Sources of Stem Cells

Stem cells can be found anywhere in the body, but in some areas there are more of these cells than in other areas. You can find stem cells in tissues, organs, bloodstream, and almost any main part of an individual’s body. However, the removal of these cells from certain parts like organs and tissues can be very painful and presents a higher risk. Some parts don’t give sufficient amounts of stem cells to doctors to ensure a successful transplant. The most popular place to get stem cells is the bone marrow, and for many decades, it has been used by doctors to extract the cells. The three main sources of stem cells where doctors can extract them from include:

  • The bone marrow
  • The bloodstream or peripheral blood
  • Umbilical cord or cord blood
  • Fat tissue

Bone Marrow

The bone marrow (BM) is considered to have a high amount of CD34+ stem cells but it is not an ideal source for mesenchymal stem cells. Cells derived from the bone marrow can be used to provide support for tissue to regenerate in what is known as revascularization. They also help support mesenchymal stem cells.2

A bone marrow transplant (BMT) refers to the procedure of using blood stem cells that have been collected from a person’s bone marrow or a donor’s bone marrow to perform a transplant. Extracting stem cells from bone marrow involves a surgery procedure under a general anaethesic agent. The cells are taken from the iliac crest or hip of the person or donor. Using a special needle, a surgeon passes it through the skin to reach the central part of the iliac crest where bone marrow fluid is siphoned into a syringe. The bone marrow fluid is then processed to get rid of bone fragments, fat, red cells, and other unwanted materials. It is then frozen through cryopreservation for a later use.1

Peripheral Blood

Stem cells can also be collected from bloodstream. The collection is done in advance and the cells are frozen until they are needed for a transplant. Because stem cells reside in the bone marrow, there are procedures that can be conducted to increase their number in the marrow and make them to spread and enter the bloodstream for collection. Such processes are; use of a growth factor known as granulocyte-colony stimulating factor (G-CSF) that is aimed at stimulating the cells, and use of chemotherapy drugs.

Bone marrow (BM) is considered as the major site for the hematopoiesis (blood-forming) process in humans. Under normal conditions, there is only a slight number of hematopoietic stem cells and progenitor cells (HSPCs) in peripheral blood or bloodstream. However, to make these cells move from the bone marrow to bloodstream, doctors may use a kind of treatment to stimulate their expansion. Treatment using cytokines and particularly granulocyte colony-stimulating factor (G-CSF) and chemotherapy drugs like myelosuppressive drugs for cancer treatment along with other compounds that interrupt how hematopoietic and BM stromal cells interact can create rapid mobilization of stem and progenitor cells pushing them into the bloodstream where they can be collected.5

When the peripheral blood stem cells (PBSC) reach a specific level within the bloodstream, a patient or a donor is put on a blood cell separator machine which withdraws the cells from the blood the way it happens in dialysis. The machine extracts blood from the patient’s or donor’s body, then spins it quickly, and collects the part containing stem cells while the remainder goes back to the individual’s body. All this is done in a continuous process. When collected, the stem cells may be frozen or crypreserved until they are needed to be used in a transplant.1

Peripheral stem cell transplant ((PSCT) refers to the procedure of using blood stem cells that have been extracted from bloodstream to perform a transplant.

Umbilical or Placental Cord Stem Cells

Cord blood is considered another rich source of the CD34+ stem cells though it has fewer mesenchymal stem cells. Cord blood requires human-leukocyte antigen (HLA) typing so that a match is found between the donor and recipient. The stem cells taken from umbilical cord blood can repopulate bone marrow and produce blood cells. Umbilical cord blood cells can be collected by a doctor or midwife during delivery. The collection occurs immediately after delivery and involves clamping and cutting the cord to extract the blood from the cord and placenta. This procedure doesn’t cause harm to the baby or the mother. The collected blood is then taken for processing and preservation in cord blood banks. Many things happen during the collection, testing procedures, processing activity, preservation measures, and storage.

Adipose or Fat Tissue Stem Cells

Another source of stem cells is the adipose or fatty tissue and it provides a type of cells known as mesenchymal stem cells (MSCs) as well as T-regulatory cells that help with immune system modulation. MSCs are isolated from the connective tissue surrounding organs and other tissues, and this tissue is known as stroma3. That’s why scientists refer to them as stromal cells.

Stem cells derived from adipose tissue may be used in the treatment of systemic autoimmune as well as inflammatory conditions. The cells may also help in treating injured tissue through regeneration. Since the anti-inflammatory properties and immune modulatory properties of cord tissue mesenchymal stem cells (HUCT-MSCs) are believed to be more superior than those extracted from fat, it means cord-derived mesenchymal stem cells may be more preferred for treatment.1

Today, cord blood stem cells provide alternative blood-forming or hematopoietic stem cells that are used to treat various malignant and non-malignant disorders. There is also increasing demand for the cord blood cells something that has prompted the need to have more reserves for cord blood banking.

Keywords: stem cells; cord blood; umbilical cord blood; cord blood banks; cord blood stem cells; cord blood banking

Reference List

  1. Sources of stem cell transplants. https://www.leukaemia.org.au/disease-information/transplants/sources-of-stem-cell-transplants/
  2. Sources of Adult Stem Cells. https://www.cellmedicine.com/sources-of-adult-stem-cells/
  3. Types of Stem Cells. http://www.closerlookatstemcells.org/learn-about-stem-cells/types-of-stem-cells
  4. Hematopoietic Stem and Progenitor Cells (HSPCs) https://www.stemcell.com/hematopoietic-stem-and-progenitor-cells-lp.html

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