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
damage.
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.
Ethical Issues:
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
disorders.
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?
stringent and cord blood has fewer mature immune cells and
thus poses a
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.