What are stem cells?
Bone marrow is a spongy material that’s found inside some of our hollow bones. Stem cells are produced in the bone marrow. These are cells in their earliest stage of development. They will eventually become red blood cells, white blood cells and platelets. When the cells are fully mature, they are released into the bloodstream.
Why have a stem cell transplant?
Your child may need a stem cell transplant because:
- their own bone marrow cells are diseased, for example, in leukaemia
- their bone marrow is not working properly, for example, in aplastic anaemia or thalassaemia
- their bone marrow is suppressed, for example, after chemotherapy or radiotherapy
- their immune system is not working properly, for example, in combined immune deficiency
A stem cell transplant is used as part of standard treatment for some cancers in children and young people. It is also used as a treatment for relapsed disease. A stem cell transplant (sometimes called a bone marrow transplant) allows your child to have much higher doses of chemotherapy than usual. This can improve the chance of curing their cancer but has more side effects.
What is a stem cell transplant?
During a stem cell transplant (SCT), new healthy stem cells are put into the bloodstream. These new cells attach to the bone marrow and start to make new healthy blood cells.
There are two different types of transplants. The type of transplant recommended will depend on your child's disease type and treatment plan.
- Autologous: this uses your child’s own stem cells. The stem cells are collected some time before intensive high-dose treatment and are stored until needed.
- Allogeneic: this uses stem cells from a close relative or unrelated donor – it is also known as an allograft. A donor transplant is a more complicated procedure than an autologous one and is only carried out in specialist hospitals. Recovery may take several months or longer.
If your child needs a donor transplant, usually parents and siblings are tested first to see if their tissue type is a match. A sibling has a 1 in 4 chance of being a match. If no suitable match is found within the family, a search for a potential match from UK and international stem cell registries will be made.
What happens during a stem cell transplant?
Collecting the stem cells
Before a stem cell transplant, stem cells are collected. These can come from bone marrow, blood or umbilical cord cells. Cells taken from the bone marrow are collected under anaesthetic. This is called a bone marrow harvest. Cells taken from the blood are collected using a machine which is connected to a cannula or central line. A drug is given to trigger the bone marrow to produce extra stem cells which are collected from the circulating (or peripheral) blood. This is called a peripheral blood stem harvest (PBSC harvest). Cells can also be collected from the umbilical cord at the time of a delivery of a baby. Only a limited amount of stem cells can be collected from umbilical cord blood.
The method used depends on which type of transplant your child needs.
Conditioning treatment
Your child will then be given very high doses of chemotherapy, usually over a few days. Sometimes, radiotherapy to the whole body, known as total body irradiation (TBI), is also given. As well as destroying any remaining cancer cells, the high doses of chemotherapy also destroy the stem cells in the bone marrow. These treatments can have significant side effects but they are needed to destroy the bone marrow effectively, which is important for the new cells to work.
Receiving the stem cells
After the high dose chemotherapy or total body irradiation (TBI), your child is given the stem cells that were collected before the treatment through a drip. The amount of stem cells needed is calculated based on your child's weight. Your child will be given medicines to precent sickness or an allergic reaction and they will be monitored closely throughout the transfusion.
The new stem cells make their way into the empty bone marrow and gradually start producing mature blood cells again. This is known as engrafting. It takes some time before the new stem cells start making enough white cells to fight infections. Transfusions of red blood cells and platelets are usually needed until the stem cells produce enough blood cells of their own.
It takes longer for the bone marrow to be fully working after a donor transplant, than after an autologous transplant.
Find out more:
Our booklet 'A guide to donor stem cell transplants' has more information for families and young patients about having a donor (allogeneic) transplant and what to expect.
