Graft-versus-host disease (GVHD) remains as the major obstacle for successful hematopoietic stem cell transplant (HSCT). Roughly half of the patients undergoing HSCT develop GVHD which requires treatment, and above 10 % of the patient may die because of it. However, GVHD presents with anti-tumor activity, called graft-versus-tumor (GVT) effect, and it carries significant anti-tumor activity, thus suppressing GVHD completely may increase the relapse of original disease. Thus, it is important to control GVHD to the appropriate level.