Allogeneic stem cell transplants
What is an allogeneic stem cell transplant?
In an allogeneic transplant, stem cells are donated to the patient from another person who is a genetically matched stem cell donor. This is usually a sibling 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, but it 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.
Allogeneic transplants can offer the best chance of curing a number of blood and bone marrow cancers and other diseases. They are complex procedures that carry significant risks. The complexities and risks may be increased even more with a mismatched or volunteer unrelated donor (VUD) transplant. As such, allogeneic transplants are usually not suitable for all patients.
A “mini-allogeneic” or “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.
It is important to realise that the processes involved in a stem cell transplant are often long and complex. A transplant involves a lot of preparation and a lot of aftercare. The process of a stem cell transplant can be divided into these nine different stages:
- planning for your transplant
- pre-transplant “work-up”
- conditioning therapy
- the transplant
- potential post-transplant complications
- leaving hospital
- potential late side effects
How does the pre-transplant work?
During the weeks leading up to your transplant you will undergo a number of tests to make sure that your vital organs (heart, lungs, liver and kidneys) are physically fit enough for the transplant process. You may also need to see other specialists depending on your particular circumstance.
Conditioning therapy and total body irradiation
Before you receive your transplant you will have a few days of what is known as conditioning therapy. Conditioning therapy is used to help destroy any leftover cancer cells in your body and make space in your bone marrow for the new stem cells. Conditioning therapy is also used to suppress your immune system to reduce the risk of it rejecting the donor stem cells. Total body irradiation (TBI) involves exposing your whole body to high doses of ionising radiation. TBI is sometimes used in combination with chemotherapy because it can penetrate and treat areas of your body less easily reached by chemotherapy (for example your brain and spinal cord). This is generally used in volunteer unrelated donor (VUD) transplants.
After you have finished conditioning, 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 set up home and begin to repopulate the bone marrow with families of immature white cells, platelets and red cells. This process is known as engraftment and it takes anywhere between 10 and 28 days, depending on the type of transplant you have.
Your blood counts initially 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 experience some of the common sideeffects of chemotherapy and radiotherapy which may include nausea, vomiting, mucositis (sore mouth) and bowel problems (diarrhoea). Some side effects can persist for months and occasionally years after the transplant.
Leaving hospital after a transplant
Once your blood stem cells have engrafted, your blood counts start to rise, and you are otherwise well enough, it is time to leave the transplant unit. Generally the doctors like to keep you close to the hospital where you have had your transplant, so that they can keep a close eye on you during the early weeks of your recovery. 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.
Although the stem cells have engrafted, your body will take some time to recover to a normal level of functioning. This may take up to six months. While many of the side effects of a stem cell transplant last for a short time, some can last longer. Some side effects, such as graft versus host disease (GvHD), persist for months and occasionally years after the transplant.
Vaccinations after an allogeneic transplant
In general, following an allogeneic transplant you will lose the immunity to many of the diseases you were vaccinated against as a child.
These include measles, mumps, rubella and polio. Your doctor will assess when your immune system has recovered enough to allow you to be re-vaccinated as the vaccinations need to be able to stimulate the immune system to work. This will usually be no earlier than twelve months after the transplant. There may be some vaccines that your haematologist may consider unsafe to give (especially live vaccines), and these will be discussed with you. In the meantime it is important that you avoid anyone who is sick or has had contact with someone with a ‘catching’ illness.
Also, if you are planning to travel overseas, vaccinations may be required to safely prevent some serious infections. Once more, some of these vaccinations may not be safe to be given to you, so please let your doctor know well in advance about your plans, so a vaccination schedule may be organised. Advice from an infectious diseases or travel health specialist may also be required.