Where Are Stem Cells Found In The Body?

Stem cells, artistic rendering. The type of cells used in stem cell transplants for cancer patients come from a living donor. Not to be confused with embryonic stem cells, which are obtained by destroying a human embryo..

Question:

Where are stem cells found in the body?

Answer:

Stem cells come from different places, depending on the type of stem cell you are talking about.

In leukemia and lymphoma, stem cells may be transplanted into the person with cancer to help replenish the bone marrow for production of new blood cells. In these cases, the stem cells come from the bone marrow or bloodstream of a living donor. Stem cells of this type are also known as adult stem cells and, more specifically, hematopoietic stem cells, since they give rise to blood cells.

The stem cell transplants performed in people with cancer do not use any embryonic cells.

When it comes to stem cell research, however, stem cells might come from any number of different sources, including from specialized tissues of living human donors or sacrificed human embryos. See "Other Stem Cells," below.

Stem Cells for Transplants (HSCT) in Cancer

The bone marrow makes all of your blood cells: red cells, white cells, and other cells called megakaryocytes that make platelets to help with clotting. Hematopoietic stem cells within the bone marrow are the “parents” or progenitors of all of these different cell types that form the blood.

These hematopoietic stem cells are transplanted into a person with cancer to help replenish healthy bone marrow and blood cells; high doses of chemotherapy kill cancer cells effectively, but also kill stem cells in the bone marrow. So, shortly after chemotherapy, stem cells are given into a vein, much like a blood transfusion.

The cells take some time to settle into the bone marrow and begin to grow and make new healthy blood cells.

Bone Marrow vs. Peripheral Blood

Years ago, the only source for stem cells used in transplants was bone marrow. Then a small number of blood-forming stem cells was discovered circulating out in the peripheral bloodstream.

Doctors learned to collect these stem cells from the circulating blood -- and to use them for transplants. This type of transplant, known as a peripheral blood stem cell transplant, or PBSCT, has become more common than transplants from bone marrow, however both methods are in use today.

Other Stem Cells

In other cases, and in the absence of additional information, the term "stem cell" is ambiguous as to the source of the cells. Additional descriptors are needed to tell you what type of stem cell it is and where it comes from. There are currently three main categories of stem cells; each one has a different source:

Embryonic stem cells are the most controversial stem cells, since they come from human embryos that have been destroyed, or harvested for science. According to the National Institutes of Health (NIH) stem cells from sacrificed human embryos were first grown in a laboratory in 1998; they were originally “created for reproductive purposes,” but when they were no longer needed, they were donated with informed consent of "the donor" -- presumably the egg donor, but possibly the sperm donor -- or perhaps both -- in any case, consent obviously does not refer to the developing human embryo.

Children are usually deemed unable to provide consent for medical procedures prior to the age 16 years; sometimes 18 years of age is used as the threshold age for consent.

Adult stem cells are also called somatic stem cells. These stem cells are obtained without the destruction of a human embryo. Hematopoietic or blood-forming stem cells are an example of this kind of stem cell, and they have been used for generations. The term “somatic” means “body” and underscores that these cells come from a living body and not from a sacrificed embryo. Scientists have found adult stem cells in many more tissues than once thought possible. According to the NIH, adult stem cells have been found in many organs and tissues, including brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian cells, and testis.

Induced pluripotent stem cells, or iPSCs, are adult cells that have been genetically reprogrammed to be more like embryonic stem cells. The source is adult or somatic cells and not embryonic cells, but these are adult cells that have undergone genetic engineering. According to UCLA's Center for Regenerative Medicine and Stem Cell Research, iPSCs usually start out as skin cells or blood cells, which then undergo genetic programming. It is currently possible to produce almost any desired cell type from any patient's cells. Laboratory research has shown promising results using these cells to correct a number of genetic disorders of the blood, nervous system and muscles.

Updated February 2016, TI.

Sources:

National Institutes of Health. Stem Cell Information. Stem Cell Basics. Accessed February 2016.

Simara P, Motl JA, Kaufman DS. Pluripotent Stem Cells and Gene Therapy. Transl Res. 2013;161(4):284-292.

Al-Shamekh S, Goldberg J. Retinal Repair with Induced Pluripotent Stem Cells. Transl Res. 2014;163(4):377-386.

Finkbeiner SR, Spence JR. A Gutsy Task: Generating Intestinal Tissue from Human Pluripotent Stem Cells. Digestive Diseases and Sciences. 2013;58(5):1176-1184.

Priori SG, Napolitano C, Di Pasquale E, Condorelli G. Induced pluripotent stem cell–derived cardiomyocytes in studies of inherited arrhythmias. J Clin Invest. 2013;123(1):84-91.

UCLA. Induced Pluripotent Stem Cells (iPS). Accessed February 2016.

Continue Reading