Donating bone marrow stem cells
There are two ways of collecting stem cells from donors for a transplant:
• peripheral blood stem cell (PBSC) harvest: where donor stem cells are collected from the circulating blood using a process called leukapheresis (see below)
• bone marrow harvest: where bone marrow is collected from bone while the donor is under general anaesthetic.
Most transplants from related donors use PBSC, while transplants from unrelated donors use either PBSC or bone marrow harvest depending on a number of factors, including the patient’s disease and donor preference.
Collecting peripheral blood stem cells
Many donors prefer this method because they don’t need an anaesthetic and won’t have pain after it is done. They need to be injected with a drug called granulocyte colony stimulating factor (G-CSF) for a few days before the procedure, which may have some temporary side effects.
Pre-treatment with G-CSF
The transplant team will prescribe G-CSF. The donor takes it home, and has it injected under the skin once or twice a day for about four days before stem cells are collected on the fifth, and occasionally the sixth day. Some donors choose to inject themselves, but others have someone else – a relative, a nurse or their local doctor – inject the drug.
G-CSF is a synthetic copy of a naturally occurring bone marrow hormone. The hormone is not usually detectable in the body, but the immune system makes it in response to infection. Its natural action is to stimulate the growth of bone marrow stem cells, which can become white cells to fight infection. It also causes the release of stem cells from the marrow into the blood. When enough G-CSF is given, large numbers of stem cells are released into the blood, which can be collected for the transplant.
Side effects
Most donors experience some side effects from G-CSF. These are mostly flu-like symptoms, such as aches and pains, fatigue and generally feeling a “bit off.” The symptoms usually are mild and controlled by paracetamol, but occasionally donors can feel more unwell and need stronger painkillers.
Severe side effects are rare but there have been rare reports of a ruptured spleen in donors, as G-CSF enlarges the spleen (a large organ under the left side of the rib cage). However, many thousands of normal donors have been treated with G-CSF without any serious short- or long-term side effects.
Donating bone marrow stem cells
Harvesting the cells – leukapheresis
On the day of collection, the donor is attached to a machine that collects or ‘harvests’ stem cells from the blood. The collection process, which is called leukapheresis, is usually done at the transplant centre if the donor is related, but always at another collection centre if the donor is unrelated, on an outpatient basis over 3-6 hours.
The donor is awake throughout the procedure. At the beginning, a needle is put into a large vein in the crook of each elbow, and connected by tubes to the apheresis machine. This is basically a big centrifuge, which spins the blood and separates it into white blood cells, red cells and plasma.
The blood is withdrawn from one arm of the donor, passed through the machine, and the portion of the white blood cells that includes the stem cells are collected – a bit like skimming cream off milk. The rest of the blood is then returned to the donor through the other arm. About 12L of blood is processed through the machine.
The donor usually notices no side effects, but occasionally changes in the calcium level in the blood, caused by the anticoagulant solution (citrate) used to stop the blood clotting in the machine, may cause a tingling feeling. Calcium treatment will reverse this. More rarely, donors can feel faint during the procedure because of low blood pressure. The collection will be stopped if this happens.
Some donors don’t have accessible veins in their arms and may need to have the needle put into a large vein in the groin. The insertion of this needle is less pleasant and has a greater risk of bruising, so is only used if there is no alternative.
Most donors can go home within a few hours of the collection. The side effects of G-CSF usually go away within a few days of the drug being stopped.
Most donor leukapheresis procedures collect enough stem cells for a successful transplant. The cells are collected in a bag, usually in a volume of 150-200mL, and the stem cells are counted in the laboratory. About one in three donors will need to have a second collection the next day, after another dose or two of G-CSF.
Donating bone marrow stem cells
Bone marrow harvest
A bone marrow harvest is done in a hospital operating room, usually under general anaesthesia. It is a low-risk procedure, but the donor will feel sore afterwards. While the donor is under anaesthesia, a needle is put inside the rear hipbone (the iliac crest), which contains a lot of bone marrow.
The bone marrow is a thick, red liquid and is extracted with needles and syringes. Several skin punctures on each hip and multiple bone punctures are usually needed to extract the required amount of bone marrow. No surgical cuts or stitches are involved – only skin punctures where the needle was inserted.
The amount of bone marrow harvested depends on the size of the patient. Usually 1L of marrow and blood is harvested. Although this may sound like a lot, it is only about 2% of a person’s bone marrow and the body replaces it in four weeks.
When the anaesthesia wears off, the donor will feel some discomfort at the harvest site, as if they have had a hard fall. It can usually be relieved with paracetamol. There may be some colourful bruising at the back of the hips in the week after the harvest.
Donors can usually go home after an overnight stay in hospital and can resume their normal activities in a few days. Regular blood donors will probably need to wait a while before giving blood, at least until they have their haemoglobin level checked after the harvest.
Sometimes the bone marrow may be treated to remove T cells (T cell depletion) to reduce the risk of graft-versus-host disease.
Donating bone marrow stem cells
Key points
• Most transplants from related donors use stem cells collected from the circulating blood using a process called leukapheresis.
• Most transplants from unrelated donors use bone marrow cells, which are collected from bone while the donor is under general anaesthetic.
• Before the harvest donors will be injected with a drug called G-CSF, which stimulates bone marrow stem cells to grow and multiply.
• G-CSF often causes mild side effects, such as flu-like symptoms. The side effects of G-CSF usually go away within a few days of the drug being stopped. Severe side effects are rare.
• Leukapheresis is a relatively painless procedure. Almost all donors can go home within a few hours of it being done.
• Bone marrow harvest is done in a hospital operating room, usually under general anaesthesia. It is a low-risk procedure, but the donor will feel sore afterwards.
Donating bone marrow stem cells
