What is an allogeneic stem cell transplantation?

There are two main types of stem cell transplants – allogeneic and autologous. An allogeneic stem cell transplant is a procedure in which a patient receives blood-forming stem cells from a donor. In contrast, for an autologous stem cell transplant, the patient provides his own stem cells for the procedure. Blood stem cells collected from the patient while he is in remission are stored and then returned following conditioning chemotherapy or radiation.

The rationale for allogeneic stem cell transplantation is two-fold. A chemotherapy or radiation-based treatment before transplantation, called conditioning, enables the elimination of the harmful leukemic cells. An undesirable effect however is the destruction of the patient’s immune and blood building systems

Therefore, the first goal of allogeneic stem cell transplantation is to replace the patient’s blood and immune system with a healthy one from a donor. The second goal and major advantage of this approach is that newly generated immune cells attack residual leukemic cells, called the graft-versus-leukemia (GvL) effect. This makes the disease less likely to return.

Stem cells can be collected from bone marrow, the blood stream (peripheral blood stem cells), or umbilical cord blood. Harvesting stem cells from bone marrow was the original collection method and has the longest history in stem cell transplantation. Frequently “bone marrow transplantation” is used as the umbrella term for stem cell transplantation. The transplanted cells are called the “graft”

Our blood cells develop from a small number of precursor bone marrow cells called blood stem cells. These stem cells have not committed to a specific blood cell type. Blood stem cells will develop into white blood cells, red blood cells, or platelets in the presence of specific chemical signals.

White blood cells are cells of the immune system with the function to fight infections caused by bacteria, viruses, and fungi.

Red blood cells carry oxygen from the lungs to the cells in the body

Platelets, also called thrombocytes, are pieces of cells that seal damaged blood vessels and help blood to clot. Both functions are important in stopping bleeding.

Following a successful stem cell transplant, the bone marrow is repopulated with blood stem cells from the healthy donor, which will rebuild the patient’s blood and immune systems. This step is critical for the effective treatment of AML.