Finding a donor and collecting stem cells

The first step in finding a donor is taking a blood test to identify your tissue type. Each cell in the body has a combination of a group of proteins (HLA) on their surface.

Once your tissue type is known, other people can have their blood tested to see whether their tissue type is the same as yours. This is known as HLA matching. Having a close match increases the chances of a successful transplant.

Brothers and sisters (siblings) are mostly likely to be a good match for you. If you don’t have a match amongst your relatives, your doctors will look for a volunteer unrelated donor – in the UK or abroad. Another source of stem cells is from umbilical cord blood. This is stored in cord blood banks. Matches can now be found for most people using one of these methods.

Possible donors will have tests and counselling before donating their cells. Stem cells can then be collected from the donor’s blood or bone marrow.

Finding the donor

The first step in finding a donor is taking a blood test from you to identify 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 cells in the body as your own.

Blood tests usually identify 8–10 markers. Once your tissue type is known, other people can have their blood tested to see whether their tissue type is the same as yours. Having a close match to your tissue type increases the chances of the transplant being successful. The closer the match, the less risk of the donor’s cells attacking your cells, or of graft failure.

You don’t have to be the same blood group as your donor.

After the transplant, your blood will change to their blood group.

Related donor

Brothers and sisters (your siblings) are most likely to be a match for you. They will be contacted to ask if they are willing to be tested. This will be done by a different medical team from the one looking after you. Your siblings can be tested even if they live abroad. Their blood sample can be taken by their doctor or local hospital.

Each sibling has a 1 in 4 (25%) chance of having the same tissue type as you. If one of your siblings is completely matched to you, they are known as an HLA identical donor. But the match is unlikely to be exactly the same unless you are identical twins.

For some markers, doctors may accept small differences to improve the chances of finding a donor. This is known as a mismatched transplant.

Parents, half-brothers and half-sisters will not usually be a good match.

Volunteer unrelated donor

If you don’t have a match among your relatives, your doctors can look for a volunteer unrelated donor (VUD). There are donor registries in the UK which have lists of possible volunteer unrelated donors.

There are a large number of registries in other countries that your doctor can also search if there’s no suitable UK donor for you.

But this can take time and a suitable match is not always found.

Stem cells from cord blood

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 and stored in a cord blood bank, so it’s available for people needing transplants. There is no risk to the mother or baby.

All cord blood is tested to make sure it is safe to use. It may be possible to use cord blood for people who don’t have a suitable donor. With cord blood, you don’t need to have as close a match as with an adult donor. And because it is already stored it can be accessed quickly.

Your weight is important when deciding whether a cord blood transplant is suitable. People who are heavier need more stem cells for a successful transplant, and it’s not always 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.


Likelihood of finding a match

About 9 out of 10 (90%) of white people from northern Europe find a match from a related or unrelated donor, or from cord blood.

People from black, Asian and minority ethnic groups, without a related donor, often have difficulty finding a good match from volunteer registries because most people registered are white. Tissue types rarely match across the different ethnic groups.

Black, Asian and minority ethnic groups have about a 4 in 10 (40%) chance of finding a suitable match from a registry.

This figure is lower if you’re mixed race. Organisations and charities are trying to recruit more donors from all ethnic groups.

Cord blood banks have increased the chances of black, Asian and minority ethnic groups finding a suitable donor. Matches can now be found for most people.


Before donating stem cells

Before donating stem cells, donors are given counselling so they know what’s involved. Donors will then be asked to sign a consent form. Even after signing a consent form, the donor has the right to change their mind about going ahead with the donation.

All information about the donor will be kept confidential. No information can be shared without their permission. These rules apply to related donors and unrelated donors. Donors are looked after by different doctors from the one looking after the person waiting for a transplant.

The donor will have tests to make sure that the procedure is safe for them. These can include a chest x-ray, an ECG and a weight check. Blood tests are then taken to check their general health and to check for infections including HIV, hepatitis and cytomegalovirus (CMV).

Female donors may be asked to take a pregnancy test before donating.

Stem cells can be collected either straight from a donor’s blood or from their bone marrow.


Collecting stem cells from the blood

Mobilising the stem cells

The donor has daily injections of a growth factor (G-CSF) for several days before collection. Growth factors stimulate the bone marrow to make stem cells and increase the number of stem cells which move from the marrow into the blood (mobilise). The growth factor is given as a small injection under the skin (subcutaneously). The donor can be taught to inject themselves, or they can go to their GP or hospital to have injections.

The donor’s blood is checked around five days after the start of the injections. When there are enough stem cells in the blood, they are collected.

Collecting the stem cells

The collection takes 3–4 hours, and can usually be done as a day patient. A nurse or doctor puts a short, thin tube (cannula) into a vein in each of the donor’s arms. Each cannula is connected by a line of thin tubing to a machine called a cell separator.

The donor’s blood goes out from one arm through the line into the cell separator. As the blood travels through the cell separator, it is spun to separate out the stem cells, which are collected in a bag. The rest of the blood is returned to the donor through the cannula in their other arm.

The collected stem cells are counted to make sure there are enough. If more stem cells are needed, the donor may have to come in for another collection the next day. The stem cells will be collected a day or two before the transplant date.


Collecting stem cells from the bone marrow

Although it’s more common to collect stem cells from the blood, sometimes they are collected from the bone marrow. These are usually collected a few days or weeks before you have the transplant. You will have a general anaesthetic or an anaesthetic given into the spine, so you won’t feel any pain. Usually, bone marrow is taken from the back of the hip bones (pelvis).

Rarely, bone marrow is taken from the breastbone (sternum) or the front of the pelvis. If this needs to be done, the doctor will explain more about it to you.

The doctor inserts a needle through the skin and into the bone. Bone marrow is then drawn into a syringe and placed in a sterile container. The doctor may do this a number of times during the collection, taking bone marrow from more than one area of the pelvis.

For an adult, about one litre of bone marrow is removed – only about 10–15% of the body’s total. This leaves plenty for your body’s needs. The body quickly replaces the bone marrow that’s been removed.

You may have to stay in hospital overnight after the collection.

It’s common to feel sore for a few days, but regular painkillers can help. You’ll be given a supply to take home if you need it. There may also be some bruising from where the bone marrow was taken, which may last for a few weeks.


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