MTOR and graft versus host disease: Progress has been made in understanding the molecular genetics and mechanisms of this disorder, implicating hyperactive RAS as essential initiating event.5 Hyperactive RAS mutation also has an effect on the PI3K/Akt/mTOR pathway, which is involved in numerous cellular processes such as cell growth, survival, and death.6, -8 Rapamycin, a commonly used immunosuppressant, inhibits the mTOR pathway, and it is currently being used after HSCT for prevention of graft-versus-host disease (GVHD).