Acute graft-versus-host disease (aGVHD) is a common complication of allogeneic hematopoietic stem cell transplantation and is a major cause of morbidity and mortality. Although systemic corticosteroids are traditional first-line treatment for aGVHD, about half of patients are refractory to therapy. So what options are available for the treatment of steroid-refractory aGVHD?