What is an allogeneic transplant?
In an allogeneic transplant, stem cells are donated to the patient from another person, a genetically matched stem cell donor. This is usually a family member, a brother or sister with the same tissue type as the patient. Where no sibling is available, a search is made of Australian and overseas donor registries to find a suitably matched, unrelated stem cell donor. Sometimes there is a slight mismatch between the donor (usually a family member) and patient’s tissue type, but they may still be the best possible match for the patient.
In an allogeneic transplant the donor’s healthy stem cells are used to replace the patient’s unhealthy ones, which have been damaged by disease, by giving high doses of chemotherapy and radiotherapy used to treat the underlying disease. The cells of the donor’s immune system (white blood cells) are transplanted along with the donor’s stem cells. It is hoped that these cells will also attack and destroy all traces of the underlying disease.
When is it used?
An allogeneic transplant offers the best chance of curing a number of blood cancers and other serious diseases. These include: leukaemias, some types of lymphomas, myeloma, myelodysplastic syndromes, aplastic anaemia and other rare bone marrow diseases.
These are however complex procedures that carry significant risks. The complexities and risks increase even more with when the donor is unrelated to the patient, or when there is a slight mismatch between the donor and patient’s tissue type. As such, allogeneic transplants are usually not suitable for patients over the age of 60 years, or for people with certain types of health problems.
A ‘mini-allogeneic’, ‘reduced intensity’ transplant uses less intensive and therefore less toxic chemotherapy. This is also called a nonmyeloablative transplant’, because the treatment used doesn’t completely destroy your bone marrow. This may be an option for older people and others who could benefit from receiving donated stem cells but for whom a standard allogeneic transplant would be considered too risky. Using this approach it is hoped that the donor’s immune system will attack and destroy cancer cells in your body. Meanwhile the chemotherapy helps to treat the underlying disease and suppress your immune system, reducing the risk of rejection.
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’s 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 to be expected. 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 amongst others: 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.
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.
The donor’s stem cells can cause a common, sometimes serious complication of allogeneic transplants called graft-versus-host-disease (GVHD). This is an immune reaction whereby cells from the donor’s immune system recognise the patient’s body as foreign and attack it. GVHD can vary in severity and the extent to which it causes problems in the body. When it develops soon after the transplant it is called acute GVHD and is usually managed with drugs, including steroids to further suppress the new immune system and reduce the symptoms. It can also develop at a later stage, or persist for months and sometimes years after the transplant. If you are having an allogeneic transplant you will be given special drugs called immunosuppressants (anti-rejection drugs) before, during and for some time after the transplant. They also help to suppress the ‘new’ (donor’s) immune system to reduce GVHD and prevent it from causing serious problems in the body . These drugs also help to reduce the risk of the donor’s stem cells being rejected by your body.
It can take a year or even longer for the immune system to fully recover following an allogeneic transplant. As such there is a risk of infection for some time after your transplant. It is important to take some sensible precautions to prevent infections during this time (for example avoid contact with people with an illness like flu or chicken pox.
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 patients 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.