An allogeneic donor is one other than the patient. Allogeneic transplants have the lowest risk of tumor relapse because of the GVL (graft vs. leukemia) effect. However, GVHD (where the new transplanted immune system sees the patient as foreign), graft failure, and immune deficiency are potential problems. Allogeneic donors are chosen based on a blood test for human leukocyte antigens (HLA). HLA antigens are part of the biological process that allows each individual’s immune cells to differentiate between itself and the cells of other people or foreign organisms. A matched donor, either a relative (usually a brother or sister) or an unrelated individual from a registry, shares all 12 HLA-antigens with the patients. Historically, all allogeneic transplants have utilized matched donors because HLA mismatches were associated with high risks of GVHD.
When is it used?
An allogeneic transplant offers the best chance of curing a number of blood cancers and other serious diseases. These include: leukemia, some types of lymphoma, myeloma, myelodysplastic syndromes, aplastic anemia and other rare bone marrow diseases. These are however complex procedures that carry significant risks.
How are the stem cells collected?
The donor has to undergo a series of injections called Granulocyte Colony Stimulating Factor (G-CSF) (usually four doses given over four days) to stimulate the stem cells to enter the blood stream. Once the Peripheral Blood Stem Cells (PBSC) are at a certain level in the blood stream, the donor is attached to a blood cell separator (apheresis machine) where the cells are withdrawn from the blood of the donor.
During the procedure, the donor relaxes in a chair or bed and can often read a book or watch TV. The procedure is painless and when it is over the donor may feel slightly tried but can resume normal activities.
In the week leading up to your transplant, you are given a few days of very high doses of chemotherapy, and sometimes radiotherapy, to destroy your underlying disease, and suppress your immune system so that it will accept the donor stem cells. This is called conditioning therapy. After you have finished this part of your treatment, the donated stem cells are infused through a vein into your blood stream. This is similar to a blood transfusion. From here the stem cells make their way to your bone marrow where they become established and start making new blood cells.
Your blood counts drop dramatically in the week following conditioning therapy. This is normal. During this time you will be more at risk of infections (due to the lack of infection-fighting white blood cells) and bleeding (due to a lack of platelets).
Antibiotics and other drugs are commonly prescribed to help prevent or treat infections during this time, and you are likely to need platelet transfusions to reduce the risk of bleeding. Red blood cell transfusions are given when haemoglobin levels are too low. During this time you are likely to be experiencing some of the common side effects of chemotherapy, and radiotherapy including nausea and vomiting, mucositis (sore mouth) and bowel problems (diarrhoea).
Once the blood counts start to rise and you are otherwise well enough, you are usually allowed to leave the hospital. In the early weeks and months after your transplant you will need to come in to the hospital or clinic regularly so that the doctor can check your blood counts, see how you are progressing and deal with any problems that may arise.
Does it work?
The success of your transplant will depend on a number of factors including the type and stage of disease you have, your age and your general health.
Important advances have been made in recent years, and continue to be made, improving the success of all types of transplants. Despite this, allogeneic transplants are still associated with serious and sometimes lifethreatening complications. Unfortunately, a small number of people will not survive the transplant process. Your doctor will spend time discussing with you and your family the risks and benefits of an allogeneic transplant.
It generally takes 12 months or longer to recover after an allogeneic transplant. During this time it is important to look after yourself and to try to focus on the things you can do to help yourself recover well both physically and emotionally.
What are the side effects of an allogeneic transplant?
Most of the side effects of an allogeneic transplant are caused by the conditioning therapy used. While many of these side-effects last for a short time, some can last longer. Some side-effects persist for months and occasionally years after the transplant.