Graft versus host disease (GVHD) is a complication that can develop after a person has had a bone marrow or stem cell transplant. In the disease, the host body comes under attack from the donated cells.
Bone marrow and stem cell transplants involve the patient having high doses of chemotherapy or radiotherapy. Chemotherapy is used to try to cure the cancer in a patient’s body, help other treatments work more effectively or reduce cancer symptoms. In radiotherapy, x-rays are used to target and kill the cancer cells. Sometimes this involves placing radioactive material in the patient’s body.
However, there are side effects of high doses of chemotherapy and radiotherapy. Alongside killing cancer cells, they can also kill the stem cells in the body’s bone marrow. Stem cells are cells that have the capability to become other kinds of cells such as blood cells. They are produced by bone marrow found inside of bones.
After a transplantation, the patient needs to have a donation of stem cells or bone marrow from the donor to kick start their own blood cell production. The donation is comprised of white blood cells called leukocytes that fight viruses and bacteria in the body. They do not usually attack cells in their own body unless the patient is suffering from a disease, such as an autoimmune disease.
Doctors will test the host and the potential donor to see how closely their tissues genetically match before the donation. Clinicians will try to get as close a match as possible, because GVHD develops when the donor white blood cells (T-cells), also known as the graft, identify the host cells as foreign.
Human cells have inherited genetic markers on them called human leukocyte antigens. These are individual to each person. The only time that they will completely match is in identical twins. T-cells from the donated bone marrow can tell the difference between their own HLA markers and the ones on the host cells. This results in them targeting the host cells for destruction.
How does it affect patients?
GVHD develops in about 20% – 80% of people who have had a donor transplant. The disease can vary in its severity in different people. Patients can experience diverse effects on their organs. Primary regions that are impacted include the skin, liver and gastrointestinal tract (GI).
There are two types of the disease. Acute GVHD begins within 100 days after the patient has had the transplant. About 70% of transplant patients get this type. It tends to focus primarily on the skin, liver and GI tract. Chronic GVHD focuses on the same regions, but can also spread to other organs in the body as well. Moreover, chronic GVHD develops after 100 days have elapsed post transplant. Around 40% of patients develop this kind. Acute and Chronic GVHD can also occur at the same time in patients. Furthermore, some patients develop the acute version first and then have the chronic version months afterwards.
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