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Mayo Clinic FAQs on Stem Cells posted on Sep 28, 2007

Stem cells: What they are and what they do

You've heard about stem cells in the news, and perhaps you've wondered if they might help you

or a loved one with a serious disease. You may struggle with understanding what stem cells are,how they're being used to treat disease and injury, and why they're the subject of such vigorous

debate.

Here, you can sort through the hype and the hope and get answers to frequently asked questions

about stem cells.

Why is there hih interest in stem cells!

Researchers are interested in stem cells for two main reasons

"nowlede#!y studying how stem cells mature into cells that eventually become bones,

heart muscles, other organs and tissue, researchers hope to learn more about the function ofstem cells and what can go wrong in development. "his knowledge may shed new light on

how a variety of diseases and conditions develop, such as heart disease, cancer or birth

defects.

$herapy#Researchers hope they can manipulate stem cells into becoming specific types of

cells. #f this is done successfully, stem cells may be used to regenerate and repair tissues andorgans to treat diseases and conditions such as diabetes, heart failure, $arkinson's disease,

inherited genetic diseases or spinal cord injuries. %tem cells could also be grown to become

organs to use in transplants, since donor organs are often in short supply. %tem cells may also

one day be useful in testing e&perimental medications before human clinical trials.

What e%actly are stem cells!

%tem cells are master cells of the body cells from which all other cells with speciali(ed

functions are created. )nder the right conditions in the body or a laboratory, stem cells divide toform more cells, called daughter cells. "hese daughter cells either become new stem cells *self+

renewal or become speciali(ed cells *differentiation with a more specific function, such as

blood cells, brain cells, heart muscle or bone. %tem cells are unique no other cell in the body

has the ability to self+renew or to differentiate.

Where do stem cells come &rom!

Researchers have discovered several sources of stem cells

'm(ryonic stem cells# "hese stem cells come from embryos that are four to five days old.

-t this stage, an embryo is called a blastocyst and has about / to 0/ cells. "hese are

pluripotent *ploo+R#$+o+tunt stem cells, meaning they can divide into more stem cells or

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they can speciali(e and become any type of body cell. #n this way, embryonic stem cells have

the highest potential for use to regenerate or repair diseased tissue and organs in people.

Ad)lt stem cells# "hese stem cells are found in small numbers in most adult tissues, such as

bone marrow. -dult stem cells are also found in children and in placentas and umbilicalcords. !ecause of that, a more precise term for these cells is somatic stem cell, meaning 1of

the body.1 )ntil recently, it was felt that adult stem cells could only create similar types of

cells. 2or instance, it was thought that stem cells residing in the bone marrow could give riseonly to blood cells. However, a controversial new theory suggests that adult stem cells may

be more versatile than previously thought and able to create unrelated types of cells after all.

2or instance, bone marrow stem cells may be able to create muscle cells. "his research is inthe very early stages.

'm(ryonic erm cells# "hese are stem cells that come from areas within an embryo or fetus

that are destined to become either the testicles or ovaries. 3ike embryonic stem cells,

embryonic germ cells can become any type of cell. 3ess research has been done onembryonic germ cells because the embryos used to obtain them must be aborted. #n addition,

these cells tend to differentiate spontaneously, so they may be more difficult to use in a

controlled manner. Amniotic &l)id stem cells# Researchers have also discovered stem cells in amniotic fluid.

-mniotic fluid fills the sac that surrounds and protects a developing fetus in the uterus.

Researchers identified stem cells in samples of amniotic fluid drawn from pregnant women

during a procedure called amniocentesis. 4uring this test, a doctor inserts a long, thin needleinto a pregnant woman's abdomen to collect amniotic fluid. "he fluid can be tested for

abnormalities, such as 4own syndrome, and is generally considered safe for the developing

fetus and the mother. Researchers were able to use amniocentesis fluid to identify stem cellsthat could develop into several other types of cells. 5ore study of amniotic fluid stem cells is

needed to understand their potential.

Why is there a contro*ersy a(o)t )sin em(ryonic stem cells!

6mbryonic stem cells are obtained from early+stage embryos a group of cells that forms whena woman's egg is fertili(ed with a man's sperm. 6&tracting stem cells from the embryos destroys

the embryos. %ome people view this as taking a human life, which raises moral and ethical

considerations.

Where do these em(ryos come &rom!

"he embryos being used in embryonic stem cell research come from eggs that were fertili(ed at

in vitro fertili(ation clinics but never implanted in a woman's uterus because they were no longerwanted or needed. "he e&cess embryos were fro(en and later voluntarily donated for research

purposes. "he stem cells can live and grow in special solutions in test tubes or petri dishes inlaboratories.

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Why can+t researchers )se ad)lt stem cells instead!

Researchers believe that adult stem cells may not be as versatile and durable as embryonic stem

cells are. -dult stem cells may not be able to be manipulated to produce all cell types, which

limits how they can be used to treat diseases, and they don't seem to have the same ability tomultiply that embryonic stem cells do. "hey're also more likely to contain abnormalities due to

environmental ha(ards, such as to&ins, or from errors acquired by the cells during replication.

What is a stem cell line and why do researchers want to )se them!

- stem cell line is a group of cells that all descend from a single original stem cell. 8ells in astem cell line keep dividing but don't differentiate into speciali(ed cells. #deally, they remain free

of genetic defects and continue to create more stem cells. 8lusters of cells can be taken from a

stem cell line and fro(en for storage or shared with other researchers. "his way, researchers don'thave to get stem cells from an embryo itself.

