The white blood cells present in the transplanted tissue then attack the recipient's body cells, which leads to GvHD. This should not be confused with transplant rejection, which occurs when the transplant recipient's immune system rejects the transplanted tissue; GvHD occurs when the donor's immune system's white blood cells reject the recipient. The underlying principle (alloimmunity) is the same, but the details and course may differ.

GvHD can also