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What Are Stem Cells?

Updated on November 18, 2013

Stem Cell Differentiation

In this example, multipotent adult stem cells from bone marrow give rise to many different blood cells.
In this example, multipotent adult stem cells from bone marrow give rise to many different blood cells. | Source

Types of Cells

The human body (and every other multi-cellular organism) has millions of cells, which perform different functions within the body. The cells in the liver are different from the cells in the brain, and both of these cell types are different from the cells that form bone. These cells are differentiated, which means they are specific to the function they need to perform.

Early in development, however, cells are not differentiated: the cells in a very early embryo (called a blastocyst) can become any cell type. These cells are pluripotent, with the potential to become a bone cell, cardiac cell, or any other cell within the body. Stem cells are pluripotent cells, and occur in embryos and in some adult tissues (namely, skin and blood).

Embryonic Stem Cells

Embryonic stem cells, as seen under a microscope.
Embryonic stem cells, as seen under a microscope. | Source

Where Are Stem Cells Found?

Embryonic Stem Cells are found in early embryos, before cellular differentiation has begun. Early embryos are usually obtained from in-vitro fertilization, with the donor’s consent. The cells are grown in a nutrient rich broth called a culture medium. Cells that grow successfully and do not have any genetic defects, mutations, or signs of differentiation become an embryonic stem cell line.

Cord Blood Stem Cells are stem cells circulating through a baby’s blood system at the time of birth. Blood is taken from the infant’s umbilical cord to harvest these cells. While not as pluripotent as embryonic stem cells, the cells found in an umbilical cord are more flexible than adult stem cells. These “cord blood derived embryonic-like stem cells” (CBEs) can be induced to form many different tissue types, and are easier to grow than adult stem cells.

Adult Stem Cells are found in many different tissues. Stem cells have been found in skin, bone marrow, muscle, the intestinal tract, and in many other organs. These stem cells reside in what is called a stem cell niche, and are very difficult to grow outside the human body. Once identified, the cells are grown in cell culture media, and scientists try to induce them to differentiate into the tissue they were derived from. If successful, these induced stem cells can be used to treat diseases like Type I Diabetes (pancreatic cells) or injuries. For example, burns may be treated with the use of skin stem cells, which grow new skin over the patient’s wounds.

Some scientists are working on inducing adult stem cells to turn into a tissue that differs from the “parent” tissue – this is called transdifferentiation. Genetic modification is used to program these cells to differentiate into a new tissue type – in this case, a neural stem cell might be induced to become a hematopoietic stem cell. Another method for transdifferentiation is programming the adult stem cells to return to an embryonic stem cell state – a process known as Induced Pluripotent Stem Cells (iPSCs).

Types of Adult Stem Cells

Cell Type
Gives Rise to These Tissues
Potential Therapies
red blood cells, macrophages, lymphocytes, eosinophils, basophils, monocytes
Transplants for leukemia and multiple myeloma
fat cells, bone cells, cartilage cells
Reconstruction of damaged bone and vascular tissue
astrocytes, oligodendrocytes, and neurons
Treatment of ALS, strokes, and spinal cord injuries
cells lining the intestinal tract: goblet cells, absorptive cells, endocrine cells, and paneth cells
Treatment of ectodermal dysplasias, burn wounds, and ulcers
hair and skin
Wound treatment from burns, baldness

Stem Cell Controversy

There is little controversy over the use of cord blood stem cells or adult stem cells, but the use of embryonic stem cells has generated a significant ethical debate. The acquisition of embryonic stem cells from donated embryos requires the destruction of that embryo. For some, this is the same situation as infanticide. For others, the early stage embryos have no moral status at all. The basic beliefs about the use of embryonic cells are:

No Moral Status

There are those who believe the embryonic cells have absolutely no moral status, as they have no thoughts, expectations, or beliefs.

Full Moral Status at Fertilization

For some, the early embryos are viewed as "persons," with the same rights and protections as any other member of society. Since the development from zygote (fertilized egg) to infant is a continuous process, a single point of time for becoming a "person" cannot be established. The embryo will become a person and should be protected as such from the moment of conception.