Why do researchers want to create more em(ryonic stem cell lines!

Researchers who receive federal funding to support their e&periments as most academic

researchers do are limited by law to working with about 7/ stem cell lines. "hose who want toe&periment using other stem cell lines must find private funding for separate laboratory space

and private funding must also be used to buy separate equipment for research.

"he 7/ or so stem cell lines approved for research date back to the late 099/s, and some

researchers contend that they pose several problems

$he limited n)m(er o& stem cell lines limits the enetic di*ersity a*aila(le, so cells may(e )se&)l only &or certain diseases or people#

$he lines are old, so cells don+t row as well as new ones#

$he lines may ha*e (een contaminated (y nonh)man cells in the rowth c)lt)res,

compromisin their sa&ety#

$he -A in some o& the cells may s)(tly chane o*er time, ca)sin enetic &laws that

co)ld (e passed alon to da)hter cells or to h)mans#

.ow can additional stem cell lines (e made a*aila(le more /)icly to 1#S#

researchers!

#t will take a presidential order or an act of 8ongress signed by the president to make federalfunding available for research on other stem cell lines. "his would speed the development of

embryonic stem cell research in the )nited %tates.

%ome researchers have turned to private funding to finance their embryonic stem cell studies and

have created their own stem cell lines. -lso, individual states can pass their own laws allowingfunding of embryonic stem cell research with state money.

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What is stem cell therapy and how does it wor!

%tem cell therapy is the replacement of diseased, dysfunctional or injured cells with either adult

or embryonic stem cells. #t's somewhat similar to the organ transplant process but uses cellsinstead of organs. %tem cell therapy is sometimes called regenerative medicine.

Researchers grow stem cells in the lab. "hese stem cells are manipulated to make them

speciali(e into specific types of cells, such as heart muscle cells, blood cells or nerve cells. "his

manipulation may involve changing the material in which the stem cells are grown or eveninjecting genes into the cells. "he speciali(ed cells are then implanted into a person. #f the person

has heart disease, the cells would be injected into the heart muscle. "he normally functioning

implanted heart cells, in theory, could replace the defective heart cells.

.a*e stem cells already (een )sed to treat diseases!

Yes, stem cell transplants, also known as bone marrow transplants, have been performed in the

)nited %tates since the late 09;/s. "hese transplants have proved highly successful in treating anumber of cancerous diseases, such as leukemia, and noncancerous diseases, such as aplastic

anemia.

%tem cell transplants use cells harvested from a donor's or person's own bone marrow, circulating

blood or umbilical cord blood. "hese are all adult stem cells. #n addition, adult stem cells have

been used in human e&periments testing the potential treatment of diabetes, heart disease andother conditions.

6mbryonic stem cell treatment is just beginning to be tested in people. 8linical trials using stem

cells to treat neurological diseases are the first to begin recruiting participants.

What are the potential pro(lems with )sin em(ryonic stem cells in h)mans!

"o be useful in people, researchers must be certain that embryonic stem cells will differentiateinto the specific cell types desired. Researchers, for instance, don't want to transplant a stem cell

into a person hoping it'll become a heart cell only to learn that it's become a bone cell, with

potentially dangerous consequences. Researchers have found ways to direct stem cells to becomespecific types of cells, and research into this area continues.

6mbryonic stem cells could also become tumor cells something that's happened in animal

e&periments or travel to a part of the body where they're not intended to go. "hey also might

trigger an immune response in which the recipient's body attacks the stem cells as foreigninvaders, or simply fail to function normally, with unknown consequences. Researchers have

found ways to avoid these complications and continue studying ways to control stem cells.

What is therape)tic clonin and what (ene&its miht it o&&er!

"herapeutic cloning is a technique to create embryonic stem cells without using fertili(ed eggs.

#n this technique, the nucleus is removed from a woman's unfertili(ed egg. "he nucleus is also

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removed from a somatic cell of a donor a person with a disease or injury, such as type 0

diabetes. "his donor nucleus is then injected into the egg, replacing the nucleus that was

removed, a process called nuclear transfer. "he egg is allowed to divide and soon forms ablastocyst. "his creates a line of embryonic stem cells that is genetically identical to the donor's

in essence, a clone. "his technique is also called somatic cell nuclear transfer.

%ome researchers believe that embryonic stem cells derived from therapeutic cloning may offer

benefits over those from fertili(ed eggs because they're less likely to be rejected oncetransplanted back into the donor, and they may allow researchers to see e&actly how a disease

develops.

#n addition, some researchers consider therapeutic cloning a good alternative to creatingembryonic stem cell lines from fertility treatments, since they come from cells that were never

fertili(ed. However, this technique is not without opponents. 8ritics contend therapeutic cloning

can also be perceived as destruction of a human life or potential human life.

.as therape)tic clonin in people (een s)ccess&)l!

Researchers haven't been able to successfully perform therapeutic cloning of humans. #n 7//,%outh =orean researchers reported creation of human embryonic stem cells this way, but their

claims were ultimately not substantiated.

What does the &)t)re hold &or stem cell therapy!

Researchers say the field has promise. %tem cell transplants using adult stem cells continue to berefined and improved. -nd researchers are discovering that adult stem cells may be somewhat

more versatile than originally thought, which means they may be able to treat a wider variety of

diseases. %tudies using embryonic stem cells to regenerate tissue and organs in people are justgetting started. Researchers are enthusiastic about the potential for these treatments.