IT-901 is a c-Rel Inhibitor That Mediates Anticancer Properties in Hematologic Malignancies by Blocking NF-κB-Controlled Oxidative Stress Responses. IT-901 potently inhibits the NF-κB subunit c-Rel. IT-901 suppressed graft-versus-host disease while preserving graft-versus-lymphoma activity during allogeneic transplantation. Further preclinical assessment of IT-901 for the treatment of human B-cell lymphoma revealed antitumor properties in vitro and in vivo without restriction to NF-κB-dependent lymphoma. IT-901 did not elicit increased levels of reactive oxygen species in normal leukocytes, illustrating its cancer selective properties. IT-901 is a novel therapeutic agent to treat human lymphoid tumors and ameliorate graft-versus-host disease.