graft-versus-host disease
Graft-versus-host disease, or GvHD, is rejection turned inside out. In ordinary rejection the recipient's body attacks the graft. In GvHD the graft attacks the recipient: transplanted donor immune cells, finding themselves in a body they read as foreign, turn on the host's own tissues. Imagine inviting a security team into your home and having them decide that you are the intruder.
It happens mainly after bone-marrow or blood-stem-cell transplants, because those grafts include living donor immune cells. Once inside, those cells scan the recipient's markers, judge them 'not self', and attack — often hitting skin, gut, and liver, the way an immune system would attack any invader.
GvHD is a serious, sometimes life-threatening risk of these transplants. Doctors guard against it by matching donor and recipient closely and by carefully managing the immune system, balancing this danger against the benefit the transplant is meant to provide.
It is the mirror image of ordinary rejection: instead of the house evicting the guest, the guest decides the house belongs to intruders and starts clearing it out.
When the transplant attacks the patient, not the other way round.
GvHD is a serious, sometimes life-threatening complication, mainly of bone-marrow and blood-stem-cell transplants.