An allogeneic blood and marrow transplant (BMT) or allogeneic stem cell transplant is when doctors transfer bone marrow cells from a donor into your child.
Preparing for your child’s allogeneic transplant involves many steps. You will first sit down with the primary BMT physician and nurse to discuss your child’s transplant procedure. This may be a difficult meeting while you are still dealing with your child’s diagnosis. You may feel overwhelmed with the information you are learning. It may help to bring a notebook to write down notes. Do not be afraid to ask the doctor to explain anything you do not understand.
Finding a donor
Before proceeding with your child’s BMT, it is essential to find a donor. This is someone who can donate their stem cells to your child. The donor’s stem cells will be harvested the day of or day before your child’s transplant. If your child is receiving stem cells from an unrelated donor, the procedure will be arranged at a hospital close to the donor. A member of your hospital staff will travel to that hospital to pick up the donated marrow for your child.
To minimize the chances of your child’s body rejecting the donor’s stem cells, doctors need to find a donor with a similar type of tissue as your child’s tissue. To find a match, doctors look for unique genetic markers on the surface of the cells inside the tissue. Since we inherit these genetic markers from our parents, it is more likely that siblings will have the same tissue type than a parent, grandparent, or other relatives. In fact, there is a 25% chance that siblings will share the same tissue type. There is a smaller chance – about 1% to 2% - that a parent may be a close enough match to be a donor.
If no related (family) donor is available, then the doctor will need to take blood stem cells from an unrelated donor.
How do you know if the donor is a suitable match?
The more closely the donor’s stem cells “match” your child’s stem cells, the more likely the transplant will be successful.
Most of our cells have proteins on their surface which are like “barcodes.” These barcodes help our immune system distinguish between cells that are part of our body and those that are not, such as bacteria or other organisms that can cause infection. These proteins are called human leukocyte antigens (HLA).
To find out if the donor is a match with your child, lab specialists will compare the barcode on the white blood cells in your child’s marrow to the barcode on the donor’s marrow cells. This is called HLA typing. To do this, they look at a small section of one chromosome. If your child and the donor share the same HLA protein at the same part of the chromosome, then the donor is a match for your child.
Currently, we look for 10 types of HLA proteins. The more of these proteins the donor and patient have in common, the better the match.
To find a match, your child’s transplant physician will first do a simple blood test on you and the rest of your family members. If a related donor is not found, then they will initiate a search through the unrelated donor registry.
Tests
After the initial consultation, your child’s doctor will perform standard tests to assess how well their vital organs are working. Your child may also need to take tests which are specific to the disease.
Conditioning regimen
Your child’s body first needs to be prepared so that it is ready to take in the new, healthy marrow cells. This is called the conditioning regimen.
The purpose of conditioning your child’s body prior to the transplant is to:
- suppress your child’s immune system so that the new stem cells can be accepted into your child’s bone marrow space. This is called engraftment. When the transplanted cells engraft, your child’s marrow should start producing new, healthy blood cells.
- kill your child’s diseased marrow cells: This depends on your child’s diagnosis.
Your child's conditioning regimen consists of two main treatments:
- high-dose chemotherapy. Chemotherapy can last from four to 10 days, depending on your child’s illness.
- total body irradiation (TBI), which is radiation to the entire body (from head to toe). Usually, TBI is given to children with some forms of leukemia.
Each treatment protocol is individualized to the child.
The preparative regimen is intense, and your child may experience side effects such as fatigue, nausea, and vomiting. Your child’s immune system will also be very weak. This is why they are usually hospitalized as soon as chemotherapy starts.
Compared to the conditioning regime, the actual transplant procedure itself is straight forward.
This section describes what to expect before and during the transplant procedure in more detail.