For the latest COVID-19 campus news and resources, visit

Search Close Search
Search Close Search
Page Menu

Stem Cell Facts

What Are Embryonic Stem Cells?

Embryonic stem (ES) cells are a collection of cells found only in very early development which are the precursors to every cell    type in the human body.  The vast majority of cells in the body (somatic cells) fall into specific classes or types, such as muscle, bone and neurons, each of which have unique characteristics and functions.  However, these cells are not interchangeable (a muscle cell cannot become a neuron) and most of these cells have lost the ability to multiply to create new cells.  ES cells differ from all other cells in two important ways.  First, they can be induced tochange, or differentiate, into virtually any cell type.  Second, unlike somatic cells which have finite lifespans, ES cell can grow indefinitely in culture.  These two unique characteristics give ES cells enormous potential to medicine and science.


hesc small 

Why Are Embryonic Stem Cells So Important?

Embryonic stem cells are important to medicine because of their ability to change into other cell types.  This ability means that ES cells have the potential to repair damaged organs and replace cells that do not function properly. Since they can multiply indefinitely, the large numbers of cells necessary to repair or replace these tissues can be produced.  Thus, the hope is that ES cells can be a renewable source of replacement cells that can be used to treat a number of medical problems including Parkinson's and Alzheimer's disease, strokes, burns, spinal cord damage and heart disease.

What are iPS Cells?

Recent publications have described the derivation of ES-like induced pluripotent stem (iPS) cells from adult mouse and human cells (Nakagawa et al., 2008; Takahashi et al., 2007; Yu et al., 2007).  These researchers introduced specific sets of genes encoding transcription factors which are normally expressed in undifferentiated ES cells.  The expression of these genes resulted in the “reprogramming” of the adult cells to a more ES-like or pluripotent state.   While the initial studies indicate that these cells share characteristics of “true” ES cells, more detailed work is needed to determine how closely they resemble ES cells.  In addition, the reintroduction of these genes can have adverse consequences.  For instance, the use of retroviruses and the potential for reactivation of introduced genes such as c-myc and Oct-4 can increase the risk of cancer. These issues will need to be addressed if iPS technology will have clinical applications. 

ips small

What About Adult Stem Cells?

The human body has a relatively small number of cells, called adult stem cells that are capable of differentiating into a limited range of cell types.  For instance, blood stem cells are capable of changing into a number or different types of blood cells.  These adult ES are also of enormous importance to medicine.  However, they have limitations that ES cells do not.  First, they are limited in the number of types of cells into which they can change.  For instance, blood stem cells cannot form bone.  In addition, unlike ES cells adult stem cells do not appear to have the same capacity to multiply indefinitely.  They have also been more difficult to grow in the laboratory.  So, while adult stem cells are important, they cannot be viewed at this time as a replacement for ES cells.  Research into all types of stem cells is needed in order to advance medicine’s ability to treat disease.

Types of Stem Cells


hES Cells


iPS Cells

Adult Stem Cells

Derivation Method

Removal of cells from ICM of blastocyst embryo from IVF.

Somatic Cell Nuclear Transfer.  Transfer of somatic cell nucleus to enucleated egg, development to blastocyst, removal of ICM.

Reprogramming of somatic cells by introduction of specific regulatory factor genes.

Isolation from adult tissues.


Differentiate into all cell types.

Excess of IVF embryos exist.

Differentiate into all cell types.

Stem cells can be matched to patient

“ES cell – like” characteristics.

Stem cells can be matched to patient

Doesn't require embryos.

Successful treatments demonstrated.

Stem cells can be matched to patient


Limited number of lines available for federally funded research.

Immune rejection issues

Risk of tumors (teratomas) from transplanting undifferentiated cells.

Requires use of embryo.

Risk of tumors (teratomas) from transplanting undifferentiated cells.

Eggs difficult to obtain.



Unknown if cells can differentiate into all cell types.

Risk of tumors (teratomas) from transplanting undifferentiated cells and from expression of introduced genes.

Cells not found in all tissues.

Produce a limited number of cell types.

Difficult to identify, isolate and grow.


Links to More Information

Basic Information on Stem Cells

Stem Cell Basics  Prepared by the National Institutes of Health, this primer on stem cells answers a number of fundamental questions about the properties and potential uses of embryonic and adult stem cells with a glossary of terms and illustrations.

Tell Me About Stem Cells This site, created by Harvard and MIT, provides basic information about stem cells in plain language with illustrations.

Understanding Stem Cells  Developed and published by the National Academy of Sciences, this free booklet (available as a 1.13 MB PDF, 24 pages) provides information on what stem cells are and why stem cell research is important, as well as the ethical and legal issues surrounding stem cells.

EuroStemCell  This website presents information and educational resources about stem cells from a European perspective.

Frequently Asked Questions about Stem Cells

National Institutes of Health Stem Cell FAQs  This page contains a wealth of information, from basic questions about stem cells, to research and potential clinical uses of stem cells as well as US government policies. 

ISSCR Stem Cell FAQs  Prepared by the International Society for Stem Cell Research, this page addresses a number of basic questions about embryonic and adult stem cells, their origins and potential uses.

MedlinePlus: Stem Cells   This site offers a number of useful links for those seeking health-related information about embryonic and adult stem cells; from basic information to disease specific sites to links to clinical trials.

Facts about Stem Cell Treatments

A Closer Look at Stem Cell Treatments This site is designed to arm patients, their families and doctors with information they need to make decisions about stem cell treatments. The content of this site is based on recommendations from the ISSCR's Task Force on Unproven Stem Cell Treatments.

21st Century Snake Oil  A CBS 60 minutes story from 2010 that serves as a warning about unscrupulous stem cell therapies.


Our collaborators:

Stembook Link