues arise.
Stem Cells for Hope operates by the highest bioethical
standards in our use of Adult Stem Cells and Cord Blood Stem
Cells to treat our patients. Our Clinics and Hospitals, in turn
operate under the highest Medical standards in the care and
treatment of all our patients.