Moral Status at 14 Days

Prior to 14 days post-fertilization, an embryo may still split into twins (or more), has no central nervous system, and cells are undifferentiated. Some believe this is the cut-off point for the use of embryonic stem cells: once the primitive streak appears to form the central nervous system, full moral status should be granted to the embryo.

Embryonic Stem Cell Poll

When should an embryo be considered a person?

See results

Gradual Onset of Moral Status

As a developing embryo goes through many "milestones" of development, there are a number of stages where increasing moral status could be granted. Some milestones include:

  • Six days after fertilization, the embryo implants into the uterine wall. This is approximately the timea pregnancy test would turn positive.
  • 14 days after fertilization, the embryo develops the beginning stages of the central nervous system.
  • Four weeks after fertilization, when the embryo develops a heart beat.
  • 8 weeks after fertilization, when the fetus has detectable brain waves.
  • 21-22 weeks after fertilization, the limit of viability outside the womb (with intensive care).
  • 38 weeks after fertilization, or birth.

Pluripotent Stem Cells

Pluripotent stem cells naturally occur in early embryos.
Pluripotent stem cells naturally occur in early embryos. | Source

Induced Pluripotent Stem Cells

Due to the controversy surrounding the use of embryonic cells, there has been an emphasis on creating "embryonic-like" cells from adult stem cells. These cells are called induced pluripotent stem cells (iPSCs), and are often difficult to discern from embryonic stem cells by genetic analysis. Since the iPSCs have been reprogrammed to behave like embryonic cells, there may be sporadic "errors" in some of the clones. Careful selection and evaluation must be used when selecting cells for use in medical applications.

The very first iPSCs were created from mouse cells in 2006 - by 2007, the same feat was accomplished in human cells. Four critical genes (Oct3/4, Sox2, klf4, and c-Myc) were introduced into the adult stem cells using a retrovirus. These genes are master transcriptional regulators, and induce the cells to become pluripotent.

Adult Stem Cells to Heal Burns

Stem Cell Research and Therapies

There are many clinical trials currently underway to create treatments for genetic diseases with stem cells. Lou Gehrig's Disease, or Amyotrophic Lateral Sclerosis (ALS) is one such disease currently in the clinical trial phase. Neural stem cells are injected into different areas of the spinal cord, in the hope that they will form new, healthy nerve cells, preserving the functionality of the diaphragm (allowing the patient to keep breathing, since respiratory failure is a fatal complication of this disease).

Stem cells may also treat victims of traumatic injuries and burns. A "skin gun" was developed by Dr. Jörg Gerlach as a way to apply skin stem cells to burn victims. Skin stem cells are isolated from an area of healthy skin on the patient, grown in a bioreactor, and then sprayed on the burn area with the specialized spray gun. The skin will regrow over the burned area in a matter of days, much faster than traditional skin graft methods. In addition, since the skin comes from the patient's own skin cells, there is no chance of rejection by the immune system. The skin cells simply grow and cover the burned area, preventing infection and other complications. This treatment is not a future possibility, but a real, current treatment option at the Berlin Burn Center in Germany.

Stem Cell Therapy Stories, Part 1

Stem Cell Therapies, Part 2

Stem Cell Therapies, Part 3


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    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      CassyLu1981, the future is very bright with the promise of new treatments with stem cells. The ability to turn adult stem cells into pluripotent cells removes the ethical dilemma from the issue.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      There is a lot of promise for stem cell therapy - there is a case of a young woman who had her hearing restored after autoimmune inner ear disease with her own adult stem cells - this makes me very excited for the future, lindacee! The future holds much promise.

    • CassyLu1981 profile image

      CassyLu1981 5 years ago from Spring Lake, NC

      Love the hub!!! There is so much that stem cell research can help these days. Voted up and shared!

    • lindacee profile image

      lindacee 5 years ago from Arizona

      Wow, excellent article Leah! Stem cell research and therapy holds such promise for so many people. Voted up, useful and interesting.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Thanks, meloncauli! I am glad you found it interesting - I can't wait to see what future therapies come from the use of stem cells.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      I agree, watergeek. Stem cell research is a good thing, particularly since there are a variety of sources for obtaining the pluripotent cells. There is a lot of misinformation about how stem cells are obtained and where they come from - I did make the DNA divider in GIMP (a free online photo editor).

