Fujita Health University Feb 20 2026 A Japanese study of more than 7,400 patients has identified a genetic mismatch that sharply increases the risk of severe acute graft-versus-host disease (GVHD) following umbilical cord blood transplantation. The specific donor–recipient human leukocyte antigen mismatch triples the likelihood of life-threatening immune complications, and severe acute GVHD itself is associated with significantly worse survival. These findings may help refine donor selection