What Is a Transplant?

What Is a Bone Marrow Transplant?

Bone marrow transplantation (BMT) is a procedure that helps the body make normal blood-forming stem cells. The goal is to cure an otherwise fatal condition by destroying diseased cells (such as cancer cells or faulty immune cells or red blood cells) with chemotherapy and sometimes radiation therapy and then replacing them with healthy transplanted cells.

What Healthy Bone Marrow Does

The young blood-forming cells in healthy bone marrow are called hematopoietic stem cells. (“Hematopoietic” means related to the formation of blood cells.) These immature blood cells in the marrow can divide to make all the different mature types of blood cells—white blood cells, red blood cells, and platelets. (White blood cells fight infection. Red blood cells carry oxygen to other cells. Platelets help your blood to clot.) Stem cells are made in the bone marrow, but they are also found in smaller numbers circulating in the blood stream and in the umbilical cords of babies.

What Happens When Bone Marrow Malfunctions

Certain diseases disrupt the function of the bone marrow. These diseases may cause the bone marrow to fail, to produce an excess of some types of blood cells, or to make blood cells that don’t mature and can’t perform their normal functions. For example, in aplastic anemia, the bone marrow stops making new blood cells. In leukemia, the bone marrow makes too many immature white blood cells. In autoimmune diseases, immune-system cells malfunction and attack rather than protect the body. A bone marrow transplant may help treat these diseases.

The Main Steps of a Bone Marrow Transplant

The core steps of a BMT are stem cell collection, conditioning, and engraftment.

Finding and Collecting Stem Cells

In a BMT, the healthy stem cells are collected either from a donor or from the child needing the transplant. If the cells are to come from a donor (for example, a brother or sister or an unrelated volunteer donor), then careful testing must first be performed on the cells to find a good tissue match. Learn more by reading about the types of transplants and finding or becoming a donor.

Conditioning: Preparing the Body for Transplant

The child receives chemotherapy, with or without radiation therapy, to attack and kill some or all of the malfunctioning cells in the body. There are two types of conditioning: high-dose conditioning, which aims to eliminate all of the diseased cells, and reduced-dose conditioning, which weakens but does not completely destroy the diseased cells.

Engraftment: Healthy Cells Start to Grow

After conditioning, doctors infuse the collected stem cells into the child’s bloodstream, where they travel to the bone marrow. After a few weeks, they start to grow and mature into a mix of healthy white blood cells, red blood cells, and platelets. These new blood cells function normally. Also, in those who had reduced-dose conditioning, the new immune cells help attack the remaining diseased cells.

For a more complete description of the steps involved, read about the entire transplant process.

Different Names for Transplants

You may see transplants called by one of these names based on the source of the stem cells:

  • Bone marrow transplant, or BMT, which uses stem cells taken from the bone marrow
  • Peripheral blood stem cell transplant, or PBSC transplant, which uses stem cells taken from blood circulating around the body
  • Cord blood transplant, which uses stem cells collected from umbilical cord blood donated by a mother right after her baby’s birth

The general term for all three is “hematopoietic cell transplant,” or HCT. Because the first HCTs were done using bone marrow, many people are most familiar with the term “bone marrow transplant,” and they use this term regardless of the source of the stem cells. For simplicity, SCCA refers to this treatment generally as bone marrow transplant.