What Are Stem Cells?

Haematopoietic stem cells also referred to as stem cells are unique cells that are primarily located in the bone marrow. Haematopoietic stem cells have the remarkable potential to develop into many different cell types in the body for example more blood-forming stem cells, or they mature into one of three types of blood cells:

  • white blood cells which are responsible for protection against infections
  • red blood cells which are the oxygen carriers
  • platelets which help the blood to clot.1

Where Are Stem Cells Found?

There are several known accessible sources of autologous adult stem cells (a patient's own blood-forming stem cells) in humans:

  • Bone marrow, which requires extraction by harvesting, that is drilling into the femur (thigh bone) or iliac crest (pelvic bone).
  • Adipose tissue (lipid cells), which requires extraction by liposuction.
  • Blood, which requires extraction through apheresis, wherein blood is drawn from the donor (similar to a blood donation) and passed through a machine that extracts the stem cells and returns other portions of the blood to the donor.
  • Stem cells can also be taken from umbilical cord blood just after birth.2

Most hematopoietic stem cells are found in the bone marrow, but some cells, called peripheral blood stem cells (PBSCs), are found in the bloodstream.1

Although very few cells in the periphery (outside the bone marrow space) are PBSC’s, their numbers can be increased through administering medications, this process is referred to as stem cell mobilisation.3

What Is a Stem Cell Transplant (SCT)?

Stem cell transplant (also called peripheral blood stem cell transplant) is a treatment to try to cure some types of cancer, such a leukaemia, lymphoma and myeloma. Patients receive very high doses of chemotherapy, sometimes with whole body radiation. This has a good chance of killing the cancer cells but also kills the stem cells in the bone marrow.2

Types of Stem Cell Transplants

Bone marrow transplantation (BMT) and peripheral blood stem cell transplantation (PBSCT) are procedures that restore stem cells that have been destroyed by high doses of chemotherapy and/or radiation therapy. There are three types of transplants:

Autologous transplants, patients receive their own stem cells.

Syngeneic transplants, patients receive stem cells from their identical twin.

Allogeneic transplants, patients receive stem cells from their brother, sister, or parent. A person who is not related to the patient (an unrelated donor) also may be used.1

Why Are stem cell transplants performed?

The basic idea behind an autologous stem cell transplant is to allow administration of higher chemotherapy and/or radiation therapy doses to kill rapidly dividing cancerous cells and to make room for new, healthy cells. Although these anticancer treatments are among the most effective available, they do not have a precise aim and can destroy rapidly dividing normal cells as well. A stem cell transplant enables the patient to produce new blood cells to replace those destroyed during treatment.1

The Stem Cell Transplant Process

Apheresis is the process by which stem cells that circulate in the blood are separated from the other components of the bloodstream and collected for reinfusion at a later date.A few days before the blood collection, the patient will receive a medication, which forces the stem cells to leave the bone marrow and move into the circulating blood.2


  1. National Cancer Institute. Bone marrow transplantation and peripheral blood stem cell transplantation fact sheet. Available at https://www.cancer.gov/cancertopics/factsheet/Therapy/ bone-marrow-transplant. Accessed March 2, 2020.
  2. MC Herbst. Fact Sheet on Stem Cells and Stem Cell Transplant. Oct 2018 CANSA. Available at https://www.cansa.org.za/files/2018/10/Fact-Sheet-Stem-Cells-Stem-Cell-Transplant-Oct-2018.pdf. Accessed March 2, 2020.
  3. Hoggatt J & Pelus LM. Mobilization of hematopoietic stem cells from the bone marrow niche to the blood compartment. 2011. Stem Cell Research & Therapy 2011, 2:13 Available at http://stemcellres.com/content/2/2/13. Accessed March 10, 2020.