Stem cell transplant for acute myeloid leukemia

The usual doses of chemotherapy drugs can cause serious side effects to quickly dividing tissues such as the bone marrow. Even though higher doses of these drugs might be more effective, they are not given because they could severely damage the bone marrow, which is where new blood cells are formed. This could lead to life-threatening infections, bleeding, and other problems due to low blood cell counts.

A stem cell transplant (SCT) allows doctors to use higher doses of chemotherapy (sometimes combined with radiation therapy). After that treatment is finished, the patient receives an infusion of blood-forming stem cells to restore the bone marrow.

Blood-forming stem cells used for a transplant are obtained either from the blood (for a peripheral blood stem cell transplant, or PBSCT) or from the bone marrow (for a bone marrow transplant, or BMT). Sometimes stem cells harvested from a babys umbilical cord are used.

There are 2 main types of stem cell transplants: allogeneic and autologous. They differ with regard to the source of the blood-forming stem cells.

Allogeneic stem cell transplant

This is the most common form of SCT used to treat acute leukemia. In an allogeneic transplant, the stem cells come from someone else usually a donor whose tissue type is almost identical to the patients. Tissue type is based on certain substances on the surface of cells in the body. These substances can cause the immune system to react against the cells. Therefore, the closer a tissue match is between the donor and the recipient, the better the chance the transplanted cells will take and begin making new blood cells.

The ideal donor is a close relative, such as a brother or sister, if they are a match. If no close relatives match, a matched unrelated donor (MUD) may be an option in some cases, but use of stem cells from a MUD is linked to more complications. The stem cells from an unrelated donor come from volunteers whose tissue type has been stored in a central registry and matched with that of the patient. Sometimes umbilical cord stem cells are used. These stem cells come from blood drained from the umbilical cord and placenta after a baby is born and the umbilical cord is cut.

Using donor cells for SCT for acute myeloid leukemia (AML) is preferred because leukemia is a disease of the blood and bone marrow, so giving the patient his or her own cells back may mean giving leukemia cells. Donor cells are also helpful because of the graft versus leukemia effect. When the donor immune cells are infused into the body, they may recognize any remaining leukemia cells as being foreign to them and will attack them. This effect doesnt happen with autologous stem cell transplants

An allogeneic transplant is often the preferred type of transplant for AML when it is available, but its use is limited by the need for a matched donor. It is also limited by its side effects, which are too severe for most older people.

Non-myeloablative transplant (mini-transplant): Many older people cant tolerate a standard allogeneic transplant that uses high doses of chemotherapy. Some may be able to have a non-myeloablative transplant (also known as a mini-transplant or reduced-intensity transplant), where they receive lower doses of chemotherapy and radiation that do not completely destroy the cells in their bone marrow. They then receive the allogeneic (donor) stem cells. These cells enter the body and establish a new immune system, which sees the leukemia cells as foreign and attacks them (a graft-versus-leukemia effect).

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Stem cell transplant for acute myeloid leukemia