Graft versus host disease (GVHD) is a multi-system complication of allogeneic bone marrow transplantation. Less frequently, it may also occur following solid organ transplantation or transfusion in immunocompromised patients. The disease occurs when T cells in the donor tissue (the graft) mount an immune response toward recipient (host) cells. It is not to be confused with transplant rejection (in which recipient immune cells activate an immune response toward the donor tissue). Prognosis is generally poor.

Three conditions required for diagnosis of GVHD, known as the Billingham criteria:

• The transplanted tissue contains immunologically functioning cells
• The recipient and donor are immunologically different
• The recipient is immunocompromised

Estimates of incidence vary from 9-50% post allogeneic bone marrow transplant despite prophylaxis with calcineurin inhibitors. The following principal risk factors have been identified:

• Poorly matched donor and recipient (particularly HLA)
• Type of conditioning used prior to transplantation
• Gender disparity between donor and recipient
• Graft source (bone marrow or peripheral blood source associated with higher risk than umbilical cord blood)

Acute and chronic GVHD are considered separate syndromes:

Acute GVHD

• Is classically defined as onset is classically within 100 days of transplantation*
• Usually affects the skin (>80%), liver (50%), and gastrointestinal tract (50%)
• Multi-organ involvement carries a worse prognosis**

Chronic GVHD

• May occur following acute disease, or can arise de novo
• Classically occurs after 100 days following transplantation
• Has a more varied clinical picture: often lung and eye involvement in addition to skin and GI, although any organ system may be involved