You have treatment to reduce your risk of developing GvHD.
Getting the best donor match
GvHD can develop when the donor and the person receiving donor cells have a different tissue type. So your transplant specialist will make sure your donor is as closely matched to you as possible. This is called tissue typing and helps reduce your risk of GvHD.
The HLA (human leukocyte antigen) system describes the proteins found on your blood cells. Your doctors aim to find a donor with the closest HLA match possible.
Doctors usually test for 5 pairs of major HLA antigens. This gives a total of 10 antigens. We inherit one half of the pair from each of our parents. When choosing a donor, doctors aim to match 10 out of 10 HLA proteins. But it might be possible to do a transplant if they don't all match.
Finding a donor
We inherit the proteins from our parents so your best chance of a match is with a relative. You have a 1 in 4 (25%) chance of an exact match if you have a brother or sister. Other members of family can be tested if you don’t have siblings or if they don’t match your tissue type. Parents may be a close enough match.
Your doctor searches for a bone marrow match on a register of the general population if no one in your family is a match. The British Bone Marrow Registry (BBMR) and the Anthony Nolan Trust keep registers. Another possibility is to look at cord blood registries. Cord blood contains blood from umbilical cords. Parents consent to donate this when their baby is born. Doctors can use the stem cells from the cord blood.
About T cells
Before and after your transplant, your doctor uses treatments to reduce the chance of GvHD. These treatments destroy
T cells are white blood cells that are part of the immune system. They attack cells that are foreign to the body. GvHD happens when T cells in the donated stem cells or bone marrow (the graft) attack your own body cells (the host).
So reducing the number of T cells in the donor marrow or stem cells (the graft) reduces GvHD.
Sometimes GvHD is a good thing. The T cells in the graft also attack any remaining cancer cells. This reduces the risk of your disease coming back. This is called the graft versus disease effect. Doctors try to strike a balance between preventing severe GvHD and getting some possible benefits from mild GvHD.
To lower your risk of GvHD you might have treatment:
- before your transplant
- to remove T cells from the bone marrow or stem cells
- after your transplant
Treatment to prevent GvHD
Your doctor gives you drugs before and after the transplant. This is to reduce the number of T cells in your stem cells or bone marrow.
You usually have a drug called ciclosporin which is also called Deximune, Neoral or Sandimmum.
You start having it as a drip into the bloodstream a few days before your transplant. Before you go home you start taking it every day as a capsule.
You take ciclosporin for about 6 months after the transplant. As an alternative to ciclosporin, you might take a combination of mycophenolate mofetil (MMF) and tacrolimus.
Low doses of methotrexate can suppress your immune system. Methotrexate is a chemotherapy drug. It helps keep the T cells down and so stops them attacking your body cells.
You may have a chemotherapy drug called cyclophosphamide after a stem cell transplant. This is more likely after a half matched transplant from a family member, usually a parent or child. This is called a haploidentical transplant. The donor is a 50% match with the person having the transplant.
Before the transplant, you have chemotherapy to lower your immune system. These are usually lower doses of chemotherapy than in a traditional stem cell transplant. This is called reduced intensity conditioning or RIC.
A few days after the transplant, you have a high dose of cyclophosphamide. The donor's immune cells recognise your body cells as foreign, and start to multiply to attack them. The cyclophosphamide kills these rapidly growing immune cells, and so stops them attacking your body cells. This reduces side effects such as GvHD. You might have this treatment as part of a clinical trial.
You might have treatment with other drugs before your transplant, such as:
- alemtuzumab (Campath)
- antithymocytic globulin (ATG)
- newer drugs, including sirolimus (Rapamide)
Removing T cells from the stem cells or bone marrow
Your doctors can remove T cells from your donor’s bone marrow after it has been donated, or during the donation of stem cells. This is called T cell depletion. It isn't commonly used.