There are two types of blood stem cell transplants: autologous and allogeneic.
- Autologous transplants use the patient’s own stem cells, which are collected before the patient receives high-dose chemotherapy or radiation therapy. After the treatment, the patient’s stem cells are infused back into their body to help restore the blood-forming cells that were destroyed by the treatment.
- Allogeneic transplants use stem cells from a donor who is a close genetic match to the patient. The donor’s stem cells are collected either from the bone marrow or peripheral blood or cord blood and then infused into the patient’s bloodstream. An allogeneic donor can be either be a relative of the patient or a completely stranger.
To find a matching donor, the patient’s tissue type is determined using a simple blood test. This test checks the patient’s human leukocyte antigens (HLA), which are proteins found on the surface of cells that help the immune system recognize self from non-self. Once the HLA type is determined, the search for a matching donor begins.
The first step in the search for a matching donor is to look for a donor within the patient’s family. Siblings have a 25% chance of being a full HLA match, while parents and children have a 50% chance of being a half HLA match. If a suitable family donor cannot be found, the search is extended to the global database: Search & Match Service.
The global donor database of volunteer donors, which is managed by the World Marrow Donor Association (WMDA), is made up of over 40 million volunteer donors from around the world. The registry includes both unrelated adult volunteers and units of cord blood from public cord blood banks. The WMDA coordinates the search process and identifies potential matching donors and/or cord blood units for the patient.
The WMDA Search & Match Service uses sophisticated computer algorithms to match the patient’s HLA type with that of potential donors and/or cord blood units. The search is not limited to donors from the patient’s own country or ethnicity, as matches can be found from anywhere in the world.
If a matching donor is found, the donor will be contacted to confirm their willingness to donate by its local registry. The donor will then undergo a thorough medical evaluation to ensure that they are healthy and able to donate. If the donor is cleared for donation, the stem cells are collected and transplanted into the patient.
In some cases, a suitable match cannot be found in the registry. In these situations, the patient’s medical team will explore other treatment options or consider a transplant from a partially matched family member or an unrelated donor with a less than perfect match.
After the donor has been confirmed, you will need treatment before the transplantation can be carried out. Usually, patients receive high doses of chemotherapy and possibly radiation. These treatments destroy the defective blood stem cells in the bone marrow and create space for the new, healthy stem cells. It also suppresses your immune system so that it will not attack the new stem cells after transplantation.
After the transplantation, you will stay in hospital until your immune system recovers and physicians are sure that the procedure was successful. During your time in hospital, specialist doctors and nurses will carefully watch for signs of chemotherapy and radiation side effects, infections, Graft vs. Host Disease or graft failure.