Allogeneic BMT is a well-established treatment modality for malignant and non-malignant hematological diseases. Mature donor T cells within the stem-cell graft are the main mediators of the beneficial immune effects, but they are also responsible for the induction of GVHD, which becomes the major cause of morbidity and mortality post-transplant. Acute GVHD occurs within a 100-day period post-transplant and generally is manifested by dermatitis, enteritis, and hepatitis. The treatment of GVHD continues to be a challenge. To eliminate undesirable host-derived hematopoietic elements before BMT, patients are traditionally treated with myeloablative conditioning regimens involving high-dose chemotherapy and total-body irradiation. Standard GVHD prophylaxis and therapy comprise drugs that cause generalized immune suppression and place patients in danger of opportunistic infections and tumor relapse. For acute GVHD prevention, cyclosporine is often used; however, it is frequently necessary to administer long-term high-dose steroids as well.