What Is an Allogeneic Blood and Marrow Transplant (BMT)?
Some blood-based cancers, including leukemia and certain lymphomas, are treated by replacing the diseased blood and marrow system with that of a healthy donor. This is called an allogeneic transplant.
Matching Patient and Donor: Three Possibilities
Before the transplant can take place, your human leukocyte antigen (HLA) tissue type will be matched with that of a donor. HLA refers to the proteins found on the surface of the cells that make up your tissue type. Your HLA tissue type is different from your blood type. The outcome of the transplant depends largely on how similar your HLA tissue type is to your donor’s.
There are several possible donor sources. Here are three:
Related Donor: A blood relative — someone who is related to you biologically, not through marriage or adoption — could be a possible donor. This type of match, especially between brothers or sisters, may lower the risk of some transplant complications. (When the patient and donor are identical twins, their HLA profiles are identical, which gives the patient a unique advantage. A transplant between identical twins is called a syngeneic transplant.)
When your donor is a blood relative who lives in Canada or the U.S., the donation process usually takes place much faster than it would with an unrelated donor living halfway around the world.
Unrelated Donor: When no matching relative is available, Roswell Park’s transplant coordinators will search donor registries for an unrelated donor. A match from someone listed in these registries is often referred to as a Matched Unrelated Donor (MUD). Canada’s OneMatch and the National Marrow Donor Program (NMDP) in the U.S. provide access to a large number of potential volunteer donors, both local and international. If your referring center has already identified a donor, OneMatch and the NMPD will collaborate to transfer the search process to Roswell Park Comprehensive Cancer Center.
Haploidentical Donor: When neither a related nor unrelated donor can be identified, it is possible to receive a transplant from a partially matched blood relative, also called a haploidentical donor. A haploidentical donor is usually a “half” match and may be the patient’s parent, sibling, or child. Almost everyone has at least one haploidentical donor. This improves the transplant options for people who don’t have a related donor or who have a poor unrelated donor match.
The Transplant Begins
First Step: Conditioning Regimen
After a donor has been identified, your bone marrow and the abnormal cells inside it are destroyed with chemotherapy and/or radiation. At the same time, for several weeks you will be given immune-suppressing drugs. This part of the process is called a conditioning regimen. The drugs serve two purposes: to keep your body from rejecting the donor’s cells and to prevent graft-versus-host disease (GVHD), which occurs when the donor’s cells attack your body.
Allogeneic BMT also has a benefit called the graft-versus-cancer effect, which occurs when the donor’s cells recognize and attack cancer cells in your body. This effect is strongest in blood and marrow cancers, making it possible for allogeneic BMT to cure patients of life-threatening hematologic (blood-based) cancers.
Second Step: Rescue/Infusion
In the next step, called the rescue/infusion, you receive either healthy marrow or blood stem cells (also called hematopoietic cells) provided by the donor. The cells are given intravenously, in a process very similar to a blood transfusion. The cells travel through your bloodstream to your bone marrow, where they can start producing healthy blood cells.