This document discusses using ex vivo expanded and fucosylated regulatory T cells (Tregs) from third party umbilical cord blood to prevent graft-versus-host disease (GVHD) after transplantation. Experiments in mice show that fucosylated Tregs home more effectively to sites of inflammation, persist longer in vivo, and reduce GVHD symptoms and mortality more than untreated Tregs. The document proposes a clinical trial to evaluate the safety and efficacy of fucosylated Tregs for preventing GVHD in patients receiving double cord blood transplants.