Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) is a successful treatment option for multiple malignant diseases (i.e. leukemia) and non-malignant disorders (i.e. metabolic disorders, genetic disorders, immunodeficiencies). Unfortunately, transplantation from an HLA-related family member is only available in 30-40% of stem cell transplant recipients. The other patients requiring HSCT must then receive their stem cells from either a matched-unrelated donor (MUD) or from cord blood. One major limitation upon receiving these unrelated stem cells are acute and chronic graft-versus-host disease. Specifically looking at acute graft-versus-host disease (aGVHD), up to 30% of the recipients of stem cells from an HLA-identical related donor will develop greater or equal to grade 2 of aGVHD despite immunosuppressive prophylaxis. The percentages of patients who develop aGVHD from unrelated donors are even higher.