What is syngeneic stem cell transplant?
A syngeneic stem cell transplant is a special type of allogeneic transplant in which the donor is an identical twin (or triplet) to the recipient. This means that the donor and the recipient both have identical tissue types.
This type of stem cell transplant is rare as identical twins or triplets are not very common. If you have an identical twin or triplet, their stem cells can be used to treat your leukemia or other blood disorders you may have.
How it works
A syngeneic stem cell transplant uses the stem cells from your identical twin to replace your abnormal bone marrow.
Before the stem cells transplant, you will receive high doses of radiotherapy or chemotherapy, or both, to destroy all of your cancer cells as well as the normal blood cells in your bone marrow.
You will then receive the new healthy stem cells, which are free of cancerous cells and will produce their own immune cells. These immune cells will fight any cancer cells remaining after treatment.
If more stem cells are needed, your identical twin will have to be recalled.
Why do you need a syngeneic stem cell transplant?
Syngeneic stem cell transplants are used to treat conditions such as:
- Hodgkin lymphoma
- Multiple myeloma
- Myelodysplastic syndrome
- Non-Hodgkin lymphoma
- Severe aplastic anaemia
- Testicular cancer
The advantages of syngeneic stem cell transplants include:
- Your body readily accepts the cells. Graft-versus-host disease (GVHD) will not be an issue because your immune system recognises your identical sibling’s stem cells as your own (donor’s tissue type matches 100% with recipient).
- You get cancer-free donor cells. Donors are required to undergo rigorous medical screenings, so their stem cells are verified to be free of cancer.
The disadvantages of syngeneic stem cell transplants include:
- Your body may not fight the cancer cells. This type of transplant will not destroy the cancer cells as the newly-infused stem cells are identical to your own cells. Like your old immune system, your new immune system may not recognise and fight cancer cells, possibly leading to a relapse.
What are the risks and complications of a syngeneic stem cell transplant?
The side effects of a stem cell transplant may vary from person to person. Some individuals experience multiple side effects, while others may have fewer. Some side effects are short-term (acute), while others are long-term (chronic).
Many of the side effects result from the chemotherapy or radiation therapy given before the transplant. Others are related to the stem cell transplant.
Initial side effects can include:
- Mouth and throat pain
- Nausea and vomiting
- Bacterial, viral or fungal infections
- Bleeding and anaemia (low red blood cell count)
- Lung problems such as pneumonitis, an inflammation of lung tissue
- Veno-occlusive disease (VOD), when small blood vessels that lead to the liver become blocked
Longer-term side effects can include:
- Eye problems such as cataracts
- Organ damage
- Return of the cancer
- Secondary cancers
- Lymph tissue problems
- Thyroid problems caused by hormone changes
After your stem cell transplant, your doctor will monitor you closely. They will take measures to prevent side effects and to quickly deal with any that develop.
How do you prepare for a syngeneic stem cell transplant?
To find out if a stem cell transplant will work for you, your doctor may need to do the following tests and procedures:
- Take your complete health history
- Do a physical examination
- Conduct human leukocyte antigen (HLA) testing, a blood test to ensure a good tissue match with the donor
- Conduct a bone marrow biopsy
- Do a computerised tomography (CT) scan or a magnetic resonance imaging (MRI) scan
- Do an electrocardiogram (ECG), echocardiogram (echo) or a wall motion study to check your heart
- Do a chest X-ray and pulmonary function tests to check your lungs
- Carry out blood tests such as complete blood count, blood chemistry tests and to check for viruses such as hepatitis, cytomegalovirus (CMV) and HIV
You may also be asked to go for other forms of evaluation such as psychological assessment or fertility counselling.
What can you expect in a syngeneic stem cell transplant?
You will need to undergo conditioning therapy in preparation for the stem cell transplant.
Conditioning therapy is used to:
- Remove any remaining cancer cells left in the body
- Prepare your bone marrow to receive the donor stem cells
- Suppress your immune system to lower the chance of rejecting the donor stem cells
Conditioning includes myeloablative therapy, where you will be given high doses of chemotherapy through a central venous catheter (tube). You may also require total body irradiation (TBI), a form of radiation therapy in which the whole body is treated with radiation. The treatment plan will vary depending on the disease being treated.
The treatment is usually given over a few days.
Stem cells transplant
The transplant is usually done 1 – 3 days after the end of conditioning therapy. The day of the transplant is usually referred to as day 0.
You will be given the stem cells through a central venous catheter. The number of stem cells you receive is calculated based on your weight.
The duration of the transplant depends on the number of stem cells given. It usually takes about 1 – 2 hours.
You will be monitored closely for any side effects while you are receiving the stem cells. Side effects could include chills, fever, chest pain, headache, nausea, shortness of breath and hives.
After the procedure
After the procedure, the transplanted stem cells enter the blood and make their way to the bone marrow to start making new blood cells. This process is known as engraftment.
It may take 2 – 6 weeks before your blood cell counts return to normal.
During this time, you may need to stay in an isolated room in the hospital due to the increased risk of infection. You may:
- Feel tired and generally unwell
- Have to take daily blood tests and regular temperature checks
- Be watched closely for bleeding, nausea, vomiting, diarrhoea and any other reactions
- Be given medicine including antibiotics, antifungals and antivirals to prevent and treat infections
- Be given nutrition and supplements through a central venous catheter until you are ready to eat by mouth
- Be given colony-stimulating factors (CSF) to speed up the healing
- Need blood transfusions and platelet transfusions
You will only be discharged from the hospital if you:
- Have not had a fever for 24 – 48 hours
- Have been able to take medication and keep it down for 48 hours
- Are able to control your symptoms such as nausea, vomiting and diarrhoea with medication
- Are able to eat food and drink enough fluids
- Have safe levels of blood cell counts
- Have a caregiver at home to assist you during your recovery
Care and recovery after a syngeneic stem cell transplant
Your recovery process may take several months or longer. During this period you may not be able to return to work or resume your previous lifestyle.
You will be at risk of infections for the next 1 - 2 years as it takes a while for your immune system to return to full strength.
During the recovery period, you will have to attend follow-up appointments with your doctor to check on your health and progress.