GvHD is a possible complication of a bone marrow or stem cell transplant from another person.
About bone marrow and stem cell transplants
A bone marrow or stem cell transplant from another person is called a donor or an allogeneic transplant.
Bone marrow and stem cell transplants are treatments that use very high doses of chemotherapy, sometimes with radiotherapy. The high dose treatment can kill cancer cells but it also kills off the stem cells in your bone marrow that produce your blood cells.
So after the high dose treatment you have stem cells or bone marrow from your donor through a drip. The donor stem cells make their way into your bone marrow and start to produce blood cells again.
What GvHD is
GvHD means the graft reacts against the host. The graft is the donated marrow or stem cells. The host is the person receiving the transplant. GvHD can cause diarrhoea, skin rashes and liver damage.
GvHD happens when particular types of white blood cell (T cells) in the donated bone marrow or stem cells attack your own body cells. This happens because the donated cells (the graft) see your body cells (the host) as foreign and attack them.
Some people have a very mild form which doesn’t last long. For others, GvHD can be severe. It may even be life threatening in a few cases. Some people may have GvHD over many months, or even years.
How GvHD develops
GvHD happens because the transplant affects your immune system.
The donor's bone marrow or stem cells will contain some T cells. T cells are a type of white blood cell that help us fight infections. T cells attack and destroy cells they see as foreign, and potentially harmful such as viruses.
Normally T cells don’t attack our own body cells, because they recognise proteins on the cells called HLA (human leukocyte antigens). We inherit our HLA from our parents. Apart from identical twins, HLA is unique to each person.
Before a bone marrow or stem cell 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.
The GvHD may affect different areas of your body. Most commonly it affects the skin, digestive system (including the bowel and stomach) or the liver.
Types of GvHD
The type of GvHD you have depends on when it starts after your transplant. Doctors also look at:
- what parts of the body are affected
- how badly your body has been affected
- the biopsy results
Acute GvHD generally starts within 100 days of your transplant but it can sometimes happen after this time. It usually happens about 2 to 3 weeks after your transplant when your new bone marrow begins to make blood cells. This is called engraftment.
It can be mild or severe, and often starts with a rash on:
- the palms of your hands
- the soles of your feet
- your ears
- your face
The rash may be itchy or painful. It may also affect your mouth, gut (digestive system) and liver. This can cause:
- loss of appetite
- yellowing of the skin (jaundice)
Chronic GvHD starts more than 100 days after your transplant. You are more likely to get it if you have had acute GvHD but it can happen even if you haven't. It can be mild or severe, and for some people can go on for several months or even years.
It may affect your:
Late acute GvHD and overlap syndrome
There are two other types of GvHD known as:
- late acute GvHD which starts after day 100
- overlap syndrome with features of both acute and chronic GvHD
They are both more likely to happen after mini transplants (reduced intensity conditioning). Nowadays, doctors use mini transplants more often.
Who develops GvHD
It is difficult to say who will develop GvHD after a transplant. We don’t know exactly, but somewhere between 1 and 4 out of every 5 people (20 to 80%) having a donor transplant will develop some degree of GvHD.
You are at higher risk of GvHD if:
- your donor is not related to you
- your best available bone marrow 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
Balancing the benefits and disadvantages of GvHD
The symptoms of GvHD can be difficult to cope with. In some cases GvHD is a serious, even life threatening, problem.
But having mild GvHD could 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. The graft means the donor T cells.
There are treatments to prevent GvHD. Doctors fine tune the use of these treatments. They try to lower the risk of serious GvHD as far as possible, but still keep some benefits of GvHD.
This may help to stop the disease coming back.