In bone marrow transplantation, commonly used to treat haematological malignancies, the patient's own immune system is destroyed following cytotoxic or radiotherapeutic destruction of bone marrow cells.

When healthy bone marrow cells are transplanted into the recipient, there is a danger of a graft-versus-host reaction (GVH), which may be acute or chronic.

In the GVH reaction, transplanted immunologically competent bone marrow cells (including T-lymphocytes) may mount an immune response against various components of the recipient's tissues, which bear antigens that the transplanted immune cells recognize as foreign.

Acute GVH} occurs within 3 months of graft in up to 70% of recipients.
It produces features of diarrhoea, dermatitis, malabsorption, and jaundice.
The proliferating transplanted immune-competent cells destroy epithelial cells in the gut, liver and skin.

This is a potentially life-threatening condition, the risk of which is minimized by careful HLA matching.

Although recent efforts to remove T-cells from donor marrow have reduced the risk of GVH reactions, they have increased the risk of graft failure.
Chronic GVH occurs 3-15 months after transplantation in about 40% of recipients.
It produces a syndrome similar to progressive systemic sclerosis.