    • meloncauli profile image

      meloncauli 5 years ago from UK

      Fascinating article Leah! Really interesting read and well executed.

    • watergeek profile image

      watergeek 5 years ago from Pasadena CA

      Great article, Leah. I would only like to have known early in it who was doing all this research. I'm now convinced that stem cell research is a good thing, whereas I was unsure before. I like your chart too, and the DNA strand divider is pretty cool. You developed that, didn't you?

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Hi krsharp05 - I am not sure what your question is asking - how a woman with a hysterectomy is related to stem cell production? Most embryonic stem cells are generated from leftover embryos from in-vitro fertilization (which is done by women who have uteri and would generally like to conceive a child, but have extra embryos left over once the process is complete). These embryos are often donated to science, which may use them to generate new embryonic stem cell lines. The adult stem cells may be gathered from whichever tissue is desired - from muscle, skin, blood, etc. These cells can then be induced to become pluripotent like the embryonic stem cells, or simply used ot regenerate the type of tissue they were derived from.

    • krsharp05 profile image

      Kristi Sharp 5 years ago from Born in Missouri. Raised in Minnesota.

      Wow. What about women who have had hysterectomies and still have ovaries? Very interesting information leah. Awesome hub. -K

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Thanks, Emma! My own son has a congenital hearing loss and we hope that stem cells may one day provide a path to restoring his hearing - there is a lot of research into this area, and there are a few adults with autoimmune hearing loss who have been helped with that type of therapy already!

    • Emma Harvey profile image

      Emma Kisby 5 years ago from Berkshire, UK

      This is such an interesting hub which is well written. I have learned a lot about stem cells here, and it has bought a lot to my attention..

      Really like this - voting up and interesting.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Thanks, teaches12345 - stem cells are a fascinating area of study. They have recently found cancer stem cells, which explains why traditional chemotherapy is not always effective for some cancers, as the cancer stem cells generate more cancer cells. There is hope that by learning to identify and destroy the cancer stem cells, treatment could be made more effective.

    • teaches12345 profile image

      Dianna Mendez 5 years ago

      Leah, this is another well written article and shows your creative talent well. This is one that could be part of a medical journal reference. Good post!

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      The ethics are the most difficult question with regard to embryonic stem cells, Robert. The use of induced pluripotent stem cells really avoids the entire dilemma, since these cells are created from adult stem cells.

    • Robert Erich profile image

      Robert Erich 5 years ago from California

      Another fantastic hub! And yes, I think that the use of adult stem cells are an important thing to research more. The benefit that stem cells can have on countless health problems make them very important. It is simply challenging to know where the line is ethically with the embryonic stem cells. Great article and useful information!

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      There is a lot of promising data from new clinical trials regarding stem cells, healthylife2. A recent trial demonstrated an improvement in vision in two legally blind adults. I am excited to see all the new treatments that are generated from the technology!

    • healthylife2 profile image

      Healthy Life 5 years ago from Connecticut, USA

      Very informative...other countries are much farther ahead with stem cell research because of all the controversy in our country. There is no real way to resolve the when does life begin question but adult cells are a great alternative. So many diseases can be cured with stem cells.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Thanks, Riverfish! I love the "skin gun" - I hope these technologies improve over time to improve people's quality of life!

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      There is a lot of controversy over the use of embryonic stem cells, moonlake - the advent of induced pluripotent stem cells (turning adult stem cells into pluripotent cells) is very important, as it removes the need for embryonic cells.

    • Riverfish24 profile image

      Riverfish24 5 years ago from United States

      Great hub, informative, useful and very well usual leahlefler!

    • moonlake profile image

      moonlake 5 years ago from America

      I'm all for stem cell research but not embryonic stem cells. Interesting hub.

    • leahlefler profile image

      Leah Lefler 5 years ago from Western New York

      Stem cells are generating a lot of buzz, Carol7777 - there is controversy over the use of embryonic stem cells, but many therapies have also been developed from adult stem cells (which do not carry the same controversy).

    • carol7777 profile image

      carol stanley 5 years ago from Arizona

      I have heard the word stem cells, but never had a clue as to to what they were. You have explained all this very well. Voted UP.