How Does a Bone Marrow Transplant Work?

A person needs a bone marrow transplant if his or her own bone marrow no longer performs its job of creating new blood stem cells and releasing them into the body. This could be happening for any number of reasons.

There are two basic types of bone marrow transplants: in one (autologous), a patient banks his or her own bone marrow and then receives it again. In the one relevant to this entry, allogeniec, a patient is given the bone marrow from a donor—whether that donor is a sibling or a stranger.

How It Works

Because the patient's bone marrow is dysfunctional, the patient requires a new set of blood stem cells to restock the bone marrow and to begin creating those future blood cells. Therefore, the first job of the medical team is to kill off the old bone marrow. This is accomplished through high-dose chemotherapy and radiation. When that part is finished, the patient is susceptible to any manner of infections because he or she no longer has an active immune system.

This is when the actual transplant takes place.

Unlike other organ transplants, which are typically major surgical interventions, in a bone marrow transplant, the procedure itself is as simple as an intravenous infusion. The donor marrow or circulating stem cells are fed through an IV into the patient's body, where they will find their own way to the bone marrow and—assuming all goes well—begin the job of rebuilding the patient's immune system and the successful production of blood cells.

Complications

A bone marrow transplant is in many ways no different than any other organ transplant, in that the patient (referred to as the 'host') is receiving some form of tissue (referred to as the 'graft') from a donor.

The major difference is that when a patient receives a kidney from a donor, there is a concern that the host's immune system will reject the graft. In a bone marrow transplant, the host has had his or her immune system—created in the bone marrow in the form of white blood cells—wiped out by high-dose chemotherapy and radiation. So there is no concern that the host will reject the graft.

However, because the graft in this case is donor bone marrow, the concern is that the graft will reject the host. In other words, the new bone marrow and immune system will reject the patient. This is known as Graft-Versus-Host-Disease (GVHD).

This is of course a simplified explanation of what is otherwise an extremely complicated and risky procedure. It is not performed lightly, and for lymphoma patients, it is often considered the last line of treatment.