A stem cell transplant (also known as a bone marrow transplant) is a procedure in which defective or cancerous bone marrow is replaced with new, healthy bone marrow cells. A stem cell transplant may be used to treat leukemia and lymphoma, cancers that affect the blood and lymphatic system. Additionally, transplants are used to treat hereditary blood disorders, such as sickle cell anemia, and autoimmune diseases, such as multiple sclerosis. They also can help patients recover from or better tolerate cancer treatment.

Stem cells are specialized cells that can mature into different kinds of cells, depending on what your body needs. They are located in various places throughout your body, including your bone marrow. Bone marrow contains hematopoietic stem cells that constantly divide to produce all the different kinds of blood cells. Young hematopoietic stem cells can mature into any of the following cell types:

Any disease or condition that impacts the ability of your bone marrow to produce new blood cells can have serious health consequences. Bone marrow transplantation may be an effective treatment for such conditions.

In general, the first step to a successful stem cell transplant is harvesting healthy bone marrow, either from the patient or from a donor. This involves putting the patient or donor under general anesthesia and using a large needle to remove bone marrow from their pelvis. The bone marrow can then be frozen and stored. When it is ready for use, it is thawed and injected into a patient, much like a blood transfusion. The healthy stem cells will travel to bone marrow sites and start making blood cells.

There are two types of stem cell transplantation:

In an autologous stem cell or bone marrow transplant, healthy cells are harvested from the bone marrow of a patient. The harvested bone marrow is frozen and stored until it is ready for use. In the meantime, the patient undergoes a 'conditioning regimen' to prepare their body for the transplant. In this regimen, they may receive high dose chemotherapy r radiation therapy. These treatments destroy cancer cells, but they also kill bone marrow cells. This is where the transplant comes in. The patient is injected with their own stored blood stem cells. These cells 'take' to the body and restore its ability to produce blood cells.

Autologous transplantation is most often used to treat diseases like lymphoma and multiple myeloma. Because autologous transplants use the cells of a patient, they have little to no risk of rejection or graft-versus-host disease (GVHD).This makes it safer than allogeneic transplants.

An allogeneic bone marrow or stem cell transplant uses donor stem cells to treat blood cancers that affect the bone marrow, like leukemia. The cell transplants come from a donor whose tissue most closely matches that patient. The donor cells are injected after the patient has undergone chemotherapy. But beyond restoring the blood-producing ability of the body, allogeneic stem cell transplantation can help fight cancer directly. The donated cells generate a new immune response, meaning they find and kill cancer cells, sometimes better than the original immune cells of the patient. This is called the graft-versus-cancer effect, and it can help fight cancer. Unfortunately, allogeneic stem cells come with an increased risk of rejection or GVHD.

For allogeneic transplants to work, a patient needs to be matched with a donor whose human leukocyte antigen (HLA) proteins closely match theirs. HLA proteins dot your cells' surface and help your body distinguish normal cells from foreign cells. If the HLA proteins of a donor are a poor match to a patient, there is an increased risk of GVHD.

HLA typing is the process by which stem cell transplant patients are matched with eligible donors. In HLA typing, a blood sample from a patient is compared with samples from family members or a donor registry. The best match is usually a first-degree relative (children, siblings, or parents). However, about 75% of patients do not have suitable donors in their family and require cells from a matched unrelated donor (MUD). Stem cell donors are located through registries such as the National Marrow Donor Program. It can sometimes take several weeks or longer to find a suitable donor.

If a suitable donor cannot be found, there are other options, including:

Before the transplant, your doctors will need to prepare your body to receive the new stem cells. This is called the preparative or conditioning regimen. It consists of chemotherapy and radiation given several days before your transplant.Stem cell transplant side effects can be caused by the preparative regimen or by the transplant itself.Your transplant team can help you cope with side effects. Some can be prevented, and most can be treated to help you feel better.

Read more:
Stem Cell (Bone Marrow) Transplants - MD Anderson Cancer Center