The current standard treatment for aGVHD is corticosteroids. Unfortunately, only 40% of matched-siblings HSCT cases and 25% of MUD SCT cases show a complete response to these steroids. Those patients who do not respond to corticosteroids can show a dismal outcome. Given the poor outcome with refractory GVHD, there has been a lot of interest in trying to predict who will get GVHD. These findings could lead to augmentation of GVHD prophylaxis.