Frequently Asked Questions (FAQs)
- What are stem cells?
Stem cells are cells that have the potential to develop into
some or many different cell types in the body, depending on
whether they are multipotent or pluripotent. Serving as a sort
of repair system, 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.
discussion of the different kinds of stem cells, such as
embryonic stem cells, adult stem cells, or induced pluripotent
stem cells, see
- What classes of stem cells are there?
Stem cells may be pluripotent or multipotent.
- Pluripotent stem cells can give rise to any type of cell
in the body except those needed to support and develop a
fetus in the womb.
- Stem cells that can give rise only to a small number of
different cell types are called multipotent.
- Where do stem cells come from?
There are several sources of stem cells. Pluripotent stem
cells can be isolated from human embryos that are a few days
old. Cells from these embryos can be used to create
pluripotent stem cell "lines" ócell cultures that can be grown
indefinitely in the laboratory. Pluripotent stem cell lines
have also been developed from fetal tissue (older than 8 weeks
In late 2007, scientists identified
conditions that would allow some specialized adult human cells
to be reprogrammed genetically to assume a stem cell-like
state. These stem cells are called
induced pluripotent stem
cells (iPSCs). IPSCs are adult cells that have been
genetically reprogrammed to an embryonic stem cellĖlike state
by being forced to express genes and factors important for
maintaining the defining properties of embryonic stem cells.
Although these cells meet the defining criteria for
pluripotent stem cells, it is not known if iPSCs and embryonic
stem cells differ in clinically significant ways. Mouse iPSCs
were first reported in 2006, and human iPSCs were first
reported in late 2007. Mouse iPSCs demonstrate important
characteristics of pluripotent stem cells, including
expressing stem cell markers, forming tumors containing cells
from all three germ layers, and being able to contribute to
many different tissues when injected into mouse embryos at a
very early stage in development. Human iPSCs also express stem
cell markers and are capable of generating cells
characteristic of all three
Although additional research is needed, iPSCs are already
useful tools for drug development and modeling of diseases,
and scientists hope to use them in transplantation medicine.
Viruses are currently used to introduce the reprogramming
factors into adult cells, and this process must be carefully
controlled and tested before the technique can lead to useful
treatments for humans. In animal studies, the virus used to
introduce the stem cell factors sometimes causes cancers.
Researchers are currently investigating non-viral delivery
Non-embryonic (including adult and umbilical cord blood)
stem cells have been identified in many organs and tissues.
Typically there is a very small number of multipotent stem
cells in each tissue, and these cells have a limited capacity
for proliferation, thus making it difficult to generate large
quantities of these cells in the laboratory. Stem cells are
thought to reside in a specific area of each tissue (called a
"stem cell niche") where they may remain quiescent
(non-dividing) for many years until they are activated by a
normal need for more cells, or by disease or tissue injury.
These cells are also called somatic stem cells.
- Why do scientists want to use stem
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
- 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.
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
disease, amyotrophic lateral sclerosis, spinal cord injury,
burns, heart disease, diabetes, and arthritis.
- Have human embryonic stem cells been
used successfully to treat any human diseases yet?
Stem cell research offers hope for treating many human
Click here to read a description of the current status of
stem cells and human disease therapies.
- 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.
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
There are currently several limitations to using
traditional 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 abnormalitiesócaused 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.
It is now possible to reprogram adult somatic cells to
become like embryonic stem cells (induced
pluripotent stem cells, iPSCs) through the introduction of
embryonic genes. Thus, a source of cells can be generated that
are specific to the donor, thereby increasing the chance of
compatibility if such cells were to be used for tissue
regeneration. However, like embryonic stem cells,
determination of the methods by which iPSCs can be completely
and reproducibly committed to appropriate cell lineages is
still under investigation. Since they are derived from adult
cells, iPSCs may also suffer DNA abnormalities, as described
in the previous paragraph.
- I have Parkinson's Disease. Is
there a clinical trial that I can participate in that uses
stem cells as therapy?
The public may search a database of NIH-sponsored clinical
www.clinicaltrials.gov. Enter the search terms of interest
(in this case, Parkinson's Disease and stem cells) to
search for applicable clinical trials.
