Cancer and its treatments — such as chemotherapy — can damage healthy stem cells. A stem cell transplantation (also called a bone marrow transplant) may be necessary to replace these cells in the bone marrow. There are two types of stem cell transplants used to treat leukemia, allogeneic and autologous. In an allogeneic stem cell transplant, stem cells come from a donor. In an autologous transplant, the stem cells come from the person undergoing the procedure.
Each type of stem cell transplant requires a slightly different procedure, offers different benefits, and comes with different potential drawbacks. If you or a loved one are living with leukemia, you may benefit from understanding how stem cell transplants work and how the two types differ.
Stem cells are an important part of the body because they can develop into any type of cell. Blood stem cells live in the bone marrow, where they divide and mature into many different types of blood cells. These types of cells include:
New cells help replace old, worn-out cells in the body to keep you healthy. Transplanting stem cells can help prevent issues like severe infection, bleeding, and anemia that can result after chemotherapy destroys healthy cells.
Read more about stem cell transplants for leukemia.
One option for treating leukemia is an allogeneic stem cell transplant. The term “allogeneic” refers to the fact that the stem cells come from a healthy donor who may not necessarily be a genetic match to the person receiving them. The transplant can come from a family member — or from unrelated donors. who may be found in a national marrow donor program such as Be The Match.
The stem cells are collected from the donor’s blood through a needle inserted into a vein in the arm. The blood is then processed through a specialized machine that removes the stem cells and returns the rest of the blood to the donor. The stem cells can then be frozen and used in a recipient even many years later.
Before the stem cell transplant, the recipient undergoes treatment with high-dose chemotherapy, and occasionally, radiation therapy. This process is known as a “conditioning treatment” because it prepares the body for receiving the new stem cells. It is also referred to as a myeloablative treatment plan.
The chemotherapy and radiation destroy any lingering leukemia cells in the body and weaken the immune system to make the transplant successful. The treatment also clears the bone marrow so that the new stem cells can begin to grow there and make healthy blood cells.
Once the conditioning phase is done, the donor stem cells are injected into the recipient using a catheter placed into a blood vessel. The stem cells travel through the body to the bone marrow and begin producing new blood cells.
Because donor stem cells come from another person, the cells can create a new immune system in the recipient. Ideally, the stem cells will begin making new WBCs and immune cells that recognize and kill lingering leukemia cells in the body. This benefit is known as the graft-versus-tumor effect, and it can only happen in cases of allogeneic stem cell transplants.
Every cell in the human body has a special type of protein on its surface known as a human leukocyte antigen (HLA). This protein is especially important in transplants because a person’s immune system recognizes HLA proteins that are different from their own. The immune system and transplant may attack one another, resulting in a condition known as graft-versus-host disease (GVHD), which can cause the transplant to be rejected.
There are limited ways to prevent GVHD in allogeneic stem cell transplants: One is for the donor to be an identical twin to the person receiving the transplant, and the other is to give the recipient medications, such as chemotherapy or immunotherapy. These medications may include:
Another option for treating leukemia is an autologous stem cell transplant. The word “auto” means self, and this procedure uses the recipient’s own stem cells rather than a donor’s for the transplant. Autologous stem cell transplants are typically used to treat blood cancers such as myeloma, Hodgkin lymphoma, and non-Hodgkin lymphoma.
In the first step of an autologous stem cell transplant, the recipient is treated with medications that cause the body to make more stem cells and move them into the bloodstream. This makes it much easier to collect the stem cells through a needle inserted into a vein in the arm. The blood is then processed through a specialized machine that removes the stem cells and returns the rest of the blood to the recipient. The collected stem cells are then frozen for later use.
The recipient also undergoes a conditioning treatment (similar to the treatment in an allogeneic stem cell transplant) that uses high-dose chemotherapy and radiation to kill any remaining leukemia cells and clear the bone marrow for the new stem cells.
Once the conditioning phase is done, the recipient's stem cells are injected using a catheter placed into a blood vessel. The stem cells travel through the body to the bone marrow and begin producing new blood cells.
One benefit of an autologous stem cell transplant is there is absolutely no risk of GVHD. Because the recipient is receiving their own stem cells, their immune system does not recognize the cells as foreign.
However, unlike allogeneic transplants, autologous stem cell transplants do not offer the benefit of a graft-versus-tumor effect, because the recipient’s cells cannot make a new immune system. Accordingly, the person undergoing the autologous transplant has a higher risk of developing leukemia again.
Stem cell transplants offer one of many ways to treat — and even cure — leukemia. Although stem cell transplants may seem like an attractive option, there are some drawbacks. Stem cell transplants are generally not recommended for people who are older or have other health complications. The conditioning treatment is intensive and may not be well tolerated in people with organ dysfunction.
Allogeneic stem cell transplants are the more common type used to treat acute myeloid leukemia (AML) in adults because of the added graft-versus-tumor effect that comes with receiving donor stem cells. However, autologous stem cell transplants can be used in people with AML who are in remission after their first rounds of treatment but who cannot find a matched donor for an allogeneic transplant.
In children, stem cell transplants can also be used to treat AML, especially if they have a sibling with the same HLA type. AML relapses more than other types of leukemia, and stem cell transplants can help prevent relapse. If a child relapses after their first round of standard chemotherapy, a stem cell transplant is typically done as soon as they go into remission again.
Allogeneic stem cell transplant is most commonly used to treat acute lymphocytic leukemia (ALL) in adults. Stem cell transplants can be used to treat children with ALL who are more likely to relapse after the first round of standard chemotherapy. Stem cell transplants are also used in children with ALL who have specific genetic mutations.
Stem cell transplants used to be a common treatment for chronic myeloid leukemia (CML). Allogeneic stem cell transplants might be the only known cure for some adults with CML, and they can be used in children whose leukemia does not respond to other treatments. Adults with CML, however, are typically treated with an extremely successful type of medication, tyrosine kinase inhibitors (TKIs), as first-line therapy.
In certain types of chronic lymphocytic leukemia (CLL) that are difficult to treat with traditional therapies, stem cell transplants have been proposed as a treatment option. It is currently unclear how helpful these are in adults with CLL, but clinical trials are investigating their effectiveness.
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