Graft-versus-host disease (GVHD) is treated with high doses of systemic steroids which can
lead to serious complications. A new blood test can identify patients whose GVHD is most
likely to respond to well to treatment (low risk GVHD). This study will test whether patients
with low risk GVHD can be successfully treated without steroids. Patients who participate
with this study will be treated with itacitinib instead of steroids. Itacitinib is an
experimental drug with an excellent safety record and appears to have activity as a GVHD
treatment.