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A stem cell or bone marrow transplant replaces damaged blood cells with healthy ones. It can be used to treat conditions affecting the blood cells, such as leukaemia and lymphoma.

Stem cells are special cells produced by bone marrow (a spongy tissue found in the centre of some bones) that can turn into different types of blood cells.

The three main types of blood cell they can become are:

  • red blood cells – which carry oxygen around the body
  • white blood cells – which help fight infection
  • platelets – which help stop bleeding

A stem cell transplant involves destroying any unhealthy blood cells and replacing them with stem cells removed from the blood or bone marrow.

Why are stem cell transplants carried out?

Stem cell transplants are used to treat conditions in which the bone marrow is damaged and is no longer able to produce healthy blood cells.

Transplants can also be carried out to replace blood cells that are damaged or destroyed as a result of intensive cancer treatment.

Conditions that stem cell transplants can be used to treat include:

  • severe aplastic anaemia (bone marrow failure)
  • leukaemia – a type of cancer affecting white blood cells
  • lymphoma – another type of cancer affecting white blood cells
  • myeloma – cancer affecting cells called plasma cells
  • certain blood, immune system and metabolic disorders – examples include sickle cell anaemiathalassaemia, severe combined immunodeficiency (SCID) and Hurler syndrome

A stem cell transplant will usually only be carried out if other treatments haven't helped, the potential benefits of a transplant outweigh the risks and you're in relatively good health, despite your underlying condition.

What does a stem cell transplant involve?

A stem cell transplant can involve taking healthy stem cells from the blood or bone marrow of one person – ideally a close family member with the same or similar tissue type (see below) – and transferring them to another person. This is called an allogeneic transplant.

It's also possible to remove stem cells from your own body and transplant them later, after any damaged or diseased cells have been removed. This is called an autologous transplant.

A stem cell transplant has five main stages. These are:

  1. Tests and examinations – to assess your general level of health.
  2. Harvesting – the process of obtaining the stem cells to be used in the transplant, either from you or a donor.
  3. Conditioning – treatment with chemotherapy and/or radiotherapy to prepare your body for the transplant.
  4. Transplanting the stem cells
  5. Recovery

Having a stem cell transplant can be an intensive and challenging experience. You'll usually need to stay in hospital for a month or more until the transplant starts to take effect and it can take a year or two to fully recover.

Read more about what happens during a stem cell transplant.

Risks of a stem cell transplant

Stem cell transplants are complicated procedures with significant risks. It's important that you're aware of both the risks and possible benefits before treatment begins.

Possible problems that can occur during or after the transplant process include:

  • graft versus host disease (GvHD) – this occurs in allogeneic transplants when the transplanted cells start to attack the other cells in your body
  • reduced number of blood cells – this can lead to anaemia, excessive bleeding or bruising, and an increased risk of infections
  • chemotherapy side effects – including sickness, tiredness, hair loss and infertility

Read more about the risks of having a stem cell transplant.

Stem cell donation

If it isn't possible to use your own stem cells for the transplant (see above), stem cells will need to come from a donor.

To improve the chances of the transplant being successful, donated stem cells need to carry a special genetic marker – known as a human leukocyte antigen (HLA) – that's identical or very similar to that of the person receiving the transplant.

The best chance of getting a match is from a brother or sister, or sometimes another close family member. If there are no matches in your close family, a search of the British Bone Marrow Registry will be carried out.

Most people will eventually find a donor in the registry, although a small number of people may find it very hard or impossible to find a suitable match.

The NHS Blood and Transport website has more information about stem cell and bone marrow donation.

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How is it performed?

A stem cell or bone marrow transplant is a long and complicated process that involves five main stages.

These stages are:

  1. Tests and examinations – to assess your general level of health.
  2. Harvesting – the process of obtaining the stem cells to be used in the transplant, either from you or a donor.
  3. Conditioning – treatment to prepare your body for the transplant.
  4. Transplanting the stem cells.
  5. Recovery – you'll need to stay in hospital for at least a few weeks until the transplant starts to take effect.

The stages are described in more detail below. You can use the links above to navigate to each section.

Tests and examinations

Before a stem cell transplant can be carried out, you'll need a series of tests and examinations to ensure you're healthy enough for the procedure to be carried out.

Transplants tend to be more successful in people who are in good general health, despite their underlying condition.

The tests you might have include:

If you have cancer, you may also need to have a biopsy. This is where a small sample of cancerous cells is removed and analysed. It can show whether your cancer is under control (in remission) and whether there's a high risk of it returning after your transplant.

Harvesting stem cells

After you've had tests to check your general health, the stem cells that will be used for the transplant will need to be removed and stored.

There are three main ways stem cells can be harvested, these are:

  • from blood – where the stem cells are removed from your blood using a special machine (see below)
  • from bone marrow – where a procedure is carried out to remove a sample of bone marrow from the hip bone (see below)
  • from cord blood – where donated blood from the placenta and umbilical cord of a newborn baby is used as the source of stem cells (find out more from the NHS Cord Blood Bank)

It may be possible to remove stem cells from your own blood or bone marrow and transplant them later after any damaged or cancerous cells have been removed.

If this isn't possible, stem cells from a donor's blood or bone marrow will usually be used.

Removing stem cells from blood

The most common way to harvest stem cells involves temporarily removing blood from the body, separating out the stem cells, and then returning the blood to the body.

