Hematopoietic stem cell transplantation (HSCT) has become a standard treatment option in the management of a variety of hematologic malignancies and also is indicated in a number of other malignant and nonmalignant disease states (Saria & Gosselin-Acomb, 2007). Advances in this treatment modality have produced therapies designed to control, or even cure, specific hematologic diseases. The goal of allogeneic HSCT is to rescue and restore function of the hematopoietic system after high-dose chemotherapy with or without total body irradiation. Despite decades of improvement in care and recipient quality of life, allogeneic stem cell transplantation continues to produce significant, long-term complications. Specifically, the process of allogeneic HSCT can initiate a cascade of autoimmune events known as graft-versus-host disease (GVHD). In GVHD, the new donor immune system recognizes antigen-presenting cells (APCs) in the host (i.e., patient) as foreign, thus producing an inflammatory response (Neumann, 2004). GVHD can be divided into two types, acute and chronic. Collectively, acute and chronic GVHD (cGVHD) continue to cause significant morbidity and mortality in patients undergoing HSCT.