- Where can I donate umbilical cord
NIH cannot accept donated umbilical cord stem cells from the
general public. The National Marrow Donor Program maintains a
Web page on donating cord blood at
Research and Policy Questions
- Can a scientist use federal funds to
conduct research using derivatives of human embryonic stem
cell lines that are not listed on the NIH Human Embryonic Stem
No federal funds may be used, either by an awardee or a
sub-recipient, to support research using derivatives of human
embryonic stem cell lines (hESCs) that are not listed on the
NIH Human Embryonic Stem Cell Registry, with the exception
described below. Derivatives include, but are not limited to,
subclones of hESC lines, modified hESC lines (such as a line
expressing green fluorescent protein), differentiated cells
developed from hESC lines (such as muscle progenitor cells),
and cellular materials (such as DNA, RNA, and proteins).
Ongoing NIH-supported research involving derivatives of hESC
lines that were listed on the NIH Registry before April 17,
2009, is subject to the same policy explained in NIH Guide
NOT-OD-09-123 for hESC lines.
- Which research is best to
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 cell 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 pluripotentóthat is, able to give
rise to cells found in all tissues of the embryo except for
germ cells rather than being merely multipotentórestricted to
specific subpopulations of cell types, as adult stem cells are
thought to be. However, a newer type of reprogrammed adult
cells, called induced pluripotent stem cells, has proven to be
pluripotent. Please refer to Basic
Questions FAQ #3, above.
- What are the NIH Guidelines on the
utilization of stem cells derived from human fetal tissue
(embryonic germ cells)?
The Federal Register Announcement
National Institutes of Health Guidelines for Research Using
Human Pluripotent Stem Cells (230k PDF;
get Adobe Reader), published August 25, 2000, was "superceded
as it pertains to embryonic stem cell research" on
November 14, 2001). However, Section II. B, titled
"Utilization of Human Pluripotent Stem Cells Derived from
Human Fetal Tissue," still governs human embryonic germ cell
research. In addition, Section III, titled "Areas of Research
Involving Human Pluripotent Stem Cells That Are Ineligible for
NIH Funding," governs both human embryonic stem cell and human
embryonic germ cell research.
- 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.
- Where can I find information about
patents obtained for stem cells?
The U.S. Patent and Trademark Office offers a
full-text search of
issued patents and published applications. Try searching for
"stem cell" or "stem cells."
Cell Line Availability and the Registry
- I am a scientist funded by the NIH.
How many cell lines are available to me, and how do I get
The NIH has developed the
NIH Human Embryonic Stem Cell Registry. This Registry
lists all cell lines that are eligible for use in NIH funded
The number of lines available for use in NIH
funded research continues to expand, as we continue to review
new lines that have been submitted for NIH's consideration.
Please check the current
NIH Human Embryonic Stem Cell Registry page for the most
To obtain these cells, please follow the "see details"
link, which is found under the Cell Line name, within the
NIH Human Embryonic Stem Cell Registry. This link includes
more information about the selected cell line, as provided to
the NIH. Some of this information may include: whether or not
the cell line is available for distribution, the provider's
name, telephone number, email address, and URL.
- Who owns the cells?
The stem cell lines remain the property of the individual stem
cell providers, as listed on the NIH Human Embryonic Stem Cell
Registry. Researchers may negotiate a material transfer
agreement (MTA) with the cell providers in order to specify
their rights and responsibilities concerning resulting data,
publications, and potential patents.
- Are there any restrictions on the use
of lines listed on the NIH Human Embryonic Stem Cell Registry?
The "see details" link on the
NIH Human Embryonic Stem Cell Registry includes
information on two categories of possible use restrictions:
Provider Restrictions and NIH Restrictions. Provider
Restrictions include things such as experiments that are
prohibited with the cell line, or requirements that proposed
research be approved by an ESCRO or other type of ethical
review committee. NIH Restrictions are imposed on the use of a
line based on the usage of the cells as agreed to by the
donors in their informed consent process.
Subclones and Modified HESC Lines
- Once a human embryonic stem cell line is
listed on the NIH Human Embryonic Stem Cell Registry, are
lines derived from it also eligible?
The NIH Guidelines on Human Stem Cell Research focus on the
requirements for donation of the embryo that was used for
derivation. Once that determination has been made for a
particular line, it applies to all subclones or modifications.
For example, now that WA01 (H1) is eligible for NIH funding,
WA01 lines that express GFP are also eligible.
- Should scientists list the name of the
subclone in their NIH grant application?
Yes, scientists should refer to the parent hESC line and list
the cell line name of the modified line or subclone in the
research plan of their application.