To boost the number of stem cells in the blood, medication that stimulates their production will be given for about four days beforehand. On the fifth day, a blood test will be carried out to check there are enough circulating stem cells.

If there are enough cells, veins in each arm will be connected by tubes to a cell-separator machine. Blood is removed from one arm and passed through a filter, before being returned to the body through the other arm.

This procedure isn't painful and is done while you're awake. It takes around three hours and may need to be repeated the next day if not enough cells are removed the first time.

Removing a bone marrow sample

An alternative method of collecting stem cells is to remove around a litre of bone marrow from your hip bone using a needle and syringe.

The needle may need to be inserted into several parts of your hip to ensure enough bone marrow is obtained. This is done under a general anaesthetic, so you'll be asleep and won't feel any pain while it's carried out.

However, the area where the needle is inserted may be painful afterwards and you'll have two marks on your skin where the needles were inserted (usually one on each side).

Conditioning treatment

Treatment with high doses of chemotherapy and sometimes radiotherapy will be needed before the stem cells can be transplanted to:

  • destroy existing bone marrow cells – this is to make room for the transplanted tissue
  • destroy any existing cancer cells
  • stop your immune system working – this is to reduce the risk of the transplant being rejected

As part of the conditioning treatment, you'll be given a range of medicines, so a tube called a central line will usually be inserted into a large vein near your heart. This means medication can be passed into your body without the need for numerous injections.

The conditioning process usually lasts up to a week. You'll probably need to stay in hospital throughout the treatment.

Conditioning can cause a number of unpleasant side effects, such as sickness, hair loss and tiredness. These are usually temporary. Your treatment team will discuss the risks of treatment with you beforehand.

Read more about the risks of stem cell transplants.

The transplant

The transplant will usually be carried out a day or two after conditioning has finished.

The stem cells will be passed slowly into your body through the central line. This process often takes around a couple of hours.

The transplant won't be painful and you'll be awake throughout.


Once the transplant is finished, you'll need to stay in hospital for a few weeks while you wait for the stem cells to settle in your bone marrow and start producing new blood cells.

During this period you may:

  • feel weak, and you may experience vomiting, diarrhoea and/or a loss of appetite
  • be given fluids by mouth or through a tube running from your nose to your stomach (a nasogastric tube) to prevent malnutrition
  • have regular blood transfusions, as you'll have a low number of red blood cells
  • have regular platelet transfusions, as you'll have a low number of platelets
  • stay in a special germ-free room, and visitors may need to wear protective clothing to prevent infections, as you'll have a low number of infection-fighting white blood cells

Many people are well enough to leave hospital between one and three months after the transplant. However, if you develop complications such as an infection, you may not be able to leave hospital for longer.

Even after going home, you'll still be at risk of infections for potentially a year or two because it can take a while for your immune system to return to full strength.

If donated stem cells were transplanted, you'll also usually need to take medicines that stop your immune system from working so strongly, to reduce the risk of your body attacking the transplanted cells (immunosuppressants), or to reduce the risk of the transplanted cells attacking other cells in your body.

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Stem cell or bone marrow transplants are complex treatments that carry a significant risk of serious complications.

It's important that you're aware of both the risks and possible benefits before treatment begins. You may wish to discuss them with your treatment team and your family.

Generally speaking, younger people who don't have any other serious conditions or those who receive transplants from a closely matched sibling are less likely to experience serious problems. People receiving transplants of their own stem cells (autologous transplants) are also less likely to experience serious side effects.

The main risks associated with a stem cell transplant are outlined below.

Graft versus host disease

In some cases, the transplanted cells recognise the recipient's cells as "foreign" and attack them. This is known as graft versus host disease (GvHD).

GvHD can occur within a few months of the transplant or develop several months or occasionally a year or two later. The condition is usually mild, but can sometimes be life-threatening.

Symptoms of GvHD can include:

Tell your treatment team if you develop these symptoms. GvHD can be treated with medications that suppress your immune system and stop the transplanted stem cells attacking the rest of your body.

Reduced number of blood cells

In preparation for a stem cell transplant, you'll need to have chemotherapy to destroy the damaged or diseased blood cells. These will eventually be replaced by the transplanted stem cells, although this process can take several weeks or more.

Until your body starts being able to produce healthy blood cells again, you may be at risk of:

  • anaemia – a lack of red blood cells that can make you feel tired and short of breath; this may be treated with regular blood transfusions
  • excessive bleeding or bruising caused by a lack of clotting cells called platelets; you may need transfusions of platelets if this is a problem
  • infections – a lack of white blood cells and any immunosuppressant medication you're taking will mean your body isn't able to fight off infections

You'll need to stay in a special germ-free hospital room during the first few weeks after the transplant. After going home, you'll need to be careful about coming into contact with people with infections and take steps to prevent food poisoning.

You may also be given antibiotics to prevent or treat any bacterial infections.

Chemotherapy side effects

Common side effects of chemotherapy include:

These side effects are usually temporary and only last a few weeks. Hair usually grows back within a few months.

However, high-dose chemotherapy can also have some long-lasting effects, including permanent infertility, which affects most people who have the treatment.

Your treatment team will tell you about this before treatment starts if it's a risk and they can discuss possible ways of having children in the future. In some people this may include procedures to collect and freeze eggs or sperm, although this isn't always possible.

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The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website
Last Updated: 11/05/2018 10:39:56