What is graft versus host disease (GvHD)?

GvHD is a possible complication of a stem cell or bone marrow transplant from another person. 

What is a stem cell and bone marrow transplant?

Having a transplant means destroying as many cancer cells as possible and replacing these with healthy stem cells . 

Transplants use very high doses of chemotherapy and sometimes other treatments such as radiotherapy. The high dose treatment kills cancer cells but it also kills off the stem cells in your bone marrow that produce your blood cells .

After the high dose treatment you have healthy stem cells through a drip. The healthy stem cells make their way into your bone marrow and start to make blood cells you need again.

The difference between a stem cell and bone marrow transplant is where the stem cells are collected from. A stem cell transplant uses stem cells from the bloodstream. This is also called a peripheral blood stem cell transplant (PBSCT). A bone marrow transplant uses stem cells directly from the bone marrow.

A transplant from another person is called a donor or an allogeneic transplant. A transplant using your own stem cells is called an autograft or autologous transplant.

GvHD is a possible side effect of a transplant from another person. 

How does GvHD develop?

GvHD means the graft reacts against the host. The graft is the marrow or stem cells from the donor. The host is the person having the transplant. 

GvHD happens when particular types of white blood cell (T cells) in the donated stem cells or bone marrow attack your own body cells. This is because the donated cells (the graft) see your body cells (the host) as foreign and attack them.

Normally T cells don’t attack our own body cells, because they recognise proteins on the cells called human leukocyte antigens (HLA). We inherit our HLA from our parents. Apart from identical twins, HLA is unique to each person.

Before a transplant you and your donor have blood tests to check how closely your HLA matches. This test is called tissue typing. If you and your donor have very similar HLA this lowers the chance of GvHD. The more differences there are between your HLA and your donor's, the more likely you are to get GvHD.

After a transplant your bone marrow starts making new blood cells from the donor stem cells. These new blood cells have the donor's HLA pattern. They recognise the HLA pattern on your body cells as different (foreign) and may begin to attack some of them.

Who develops GvHD?

It is difficult to say exactly who will develop GvHD after a transplant and how bad they will get it. 

Some of the factors that increase your risk of GvHD include if:  

• your donor is not related to you

• your best available donor is still a slight mismatch - your donor will be as close an HLA match as possible

• the donated stem cells or bone marrow contain high numbers of T cells - but this may also lower the chance of relapse

• you or your donor are older - the older you are, the higher the risk

• your donor is a different sex to you - this is particularly true if a male has a female donor who has had children or been pregnant in the past

• you don't have a very common virus called cytomegalovirus (you are CMV negative) but your donor is CMV positive

• you have a donor lymphocyte infusion (DLI), using white blood cells from the donor - you might have this if your disease comes back after a donor transplant

Types of GvHD

There are 2 main types of GVHD. They are:

• acute GVHD
• chronic GVHD

But sometimes the 2 can overlap. This is called overlap syndrome.

GvHD may affect different areas of your body. Most commonly it affects the skin, the gut (including the bowel and stomach) or the liver.

Balancing the benefits and disadvantages of GvHD

The symptoms of GvHD can be difficult to cope with. In some cases GvHD is serious, and can even life threatening.

But having mild GvHD can be a good thing. As well as attacking your body cells, the donor T cells will also attack any remaining cancer cells.

Doctors call this the graft versus disease effect. 

You have treatment to prevent GvHD. The aim is to try to lower the risk of serious GvHD as far as possible, but still keep some benefits of GvHD.

This might help to stop the disease coming back.