More than 90 percent of patients can find a haplo-identical donor if they are willing to accept a 3-antigen match. Sometimes this is medically necessary, as when severely ill patients cannot wait the several months it may take to find a 4-, 5-, or 6-antigen matched donor. Patients accepting a 3-antigen haplo-identical match also accept a serious risk of suffering an immune cell attack on their tissues by the transplant (graft vs. host disease), or of having their body reject the transplant (host vs. graft).