Your donor is the person who gives their cells for your stem cell transplant. The first step in finding a donor is for you to have a blood test to find your tissue type. Your tissue type is the combination of proteins on the surface of your cells called human leukocyte antigen (HLA) markers. Your immune system uses your HLA markers to recognise your own normal body cells.
Doctors use your HLA markers to match you with a donor. When they know your tissue type, they compare it with close relatives or with donors on a registry. They look to see if the tissue type is the same as yours (a match). Doctors look for between 8 to 10 markers that match with yours. Occasionally all 10 will match. Having the best possible match means less risk of:
the new immune cells reacting against your other body cells (graft-versus-host disease).
The best match is usually a brother or sister (your siblings). If you do not have close family, or they are not a match, your doctors look for a matched donor through a volunteer registry.
Your donor does not need to have the same blood group as you. After the transplant, your blood group changes to their blood group.
If doctors cannot find a well-matched donor, there are other possible approaches. They may accept small differences to improve the chances of finding a donor. This is known as a mismatched transplant. This could be someone in your family or someone on a donor registry. A more recent option is a relative whose tissue is a half-match to yours (haploidentical). Another possible option could be using a cord blood transplant.
Brothers or sisters each have a 25% chance of having the same tissue type as you and being a match. Our tissue types are a combination of both parents. Not every combination will be the same. So not every sibling will be a close enough match to be a donor. Parents, half-brothers, and half-sisters are not usually a good match.
Occasionally a sibling has one HLA marker that is different but can still be used as a donor. This is known as a mismatched transplant.
A different team from the one looking after you will contact your family to ask if they are willing to be tested. Your siblings can be tested even if they live abroad.
If you do not have a close match in your family your doctors will look for a volunteer donor who is not related to you. There are donor registries in the UK, such as Anthony Nolan, which have lists of possible volunteer unrelated donors.
If there is not a suitable UK donor for you, there are registries in other countries that your doctor can search. It usually takes longer to prepare an international donor than a UK donor. Occasionally no suitable donor can be found.
When there is no matched donor available, your specialist may advise using stem cells from a close relative whose tissue type is a 50% match to yours. A close relative is a brother or sister, child, or parent. Almost everyone will have at least one possible donor. Doctors call this type of transplant a haploidentical transplant.
As your donor is related, it can usually be done quickly. But it is still quite a new approach and will not be suitable for everyone.
Because it is only a 50% match, there is more risk of complications, such as graft-versus-host-disease, graft rejection and slow recovery of the immune system. But doctors are finding different ways to deal with these problems.
Another source of stem cells is blood from an umbilical cord. This is the cord that connects a baby to its mother during pregnancy. Cord blood can be donated after birth and frozen. It is stored in a cord blood bank and used for people needing transplants. There is no risk to the mother or baby and all cord blood is tested to make sure it is safe to use.
It may be possible to use cord blood for people who do not have a suitable donor. With cord blood, you do not need as close a match as with an adult donor. You can also get it quickly.
A person’s weight can be a factor when doctors are deciding whether a cord blood transplant is suitable. People who weigh more need more stem cells for a transplant to be successful. It may not always be possible to get enough stem cells from cord blood.
Sometimes doctors can use cord blood from two different cords in one transplant if they are both a close match. This is called a double cord blood transplant.
Most people who are white Europeans find a match from a related or unrelated donor, or from cord blood.
But people from black, Asian and minority ethnic groups, without a related donor, often have difficulty finding a good match from volunteer registries. Most people registered as donors are white and tissue types rarely match across the different ethnic groups. If you are mixed race, it can be even more difficult.
Organisations and charities are working to increase the number of registered donors from all these groups. Cord blood banks have also increased the chances of finding a suitable donor.
Donors are given counselling before they agree to donate stem cells. Once they understand what is involved, they are asked to sign a consent form. They can still change their mind after this.
Information about the donor is confidential and cannot be shared without their permission. This is the same for related donors and unrelated donors. They are looked after by a different team to the one looking after you.
The donor has tests to make sure they are fit to donate and that it is safe for them. These include blood tests, a chest x-ray, and an electrocardiogram (ECG) to check the heart. They also have their weight checked.
They will have different blood tests to check:
- their general health
- for infections including HIV, hepatitis and cytomegalovirus (CMV).
Your donor’s stem cells can be collected either from their blood or, less commonly, from their bone marrow.
Taking stem cells from the blood
The donor needs to have drugs to encourage the stem cells to move from the bone marrow into the blood. They have a small daily injection of a drug called a growth factor (G-CSF) under the skin for a few days leading up to the collection. It increases the number of stem cells in the bone marrow to make them move out into the blood. Doctors sometimes call this mobilising the stem cells.
Donors can be shown how to give the injection themselves or it can be done at the GP practice or hospital. Their blood is checked about 5 days after the injections started. When the results show enough stem cells in the blood, they are collected.
The stem cells are collected 1 or 2 days before the transplant. It is a straightforward procedure that takes 3 to 4 hours, usually as a day patient.
A nurse or doctor puts a short, thin tube (cannula) into a vein in each arm. The donor’s blood is removed through one arm and passes through tubes that are connected to a machine called a cell separator. This separates the stem cells and collects them. The remaining blood is then returned to the donor through the tube in their other arm. If not enough stem cells are collected, the donor may have to come back the next day.
Taking stem cells from the bone marrow
Sometimes stem cells are taken from the donor’s bone marrow, usually from the back of the hip bones (pelvis). This is done under a general anaesthetic and usually means staying in hospital overnight.
The doctor passes a needle through the skin into the bone marrow. They then draw the liquid marrow through the needle into a syringe. They may do this a few times from different parts of the pelvis.
The donor’s body usually replaces the bone marrow that was removed within a few weeks. They will have blood tests to check their blood counts have returned to normal.
The area may feel sore for a few days afterwards, but taking regular painkillers will help. There may also be some bruising which will go away within a few weeks.